GCr15轴承钢BOF-LF-RH-CC流程夹杂物的生成及演变

 为研究GCr15轴承钢中夹杂物的演变规律,对某钢厂BOF-LF-RH-CC工艺流程生产的GCr15轴承钢进行了全流程取样,并利用ASPEX扫描电镜和热力学计算对各工序钢中夹杂物的演变进行了系统的分析。研究表明,在LF精炼初期,钢中夹杂物主要为高Al₂O₃(w(Al₂O₃)=84%)的MgO-Al₂O₃和CaO-MgO-Al₂O₃夹杂物;LF精炼结束时,MgO-Al₂O₃和CaO-MgO-Al₂O₃夹杂物的数量所占比例分别为74%和26%,此时钢液中夹杂物尺寸主要为1～6 μm,数量所占比例为87%。LF-RH精炼期间,夹杂物总数量由LF精炼结束时的198 个/(20 mm2)降低至RH破空后的103 个/(20 mm2),降幅为48%,其中MgO-Al₂O₃夹杂物主要在LF精炼期间生成,然后在RH精炼时基本被去除,具体表现为,其数量由LF进站时的88 个/(20 mm2)增加至LF出站时的139 个/(20 mm2),在RH软吹结束时降低为4 个/(20 mm2);CaO-MgO-Al₂O₃夹杂物主要在RH精炼期间生成,其数量由LF出站时的49个/(20 mm2)增加至RH软吹结束时的108 个/(20 mm2),这表明RH真空精炼对夹杂物去除效果较好。热力学计算结果表明,二次精炼过程中钢中Al_s、Mg含量处于MgO-Al₂O₃夹杂物优势区内,这表明MgO-Al₂O₃夹杂物更易生成;当钢中w(Mg])为0.000 3%时,w(Ca])大于0.000 25%,满足MgO-Al₂O₃夹杂物转变为CaO-MgO-Al₂O₃夹杂物的热力学条件,而且当w(Al_s])为0.022%时,w(Ca])控制为0.000 25%～0.007 00%时更有利于生成液态化的钙铝酸盐。试验过程钢中w(Ca])约为0.000 1%～0.000 4%,因此夹杂物更多地转变为CaO-MgO-Al₂O₃夹杂物。

Formation and evolution of inclusions in GCr15 bearing steel produced by process of BOF-LF-RH-CC

To study the evolution of inclusions in GCr15 bearing steel, the GCr15 bearing steel produced by BOF-LF-RH-CC process was sampled in various stages in a steel factory. The evolution behavior of inclusions in various processes was systematically analyzed by ASPEX scanning electron microscopy and thermodynamic calculation. The result indicates that due to the strong deoxidation of aluminum after the converter, at the beginning of LF refining, the inclusions in molten steel consists of MgO-Al₂O₃ binary system and CaO-MgO-Al₂O₃ ternary system with high Al₂O₃(w(Al₂O₃)=84%); the account of MgO-Al₂O₃ binary system and CaO-MgO-Al₂O₃ ternary system are 74% and 26% at the end of LF refining. At this moment, the inclusions in the liquid steel have a size distribution from 1 to 6 μm account for 87%. During refining from LF to RH, the total number of inclusions decreased from 198 pcs/(20 mm2) at the end of ladle furnace refining to 103 pcs/(20 mm2) at the end of RH vacuum degassing, a drop of 48%. Among them, MgO-Al₂O₃ binary system were mainly generated during LF refining, and then removed during RH refining, specifically, the number increased from 88 pcs/(20 mm2) at the beginning of LF refining to 139 pcs/(20 mm2) at the end of LF refining, and after the end of RH soft blowing, it was reduced to 4 pcs/(20 mm2); CaO-MgO-Al₂O₃ ternary system were mainly generated during RH refining, and their number increased from 49 pcs/(20 mm2) at the end of ladle furnace refining to 108 pcs/(20 mm2) at the end of RH soft blowing. This shows that RH vacuum refining has a better effect on inclusion removal. Thermodynamic calculations show that the contents of Al_s and Mg in the liquid steel are in the MgO-Al₂O₃ inclusion formation region during the secondary refining process, indicating that MgO-Al₂O₃ inclusions are easier to form; When w(Mg])in the liquid steel is 0.000 3% and w(Ca]) is greater than 0.000 25%, the thermodynamic conditions for the transformation of MgO-Al₂O₃ inclusions into CaO-MgO-Al₂O₃ inclusions are satisfied. When w(Al_s]) is 0.022%, w(Ca])is controlled between 0.000 25% and 0.007 00%,which is more conducive to the formation of liquefied calcium aluminate. During the test, w(Ca]) in the liquid steel was about 0.000 1%-0.000 4%, and the inclusions were mostly converted into CaO-MgO-Al₂O₃ ternary system.