Multi-scale study on the heterogeneous deformation behavior in duplex stainless steel

Abstract

The heterogeneous deformation behavior of austenite and ferrite in the 2205 duplex stainless steel was subjected to multiscale analysis based on the in situ synchrotron-based high energy X-ray diffraction, microscopic digital image correlation, electron backscatter diffraction, and transmission electron microscopy. It is found that the heterogeneous deformation triggers from the yielding of austenite. During this deformation stage, austenite experiences greater strain in the area near the phase boundaries because of the impeded function of the phase boundaries to dislocations. Owing to the relatively small difference in hardness between the constituent phases, the strain in austenite grains extends into the adjacent ferrite grains when entering into the ferrite yielding stage. In addition, the strain distribution of the austenite grains is more homogeneous than that of the ferrite grains because of the lower stacking fault energy of austenite, which results in a planar slip, and higher stacking fault energy in case of ferrite, causing cross slip. The interaction between austenite and ferrite becomes considerably obvious when the strain further increases after both constituent phases yielding because of the back stress and forward stress in austenite and ferrite, respectively, which are generated by the pile-up of the geometrically necessary dislocations.