Deformation behaviors at cryogenic temperature of lean duplex stainless steel with heterogeneous structure prepared by a short process

Abstract

In this study, a lean duplex stainless steel with a heterogeneous lamellar structure is created using a quick technique of direct cold rolling combined with severe plastic deformation and short annealing. The deformation behaviors and fracture mechanisms at cryogenic temperature are investigated. In accordance with the findings, the duplex stainless steel S32304 exhibits excellent mechanical properties at 203 K, with tensile strength reaching 1160 MPa, elongation reaching 44.1%. Nearly 44.4% more elongation exists at 203 K than at 298 K. The synergistic coupling strengthening of the TRIP and TWIP effects of the austenite, HDI strengthening, and dislocation proliferation of coarse ferrite grains stimulated by the austenite grains with various orientations can all be credited for the excellent mechanical properties at 203 K. Additionally, the prominent deformation substructures, such as nanotwin bundles, and the strong interaction between dislocations and nanotwin bundles, are also contributed to strain hardening at 203 K. However, at 573 K, dislocation slip becomes the primary deformation mechanism of the two phases, and severe dislocation accumulations in the coarse ferrite grains become a possible site for crack nucleation, leading to a higher loss of ductility than at 298 K and 203 K.