2022 年 63 巻 4 号 p. 450-457
In this paper, the changing of microstructures on the surface layer of high manganese steel (HMnS) Mn15Cr2V under the impacted load was investigated. By theoretical calculations based on stacking fault energy (SFE), it was found that at 300 K, the SFE value of this steel was 34.7247 mJ/m2 and at 220 K, the SFE value was 34.72173 mJ/m2. Thus, with this result, the SFE’s value is much larger than the value of the martensitic transformation, which was about 18 mJ/m2. It can be shown that there will be no martensite changes even if the sample is heat-treated with the sub-zero process. The results of the microstructure analysis show that the microstructures were austenite with carbide particles (VC and Cr7C3) that had a small grain size (about 40 nm) and were dispersed in the microstructures. The study’s findings revealed that when the number of impact loads is 3,000 times, the surface layer exhibited twinning, slip, and austenite nanoparticles. When the number of impact loads increases by 10,000 times, the microstructure of the surface steel appears in the amorphous phase. The results of theoretical calculations based on the changing of stacking fault energy (SFE) and experimental results show that there is no appearance of martensite form on the surface layer in research conditions.
