Improved tensile properties, stable microstructures and isotropic deformation of nanocrystalline 304 stainless steel

The tensile properties of nanocrystalline 304 stainless steel plate (NSSP-304) produced by severe rolling technology and its conventional polycrystalline 304 stainless steel (CPSS-304) counterpart were studied at room temperature. The microstructures of fractured NSSP-304 and CPSS-304 were characterized. NSSP-304 had enough ductility (elongation 34.5%), larger strengths, elastic strain and the reduction of area despite its smaller volume fraction of strain-induced a0-martensite (SIM) and no obvious work hardening. The deformation of NSSP-304 was more isotropic, its microstructures were more stable and homogeneous during tensile process due to the following results about fractured NSSP-304: (1) the nar-rower variation amplitude of surface micro-hardness along and perpendicular tensile di-rections; (2) the smaller void density and few surface micro-cracks; (3) the smaller surface roughness and roughness variation, and their narrower fluctuation ranges at three di-rections; (4) only micro-cracks without macro-cracks around NSSP-304 fracture; (5) its smaller volume fraction of SIM. The voids in CPSS-304 initiated around MnS inclusion, at grain boundaries, triple junctions, the boundaries of austenite and martensite phases, and in the two phases. They became micro-cracks within their original positions and macro -cracks by passing through different grains. The voids in NSSP-304 initiated at grain boundaries, triple junctions and the boundaries of the two phases. They became micro -and macro-cracks by passing through different grain boundaries. The MnS inclusion in NSSP-304 scarcely influenced its tensile deformation. The fracture mechanisms of NSSP-304 and CPSS-304 were the intergranular fracture, and the mixture of intergranular and transgranular fracture respectively. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The tensile properties of nanocrystalline 304 stainless steel plate (NSSP-304) and its conventional polycrystalline 304 stainless steel (CPSS-304) counterpart were studied. NSSP-304 exhibited higher ductility, larger strengths, and more isotropic deformation compared to CPSS-304. The microstructures of fractured NSSP-304 and CPSS-304 were also analyzed, showing more stable and homogeneous microstructures in NSSP-304.