INTERNATIONAL
STANDARD
ISO
4042
Third edition
2018-08
Fasteners — Electroplated coating
systems
Fixations — Systèmes de revêtements électrolytiques
Reference number
ISO 4042:2018(E)
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ISO 4042:2018(E)
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ISO 4042:2018(E)
Contents
Page
Foreword .......................................................................................................................................................................................................................................... v
Introduction .............................................................................................................................................................................................................................. vii
1
2
3
4
Scope ................................................................................................................................................................................................................................. 1
Normative references ...................................................................................................................................................................................... 1
Terms and definitions ..................................................................................................................................................................................... 2
General characteristics of the coating ............................................................................................................................................ 3
4.1
4.2
4.3
4.4
4.5
5
6
7
8
Corrosion protection and testing ........................................................................................................................................................ 8
5.1
5.2
5.3
5.4
6.3
6.4
General ........................................................................................................................................................................................................ 11
Fasteners with ISO metric thread ........................................................................................................................................ 11
6.2.1 Coating thickness ......................................................................................................................................................... 11
6.2.2 Gaugeability and assemblability ..................................................................................................................... 12
Other fasteners .................................................................................................................................................................................... 12
Test methods for thickness determination .................................................................................................................. 13
7.1
7.2
7.3
7.4
7.5
General ........................................................................................................................................................................................................ 15
Appearance ............................................................................................................................................................................................. 15
Corrosion resistance related to temperature ............................................................................................................ 15
Torque/clamp force relationship ......................................................................................................................................... 15
Determination o f hexavalent chromium ........................................................................................................................ 15
8.1
8.2
General ........................................................................................................................................................................................................ 15
Tests mandatory for each lot ................................................................................................................................................... 15
Tests for in-process control....................................................................................................................................................... 16
Tests to be performed when specified by the purchaser................................................................................. 16
Mechanical and physical properties and testing.............................................................................................................. 15
Applicability of tests ...................................................................................................................................................................................... 15
8.4
Designation system ......................................................................................................................................................................................... 16
9.1
9.2
9.3
9.4
10
General ........................................................................................................................................................................................................... 8
Neutral salt spray test (NSS) for zinc based coating systems ......................................................................... 9
Sul fur dioxide test (Kesternich test) ................................................................................................................................. 10
Bulk handling, automatic processes such as feeding and/or sorting, storage and
transport.................................................................................................................................................................................................... 11
Dimensional requirements and testing ..................................................................................................................................... 11
6.1
6.2
8.3
9
Coating metals or alloys and main purposes ................................................................................................................ 3
Build-up o f basic electroplated coating systems ....................................................................................................... 3
Coating systems and coating processes............................................................................................................................. 4
Internal hydrogen embrittlement........................................................................................................................................... 4
4.4.1 General...................................................................................................................................................................................... 4
4.4.2 Fasteners with hardness below 360 HV ...................................................................................................... 5
4.4.3 Fasteners with hardness equal to and above 360 HV and up to 390 HV......................... 5
4.4.4 Fasteners with hardness above 390 HV....................................................................................................... 5
4.4.5 Fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3 ................................... 6
4.4.6 Baking and test requirements for case-hardened and tempered screws ....................... 7
4.4.7 Work-hardened fasteners ......................................................................................................................................... 8
4.4.8 Fasteners with bainitic structure ...................................................................................................................... 8
Baking ............................................................................................................................................................................................................. 8
General ........................................................................................................................................................................................................ 16
Designation o f electroplated coating systems for the order......................................................................... 17
Examples o f designation o f hexavalent chromium free electroplated coating
systems for fasteners ...................................................................................................................................................................... 18
Designation o f fasteners with electroplated coating systems for labelling ..................................... 19
Ordering requirements for electroplating ............................................................................................................................. 19
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ISO 4042:2018(E)
11
Storage conditions ........................................................................................................................................................................................... 20
Annex A (in formative) Design aspects and assembly of coated fasteners .................................................................. 21
Annex B (in formative) Hydrogen embrittlement consideration .......................................................................................... 29
Annex C (in formative) Corrosion protection related to zinc coatings with chromate
conversion coatings ........................................................................................................................................................................................ 33
Annex D (in formative) Coating thickness and thread clearance for ISO metric screw threads ........... 34
Annex E (in formative) Coating systems tested in accordance with ISO 9227, NSS —
Evaluation of cabinet corrosivity for the neutral salt spray test ..................................................................... 42
Annex F (in formative) Obsolete designation codes for electroplated coating systems on
fasteners according to ISO 4042:1999 ........................................................................................................................................ 51
Bibliography ............................................................................................................................................................................................................................. 54
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation o f national standards
bodies (ISO member bodies). The work o f preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the di fferent approval criteria needed for the
di fferent types o f ISO documents should be noted. This document was dra fted in accordance with the
editorial rules o f the ISO/IEC Directives, Part 2 (see www.iso .org/directives).
Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f
patent rights. ISO shall not be held responsible for identi fying any or all such patent rights. Details o f
any patent rights identified during the development o f the document will be in the Introduction and/or
on the ISO list o f patent declarations received (see www.iso .org/patents).
Any trade name used in this document is in formation given for the convenience o f users and does not
constitute an endorsement.
For an explanation on the voluntary nature o f standards, the meaning o f ISO specific terms and
expressions related to con formity assessment, as well as in formation about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 2, Fasteners, Subcommittee SC 14, Surface
coatings.
This third edition cancels and replaces the second edition (ISO 4042:1999), which has been technically
revised. The main changes compared to the previous edition are as follows:
— application to all fasteners, including sel f-tapping and thread forming screws, washers, rivets,
clips, etc.;
— focus on coatings designed for corrosion protection o f fasteners;
— application to electroplated coating systems with or without additional layers (conversion coating,
sealant, top coat, lubricant);
— specification o f minimum corrosion resistance (white corrosion and red rust);
— inclusion o f up-to-date knowledge about hydrogen embrittlement and prevention measures;
— definitions specified in ISO 1891-2;
— concerning corrosion tests, inclusion o f sul fur dioxide test (Kesternich) and calibration o f neutral
salt spray test;
— inclusion o f gaugeability and assemblability requirements;
— for thickness determination, addition o f adequate test methods and deletion o f the batch average
thickness;
— new designation system for all coating systems;
— specification for mechanical and physical properties and related test methods;
— in formation about design aspects and assembly o f coated fasteners;
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ISO 4042:2018(E)
—
i n formation
—
i n formation ab out eva luation o f cabi ne t corro s ivity
vi
for
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co ati ng th ickne s s and th re ad cle ara nce
for
for
I S O me tric s c rew th re ad s;
the neutra l s a lt s pray te s t.
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ISO 4042 : 2 018(E)
Introduction
T h i s do c u ment was comple tely revi s e d to ta ke i nto accou nt new developments relate d to he xava lent
ch rom ium
fre e
p a s s ivation s ,
appl ic ation
of
s e a l ants
and
top
co ats ,
re qu i rements
for fu nc tiona l
prop er tie s as wel l a s re s u lts o f re s e arch work to m i n i m i z e the ri s k o f hyd ro gen embrittlement.
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INTERNATIONAL STANDARD
ISO 4042:2018(E)
Fasteners — Electroplated coating systems
1 Scope
This document specifies requirements for electroplated coatings and coating systems on steel
asteners. The requirements related to dimensional properties also apply to fasteners made o f copper
or copper alloys.
f
It also specifies requirements and gives recommendations to minimize the risk o f hydrogen
embrittlement; see 4.4 and Annex B .
It mainly applies to zinc and zinc alloy coating systems (zinc, zinc-nickel, zinc-iron) and cadmium,
primarily intended for corrosion protection and other functional properties:
— with or without conversion coating;
— with or without sealant;
— with or without top coat;
— with or without lubricant (integral lubricant and/or subsequently added lubricant).
Specifications for other electroplated coatings and coating systems (tin, tin-zinc, copper-tin, coppersilver, copper, silver, copper-zinc, nickel, nickel-chromium, copper-nickel, copper-nickel-chromium)
are included in this document only for dimensional requirements related to fasteners with ISO metric
threads.
This document applies to bolts, screws, studs and nuts with ISO metric thread, to fasteners with nonISO metric thread, and to non-threaded fasteners such as washers, pins, clips and rivets.
In formation for design and assembly o f coated fasteners is given in Annex A .
This document does not speci fy requirements for properties such as weldability or paintability.
NOTE
Other International Standards speci fy di ffering electroplating processes. For electroplating o f
fasteners, the requirements o f this document apply, unless otherwise agreed.
2 Normative references
The following documents are re ferred to in the text in such a way that some or all o f their content
constitutes requirements o f this document. For dated re ferences, only the edition cited applies. For
undated re ferences, the latest edition o f the re ferenced document (including any amendments) applies.
ISO 1456,
Metallic an d oth er in organic coatin gs —
Electrodeposited coatin gs of nickel,
n ickel plus
chrom ium , copper plus nickel an d of copper plus n ickel plus chrom ium
ISO 1463, Metallic an d oxide coatin gs — Measurem ent of coatin g thickn ess — Microscopical m eth od
ISO 1502, ISO gen eral-purpose m etric screw threads — Gauges an d gaugin g
ISO 1891-2, Fasteners — Terminology — Part 2: Vocabulary and definitions for coatings
ISO 2081,
Metallic an d oth er in organic coatin gs — Electroplated coatin gs of zin c with supplem entary
treatm ents on iron or steel
ISO 2082, Metallic an d oth er in organic coatin gs — Electroplated coatin gs of cadmium with supplem entary
treatm ents on iron or steel
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ISO 4042:2018(E)
ISO 2093, Electroplated coatings of tin — Specification and test methods
ISO 2177, Metallic coatings — Measurement of coating thickness — Coulometric method by anodic
dissolution
ISO 2178, Non-magnetic coatings on magnetic substrates — Measurement of coating thickness —
Magnetic method
ISO 3231, Paints and varnishes — Determination ofresistance to humid atmospheres containing sulfur dioxide
ISO 3497, Metallic coatings — Measurement of coating thickness — X-ray spectrometric methods
ISO 3613:2010, Metallic and other inorganic coatings — Chromate conversion coatings on zinc, cadmium,
aluminium-zinc alloys and zinc-aluminium alloys — Test methods
ISO 4521, Metallic and other inorganic coatings — Electrodeposited silver and silver alloy coatings for
engineering purposes — Specification and test methods
ISO 6988, Metallic and other non organic coatings — Sulfur dioxide test with general condensation of
moisture
ISO 8991, Designation system for fasteners
ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests
ISO 15330, Fasteners — Preloading test for the detection of hydrogen embrittlement — Parallel bearing
surface method
ISO 15726, Metallic and other inorganic coatings — Electrodeposited zinc alloys with nickel, cobalt or iron
ISO 16047, Fasteners — Torque/clamp force testing
ISO 16228, Fasteners — Types of inspection documents
ISO 19598, Metallic coatings — Electroplated coatings of zinc and zinc alloys on iron or steel with
supplementary Cr(VI)-free treatment
ISO 21968, Non-magnetic metallic coatings on metallic and non-metallic basis materials — Measurement
of coating thickness — Phase-sensitive eddy-current method
ASME B18.6.3, Machine Screws, Tapping Screws, and Metallic Drive Screws (Inch Series)
3 Terms and definitions
For the purposes o f this document, the terms and definitions given in ISO 1891-2 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www.iso .org/obp
— IEC Electropedia: available at http: //www.electropedia .org/
3.1
reference panel
re ference material that is to be exposed to check the corrosivity level o f the test cabinet used for
fastener testing
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4 General characteristics of the coating
4.1 Coating metals or alloys and main purposes
Electroplated coating systems for steel fasteners are primarily applied for corrosion protection and
functional properties, such as torque/clamp force relationship.
In addition, other functional properties or decorative properties can be specified; see Annex A .
Table 1 shows commonly used electroplated coatings in relation with their main purposes and
re ferences to related ISO standards, which give additional general in formation not covered by this
document, e.g. for designation. Some o f the International Standards listed in Table 1 speci fy di ffering
electroplating processes. For the purpose o f fasteners, the requirements o f this document apply.
Table 1 — Electroplated coatings in accordance with their main purposes and related
ISO standards
Coating metal(s)
Symbol
Zn
ZnNi
ZnFe
Cd
Ni
Ni+Cr
Cu+Ni
Cu+Ni+Cr
CuZn
CuSn
Cu
Ag
CuAg
Sn
SnZn
Element
Zinc
Zinc-nickel
Zinc-iron
Cadmium a
Nickel
Nickel-chromium
Copper-nickel
Copper-nickel-chromium
Brass
Copper-tin (bronze)
Copper
Silver
Copper-silver
Tin
Tin-zinc
Nature
Main purpose of
the coating for
fasteners
Metal
Alloy
Alloy
Metal
Metal
Multi-layer
Multi-layer
Multi-layer
Alloy
Alloy
Metal
Metal
Alloy
Metal
Metal
P/D/F
P/D/F
P/D/F
P/F
D/F
D
D
D
D
F
F/D
F/D
F
F
F/P
ISO standard
ISO 2081, ISO 19598
ISO 15726, ISO 19598
ISO 15726, ISO 19598
ISO 2082
ISO 1456
ISO 1456
ISO 1456
ISO 1456
—
—
—
ISO 4521
—
ISO 2093
—
P corrosion p rotection
F functional properties
D decorative properties (colour, aspect)
a
Cadmium is restricted or prohibited for many applications (remaining cadmium users are predominantly military and
aerospace industries).
4.2
Build-up of basic electroplated coating systems
Figure 1 shows basic electroplated coating systems.
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ISO 4042:2018(E)
Key
1
2
3
4
5
only metal layer(s)
metal layer(s) + conversion coating
metal layer(s) + conversion coating + additional lubricant
metal layer(s) + conversion coating + sealant/top coat
metal layer(s) + conversion coating + sealant/top coat + additional lubricant
Figure 1 — Basic electroplated coating systems (schematic)
A conversion coating increases corrosion protection on zinc, zinc alloys and cadmium coatings. It may
be a passivation (chromium VI free) or a chromatation (chromium VI containing). The conversion
coating can also provide better adhesion for additional layer(s) and/or additional colour/paint.
An additional sealant/top coat (with or without integral lubricant) may be chosen to increase corrosion
resistance and to achieve other specific properties (e.g. torque/clamp force properties, resistance to
chemicals, mechanical resistance, aspect, colour, thermal stability, increased electrical resistance, UV
radiation resistance). The selection o f the nature o f a sealant or top coat should be based on desired
additional properties.
An additional lubricant may be applied to adjust or amend the torque/clamp force relationship.
4.3 Coating systems and coating processes
The type and geometry o f the fasteners should be considered when selecting a coating system and the
related coating process (see Annex A) as well as hydrogen embrittlement considerations (see Annex B ).
The electroplating process shall be under control, in accordance with a recognized standard and/or a
specification by agreement with the customer.
