International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 1, January 2019, pp. 2095–2108, Article ID: IJMET_10_01_205
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=01
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
STUDY THE MICROSTRUCTURE OF WELDING
JOINT OF DIS-SIMILAR METALS
Dr. Abdul Wahab Hassan Khuder
Asst. Prof, Engineering Technical College-Baghdad
Middle Technical University, Iraq
Essam Jabar Ebrahim
Lecture, Engineering Technical College-Baghdad
Middle Technical University, Iraq
ABSTRACT
This article is about studying the microstructure of welding joint of dissimilar metals,
stainless steel to low carbon steel that is thickness (4mm) for both by using the metal
active gas (MAG) spot welding process. The welding wire (E80S-G) is used and have
(1.2mm) diameter depend of (AWS), and Co2 gas was used as shielded gas with (7L/min)
flow rate in all times used in this study.
In this work, we select many samples from the welding joints from welding region and
heat effective zone, these samples will change in there welding from the welding time,
current and the wire feed. A different region that represents regions of joint interface
between the two metals, and heat effected zone we noted that. The ratio of pearlite in low
carbon steel more than in base metal and the ratio of ferrite is less than in parent metals.
Furthermore, the microstructure of stainless steel has no change as compact with low
carbon steel because most of heat concentrated in the low carbon steel.
Key words: Microstructure of Weldment, Weldment of Dissimilar Metals. Stainless
Steel, Low Carbon Steel.
Cite this Article: Dr. Abdul Wahab Hassan Khuder and Essam Jabar Ebrahim, Study the
Microstructure of Welding Joint of Dis-Similar Metals, International Journal of
Mechanical Engineering and Technology, 10(01), 2019, pp.2095–2108
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&Type=01
1. INTRODUCTION
Low alloy steel and Carbon steel welding rods and bare electrodes were obtainable for utilized
with the process of "gas metal arc welding". The electrodes were assorted on the basic of
mechanical property and chemical structures of the un-diluted welded metals.
Shielding gas commonly use for "gas metal arc welding" (GMAW) of carbon selection relying
on composition of the electrodes and metal transfer type. In general shielding of carbon dioxide
was suitable for low carbon steel and steel [1].
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The weld ability is defined as a capable of the metal and alloy to weld with others and employ
once welding methods to purpose of production good life and free from defects. Weld ability of
stainless steel not take only mechanical properties but take chemical properties which important
in corrosion resistance because reaction which can be among chromium, carbon and (oxygen) in
high temperature during welding generally most maybe weld stainless steel by weld method
which known. The important factor affection the weld is the carbon equivalent (C.E):C.E = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) /15
(1)
And alloying elements have advantage of the weld ability like:1. Increase the strength ability.
2. Improve resistance and mechanical properties at elevated temperature.
3. Increase corrosion resistance.
4. Increase fraction resistance [1, 2].
2. "GAS METAL ARC WELDING (GMAW)
Arc is used in this process of welding in the middle of a continual metal electrode filler and a
welded metals, as shown in figure (1) the MIG/MAG equipment. The method was used with
shielding from gas supplied externally and without applied the pressure it was developed in
1940, for welding aluminum and had be very common, furthermore this process was named
"metal in arc gas" ("MIG") welding. There were a lot of differences relying in the kind of shielded
gas and the kind of metals transfer and metals welded, therefore called by many names like ("MIG
Welding" , "Co2 welding" , "Fin wire welding" ,"Spray arc welding" , "Pals arc welding" ,"Dip
transferring welded" , "Short circuit arc welding" , etc.) [3].
Figure (1) showing the MIG/MAG equipment [2].
When gas metal arc welding is first generated, it's supposed to be essentially ("high- current")
density, small diameters, process of bare metals electrode, Inert gas was used to shielding the arc
its principal applications in welding of aluminum as a consequence, the inert gas term (MIG) had
been utilized and are yet the widespread in the operation. Evolution contain operations at "low
current densities" and "pulse direct current" utilization for a wide ranges of materials, as well as
the use of interactive gases (especially CO2) or gas mix. This final evolution had been lead up to
formal agreement of the expression "gas metal arc welding" ("GMAW") for the operation since
both inert and interactive "gases" were utilized. Gas metal arc welding was operate in semiautomatic instrument and automatic style; it was used especially in high production operation of
welding. All commercially significant like "carbon steel", "stainless steel", "copper and aluminum"
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could be welded in this process, in every locations by selecting the convenient "shielding gas",
"electrodes" and "welding" circumstances [3].
