Surface hot shortness due to copper in IF steel and effect of boron and phosphorus

Abstract

In recent years, the promotion of recycling of steels is desired from the viewpoints of effective usage of resources and restraint of CO2 emission. When steel scrap containing copper is used, surface cracking occurs during hot rolling process, which poses a serious problem. Copper-enriched phase is formed at the steel/scale interface through selective oxidation of Fe during heating for hot working. The copper-enriched phase liquefies at the temperature beyond 1356K and penetrates into austenite grain boundaries to cause surface cracking by liquid embrittlement. This phenomenon is called surface hot shortness due to Cu. In this research, effect of C on the surface hot shortness and effects of B and P on the hot shortness of an IF steel are investigated using steels containing 0.2% Cu. The susceptibility to the hot shortness of an IF steel is larger than that of 0.1% and 0.5% carbon steels. Addition of boron and phosphorous in IF steel is effective on the suppression of surface hot shortness in IF steel. The reasons for the effects of carbon, phosphorus and boron were discussed from the viewpoints of the effects of these elements on the amount, the shape and the penetration easiness of Cu-enriched phase.