Effect of Austenitizing Temperature on Structural Transformation of TRIP Steel in Continuous Cooling

The continuous cooling transformation(CCT) curves of experimental steel were determined by thermal expansion tests at three different austenitizing temperatures.In view of the changes of the ferrite and bainite phase transition region,the effects of austenitizing temperature on the microstructure of samples at room-temperature were studied by OM and SEM.The results show that the lower the austenitizing temperature,the finer the grain.With the austenitizing temperature decreasing,the ferrite and bainite transformation were affected by excitation nucleation,which resulted that the phase transition range is gradually expanded and the curves were shifted to the left.The driving force of the pearlite and martensite transformation is only affected by the enrichment of the alloying elements in the initial austenite.The pearlite and martensite starting points are gradually decreasing with the austenitizing temperature decreasing.