Effect of Si on bainitic transformation kinetics in steels explained by carbon partitioning, carbide formation, dislocation densities, and thermodynamic conditions

The effect of Si addition on the evolution bainitic transformation, carbon diffusion, carbide formation, and dislocation density in steel was investigated using in-situ high-energy X-ray diffraction (HEXRD). Alloys Fe-0.4C-1.7Mn (in wt%) with 1–4 wt% were austenitized at 1273 K then isothermally heat treated 573, 623, 673 K. According to HEXRD results, increasing content reduces transformation kinetics causes incompleteness occur lower bainite volume fraction. This is because i) retards impeding eutectoid leads accumulation migrating interface; ii) higher strain energy more dislocations austenite that also hinders migration interface. Carbide formation observed prior incomplete stage. During further isothermal holding, decrease due annihilation had little or diffusion. Finally, has a minor calculated T0, T0’, WBs lines. measured enriched agrees well T0 but not T0’.