BOF-LF-CC工艺生产50 CrVA弹簧钢洁净度研究

通过对国内某钢厂BOF-LF-CC工艺生产50CrVA弹簧钢进行全流程连续取样,综合分析了冶炼过程中总氧( T. O.)、N含量变化,非金属夹杂物的衍变规律,以及铸坯中大型夹杂物的特征.结果表明,LF精炼前T. O.和N的平均含量分别为106×10-6和13×10-6,铸坯中分别为15×10-6和39×10-6,LF过程脱氧效果明显；运输和浇注过程存在较明显的二次氧化现象,需要加强大包到中间包的保护浇注；铸坯中夹杂物主要为CaO-Al2 O3-MgO和CaO-Al2 O3-SiO2复合氧化物夹杂,其中Al2 O3含量(质量分数)较高,达到60%~70%,未得到低熔点夹杂物,可通过适当提高精炼渣碱度,或喂入适量钙线促使夹杂物充分转变为成分更加均匀的低熔点夹杂物；大型夹杂物以CaO和CaO-Al2 O3-SiO2-( MgO)球状氧化物为主,还存在一定比例的纯Al2 O3夹杂物,需要延长钢包弱搅拌时间使夹杂物充分上浮.

Research on the cleanliness of 50 CrVA spring steel produced by the BOF-LF-CC process

The changes of total oxygen ( T. O. ) and N contents, the evolution of non-metallic inclusions, and the characteristic of macro-inclusions in casting billets of 50CrVA spring steel produced by the BOF-LF-CC process were studied by continuous sampling at different stages. Results show that the average contents of T. O. and N are 106í10 -6 and 13í10 -6 at LF-start, respectively, and they become 15í10 -6 and 39í10 -6 in billets, indicating that the deoxidization effect in the LF refining process is obvious. Howev-er, reoxidation phenomenon is obvious in the transportation and casting processes, so it is necessary to strengthen the steel stream protection from ladle to tundish. The CaO-Al2 O3- MgO and CaO- Al2 O3- SiO2 composite oxide inclusions are the main inclusions in billets, the Al2 O3 content in those inclusions is as high as 60% -70%, and no low-melting inclusion is obtained. The low-melting inclusion can be obtained by increasing the slag basicity or feeding a proper content of Ca wire. Large-size inclusions are primarily composed of CaO and CaO-Al2 O3-SiO2-( MgO) spherical oxides as well as a certain proportion of pure Al2 O3 inclusions. It is neces-sary to extend the soft stirring time in the ladle to make inclusions float fully.