Effect of prior martensite on bainitic transformation of high Si hypereutectoid steel

Abstract

The paper discusses the effect of prior martensite on the bainitic transformation of a high Si hypereutectoid steel. The research uses a combination of experimental techniques, high-resolution dilatometry and X-ray diffraction analysis, and theoretical calculations to investigate the impact of martensite on the transformation kinetics and microstructure evolution. The study shows that the presence of martensite, regardless of the amount, accelerates the bainitic transformation, particularly in the early and fastest stages, and at higher isothermal transformation temperatures. At lower temperatures, the preconditioning of the austenite prior to the bainitic transformation is such that its mechanical stability increases to the point where the whole transformation is inhibited. It is also suggested that the formation of cementite due to the tempering of martensite at the isothermal stage controls the final fraction of bainitic ferrite. The findings provide valuable insights into the role of prior martensite in bainitic transformation kinetics and microstructure development.

Keywords

• Bainite
• Martensite
• Transformation kinetics
• Retained austenite
• Stabilization