4.4 Internal hydrogen embrittlement
4.4.1
General
I f the three following conditions are concurrently present for fasteners:
— with high tensile strength or hardness or which have been case-hardened and tempered or cold
worked to high hardness,
— which are under tensile stress, and
— which have absorbed hydrogen,
there is a risk o f Internal Hydrogen Embrittlement (IHE).
The susceptibility to IHE increases with increasing hardness o f the fastener material. Appropriate
measures for prevention o f IHE for quenched and tempered fasteners depending on hardness are
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ISO 4042:2018(E)
s p e ci fie d i n Table 2 . For
fa s teners
i n accordance with I S O 8 9 8 -1 , I S O 8 9 8 -2 a nd I S O 8 9 8 -3 , Table s 3 , 4
and 5 apply.
Table 2 — Measures related to IHE for quenched and tempered fasteners with regard to
hardness
360 HV
A
N o s up p lementa l p ro ce s s veri
390 HV
B
-
OR
re ga rd to I H E
B a ki n g
B a ki n g
AND
N o b a ki n g ne ce s s a r y
(at the choice o f the
See 4.4.2
m a nu fac tu rer)
( b a ki n g temp eratu re a nd du ra
-
tio n s h a l l b e s p e c i fie d)
See 4.4.4
a nd B . 6
a nd B . 6
Fasteners with hardness below 360 HV
When ele c tropl ati ng
5
AND
fa s tener
See 4.4.3
-
tion a nd/or p ro duc t te s ts with
pro duc t te s ti ng with re ga rd to I H E
re ga rd to I H E
and
S up p lementa l p ro ce s s ver i fic a
Sup p lementa l p ro ce s s ver i fic ation a nd/o r
fic ation or pro duc t te s ti n g with
4.4.2
C
A
fas teners
with s p e c i fie d ma xi mum h ard ne s s b elow 3 6 0 H V (
in
Table s 2 ,
34
,
) , no s upplementa l pro ce s s veri fic ation with regard to I H E a nd no b a ki ng a re ne ce s s a r y.
4.4.3
Fasteners with hardness equal to and above 360 HV and up to 390 HV
When ele c troplati ng
fas teners
and i nclud i ng 3 9 0 H V (
with s p e ci fie d ma xi mu m ha rd ne s s e qua l to and ab ove 3 6 0 H V a nd up to
B in Table s 2 , 3 , 4 and 5 ) , b a ki ng i s no t re qu i re d provide d s upplementa l pro ce s s
veri fic ation and/or pro duc t te s ti ng with re ga rd to I H E have b e en p er forme d . H owever, the pu rcha s er i s
fre e
For
to re qu i re b a ki ng genera l ly.
fas teners
fa i lu re
the
i n th i s s p e c i fie d ha rd ne s s range, ele c troplati ng do e s no t p o s e a ri s k o f I H E . I n c a s e o f a
i n a pro duc t te s t, it c an no t b e as s u me d th at b a ki ng the p a r ts wou ld have prevente d s uch
me ta l lu rgic a l
a nd phys ic a l
cond ition s
o f the
con formance s . For more i n formation, s e e B .4
4.4.4
.
fa s tener
materi a l
shou ld b e
i nve s tigate d
fa i lu re:
for
non-
Fasteners with hardness above 390 HV
When ele c troplati ng
fa s teners
b a ki ng i s re qu i re d; s e e B .4
T he
fol lowi ng
—
for fas teners
for
C in Table s 2 , 3 and 5 ) ,
with s p e ci fie d ma xi mu m h ard ne s s ab ove 3 9 0 H V (
m i n i mu m re com mende d b a ki ng temp erature and du ration .
exemp tion s apply:
wh ich are no t s p e ci fie d to b e u nder ten s i le s tre s s b y de s ign or s ta ndard (e . g. s e t s crews
i n accorda nce with I S O 8 9 8 -5 ) , b a ki ng i s no t re qu i re d (s e e B . 2 ) ,
—
i nduc tion ha rdene d end s (e . g.
for
th re ad
form i ng
s c rews) s ha l l no t b e con s idere d
for
de term i n i ng
me a s ure s relate d to I H E i n relation to Table 2 , b e c au s e they a re norma l ly no t s ubj e c te d to ten s i le
s tre s s provide d th at the end pro trude s th rough the mati ng th re ad .
For a l ka l i ne z i nc-n ickel ele c tropl ati ngs (and n ickel content
from
1 2 % to 16 %) , it i s p o s s ible to avoid
b a ki ng b e c au s e o f low ri s k o f I H E (s e e B . 3 ) . T he de ci s ion no t to ca rr y out b a ki ng s ha l l b e b a s e d on
testing (see
NO TE
B . 6) and b e agre e d b e twe en the s uppl ier a nd the purch as er.
Fo r ac id z i nc-n ickel ele c trop l ati n gs , s tud ie s h ave s hown s i m i l a r b ene fits a s
fo r
a l ka l i ne z i nc-n ickel
ele c trop l ati ng , howe ver more d ata i s ne ce s s a r y with re ga rd to b a ki ng avoid a nce .
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4.4.5
Fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3
For fasteners in accordance with ISO 898-1, ISO 898-2 and ISO 898-3, Tables 3, 4 and 5 apply.
Table 3 — Measures related to IHE for fasteners in accordance with ISO 898-1
Bolts, screws, studs in accordance with ISO 898-1
Property class
≤ 9.8
10.9
12.9 and 12.9
A
B
C
AND
OR
AND
No supplemental process Supplemental process ver- Supplemental process ververification or product
ification and/or product ification and/or product
testing
with
regard
to
IHE
testing
with regard to IHE testing with regard to IHE
Measures related to IHE
No baking necessary
Baking
Bakinga
Baking temperature and
At the choice o f the fasten- duration
shall be specified
er manu facturer
(see also B.4)
See 4.4.3 and B.6
See 4.4.4 and B.6
—
See 4.4.2
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), the decision not to carry out baking
shall be based on testing (see B.6) and be agreed between the supplier and the purchaser.
a
Table 4 — Measures related to IHE for nuts in accordance with ISO 898-2
Property class
Nuts in accordance with
ISO 898-2
≤
2
Nuts with specified maximum
hardness ≥ 360 HVa
A
B
No supplemental process verification
Measures related to IHE
1
Nuts with specified maximum
hardness < 360 HV
AND
No baking necessary
—
See 4.4.2
Supplemental process verification
with regard to IHE
OR
Baking
At the choice o f the fastener
manu facturer
Only:
— for regular nuts (style 1) with fine pitch thread, property class 10, and
— for high nuts (style 2) with fine pitch thread, property class 12, and diameters above 16 mm.
a
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See 4.4.3
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Table 5 — Measures related to IHE for flat washers in accordance with ISO 898-3
Property class
Flat washers in accordance with ISO 898-3
Measures related to IHE
≤ 200HV
300HV
380HV
A
B
C
AND
OR
AND
No supplemental process Supplemental process veri - Supplemental process veriverification
fication with regard to IHE fication with regard to IHE
No baking necessary
—
Baking
At the choice of the
astener manu facturer
f
See 4.4.2
See 4.4.3
Bakinga
Baking temperature and
duration shall be specified
(see also B.4)
See 4.4.4
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), the decision not to carry out baking
shall be based on testing (see B.6) and be agreed between the supplier and the purchaser.
a
4.4.6
Baking and test requirements for case-hardened and tempered screws
Case-hardened and tempered fasteners include sel f-tapping screws (see ISO 2702), thread- forming
screws for metallic materials, sel f-drilling screws (see ISO 10666) and screws for so ft materials (e.g.
plastic, wood). The sur face o f these screws is usually intentionally hardened to fulfil their specific
functions.
The susceptibility to IHE o f case-hardened and tempered screws depends not only on core hardness;
see B.3 .
Requirements for case-hardened and tempered fasteners (except for sel f-tapping screws and screws for
so ft materials) are specified in Table 6 .
Requirements for sel f-tapping screws and screws for so ft materials are specified in Table 7.
Testing with regard to IHE for case-hardened and tempered screws with core hardness above 370 HV
(C in Table 6) and for sel f-tapping screws above 390 HV (C in Table 7) shall be performed in accordance
with ISO 15330 or ASME B18.6.3.
Table 6 — Measures related to IHE for case-hardened and tempered screws
(except self-tapping screws and screws for soft materials)
Core hardness
≤ 370 HV
B
Measures related to IHE
Supplemental process verification with
regard to IHE
AND
Product testing and/or baking
At the choice o f the fastener
manu facturer
> 370 HV
C
Supplemental process verification with
regard to IHE
AND
Baking
AND
Product testing for each manu factur-
ing lota
Baking temperature and duration shall
be specified (see also B.4)
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), product testing shall be considered as
part o f in-process control (not mandatory for each manu facturing lot).
a
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Table 7 — Measures related to IHE for self-tapping screws and screws for soft materials
Core hardness
≤ 390 HV
B
Measures related to IHE
Supplemental process verification with
regard to IHE
AND
Product testing and/or baking
At the choice o f the fastener
manu facturer
> 390 HV
C
Supplemental process verification with
regard to IHE
AND
Baking
AND
Product testing for each manu factur-
ing lota
Baking temperature and duration shall
be specified (see also B.4)
For alkaline zinc-nickel electroplatings (and nickel content from 12 % to 16 %), product testing shall be considered as
part o f in-process control (not mandatory for each manu facturing lot).
a
4.4.7
Work-hardened fasteners
For fasteners work-hardened to high hardness resulting in residual stresses and not intended to be
quenched and tempered, see B.5 .
Table 3 for fasteners with ISO metric thread shall apply regardless o f thread rolling be fore or a fter
heat treatment: a local increase o f sur face hardness by work-hardening has no negative impact on
susceptibility to IHE.
4.4.8
Fasteners with bainitic structure
Fasteners with bainitic structure are not addressed in 4.4 . A written agreement between the supplier
and the purchaser with regard to IHE is necessary.
4.5 Baking
When baking is per formed, baking conditions including temperature and duration shall be based on
fastener material properties, electroplating process, and coating material. See B.4 for more detailed
guideline/advice.
Baking is usually per formed be fore application o f a conversion coating and/or be fore application o f an
additional sealant/top coat. In case o f passivations (with or without sealant) and depending on baking
temperature, baking in the passivated and/or sealed condition may be suitable provided corrosion
resistance is not impaired.
NOTE
With proper care, many steel fasteners are electroplated without baking by correlating process
conditions and coating material to the susceptibility o f the fastener material to hydrogen embrittlement, and by
applying adequate process control procedures. Methods according to DIN 50969-2 or ASTM F1940 are recognized
investigation methods for process control to minimize the risk o f IHE. These or other similar test methods can be
used as the basis for speci fying baking requirements in a controlled process.
However, prevention o f the risk o f IHE does not only depend on baking (see 4.4 and Annex B ).
5 Corrosion protection and testing
5.1 General
The corrosion protection o f an electroplated coating system depends to a considerable extent on the
thickness o f the metal layer(s). Conversion coatings and/or sealants/top coats on zinc, zinc-iron, zinc8
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nickel and cadmium coatings provide protection against coating metal corrosion (formation o f white
corrosion), thus providing additional protection against basis metal corrosion.
Coatings o f zinc, zinc alloys and cadmium are less electropositive than the steel basis metal, which is the
condition to provide cathodic protection. In contrast, metals more electropositive than the steel basis
metal (e.g. nickel, copper, silver) cannot provide cathodic protection, which can intensi fy corrosion o f
the fastener i f the coating is damaged or pitted.
The frequency and duration o f wetting and service temperatures, contact with corrosive chemicals
and contact with other metals and materials (galvanic corrosion/contact corrosion) can influence the
protective per formance o f coatings.
Corrosion resistance is considered to be a product characteristic that can be altered as a consequence
o f the following factors:
— physical damage to the coating from handling and transportation, and
— oxidation o f the coating or reaction with the environment during transportation and storage.
Be fore selecting a coating system, all functions and conditions o f the assembly should be considered
and not just the fastener; see Annex A. An appropriate choice for a given application should be made
between the purchaser and the fastener supplier and/or the coater and/or the chemical supplier.
Corrosion resistance in accelerated corrosion tests (e.g. neutral salt spray test, sul fur dioxide test)
cannot be directly related to corrosion protection behaviour in service environments. However,
accelerated tests are commonly used to evaluate the corrosion resistance o f the coating system.
5.2
Neutral salt spray test (NSS) for zinc based coating systems
The neutral salt spray test (NSS) in accordance with ISO 9227 is used to evaluate the corrosion
resistance o f the coating system.
When evaluation o f the cabinet corrosivity is requested, it should be per formed in accordance with
Annex E .
The NSS test in accordance with ISO 9227 shall be used to monitor the consistency o f the process by
quanti fying corrosion resistance on sample fasteners taken periodically from the electroplating
process (i.e. in-process control). For these reasons, the NSS test shall be carried out on sample fasteners
in the “as-coated” condition.
The “as-coated” condition is defined as the condition a fter completion o f all steps o f coating (including
application o f any sealant, top coat or lubrication) without the occurrence o f deterioration from the
factors listed in 5.4 , i.e. be fore any sorting, packaging, assembling, transportation or storage.
NOTE 1 Customers or end-users o ften wish to separately use the NSS test as a re ference to evaluate corrosion
resistance as a “per formance characteristic” and/or for supplier monitoring. In such cases, corrosion resistance
is evaluated on sample fasteners in the “as-received” condition, i.e. a fter the occurrence o f deterioration from
sorting, packaging, assembling, transportation and/or storage; in these cases, it is not appropriate to use the
minimum neutral salt spray test duration in Table 8. Rather, the values in Table 8 serve as a starting basis to
evaluate corrosion resistance in the as-received condition, taking into account factors that cause deterioration o f
the corrosion resistance. See 5.4.
The neutral salt spray test duration specified in Table 8 for coating systems with Cr(VI)- free passivation
shall apply for fasteners alone, tested no sooner than 24 h a fter coating and in the “as-coated” condition.
For neutral salt spray test duration o f zinc coating systems with chromate conversion coatings, see
Annex C .
Contact points o f the fastener with a holding fixture, i f any, shall not be considered in the evaluation o f
the corrosion test.
Fasteners with a captive washer have areas between the mating fastener and the washer with less
coating thickness due to intrinsic electrochemical deposition behaviour; this is similar for fasteners
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with blind holes. Both result in reduced corrosion resistance in these areas during the corrosion test
and should not be cause for rejection. In service, these areas are not normally exposed to environmental
corrosion.
NOTE 2 For fasteners intended to be subjected to a high level o f plastic de formation a fter coating (crimping,
riveting, etc.), corrosion resistance is reduced in the de formed area.
