LF-RH双联工艺生产IF钢精炼过程夹杂物的演变

Evolution of inclusion in refining process of IF steel produced by LF-RH duplex process

国内某钢厂采用LF-RH-CSP工艺生产IF钢,该工艺对钢中C、N含量及钢液洁净度要求较高。为探究IF钢中主要增C和增N来源及LF-RH精炼过程中夹杂物成分、尺寸、数量的变化规律,对不同工艺节点取钢样进行分析。结果表明,升温造渣和炉渣改质时伴随底吹氩强翻洗现象,钢液剧烈翻腾使钢水裸露而导致严重的增C和增N。LF进站Al脱氧后夹杂物主要是不规则的Al_(2)O_(3),LF造渣至出站期间夹杂物转变为MgO·Al_(2)O_(3)尖晶石。RH进站二次Al脱氧后夹杂物为MgO·Al_(2)O_(3)和少量单独存在的Al_(2)O_(3),RH出站时夹杂物全部被改性为球状的CaS-12CaO·7Al_(2)O_(3)-MgO·Al_(2)O_(3)复合夹杂物。夹杂物数量密度整体呈下降趋势,平均直径从6.0μm逐步降低至2.3μm,钢液洁净度得到显著提升。热力学计算表明,MgO·Al_(2)O_(3)夹杂物生成趋势强,是CaS-12CaO·7Al_(2)O_(3)-MgO·Al_(2)O_(3)复合夹杂物的形核核心。建立了夹杂物演变动力学示意图。研究结果为优化IF钢生产工艺、提升钢水可浇性提供了理论支持。

IF steel is produced by the LF-RH-CSP process in a domestic steel mill, the process has high requirements for the C and N content and the cleanliness of the molten steel. Samples were taken and analyzed at different process nodes to investigate the main source of increasing C and N and the variation of composition, size, and quantity of inclusions in the LF-RH refining process. The results show that the heating slag-making and the slag modification are accompanied by bottom argon blowing and strong stirring phenomenon, which exposes the molten steel and thus lead to a severe C and N increase. The inclusions are mainly irregular Al_(2)O_(3) after Al deoxidization in the LF station, and the inclusions are transformed into MgO·Al_(2)O_(3) spinel during LF slagging and leaving the LF station. The inclusions are MgO·Al_(2)O_(3) and a few single Al_(2)O_(3) after secondary Al deoxidization at the RH station, and all of the inclusions are modified into spherical CaS-12CaO·7Al_(2)O_(3)-MgO·Al_(2)O_(3) composite inclusions when leaving the RH station. The inclusion number density shows an overall downward trend, the average diameter gradually decreases from 6.0 μm to 2.3 μm, and the cleanliness of molten steel is significantly improved. Thermodynamic calculations show a strong tendency for the generation of MgO·Al_(2)O_(3) inclusions, which are the nucleation core of CaS-12CaO·7Al_(2)O_(3)-MgO·Al_(2)O_(3) composite inclusions. A kinetic model of inclusion evolution was established. The research results provide theoretical support for optimizing the IF steel production process and improving the castability of the steel.