Stability of retained austenite through a combined intercritical annealing and quenching and partitioning (IAQP) treatment

Abstract

Intercritical annealing (IA) at various temperatures followed by quenching and partitioning (IAQP) treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-1.87Mn (wt%) sheet steel. Optimized microstructure and enhanced mechanical properties were achieved through appropriate adjustment of IA temperatures. The steel which was annealed at 1,033 K for 600 s, then quenched to 573 K and partitioned at 693 K for 20 min, designated as 1033QP steel, exhibits maximum 16.3 vol% retained austenite (RA) with good mechanical properties (ultimate tensile strength 886 MPa and total elongation 27%). It was found that the thermal and mechanical stabilities of RA are mainly influenced by the combined effect of its average carbon content and amount of adjacent martensite. Furthermore, the transformation-induced plasticity effect increased the peak n-values observed at the second stage of the work hardening of IAQP steels.