Role of austenitization and pre-deformation on the kinetics of the ısothermal bainitic transformation

Abstract

The role of time-temperature path on the isothermal austenite-to-bainite phase transformation of low alloy 51 CrV 4 steel was investigated and the corresponding microstructures were analyzed. The important finding is that an incomplete initial austenitization treatment leaves undissolved carbides in the matrix, such that lower carbon and chromium content in the matrix result, eventually accelerating the phase transformation. Furthermore, the residual carbides constitute additional nucleation sites for the bainite plates, speeding up the process even further. Also, both plastic pre-deformation of the supercooled austenite and application of external elastic stresses during the phase transformation lead to transformation plasticity by enhancing the stress fields, providing a driving force for the growth of bainite plates along a preferred orientation. Overall, the current results constitute the first step toward establishing a database for constructing a realistic microstructure-based model for simulating metal forming operations involving austenite-to-bainite phase transformation.