Effects of rolling-pass reduction on microstructural evolution and mechanical properties of SUS316LN stainless steel

Abstract

Effects of rolling-pass reduction on microstructural evolution and mechanical properties of a SUS316LN austenitic stainless steel sheet were investigated. Pass reductions of 3%, 10% and 20% were employed and samples were cold rolled up to 92% reduction using a compact double-rolling mill. After rolling, mechanical properties were investigated by hardness and tensile tests, and microstructure was observed using SEM-BSE and TEM.Although some pass reductions were applied for cold rolling, the difference in reduction evidently appeared only just at the beginning of rolling process. During rolling, actual pass reduction achieved was rapidly reduced because of heavy work hardening. While the 92%-rolled samples exhibited quite high hardness, difference in the final hardness was not so distinct irrespective of the rolling pass reduction. The cold-rolled samples were followed by aging at 773 K. Clear peaks at around 5×103 s appeared and maximum hardness of about 5.0 GPa was achieved. Tensile property exhibited a large anisotropy and tensile strength along transverse direction was higher than that along rolling direction. The as-rolled sample possessed a good balance of tensile strength of 1.7 GPa, and ductility of 10%. Tensile strength gradually increased by the aging and maximum value around 2.0 GPa irrespective of rolling conditions was achieved. Even while high tensile strength was attained, plastic strain to failure was rather good and around 5%.When investigated the microstructure, a typical heterogeneous-nano structure, in which all the component structures were of deformation-induced ones as mechanical twins, shear bands and “eye-shaped” twin domains as well as low-angle lamellae, was observed in all the samples.