Table 8 — Corrosion resistance for commonly used zinc and zinc alloy coating systems
Minimum neutral salt spray test duration for
barrel coatinga
Zinc based coating system
Zn, transparent passivatedb
Zn, iridescent passivatedb
Zn, iridescent passivated, sealedb
Zn, black passivated, sealed
ZnFe, iridescent passivatedb
ZnFe, iridescent passivated, sealedb
ZnFe, black passivated, sealed
ZnNi, silver grey, passivated
ZnNi, silver grey passivated, sealed
ZnNi, black passivated
ZnNi, black passivated, sealed
Code
(see Table 11)
hours
No coating
metal corrosion
(white corrosion)
Zn//An/T0
Zn//Cn/T0
Zn//Cn/T2
Zn//Fn/T2
ZnFe//Cn/T0
ZnFe//Cn/T2
ZnFe//Fn/T2
ZnNi//Cn/T0
ZnNi//Cn/T2
ZnNi//Fn/T0
ZnNi//Fn/T2
No basis metal corrosion
(red rust)
Coating thickness
8 µm
72
5 µm
48
120
96
144
216
8
120
24 c
120
96 c
120
168
48 c
120 c
72
192
168
72
240
144
216
192
288
240
480
600
360
480
720
720
600
720
12 µm
96
240
288
192
264
360
312
720 d
720 d
720 d
720 d
Minimum neutral salt spray test duration shall not be regarded as a direct guide for the corrosion resistance o f coated
asteners in all environments where they might be used. See ISO 9227.
a
With a rack plating process, the e ffect o f possible damage to coating is reduced and there fore increased corrosion
resistance can be achieved.
b
Black spots shall not be cause for rejection because they do not impair corrosion resistance, see A.1.4.4.
c White haze is not considered as white corrosion, see A.1.4.2.
d Typically higher corrosion resistance is achieved, however for the purpose o f this document, corrosion tests are
stopped a fter 720 h.
f
See also 7.3 for corrosion resistance related to temperature.
5.3
Sulfur dioxide test (Kesternich test)
This test is intended for outdoor building fasteners with zinc based coating systems.
When required, the sul fur dioxide test with general condensation o f moisture in accordance with
ISO 6988 or ISO 3231 shall be used to evaluate the corrosion resistance o f the coating systems; however,
as opposed to ISO 6988 or ISO 3231 for outdoor building fasteners, this test shall be carried out with
two litres of SO2 .
This test is used to monitor the consistency o f the process by quanti fying corrosion resistance on
sample fasteners taken periodically from the electroplating process (i.e. in-process control). For these
reasons, the sul fur dioxide test shall be carried out on sample fasteners in the “as-coated” condition.
The “as-coated” condition is defined as the condition a fter completion o f all steps o f coating (including
application o f any sealant, top coat or lubrication) without the occurrence o f deterioration from the
factors listed in 5.4 , i.e. be fore any sorting, packaging, assembling, transportation or storage.
10
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The sul fur dioxide test shall apply for fasteners alone and shall be carried out no sooner than 24 h a fter
coating in the “as-coated” condition.
The minimum number o f cycles shall be agreed between the supplier and the purchaser at the time o f
the order (i.e. 2, 3, 5, 8, 10, 12, 15 cycles, etc.)
Contact points o f fasteners with a holding fixture, i f any, shall not be considered in the evaluation o f the
corrosion test.
Fasteners with a captive washer have areas between the mating fastener and the washer with less
coating thickness, due to intrinsic electrochemical deposition behaviour; this is similar for fasteners
with blind holes. Both result in reduced corrosion resistance in these areas during the corrosion test
and should not be cause for rejection. In service, these areas are not normally exposed to environmental
corrosion.
5.4 Bulk handling, automatic processes such as feeding and/or sorting, storage and
transport
Bulk handling, automatic processes such as feeding and/or sorting, storage and transport can cause a
significant reduction o f corrosion protection (especially o f protection against coating metal corrosion)
depending on the coating system and the type and geometry o f the fasteners. This can especially occur
for Cr(VI)- free coating systems where less sel f-healing e ffect takes place and/or where sealants/top
coats are sensitive to impact damage and/or abrasion.
I f corrosion protection is to be checked a fter any o f these or similar processes/steps, an agreement
should be reached between the supplier and the purchaser, e.g.:
— reducing the minimum duration to neutral salt spray test;
— adjusting coating parameters;
— increasing the thickness o f the coating system; and/or
— changing the electroplated coating system.
6 Dimensional requirements and testing
6.1 General
Be fore coating, all fastener dimensions shall be within the specified tolerances specified in product
standards or technical specifications.
Coating thicknesses which can be applied on ISO metric threads in accordance with ISO 965-1, ISO 965-2
and ISO 965-3 depend on the fundamental deviation available, which itsel f depends on the thread and
the following tolerance positions:
— g, f, e for external threads;
— G or H for internal threads.
For more in formation, see Annex D .
6.2 Fasteners with ISO metric thread
6.2.1
Coating thickness
Coating thickness has a significant influence on gaugeability and assemblability, there fore thread
tolerance and clearance in the thread shall be taken into account. The coating shall not cause the zero
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line (basic size, i.e. h/H) to be exceeded in the case o f external threads, nor shall it fall below in the case
o f internal threads; see D.5.
When coating thickness in excess o f clearance is desired, special requirements shall apply; see Annex D .
6.2.2
Gaugeability and assemblability
Coated ISO metric threads shall be gauged with a GO-gauge in accordance with ISO 1502 o f tolerance
position h for external threads and H for internal threads.
When gauging coated threads o f bolts, screws and studs, a maximum torque o f 0,001 d3 (Nm) on a length
of 1 d, beginning from thread end, is acceptable. When gauging coated threads of nuts, a maximum
torque o f 0,001 D3 (Nm) is acceptable. See Table 9 .
Table 9 — Maximum torque for gauging of coated ISO metric threads
Nominal thread diameter, d or D
mm
3
4
5
6
8
10
12
14
16
18
20
22
24
27
30
33
36
39
Maximum torque for gauging
Nm
0,03
0,06
0,13
0,22
0,51
1,0
1,7
2,7
4,1
5,8
8,0
11
14
20
27
36
47
59
For other diameters, the torque shall be calculated in accordance with 0,001 d3 or
0,001 D3 (Nm) and rounded to 2 significant figures.
Acceptance procedures for assemblability may be applied by agreement between the supplier and the
purchaser:
— for external thread, the use o f a suitable nut or the original mating fastener;
— for internal thread, the use o f a suitable mandrel (e.g. the mandrel specified for proo f load in
accordance with ISO 898-2) or the original mating fastener.
6.3
Other fasteners
A fter coating, there is no dimensional requirement for fasteners with non-ISO metric thread and for
non-threaded fasteners specified in this document. For additional in formation, see Annex A .
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6.4 Test methods for thickness determination
O ne o f the
—
—
fol lowi ng
te s t me tho d s sh a l l b e u s e d to de term i ne the lo c a l th ickne s s o f the me ta l l ayer(s) :
X-ray te ch nique s i n accordance with I S O 3 49 7.
C ou lome tric me tho d i n accorda nce with I S O 2 17 7; th i s me tho d shou ld no t b e u s e d when add itiona l
non- conduc tive layers are pre s ent.
—
M ic ro s copic me tho d i n accordance with I S O 14 6 3 (on a ny are a(s) o f the
fas tener) .
—
M agne tic i nduc tive te ch n ique s i n accordance with I S O 2 178 ( b e fore add ition o f any s e a l ant a nd/or
lubric a nt) ; th i s me tho d c an a l s o b e u s e d to de term i ne the to ta l lo c a l th ickne s s .
—
E ddy c urrent ( pha s e s en s itive) te s ti ng i n accorda nce with I S O 2 19 6 8 .
I n c a s e o f d i s pute, the m icro s copic me tho d i n accorda nce with I S O 14 6 3 sh a l l b e u s e d, a nd the th ickne s s
sh a l l b e de term i ne d on one o f the re ference are a s s p e c i fie d i n
not shown in Figure 2
Figure 2
. For
fas tener
shap e s wh ich are
, the re ference a re a s shou ld b e agre e d (s e e a l s o No te 2 ) .
a) Reference areas for threaded fasteners
b) Reference areas for captive washers
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ISO 4042:2018(E)
c) Reference areas for non-threaded fasteners (examples)
Key
1
re ference areas
fo r
lo cal co ating thicknes s determinatio n
Figure 2 — Reference areas for fasteners
fre e
For
was hers a nd s i m i l ar flat
th ickne s s i s given
for
fas teners ,
corro s ion re s i s tance s p e ci fie d i n Table 8 i s de c i s ive . C o ati ng
gu ida nce on ly. For c ap tive wa shers , the re ference are a s ha l l b e the opp o s ite s ide
to the b e a ri ng s u r face o f the b olt, s c rew o r nut; s e e
Fo r more i n for m atio n re ga rd i ng co ati ng u n i for m ity o n wa s hers a nd s i m i l a r fl at
NO TE 1
T he
Figure 2 b).
co ati ng th ickne s s
Figure 2
o f the
me ta l
layer(s) ,
me as u re d
on
the
re ference
are as
fa s teners ,
in
see
A.3.4.
accord ance
with
, s ha l l comply with the m i n i mu m va lue s o f Table 10 . L ower lo c a l th ickne s s i n a lo c ation o ther
than re ference are as s ha l l no t b e c au s e
for
rej e c tion .
Table 10 — Coating thickness for the metal layer(s)
Designation for
coating thickness
Minimum local thickness on
reference areas
µm
3
5
8
10
12
15
20
25
30
3
5
8
10
12
15
20
25
30
NO TE 2
Mos t
b ol ts
a nd
s cre ws
a re
th ickne s s i s at b o th e x trem itie s o f the
the
fa s tener
re a s on s
fo r
ele c trop l ate d
fa s teners
in
b a rrel s ,
a nd
as
a
con s e quence
the
gre ate s t
co ati ng
( known a s do g- b o ne e ffe c t) . T h i s e ffe c t i s i nc re a s e d the lon ger
i s i n rel ation to its d i a me ter a nd tend s to re duce the co ati ng th ickne s s o n the s h a n k. T h i s i s one o f the
the s p e c i fic atio n o f he ad s a nd end s a s re ference a re a s i n order to h ave a rep ro duc ib le de term i n ation
o f the co ati n g th ickne s s .
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7 Mechanical and physical properties and testing
7.1 General
Electroplated coating systems shall comply with the provisions o f ISO 1456, ISO 2081, ISO 2082,
ISO 2093, ISO 4521, ISO 15726, ISO 19598 (see also Table 1) for the coating concerned in respect o f
appearance, adhesion and ductility, together with the requirements specified in 7.2 to 7.5 .
7.2
Appearance
The coated fastener shall be free from blisters, delamination and uncoated areas which can adversely
a ffect the corrosion protection. Local excess o f coating (e.g. in case o f top coats) shall not impair
functional properties (gaugeability, torque/clamp force relationship, etc.).
It is possible to add dyes/pigments to the passivation or chromatation solution in order to give a
coloured aspect to the conversion layer, o ften used for distinction purposes. Dyes/pigments may also
be added to sealants/top coats to obtain coloured sur faces.
7.3
Corrosion resistance related to temperature
Elevated temperature can a ffect the corrosion protection o f coated fasteners.
When agreed at the time o f the order, the corrosion resistance may be tested a fter a specified heating
cycle. Temperature and duration shall be agreed upon, e.g. 1 h at 120 °C, 24 h at 120 °C, 1 h at 150 °C. For
zinc-based coatings, a fter heating the fasteners at part temperature for a specified cycle, the corrosion
resistance requirements specified in 5.2 shall still be met.
7.4 Torque/clamp force relationship
When required, torque/clamp force relationship may be determined for fasteners with ISO metric
threads with electroplated coating systems including sealants and/or top coats with integral lubricant
and/or subsequently added lubricant.
The test method shall be agreed between the supplier and the purchaser, in accordance with ISO 16047
or fasteners with ISO metric thread, and/or in accordance with other relevant technical specifications.
f
The requirements for torque/clamp force relationship shall be agreed between the supplier and the
purchaser. See A.2 for in formation.
7.5 Determination of hexavalent chromium
When required, the presence or absence o f Cr(VI) shall be determined in accordance with
ISO 3613:2010, 5.5.2.
8 Applicability of tests
8.1 General
All requirements specified in Clauses 5 to 7 apply as far as they are general characteristics o f the
coating. When required by the purchaser, optional testing shall be agreed at the time o f the order.
8.2
Tests mandatory for each lot
The following tests shall be carried out for each lot o f fasteners:
— coating thickness (see 6.4);
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— gaugeability/assemblability o f fasteners with ISO metric thread (see 6.2.2);
— appearance (see 7.2 ).
8.3
Tests for in-process control
The following tests are not intended to be applied for each fastener lot but shall be used for in-process
control (see ISO 16426), when relevant:
— corrosion resistance: NSS test (see 5.2 );
— in accordance with 4.4, supplemental/additional process verification with regard to IHE.
8
.
4
T
e
s
t
s
t
o
b
e
p
e
r
f
o
r
m
e
d
w
h
e
n
s
p
e
c
i
f
i
e
d
b
y
t
h
e
p
u
r
c
h
a
s
e
r
The following tests are per formed when specifically required by the purchaser. In-process control
(see 8.3 ) may be used to supply test results to the purchaser:
— corrosion resistance: NSS test (see 5.2 ) or alternatively and only when specifically required, sul fur
dioxide test (see 5.3 );
— temperature resistance (see 7.3);
— torque/clamp force relationship (see e.g. ISO 16047);
— determination o f presence or absence o f hexavalent chromium (see 7.5 ).
9 Designation system
9.1 General
A coating system can be built-up by a number o f layers as shown in Table 11. However, not all layers
need to be present; see Figure 1.
Table 11 — Key to designation for electroplated coating systems
Element
Basis metal
Metal layer(s)
Description
Zinc
Zinc-nickel
Zinc-iron
Conversion coating (pas sivation)
(for other metal layers, see Table 1)
Transparent
Iridescent
Black
Yellow
Sealant/top coat
Additional lubricant
a
16
No conversion coating
Sealant (see also A.1.3)
Top coat (see also A.1.3)
No sealant, no top coat
No lubricant
Subsequently added lubricant
For chromate conversion coatings, see Table 14 .
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Steel
Symbol
Zn
ZnNi
ZnFe
An
Cn
Fn
Designation
Table 12
Table 13 a
Gn
U
T2
T7
T0
nL
T4
Table 15
Table 15
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ISO 4042:2018(E)
9.2 Designation of electroplated coating systems for the order
The designation o f the coating shall be added to the fastener designation in accordance with the
designation system specified in ISO 8991. The electroplated coating system shall be designated in
accordance with Table 11 and in the same order. A slash (/) shall be used to separate data fields in the
coating designation. See examples in 9.3 .
The designation o f electroplated coating systems in accordance with this document is based on the
system specified in ISO 2081 and ISO 19598 for zinc and zinc alloy electroplated coatings.
The obsolete designation codes according to ISO 4042:1999 1) are given in Annex F for in formation.
NOTE
For other electroplated coatings, the designation shall be in accordance with the relevant standards
referenced in Table 1 .
When a stress relie f process and/or baking is required, it shall not be included in the designation but be
specified separately.
