An EBSD investigation on deformation-induced shear bands in a low nickel austenitic stainless steel under controlled shock-loading conditions

Adiabatic shear band is an important materials phenomenon often observed in metals when processed at high strain rates. The mechanical responses and microstructure evolution in it attract strong interests from the scientists of materials science and engineering. We report the results of the microstructure characteristic of a 200 series Fe-Cr-Ni austenitic stainless steel with low nickel contents deformed at high strain rates (about 5.8×10⁵s^-1) by a split Hopkinson pressure bar. The hat shaped specimens are used to induce the formation of the adiabatic shear bands under shock-loading tests. The microstructure and microtexture of the shear band in a 200 series Fe-Cr-Ni austenitic stainless steel are investigated by means of optical micrograph electron backscatter diffraction. The shear bands can be generated at about 78μs after the true flow stress reaches the value about 923MPa. The grains in the boundary of the shear band are elongated along the shear direction, and the core of the shear band consists of ultrafine equiaxed grains with diameter 0.1-0.3μm and low dislocation density. According to the orientation distribution, the microtexture peaked at (45°, 65°, 0°) in the matrix slightly shifts towards the recrystallization microtexture (60°, 60°, 0°) in the shear band center, and the grain boundaries in the shear band are geometrical necessary boundaries with high-angles. Calculations of temperature rise about 943K suggest that the temperature in the shear band is above the recrystallization point. Finally, the grain refinement in an adiabatic shear band in the 200 series Fe-Cr-Ni austenitic stainless steel is described as a consequence of the rotational dynamic recrystallization.