Abstract: The formation and performance of Mn-based inclusions in RH refining process of ultra-low carbon Al-Si killed steel and the impact of ladle slag composition on the inclusions were investigated. The online observation of microstructure of steel during reheating was carried out by ultra high-temperature laser confocal microscope, and the impact of inclusions on the grain growth of steel examined. The results show that the inclusions are Fe-Mn oxide based complex inclusions before RH refining and the number and size of inclusions greatly impacted by slag basicity, Al2O3 content and ratio of CaO to Al2O3. The number of inclusion is the lowest when the basicity is 1.5 and the content 20%. The experimental results show by optimized ladle slag equilibrated with the steel, the final steel at the end of RH refining contains mainly Al2O3-MgO and Al2O3-MgO-SiO2-MnO complex inclusions. The Mn content of complex inclusions increases with increasing of MnO content in slag, which makes the grain growth of steel need higher reheating temperature. After reheating, the inclusions are mainly Al2O3-MgO-SiO2 complex with 90 % of the inclusions or more, the MnO content of complex inclusions is affected by experimental conditions during reheating treatment.

Key words: RH refining process, ultra-low carbon steel, Al-Si killed steel, inclusion, ultra-high temperature laser confocal microscope

摘要： 针对RH精炼并结合典型的渣-钢化学平衡实验，研究了超低碳铝硅镇静钢精炼过程中夹杂物的变化以及钢包顶渣组成对钢中夹杂物的影响. 用激光共聚焦高温扫描显微镜在线观察了再加热过程中钢的微观组织变化，讨论了夹杂物对钢的晶粒长大的影响. 结果表明，本实验条件下精炼前钢中夹杂物是以Fe-Mn氧化物为主的复合夹杂，夹杂物数量和大小受渣碱度、Al2O3含量及CaO/Al2O3比值的影响较大，当碱度为1.5及Al2O3含量为20%时，夹杂物数量最少. 以成分优化的钢包渣与精炼末期钢样进行的平衡实验显示，夹杂物为Al2O3-MgO或Al2O3-MgO-SiO2-MnO为主的复合夹杂，随渣中w(MnO)的增加，复合夹杂中Mn含量有增加的趋势，使钢的晶粒长大过程需要更高的再加热温度. 钢样再加热后，钢中夹杂物变为以Al2O3, MgO, SiO2复合夹杂为主，三者总量占夹杂物总量的90%或以上，复合夹杂中MnO含量受加热制度影响.

关键词: RH精炼, 超低碳钢, Al-Si镇静钢, 夹杂物, 激光共聚焦高温扫描显微镜