Effect Of Cold Rolling And Annealing Process On Microstructure And Mechanical Properties Of SUS304

The present thesis investigated a kind of low elongation of SUS304 austenitic stainless steel sheet made by JISCO. Systemic tests were conducted to study the microstructural evolution process of 304 austenitic stainless steel, the regularity for change of the strain-induced martensite's content and the relationship between the content and the plasticity in 304 austenitic stainless steel during the cold rolling process. It had indicated influence law of annealing procedure on 304 austenitic stainless steel′s structure property , and a reasonable annealing procedure was put forward through experimental research. Through the experiments and analyses, the main conclusions are as follows:During cold rolling deformation process, the grain deformation increased as the deformation increased. When the deformation increased to a certain degree, the grain boundary became vague, it was a kind of fibrous structure and the grains were recognized hardly. Meanwhile, there was a great deal of annealing twin, dislocation and lath martensite. As the increasing of lamellar structure and deformation twin, deformation twin′s grain boundary led to the dislocation obstacles and ever-increasing dislocation. The interaction of deformation twin and dislocation prevented dislocation from moving, so both the tensile strength and yield strength increased, while the elongation decreased.During the annealing process, with the increment of annealing temperature and holding time, there was varying degree recrystallization, the tensile strength and yield strength gradually decreased, and the elongation ever-increasing. After fully recrystallization, there was equiaxial austenite structure and the elongation increased to the maximum. At a certain temperature, it was easy to find a mass of annealing twin. The grain dimension grew unceasingly and annealing twin was ever-increasing as the extension of holding time. When the density of twin crystal was low, the high density twin boundary was separated to block-shape grain. When the density of twin crystal was increasing, the high dislocation density block-shape grain was separated further by twin boundary and became lath. The elongation increased as the gain size increased, while the elongation would decrease if the lath structure was too much in the structure.After annealing process, it was clear to find that the heavier deformation, the easier to recrystallization and the shorter the time for fully recrystallization, that′s because the heavy deformation collected vast amounts of energy during the deformation and it′s easier to recrystallize during annealing process.