1. ME 492 Welding Metallurgy Project (Group A-2)
Hardness Testing of Automatic GMAW
Welding on 1075 Steel
Leonardo Minier Kris Saladin Cahill Wilson
minierla@clarkson.edu saladikm@clarkson.edu wilsoncd@clarkson.edu

2. Objective:
The objective of our project was to determine the effect variable travel speed and arc current
from an autonomous Gas Tungsten Arc Welding (GTAW) machine weld on the material
properties of 1075 steel. Specifically, our experiment analyzed the crystal structure and hardness
of the metal through a Vickers Hardness Test and Optical Microscopy. Findings from the
experiment will shed light on suggested operating parameters for carbon steel using the Linde
Type “C” as well as support existing publication material on the subject matter. However, this
testing only required a short amount of time. The majority of the time was spent preparing the
samples for testing. Preparation consisted of welding, cutting, mounting, and polishing and
etching.
Introduction:
The Linde Type “C” has been functioning as a student-operated piece of lab equipment since the
late 1970’s. For years it has provided automated GTAW services, also referred to as TIG welds.
The experiments conducted using this machine serve two purposes: Firstly, the results from the
test specimens will allow us to draw conclusions on what settings the machine accurately welds
at for 1075 steel. Results from the LECO M-400 Hardness Tester will also allow us to support
existing publications that suggest that the hardness of the weld zone is greater than that of the
base metal.
Experimental Procedures:
A 1075 steel sheet (thickness 0.125”) was acquired to cut six specimens of dimensions 2”x 6”x
0.125” to perform the bead on plate using the automatic welding system: Linde Type “C”, Serial
# 1S1 & 1S2.
Table (1) – Material Properties of 1075 Steel
Metal
Wt. %Carbon
(C)
Wt.% Iron
(Fe)
Wt. %Manganese
(Mn)
Wt. % Phosphorous
(P)
Wt. %Sulfur
(S)
1075 Steel 0.70 - 0.80 % 98.41 - 98.9 % 0.40 - 0.70 % <= 0.040 % <= 0.050 %
Table (1) breaks down the material properties of the specimens in question by weight percent
composition of each element. A range of values has been provided due to the fact that the quality
of this easily attainable steel varies from one manufacturer to the other. Due to the uncertainty in
the quality of the manufacturing process, we must assume that our test pieces have values that lie
between those listed above.

3. Preparation
Once the material order had been received it was prepared for welding. The first step was to cut
the sheet of stock 1075 steel into six (6) individual 2”x6” lengths. To ensure a contaminant free
weld surface and safe handling the specimens were de-burred using a standard grinding wheel,
polished with 1200 girt polishing paper, then rubbed down with Ethanol and dried using
compressed air.
Welding
The following experimental process was repeated three times at 7 inch per minute travel speed
for the tungsten electrode. The 2”x 6”x 0.125” test pieces were oriented parallel to the path of
machine. Traveling from left to right, each pass was executed at increasing arc current amperage.
This entire process was then conducted three more times at a higher travel speed of 10 ipm.
Table (1) below shows the procedure used for all six welded plates.
Table (2) – 6 Welding Cases
Welding Sample –
1075 Steel
Test Case #1 – 7
Inches/Min
Welding Sample –
1075 Steel
Test Case #2 – 10
Inches/Min
Sample (1) 100 Amps, 14 Volts Sample (4) 100 Amps, 13 Volts
Sample (2) 125 Amps, 13 Volts Sample (5) 125 Amps, 14 Volts
Sample (3) 150 Amps, 15 Volts Sample (6) 150 Amps, 15 Volts
Arc Length (wire diameter) for all cases = 0.094”
Sample (2) was done a second time due to poor welding appearance (125A, 14V). Post welding
results are shown below in picture (1).
Picture 1 (above): Six welds + Second Weld of Sample (2)

4. Picture 2 (left): Samples cut to length
Cutting
In order to analyze the effects after different welding
conditions with a Vickers micro hardness test, the plates
needed to be cut into smaller pieces. The pieces also
required a smooth surface to get accurate results. A large
rough cut was completed to dimension of 2” x 2” using
Clarkson Shop’s vertical saw machine and then cut more
finely to 1” x 2” with the band saw. At this point the
surface of the cut was still not ready to be polished, so a
finish cut with a finer blade was made with the Buehler
Isomet Low-Speed diamond saw.
Picture 3 (right): Mounted and polished
Mounting and Polishing
Two of the samples, #3 and #6, were selected for further
processing. The specimen were placed weld face down in
cylindrical forms and a two part clear 24 hour epoxy was
added and left to set. Upon drying, the samples were
removed from their forms and labeled with a ultrasonic
marker.
The test pieces were then brought to the material
processing lab in CAMP, and polished using a Buehler
EComet IV automated polishing table. Starting at 400 grit
SiC polishing paper, the samples were polished using this
technique up to 1200 grit in 200 grit stages. With the help
of the T.A./Lab assistant Melissa the samples were then
ultrasonically cleaned and washed with M.E.K before
being stored in a vacuum overnight to reduce the chance of
corrosion.

