Recycling High-Residual Scrap in EAF – Fundamental Research Aimed at pushing the limits

The use of scrap steel as the main source of starting material, instead of reduced iron-ore and coal, results in a reduction of costs, energy, raw materials and emitted pollutants such as CO2, SOx, and NOx when compared to BF/BOF steel making.An EAF steel plant also involves less capital cost than an integrated BF/BOF plant, which also requires coke and sinter plants. In the United States, over 60% of the domestic steel is today produced through the route of EAF. It is, however limited by a surface cracking problem, known as surface hot shortness. This problem originates from the excessive amount of residuals, Cu and Sn originating from wiring and tin cans respectively, in the steel scrap that during oxidation of the Fe enriches, melts and penetrates into the austenite grain boundaries. This necessitates that high-residual scrap is diluted with virgin iron thus compromising the aforementioned
advantages of the EAF route. This paper reviews laboratory work on how hot-shortness can be reduced through control of furnace conditions (atmosphere and temperature) or off set by mixing appropriate scrap sources based on alloying elements. The strategy is to reduce the amount of separated copper and grain boundary infiltration by reducing the external oxidation rate and/or promoting occlusion. A critical ratio of (Cu+Sn)/(Ni+Si) is discussed whereby hot-shortness is avoided and the roles of processing conditions during secondary-cooling from the caster , re-heating and hot-rolling are discussed.