Abstract: The causes of outer fold defects of 0. 20% C steel pipe are studied by means of pickling, morphology observation and metallographic examination. The results show that the subsurface blowholes and pinholes defects of the continuous casting billet lead to the longitudinal cracks on the surface of the round steel, which are the direct causes of the outer fold defects of the steel pipe. By increasing the acid-soluble aluminum content from 0.006% ~ 0.010% to 0.010% ~ 0. 020% , controlling casting speed (1.8 ± 0.03 ) m/min and superheates extent 15 ~30℃ , and increasing the temperature of Rotary hearth furnace from 1250 ℃ to 1270 ℃ etc improvement measures, the first qualified steel rate of the 0.20% C steel piercing pipe is increased from 47. 01% to above 96%.

摘要： 采用酸洗、形貌观察和金相分析等方法对20钢管外折缺陷原因进行了研究。结果表明,连铸坯皮下气泡和针孔缺陷导致了圆钢表面纵裂纹,圆钢表面纵裂纹是导致钢管外折缺陷的直接原因。通过将钢中酸溶铝含量由0.006%～0.010%提高到0.010%～0.020%,连铸拉速稳定在(1.8±0.03)m/min,过热度控制在15～30℃和环形加热炉温度由1250℃提高到1270℃等措施,20钢穿管一次合格率由47.01%提高到96%以上。