连铸板坯轻压下过程中间裂纹产生机理

Formation mechanism of internal cracks in continuous casting slabs with soft reduction

针对板坯连铸过程中间裂纹严重的问题,对中间裂纹的形貌、元素偏析等情况进行分析.通过建立有限元模型,对不同压下位置和不同压下量凝固前沿的受力情况进行计算并与临界应力值进行对比.结果表明:C、P、S等元素在晶界处富集只是促使中间裂纹开裂的内因,真正造成铸坯开裂的原因是凝固前沿所承受的拉应力.铸坯通过矫直段时,多处位置的凝固前沿所承受的拉应力超过钢的临界值,导致凝固前沿容易开裂延伸,形成中间裂纹;而弧形段和水平段处凝固前沿所承受的拉应力不超过钢的临界值,无裂纹产生.统计现场大量轻压下的实验结果显示:轻压下避开矫直区进行时,中间裂纹的发生率降低约41.3%.

The crack morphology and element segregation in continuous casting slabs were studied to solve the problem of internal cracks. The stress of the solidification front was analyzed by a finite element model at a series of reduction parameters and compared with the critical value. It is found that C,P and S enrich in dendrites and exist in grain boundaries,these are just the internal causes,but the true cause for internal cracks is the tensile stress of the solidification front. When the slab passes through the straightening segment,the reduction effect of rollers results in the stress of the solidification front exceeding the critical value,however,the corresponding stresses in the arc and horizontal segments do not exceed the critical value,so the solidification front in the straightening segment would be much easy to crack. Statistics analysis shows that when soft reduction and straightening are separately carried out,the occurrence rate of internal cracks reduces by about 41. 3%.