Isothermal and Step Isothermal Oxidation of Copper-Containing Steels in Air at 980–1220°C

Abstract

The oxidation and copper enrichment behaviors of several copper-containing mild steels under isothermal and step-isothermal conditions at 980–1220^°C in ambient air, and the effects of nickel additions, are examined. The oxidation kinetics for all steels does not obey the parabolic law because of the formation of blisters in the scale. At 980^°C, decreased parabolic oxidation kinetics is observed, whereas at 1120 and 1220^°C, the oxidation kinetics exhibits an undulating pattern. High nickel content and high oxidation temperature are two prerequisites for the occlusion mechanism to operate during steel oxidation. For the low nickel steel, a planar scale-steel interface develops at all temperatures, and a copper phase is always seen to form and spread along the scale-steel interface. For the high nickel steels, a planar scale-steel interface develops at 980 and 1120^°C, but at 1220^°C, the scale-steel interface becomes rugged and the copper-rich phase is occluded into the scale. Introduction of a 980^°C and/or 1220^°C oxidation step significantly affects the copper enrichment behaviors of all steels normally exhibited at 1120^°C.