Bainite Transformation Behavior and Mechanical Characteristics of Medium-Carbon High-Silicon Steel via Austempering

A series of austempering processes above and below the martensite start temperature (Ms) were employed to evaluate the effect of various austempering temperatures on bainite transformation kinetics, microstructural characterization and mechanical properties of medium-carbon high-silicon steel. The results demonstrated that lowering austempering temperature from above Ms to below Ms brought about the increase of prior martensite content, the refinement of bainitic ferrite lath and the reduction of blocky retained austenite amount and size, which simultaneously accelerated the bainite transformation kinetics and improved the tensile strength as well as impact toughness. Unfortunately, decreasing the austempering temperature reduced the retained austenite content and, thus, led to a marginal drop in elongation. By an integrated consideration of phase transformation kinetics and mechanical performance, the austempering process below and close to the Ms temperature would impart outstanding overall mechanical properties.