Advanced Binder Treated FY-4500
Francis Hanejko & William Tambussi
Hoeganaes Corporation
Cinnaminson, NJ 08077
USA
Abstract:
The benefits of utilizing phosphorous as an alloying element in pure iron are well documented.
These include improved DC magnetic performance, higher sintered densities, and good
mechanical properties. A major disadvantage of alloying phosphorus in iron is the greater tool
wear experienced with the using of ferro-phosphorous additives. Utilizing an experimental
binder treatment process, a reduction in the strip and slide was observed during laboratory testing
of both traditional binder treated premixes at sintered densities less than 7.0 g/cm³ and with warm
die compaction materials at sintered densities of >7.2 g/cm³. This reduction in strip and slide has
the potential to minimize die wear. Both the mechanical and magnetic properties of the new
material will be presented.
Introduction:
Advantages of using phosphorus in PM steels include good magnetic properties, higher magnetic
resistivity, and good mechanical properties with excellent elongation and impact toughness. [1,2]
Typical applications for phosphorous containing materials (FY-4500) include automotive speed
sensors, flux rings for DC electric motors, and electromagnetic actuators. [3] Additionally,
phosphorous is added in FC-0205 type steels utilized in automotive main bearing caps because of
the unique combination of strength, ductility, and good sintering response. [4]
The major disadvantage of phosphorous containing materials is that phosphorous is added as a
ferro-phosphorous inter-metallic. Whether Fe2P or Fe3P, these inter-metallic compounds possess
high hardness, which then results in a powder premix consisting of a relatively soft iron matrix
incorporating a high hardness second phase particle that can cause significant die wear. The
hardness values of Fe2P and Fe3P are ~1050 HV and 1000 HV, respectively; this is compared to
an iron particle hardness of ~100 BHN (no conversion to HV is realistic at this low hardness). [5]
These high hardness particles result in abrasive wear of the punches and often the actual tool
material. Frayman has reported that the hard particle additions abrade the metallic binder of
carbide inserts. [6] The consequence of these hard particles is excessive tool wear with
subsequent more frequent tool repair and replacement. Utilizing advanced die coatings has
lessened tool wear but not eliminated it. [7] Thus for the mainstream users of FY-4500, they have
to simply “live with” the inherent high tool wear and frequent die repair associated with ferrophosphorus containing materials.
Hoeganaes Corporation produces FY-4500 materials as a binder treated premix
(ANCORBOND™). Although this binder treatment does not reduce the abrasive nature of ferrophosphorus, it minimizes segregation thus preventing potential localized excessive tool wear.
The experimental work described in this report focuses on an experimental enhanced binder
treatment system designed to counteract the abrasive characteristic of ferro-phosphorus particles.
Although the exact nature of this new binder system is proprietary, it does function with both
conventional PM lubricants designed for both conventional compaction and with modifications
can be utilized with warm die compaction processes. The work discussed in this report will
document the mechanical properties, laboratory measured ejection characteristics of this
experimental binder treatment system.
Additionally, this paper will report on the use of a 0.85% molybdenum prealloy material that is
premixed with an equivalent amount of ferro-phosphorus to yield a 0.45% phosphorus material.
This 0.85% molybdenum iron powder premixed with ferro-phosphorus has shown increases in
both the yield and tensile strengths of a material with minimal decreases in magnetic response. [8]
Combining this advanced binder treatment of traditional FY-4500 materials with a 0.85%
molybdenum prealloyed steel can produce mechanical properties higher than FY-4500 materials
with the added advantage of reduced die and punch wear.
Experimental Procedure:
In this study, six laboratory premixes were prepared and evaluated; these premixes are listed in
Table 1. All premixes were prepared by adding 2.9% Fe3P plus the appropriate powder lubricant;
thus producing a final sintered phosphorus content of ~0.45%.
The premixes were evaluated for compressibility, transverse rupture strength, green strength,
tensile and impact properties. Compaction conditions for the “cold” compaction conditions were
a die temperature of ~25 °C (75 °F) and compaction pressures of 415, 550, and 690 MPa. For the
warm die premixes, the die temperature was ~93 °C (200 °F) with compaction pressures of 550,
690, and 830 MPa. In addition to the mechanical property specimens magnetic toroids were
pressed from mixes 1 and 2 to a density of 6.9 g/cm³ and from mixes 3 through 6 to a density of
7.25 g/cm³.
After compaction, all samples were sintered in a laboratory belt furnace on ceramic trays.
Sintering conditions were 1120 °C (2050 °F) in a 90% nitrogen / 10% hydrogen atmosphere, with
a cooling rate after sintering of ~0.6 °C per second. The time above 1095 °C (2000 °F) was
approximately 20 minutes.
