Analysis of White Spot Defect on Inner Surface of 25Mn Cold-drawn Oil Cylinder Tube

Physical and chemical methods are adopted to analyze the white spot defect appearing on the inner surface of the 25 Mn cold-drawn oil cylinder tube during skiving and roller-burnishing after cold drawing and stress relief. The results show that the main components of the said white spot defect are Al₂O₃,CaO and Mg O which are similar to those of the ladle slag, so it is determined that the defect is caused by slag entrapment occurring during the casting process.Reducing the formation of Type B inclusions in the steel for the oil cylinder tube can decrease the occurrence probability of the white spot defect. Accordingly specific improvement measures are taken, including controlling the oxygen content in the steel during smelting, reducing the introduction of inclusions from raw materials, strengthening the floating and removal of inclusions in the steel,avoiding mold slag entrapment,and improving the quality of refractory materials.