Microstructure Development and Mechanical Properties of Low-Silicon-Content TRIP-Assisted Steels after Coiling Process

Abstract

In the present study, laboratory simulation of hot-strip rolling followed by coiling process was carried out in order to investigate the effect of bainite transformation on microstructure development and mechanical properties of low-silicon-content TRIP-assisted steels. Following a typical multistage isothermal deformation and cooling path, compression samples were quenched into a salt bath at various temperatures within bainite transformation range and held for different periods of time. The results indicated a decrease in either bainite holding time or temperature resulted in an increase in TS, whereas both T-El% and formability index have shown maximum values at some intermediate bainite holding temperature and time. Variation of TS with holding time was correlated to the fraction of martensite and microstructural coarsening whilst the changes in T-El% and formability index were appeared to follow the same trend as VRA. Additionally, the presence of thermal martensite provides a shielding effect on RA particles during straining, thereby postponing strain-induced transformation of austenite to martensite during subsequent deformation. Variations of T-El% and formability index with bainite holding temperature were also rationalized by considering the effect of bainite holding temperature on the characteristics of retained austenite and its surrounding matrix.