Table 1
Premixes Evaluated in this Investigation
Premix ID
1
(ANCORBOND
FY-4500)
Lubricant
added
% Lubricant
Added
Acrawax
0.75%
Proprietary
0.75%
Proprietary
0.40%
Proprietary
0.40%
Warm die
compaction,
conventional
Proprietary
0.40%
Enhanced binder
treated, warm die
compaction
Proprietary
0.40%
Base Iron Type
High
Compressibility
Iron Powder
High
Compressibility
Iron Powder
High
Compressibility
Iron Powder
High
Compressibility
Iron Powder
Premix Type
Conventional
Binder treated,
cold compaction
Enhanced binder
treated, cold
compaction
Warm die
compaction,
conventional
Enhanced binder
treated, warm die
compaction
5
(AncorMax 200
FL-4400 with
0.45%
Phosphorus)
0.85% prealloyed
Molybdenum
6
0.85% prealloyed
Molybdenum
2
3
(AncorMax 200
FY-4500)
4
After sintering, the samples were tested via the appropriate MPIF test standard. [9] In addition to
the mechanical property test samples, ejection characteristics were quantified. The methodology
employed was to compact a green strength bar at 690 MPa, then measure two key characteristics,
strip and slide. Strip is defined as the initial break free load required to initiate movement of the
test specimen and slide is defined as the load immediately before the specimen is ejected from the
die. Strip and slides pressures are then calculated by dividing the measured force by the area of
the bar in contact with the die surface.
Results:
Shown as Table 2 are the powder properties of the six premixes evaluated in this study. The
advanced binder treatment utilized in combination with either high compressibility iron or the
0.85% molybdenum prealloyed material does not affect the apparent density (AD) or flow
characteristics relative to ‘conventional’ processing. The data presented in Table 2 was collected
on 250 kg premixes. No data is presented for the FL-4400 material because the premix size was
only 10 kg. However, it is assumed that comparable AD and flow to the FY-4500 will be
observed with this material.
Table 2
Powder Properties of Materials Evaluated
Flow,
Premix ID
Base Iron Type
1
FY-4500
2
FY-4500
3
FY-4500
4
FY-4500
5
FL-4400
6
FL-4400
Premix Type
Conventional,
cold compaction
Enhanced, cold
compaction
Warm die,
conventional
Enhanced, warm
die
Conventional,
warm die
Enhanced, warm
die
sec /
AD, g/cm³
50 g
3.15
29.2
3.16
29.0
3.09
25.9
3.10
26.3
NA
7.50
7.40
Cold die compacted FY-4500
Warm Die FY-4500
Warm Die, FLN4400
Green Density, g/cm³
7.30
7.20
7.10
7.00
6.90
6.80
6.70
6.60
0
200
400
600
800
1000
Compaction Pressure, MPa
Figure 1:
Compressibility data for six materials evaluated, all premixes with 2.9% added
ferro phosphorus
Compressibility information is presented in Figure 1. As expected the warm die compaction
premixes show ~0.10 to 0.20 g/cm³ improvement in compressibility compared to the
conventional premixes. Although not clearly shown, compressibility of FY-4500 for the standard
and experimental enhanced binder systems are identical for both cold and warm die compaction
grades. A similar trend was noted for the FL4400 with 0.45% sintered phosphorus. Thus, the
experimental binder system had no detrimental effects on the compressibility of the FY-4500
alloy system.
4500.0
30.0
4000.0
25.0
3000.0
20.0
2500.0
15.0
2000.0
10.0
1500.0
ANCORBOND FY-4500
1000.0
EXP BInder RT Compaction
5.0
Green Strength, psi
Green Strength, MPa
3500.0
AncorMax 200 FY-4500
500.0
Exp Binder, warm die FY-4500
0.0
0.0
6.60
Figure 2:
6.70
6.80
6.90 7.00 7.10 7.20
Green Density, g/cm³
7.30
7.40
7.50
Green Strength of Tested Materials
Figure 2 presents the green strength of the FY-4500 materials compacted at both room
temperature and at 93 °C (200 °F). The experimental binder system has no detrimental effect on
the green strength of FY-4500 regardless of compaction conditions. It is noteworthy; warm die
compaction gives an approximate 75% increase in green strength over the range of green
densities evaluated. This higher green strength can result in a potential reduction in green part
damage during part handling prior to sintering.
Table 3 presents the mechanical properties developed for the six alloys investigated. Transverse
ruptures test samples were prepared for each of the materials; however, the ductility of the six
materials invalidated these data. The TRS samples were utilized to quantify the DC after
sintering. Referring to Table 3, premixes 1, 3, and 5 represent commercially available material
with ferro phosphorus additives. Premixes 2, 4, and 6 are the experimental binder system
materials. Comparing the commercial premix to the experimentally prepared premix, there is no
difference in either the measured tensile or impact properties.