3. "GAS METAL ARC SPOT" WELDING
The fundamental variations between traditional (GMAW) and "gas metal arc spot welding" are:1. In spot welding there was no activity of the gun.
2. The welding time was short it's only for a few seconds.
The operation was applied to "spot weld" two plates overlapping with each other, and to join
other weld types together, the operation could be utilized in the same technique as "resistance
spot welding". Aluminum, Build steels, and stain-less steel were usually "spot weld" with the
operation.
Welding the welding gun is firmly on the joint so the spot welding will be made in the
appropriate location, the gun was hold Consistently "when the trigger" was "depressed shielding"
flow of gas was started. Afterward a pre-flow period, electrode feed was activated and the arc
begins in the accomplishment of a predetermined welding time. The presented electrodes feed of
the welding were stopped. Thus the gas flow paused automatically. Due to the variations in the
welding shape of convention and spot weld, the influence of the factors could be reconsidered so
best comprehension of the operation will be obtained. [3,4].
4. WELDING VARIABLES EFFECT
4.1. Welding Current"
The weld current had a direct action on the rate of feed electrode and had a great effect on the
penetration of welded metal. "Penetration" is rising "about as the square of" the "current with
CO2 spot welding". Usually the high penetration rate leads to large diameter welding at the
interface between steel "and consequently greater weld shear strength" practically all "gas metal
arc spot welding" was accomplished with "direct current" opposite polarity, in spite of straight
polarity could be utilized under specific circumstances [6].
4.2. Welding Time
The period of "welding current" had a significant influence on "weld size and penetration at the
interface. "Penetration" raises with welding time at a rate of decline to the shorten "value which"
relays "on the current" .electrode and Voltage also, the welded supplementing high raises with
"weld time". Domination of the "weld time" was better given with an "electronic timer". "even
with the most" proportionate time, nevertheless, the real weld time could vary greatly, since the
arc was not constantly started the immediate of the progress "electrode touches the work surface"
occasionally, the electrode makes the wire melt and from to a short arc, which was usually of
short period "stubbing of the wire electrode" could happened different "times before an arc" was
finally accomplished. Unluckily over this time small "or no heating of the base metal" was
recognize. In uniform welding time could be defeated by use of a control that doesn't waste the
welding time "until the arc voltage" attains a certain value [6].
4.3. Arc Voltage
Arc voltage is an indirect measure of arc length and therefore had a great endure "on the shape of
the arc spot". If the welding "amperage" was kept unchanged, any increase in arc voltage will
result" "the diameter" of the weld at the "interface increase and the" supplementing high, and
penetration metal to small "decrease if the arc voltage" was very high, heavy spatter was probable
to occur. In addition, poor arc voltage may effect "in the formation of" a decreasing at "the center
of" supplement and insufficient fusibility at the border of the weld [6].
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4.4. "Electrode Size"
The "electrode size" was chosen based "on the" welding of pant "thickness". There was an overlap
of the properties "electrode wire feeder" should also be "considered for electrode size" choice [6].
4.5. Shielding Gas
The "shielding gases" for "arc spot welding" were chosen by employed "the same" standard as
those" utilized for "filler metal transfer", "continuous welding", "weld penetration", "arc
characteristic" ,"material joined", "weld shape", and "cost arc", all serious features to be
respected in "shielding gas" chosen, the "shielding gas" implement "the same" purpose as "in
continues gas metal arc welding", but usually using a flow rate of (25 – 50)% in factory [6,7].
4.6. Joint Design
Gas metal arc spot welding" was appropriate "to all the" welded "materials with" operation. Plenty
of "weld joint" kinds were utilized, with small adjustment to the design of "shielding gas nozzle",
consist of "lap fillet" ("inside corner or edge of lap joint"), corner ("outside corner") "and plug welds
for" good result. The "top member" must "be no thicker than the bottom member" was lap joint; if
"the top member" have to "be thicker than the bottom one, plug welding" must be applied "in plug
welding care" have to be taken to assure perfect penetration for "the base plate" moreover to the
side wall "of the top member" [7].
