Behaviour of copper during high temperature oxidation of steel containing copper

It is well known that copper causes the hot shortness problem in steels and is a difficulty when using steel scrap in the steelmaking process. This is due to the property of copper enriching at the scale/metal interface and precipitating there as liquid during the high temperature oxidation of steels containing copper. In this paper, the behaviour of copper during oxidation is investigated. A steel containing copper is oxidized and the distribution of copper in the scale is examined. It is found that copper is not only enriched at the scale/metal interface, but also exists in the upper magnetite (Fe3O4) layer as a state of solid solution and along the grain boundaries of the wustite layer as a metal. From these results an assumption has been proposed that the liquid copper migrates from the scale/metal interface to Fe3O4 layer along the grain boundaries. Quantitative analysis revealed that the copper amount in the scale is greater than that at the scale/metal interface. Further analysis discovered that the amount of copper eliminated from the steel by oxidation is greater than the total amount of copper detected in the sample i.e. at the scale/metal interface, in the Fe3O4 layer, and along the grain boundaries in the scale.