Effect of Temperature Gradient in a Blank on the Microstructure of Type 304 Stainless Steel in Square-Shaped Deep Drawing

摘要

Deformation microstructures of type 304 stainless steel sheet worked in square-shaped deep drawing of the single and double temperature processes, in the range 25-150 deg C, were investigated. Better drawability was generated in the double temperature performance than in single temperature. In single temperature performance, the deformed grain structure of the failure point tended to be easily elongated in a single direction causing a greater rate of thickness straining. A nonhomogeneous deformation of the double temperature process with temperature gradient on both sides of specimens, in which more equiaxed grains were generated, diminished the rate of thickness straining and resulted in improvement of the drawability. Those microstructures created in each process to influence the thickness straining rate and formability, are explained by a mechanism of stepwise deformations. The unidirectional structure of dense deformation twins and coarse slip bands caused the occurrence of failure under single temperature cold and warm workings, respectively. In double temperature workings, the intersections of two slip bands having bi-directional feature exhibited as a stable structure of one type and produced a decreased rate of thickness straining at the failure point.