Metallography & Microhardness
Testing
Maura Chmielowiec, Mechanical Engineering
Materials Science Lab, Section 44
May 3rd 2012
Group Members: All of Section 44
Abstract:
By examining 3 different steel specimens with varying carbon content
under magnification the primary ferrite and pearlite formed can be observed.
Using 1018, 1045, and 1095 steel samples after they were mounted,
ground, polished and etched, the microstructures were observed and the
Vickers hardness values were measured. By comparing the Vickers Hardness
to the Rockwell Hardness taken later there was a difference in the trends
observed. The 1045 steel specimen was observed to have the hardest ferrite
in the Vickers hardness but when comparing to Rockwell hardness values the
1095 sample was equally as hard. From these results it can be concluded
that the pearlite found in the 1045 sample may have been harder but due to
the composition of pearlite found in the 1095 sample exceeding the amount
of pearlite in the 1045 they appear to have the same hardness overall in a
Rockwell hardness test which includes both the primary ferrite and the
pearlite. The 1018 steel proved that the primary ferrite is indeed softer than
the pearlite found in the sample.
Metallography & Microhardness
Maura Chmielowiec, Mechanical Engineering
Materials Science Lab Section 44
Objective: By examining the microstructure of 3 different steel specimens
with differing carbon content observations can be made based on the
differences in the primary ferrite and the pearlite formed. By using the
Vickers micro-indentation hardness test in the ferrite and pearlite region of
the specimen the hardness formula can be used to compute the hardness
value. Using the same specimen in a Rockwell HR30T hardness test
conversions can be made to compare to the Vickers hardness. This
establishes an understanding of the present primary ferrite and pearlite in
the specimen based on the microscopic and macroscopic property
comparison.
Procedures:
Experimental Procedure:
Materials:

1018 Annealed Steel

1045 Annealed Steel

1095 Annealed Steel

Plastic molding material in green black and red

Diamond Suspension solution

Sand Paper

Leco Micro Hardness Tester LM 247 AT (for microhardness testing)

the LECO Cutoff Machine MC-15 (for sample cutting)

Buehler Simplimet 2 Mounting Press( for mounting )

Tegra Equipment( for grinding and polishing)

