高品质轴承钢BOF-LF-RH-CC和EAF-LF-VD-CC工艺夹杂物演变规律

Evolution rules of inclusions in high quality bearing steel produced by BOF-LF-RH-CC and EAF-LF-VD-CC process

以某公司两种不同轴承钢生产工艺为例,对BOF-LF-RH-CC和EAF-LF-VD-CC工艺生产的轴承钢中夹杂物进行了对比分析。初炼炉的出钢碳含量会对LF精炼前期夹杂物的数量以及成分产生影响,BOF出钢w(C)=0.07%的炉次,LF精炼初期夹杂物数量为5.04个/mm2且主要为Al2O3夹杂物;EAF出钢w(C)=0.58%的炉次,LF精炼初期夹杂物数量为2.49个/mm2且主要为MgO·Al2O3夹杂物,但在LF精炼结束时出钢碳含量对夹杂物数量的影响较小。LF精炼炉渣中CaO活度会对夹杂物中CaO的含量产生影响,BOF-LF-RH-CC工艺LF精炼渣CaO活度为0.632,对应的精炼结束时夹杂物中w(CaO)=5%;EAF-LF-VD-CC工艺LF精炼渣CaO活度为0.965,对应的精炼结束时夹杂物中w(CaO)=18%。对比分析过RH、VD后轴承钢夹杂物的成分和数量变化情况,发现经RH处理后MgO·Al2O3类高熔点夹杂物数量由1.02个/mm2降低至0.01个/mm2;经VD处理后MgO·Al2O3类高熔点夹杂物数量由0.18个/mm2降低至0.01个/mm2,夹杂物主要为低熔点的CaO-Al2O3。但从CaO-Al2O3-MgO类夹杂物总数量分析上发现RH处理后夹杂物数量急剧降低,而经VD处理后夹杂物数量并没有较大下降,认为VD过程MgO·Al2O3夹杂物的减少是由于VD过程剧烈钢渣混冲导致炉渣对MgO·Al2O3变相"钙处理"的结果。

The inclusions in bearing steel produced by BOF-LF-RH-CC and EAF-LF-VD-CC were compared and analyzed. The number and composition of inclusions in the early stage of LF refining will be affected by the carbon content of primary melting furnace tapping. The carbon mass fraction of steel is 0.07 % in the BOF tapping, the number of inclusions is 5.04 per mm2 and mainly Al2O3 at the early of LF refining;the carbon mass fraction of steel is 0.58 % in the EAF tapping, the number of inclusions is 2.49 per mm2 and mainly MgO·Al2O3 at the early of LF refining. But at the end of LF refining, the carbon content of tapping have less effect on the number of inclusions. The CaO activity in LF refining slag has an impact on CaO content in inclusions, CaO activity of LF refining slag in BOF-LF-RH-CC process is 0.632, the CaO mass fraction in inclusion is 5 % at the end of refining;CaO activity of LF refining slag in EAF-LF-VD-CC process is 0.965, the CaO mass fraction of inclusion at the end of refining is 18 %. By comparing and analyzing the composition and quantity changes of bearing steel inclusions after RH and VD, it is found that the number of MgO·Al2O3 high-melting point inclusions decreases from 1.02 per mm2 to 0.01 per mm2 after RH treatment;the number of MgO·Al2O3 inclusion decreases from 0.18 per mm2 to 0.01 per mm2 after VD treatment and the inclusions are mainly low melting point of CaO-Al2O3. However,from the analysis of the total number of CaO-Al2O3-MgO style inclusion, it is found that the number of inclusions has a sharp decline after RH treatment but has not decrease after VD treatment. Therefore, it is considered that the decrease of MgO·Al2O3 inclusions in VD process is due to the disguised "calcium treatment" of MgO·Al2O3 caused by the sharp steel slag mixing in VD process.