Microstructure evolution of TRIP-assisted lean duplex stainless steel 2101 during in-situ tensile test after a thermomechanical treatment

Abstract

A thermomechanical treatment process which can regulate the lamellar structure of duplex stainless steel into equiaxed austenite and ferrite matrix is proposed in this paper. The effects of solution temperatures on the microstructure and mechanical properties as well as the plastic deformation behavior of LDSS 2101 during tension are investigated using in-situ electron back-scattered diffraction (EBSD). The results indicate that the optimum temperature range for secondary solid solution is 1000–1050 °C. Strain induced martensite transformation (SIMT) occurs in the metastable austenite during the deformation, following two typical sequences of γ → α′ and γ→ ε → α′. Meanwhile, numerous deformation nano-twins are observed in the austenite, acting as strong obstacles to dislocation glide. Furthermore, α′-martensite nucleates preferentially at the large angle grain boundaries (HAGBs) between austenite grains as well as the intersection of annealing twin boundaries (TBs) and grain boundaries (GBs), growing rapidly along annealing TBs, GBs and slip bands. However, ε-martensite nucleates not only at the intersection of slip bands, but also inside the slip bands within the austenite. A high Schmid factor of 0.47 is necessary for γ→ε transformation to supply the driving force demand. Moreover, the ε→α′ transformation occurs dominantly after strain ε = 0.3.