Microstructures and mechanical properties of cold-rolled 21Cr lean duplex stainless steel with medium to high cold rolling reductions

Abstract

The effects of medium-high cold rolling reduction (40%~80%) on the microstructure, phase transformation, and mechanical properties of 2101 lean duplex stainless steel (LDSS) are studied. The results show that the alternately arranged band-like microstructure is formed along the cold rolling direction. A large number of dislocations appear in the ferrite and gradually evolve into dislocation plug clusters, dislocation walls, and dislocation cells with the deformation. The nanoscale dislocation substructures can refine the ferrite. Shear bands, mechanical twinning, and α' -martensite are detected in the austenite. The content of α' -martensite increases with the increase in the deformation degree, and a wavy "pancake structure" form under large strains. The strength and hardness of the steel after the cold rolling deformation increase significantly, while the plasticity is drastically reduced. Nevertheless, with the cold rolling reduction increasing from 40% to 80%, the plasticity remains almost unchanged, which may be related to the ultrafine ferrite, fine α' + γ mixed grains, and reduced transformation induced plasticity effect. The high-density dislocations in the ferrite, strain-induced martensite, and retained austenite synergistically transform the fracture mode from a typical ductile fracture to a ductile and quasi-cleavage mixed fracture. • The austenite phase is filled with shear bands, twins, and α' -matensite. • The transformation route follows γ → twins → α' -matensite and γ → α' -matensite. • The ferrite grain size is refined by a large number of dislocation substructures. • The maintained elongation is related to the fine ferrite and α′ + γ mixed structure.