Identifying Factors for Cu Contained in Carbon Steel Produced in Japan

Abstract

The steel industry has been concerned with contamination by tramp elements during repeated recycling of carbon steel. Increase of Cu content has never been observed at least by monitoring EAF steel bars from the late 1980s. However, the increase may happen in future. To surely avoid the increase which leads to ineffective recycling, mechanisms of Cu mixing in carbon steel should be understood. The factors for Cu in carbon steel produced in Japan were identified. We distinguished two sources of Cu in obsolete steel scrap: Cu alloyed in carbon steel which has been contaminated by previous recycling and Cu contained in materials beside carbon steel. We found that, by dynamic material flow analysis, the Cu content derived from the former source has gradually increased because of increasing shares of bar and section which have a relatively high Cu content, which leaded to 0.05% increase in Cu content during three decades. On the other hand, Cu derived from the latter has become smaller from the late 1990s. One of the reasons was thought as increase of exporting scrap-mixed metal (often termed “zappin scrap”) from around the year. In the near future, it is predicted that the substantial part of the export will be rapidly reduced by amendment of relevant regulations. We estimate that Cu content in steel bars will become 0.49% on the average, if scrap-mixed metal is domestically recycled in a commercial way. This result underlines the necessity of improving the separation of Cu materials from carbon steel scrap.