4.7. Welding Position
Perpendicular and elevated "arc spot weld" could be made successful thickness on sheets reach
to (1.3mm), to weld out location. In general "short circuiting made of metal transfer" should be
utilized. "Spot welding" of heaver "gage material" was normally limited to the flat location in order
to effect of "gravity on the molten weld pool." [7].
4.8. "Weld Quality
All of the above welding" factors had an effect to varied "degrees on the goodness of weld". They
must be planned "as much as" possible, moreover, good practices recommended that results of
welding quality must be observed directly. unluckily the size and shape of weld supplementing
was not a dependable indicator "of weld size one inspection" mechanism includes checking the
"back side of the" join for small melt ,"through or bump indicating" sufficient penetration but when
the back side was in attainable or the "gage combination" was not appropriate , "coupons welded
periodic destructive" testing was the only reliable way to evaluate welding standard this might
be achieved with "tension - shear" test to locate "the spot weld strength" or be "metallographic" to
locate the "weld size" and durability [7].
4.9 Dissimilar Metals
Most groups of dis-similar metal could be connected by solid "state welding brazing", "or
soldering where alloying between the metals" was usually unimportant, in these status only the
variations in the mechanical properties and physical "of the base metals and their" effect on the
service ability of the joint must be considered. When dis-similar metal were connected by a
melting "welding alloying between" the filler metal and a base metal, when applied becomes
different "from one or base metals" through following "processing or in service". A collection of
metals with importantly "different chemical", physical and mechanical properties could simply
problems through "and after welding the combination" could be two "or three different metals one
of which" was a filler metal. The resulting weld "metal composition" shall vary from that of each
of the ingredients, and could "vary with the" design of "joint welding process", "filler metal", and
the weld process .thus these "factors and also any thermal treatment of the weldment" should be
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determined and properly assess before "to production the major" pool of dis-similar metal welding
must "be produce a weldment that" fulfill "the intended service" necessity [8].
5. METALLOGRAPHIC
Metallographic or microscopy consists of the structural features of an alloy or a metal. The
microscope was by for the nearly an important tools of the "metallurgist" from both the technical
and scientific stand points; it was reasonable to locate size shape and grain size and distribution
of different stages and inclusion which had a great influence on metal mechanical properties.
The microstructure ought to expose the thermal and mechanical "treatment of the metal", and it
might "possible to predict" had suppose "behavior under a given set of conditions". Experience had
specified that success in microscope studies relay largely onto "the care taken in" the arrangement
of the specimens [5].
5.1. Sampling
Sample selection for microscopic study was very important. If failures are selected in the area as
much as possible from the failure zone, compare with one taken from a normal area [5].
5.2. Rough Grinding
Whenever possible the sample" must be of a size that was appropriate to "handle a soft sample
might be made flat by slowly moving it up and back across the surface of a flat smooth file". Hard
or soft sample "may be rough ground on a belt sander. With the specimen kept cool by frequent
dropping in water during the grinding operation". "In all grinding and polishing" operation the
sample must be moved vertical of the soften abrasive the rough grinding was continuous till the
surface was and nicks ,"burrs" ,flat, etc., "and all scratches lead" to the cutoff or hacksaw wheel
were no longer apparent [5].
5.3. Mounting
Specimens that" were small or inappropriate shape must be simplify middle "and final polishing
wires", small sheet, rods, "metal specimens", than sections etc., It should be fitted properly with
appropriate metal or firmly anchored with a mechanical holder. "Synthetic plastic materials" used
"in special mounting press will yield mounts" to an uniform suitable size (generally "2.5mm, 3mm,
3.6mm", in diameter) for handing following polishing process. These mounts when properly
made were very reluctant to "attack by the etching reagents ordinarily" used. The most usual
thermosetting resin for mounting was "Bakelite". Which madding powders were obtainable in a
set of colors, which facilitate the recognition "of mounted specimens, the specimen and the" right
amount of "Bakelite powder" or perform were placed in the cylinder of the "mounting press".
