1. School of Metallurgy and Environment Central South University Changsha 410083 P. R. China
2. National Center for International Research of Clean Metallurgy Changsha 4100083 P. R. China
3. Steelmaking Research Department Baosteel Group Corporation Research Institute Baoshan District Shanghai 201900 P. R. China
4. Materials Science and Engineering Department Yonsei University Seoul 120-749 South Korea