An investigation of microstructural evolution in 304L austenitic stainless steel warm deformed by cyclic channel die compression

Abstract

Microstructural evolution during warm severe plastic deformation of 304L austenitic stainless steel is investigated in the present work by employing Electron backscattered diffraction (EBSD) analysis. A total effective plastic strain of 4.8 is imparted through cyclic channel die compression technique at 500 °C. Macrostructural studies revealed distinct flow lines characterized by heterogeneous deformation bands indicative of deformation inhomogeneity. EBSD based microstructural analysis indicated substantial grain refinement wherein the grain size is decreased from ∼15 μm in the initial condition to ∼0.27 μm in warm deformed condition. Continuous dynamic recrystallization (CDRX) is identified as the dominant grain refinement mechanism evidenced by strain induced boundaries, subgrains bounded by low angle grain boundaries and thin deformation microbands. The role of deformation bands in facilitating grain refinement is evidenced. CDRX driven grain subdivision/fragmentation through the evolution of spatially distributed misoriented subgrains is corroborated to the significant increase in low angle grain boundaries in deformed condition. Considerable improvement in strength is evidenced from the evolution of microhardness and tensile behaviour. Two-fold increase in microhardness and three-fold increase in yield strength is observed. Towards the end, the grain size dependence on yield strength and microhardness is suitably described by Hall-Petch behaviour.