Table 12 — Designation for electroplated coating systems in ordering fasteners
Electroplated coating system
Metal layer(s)
Coating material Thickness c
Zn
In accordance
ZnNi a
ZnFe b
with
Table 10
Conversion
coating
Sealant, top coat
and/or lubricant
In accordance
with Table 13
or Table 14
In accordance
with
Table 15
Neutral salt
Torque/clamp
spray test
duration
(red rust) c
force
specification,
if any
e.g. 480 h
Cd
Zinc-nickel electroplated coatings for fasteners have a typical content o f 12 % to 16 % nickel by mass and are designated
by ZnNi(12) in ISO 15726. I f further nickel content is desired, see ISO 15726.
b Zinc-iron alloy is specified as 0,3 % to 1 % o f iron by mass.
c Thickness can be replaced by minimum neutral salt spray test duration in accordance with Table 8: in this case,
thickness shall be omitted in the coating system designation and corrosion resistance shall be added at the end o f the
designation; see 9.3, Example 1.
d Range o f µtot or K values to be specified at the time o f the order; see also A.2.1.
a
Table 13 — Designation for hexavalent chromium free conversion coatings
(only for zinc and zinc-alloy electroplated coatings)
Passivation a
Code b
Name
An
Transparent
Cn
Iridescentd
Fn
Black
Gn
Yellow
U
—
Typical aspect
Transparent, clear to bluishc
Transparent, clear to iridescent
Black, dark iridescent permitted
Yellow to yellow iridescent
No conversion coating
Nanoparticles may be incorporated in all types o f passivation to improve the aspect and/or functional properties.
b The first letter corresponds to the conversion coatings as specified in ISO 2081; the second letter (n) indicates
hexavalent chromium in the conversion coating in accordance with ISO 19598.
c Bluish can vary from light-blue to dark iridescent blue, depending on the coating system.
d Also called thick layer passivation.
a
1)
no
Withdrawn.
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Table 14 — Designation for hexavalent chromium conversion coatings (only for zinc and zincalloy coatings)
a
Chromate conversion coating
Typical aspect
a
Code
Name
A
Clear
Transparent, clear to bluish
C
Iridescent
Yellow iridescent
D
Opaque
Olive-green
F
Black
Black, dark iridescent permitted
U
—
No conversion coating
The letter corresponds to the conversion coatings as specified in ISO 2081.
Table 15 — Designation for sealants, top coats and/or lubricants
Code a
—
T0
T2
T4
T7
nL
Name
Requirement
When no code T is specified, sealant or top coat can be used at the choice o f the coater.
No sealant, and
Sealant and top coat shall not be applied for a certain application
(e.g. for adherence, conductivity, electric contact, welding).
no top coat
Sealant shall be applied, it may be with or without integral
Sealantb
lubricantc .
Lubricant or wax shall be applied.
Subsequently added lubricantd
Lubricant can be applied directly on the metal layer, or on the
passivation, or on a sealant, or on a top coatc .
A top coat shall be applied.
Top coat is o ften used to achieve particular characteristics, e.g.
Top coatb
chemical resistance, colour.
Top coat may be with or without integral lubricantc .
Integral lubricant shall not be present (this code shall be added
No lubricant
to T2 or T7, as relevant).
NOTE For more in formation about sealants and top coats, see A.1.3.
a
Coding for fasteners was developed to be consistent with ISO 2081 and ISO 19598.
b Sealant and top coat may be organic or inorganic, or a combination o f both.
c When torque/clamp force relationship (e.g. range o f friction coe fficient) is specified, integral lubricant or subsequently
added lubricant shall be applied as appropriate.
d When a subsequently added lubricant is specified, the code T4 shall be placed a fter a slash and directly a fter the
designation o f the sealant or top coat; see 9.3, Example 4.
9.3 Examples of designation of hexavalent chromium free electroplated coating
systems for fasteners
When a minimum corrosion resistance is specified in the designation, the compatibility o f the
requirement with the coating system included in the designation shall be checked in accordance with
Table 8 .
EXAMPLE 1 Fastener with an electroplated coating (ISO 4042) o f zinc-nickel alloy (ZnNi) with the typical
nickel content o f 12 % to 16 %, without required coating thickness but with a minimum corrosion resistance
to neutral salt spray test o f 720 h without occurrence o f basis metal corrosion (red rust), with a hexavalent
chromium free transparent conversion coating (An), with no specific sealant, top coat or lubricant, is designated
as follows:
[fastener designation] – ISO 4042/ZnNi/An/720h
18
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ISO 4042:2018(E)
EXAMPLE 2 Fastener with an electroplated coating (ISO 4042) o f zinc (Zn), with a required coating thickness
o f 8 μm and hexavalent chromium free transparent passivation (An), is designated as follows:
[fastener designation] – ISO 4042/Zn8/An
EXAMPLE 3 Fastener with an electroplated coating (ISO 4042) o f zinc (Zn) and a required coating thickness
o f 12 μm, with a hexavalent chromium free iridescent conversion coating (Cn), with a subsequent sealant with or
without integral lubricant (T2), is designated as follows:
[fastener designation] – ISO 4042/Zn12/Cn/T2
EXAMPLE 4 Fastener with an electroplated coating (ISO 4042) o f zinc (Zn) and a required coating thickness
o f 12 μm, with a hexavalent chromium free black conversion coating (Fn), with a subsequent top coat (T7), with
a subsequently added lubricant (T4), and with a coe fficient o f friction µtot within the range o f [0,10 to 0,20], is
designated as follows:
[fastener designation] – ISO 4042/Zn12/Fn/T7/T4 (µ0,10–0,20)
EXAMPLE 5 Fastener with an electroplated coating (ISO 4042) o f zinc (Zn) and a required coating thickness
o f 8 μm, with a hexavalent chromium free iridescent conversion coating (Cn), where a subsequent sealant is
prohibited (T0), is designated as follows:
[fastener designation] – ISO 4042/Zn8/Cn/T0
EXAMPLE 6 Fastener with an electroplated coating (ISO 4042) o f zinc (Zn) and a required coating thickness
o f 8 μm, with a hexavalent chromium free black conversion coating (Fn), where a subsequent sealant is le ft to the
choice o f the coater, is designated as follows:
[fastener designation] – ISO 4042/Zn8/Fn
EXAMPLE 7 Fastener with an electroplated coating (ISO 4042) o f zinc-nickel alloy (ZnNi) with the typical
nickel content o f 12 % to 16 % and a required coating thickness o f 8 μm, with a hexavalent chromium free
transparent conversion coating (An), and with no specific sealant, top coat, lubricant or torque/clamp force
requirement is designated as follows:
[fastener designation] – ISO 4042/ZnNi8/An
9.4 Designation of fasteners with electroplated coating systems for labelling
At least the following in formation shall be added to labelling, separated by a slash (/):
— ISO 4042 for the electroplated coating system in accordance with this document;
— the material o f the coating;
— the thickness o f the metal layer(s), or minimum neutral salt spray test duration in accordance with
Table 8;
— the conversion coating in accordance with Table 13 (the su ffix n indicating that it does not contain
hexavalent chromium) or with Table 14;
— the sealant, top coat and/or subsequently added lubricant, i f any, in accordance with Table 15 .
EXAMPLE
[fastener designation] – ISO 4042/ZnNi8/Fn/T7/T4
10 Ordering requirements for electroplating
When ordering an electroplated coating system for fasteners in accordance with this document, the
following in formation shall be supplied:
a) the re ference to this document (ISO 4042:2018);
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19
ISO 4042:2018(E)
b)
c)
the co ati ng de s ignation (s e e C lau s e 9) ;
the
prop er tie s
o f the
fas teners
relevant
for
the
co ati ng
pro ce s s ,
e . g.
b as i s
materi a l ,
s ur face
cond ition, h ard ne s s , ten s i le s treng th and/or prop er ty cla s s;
d)
the s tre s s rel ievi ng cond ition s , i f any,
e)
for fa s teners
for
s tre s s rel ievi ng prior to ele c tropl ati ng;
with I S O me tric th re ad, the s p e c i fic th re ad tolerance o f the non- co ate d
fa s tener with i n
a th re ad tolera nce p o s ition, i f any;
f)
the re qu i rement, i f a ny,
a nd
g)
the
4.5
fo r
p re c autio n s to b e ta ken aga i n s t the r i s k o f I H E , e . g. b a ki n g (s e e
4.4
);
re qu i rements
for
torque/cla mp
force
relation s h ip,
if
any,
a nd
relate d
te s t
me tho d
(e . g.
I S O 16 0 47 ) , a s agre e d b e twe en the s uppl ier and the pu rcha s er;
h)
o ther re qu i rements i f any (e . g. chem ic a l re s i s tance, s uitabi l ity
for ad he s ive s , ele c tric a l conduc tivity/
i n s u l ation) ;
i)
the add itiona l te s ts to b e c a rrie d out, i f a ny (s e e
j)
re qui rements
for
8.4
) and rel ate d s ampl i ng;
te s t rep or t, i f any, i n accordance with I S O 162 2 8 .
11 Storage conditions
Storage cond ition s s ha l l no t i mp ai r the torque/clamp
co ate d
20
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(s e e a l s o
A.4).
force
prop er tie s and corro s ion re s i s tance o f the
© ISO 2018 – All rights reserved
ISO 4042:2018(E)
Annex A
(informative)
Design aspects and assembly of coated fasteners
A.1 Design
A.1.1 General
Be fore selecting a coating system, all functions and conditions o f the assembly should be considered and
not just the fastener; see A.2.2 . The purchaser should consult the supplier to determine the appropriate
choices for a given application.
Today, Cr(VI) is widely restricted. It is there fore recommended to use exclusively Cr(VI)- free conversion
coatings (passivations) for new applications.
For sealants and top coats (see A.1.3 ), an integral lubricant or an additional lubricant may be chosen
to achieve torque/clamp force properties. Sealants and top coats may be chosen to increase corrosion
resistance and to achieve other specific properties and/or per formances (e.g. chemical resistance,
mechanical resistance, impact/abrasion resistance, aspect, colour, thermal resistance, electrical
insulation/conductivity, UV resistance).
A.1.2 Coating process
Electroplated coating systems can be applied in bulk process using barrels or in rack process. Top coats
are usually applied using a dip-spin process.
Electroplating for fasteners is generally a mass process. When lots o f small quantities are to be coated,
a suitable coating line and/or process can be necessary in order to achieve the required properties
and per formances for the coated fasteners. For fasteners o f large size or mass, or when the risk o f
thread damage is to be reduced or avoided, rack processing instead o f bulk/barrel processing may be
considered.
When top coats are applied, the curing process (especially with higher temperature and/or longer
duration) can have a detrimental e ffect on the properties/per formances o f fasteners, e.g.
— for cold worked fasteners,
— for fasteners with thread rolled a fter heat treatment where intentionally introduced residual
stresses may be reduced,
— for prevailing torque nuts with non-metallic insert.
A.1.3 Sealants and top coats
Sealants and/or top coats are generally intended to improve the corrosion resistance o f zinc based
coating systems. However, both show di fferent characteristics:
— A sealant is usually applied in the wet state without drying prior to its application. This allows the
sealant to be partly incorporated in the passivation layer forming a composite layer, which improves
corrosion resistance. Sealants are also used for several other purposes such as lubrication, reduction
o f the iridescence o f passivation layers, matting or brightening e ffect, etc. The layer thickness is
typically about 0,5 µm to 2 µm.
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ISO 4042:2018(E)
— A top coat is usually applied in the dry state a fter an intermediate drying step. Top coats are o ften
used when particular requirements shall be met, such as incorporation o f pigments to achieve
intensive colour (e.g. black), high chemical resistance, etc. The layer thickness is typically about
2 µm to 10 µm.
The selection o f the nature o f a sealant or top coat should be based on desired additional properties;
see A.2.2.
A.1.4 Possible effects of coating corrosion on appearance
A.1.4.1
General
Corrosion testing in accordance with ISO 9227 leads to two kinds o f corrosion products:
— coating corrosion o f the zinc or zinc alloy layer, generally known as white corrosion (or “white rust”);
— basis metal corrosion, generally known as red rust.
Further optical changes can occur in the initial phase o f corrosion testing, such as a slight whitish film
known as white haze (or “grey veil”), or such as small black spots.
A.1.4.2
White haze
White haze results from slight reaction o f the test media with the zinc, mainly occurring in natural
micro-cracks o f the metal layer and/or the passivation layer. In case o f zinc-nickel alloy layers, white
haze stops further corrosion and is considered to be the condition for the high corrosion stability.
a) White haze on zinc-nickel after 72 h NSS
testing
b) White haze on zinc-nickel after 1 000 h
NSS testing
Figure A.1 — White haze (examples)
Typically white haze appears on zinc-nickel layers without or with transparent or iridescent passivation
a fter about 24 h to 72 h o f corrosion testing; see Figure A.1 a). White haze can also appear on nonalloyed zinc layers as well as zinc-iron or zinc-nickel alloy in combination with a black passivation layer
a fter about 24 h to 120 h o f corrosion testing.
White haze is not voluminous and is not visible in the wet state, but only on dry parts; see Figure A.2.
22
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ISO 4042:2018(E)
a) Part in wet state
b) Part in dry state
Figure A.2 — Examples of white haze on a zinc-nickel layer after 720 h NSS testing in wet and
dry state
Wh ite h a z e i s a natu ra l phenomenon i n p ar tic u la r
for
z i nc-n ickel layers and s hou ld b e accep te d . I n
c as e o f h igher re qu i rements to co s me tic/de corative app e arance, a written agre ement b e twe en the
pu rcha s er and the s uppl ier i s re com mende d .
A.1.4.3
White corrosion
I n contra s t to wh ite ha ze, wh ite corro s ion o f z i nc a nd z i nc a l loy layers re s u lts
from
ex ten s ive corro s ion
o f the co ati ng me ta l, i s more volu m i nou s and ca n b e a l re ady identi fie d i n the we t s tate o f the p ar ts; s e e
Figures A.3
a nd
A.4.
a) White corrosion of iridescent passivated
zinc layer after 240 h NSS testing
b) Severe white corrosion of iridescent passivated zinc layer after 480 h NSS testing
Figure A.3 — Examples of white corrosion
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ISO 4042:2018(E)
a) Parts in wet state
(only white corrosion is visible)
b) Same parts in dry state
(white haze and white corrosion visible)
Key
1 white corrosion
2
white haze
Figure A.4 — Examples of white corrosion and white haze on a zinc layer with black passivation
and transparent sealant after 240 h NSS testing
A.1.4.4 Black spots
Black
s p o ts
can
corro s ion; s e e
app e a r
Figure A.5
duri ng
accelerate d
corro s ion
te s ti ng
b e fore
i n itia l
o cc u rrence
o f co ati ng
. M ai n ro o t c au s e i s m icro - de fe c ts o f the b as i s me ta l and/or the co ati ng me ta l .
C orro s ion me d i a c an m igrate or b e entrapp e d i n the b a s i s me ta l a nd c a n c au s e corro s ion u nder lack o f
ox ygen,
NO TE
form i ng
black corro s ion pro duc ts .
