Effect of Initial Grain Size Prior to ECAP-Cold Rolling Processing on the Riding and Form-ability of Ferritic Stainless Sheets

Equal-channel angular pressing (ECAP) was applied to hot-bands by one pass prior to cold-rolling and annealing in order to modify the texture, and improve the ridging and formability of ferritic stainless steel sheets. The present study focuses on the effect of initial grain size before ECAP, using the samples having extremely large grain size of 210 mu m and smaller ones of 30 mu m. The final grain sizes of cold-rolled and annealed sheets were about 30 mu m for both processes. It was found that Rankford value (r-value) of large grain size was higher compared with that of smaller one while ridging was alleviated in the latter. The recrystallization temperature of cold-rolled sheets was about 50 degrees C lower in the larger grain size. It is considered that higher density of grain-scale shear bands in the sample of larger grain size promotes recrystallization and reduction of <001>//ND grains and increase <111>//ND grains, resulting in higher r-value. However, coarser arrangement of <001>//ND colony parallel to the rolling direction in large grain size may causes higher ridging in spite of the lower fraction <001>//ND grains.