Nitric Acid, cotton swab, ethanol and water (for etching)
Specific Test Procedures:
Cutting Procedure
Using the LECO Cutoff Machine MC-15, the specimens were cut to length and
prepared for the experiments. Procedure for cutting is as follows:
1. Align the specimen in the grips and secure
a. Approximately 2 mm specimen
2. Follow cautionary procedures by lowering hood before starting
machine
3. Turn the machine on and begin lubrication fluid flow
4. Begin the cutting process as the blade begins to spin and lowers to the
specimen applying constant pressure until finishing cut
5. Turn off the machine but do not raise hood until machine blade has
fully stopped
6. “Go fishing” for piece in solution
7. Dry lubrication from specimen
Molding Procedure
Using the Buehler Simplimet 2 Mounting Press, the cut specimens were
molded in a plastic puck. Procedure for the molding is as follows:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Stick metal flat side down
Turn knob and plunge down all the way (release pressure)
Put one level cup full of plastic (Phenolic powder) in over the metal
Screw the stopper over the powder, but not too tight, leave a little
room for air so the specimen is easier to remove later
Pump the pressure up to 5 Ksi
a. For the first five minutes it can be greater than this
Let sit for 12 minutes then remove specimen
Release pressure
Pump the stopper up and remove the specimen from the stopper
Use scalpel and toothbrush to clean off base and stopper
Grinding and Polishing Procedure
Using the Tegra Equipment for mechanical polishing of steel, the specimens
were grinded and polished to produce a mirrored finish. The procedure is as
follows:
For the grinding procedure:
1. Using the arrow keys on the machine, set the speed to 300 RPM,
switch the water on, set the force to 15N, and set the time to 3
minutes.
2. Lift the specimen holder and then place the grit disk on the magnetic
holder (grit disks are 220, 600, and 1200 respectively).
3. Pull the holder back down into place and position the specimens into
the holding stage.
4. Press start to begin the grinding
a. Adjust the water flow as necessary.
5. After the test is conducted, lift the holder, remove the specimens,
rinse with water and dry thoroughly.
6. Repeat for all three grinding disks.
For the polishing procedure:
1. Adjust the speed to 150 RPM, mount the diamond suspension to the
machine (this should turn off the water supply), all other conditions
remain the same as the grinding procedure.
a. For the 9µ diamond suspension, the doser should read 4
b. For the 3µ diamond suspension, the doser should read 5
c. For the 1µ diamond suspension, the doser should read 6
2. Lift the specimen holder and then place the polishing disk on the
magnetic holder (polishing disks are (MD-PLAN, MD-DAC, and MDFLOC respectively).
3. Lightly apply green lubricant to the disk.
4. Pull the holder back down and position the specimens into the holding
stage.
5. Press start to begin the polishing.
6. After the test is conducted, lift the holder, remove the specimens,
rinse with water, and dry thoroughly.
7. Repeat for all three polishing disks, changing the diamond suspension
with each disk.
8. After the last disk is completed, rinse the specimens with water and
apply ethanol to the specimens, and dry under an air dryer until no
water remains.
9. Turn off the unit.
Micro-indentation Hardness Procedure:
Using the Leco Micro Harndess Tester LM 247 AT according to ASTM E384
Standards[1]
1.
2.
3.
4.
5.
6.
7.
8.
Slide sample into clamp and secure sample by tightening the clamp
Start with low magnification and slowly increase until desired image
Set load to 200g for Vickers (HV)
Locate test location and press start to initiate the process of
indentation
Once the indentation is complete place reticules on the edge of the
diagonal, rotate 90 degrees and repeat
You now have the indent dimensions, record in data sheet
Also record given HV that the machine provides on the screen.
Save picture of the micro indentation and sample for further future
analysis
Micro Graphing Procedure:
1. After completing the procedure above take a picture of the specimen
with the indentation
2. Save the picture for further analysis
We also conducted the Rockwell Hardness on all 3 samples using the Clark Model
CR-3e Rockwell Tester.
Analysis:
Micrographs
Pro-Eutectoid Primary
Surface Blemish
Micro Hardness
Indent
Grain Boundaries
Pearlite Colonies
1018 Ferrite
Grain Boundaries
1018 Pearlite
Pro-Eutectoid Primary
Micro Hardness
Indent
Pearlite Colonies
1045 Pearlite
Scratch
Surface Blemish
1095 Pearlite
Data and Averages:
Chart 1
Annealed 1018 Steel ("Black", .18 wt% C)
Vickers Micro-Indent
Hardness