O ther ro o t c au s e s
fo r
B lack s p o ts sha l l no t b e c au s e
b l ack s p o ts e xi s t b ut a re no t
for
fu l l y
i nve s tigate d at th i s ti me .
rej e c tion b e c au s e they do no t i mp a i r corro s ion re s i s ta nce a nd do no t
typic a l ly app e ar under s er vice cond ition s .
24
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ISO 4042:2018(E)
a) Part after 168 hrs NSS
testing
b) Same part after 408 h NSS
testing
c) Typical black spots
d) Black spots after 240 h NSS test of fasteners with iridescent passivated zinc layer
Figure A.5 — Examples of black spots on a zinc layer with iridescent passivation after NSS testing
A.2 Functional properties
A.2.1 Assemblability and mountability
In case o f applying an additional top coat or additional coatings by a dip spin process, clearance
between assembly components (e.g. clearance hole), dimensional tolerances o f the functional parts o f
the fasteners, tool gripping (e.g. for retaining rings), tool insertion (e.g. for recess and internal drives)
and assembly should not be impaired.
For dimensional requirements a fter coating for ISO metric screw threads, see 6.2 and Annex D .
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ISO 4042:2018(E)
The compatibility o f the coating system with the tightening process should be considered, especially
with high speed tightening e.g. 100 min−1 and above (risk of overheating, increase of coefficient of
friction, stick/slip, etc.).
In addition, the compatibility o f the coated fasteners with the clamped parts, e.g. tapped holes, clamped
parts in aluminium, magnesium, stainless steel, parts with electrophoretic coating, hot dip galvanised
parts, plastic, wood, should be considered.
For fasteners with ISO metric thread, at least one o f the mating threaded fasteners should be lubricated
for a consistent torque/clamp force relationship and to achieve a specific clamp force. Electroplated
coating systems provide lubricated solutions (see A.1.1). Torque/clamp force relationship can be
determined in accordance with ISO 16047 and expressed as a coe fficient o f friction µtot or by means o f
a K- factor.
A.2.2 Other properties of coated fasteners and assemblies
A.2.2.1
Chemical resistance
I f chemical resistance is required, organic top coats applied on electroplated coating systems are
typically more resistant against acids and alkaline chemical than inorganic top coats or sealants.
A.2.2.2
Electrical conductivity
The electrical conductivity o f electroplated coating systems with a sealant is generally su fficient for
application o f electrophoretic coatings and antistatic purposes. Electroplated coating systems in
combination with sealants and top coats are usually not suitable for electrical grounding.
A.2.2.3
Galvanic corrosion
In order to reduce the risk o f galvanic corrosion, each part o f the assembly should be considered (coated
asteners and clamped parts). A direct metal contact o f coated fasteners with non-coated clamped
parts should be avoided, especially for stainless steel, aluminium, magnesium, copper or copper alloys,
carbon fibre materials, and carbon filled rubber. Due to their higher insulating e ffect, organic top coats
can improve the resistance against galvanic corrosion.
f
The most suitable measure to reduce the risk o f galvanic corrosion is to select a coating or coating
system for the fastener with the same or a similar electrical potential compared to the clamped parts.
A.2.2.4
Cleanliness
For cleanliness requirements, the suitability o f the electroplated coating system should be checked (e.g.
dust, particle size, particle type, number o f particles, applicability o f cleanliness test methods).
A.3 Particular issues related to fasteners and coating processes
A.3.1 General
The type o f fasteners should be considered when choosing a coating system and related coating process:
A.3.2 to A.3.9 list the main issues for each type of fasteners. Suitable measures should be taken into
account for the following types o f fasteners, and potential issues should be considered.
When sorting is required for one or more specific selected characteristic(s), agreement should be
reached between the purchaser and the supplier.
26
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ISO 4042:2018(E)
A.3.2 Fasteners with ISO metric thread
M a i n i s s ue s to b e con s idere d are
—
th re ad damage s (the he avier the p ar t, the more s en s itive it i s) ,
—
fi l l i ng o f d rive s/re ce s s e s and i nterna l th re ad s i n c a s e o f an appl ic ation o f top co ats ,
—
p ar ticle s i n th re ad s ,
—
contam i nation with
For ele c troplate d
foreign
fas teners
p a r ts .
to b e co ate d with an add itiona l top co at and with pitch
P < 1 m m, a s p e ci a l
agre ement b e twe en the s uppl ier and the pu rcha s er shou ld b e re ache d .
A.3.3 Fasteners with captive washer
M a i n i s s ue s to b e con s idere d are:
—
re tention o f p ar ticle s (e . g. when s ho t bla s ti ng i s u s e d as pre -tre atment) ;
—
non-u n i form co ati ng dep o s ition with lower lo c a l th ickne s s due to the tendenc y o f s ticki ng to thei r
mati ng
—
fa s tener
du ri ng a b arrel ele c tropl ati ng a nd d ip - s pi n pro ce s s , e . g. s e a la nt, top co at;
contam i nation with
foreign
p a r ts .
A.3.4 Washers and similar fasteners
Fre e wa shers a nd s i m i lar
fa s teners
tend to s tick to ge ther du ri ng b arrel ele c tropl ati ng a nd a d ip - s pi n
pro ce s s , e . g. s e a la nt, top co at. T h i s typic a l ly re s u lts i n a non-u n i form co ati ng dep o s ition with lower
lo ca l th ickne s s and c an c au s e lower corro s ion re s i s tance .
A.3.5 Fasteners with adhesive or patch
M a i n i s s ue s to b e con s idere d are
—
appl ic abi l ity o f ad he s ive or p atch to the s ele c te d ele c troplate d co ati ng s ys tem,
—
fu nc tiona l
—
prop er tie s ( l ack o f ad he s ion, i mp ai rment o f torque/cla mp
force
relation s h ip) ,
re duc tion o f corro s ion re s i s tance (e . g. elevate d temp eratu re appl ic ation/c u ri ng temp eratu re
for
p atche s) ,
—
p er formance o f ad he s i ve or p atch i n combi nation with lubricate d co ati ng s ys tem s .
A.3.6
Prevailing torque nuts
For a l l me ta l prevai l i ng torque nuts , ele c tropl ate d co ati ng s ys tem s i n combi nation with s i l ic ate b a s e d
s e a la nts or top co ats c an c au s e i ncre as e d
fric tion
i n the engage d th re ad up to ga l l i ng du ri ng tighten i ng;
an a lternative s e a lant or top and/co at or a n add itiona l lubrica nt s hou ld b e u s e d
For
prevai l i ng
torque
nuts
with
non-me ta l l ic
i n s er t,
a
p o s s ible
for
de tri menta l
s uch appl ic ation s .
e ffe c t
o f the
c u ri ng
temp eratu re (e . g. i n c as e o f organ ic top co ats) s hou ld b e con s idere d .
A.3.7 Fasteners with recess, internal drive, cavity or hole
E s p e ci a l ly
for s ma l l fas teners ,
s p e ci a l te ch nique s c an b e ne ce s s ar y to prevent re tention o f p ar ticle s (e . g.
when s ho t bla s ti ng i s u s e d a s pre -tre atment) and exce s s o f co ati ng i n re ce s s e s , i nterna l d rive s , c avitie s
or hole s ( bl i nd or th rough hole s) i n c as e o f add itiona l ly appl ie d top co at.
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ISO 4042:2018(E)
A.3.8 Screws which form their own mating thread
When s ele c ti ng ele c tropl ate d co ati ng s ys tem s , the re qu i rements
for
th re ad- form i ng prop er tie s s hou ld
b e con s idere d, e . g. me tric th re ad- form i ng s crews , s el f-tappi ng , s el f- d ri l l i ng , ch ip b o ard s crews a s wel l
as s c rews
for
pla s tics .
A.3.9 Clips and retaining rings
T he mai n i s s ue s to b e con s idere d are as
—
—
fol lows:
Tangl i ng a nd damage s o f cl ip s and re tai n i ng ri ngs s hou ld b e avoide d du ri ng the co ati ng pro ce s s .
Sp e c ia l te ch n ique s c an b e ne ce s s a r y to prevent re tention o f p a r ticle s a nd/or exce s s o f co ati ng i n
c a s e o f add itiona l ly appl ie d top co ats .
A.4 Storage of coated fasteners
D u ri ng
s torage
a nd
b e fore
i n s ta l l ation,
d i re c t
contac t
with
water
or
o ther
l iquid,
exp o s u re to du s t, e tc . s hou ld b e avoide d; s uch cond ition s c an i mp ai r torque/cla mp
conden s ation,
force
relation s h ip
and/or corro s ion re s i s tance .
28
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ISO 4042:2018(E)
Annex B
(informative)
Hydrogen embrittlement consideration
B.1 General
A typical definition for Hydrogen Embrittlement in literature and standards is as follows:
A permanent loss o f ductility in a metal or alloy caused by hydrogen in combination with tensile stress,
resulting from externally applied load and/or internal residual tensile stress.
Hydrogen Embrittlement (HE), o ften also called Hydrogen Assisted Cracking (HAC), is classified
under two categories based on the source o f hydrogen: Internal Hydrogen Embrittlement (IHE) and
Environmental Hydrogen Embrittlement (EHE). IHE is triggered by residual hydrogen from steelmaking
or from processing steps such as pickling, electroplating. EHE is triggered by hydrogen introduced into
the metal from external sources while it is under tensile stress, e.g. in the case o f in-service fasteners.
The term Stress Corrosion Cracking (SCC) is commonly used to define EHE that occurs when hydrogen
is produced as a by-product o f sur face corrosion and is absorbed by the steel fastener.
Measures to prevent IHE do not eliminate the risk o f EHE when a susceptible fastener is exposed to
corrosion generated hydrogen. See ISO/TR 20491 2) [18 ] for more detailed in formation about hydrogen
embrittlement o f fasteners.
B.2 Conditions for hydrogen embrittlement failure
For Hydrogen Embrittlement failure to occur, the three following conditions are concurrently necessary:
— material condition that is susceptible to hydrogen damage (root cause o f hydrogen embrittlement),
— tensile stress (typically the result o f an applied load; including residual tensile stress), and
— atomic hydrogen.
See HE in Figure B.1 .
I f all three o f these elements are present in su fficient quantities and given time, hydrogen damage
results in crack initiation and growth until the occurrence o f delayed fracture. Time to failure can vary,
depending on the severity o f the conditions and the source o f hydrogen.
NOTE
2)
IHE failures occur within hours a fter installation, typically less than 72 h.
Under preparation.
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ISO 4042:2018(E)
Figure B.1 — Conditions for Hydrogen Embrittlement (HE/HAC) failure
B.3 Electroplating and Internal Hydrogen Embrittlement (IHE)
The most relevant manu facturing processes to consider with respect to IHE are primarily coating
processes and related sur face cleaning and preparation processes (e.g. pickling). These processes are
significant because they are typically the final manu facturing step and the coating materials (e.g. zinc)
act as a barrier to hydrogen e ffusion.
Electroplating processes generate hydrogen; however, the amount o f hydrogen absorbed by the
asteners is not directly related to the quantity o f hydrogen generated. The amount o f hydrogen which
may be absorbed depends on the process type (e.g. alkaline zinc, acid zinc, zinc alloy) and process
parameters (e.g. current density, electroplating time, rack/barrel plating). The most important factor
that influences the quantity o f hydrogen that remains in a fastener is the perm eability o f the coating to
hydrogen e ffusion. The permeability o f the coating determines i f it allows hydrogen to e ffuse outward
or i f the coating is an e ffective barrier that blocks hydrogen e ffusion, thus forcing it to stay in the steel.
f
Typical cleaning for electroplating comprises hot alkaline cleaning followed by acid pickling and
anodic electrolytic alkaline cleaning. Acid pickling is a significant source o f hydrogen in coating
processes. There fore a suitable inhibitor and minimum cleaning cycle time should be used to
minimize the risk o f IHE.
For fasteners with hardness above 390 HV, such as property class 12.9, special pre-treatments are
advisable using non-acidic methods such as mechanical cleaning (e.g. dry honing, shot blasting) or
alkaline cleaning. However, for small size fasteners (e.g. below M6), fasteners with captive washers,
with small internal drive/recess, with internal thread or for some non-threaded fasteners (e.g. spring
pins, conical washers), acid cleaning could be the only method that works.
Studies have shown that there is no risk o f IHE for phosphate coated property class 12.9 fasteners when
le ft at ambient temperature for more than 24 h, because phosphate coatings are very porous.
Similarly, studies have shown that the risk o f IHE is significantly lower for alkaline zinc-nickel coatings
containing 12 % to 16 % nickel compared to pure zinc coatings. One o f the reasons is that zinc-nickel
coatings (ZnNi) are more permeable than zinc (Zn) or zinc-iron (ZnFe) coatings.
For aerospace applications, specific Low Hydrogen Embrittlement zinc-nickel (LHE-ZnNi) processes
have been developed to replace Low Hydrogen Embrittlement cadmium (LHE-Cd) coatings.
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ISO 4042:2018(E)
T he s u s cep tibi l ity to I H E o f c a s e hardene d and temp ere d s c rews dep end s no t on ly on core hard ne s s ,
but a l s o on variable s s uch a s c a s e hard ne s s a nd c a s e dep th . T he s u s cep tibi l ity to I H E i nc re a s e s as the s e
vari able s i ncre as e . T he s crew ge ome tr y/s hap e c an a l s o i mp ac t the s u s cep tibi l ity as there cou ld b e no
d i s ti nc t tran s ition are a
from
h igh c as e h ard ne s s to the lower h ard ne s s i n the core i n th i n s e c tion s o f
the s crew, e . g. i n c as e o f a flange, s e e I S O/ T R 2 0 49 1 . T he gre ater prop or tion o f the c as e dep th i n th i n
s e c tion s i s the c au s e o f a h igher s u s cep tibi l ity.
B.4 Baking
T he key
fac tors
that i n fluence b a ki ng e ffe c tivene s s are
—
temp eratu re,
—
du ration,
—
p erme abi l ity o f the co ati ng ,
—
co ati ng th ickne s s .
For s u s cep tible
fa s teners
(e . g. with ha rd ne s s/core ha rd ne s s ab ove 3 9 0 H V ) that a re z i nc ele c troplate d,
8 h to 10 h at 19 0 ° C to 2 2 0 ° C i s a m i n i mu m re com mende d b a ki ng du ration . H owever:
—
dep end i ng on typ e, s i z e a nd s treng th/ h ard ne s s level o f the
fas teners
i n combi nation with co ati ng
s ys tem and co ati ng pro ce s s , s hor ter du ration s are s ucce s s fu l ly appl ie d;
—
dep end i ng on typ e, s i z e and s treng th/ h ard ne s s level o f the
fa s teners ,
b a ki ng du ration s up to 2 4 h
c a n b e re qui re d to s u fficiently re duce mobi le hyd ro gen .
T he
com mon
prac tice
for
i nade quate
o f b a ki ng
z i nc
fa s teners for
ele c troplate d
4
h
at
approxi mately
19 0
°C
is
e xtrac ti ng hyd ro gen b e c au s e z i nc i s an e ffe c tive b arrier to hyd ro gen d i ffu s ion . I t ha s
b e en shown th at a b a ki ng duration o f 4 h c a n even b e de tri menta l and c an le ad to o cc as iona l
fai lu re s .
