Effect of Multiscale Microstructure on Tensile Properties and Deformation Behavior of 304 Austenitic Stainless Steel

Optimizing tensile properties through the construction of multiphase microstructures is a central issue in the microstructural design of austenitic stainless steels. In this work, 304 austenitic stainless steel was strengthened using a cryogenic cyclic plastic strengthening (CCPS) process, followed by a medium-temperature heat treatment to further tailor the microstructure. The tensile properties of the CCPS-processed and post-heat-treated materials were systematically investigated. Multiple multiscale characterization techniques, including in-situ neutron diffraction and high-resolution digital image correlation, were employed to elucidate the microstructural evolution and stress–strain partitioning during deformation. The results demonstrated that CCPS introduced a hierarchical multiscale microstructure, resulting in a pronounced enhancement in strength, accompanied by an initially aggravated strength–ductility trade-off. Subsequent medium-temperature heat treatment preserved the multiscale microstructural characteristics while reconstructing the austenitic dislocation configuration and inducing the reverse transformation of partial martensite, thereby significantly improving plastic deformability at a relatively high strength level. The observed improvement in tensile behavior was attributed to the synergistic contributions of the transformation-induced plasticity (TRIP) effect, interphase load transfer, and constrained deformation between phases, which is expected to promote additional strain hardening. This work provides experimental evidence and mechanistic insights into the coupled regulation of microstructure and mechanical properties in austenitic stainless steels through integrated deformation–heat treatment. • Multiscale microstructures in 304 steel were prepared via CCPS and heat treatment. • Deformation behavior was studied via in-situ neutron diffraction, EBSD and HR-DIC. • Multiscale microstructure promoted a sustained and uniform TRIP effect. • Multiscale microstructure enabled a phase-constrained deformation effect.