5. Etching
After it was taken out of storage, the samples needed to be etched in order to see the weld zone
and heat affected zone more clearly. Macro etching allows the boundaries of the weld to be seen,
including: the weld metal, heat affected zone, fusion boundary, and weld zone. Penetration can
be identified as well as any weld defects. The etchant used was a 2% H2NO3 (Nital) and 98%
Ethanol. This is a good general purpose reagent and is used for macro etching carbon and low
alloy steels.
Hardness Test
Using the LECO M-400 Hardness Tester, the
Vickers micro-hardness measurements of our
welds could finally be taken. The machine was
set to a point load on the diamond tip of 500gf
(g/𝑚𝑚2
). Measurements were calibrated to this
value on the VHN measurements due to the fact
that, during set up, the marks left by the diamond
tip were too small to accurately measure at 300gf
and below. This was the initial indication that
hardness values would be on the high side. Figure (1)
Results & Discussion:
Measurements were taken in 5 different regions, at the same depth, working from the base metal
to the heat affected zone (HAZ) and then to the weld zone (WZ). The locations of these sample
regions can be seen in Figure (1) above, and the Vickers Hardness values for each region can be
found in Table (3) below.
Table (3) – Hardness Testing for Mounted Samples
Testing Area Sample (3) Hardness Testing Area Sample (6) Hardness
(1) – Base Metal 190.3 HV (1) – Base Metal 184.4 HV
(2) – Heat Zone
(Edge)
386.1 (2) – Heat Zone
(Edge)
181.8
(3) – Heat Zone
(Middle)
561.1 (3) – Heat Zone
(Middle)
357.8
(4) – Weld Zone
(Edge)
675.4 (4) – Weld Zone
(Edge)
389.3
(5) – Weld Zone
(Middle)
754.7 (5) – Weld Zone
(Middle)
357.8
Setting for machine = 500g/𝑚𝑚2
at 40x magnification

6. The results of sample #3 indicate that fusion zone created at a travel speed of 7ipm is much
harder than that of sample #6 which traveled at a rate of 10ipm. By this result, it is assumed that
the 7ipm travel speed results in better penetration and therefore a better weld. However, this
relationship is not linear, in that, slower travel speeds create better welds. Too slow of a speed
will cause excessive piling up of weld metal and overlapping penetration. Too fast will cause a
small weld bead with an irregular contour and not enough weld metal in the cross section (poor
penetration).
Picture 4 (left): Sample #3 Picture 5 (right): Sample #6
The cross sectional pictures above show the weld zone and penetration for both samples. These
pictures were taken by an optical microscopy (OM). The picture on the left (sample #3) shows a
larger weld zone indicating good penetration while the picture on the right (sample #6) shows a
smaller and more defined weld zone indicating less penetration. It is worth noting that sample #3
had to be etched twice after the first etching came out unclear.
Hardness is defined as “the measure of a material’s resistance to deformation by surface
indentation or by abrasion” by the Fundamentals of Material Science and Engineering 3rd
Edition, William D. Callister, Jr., and David G. Rethwisch. Hardness values for metals have been
tested by industry standards and correlated to tensile strength allowing for easy conversion. A
chart of hardness measurements to tensile strength (psi) was used to better understand the
microstructure of each weld created [1]. Figure (2) below shows the results of our test in a
graphical form to more easily compare both welds.

7. Figure (2)
Comparing the results of the hardness testing between the two samples above, it concludes that
sample #3 has a steeper slope and higher values of hardness. This can be correlated with the
tensile strength of the weld. For example: a Vickers hardness value of 300 has a tensile strength
of 140,000 psi. As the hardness increases, so does the tensile strength of the weld: in this case
making sample #3 the stronger weld. While the strength and composition of the microstructure is
to be determined from this data, typical 1075 steel hardness values do not relate to those found in
sample #3. This led us to believe that the measurements may have been skewed due to limited
technical experience with the M-400 testing machine. Sample #6 shows a more accurate
representation of 1075 steel and also increasing values of hardness as the measurements move
closer to the weld zone (as expected).
Conclusion/Summary:
After reviewing our objective of determining the effects of travel speed and arc current from an
autonomous GTAW process we concluded that a 7ipm travel speed and 150 amp arc current
produced the best penetration and highest weld tensile strength. Although, as stated, our data
could have been skewed due to testing error – these results still seem accurate. While sample #3
produced the highest values, the application that the weld will be used in determines which
process is better. Given more time, we may have been able to analyze the effects of different
amperages on hardness and strength values.
0
100
200
300
400
500
600
700
800
1 2 3 4 5
Vicker'sHardnessValue
Testing Region
Hardness Testing Results
Sample #3
Sample #6

8. Acknowledgements
Alireza Bahrami - Helped us mount the samples and etch them. He also helped us take pictures
of the samples with the microscope and how to use the hardness testing device.
Marissa LaCoursiere - Showed us the process of polishing the metal after it had been mounted in
epoxy. She also set our samples in the sonic cleaner and the vacuum Tupperware to keep from
rusting.
References:
[1] – Hardness conversion chart:
http://www.carbidedepot.com/formulas-hardness.htm
[2] – Material properties of 1075 steel:
http://www.matweb.com/search/datasheet.aspx?matguid=2aa9abfbb55e4aceaabe986e8be7cf4a&
ckck=1
[3] – Fundamentals of Material Science and Engineering 3rd Edition, William D. Callister, Jr.,
and David G. Rethwisch