Two kinds of stainless steels with different ferrite and austenite volume fractions were deformed by torsion at a temperature range of 900 to 1250°C. Steel A (25.5Cr - 4.9Ni - 1.6Mo) has Cr eq/Ni eq = 4.8 and grade B (22.2Cr - 5.6Ni - 3Mo) has Cr eq/Ni eq = 3.5. The results show that the shape of the flow stress curves depends on the material and deformation conditions. Four different shapes of flow curves were observed. At high temperatures, steel A has a typical behavior of ferritic stainless steels. As the straining temperature was decreased, flow curves with peek stresses at low deformation were observed. When the austenite particles are coarsened inside the matrix (steel B), the flow stress displays a peak stress, dividing extensive hardening and softening regions. When the volume fraction of both phase are comparable and the microstructure is characterized by percolation of the both phases present in the samples, the flow stress curve acquires a very particular shape in hot torsion tests.
Duplex stainless steels; microstructure, flow plastic behavior; hot torsion tests
