Microstructure of 38CrSi Steel (1100℃×20min W.C.)
38CrSi steel is a type of alloy steel which takes into consideration high strength and toughness, so it may be well suited for applications such as shafts, gears, and military applications. This study focused on the microstructure of 38CrSi steel after water cooling from 1100°C for 20 minutes.
Optical micrographs of the 38CrSi steel samples revealed a microstructure composed of mixed ferrite and martensite. The grain boundary ferrite (GBF) were found to have resulted from the rapid cooling of the samples. The ferrite particles were observed to be smaller and more abundant than the martensite particles, with the latter appearing as vague, elongated or asymmetrical structures. The GBF particles were found to be relatively uniform in size and had subgrain boundaries. The distribution of ferrite and martensite was also described as being equally spread across the samples, indicative of an ideal metallurgical representation.
The hardness of the 38CrSi steel microstructure was found to be much higher than that of pure ferrite and comparable to that of martensite. The microhardness profile indicated that the 38CrSi steel had a maximum hardness of approximately 300HV1, which is higher than the average hardness of pure ferrite but lower than that of pure martensite. The presence of GBF was found to be beneficial in terms of improving the hardness of the microstructure.
The differences between the 38CrSi steel microstructure before and after water cooling were also studied. Prior to water cooling, a microstructure consisting only of ferrite and pearlite was observed. After water cooling, the amount of ferrite was observed to have decreased considerably and the microstructure was observed to have changed to a mixed ferrite and martensite microstructure. The decrease in ferrite was attributed to the rapid cooling of the samples, which led to greater decarburization and the formation of martensite.
The 38CrSi steel microstructure was observed to have a mixture of ferrite and martensite, with the former being the primary phase present. The structure also benefited from the presence of GBF, which improved the hardness and improved the mechanical properties of the steel. After water cooling, the microstructure was observed to have changed to a mixed ferrite and martensite structure, with a quite uniform size, and there was an overall decrease in the amount of ferrite present. The microstructure was found to have a hardness that exceeded that of pure ferrite but was lower than that of pure martensite. Overall, these results demonstrate the advantages of rapid cooling and the presence of GBF on the microstructure of 38CrSi steel.
