抄録
The most serious problem in recycling of steel is surface hot shortness during hot deformation due to Cu mixed from scrap into steels. Tin accelerates the effect of Cu. Several methods have been researched to suppress this shortness. However, it is difficult to separate Cu and Sn from steel scrap using physical and chemical methods and to remove these elements from steels by current smelting process. Therefore, Cu and Sn accumulate in steels produced using steel scrap: such elements are called tramp elements. On the other hand, Cu has a potential to increase strengths and corrosion resistance of steels, which might decrease environmental load during the life cycle of steels. The surface hot shortness occurs through preferential oxidation of Fe atoms during heating for hot deformation and formation of liquid Cu-enriched phase at the steel/scale interface. Therefore, there exist tolerable contents of Cu and Sn in commercial steels. The amount of Cu in steel scrap is increasing in Japan year by year. Therefore, in the present research, the details of the mechanism of the surface hot shortness are examined in order to find the ways for the suppression of the shortness by controlling microstructures near the steel/scale interface through physical metallurgy. Controlling of microstructures can be performed by the optimization of contents of harmless alloying and impurity elements, heating temperature, heating atmosphere and deformation rate.
