1. School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 P. R. China
2. Institute for Advanced Materials and Technology University of Science and Technology Beijing Beijing 100083 P. R. China
3. Technology Center Xining Special Steel Co. Ltd. Xining 810005 P. R. China
4. SAIC General Motors Wuling Automobile Co. Ltd. Liuzhou 545007 P. R. China