Accelerating bainitic transformation and enhancing mechanical properties by chemical heterogeneity in ultrafine bainitic steel

This study employed a processing route (CPBT) integrating a cold-rolled pearlite precursor with rapid heating to regulate bainitic transformation and mechanical properties of ultrafine bainitic steel. The results indicated that the bainitic transformation was significantly accelerated by the CPBT treatment, promoted by both an increased density of nucleation sites from cold-rolling-induced grain refinement and preferential nucleation in Mn-/Cr-depleted austenite regions. The enhanced transformation kinetics also resulted in a pronounced refinement of blocky retained austenite. Furthermore, the CPBT process introduced chemically heterogeneous bainite, characterized by refined bainitic ferrite laths and thickened Mn-/Cr-enriched film-like retained austenite, in contrast to the elemental homogeneity of conventional bainite. This microstructure improved tensile strength through grain refinement strengthening, while the sustained transformation-induced plasticity effect from the chemically heterogeneous retained austenite during deformation enhanced elongation.