Pro-Eutectoid Ferrite
Pearlite
Indent Dimensions
Indent
(um)
HV(200g) Dimensions (um)
HV(200g)
55.7 X 56.7
117.5
50.1 X 50.4
146
54.3 X 51.3
133.1
47.4 X 47.4
165.1
53.6 X 53.7
128.4
51.4 X 49.8
144.9
Average
54.5 X 53.9
126.3
49.6 X 49.2
152
Chart 2
Rockwell
Hardness(HR30T)
Annealed 1045 Steel("Green", .45 wt% C)
Vickers Micro-Indent
Rockwell Hardness
Hardness
(HR30T)
Pearlite
Indent
Dimensions(um)
HV(200g)
39.9 X 38.8
233.4
67.6
37.5 X 37.0
267.3
70.9
36.4 X 39.8
255.6
67.4
Average
37.9 X 38.5
252.1
68.6
Chart 3
Annealed 1095 Steel("Red", .95 wt% C)
Vickers Micro-Indent
Rockwell Hardness
Hardness
(HR30T)
Pearlite
Indent
Dimensions(um)
HV(200g)
39.2 X 36.4
259.6
69.6
38.7 X 39.2
244.4
70.8
42.5 X 42.2
206.4
68
Average
40.1 X 39.3
236.8
69.5
58.8
59.5
56.2
58.2
Chart 4: Microconstituent Percentages:
Lever
Sample Microstructure Observed Law
Primary
Ferrite
80% 78.6%
1018
Pearlite
20% 21.4%
Primary
Ferrite
40% 42.0%
1045
Pearlite
60% 58.0%
Primary
Ferrite
3% 3.2%
1095
Pearlite
97% 96.8%
Lever Law
Percent
Error
1.8%
6.5%
4.8%
3.4%
6.3%
0.21%
Chart 5: Vickers Hardness (First 1018 Measurment)
Indent
Percent
Sample Microstructure Diagonal
Experimental Error
Ferrite
126.2
126.3
0.08%
1018
Pearlite
151.9
152
0.07%
Sample
1018
1045
1095
Rockwell
Hardness
58.2
68.6
69.5
Chart 6: HR30T to HV
HV
Percent Error(Converted to
Conversion Experimental Experimental)
122
152
24.6%
142
252
44.6%
160
236.8
32.40%
Graph 1: MicroHardness vs Pearlite Structure
300
Micro Hardness: HV
250
200
150
100
50
0
Fine
Medium
Coarse
Graph 2: Converted Vickers Hardness from HR30T vs.
wt% Carbon
180
160
Vickers Hardness
140
120
100
80
60
40
20
0
0
0.2
0.4
wt %
0.6
0.8
1
Discussion, Observations, and Conclusion:
By examining the photos of the specimen under magnification
estimates were taken in regards to the amount of pearlite and primary
ferrite that were present. By comparing these estimates to the calculated
inverse lever law it becomes evident that the visual estimate made were
extremely close to the theoretical composition. Chart 3 reflects our
estimated composition vs. calculated composition showing that we were
never more than 6.5% different from the theoretical to our estimate. This
shows that the pearlite and primary ferrite make up is visible under
magnification.
The bulk hardness value is expected to be lower than the micro
hardness value of pearlite with the difference being greatest for the smallest
percent of pearlite, due to the hard pearlite being embedded in soft ferrite
the 1095 specimen should be the closest. The results of this experiment
didn’t follow this theory. By using a scatter plot to compare the Rockwell
hardness to a converted Vickers hardness the observed results showed
difference in our experimental hardness values to the converted values.
Shown in chart 6 it becomes evident that we were closer to the converted
value in the 1018 sample and most inaccurate with the 1045 sample. This is
contradictory because of the shear content of pearlite in 1095 there should
be closer compared values when observing the 1095 Rockwell hardness vs.
the 1095 Vickers hardness.
The experiment shows that the micro hardness values taken for the
pearlite in the 1045 specimen has the greatest Vickers hardness value.
Although this contradicts the Rockwell values that show hardness increases
as carbon content increases. Theoretically the 1045 specimen should be the
hardest because it is closest to the point where the isotherm and eutectoid
line meet creating the hardest pearlite specimen. This discrepancy within the
results can be attributed to the fact that the 1095 pearlite may theoretically
be softer but makes up nearly 100% of the microstructure. The harder
pearlite found in the 1045 steel is found intermingled within the softer
primary ferrite which lowers the overall Rockwell hardness. These two
characteristics of the 1045 and 1095 steel specimen make them appear as if
they are the same overall hardness as seen on Graph 2 when in fact the
pearlite is harder in the 1045 specimen as seen on Graph 1.
References
[1]ASTM, "ASTM E384 Knoop and Vickers Hardness "Annual Book or ASTM
Standards, American
Society for Testing and Materials, Vol. 3.01
[2]ASTM, "ASTM E3 Metallographic Specimen Prep"Annual Book or ASTM
Standards, American
Society for Testing and Materials, Vol. 3.01
[3]ASTM, "ASTM E407- Microetching Metals "Annual Book or ASTM
Standards, American
Society for Testing and Materials, Vol. 3.01
[4]Callister, William D., and David G. Rethwisch. Materials Science and
Engineering. Hoboken, NJ: Wiley, 2011. Print.
[5] Granta Design.”Hardness Conversion Chart” GrantaDesign.com. Web. 30 Apr.
2012. <http://www.grantadesign.com/images/hardness.fe1.gif>.