Effects of Heat Treatment Temperature and Cooling Rate on 38MnSiVS5 Steel
Manganese-silicon-vanadium micro-alloyed bearing steel (38MnSiVS5) has been used for complex mechanical components in a wide range of applications, such as automotive, aerospace and energy industries. As an important part of the production process, heat treatment of 38MnSiVS5 steel has a great influence on its physical and mechanical properties. Thus, the effects of heat treatment temperature and cooling rate on 38MnSiVS5 steel were studied in this research.
The surface hardness and microstructure of 38MnSiVS5 steel specimens were investigated by using a Rockwell hardness tester, optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The heat treatment process investigated in this research consists of austenitizing at 850 oC, followed by quenching in both oil and water. The specimens were cooled at different rates controlled by quenching in either oil, or water. The optical microscopy showed that the microstructures of quenched specimens were mix of ferrite, pearlite and martensite. The hardness was found to be significantly higher in the specimens quenched in oil than those cooled in water. The hardness results were confirmed by the SEM microstructure examination which showed finer particles and higher average grain size in the oil quenched specimens than those quenched in water.
TEM measurements were used to investigate the metallurgical effects produced by different cooling rates. The TEM images showed that the oil-quenched specimens had higher dislocation density and finer particles size than the specimens cooled in water. The presence of fine particles modified the mechanical properties, such as hardness and tensile strength. The hardness results showed that oil-quenching can get 12% higher hardness values than those cooled in water. The oil-quenched specimens also exhibited higher tensile strength than the water-cooled specimens. This phenomenon was due to the finer grain size in the oil quenched specimens.
To conclude, the effects of heat treatment temperature and cooling rate on 38MnSiVS5 steel were studied in this paper. Results showed that oil-quenching achieved higher hardness values and tensile strength than water quenching. The higher hardness and tensile strength are attributed to the finer grain sizes of the specimens quenched in oil and the higher dislocation density. Thus, the oil-quenched specimens are more suitable for complex mechanical components, such as automotive, aerospace and energy industries.
