Effect of superplastic deformation on microstructure evolution of 3207 duplex stainless steel

Abstract

High temperature tensile, electron backscatter diffraction (EBSD) techniques and transmission electron microscope (TEM) were combined to perform a systematic investigation for superplastic deformation behavior, mechanism and microstructure evolution of 3207 duplex stainless steel. Excellent superplasticity of this alloy is indicated by the elongation indicates and the flow curves revealing four stages of deformation: elastic deformation stage, stable deformation stage, quasi-stable deformation stage and localized necking stage. Before the initial of quasi-stable deformation stage, several low angle boundaries (LAGBs) can be observed, indicating dislocation creep-controlled deformation is the dominant mechanism. In the middle and final of the quasi-stable deformation stage, LAGBs are found evolving into high angle boundaries (HAGBs) indicating the dominant deformation mechanism to be grain boundary sliding (GBS), leading to the weakened textures. In the localized necking stage, dislocations are found generated by the combination of cavities along grain boundaries, indicating the dominant deformation mechanism of GBS and an accommodation mechanism of conventional plastic deformation. The main softening mechanism responsible for the flow behaviors of the 3207 duplex stainless steel is identified as dynamic recrystallization (DRX), which completely neutralized the effect of work hardening at the quasi-stable deformation stage.