The effect of thin surface layer of nitrogen-expanded austenite on bulk γ-α’ phase transformation in low-temperature deformation of 316L stainless steel

Abstract

Deformation-induced γ-α’ phase transformation was studied in austenitic stainless 316L steel in low-temperature deformation regime (tension at 77 K). Before deformation, the surface of the steel specimens was saturated with nitrogen by ion-plasma nitriding at 673 K for 12 h. Thin 4-μm surface layer of nitrogen-expanded austenite (S-phase) does not influence mechanical properties but affects phase transformation in the bulk 1.5 mm-thick specimens. Surface nitriding effectively suppresses the inhomogeneity in deformation-induced martensite nucleation and formation of the α’-phase prior the macroscopic neck formation.