微合金包晶钢高温奥氏体晶粒生长动力学研究

Study on kinetics of austenite grain growth of micro-alloyed peritectic steels under high temperatures

为有效控制铸坯表层奥氏体晶粒尺寸,降低铸坯表面及角部裂纹发生率,对高温下奥氏体晶粒生长动力学进行了研究。以微合金包晶钢为实验对象,在1 573~1 723 K进行等温保温实验,得到实验钢种的奥氏体晶粒长大动力学模型,并分析了其高温下奥氏体晶粒生长动力学规律。结果表明奥氏体晶粒生长存在2个明显不同的温度区间:当保温温度在1 573~1 673 K范围内时,奥氏体晶粒生长较慢,时间指数小于0.35;而当温度高于1 673 K时,奥氏体晶粒生长迅速,时间指数接近0.5。基于等温实验数据进行动力学模型分析,认为连铸过程铸坯表层晶粒粗化主要发生于1 673 K以上,因此抑制晶粒长大应在初生奥氏体形成后的高温阶段进行。

In order to control the austenite grain size on the slab surface to reduce the surface or corner cracks, the kinetics of austenite grain growth under high temperatures was studied. The isothermal heat preservation experiment of the micro-alloyed peritectic steels was carried out at the temperatures of 1 573-1 723 K. The austenite grain growth kinetic model of the experimental steels was obtained by fitting the austenite grain size data. Then the grain growth kinetics under high temperatures was investigated. The results show two distinct temperature ranges for austenite grain growth. When the holding temperature is within 1 573-1 673 K, austenite grains grow slowly, and the time exponent is smaller than 0.35. But when the holding temperature is higher than 1 673 K, austenite grains grow quickly, and the time exponent is close to 0.5. Based on the model analysis, it is believed that the austenite grain growth at slab surface mainly occurs above 1 673 K. Therefore, suppressing the initial austenite grain growth should be conducted at the high temperature range after the formation of austenite.