Copper Enrichment Behavior Of Steel With Copper Addition During Oxidation Process

Copper is nearly accumulated totally in recycled steels and is difficult to be removed during steel making processes when steel scrap is used as steel sources. Therefore, the effect of copper in steel is widely studied in recent decades. Copper segregated near steel surface either after heated at high temperature or after a certain kind of corrosion at room temperature. This kind of segregation, on one hand, would cause copper brittleness, and, on the other hand, would form a protective layer such as weathering steel to prevent steels from further corrosion.Continuous copper enriched layer were formed between steel substrate and scale after being heated at 1150℃ for two hours. While, heating at 1150℃ may cause copper brittleness and affect steel properties. Two steels with different copper contents were prepared in this paper, the steels were heated at 1000℃, 800℃ and at varied temperature for different holding time. The aim is to gain copper segregation law of steel with copper addition during high temperature oxidation.After heating at 1000℃ or below and holding a certain time, a certain amount of copper were found on the surface of copper-containing steel during high-temperature oxidation process. Most copper concentrates near the surface of steel substrate in scale, therefore, there is no direct binding between substrate and copper, and copper is not distributed continuously. Copper enrichment behavior near substrate surface is affected by a variety of factors such as heating temperature, holding time and copper content in copper-bearing steel during oxidation process. When the oxidation temperature increased, the enrichment level of copper would also increase; as well as the holding time and the copper content in steel.While, under the experimental conditions, by changing heating temperature, holding time and the content of copper, it is unchanged that the copper-rich regions are diffused and distributes discontinuously.Because copper is not precipitated continuously, copper did not play a protective role to the matrix. With the holding time increasing, the thickness of the scale increased. The thickness of the oxide scale under continuous heating is larger than that of the discontinuous one.Enrichment of copper appears not only in oxide scale or near the substrate surface but also in the matrix, while the forming reasons are different. Copper segregation in scale is due to the oxidation of iron,which form a squeeze force, and copper segregation in matrix is mainly due to copper precipitation in steel and distribution along austenite during high temperature heating and subsequent cooling process. The oxygen content increases when the holding time is elongated during high temperature oxidation process, it is deduced that copper oxidation occurred.