"The temperature" was progressively raised to (150°C) "and a molding pressure" around (4.000psi)
was utilized "simultaneously". Since, "Bakelite" was set and treat "when this temperature" was
attained "the specimen mount might" be ejected from the mold die during it was still hot.
Lucite was the most popular "thermoplastic" "resin for mounting". Lucite was fully transparent
when correctly molded. "This transparency" was advantageous when it was necessary to monitor
"the exact section" that was "being polished or when it" was eligible for any other purpose to see
the whole "specimen in the mount". The thermoplastic resins do not work at the temperature of
the casting, but they work on cooling. The specimen and a suitable quantity of "Lucite powder"
were placed in the mounting press were submitted to the same pressure and temperature as for
"Bakelite" (150°C) and (4.000psi) later this temperature had been reached, the heating coil was
removed. And cooling fins were positioned about the cylinder to cool the quantity to beneath
(75°C) in about (7min.) whereas the molding pressure was maintained. Then the mount might be
removed from the mold. Removing the "mount" while still hot or leaving to cool slowly in the
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cylindrical mold at room temperature before removing it from the mold will cause the "mount"
to be opaque. Small specimen might be appropriately mounted for "metallographic" arrangements
in a laboratory made "clamping device". The samples with thin sheet when mounted in the clamp
instrument were replaced with metal "fillers" which are approximately the same as the hardness
of the samples. The use of filler sheets preserves the sample surface from "irregularity" and
prevents the edges from being round through the polishing process. [6].
5.4. Polishing
After mounting", the samples are polished with a set of sandpaper, plus a fine abrasive brush. The
surface after intermediate polishing operations using sandpaper was commonly done dry;
"however in" specific conditions "such as the preparation of" "soft material", "silicon carbide
abrasive" might be utilized. "As compared" to sandpaper, "silicon carbide" had a better "removal
rate and", as it was "resin-bonded", could be applied "with lubricant". Using a lubricant prevents
overheat the samples, decreases "smearing of soft" metal, and also supply a rinsing operation to
expel surface "removal products so the paper" was not became clogged. The success of the
precision polishing process and the time consumed depend heavily on past polishing operations
.For a scratch-free surface, a damp swivel "wheel covered with a cloth" is used with fine particles
of abrasives, "appears to be a preference for the gamma" from "of aluminum oxide" for copper and
ferrous materials, and "cerium oxide for aluminum magnesium", and their alloys". For final
polishing, diamond paste is also used, magnesium and chromium oxide. Use of the appropriate
cloth for polishing depends on the process of "metallographic" study. "Many cloths" were
obtainable of varying fluff or pile, "from those having no pile, such as" broad cloth, "billiard cloth
and canvas duck", and finally to a "deep pile", such as "velvet" [7].
5.5. Etching
The aim of "etching" was "to make visible the" several structural features of the metal and alloy.
"The process" should "be such that the" different "parts of the microstructure" might be obviously
"differentiated". This was achieved by use of a convenient "reagent" "which subjects the polished
surface to chemical" operation, the chosen of the suitable etching "reagent" was specified by the
metal or alloy and a certain structure required for viewing. [7, 8].
6. EXPERIMENTAL WORK
6.1. Materials Descriptions and Specimens Preparations
The material used are a sheet of stainless steel that is thickness (4mm), and the low carbon steel
of thickness (4mm). Table (1) & (2) were showing the "chemical compositions" and some
"mechanical properties" of materials used.
Table (1) Chemical compositions of the alloy used.
Specimen
Materials
Stainless Steel
Low Carbon Steel
C""
0.02
0.05
Mn""
0.95
0.7
Si""
0.9
0.9
Composition wt %
P""
S""
Cr"" Ni""
0.01 0.01
18 11.5
0.03 0.025
-
"Mo"
2.6
-
Bal"."
66.01
98.29
Table (2) Mechanical properties of the alloy used.
