Nucleation Analysis of Variant Transformed from Austenite with Σ 3 Boundary in High-Strength Low-Alloy Steel

We elucidate here the effects of annealing twins on phase transformation products based on electron back-scatter diffraction analysis and corresponding microstructure visualization and quantification methods. Martensite and bainite were obtained by rapid continuous cooling and isothermal processing at different temperatures, respectively, which were designed to study variants formed in austenite with Σ 3 boundary. The isothermal transformation near martensite start ( M s ) temperature was most conducive in obtaining the highest content of twin-related V 1 / V 2 variant pair. Based on the classical nucleation theory of martensite and bainite, respectively, the role of austenite Σ 3 boundary in martensite and bainite transformation is illustrated.