铝镇静钢中夹杂物钙处理改性及其影响因素

 钙处理广泛应用于铝镇静钢中非金属夹杂物的改性,但在工业实践中的改性效果差别很大。为了探究钙处理效果差异的原因,通过工业试验和热力学计算研究了铝镇静钢钙处理前后非金属夹杂物的演变,并讨论了钙处理改性夹杂物的影响因素。结果表明,浇铸末期钢液中的TO]和TN]质量分数分别为0.002 9%和0.003 9%。精炼前期钢中夹杂物Al₂O₃质量分数达90%以上,钙处理后,钢液中钙质量分数快速增加至0.002 5%,同时夹杂物中CaO质量分数由钙处理前的4%迅速增加到23%,Al₂O₃质量分数由钙处理前的82%降低至70%,夹杂物由团簇状Al₂O₃转变为球形的Al₂O₃-CaO复合夹杂物,夹杂物平均成分靠近液相区。由于二次氧化,浇铸时钢中的TO]和TN]含量升高,夹杂物的尺寸和数密度增加,因此,需要加强钢液的保护浇铸。在连铸与轧制过程中,夹杂物中CaO质量分数由中间包中的20%增加至轧材中的37%,Al₂O₃质量分数由中间包内的77%降低至56%,夹杂物的平均成分向液相区移动,但夹杂物类型不发生改变,仍为球形的钙铝酸盐。通过热力学计算得到本研究中试验钢种夹杂物“液态窗口”对应的钙质量分数为0.001 1%～0.002 8%,此外钢液成分对钙处理的“液态窗口”影响很大。随着钢液中TO]含量升高,“液态窗口”变宽,但所需喂钙量增加;随着钢液中TS]含量增加,“液态窗口”变窄;钢液中的TAl]含量对“液态窗口”无明显影响。

Calcium treatment modification and influencing factors of inclusions in aluminum-killed steel

Calcium treatment is widely used in the modification of non-metallic inclusions in aluminum killed steel, but the modification effects vary greatly in the industrial practice. In order to explore the reasons for the difference of calcium treatment effect, the evolution of non-metallic inclusions in aluminum killed steel before and after calcium treatment was investigated through industrial trials and thermodynamic calculation, and the influencing factors of inclusion modification by calcium treatment were discussed. The results showed that the TO] and TN] in the molten steel of tundish at the end of casting were 0.002 9% and 0.003 9%, respectively. In the early period of secondary refining, the mass percent of Al₂O₃ of inclusions was more than 90%. After the calcium treatment, the mass percent of calcium in the molten steel increased rapidly to 0.002 5%. Meanwhile, the mass percent of CaO of inclusions increased rapidly from 4% before the calcium treatment to 23%, and the mass percent of Al₂O₃ of inclusions decreased from 82% before calcium treatment to 70%. The inclusions changed from clustered Al₂O₃ to spherical Al₂O₃-CaO composite inclusions with the average composition being close to the liquid region. The content of TO] and TN] in the steel increased during the casting process due to the reoxidation, leading to the increase of the size and number density of inclusions. Thus, it was necessary to strengthen the protective casting of steel. During the continuous casting and rolling process of steel, the mass percent of CaO in the inclusions increased from 20% in the tundish to 37% in the rolling, and the mass percent of Al₂O₃ decreased from 77% in the tundish to 56%. The average composition of the inclusions moved to the liquid phase, but the type of inclusions did not change, and it was still spherical calcium aluminate. According to the thermodynamic calculation, the mass percent of calcium corresponding to the "liquid window" of the inclusion of the test steel was 0.001 1%-0.002 8%, in addition, the composition of molten steel had a great influence on the "liquid window" of calcium treatment. With the increase of the TO] content in molten steel, the "liquid window" became wider, but the required calcium content increased. As the TS] content in molten steel increased, and the "liquid window" became narrower. The TAl] content in steel had no obvious effect on the "liquid window".