Deformation-induced martensitic characteristics in 304 and 316 stainless steels during room-temperature rolling

The effect of grain size on the deformation-induced martensite (α′) in 304 and 316 stainless steels (SS) during room-temperature rolling has been studied. Samples of four grain sizes of 52, 180, 229, and 285 μ in 304 and three grain sizes of 77, 125, and 200 /μm in 316 SS have been rolled from 16 to 63 pct reduction in thicknesses to characterize the microstructures during the rolling deformation. The amount of α′ formed increases with increase in the amount of deformation in both SS for a given grain size. The volume fraction of martensite formed increases with a decrease in grain size in 304 SS, while the α’ martensite formation has been found to be grain size insensitive in 316 SS. The volume fraction of α’ formed in 304 SS is always higher than that in 316 SS for a fixed percent reduction in thickness and grain size. This is attributed to the higher number of shear band intersections observed in 304 SS, which are considered to be the nucleation sites for the α’ embryos. The lath martensite obtained at small true rolling strains changes to blocky type at higher true strains. The morphology of α′ formed has been discussed and its characteristics obtained from rolling deformation have been compared with those earlier reported from the room-temperature tensile deformation.