Deformation-induced microstructure and martensite effects on transgranular carbide precipitation in type 304 stainless steels

Abstract

Plastic deformation of 304 stainless steel (SS) induces transgranular (TG) carbide precipitation, which is critically dependent on deformation-induced microstructural changes occurring during thermal treatment of the SS. Uniaxial deformation of the 304 SS to 40% strain produces a high density of intersecting micro-shear bands composed of heterogeneous bundles of twin-faults and about 12–17% strain-induced α′-martensite at the intersections of the twin-faults. Thermal treatment of 670°C for 0.1–10 h, however, results in a rapid annihilation/transformation of the strain-induced martensite and the concurrent formation of zones containing mixed thermal martensite laths and fine-grained austenite, though the thermal martensite also decreases with increasing heat treatment time. Simultaneous with these thermomechanically-induced microstructural changes, TG chromium-rich carbides form at intersections of twin-faults and on fine-austenite or thermal martensite boundaries in the SS; however, no correlation between strain-induced α′-martensite and carbides was observed in this work. The mechanisms of deformation-induced microstructure and (strain-induced and thermal) martensite effects on TG carbide precipitation in 304 SS are discussed.