Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : September 03, 2017 - September 06, 2017
The purpose of this study is to investigate the effect of initial microstructures on austenite (γ) formation behavior during intercritical annealing in high strength steel sheets. There are three kinds of specimens having different microstructures of hot-rolled sheets; specimen FP consisting of ferrite (α) and pearlite, specimen B consisting of bainite and specimen M consisting of martensite. The fraction of austenite in specimen M was larger than that in specimens FP and B below 730 °C, whereas that was in order of specimens FP > B > M above 740 °C. For specimens FP and B, martensite connecting along the rolling direction was observed. On the other hand, the distribution of martensite in specimen M was uniform compared to that in specimens FP and B. In the case of specimens FP and B, γ formation progressed by mainly local equilibrium during heating from 700 to 760 °C. In contrast, γ formation in specimen M progressed by paraequilibrium during heating from 700 to 730 °C, and that progressed by local equilibrium during heating from 740 to 760 °C. Therefore, we concluded that the kinetics of γ formation depends on initial microstructures in each specimen before annealing.
