Influence of annealing temperature on microstructure, tensile properties and tensile deformation mechanism of metastable austenitic stainless steel repetitively cold-rolled and annealed

A metastable austenitic stainless steel was repetitively cold-rolled and reversely annealed. The effect of the final annealing temperature on microstructure, tensile properties and tensile deformation mechanism was investigated by electron backscattering diffraction, X-ray diffraction, and transmission electron microscopy. The results revealed that austenite grains were significantly refined and the strength was greatly enhanced by the repetitive cold-rolling and reverse annealing treatment. The reversed austenite grains gradually grew as the final annealing temperature increased from 800 degrees C to 950 degrees C, whereas rapid growth of austenite grains has been observed in 1000 degrees C-annealed samples, which can be ascribed to the gradual dissolution of M23C6 carbide particles with increasing annealing temperature and almost complete dissolution at the annealing temperature of 1000 degrees C. The yield strength and ultimate tensile strength showed an inverse relationship with annealing temperature due to grain growth, whereas the elongation exhibited a direct relationship due to the austenite stability caused by carbides dissolution. The microstructural examination of the annealed samples, with different tensile strains, indicated that the formation of strain-induced alpha'-martensite has been retarded, whereas the formation of deformation twins has been promoted by increasing the final annealing temperature. The tensile deformation mechanisms were dependent on the annealing temperature, including a transformation from strain-induced alpha'-martensite to a hybrid of strain-induced alpha'-martensite transformation and deformation twinning, and to deformation twinning as the annealing temperature increased from 800 degrees C to 1000 degrees C.