For b a ki ng to b e e ffe c tive and b enefici a l, longer b a ki ng duration i s re com mende d .
P rop er ty clas s 10 .9
fa s teners th at are corre c tly manu fac tu re d to the i ntende d materi a l a nd me ta l lu rgic a l
prop er tie s , a s s p e ci fie d i n I S O 8 9 8 -1 , are no t s u s cep tible to
Given
the
c u rrent u nders tand i ng
b a ki ng that prevents the s e
o f b a ki ng
fai l
e ffe c tivene s s
fas teners from fa i l i ng.
due to I H E , and do no t ne e d to b e b a ke d .
a nd
materi a l
P rop er ty cla s s 10 .9
s u s cep tibi l ity,
fas teners
it i s
no t the
are s ome ti me s b a ke d
as a pre c aution aga i n s t ma nu fac tu ri ng errors or out- o f- control pro ce s s that cou ld render the materi a l
susceptible.
I n c as e o f a delaye d
shou ld
be
processes.
frac tu re
i nve s tigate d,
in
i n the appl ic ation, a l l cond ition s i nclud i ng a s s embly and s er vice cond ition s
add ition
to
the
fa s teners
and
thei r
ma nu fac tu ri ng
a nd
ele c troplati ng
B a ki ng c riteria as s p e c i fie d i n I S O 2 0 81 , I S O 9 5 8 8 a nd I S O 19 5 9 8 are to o bro ad a nd no t appl ic able
for
fa s teners .
T he
ma xi mu m
temp eratu re
and
du ration
used
in
a
b a ki ng
pro ce s s
con s ideration s . I t s hou ld no t exce e d the temp eratu re at wh ich the
are
fa s teners
l i m ite d
by
the
fol lowi ng
were origi na l ly temp ere d,
and shou ld no t i mp ai r the p er formance o f the co ati ng. E xce s s o f temp eratu re a nd/or du ration c an
i mp ai r the b enefici a l e ffe c t o f th re ad rol l i ng a fter he at tre atment.
Z i nc
ele c troplate d
p a r ts
a re
u s ua l ly
b a ke d
at
a
temp eratu re
no t
h igher
tha n
220
°C .
C ad m iu m
ele c troplate d p ar ts are u s ua l ly b a ke d to a temp eratu re no t h igher than 2 0 0 ° C .
T he b a ki ng pro ce s s i s typic a l ly p er forme d a fter ele c troplati ng , prior to appl ic ation o f a convers ion
co ati ng and/or s e a la nt and/or top co at, i f any. H owever, o ther s e quence s may b e s u itable dep end i ng on
the s p e c i fic prop er tie s o f s u r face fi n i she s .
T he ti me b e twe en ele c troplati ng and b a ki ng s hou ld b e kep t s hor t a s a matter o f go o d prac tice . T he
i ntent o f s uch prac tice i s to ma xi m i ze the e xtrac tion o f mobi le hyd ro gen o ther wi s e a p or tion o f the
© ISO 2018 – All rights reserved
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31
ISO 4042 :2018(E)
mobile hydrogen can become reversibly trapped and more di fficult to bake out. This phenomenon has
been shown to be relevant for electroplated steels at hardness in the range o f 500 HV and above. The
o ften used approach o f speci fying an exact duration (e.g. 4 h) is purely subjective and is intended as
a practical operational time- frame and also as a quality assurance mechanism for monitoring good
practice. Time between coating and baking should not be used as a rigid criterion for acceptability o f a
fastener lot and it definitely should not be used as the basis for assigning root cause to a fastener failure.
Baking furnace conditions, including methods o f loading, duration in the furnace and uni formity o f
temperature, should be controlled. Achieving a well- founded and e ffective baking strategy, including
the decision whether to bake or not to bake, should be validated by empirical test data obtained from
sustained load testing and/or by process qualification tests, e.g. as specified in DIN 50969-2 and
ASTM F1940.
B.5 Stress relief
Stress relie f prior to electroplating is not relevant or appropriate for fasteners that are quenched and
tempered without further alteration; tempering e ffectively relieves residual stress.
Residual tensile stress in fasteners that are work hardened a fter quenching and tempering and prior to
electroplating can lead to the initiation o f hydrogen assisted microcracks. I f the material is susceptible
and there is su fficient hydrogen and the residual tensile stress resulting from work hardening might
exceed the HE threshold stress o f the steel, a beneficial preventive measure is to per form a stress relie f
operation prior to electroplating.
Only operations that cause significant plastic de formation resulting in residual tensile stresses such as
cold forming, cold bending, cold straightening, and some drilling and welding operations may justi fy
stress relie f be fore electroplating. Standard secondary machining operations such as grinding, turning,
tapping and milling are not problematic.
The e ffectiveness o f stress relie f increases with increasing temperature and duration. However, the
maximum temperature is limited such that the mechanical properties o f the fasteners are not impaired.
NOTE
Stress relie f criteria recommended in ISO 9587 are too broad and not applicable for fasteners.
B.6 Hydrogen embrittlement test methods
Test methods designed to either detect or measure any mechanical loss o f strength resulting from the
e ffect o f hydrogen always include a time component.
Typically, hydrogen embrittlement testing is per formed by means o f sustained load tests. Sustained
load testing is intended as a post-production (e.g. a fter electroplating) quality assurance step for
testing high strength fasteners that are susceptible to IHE. Sustained load testing consists o f applying a
specific static load for a fixed period o f time ranging from 24 h to 200 h, depending on the specification.
The qualitative nature o f the sustained load test is such that a fastener will either pass or fail at the
given point in time. There are several methods for sustained load testing. The tests most o ften used
for fasteners are specified in ISO 15330, DIN 50969-2, NASM 1312-2, ASTM F606/F606M. Other tests
developed or agreed to by the manu facturer or purchaser can be used i f e ffective in detecting IHE for
particular types o f fasteners.
NOTE
Sustained load tests are suitable for production testing. Standard sustained load test specifications
are not intended for testing parts a fter removal from service.
32
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© ISO 2018 – All rights reserved
ISO 4042:2018(E)
Annex C
(informative)
Corrosion protection related to zinc coatings with chromate
conversion coatings
This annex gives in formation for typical corrosion resistance o f zinc coatings with chromate conversion
coatings (containing hexavalent chromium) when tested with neutral salt spray test in accordance with
ISO 9227; see Table C.1 .
Chromate conversion coatings should not be used for new applications.
Table C.1 — Neutral salt spray corrosion resistance of zinc coatings
Designation
code in
accordance
with this document
Zn5/A
Zn5/B
Zn5/C
Zn5/D
Zn5/F
Zn8/A
Zn8/B
Zn8/C
Zn8/D
Zn8/F
Zn12/A
Zn12/B
Zn12/C
Zn12/D
Zn12/F
Zn25/A
Zn25/B
Zn25/C
Zn25/D
Zn25/F
a
b
Obsolete designation code for
coatings a
Fe/Zn 5c1A
Fe/Zn 5c1B
Fe/Zn 5c2C
Fe/Zn 5c2D
Fe/Zn 5Bk
Fe/Zn 8c1A
Fe/Zn 8c1B
Fe/Zn 8c2C
Fe/Zn 8c2D
Fe/Zn 8Bk
Fe/Zn 12c1A
Fe/Zn 12c1B
Fe/Zn 12c2C
Fe/Zn 12c2D
Fe/Zn 12Bk
Fe/Zn 25c1A
Fe/Zn 25c1B
Fe/Zn 25c2C
Fe/Zn 25c2D
Fe/Zn 25Bk
Coating
thickness
µm
Minimum neutral salt spray test duration
for barrel coating
Chromate
conversion
coating
designation
A
5
8
12
25
B
C
D
F
A
B
hours
No coating metal
corrosion b
No basis metal
corrosion
(white corrosion)
(red rust)
6
12
48
72
12
6
24
C
D
F
A
72
96
C
D
F
A
72
96
B
24
6
24
24
24
36
72
96
—
48
72
120
144
72
72
96
144
168
96
B
C
D
F
Data not available
For zinc coatings with chromate conversion coating, see classification code in ISO 2081 in connection with ISO 4520.
Low coating thickness impairs the resistance o f the chromate conversion coating.
© ISO 2018 – All rights reserved
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33
ISO 4042:2018(E)
Annex D
(informative)
Coating thickness and thread clearance for ISO metric screw
threads
D.1 General
The applicability o f the required coating system to ISO metric threads is limited by the basic deviation
o f the threads, and hence limited by the pitch diameter, allowance, and tolerance positions.
Dimensional requirements and testing for fasteners with ISO metric thread are specified in 6.2 .
Electroplated coating processes usually do not produce a uni form distribution o f the coating thickness
on the whole sur face o f the fastener. As the coating thickness has a significant influence on gaugeability,
it is necessary to consider thread position, tolerance and clearance in the thread.
When designing fasteners to be electroplated, at least the following should be taken into consideration:
— type and size o f the fastener;
— tolerance position o f the thread be fore coating;
— typical dispersion o f the thickness resulting from the coating process (see D.2 );
— clearance available in the thread (see Figure D.1).
34
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ISO 4042:2018(E)
a) Internal/external thread
b) Examples for (6g/6G) and (6g/6H)
Key
1 zero line
2
3
4
5
maximum p itch diameter o f the nut thread b e fo re co ating
minimum p itch diameter o f the nut thread b e fo re co ating
maximum p itch diameter o f the b o lt thread b e fo re co ating
minimum p itch diameter o f the b o lt thread b e fo re co ating
6
D2
Td2
T
manu factured clearance (to lerance no t co mp letely us ed until lo wer limit o f 6 H )
2
2
to lerance
fo r D
to lerance
fo r d
EI
lower limit o f the
fundamental
deviatio n o f the nut thread with res p ect to zero line
es
up p er limit o f the
fundamental
deviatio n o f the b o lt thread with res p ect to zero line
a, c
The minimum clearance co rres p o nds to the
b,d
The maximum clearance co rres p o nds to the ab s o lute value o f the
fundamental
deviatio n.
fundamental
deviatio n p lus the to lerance
grade value.
Figure D.1 — Pitch diameter tolerance position and clearance for coating
Sub figu re s a) and b) give e xample s o f cle a rance re qu i re d to accom mo date a co ati ng th ickne s s o f 6 μm
on b olt/nut as s embly M 8 .
D.2 Geometrical relationship between coating thickness and pitch diameter
When a co ati ng with the ore tic a l/re ference co ati ng th ickne s s
pitch d ia me ter
2
d
i nc re a s e s b y 4
© ISO 2018 – All rights reserved
Provided by IHS Markit under license with ANSI
t as
s hown i n
Figure D.2
t
i s appl ie d on an externa l th re ad, the
and Table D .1
.
35
ISO 4042:2018(E)
Key
a
change o f p itch diameter due to co ating
P
p itch o f the thread
t
thicknes s o f the co ating
1
2
3
p itch diameter o f the b o lt b e fo re co ating,
d2
p itch diameter o f the b o lt a fter co ating
thread axis
t
0 , 5a
= sin 30 ° = 0 , 5
0,2 5
a
=t
a
= 4t
Figure D.2 — Geometrical relationship between coating thickness and pitch diameter of an
external thread
Table D.1 — Geometrical relationship between coating thickness and pitch diameter
Dimensions in micrometres
Coating thickness
Resulting increase of the pitch diameter
4t
12
t
a
3
4
5
16
20
24
32
40
48
6
8
10
12
a
T h i s p i tch d i a me ter i nc re a s e co r re s p o nd s to the m i n i mu m cle a ra nce wh ich i s ne e de d
fo r
the co ati n g th ickne s s
t
.
D.3 Coating thickness on externally threaded fasteners
E le c troplati ng c a n re s u lt i n a non-u n i form co ati ng th ickne s s ,
for
—
r e duc ti o n
th i c kne s s
i nc r e a s e
at
e x te r n a l
e d ge s
a nd
th i c k ne s s
two mai n re as on s:
in
c av i ti e s ,
e . g.
th re ad
r o o t,
i nte r n a l d r i ve ,
36
Provided by IHS Markit under license with ANSI
© ISO 2018 – All rights reserved
ISO 4042:2018(E)
— thickness increase at the extremities o f long parts known as the dog-bone e ffect, as shown amplified
in Figure D.3.
Figure D.3 — Typical distribution of coating thickness on a bolt resulting from electroplating
process (exaggerated for illustrative purposes)
For fasteners with external thread, the dog-bone e ffect typically depends on the ratio between length l
and diameter d. Typically bolts with l > 5 d could have a local thickness at mid-length down to one third
to hal f when compared to local thickness at the re ference areas (see Figure 2).
The specification o f thicker layers (in order to get a su fficient coating thickness at mid-length o f a
long bolt — typically 10 d to 15 d — for the purpose o f corrosion protection) could result in excess o f
coating at the end o f the thread, thus impairing assemblability and/or gaugeability. Reciprocally, the
specification o f thinner layers will allow easy thread engagement, but could result in lack o f coating
thickness at mid-length. It is the knowledge o f the coater to minimize the impact o f the dog-bone e ffect.
Additional layers such as sealants, top coats and/or lubricants can cause material retention in holes,
recesses, internal drives, cavities and at thread roots.
D.4 Coating thickness on internal threads
Electroplating does not deposit the same coating thickness on external sur faces in comparison with
internal sur faces such as internal threads.
A principle o f electroplating is that the distribution o f metal coating thickness is proportional to the
local current density during the electroplating process. The expected metal coating thickness in internal
threads also depends o f the nut geometry, i.e. relative height o f the nut compared to thread diameter.
Di fferent kinds o f electrolyte (e.g. acidic or alkaline) can result in di fferent thickness distribution (or
even uncoated areas in internal threads). Typically, the use o f alkaline electrolytes results in more
uni form metal distribution.
NOTE
However, contrary to the above, significant quantity o f coating can be deposited in internal threads by
using specific electroplating processes.
In practice for electroplated zinc or zinc-alloy coatings, it is possible to use a tolerance position 6H for
internal metric threads be fore coating, provided the tolerance zone is not taken up to the zero line
(basic size). I f nuts are to be coated by a third party, functional thread assemblability should be verified.
Additional sur face layers such as sealant, top coat and/or lubricant applied with a dip-spin process can
result in material retention in internal threads. I f this would not allow the acceptance o f a 6H GO-gauge,
another thread tolerance position o f the uncoated nut should be considered.
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37
ISO 4042:2018(E)
D.5 Clearance for coating thickness
D.5.1 Fasteners with external thread
Fa s teners with ex terna l th re ad shou ld b e manu fac tu re d to provide s u fficient cle a rance at the pitch
d ia me ter to accom mo date the co ati ng th ickne s s .
