Abstract
It is a great disadvantage in the use of 18% chromium stainless steel that a ridging phenomenon occurs when the cold rolled and annealed sheets are subjected to cup drawing operations. The present study has been made to clarify the origin of the ridging phenomenon and to obtain a method for its elimination using commercial 18% chromium stainless steel (α+γ) and high-purity 18% chromium stainless steel (α-phase). The results obtained were as follows : The ridging phenomenon is caused by plastic anisotropy of the elongated coarse grains in the banded structure formed during cold rolling and can be diminished by randomization of orientations. For the sheets which contain 0.02∼0.12% carbon and consequently have the α+γ region at high temperatures, a transformation heat-treatment, e.g. 1100°C×1∼3min followed by rapid cooling, is a very effective and simple method for diminishing the ridging. It is very important to make the initial ferrite grain size as small as possible and to reduce the banded structure in the rolled sheet to the minimum, especially for the sheets of below 0.01% carbon and having no α+γ region at high temperatures. Our principal interpretation for the origin of the ridging phenomenon is that only the RD⁄⁄⟨110⟩ textures (as {001}⟨110⟩) never become the origin of ridging. The existence of plastic anisotropy of elongated coarse grains in the banded structure makes the ridges, and when the elongated coarse grains have the {001}⟨110⟩ orientation, these ridges occur of the peculiar behavior of recrystallization, and the stable orientation for cold rolling. The profiles of the ridging can sufficiently be explained by the r-value theory.
