Oxidation Characteristics of Type 430 Stainless Steel in Atmospheres Containing Water Vapor

Abstract

Thermogravimetric measurement and oxide scale analysis have been done to study the oxidation characteristics of type 430 stainless steel. In atmospheres of low P_O2 with high content of water vapor, thick scale forms on specimens with commercially annealed and pickled surface (2D surface)at around 600°C. The appearance of the scale is Velvet-like and consists mainly of three layers: α-Fe₂O₃ whisker, Fe₃O₄ layer and FeO+(Fe, Cr)₃O₄ layer. The Velvet-like scale grows rapidly according to the parabolic rate law in the early stage of oxidation process. Deformation layer caused by surface grinding or atmosphere of high P_O2 prevents the formation of this scale by promoting the formation of protective (Fe, Cr) oxide. And also protective Cr₂O₃ type oxide forms at 800°C on the 2D surface of specimens.
During heating up to 800°C, nonprotective Fe oxide formed at around 600°C changes to protective (Fe, Cr, Mn) oxide. Therefore, temperature dependence of weight gain shows maximum at about 600°C and minimum at about 800°C in the atmospheres of low P_O2 with high content of water vapor, in contrast to the monotonic change in dry atmospheres.