C o ati ng th ickne s s wh ich c a n b e appl ie d on I S O me tric e xterna l th re ad s i n accorda nce with I S O 9 65 -1 ,
I S O 9 6 5 -2 or I S O 9 6 5 -3 dep end s on the
in
fundamenta l
devi ation (cle ara nce) at the pitch d ia me ter a s given
Tab le D . 2 , wh ich its el f dep end s on the s c rew th re ad a nd the tolera nce p o s ition g ,
f
or e
for
e xterna l
th re ad s .
Tab le D . 2 i nd ic ate s the
p o s ition
for
fu nda menta l
va lue s l i m iti ng the avai lable s p ace
38
deviation (cle ara nce) a s a
func tion
o f the th re ad pitch a nd tolerance
the u nco ate d e xterna l th re ad . T he m i n i mum and ma xi mu m cle a rance s are the ore tic a l
Provided by IHS Markit under license with ANSI
for
co ati ng.
© ISO 2018 – All rights reserved
ISO 4042:2018(E)
Table D.2 — Theoretical minimum clearance and corresponding maximum coating thickness
for ISO metric external threads
Tolerance position g
Nominal
thread
diameter, d
Thread
pitch
P
(co a rs e pitch
mm
mm
Fundamental
deviation
ma x
th re ad) a
0,35
μm
1,6
0 ,45
−2 0
3
0, 5
0,6
−2 0
3,5
−2 1
4
5
0 ,7
0,8
1
−2 2
6
8
10
12
1,25
1,5
1 ,75
2
−5 0
9
−5 3
−3 8
9
−5 6
9
− 60
− 40
7
− 42
−3 4
1 8 , 2 0 a nd 2 2
− 42
2 4 a nd 2 7
− 48
3,5
3 0 a nd 3 3
−5 3
3 6 a nd 3 9
− 60
42 a nd 45
− 63
4 8 a nd 5 2
−71
5
9
−3 6
−3 5
6
2,5
4, 5
−3 6
5,5
5 6 a nd 6 0
−75
6
64
−80
8
8
8
−3 4
8
8
10
10
11
12
13
14
15
− 45
− 48
9
10
12
13
15
15
17
18
20
Fundamental
deviation
μm
−2 6
−2 8
.
Tolerance position e
μm
−3 8
−3 8
4
μm
6
−3 2
ma x
−3 4
−2 4
14 a nd 16
3
4
4
5
5
5
5
−19
2 ,5
.
Coating
thickness
Fundamental
deviation
μm
−19
2
0 ,4
NO TE
Coating
thickness
Tolerance position f
−5 2
−5 8
− 63
−70
17
18
20
21
22
23
−75
−80
−85
−90
−95
Coating
thickness
ma x
.
μm
—
—
—
—
—
—
12
13
14
15
15
15
− 60
− 63
− 67
16
−71
17
−71
17
20
21
22
23
25
−80
−85
−90
−95
−10 0
−10 6
26
28
−1 1 2
−1 1 8
29
T he ore tic a l up p er l i m it o f co ati n g th ickne s s i s c a lc u l ate d on the b a s i s o f th re ad d i men s ion wh ich i s at the
upp er l i m it (e x ter n a l th re ad) o f the re s p e c ti ve th re ad to lera nce .
a
I n fo r m ation o n no m i n a l d i a me ter
men s ion i s the th re ad p itch
P.
fo r
co a rs e pitch th re ad i s gi ven
fo r
co nven ience on l y: the de ter m i n i n g d i
-
D.5.2 Fasteners with internal thread
Fa s teners with i nterna l th re ad s hou ld b e manu fac tu re d to provide s u fficient cle a rance at the pitch
d i ame ter to accom mo date the co ati ng th ickne s s .
C o ating thicknes s which can b e applied on I S O metric i nternal threads in accordance with I SO 9 65 -1 ,
I SO 9 65 -2
or
I S O 9 65 -3 dep ends on the
fundamental deviation (clearance)
at the pitch diameter as given in
Table D. 3 , which itsel f dep ends on the s crew thread and the tolerance p os ition G or H
Table D . 3 i nd ic ate s the
p o s ition
for
fu nda menta l
deviation (cle ara nce) a s a
the u nco ate d i nterna l th re ad .
va lue s l i m iti ng the ra nge o f ava i l able s p ace
© ISO 2018 – All rights reserved
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fu nc tion
for internal
o f the th re ad pitch and tolerance
T he m i n i mu m a nd ma xi mu m cle a rance s
for
thread.
a re the ore tic a l
co ati ng.
39
ISO 4042:2018(E)
Table D.3 — Theoretical minimum clearance and corresponding maximum coating thickness
for ISO metric internal threads
Thread pitch
Nominal thread
diameter
P
D
(co a rs e pitch
mm
0,35
+19
2
0 ,45
+19
2 ,5
+2 0
3
0,5
0,6
+2 0
3,5
+2 1
4
5
0 ,7
0,8
1
+2 2
6
8
10
12
1,25
1,5
1 ,75
2
+2 6
6
+2 8
7
+3 2
+3 4
1 8 , 2 0 a nd 2 2
+ 42
2 4 a nd 2 7
+48
3 0 a nd 3 3
+5 3
3 6 a nd 3 9
+60
42 a nd 45
+63
4 8 a nd 5 2
+71
5,5
5 6 a nd 6 0
+75
6
64
+80
4, 5
5
4
4
5
5
5
5
6
+3 8
4
μm
+2 4
14 a nd 16
3,5
NO TE
μm
1,6
0,4
3
Tolerance position H
th re ad) a
mm
2 ,5
Tolerance position G
Fundamental Coating thickness
deviation
ma x.
8
8
8
10
12
13
15
15
15
Po s s ib le i f the u nco ate d
th re ad o f the nut i s no t
m a nu fac tu re d up to the
zero line
16
20
T he o re tic a l up p er l i m it o f co ati n g th ickne s s i s c a lc u l ate d on the b a s i s o f th re ad d i men s ion wh ich i s at the
lower l i m it (i ntern a l th re ad) o f the re s p e c tive th re ad tolera nce .
a
I n for m atio n on nom i n a l d i a me ter
men s ion i s the th re ad p itch
40
Provided by IHS Markit under license with ANSI
P.
for
co a rs e pitch th re ad i s given
for
conven ience o n l y: the de ter m i n i ng d i
-
© ISO 2018 – All rights reserved
ISO 4042:2018(E)
D.6 Compatibility between corrosion resistance and clearance
For comp atibi l ity b e twe en corro s ion re s i s tance and cle a rance, s e e
Figure D.4 f
or i n formation .
Figure D.4 — Example of checking the compatibility between corrosion resistance and
clearance
B y cho o s i ng a combi nation o f th re ad tolerance p o s ition s
for
e xterna l a nd i nterna l th re ad s , it s hou ld b e
en s u re d that the re s i s tance agai n s t s trippi ng o f the as s embly i s gre ater th an the u lti mate ten s i le lo ad o f
the externa l th re ade d
fa s tener,
I nc re a s e d cle arance c an a l s o
fatigue
Fm .
a ffec t o ther
fu nc tiona l
as p e c ts , s uch a s prevai l i ng torque prop er tie s ,
re s i s ta nce, e tc .
© ISO 2018 – All rights reserved
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41
ISO 4042:2018(E)
Annex E
(in fo rmative)
Coating systems tested in accordance with ISO 9227, NSS —
Evaluation of cabinet corrosivity for the neutral salt spray test
E.1 Introduction
When e va lu atio n o f the c ab i ne t co rro s i vity i s re que s te d , it s ho u ld b e p er fo r me d i n acco rd a nce with
th i s a n ne x.
T h i s a n nex i s de s igne d to b e u s e d i n add ition to the te s t me tho d s p e c i fie d i n I S O 9 2 2 7
s pray te s t. I t ha s b e en e s tab l i s he d
for
the eva luation o f s te el
fas teners
for
neutra l s a lt
with z i nc b as e d co ati ngs ,
for
the
pu rp o s e o f control l i ng ma nu fac tu ri ng lo ts .
T he ma i n re a s on
for
th i s development a s a complement to I S O 9 2 2 7 wa s the ne ce s s a r y i mprovement i n
term s o f rel i abi l ity, repro ducibi l ity and re duc tion o f d i s p ers ion o f te s t re s u lts , a s neutra l s a lt s pray te s t
i s us e d
—
for
accep tance o f
fas tener
pro duc tion b y
u s i ng the s ame eva luation mo de (app e arance o f re d ru s t on z i nc-b a s e d co ate d s te el re ference p anel s
rather th an weight lo s s eva luation) , and
—
p erio d ic control s o f the corro s ivity o f the te s t c abi ne t.
T h i s me tho d i s s ucce s s fu l ly u s e d i n the
fa s tener
i ndu s tr y a nd s ign i fic antly i mprove s the repro duc ibi l ity
o f re s u lts o f d i fferent s a lt s pray c abi ne ts .
E.2 Purpose
T h i s a n nex i s a complement to I S O 9 2 2 7 th at s p e ci fie s a me tho dolo g y
the te s t c abi ne t
for neutra l
s a lt s pray te s t (NS S ) ,
for s te el fas teners
for
eva luati ng the corro s ivity o f
with z i nc and z i nc a l loy ele c troplate d
co ati ng s ys tem s i n accordance with th i s do c u ment.
Two typ e s o f te s ts are defi ne d i n order to:
—
de term i ne the corro s ivity level as a grade a nd the cond ition s under wh ich the c abi ne t i s con s idere d
compl ia nt, by control l i ng the c abi ne t corro s ivity th roughout the u s e fu l volu me, i ndep endent o f
s p e ci men s to b e te s te d;
—
mon itor the c abi ne t corro s ivity b e twe en p erio d ic control s .
E.3 Frequency of controls
T he de term i nation o f the corro s ivity level s ha l l b e c a rrie d out at le as t once a ye ar, a nd a l s o prior to the
us e o f the c abi ne t
fol lowi ng
maj or mai ntenance or rep ai r work on the e qu ipment.
T he corro s ivity mon itori ng sha l l b e c arrie d out at le a s t once a month .
42
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ISO 4042:2018(E)
E.4 Operating conditions
E.4.1 Parameters
All parameters specified in ISO 9227 shall be checked, except the method for evaluating the cabinet
corrosivity.
E.4.2 Reference panels
The re ference panels shall be made o f steel, e.g. CR24 in accordance with ISO 6932, coated at least
on one sur face with a layer o f zinc obtained by high-speed continuous hot dip galvanizing. The zinc
thickness shall be (11 ± 1) μm.
The dimensions o f the re ference panels shall be 190 mm × 90 mm; see Figure E.4.
The re ference panels may be oiled for better protection in storage.
The re ference panels shall be accompanied by an inspection certificate containing at least the following:
— the identification o f the supplier;
— the identification o f the re ference panels (coil and cast number);
— the chemical composition and mechanical properties o f the substrate metal;
— the measured thickness o f the zinc deposit;
— the re ference o f the protective oil, i f any.
E.4.3 Preparation of the reference panels
E.4.3.1
Degreasing procedure
The re ference panels shall be used within 24 h a fter the degreasing procedure has been completed.
They shall be degreased as follows:
a) Pre-degrease with acetone using a so ft cloth.
b) Degrease with ultrasonics in a cleaning solution make-up o f the following:
— sodium bicarbonate (NaHCO 3 ) (15 ± 2) g/l;
— sodium carbonate (Na 2 CO 3 ) (10 ± 2) g/l;
— trisodium phosphate (Na3 PO 4) (20 ± 2) g/l;
— volume adjusted to one litre with distilled or deionized water.
Ultrasonic conditions:
— temperature (45 ± 2) °C;
— duration (7 ± 1) min.
The service li fe o f this degreasing solution is 36 months in an opaque container and in storage
conditions ranging from 0 °C to 40 °C. Store this solution in a sealed container between uses (one
litre o f this solution is su fficient for a maximum o f 5 panels).
c) Remove the panel with tongs be fore turning o ff the ultrasonics. Rinse in distilled or deionized
water, then in a clean solvent (ethanol or acetone) and finally leave to dry in the air.
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43
ISO 4042:2018(E)
E.4.3.2
Panel protection
D egre a s e d p a nel s shou ld b e hand le d we ari ng glove s . E dge s a nd b ack o f p anel s s hou ld b e pro te c te d
with a s u itable ad he s ive tap e (e . g. the brown- colou re d P VC tap e with a width o f 3 8 m m or 5 0 m m, or
s i m i l ar ad he s ive removable pro te c tion) , a s s p e c i fie d i n
Figure E.4
, s o that the to ta l exp o s e d s u r face i s
16 0 m m × 8 0 m m .
E.4.3.3
Position of reference panels and collectors
T he s upp or t sh a l l b e made o f chem ic a l ly i ner t materia l . I t s ha l l enable p o s ition i ng o f the p a nel s i n l i ne
with an angle o f (2 0 ± 5 ) °
from
the ver tica l, with the u npro te c te d
face
upward s . T he centre o f e ach
p anel s ha l l b e level le d at the me a n s p e c i men e xp o s ure height. T he nu mb er and relative p o s ition o f the
p anel s var y i n accorda nce with the te s t me tho d a nd cabi ne t de s ign, s e e
—
at le a s t th re e p anel s s ha l l b e u s e d
for the
Figures E.1 to E.3:
a n nua l control . T he p anel s sh a l l b e p o s itione d 1 /4, 1 /2 and
3/4 o f the d i s ta nce b e twe en the s pray no z z le and the mo s t d i s tant c abi ne t wa l l;
—
at le a s t one p anel s ha l l b e u s e d du ri ng the month ly mon itori ng. T he p a nel sha l l b e p o s itione d
ha l fway b e twe en the s pray no z z le and the mo s t d i s tant c abi ne t wa l l .
T he col le c ting devices sha l l b e place d i n accordance with I S O 92 2 7. For annual control, the numb er o f
col lec ting devices sha l l b e the s ame as the numb er o f p anel s , and lo cated as clo s e as p o s s ible to the p anels .
Key
L
1
2
dis tance b etween s p ray no zzle and the mo s t dis tant cab inet wall
p anel
s p ray no zzle
Figure E.1 — Off-centred spray cabinet
44
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ISO 4042:2018(E)
Key
L
1
2
dis tance b etween s p ray no zzle and the mo s t dis tant cab inet wall
p anel
s p ray no zzle
Figure E.2 — Centred spray cabinet
Key
L
1
2
3
dis tance b etween s p ray no zzle and the mo s t dis tant cab inet wall
p anel
s p ray no zzle
door
Figure E.3 — Square-centred spray cabinet
E.4.3.4
Filling of the cabinet
T he te s t p anel s sh a l l b e a rrange d s o that they do no t come i nto contac t with the c abi ne t, and s o that
thei r s ur face s are e xp o s e d to
© ISO 2018 – All rights reserved
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fre e
ci rc u l ation o f s a lt s pray.
45
ISO 4042:2018(E)
During the annual control, the cabinet shall only contain the re ference panels.
Monthly monitoring may be conducted during normal operation o f the cabinet. The other exposed
specimens shall not obstruct the re ference panel.
E.4.4 Control mask
The control mask specified in Figure E.4 shall be reproduced on a transparent foil. The mask shall be
placed on the re ference panel.
