Quenching and partitioning (Q&P) processing of fully austenitic stainless steels

Abstract

A novel quenching and partitioning (Q&P) processing was applied to the steel Fe-15Cr-3Ni-3Mn-0.5Si-0.12N-0.16C (wt.-%) with an almost fully austenitic microstructure in the solution annealed condition. The Q&P processing consisted of a subzero cooling step and a partitioning step at 450 °C. The fraction of α′-martensite after the Q&P processing was nearly 58 vol%. During partitioning, M3C precipitates with an average size of 20 nm formed inside the α′-martensite. Concurrently, the interstitial content of austenite was increased by an average of almost 0.1 wt.-%. After Q&P processing, the stainless steel exhibited outstanding mechanical properties including a yield strength of 1050 MPa, an ultimate tensile strength of 1550 MPa, and a tensile elongation of 22% at room temperature. Reduction in the tensile test temperature from 100 °C to −40 °C facilitated the strain-induced α′-martensite formation and led to the simultaneous enhancement of strength and ductility. The enhancement of tensile ductility in spite of the strain-induced α′-martensite formation (α′-transformation-induced plasticity effect) was attributed to differences in the stability of austenite mainly caused by its non-uniform interstitial enrichment.