Surface Crack of Niobium Microalloyed HotRolled Ribbed Bar
LU Jun1,2,WANG Qian1,2,YANG Zhongmin2,WU Chunjing1,LI Liejun3
1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China; 2. Institute of Structure Materials, Central Iron and Steel Research Institute, Beijing 100081, China; 3. Technical Center, Guangzhou Iron and Steel Group Co., Guangzhou 510381, Guangdong, China
Abstract：The surface cracks of niobium microalloyed hotrolled ribbed bars and the continuously cast billets were studied respectively by means of using metallographic microscopy, scanning electron microscopy (SEM) and energy spectrum analysis. Results indicate that the continuous casting billets have serious defects such as centre porosity, interal cracks and centre cracks, caused by the combined effects of improper casting temperature, cooling intensity, casting speed and so on. On surface of bars there were the longitudinal cracks caused by inclusions on the outer layer, especially the subouter layer of bars, but not the interal cracks in billets. The effect of inclusions on the growth and branching of longitudinal cracks were discussed. The large inclusions with poor deformability could easily lead to branching of cracks during propagation. Based on the above conclusions, the relative precautions including optimization of steel refining and improvement of continuous casting parameters were offered and good effect was obtained.
2007, Vol. 42 
