Air-Oxidation Behavior of Multi-component White Cast Iron With Cobalt at High Temperature

Abstract

  Oxidation tests of multi-component white cast irons containing 0 % to 10 % mass % cobalt were carried out in air at temperature of 973 K to 1273 K for 36 ks. The mass gain was found to decrease with an increase in the cobalt content at the oxidation temperature of 1073 K and 1173 K. The effects of cobalt on the oxidation behavior at the oxidation temperatures of 1273 K were not revealed due to excessive mass gain. Breakaway oxidation occurs in cast irons containing cobalt and the start of this oxidation is delayed with the increase in the cobalt content. The oxidized layer was found to be separated into the outer and inner portions, and Fe₂O₃ and Fe₃O₄ oxides were identified in the outer layer. Cobalt was concentrated near the surface of the outer layer and at the boundary of the inner layer and cast iron. Observation of the growth of the oxidized layer using SEM, indicated that cobalt promotes the formation of a concentrated oxidized layer and works as a barrier against the diffusion of iron and other element ions from the cast iron to the oxidized layer.