Abstract: The production flow sheet of SCM435 steel is 80 t BOF-LF-RH-280 mm x 325 mm bloom casting. LF end refining slag composition is (/% ：) 45 〜55 CaO, 10 〜15SiO₂，20 〜30 Al₂O₃, ∑(FeO + MnO) ≤ 1 % . The effect of RH adding calcium (0.0013% Ca) and RH non-adding calcium (0. 0002% Ca) on D and Ds inclusion in Φ13 mm coil is analyzed. The results show that, the inclusion maximum size in steel with RH non-adding calcium treatment process is 7.65 μm,the pass rate of Ds≤0.5 is 100% ,and that with the RH ading calcium treatment process is 25.68 μm,and the pass rate of Ds≤0.5 is 95%. The inclusion index of non-adding calcium treatment process decreases from original RH adding calcium process 0. 72 to 0. 68 and pass rate of D≤1.0 increases from original RH adding calcium process 30% to 75% . With non-ackling calcium treatment process the inclusions are mainly MgO·Al₂O₃? and a small amount of Calcium aluminate ,and with RH adding calsium process the inclusions are magnesium-alumina spinel, calcium aluminate and CaS heterogeneous inclusions. Therefore,in terms of size,quantity and type control of inclusions of brittle D and Ds, the improvement of RH non-adding Calcium treatment is obvious.

Key words:  SCM435, Cold Heading Steel, Inclusion, RH Non-adding Calcium Treatment Process 

摘要： SCM435钢的生产流程为80 t BOF-LF-RH-280 mm×325 mm坯连铸。LF终点精炼渣成分为（/%）:45～55CaO,10～15SiO₂,20～30Al₂O₃,∑（FeO+MnO）≤1%。分析了RH加钙（0.0013%Ca）和RH不加钙（0.0002%Ca）对Φ13 mm盘条中D和Ds夹杂物的影响。结果表明,RH不加钙处理工艺夹杂物最大尺寸为7.65μm,Ds≤0.5级合格率为100%;RH加钙处理工艺夹杂物最大尺寸为25.68μm,Ds≤0.5级合格率为95%。在数量控制方面,RH不加钙处理工艺夹杂物指数由RH加钙工艺的0.72降至0.68,D类≤1.0合格率由RH加钙工艺的30%提高至75%;RH不加钙处理工艺夹杂物主要为MgO·Al₂O₃,少量钙铝酸盐夹杂,RH加钙工艺为镁铝尖晶石、钙铝酸盐和CaS多相夹杂。因此,在脆性D类和Ds类夹杂物尺寸、数量和类型控制上,RH不加钙处理工艺改善效果明显

关键词: SCM435, 冷镦钢, 夹杂物, 不加钙处理工艺