Dimensions in millimetres
Hot dip galvanized panel: 190 mm × 90 mm
Sur face area o f one square: 1 cm 2
Number o f squares: 128
% corroded = n squares × 0,78
Key
1 protected zone (see E.4.3.2)
Figure E.4 — Protection and control mask for reference panels
E.4.5 Determination of the corroded surface
A square is reported to be corroded as soon as it shows one point o f red rust (flow included). See
examples in Figure E.5.
All visual check shall be made on non-rinsed, still wet panels.
The final check shall be made a fter a period o f 70 h to 72 h and then every (24 ± 1) h. For practical
aspects, it is recommended to start the test on Friday.
I f one o f the panels shows evidence o f red rust during the 72 h check, repeat the test (e.g. the following
Monday) and check it every 24 h.
46
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ISO 4042:2018(E)
For the annual control, the cabinet shall be open during 30 min per day a fter the initial period o f 72 h.
For the monthly monitoring, each opening shall not exceed 60 min. The open duration shall not be
deducted.
E
.
4
.
6
Q
u
a
n
t
i
f
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c
a
t
i
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o
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r
o
s
i
v
i
t
y
The top o f the mask shall be placed exactly at the top o f the re ference panel in accordance with its
orientation in the cabinet during the test.
An example o f quantification o f corrosivity is shown in Figure E.5.
Key
1
2
3
top o f the mask and top o f the panel
re ference panel
control mask
35 squares showing red rust: the percentage o f corrosion (Red Rust Rate – RRR) is 27,3 % (35 × 0,78)
F
i
g
u
r
© ISO 2018 – All rights reserved
Provided by IHS Markit under license with ANSI
e
E
.
5
—
E
x
a
m
p
l
e
o
f
q
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a
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f
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a
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i
o
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f
t
h
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o
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47
ISO 4042:2018(E)
E.5 Corrosivity results
Red Rust Time (RRT) is the time taken for the rusting level to exceed 5 % (i.e. a minimum o f seven
squares showing red rust).
RRT for each test panel and the corresponding grade shall be expressed in accordance with Table E.1 .
See also the examples in E.6.5 .
Table E.1 — Grading system for the evaluation of the corrosivity level
Red Rust Time (RRT)
Grade
Corrosivity evaluation
RRT ≤ 72
72 < RRT ≤ 96
96 < RRT ≤ 120
A
Not compliant
C
D
Compliant
h
RRT > 120
B
Not compliant
For corrosivity evaluation, the cabinet is compliant for the purpose o f testing steel fasteners with zinc
and zinc-based coating systems, when the grade o f each panel is equal to B or C in accordance with
Table E.1 .
The cabinet corrosivity is expressed by using the same grading system o f A to D in accordance with
Table E.1 .
NOTE
When testing coated fasteners with several cabinets (e.g. at purchaser’s and supplier’s places), reliable
consistent results can only be achieved when the corrosivity level is compliant in accordance with Table E.1 .
E.6 Example of report format for annual control and monthly monitoring of
the cabinet
E.6.1 Annual control and monthly monitoring of the cabinet corrosivity level
Type o f test:
Monthly monitoring 
Annual control
Test start date:
Cabinet identification number:
Re ference panel batch number:

E.6.2 Condensate check
Collector 1
Volume collected in ml/h a
Collector 2
Collector 3
NOTE The collector device number is the same as the panel number.
a
Average measurement over the entire test duration (opening time included); in accordance with ISO 9227,
(1,5 ± 0,5) ml/h for a horizontal collecting area o f 80 cm 2 (which corresponds to three collecting devices of 10 cm in
diameter each).
48
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© ISO 2018 – All rights reserved
ISO 4042:2018(E)
E.6.3 Determination of the corrosivity level
E
Red Rust Time (RRT)
h
Grade
v
i
d
e
n
c
e
o
f
r
e
d
r
u
s
t
:
%
Panel 1
q
u
a
n
t
i
f
i
e
d
o
n
t
h
e
c
o
n
t
Panel 2
r
o
l
m
a
s
k
Panel 3
A
RRT ≤ 7 2
7 2 < RRT ≤ 9 6
B
C
D
9 6 < RRT ≤ 1 2 0
RRT > 120
Result ( grade when Re d Ru s t Rate
RRR ≥ 5 %)
E.6.4 Conclusion for the corrosivity of the cabinet

C on form ity o f a l l p ara me ters
Comments:
O p erator na me:

Non con form ity
D ate:
Signatu re:
E.6.5 Example for the determination of the corrosivity level
E xa mp le s o f de term i nation o f the corro s ivity level are given i n Table s E . 2 a nd
E.3.
Table E.2 — Example 1: Compliant cabinet
E
Red Rust Time (RRT)
h
RRT ≤ 7 2
7 2 < RRT ≤ 9 6
9 6 < RRT ≤ 1 2 0
RRT > 120
© ISO 2018 – All rights reserved
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i
d
e
n
c
e
o
f
r
e
d
r
u
s
t
:
%
q
u
a
n
t
i
f
i
e
d
o
n
t
h
e
c
o
n
t
r
o
l
m
a
s
k
Grade
Panel 1
Panel 2
Panel 3
A
Re d Ru s t: 0 s qu a re
—
Re d Ru s t: 1 s qu a re
Re d Ru s t: 0 s qu a re
Re d Ru s t: 3 s qu a re s
Re d Ru s t: 8 s qu a re s
Re d Ru s t: 10 s qu a re s
(3 × 0 ,78 = ) 2 , 3 %
(8 × 0 ,78 = ) 6 , 2 %
(10 × 0 ,78 = ) 7, 8 %
Re d Ru s t: 7 s qu a re s
Re d Ru s t: 1 2 s qu a re s
Re d Ru s t: 2 0 s qu a re s
(7 × 0 ,78 = ) 5 , 5 %
(1 2 × 0 ,78 = ) 9,4 %
(2 0 × 0 ,78 = ) 1 5 , 6 %
B
B
B
C
D
Result ( grade when Re d Ru s t Rate
RRR ≥ 5 %)
v
—
C
0 ,78 %
—
—
—
C o r ro s i vity le vel: comp l i a nt
49
ISO 4042:2018(E)
Table E.3 — Example 2: Non-compliant cabinet
E
Red Rust Time (RRT)
h
RRT ≤ 7 2
7 2 < RRT ≤ 9 6
9 6 < RRT ≤ 1 2 0
RRT > 120
50
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i
d
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r
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d
r
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t
:
%
q
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t
i
f
i
e
d
o
n
t
h
e
c
o
n
t
r
o
l
m
a
s
k
Grade
Panel 1
Panel 2
Panel 3
A
Re d Ru s t: 0 s qu a re
—
Re d Ru s t: 0 s qu a re
—
Re d Ru s t: 0 s qu a re
Re d Ru s t: 1 s qu a re
Re d Ru s t: 3 s qu a re s
Re d Ru s t: 10 s qu a re s
0 ,78 %
(3 × 0 ,78 =) 2 , 3 %
(10 × 0 ,78 =) 7, 8 %
C
Re d Ru s t: 3 s qu a re s
Re d Ru s t: 7 s qu a re s
Re d Ru s t: 2 0 s qu a re s
(3 × 0 ,78 =) 2 , 3 %
(7 × 0 ,78 =) 5 , 5 %
(2 0 × 0 ,78 =) 1 5 , 6 %
D
Re d Ru s t: 7 s qu a re s
Re d Ru s t: 1 5 s qu a re s
Re d Ru s t: 3 5 s qu a re s
(7 × 0 ,78 =) 5 , 5 %
(1 5 × 0 ,78 =) 1 1 ,7 %
(3 5 × 0 ,78 =) 2 7, 3 %
B
Result ( grade when Re d Ru s t Rate
RRR ≥ 5 %)
v
D
C
—
B
C o r ro s i vity le vel: no t co mp l i a nt
© ISO 2018 – All rights reserved
ISO 4042:2018(E)
Annex F
(in fo rmative)
Obsolete designation codes for electroplated coating systems on
fasteners according to ISO 4042:1999
WARNING — This system shall not be used for new applications; it is only included for
information and for referral to existing drawings and documents still using this system. The
Clause 9 shall be used.
d
e
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F.1 Obsolete code system
O b s ole te de s ignation co de s
are given i n Table F.1
.
for
ele c troplate d co ati ng s ys tem s on
fas teners
accord i ng to I S O 4 0 42 : 19 9 9
Table F.1 — Obsolete code system
X
X
X
C o ati ng me ta l or a l loy
(see
)
Tab le F. 2
M i n i mu m co ati ng th ickne s s
(see
)
Tab le F. 3
Fi n i s h a nd ch rom ate tre atment
(see
Tab le F. 4
)
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51
ISO 4042:2018(E)
Table F.2 — Coating metal or alloy
Coating metal/alloy
Symbol
Elements
Zn
Cd
Cu
CuZn
Nib
Ni b Cr rb
CuNi b b
CuNi b Cr rb
Sn
CuSn
Ag
CuAg
ZnNi
ZnCo
ZnFe
a
Obsolete designation
Zinc
A
C ad m iu m
B
Copper
C
D
E
F
B ra s s
Nickel
Nickel- ch ro m iu m
C opp er-n ickel
C opp er-n ickel- ch ro m iu m
Tin
Copper-tin (bronze)
Silver
Copper-silver
G
H
J
c
K
L
N
Z i nc-n ickel
P
Q
R
Z i nc- co b a lt
Zinc-iron
Us e o f c ad m iu m i s re s tr ic te d o r p ro h ib ite d i n ce r ta i n co u ntr ie s .
a
b
c
Fo r I S O cl a s s i fic atio n co de , s e e I S O 145 6 .
T h ickne s s o f ch ro m iu m ap p ro x i m ate l y 0 , 3 µm .
Table F.3 — Coating thickness (total deposit thickness)
Coating thickness
One coating metal
µm
no co ati n g th ickne s s re qu i re d
3
5
8
10
12
15
20
25
30
a
T he th ickne s s s p e c i fie d
Obsolete designation
Two coating metals
a
—
—
0
1
2
3
2 + 3
3 + 5
6 + 4
9
4
5
8 + 4
10 + 5
8 + 12
6
10 + 1 5
7
8
1 2 + 18
fo r
the fi rs t a nd the s e co nd co ati n g me ta l ap p l ie s
fo r
a l l co ati n g co mb i n atio n s
e xcep t th at ch ro m iu m i s the to p co ati n g wh ich h a s a lways a th ickne s s o f 0 , 3 µm .
52
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ISO 4042:2018(E)
Table F.4 — Finish and chromate treatment
Passivation by chromate treatment a :
typical colour
Finish
Dull
Semi-bright
Bright
High-bright
Optional
no colour
bluish to bluish iridescentb
yellowish gleaming to yellow-brown, iridescent
drab olive to olive brown
no colour
bluish to bluish iridescentb
yellowish gleaming to yellow-brown, iridescent
drab olive to olive-brown
no colour
bluish to bluish iridescentb
yellowish gleaming to yellow-brown, iridescent
drab olive to olive-brown
no colour
like B, C or D
Dull
brown-black to black
Semi-bright
brown-black to black
Bright
brown-black to black
All finishes
no chromate treatmentc
a Passivation treatments are possible only with zinc or cadmium coatings.
b Applies to zinc coating only.
c Example for such a coating: A5U.
Obsolete designation
A
B
C
D
E
F
G
H
J
K
L
M
N
P
R
S
T
U
F.2 Example of obsolete designation
EXAMPLE
Fastener with electroplated zinc coating (A from Table F.2), a required coating thickness o f 5 µm
(2 from Table F.3), brightness condition “bright”, being chromated yellow iridescent (L from Table F.4) was
designated as follows:
[fastener designation] – A2L
In the case that this obsolete designation is used, the following applies:
— I f no minimum coating thickness is explicitly required, then the symbol “0” o f the coating thickness
according to Table F.3 is indicated in the code number — for example A0P — so that the code number
contains complete specifications. Symbol “0” applies correspondingly to threaded parts below M1,6
or other very small parts.
— I f other treatments are required, for example greased or oiled, this is agreed upon. I f applicable, this
treatment is added to the designation as clear text.
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53
ISO 4042:2018(E)
Bibliography
[1]
[2]
[3]
[4]
ISO 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts,
screws and studs with specified property classes — Coarse thread and fine pitch thread
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with specified property classes — Coarse thread and fine pitch thread
ISO 898-3, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 3: Flat
washers with specified property classes
ISO 898-5, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 5: Set
screws and similar threaded fasteners with specified hardness classes — Coarse thread and fine
pitch thread
[5]
ISO 965-1, ISO general purpose metric screw threads — Tolerances — Part 1: Principles and
basic data
[6]
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general purpose external and internal screw threads — Medium quality
[7]
ISO 965-3, ISO general purpose metric screw threads — Tolerances — Part 3: Deviations for
constructional screw threads
[8]
ISO 2702, Heat-treated steel tapping screws — Mechanical properties
[9]
ISO 4042:1999, Fasteners — Electroplated coatings
[10]
ISO 4520, Chromate conversion coatings on electroplated zinc and cadmium coatings
[11]
ISO 6932, Cold-reduced carbon steel strip with a maximum carbon content of 0,25 %
[12]
ISO 7539-7, Corrosion of metals and alloys — Stress corrosion testing — Part 7: Method for slow
strain rate testing
[13]
ISO 9588, Metallic and other inorganic coatings — Post-coating treatments ofiron or steel to reduce
the risk of hydrogen embrittlement
[14]
ISO 9001, Quality management systems — Requirements
[15]
ISO 10474, Steel and steel products — Inspection documents
[16]
ISO 10666, Drilling screws with tapping screw thread — Mechanical and functional properties
[17]
ISO 16426, Fasteners — Quality assurance system
[18]
ISO/TR 20491, Fundamentals of Hydrogen Embrittlement in Steel Fasteners
[19]
ASTM F606/F606M, Standard Test Methods for Determining the Mechanical Properties of
Externally and Internally Threaded Fasteners, Washers, Direct Tension Indicators, and Rivets
[20]
ASTM F1624, Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in
Steel by the Incremental Step Loading Technique
[21]
ASTM F1940, Standard Test Method for
Embrittlement in Plated or Coated Fasteners
[22]
ASTM G129, Standard Practice for Slow Strain Rate Testing to Evaluate the Susceptibility ofMetallic
Materials to Environmentally Assisted Cracking
[23]
EN 10204, Metallic products — Types of inspection documents
54
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Process Control Verification to Prevent Hydrogen
© ISO 2018 – All rights reserved
ISO 4042:2018(E)
[24]
NASM 1312-2, Fastener Test Methods - Method 2 - Interaction
[25]
DIN 50969-2, Prevention of hydrogen-induced brittle fracture of high-strength steel building
elements — Part 2: Test methods
© ISO 2018 – All rights reserved
Provided by IHS Markit under license with ANSI
55
ISO 4042:2018(E)
ICS 21.060.01
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© ISO 2018 – All rights reserved
Provided by IHS Markit under license with ANSI