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

Abstract

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 γ-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 γ-austenite transformed initially to ε-martensite and finally to α'-martensite with increasing strain. The dislocation density increased to an exceptionally high value, of the order of ~10¹⁶ m^-2, in the main α'-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.

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Identifiers

ORCID for Yi Huang: orcid.org/0000-0001-9259-8123

ORCID for Terence G. Langdon: orcid.org/0000-0003-3541-9250

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