Microstructure, phase composition and hardness evolution in 316L stainless steel processed by high-pressure torsion

摘要

A 316L stainless steel was processed by high-pressure torsion (HPT) to evaluate the grain refinement and phase transformation. The initial material was essentially a single phase ?-austenite with a coarse-grained microstructure of ?42 µm but the grain size was reduced to ?45 nm after 10 turns of HPT. In addition, there was a phase transformation and the initial ?-austenite transformed initially to ?-martensite and finally to ??-martensite with increasing strain. The dislocation density increased to an exceptionally high value, of the order of ?1016 m?2, in the main ??-martensite phase after 10 HPT revolutions. The formation of the multiphase nanocrystalline microstructure yielded a four-fold increase in hardness to reach an ultimate value of ?6000 MPa. The Hall–Petch behaviour of the HPT-processed alloy is compared directly with coarse-grained materials.