高碳耐磨球钢大方坯连铸过程凝固定律及在轻压下过程中的应用

摘要

基于ANSYS软件建立310 mm×360 mm(长×宽)断面大方坯连铸过程二维凝固传热数学模型,通过窄面射钉试验及铸坯表面测温对模型的准确性进行验证,模拟不同碳质量分数高碳耐磨球钢大方坯宽面和窄面凝固坯壳的生长规律,将计算结果应用于轻压下过程中并进行现场试验.研究结果表明:模型能精确地获得不同工况下任意位置铸坯凝固坯壳的厚度分布、凝固终点位置及中心固相率.不同碳质量分数的高碳耐磨球钢具有相同的凝固规律:结晶器弯月面至二冷区出口,铸坯柱状晶区的凝固坯壳厚度与凝固时间的平方根呈线性关系,符合平方根定律,平方根定律的修正项与过热度有关;二冷区出口至凝固终点,相应铸坯等轴晶区凝固坯壳厚度与凝固时间的平方根呈非线性关系;根据凝固传热模型计算的高碳耐磨球钢BU铸坯中心固相率分布,结合轻压下合适的压下区间要求,拉速从0.43 m/min增加到0.52 m/min,轻压下可压区间增加,铸坯的中心碳偏析明显减少.%A two-dimensional mathematical model of solidification and heat transfer for a bloom with the cross section of 310 mm×360 mm(length×width) was established with ANSYS software, which was verified by nail-shooting experiments in the narrow side of the bloom and surface temperature testing. The solidified shell growth law of high carbon wear-resistant ball steel with different carbon mass fractions in both wide and narrow side of the bloom was simulated based on the model. The results were also applied in the soft reduction process and the field experiments were carried out. The results show that the solidified shell thickness distribution of the bloom, the position of the solidification end point and the solid fraction in the core of the solidified strand under different working conditions can be accurately obtained by using this model at any fixed location along the casting direction. In addition, high carbon wear-resistant ball steels with different carbon mass fractions obey the same law of solidification: from the meniscus of the crystallizer to the secondary cooling zone export, the solidified shell thickness in the columnar crystal zone of the bloom and the square root of solidification time show a linear relationship, which fits the square root law.The correction term of the law is relevant to the superheat. However, from the secondary cooling zone export to the end of solidification, the relationship between solidified shell thickness in the equiaxed crystal zone of the bloom and the square root of solidification in the columnar crystal zone is non-linear. In accordance with the calculated solid fraction at the centerline of strand in wear resisting ball steel BU bloom by model of solidification and heat transfer, combined with reasonable soft reduction zone, the casting speed increases from 0.43 m/min to 0.52 m/min. Consequently, soft reduction zone is prolonged and the center carbon segregation on wear resisting ball steel BU is reduced obviously.