I’m studying for my Writing class and need an explanation.
1)The steel sample (1020 steel sample) experienced two types of cooling which are quickly and slow cooling. In the first case, when the sample was cooled quickly, the resulted microstructure in the first quick cooling process composed of Martensite. While in the second quick cooling process, the resulted microstructure composed of Pearlite and Martensite. When the second method of cooling that was slow cooling process, the resulted microstructure composed of Pearlite and Martensite.
2) When the quick cooling (quenching) process was applying for the steel sample, the microstructure mainly resulted Martensite that produced a stronger steel sample as well as made the sample more brittle. On the other hand, slow cooling resulted microstructure composed of Ferrite, Pearlite and Bainite. Since the present of Bainite in this process, the steel sample was less strong comparing when fast cooling was applying. This because Bainite is not strong as Martensite even if its stronger than pearlite. However, while the process of cooling for both types were applying, the hardness of sample decreased from an average 34.67 to 33.3. This probably happened due to the super heating the sample experienced.
3) From the figure above, the expected Martensite hardness for the type steel been used (1020 steel), which is 0.2 percent of carbon, is indicating 48C of a Rockwell C hardness. The measured Martensite hardness found to be 33.3C, which is lower than expected. Different factors that may result in differences including the time it took when the hot sample pulled out of the oven and when placing it in water. As well as not filling the steel sample appropriately.
4) According to the figure 11-17 above, the value of tensile strength that matches 0.2 percent of carbon is approximately 59ksi, which indicated approximately 68B of Rockwell hardness. During the experiment, the slow-cooled hardness value found to be 22.3B, which is clearly lower than expected. Factors that may result in differences, including not filling the sample until the area were cleared as well as not recalibrating the Rockwell machine.
5) The second Martensite produced an average of 33.3B, which is the same compared with that obtained the first Martensite. The reason for that is the change of temperature in the oven is slightly when first and second quick cooling process were applying as well as the time taken to cool the sample in both times where corresponding