Ultrahigh-Strength and Ductile AISI 316L Steel Processed by Cryogenic Rolling

We demonstrate that cryogenic rolling can simultaneously achieve ultrahigh strength and significant ductility in 316L steel, thereby overcoming the existing limits of its tensile properties. The cryogenic-rolled 316L steel exhibited a 1.1 GPa yield strength (YS) at 298 K. Typically, deformed materials exhibit strain softening immediately after yielding with poor uniform ductility. However, during tensile straining, the cryogenic-rolled 316L steel underwent significant strain hardening despite being severely deformed, thus demonstrating exceptional uniform ductility. Consequently, the cryogenic-rolled 316L steel showed a significantly superior strength-ductility combination, impossible with typical cold rolling. The significantly increased YS of the cryogenic-rolled 316L steel resulted from the combined effect of the presence of the hard martensite phase and the refined austenite grains formed by high-density deformation bands. The significant strain hardening in the cryogenic-rolled 316L steel was possible because the low density of dislocations in the austenite matrix enabled the generation of substantial back stress when newly formed dislocations accumulated at obstacles such as grain boundaries during tensile deformation. Partial dislocations in the cryogenic-rolled 316L steel also contributed to considerable strain hardening by suppressing cross-slip during tensile deformation at 298 K-a well-known major mechanism that weakens strain hardening by facilitating dynamic recovery in metallic materials. Our findings suggest a new microstructural strategy for developing commercial steels with superior tensile properties.