Improvement of microstructure and mechanical properties of a low alloy cast steel processed by direct quenching-partitioning-tempering technique

Abstract

A novel direct quenching-partitioning-tempering (DQ-P-T) process was developed to produce a low-alloy Mn-Si-Cr type high performance cast steel for automobiles without using expensive alloying elements Ni, Mo, or Nb as commonly used in some rolled Q-P-T steels. The cast steel treated by DQ-P-T process exhibits a better combination of strength and ductility as well as higher impact toughness than that treated by the conventional reheat quenching and tempering (RQT) process, and shows the improved microstructure consisting of the dislocation-type lath martensite (or plus a little bainite) and nano-sized flake-like retained austenite between the martensite laths. The DQ-P-T process has shown to be more conducive to enhancing the overall mechanical properties of the cast steel compared with traditional RQT process, and is a promising technique for industrial production. A novel direct quenching-partioning-tempering (DQ-P-T) process is presented and applied to a low-alloy Mn-Si-Cr cast steel. DQ-P-T cast steels have higher volume fractions of the retained austenite than traditional reheat quenching and tempering (RQT) steel, and show the improved microstructure consisting of the dislocation-type lath martensite and nano-sized flake-like retained austenite between martensite laths, which results in enhanced mechanical properties of the cast steel.