Tribological and mechanical behavior of nano carbide free bainite high strength steel. A critical review

The investigators reviewed the effects of retained austenite and nano-carbide-free bainite microstructure on the mechanical properties of high Si (wt%) austempered and intercritically annealed steel. The microstructure comprised three phases: bainite/martensite, retained austenite, and intercritical ferrite (IF). Combining thermodynamic analysis with experimental data (XRD, TEM) enabled a review of the stabilized retained austenite during the austempering process. Retaining austenite stabilization is primarily thought to result from the second step of the austempering process, which involves the cessation of the bainitic transformation and carbon rejection into residual austenite. In this review, the product of the percent elongation and the tensile strength was 31–35 GPa, resulting in a notable increase in both total and uniform elongation (from 24% to 38%, respectively). Retaining austenite exhibited a three-stage work-hardening behavior that delayed necking. This review attributed the increased work hardening rate to the nano-carbide-free bainite microstructure and TRIP effect.