25Mn钢Φ185mm×13mm冷拔管内表面麻点状缺陷的分析和控制工艺

Analysis on Mottled Spots Defect of Internal Surface of Φ185 mm×13 mm Cold-Drawn Tube of Steel 25Mn

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-Φ250 mm圆坯HCC-穿孔-热轧至Φ197 mm×17 mm管-冷拔至Φ185 mm×13 mm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-Al_2O_3-(MgO)复合夹杂与钢基体变形量不一,凹坑状缺陷成因是Al_2O_3-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%,(Al_2O_3)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。

The production flowsheet for cold-drawn tube of steel 25 Mn（/% ： 0. 24 C, 0. 25 Si, 0. 87 Mn, 0. 016 P,0.011 S） is hot-metal pretreatment-90 t EAF-LF-VD-Φ250 mm round bloom HCC-piercing-hot rolling to Φ197 mm×17 mm tube-cold rolling to Φ185 mm×13 mm tube. The mottled spots defect of internal surface of steel 25Mn cold-drawn tube is analyzed by using optical microscope, scanning electron microscope（SEM）, energy spectrum 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 Al2 O3-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） from26. 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.