Effect of introduced vanadium carbide at the bay region on bainite transformation, microstructure and mechanical properties of high-carbon and high-silicon steel

Obtaining a fine bainitic ferrite for high carbon steel at low temperature requires a long period. Thus, creating strategies to accelerate bainite transformation is important. This investigation aims to explore the introduction of vanadium carbide at the bay region on bainitic transformation kinetics and mechanical properties by comparing isothermal bainitic transformation treatment directly and in combination with bay treatment prior to bainite transformation. Results show that introduced fine VC precipitation during bay treatment notably accelerates the initial bainite transformation with the incubation period being reduced by 91%. Decrease in activation energy for bainite nucleation at vanadium carbide/austenite interfaces and generation of preferred nucleation sites lead to a favorable acceleration of bainitic formation kinetics. However, indirect refinement of grain size for intragranular bainitic ferrite nucleation and consumption of available vanadium carbide/austenite interfaces result in overall rate of the subsequent bainite transformation. For the sample with prior bay treatment, the lath directions of bainitic ferrite are more complex and the size of block RA is smaller than that of the conventional sample. Moreover, the introduction of vanadium carbide at the bay region can simultaneously enhance the tensile strength and impact toughness of the steel.