Mechanical Properties
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Specimen Materials
Low Carbon Steel Stainless Steel
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Tensile Strength (N/mm2)
Yield Strength (N/mm2)
Elongation%
Hardness (HRB)
460
415
27
60
610
430
40
75
6.2. Welding Wire
The type of welding wire used is (E80SG) have (1.2mm) diameter depend of (AWS), table (3)
showing the chemical compositions and properties of this type of wire.
Table (3) Chemical compositions of the welding wire used.
"Elements"
Weight %
C
Si
Mn
Mo
0.08 0.99 1.65
2.6
P
S
Cr
0.012 0.013 18.5
Ni
N
Cu
Co
12
0.05
0.1
0.05
Yield strength" = 560 MPa.
Tensile strength" = (530 – 650) MPa.
Impact strength" = 47J.
Elongation" = 26%.
6.3. Shielded Gas
The type of the shielded gas used in welding is Co2 at a flow rate (7L/min) for all times.
6.4. Procedure Operation for Welding Process
1. Clean surface from gasses and oxide.
2. Preparation torch and suitable angle (90°).
3. The orifice of the torch should be suitable with the gas flow.
4. Fixed parts good from and limit suitable over lap distance.
5. Use direct current reverse polarity during welding.
6. Prepare the flow rate in the (7L/min).
6.5. Preparation the Specimens to Microstructure Examination
To study the microstructure of the joint welding, we select specimens from the welding joints
from welding region and adjacent. The specimen has some changing in found mental of process,
like the current and welding time and feed wire, table (4) shown the specimens and there
characteristics and the steps of preparation are:1. Cutting
Cutting specimens from welding joints by using manual cutter with cooling water to prevent
the effect of heat.
2. Cleaning
Cleaning the faces of specimens after cutting process by using Alcohol.
3. Mounting
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The mounting of specimens by cold mounting, by using resin and hardener with using die
and small face from class we mixed the resin and hardener and full this mixture on the die with
covering the specimens, and leave it is to solidification to some minutes about (15min).
4. Grinding
The grinding of specimens by using many grinding papers (200, 400, 800, and 1200) µm with
rotated the specimens with (90) after each stage, to remove the lines of grinding.
5. Polishing
Polishing done by using cloth and Alumina (Al2O3) to polish the face, and washes by water
and alcohol.
6. Etching
Using etchant solution that its composition, [50ml HCl + 50ml Ethanol + 2.5gm CuCl2].
Table (4) Shows the specimens and there characteristics.
Specimens
No.
1
2
3
4
5
Current
(amp)
200
200
220
240
240
Spot Diameter
(mm)
7.7
7.25
9.2
11.15
9.85
Time
(sec)
1.5
3
1.5
3
1.5
Wire Feed
(cm/min)
127
127
204
204
204
This specimens welding with flow rate of gas is (7L/min).
7. RESULTS AND DISCUSSIONS
The structure of welded joints does not homogenous and its form from many region that is weld
metal and its structure like or as cast, and heat effected zone it has metal structure is heat treble
and the last the region of base metal its part not affected by heat prom joint. The process to carbon
steel by stainless steel on of the important protection process to carbon steel surface from
corrosion the structure of weld metal insulator limit between two metals it was different in
microstructure. Because dilution in region of insulator limit between metals that is consist of three
base regions:1) Pure martensite (in region near from carbon steel).
2) Austenite + Martensite + Ferrite (in region near from the insulator limit from side the
stainless steel).
3) Austensite + Ferrite (in region welding of stainless steel).
7.1. Base Metals
7.1.1. Stainless Steel (316L)
Figure (2) represents the base metal of stainless steel without welding, which is ferrite and pearlite
structure with lens power (X 125).
7.1.2. Low Carbon Steel
Figure (3) represents the base metal of low carbon steel, which is ferrite and pearlite structure
with lens power (X 125).
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7.2. Specimens (1)
This specimen is welded by using the current welding (200Amp) and the time welding (1.5sec)
and wire feed (127cm/min). A different region that represent regions of start of joint and interface
between the two metals, and heat effected zone we noted that, for figure (4) shown start of joint
for two metals region (steel and stainless steel) which is weak region of welding and non
completes joint because it is the start of joining between two metals. Figure (5) that shown joint
region of weld metal ,and we find the ratio of pearlite in low carbon steel more than the ratio in
base metal of low carbon steel, and the ratio of ferrite is less than in parent metal. The (β and α)
interface with each other in the weld metal.
