Ultra High Strength Stainless Steels Obtained by Quenching‐Deformation‐Partitioning (QDP) Processing

Abstract

A novel Quenching‐Deformation‐Partitioning (QDP) processing is applied to the Fe–19Cr–4Ni–3Mn–0.5Si–0.14N–0.16C (wt%) TRIP/TWIP steel with a microstructure consisting of austenite and 4 vol% δ‐ferrite in the solution annealed (SA) condition. The QDP processing involves pre‐straining at −40 °C followed by partitioning at 450 °C for 3 min. The volume fraction of strain‐induced α′‐martensite after an engineering pre‐strain of 25% at −40 °C is about 56 vol%. In spite of the formation of precipitates inside the α′‐martensite during partitioning, the austenite is enriched with the interstitial elements C and N. After QDP processing, the steel exhibits outstanding mechanical properties, for example, a yield strength of 1330 MPa, an ultimate tensile strength of 1490 MPa, and a total elongation of 16% at room temperature (RT). The yield strength and the ultimate tensile strength increase by 290% and 70%, respectively, with respect to the SA condition. The reduction of the tensile test temperature from 100 °C to −40 °C results in a concurrent enhancement of strength and ductility. The enhancement of tensile ductility at lower temperatures is explained by the enhanced glide planarity originating from the facilitated dissociation of perfect dislocations into Shockley partials.