Effect of Surface Oxide Structure on the Descalability of Cold-rolled and Annealed SUS304

Abstract

In order to obtain good descalability of cold rolled and annealed Type 304 stainless steels, oxidation behavior and scale structure of the steels were investigated. The oxide scale consisted of four layers. The outer first layer was composed of Fe₂SiO₄ and Fe₃O₄, the second layer was (Fe, Mn) Cr₂O₄, the third layer was Cr₂O₃, and the fourth layer adjacent to substrate was amorphous oxide, SiO₂. The third layer became thick and the Si content in the fourth layer increased with the rise of annealing temperature. The thick third layer provided a large Cr depletion zone at the surface layer of substrate. Thus, annealing at higher than 1125°C to develop the Cr depletion zone is effective to obtain good descalability in Type 304 stainless steels.