In Table 3, utilizing a 0.85% molybdenum prealloyed steel with 0.45% sintered phosphorus, a
yield strength of ~ 275 MPa (40,000 psi) with an ultimate tensile strength of 413 MPa (60,000
psi) was achieved. Elongation values of >11% with impact energies of ~90 joules (70 ft.lbf) were
achieved. This combination of mechanical properties combined with the inherently high modulus
(because of the high sintered density) offers a unique combination of mechanical properties.
Table 3
Sintered Mechanical Properties of the Six Premixes Evaluated
Mix ID
Std FY4500 cold
compaction
Sintered
Density,
g/cm³
6.70
6.95
7.09
Exp FY4500 cold
compaction
6.71
6.94
7.1
Warm die
compaction
FY-4500
7.12
7.34
7.40
Exp warm
die
compaction
FY-4500
7.12
7.31
7.42
Warm die
compaction
FL-4400
7.12
7.33
7.45
Exp warm
die
compaction
FL-4400
7.08
7.34
7.48
Yield
Strength,
MPa (psi)
218
(31,700)
245
(35,700)
267
(38,800)
216
(31,400)
241
(35,000)
258
(37,500)
232
(33,700)
258
(37,500)
269
(39,100)
229
(33,300)
261
(37,900)
273
(39,700)
240
(34,900)
273
(39,600)
290
(42,100)
235
(34,100)
271
(39,400)
286
(41,500)
UTS,
MPa (psi)
280
(40.600)
324
(47,100)
356
(51,700)
273
(39,600)
322
(46,800)
353
(51,300)
327
(47,500)
368
(53,400)
382
(55,600)
324
(47,100)
371
(53,900)
390
(56,700)
339
(49,300)
391
(56,800)
413
(60,000)
330
(47,900)
386
(56,100)
409
(59,400)
Elongation,
%
Impact,
Joules
(ft.lbf)
Hardness,
HRA
5.6
10 (7)
28
6.8
24 (17)
34
7.8
31 (22)
38
5.0
14 (10)
28
7.8
20 (14)
34
8.9
28 (20)
37
9.1
17 (13)
34
10.6
34 (25)
38
10.6
52 (39)
41
9.8
15 (11)
34
10.5
32 (22)
38
10.9
57 (42)
40
10.2
32 (22)
34
12.1
58 (43)
38
11.1
95 (70)
42
9.3
32 (22)
35
10.5
47 (35)
39
11.1
86 (64)
42
Figure 3 presents the dimensional change data for the six materials after sintering at 1120 °C
(2050 °F) in a 90% nitrogen / 10% hydrogen atmosphere. The experimental binder system for the
“cold” die compaction showed slightly higher shrinkage by approximately 0.02% at the 6.8 g/cm³
sintered density compared to the commercial material (due to gage R&R this is essentially a zero
difference). The sintered dimensional change for the warm die compaction FL-4500 was the
same for both the conventional material and the experimental binder system. The same trend was
determined for the FL-4400 with added ferro phosphorus
0.04
0.02
Sintered DC, %
0.00
-0.02
-0.04
-0.06
AM 200 FL-4400
Cold FY-4500 conv.
Cold, FY-4500 Experimental
Warm FY-4500, conv.
-0.08
-0.10
-0.12
6.60
6.80
7.00
7.20
Green Density, g/cm³
7.40
7.60
Figure 3:
Dimensional change of the premixes, premixes 3 and 4 are excluded because of
carbon pick up during sintering.
Table 4 presents the DC magnetic data developed for each premix; two trends are apparent. First,
the experimental binder system does not affect the magnetic performance of the either FY-4500
or the prealloyed FL-4400 material at either 6.9 or 7.25 g/cm³ sintered densities. Second, the
prealloyed 0.85% molybdenum steel premixed with 0.45% sintered phosphorus has nearly
identical magnetic properties to the standard FY-4500 material. The data presented in Table 4
appears to suggest that higher density does not improve the magnetic properties of PM materials.
However, MPIF standard 35 shows that higher part density produces higher magnetic
performance. The reason for the discrepancy in the data shown is as follows: premix 1 and 2
were sintered at a different time relative to premixes 3 through 6. Chemical testing showed that
premixes 3 through 6 had higher sintered carbon thus the lower permeability and higher coercive
force. This higher sintered carbon was not a result of lubricant burn off issues but rather a result
of improper furnace conditioning.
