DEFORMATION-INDUCED MICROSTRUCTURE AND MARTENSITE EFFECTS ON TRANSGRANULAR CARBIDE PRECIPITATION IN TYPE-304 STAINLESS-STEELS

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 alpha'-martensite at the intersections of the twin-faults. Thermal treatment at 670-degrees-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 alpha'-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.