Study on the influence of pre-stress time-characteristic on microstructure transformation in GH process

Firstly, simulation is used to analyze the temperature curve in pre-stress hardening grinding (PSHG). Then, according to the start and the end time of martensitic transformation, three time nodes are selected to study the pre-stress time characteristic; they are 1 s, 3 s, and 7 s after grinding. The influence of pre-stress on the initial temperature and content of martensite transformation in cooling is analyzed; the results indicate the content of martensite increases over the pre-stressed unloading time. To test the theory, experiments of PSHG with different unloading times are carried out. The microstructure of the grinding hardening surface is observed and explored by scanning electron microscopy (SEM). Then, the SEM images are binarized to get the martensite content on the hardening surface. The experimental results show martensite content is consistent with the theoretical analysis. Lath martensite and flake martensite can also be found in these pictures. Flake martensite slightly increases while unloading at 7 s, as it forms at a lower temperature. So the pre-stress time characteristic influences both the martensite content and the morphology of martensite formed.