Table 4
Sintered DC Magnetic Data
Mix ID
Std FY4500 cold
compaction
Sintered
Density,
g/cm³
Applied
Field,
Oe
Max
Induction,
kGauss
Hc,
Oersteds
Br, kGauss
6.90
15
11.3
2.0
11.3
11.9
2.0
11.9
11.8
1.8
11.7
12.2
1.9
12.2
13.1
2.2
11.8
13.7
2.2
11.9
13.2
2.2
11.9
13.8
2.3
12.1
13.1
2.1
11.8
25
13.7
2.1
12.0
15
13.0
2.1
11.6
13.7
2.1
11.8
Max DC
Perm
2200
25
Exp FY4500 cold
compaction
6.90
Warm die
compaction
FY-4500
Exp warm
die
compaction
FY-4500
Warm die
compaction
FL-4400
Exp warm
die
compaction
FL-4400
7.25
15
2700
25
15
2600
25
7.25
15
2600
25
7.25
15
2800
7.25
2800
25
Ejection characteristics as measured by strip and slide are presented in Table 5. The data shown
is for the FY-4500 material only. At ambient compaction conditions, the experimental binder
system shows a 10% lower stripping pressure and ~5% lower sliding pressure compared to the
standard ANCORBOND treated material. At warm die compaction conditions, the standard
material has a significantly higher strip and slide compared to the lower density green strength
bars. However, the modified experimental binder produces a dramatic decrease in both the strip
and slide.
Table 5
Ejection Characteristics of FY-4500
Premix ID
Std FY-4500 cold
compaction
Exp FY-4500 cold
compaction
Warm die compaction
FY-4500
Exp warm die
compaction FL-4400
Green Density,
g/cm³
Stripping Pressure,
MPa (psi)
Sliding Pressure,
MPa (psi)
6.90
38.8 (5630)
19.8 (2870)
6.90
35.4 (5150)
19.1 (2780)
7.20
59.9 (8700)
48.2 (7000)
7.20
33.0 (4800)
29.6 (4300)
Discussion:
The experimental binder treatment described in this report showed reduced ejection forces for
FY-4500 materials as measured by strip and slide stress. In addition to the reduced ejection
forces, mechanical property testing demonstrated no deleterious effect on the compressibility or
sintered mechanical properties of the FY-4500 material system. To verify the usefulness of the
laboratory data, preliminary testing was performed on production PM components. Beta site
testing showed reduced ejection pressures, reduced die wear, and an overall improvement in the
compaction characteristics of FY-4500 material at green densities ranging from 6.8 to 7.0 g/cm³.
A qualitative observation was reduced press adjustments during extended production runs. The
fewer number of press adjustments was attributed to reduced entrapment of powder between the
punches and dies thus enabling the press to return to the fill position with less powder drag
between the punches and die assembly. In terms of die wear, measurement of the top punch
showed no measurable wear on the top punch after a production run of ~50,000 parts. This
represented a considerable improvement from the commercially available material. It was also
noted that no differences were observed concerning powder compressibility or sintered
dimensional change response.
This experimental binder system for the FY-4500 material system has demonstrated that
equivalent powder compressibility with identical sintered mechanical properties can be achieved.
The implication of this data is reduced die wear and potentially lower die repair and replacement
cost. This new development can potentially lead to further utilization of ferro-phosphorus
containing premixes in new magnetic applications.
Utilizing a 0.85% molybdenum prealloyed steel base material in combination with ferrophosphorus gives magnetic properties equivalent to standard FY-4500. The molybdenum steel
material does show an approximate 10% increase in yield strength and ultimate tensile properties
with no loss in elongation. The other interesting aspect of this data is significantly higher impact
energies found with this material system.
Conclusions:
From the results presented in this paper, the enhanced binder treatment of ferro-phosphorus
containing materials has demonstrated the following:
Warm die compaction of FY-4500 type materials gives a 0.1 to 0.2 g/cm³ increase in
green density at equivalent compaction pressures.
Warm die compaction results in an increase in green strength of ~ 75% at equivalent
green densities.
The experimental binder system reduces the stripping and sliding stresses of both cold
compacted and warm compacted FY-4500.
This experimental binder system has identical compressibility to the ANCORBOND and
AncorMax 200 materials.
Utilizing cold die compaction conditions, the experimental binder system does give
greater shrinkage over a density range of ~6.8 to 7.1 g/cm³.
No difference in DC was observed with the warm die compacted material.
Magnetic performance was unaffected, as anticipated the higher the sintered density the
better the magnetic performance.
Mechanical properties are identical.
Utilizing an 0.85% prealloyed molybdenum steel in combination with the ferro
phosphorus addition increased the yield and tensile strengths and gave a significant
increase in the impact energy.
The experimental binder system described in this report is still undergoing laboratory
development and is not currently commercially available.
References:
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