Abstract: The production flowsheet for cold-drawn tube of steel 25Mn(/%: 0.24C, 0.25Si, 0.87Mn, 0.016P, 0.011S) is hot-metal pretreatment-90t EAF-LF-VD-Φ250mm round bloom HCC-piercing-hol rolling to Φ197mmx17mm tube-cold rolling to Φ185mmx13mm tube. The mottled spots delect of internal surface of steel 25Mn cold-drawn tube is analyzed by using optical microscope, scanning electron microscope (SEM) , energy spectnam meter and electron probe analyzer. Results show that the mottled spots defect is warped skin and concave pitting；the warped skin defect is caused by aggregated CaO-Al₂O₃-(MgO) compound inclusions which deformation is different from base steel and the aggregated growing up of Al₂O₃-MnS-CaS compound inclusions fall off in cutting process to form concave pitting. With optimizing the original aluminium deoxidizing process to silico-calcium alloy deoxidizing process, decreasing the refining slag basicity from original 6.76 to 2.26, increasing the refining slag (MgO) from 5.33% to 7.23% and decreasing the ( Al₂O₃ ) from 26.05% to 12.76% to modify the brittle inclusions in steel to silicate inclusions with better ductility, therefore the internal mottled spots defect of internal surface of steel 25Mn cold-drawn tube is eliminated.

摘要： 25Mn钢（/%:0.24C,0.25Si,0.87Mn,0.016P,0.011S）冷拔管的生产流程为铁水预处理-90tEAF-LFVD-Φ250mm圆坯HCC-穿孔-热轧至Φ197mm×17mm管-冷拔至Φ185mm×13mm管。采用光学、扫描电子显微镜、能谱仪和电子探针分析了25Mn钢冷拔管内表面麻点状缺陷。结果表明,麻点状缺陷呈翘皮状和凹坑状,翘皮状缺陷成因是CaO-Al₂O₃-（MgO）复合夹杂与钢基体变形量不一,凹坑状缺陷成因是Al₂O₃-MnS-CaS复合夹杂聚集长大后磨削加工过程中脱落。通过将原铝脱氧精炼工艺优化成硅钙合金脱氧工艺,使精炼渣碱度由原6.76降至2.26,精炼渣中（MgO）由原5.33%提高至7.23%,（Al₂O₃）由26.05%降低至12.76%,使钢中的硬脆性夹杂转变为延展性优良的硅酸盐类夹杂,消除了25Mn钢冷拔管内表面麻点状缺陷。

关键词: 25Mn钢, Φ185mmx13mm冷拔管, 麻点状缺陷, 复合夹杂, 硅钙线脱氧, 精炼渣碱度