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. 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 ASTM, "ASTM E384 Knoop and Vickers Hardness "Annual Book or ASTM Standards, American Society for Testing and Materials, Vol. 3.01 ASTM, "ASTM E3 Metallographic Specimen Prep"Annual Book or ASTM Standards, American Society for Testing and Materials, Vol. 3.01 ASTM, "ASTM E407- Microetching Metals "Annual Book or ASTM Standards, American Society for Testing and Materials, Vol. 3.01 Callister, William D., and David G. Rethwisch. Materials Science and Engineering. Hoboken, NJ: Wiley, 2011. Print.  Granta Design.”Hardness Conversion Chart” GrantaDesign.com. Web. 30 Apr. 2012. <http://www.grantadesign.com/images/hardness.fe1.gif>.