齿轮钢（8620H）精炼渣优化及工业试验

利用FactSage热力学软件计算了CaO-Al2O3-SiO2-5%MgO四元系的CaO、Al2O3等活度线，通过等活度线图着重探讨精炼渣碱度、w(CaO)/w（Al2O3）、MI指数（曼内斯曼指数）与Al2O3夹杂吸附能力的影响关系，最终得到适用于杭钢生产齿轮钢（8620H）的LF精炼渣系范围为：CaO质量分数为50%~55%，Al2O3质量分数为25%~30%，SiO2质量分数为10%~12%，MgO质量分数为5%~8%。并使用该渣系进行齿轮钢（8620H）工业试验，铸坯中全氧质量分数由0.001 5%降至0.001 0%，且铸坯中显微夹杂物尺寸也明显降低，由2.1降至1.5μm，每10kg铸坯中大型夹杂物质量分数由31.9下降到26.4mg，试验效果良好。

Optimization and industrial tests of LF refining slag for gear steel (8620H)

The iso-activity lines of CaO and Al2O3 in CaO-SiO2-Al2O3-5%MgO quaternary system were calculated by FactSage thermodynamics software. And the effects of bacisity of refining slag, ratio of w(CaO)/w(Al2O3), and MI index on the adsorptioncapacity of Al2O3 inclusions were mainly discussed through the figures of iso-activity line. The results showed that the main compositions of refining slag suitable for the production of gear steel (8620H) in Hangzhou Steel were that the contents of CaO, Al2O3,, SiO2 and MgO were in the range of 50%~55%, 25%~30%, 10%~12% and 5%~8%, respectively. Applying this refining slag in industrial tests, the total oxygen content decreased from 0.001 5% to 0.001 0%. Besides, the average size of inclusions in billets also significantly decreased from 2.1 to 1.5 μm, and the large inclusion content decreased from 31.9mg/10kg to 26.4mg/10kg. Thus, the industrial tests received good results.