1. School of Mechanical Engineering, North University of China, Taiyuan 030051, P. R. China
2. Taiyuan Technician College, Taiyuan 030021, P. R. China
3. School of Energy and Power Engineering, North University of China, Taiyuan 030051, P. R. China
4. Taiyuan Iron and Steel Co., Ltd., Taiyuan 030003, P. R. China
5. College of Materials Science and Engineering, North University of China, Taiyuan 030051, P. R. China