The microstructure of stainless steel has no change as compact with low carbon steel because
most of heat concentrated in the low carbon steel. Figure (6), represent the line of joint between
two metals and show the regions (WM, HAZ of two metals), and we noted some of impurities.
Figure (7); show the weakness of joint and space in start joint.
7.3. Specimens (2)
This specimen is welded by current (200 Amp) and the time welding (3 sec) and wire feed
(127cm/min).Figure (8), show the joint with appearance for the region of steel, there is blank
point that is may be impurities or oxide that we noted it with large amount in this specimen only
because oxidation is occur because it is generated in steel only or its impurities generated during
welding processes. Figure (9), shows the "heat affected zone" for stainless steel.
Figure (10) showing the interface between the two metals and noted clearly the two metals;
also we noted impurities or oxide in both metals. Figure (11), which shows the region of heat
affected zone for stainless steel that we noted the change in its structure especially near the
(WM).Figure (12), shows the interface the heat effected zone with the (WM) for the two metals
and we noted percentage of the precipitation of pearlite because the time welding is increasing.
7.4. Specimens (3)
This specimen is welded with current (220 Amp), and welding time (1.5sec), with wire feed
(204cm/min).Figures (13) & (14), represents the regions of the interface and the (WM) for the
two metals (steel & stainless steel) and noted that some percentage of ferrite in the (WM).
Figure (15), show the heat affected zone of stainless steel, and the region of heat affected
zone is less affected by heating of welding. Figure (16); show the (WM) for the two metals with
noted large amount of ferrite in the (WM) more than the pearlite.
7.5. Specimens (4)
This specimen is welded with current (240 Amp), and welding time (3sec), and wire feed (204
cm/min).Figure (17), shows the (WM) & heat effected zone for stainless steel and we noted that
the (WM) is contain a high amount of pearlite because the use for high current (240 Amp) and
high speed of wire feed (204 cm/min).Figure (18), shows the start of the joining between the
stainless steel and the steel and we note that the space in the start of the joint spot with some
amount of impurities. Figures (19) & (20), shows the different shapes for the welding joint and
we noted some of impurities concentration between the two metals.
7.6. Specimens (5)
The specimen welded by current (240 Amp) ,and welding time (1.5 sec) and wire feed (204
cm/min).Figure (21), shows the (WM) region to stainless steel and steel, we note increasing
amount of pearlite in steel. Figure (22), shown the interface and joint between the two metals and
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filler metal precipitate, because of the increasing in wire feed noted the filler metal in clearance
and noted amount from pearlite precipitate on filler region.
Figures (23) & (24), these figures shown joint between two metals and with noted the two
metals are interfaced and no heat affected zone found, because low time and amount of heat input
is little and increasing wire feed. Figure (25), shows the interface between two metals and
appearance amount from pearlite more than ferrite in (WM).
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8. CONCLUSIONS
1. The ratio of pearlite in low carbon steel more than in base metal and the ratio of ferrite is
less than in parent metal.
2. The heat effected zone (HAZ) with the weld metal (WM) for the two metals and we noted
percentage of the precipitation of pearlite because the time welding is increasing to three second.
3. The WM for the two metals with noted large amount of ferrite in the weld metal (WM)
more than the pearlite.
4. The weld metal (WM) is containing a high amount of pearlite because the use for high
current (240Amp) and high speed of wire feed (204cm/min).
5. The two metals are interfaced and no heat affected zone found, because low time and
amount of heat input is little and increasing wire feed.
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6. The increasing current lead to increase of pearlite in (WM).
7. The region of heat affected zone of stainless steel, which effected directly with increasing
the current and noted precipitation large amount of the pearlite due to the increasing of the current.
8. The percentage of the pearlite increased more than the ferrite due to increase the heat input
rate by increased the current, but we noted no increasing in pearlite, although increasing in current
because low time and increasing in wire feed.
9. The microstructure of stainless steel has no change as compact with low carbon steel
because most of heat concentrated in the low carbon steel.
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