大型钢锭夹杂沉积区形成过程的计算机模拟

将自浇注起到钢液中自然对流衰减至不足以把允许的最大夹杂物带回底部为止的时间称为临界时间.夹杂沉积区就是在临界时间内所形成的底部等轴晶区,该区由三部分构成:顶面下落的结晶雨;侧壁树枝晶枝臂的熔断和折断所形成的自由晶和底部由于传热而造成的凝固生长.本文在以热量平衡为基本原理的凝固数值模拟的基础上,结合自然对流的边界层理论,给出了临界时间的计算方法;又结合氯化铵水溶液的模拟实验,给出了顶面结晶雨的定量计算方法;此外,还提出了侧壁树枝晶枝臂的熔断和折断所形成的自由晶,以及钢锭底部由于传热而造成凝固生长的定量计算方法.根据上述模型编制了夹杂沉积区形成过程的数值模拟程序,针对68吨27 Cr2Mo1V 转子钢钢锭进行了夹杂沉积区形成过程的计算机模拟,模拟结果求得切尾率为8.11%.而实际生产中钢锭的切尾率为8.8%.两者大体相符.

NUMERICAL SIMULATION ON THE FORMATION OF BOTTOM CONE OF INCLUSIONS IN LARGE STEEL INGOTS

The interval from the beginning of pouring to the time when the velocity of convective flow becomes too low to carry any inclusions larger than tolerant one down to the bottom is defined as critioal time.Then,the size of bottom cone of inclusions is equal to that of equiaxial crystal zone formed in the critical time.The equiaxial crystal zone consists of the showering crystallites from the top,the free dendritic arms fused and broken from dendrites growing on the side mold wall,and the growth of crystals in the bottom caused by heat transfer. In this paper,the method for determining critical time was proposed,and the numerical simulation on the formation of bottom equiaxial crystal zone was carried out.A 27Cr2MolV steel ingot of 68 tons in weight was studied.From the results of numerical simulation,the weight ratio of out tail end to ingot body was 8.11%.This result agreed with the weight ratio of 8.8% in production practice of the same ingot approximately.