坯壳鼓肚对铸机矫直区内铸坯变形的影响

Influence of bulging of solidified shell on slab deformation in straightening zone of continuous casters

在连铸机辊列矫直段,带液芯铸坯的坯壳同时受钢水静压力与矫直力的作用,坯壳固液交界面处的矫直应变与鼓肚应变发生叠加。如果总应变超过临界值,就会发生内裂。确定矫直区坯壳固液交界面处的应变与应变速率,对铸机辊列设计与工艺参数的设定有重要的意义。基于高温坯壳力学特性,建立了连续矫直理论中铸坯坯壳变形的数学模型。利用该模型计算坯壳鼓肚变形,并与实测数据进行对比,验证了模型的有效性。根据某厂由奥钢联设计的工业板坯连铸机的辊列参数,利用该模型计算铸坯横截面的应变与应变速率。最后分析了不同辊间距与不同拉坯速度情况下矫直区内铸坯坯壳固液交界面处的应变速率变化规律,结合不同钢种的临界应变速率得到铸机矫直段辊间距的取值范围。

In the straightening zone of continuous casters,as the solidifying shell containing molten steel bears the combination of ferro- static pressure and straightening foprce,the bulging and unbending deformations of the continuously cast slabs occur simultaneously. The strains caused by bulging and unbending are superimposed. If the strain exceeds the critical strain on the solid-liquid interface,internal cracks may occur. Accurate calculations of the strains and strain rates are significant to the design of strand supporting system and the decision of casting parameters. Thus,based on the elastoviscoplastic behavior of steel at elevated temperature,a mathematical model of continuously cast slabs with liquid core during the continuous straightening process is estabilished. In order to validate the mathematical model,the calculated bulging profile was compared with the measurements on a pilot caster. Then the strains and strain rates at different points on the cross section of the continuously cast slabs in an industrial caster designed by VAI were computed. Finally,base on the caster structure and process parameters,the maximum strain rate on the solid-liquid interface in the straightening zone with a certain range of roll pitches was computed,the influences of casting speed and roll pitches were analyzed.Then the results were compared with the critical strain rates of typical steel types and the study obtained a suitable roll pitches in the straightening zone.