tempering the specimen and this is also observed in the original stress strain curve (see Figure 1) It can be concluded that heat treatment plays a major role in the modification of the yield strength and the ductility of a material. 1.5 Interpretation of hardness and strength The hardness of carbon steel specimens with a carbon content of 0.45 wt% prepared for the Impact test was observed using the Rockwell hardness testing machine. A load of 1471 N was used to measure the hardness of the specimens. The hardness test was carried out in three different regions at least 3 indentations from each other to obtain the results. The mean value of the three readings for each specimen was taken to obtain the hardness of each steel specimen. It 5
MS43010 - N OVEMBER 25, 2019 Figure 5: Plot indicating interaction between UTS vs Ductility is observed that the specimen Q has the highest hardness value of all the specimen but the lowest strength and the specimen QT380 has the highest strength of all the other specimen as shown in Figure 6. Figure 6: UTS as a function of Rockwell Hardness values Further, four steel specimen were prepared and mounted for observation. The hardness of the steel specimens is measured using the Vickers Hardness testing machine using a load of 1 KgFmm - 2 . For each specimen, the hardness test was carried out in three different regions, and the observed readings are noted down. The mean value of the three readings for each specimen was taken to get the hardness of each steel specimen. It is observed that the specimen Q has the highest hardness but lowest strength whereas the specimen QT380 has the highest strength of all other specimen as shown in Figure 7. Further analysis needs to be done to understand the relation between hardness and strength. The Vickers hardness test is carried out by distributing the load implemented to indent the pyramidal diamond into the welded specimen by the area of indentation thus created. The larger the load used, the larger will be the indentation created. Hardness tests were performed to examine the effect of welding on the hardness of the material using the Vickers Hardness testing machine using a load of 0.5 KgFmm - 2 . The hardness test is carried out over the width of the 6
MS43010 - N OVEMBER 25, 2019 Figure 7: UTS as a function of Vickers Hardness values weld using trial and error to find an appropriate load level for increments between indentations. When observed, there is a significant change in the hardness across the weld. The hardness within the weld region was higher than the base material, which is likely due to the generation of fine grains induced by the plastic deformations during the welding process. Hardness varies from the weld zone to base material; with effect to the difference in the microstructure in each zone. The Heat Affected Zone (HAZ) has the maximum hardness than the weld zone and the base material as shown in Figure 8. The maximum rise in the hardness at HAZ was identified at the weld interface, after which the hardness started to decrease slightly. From the data obtained and the curve plotted using that data, the experiment concludes that
You've reached the end of your free preview.
Want to read all 13 pages?
- Spring '18
- Dr. maarten bakker