连铸工艺对方坯凝固组织影响的数值模拟

铸坯凝固组织特征对于连铸坯粗坯质量具有重要影响。通过建立重轨钢U71Mn方坯连铸过程中传热和凝固组织模拟数学模型，研究了CA模型特征参数和连铸操作工艺参数对于凝固组织特征的影响规律。研究结果表明：平均形核过冷度控制柱状晶区域，随着该值的增大，柱状晶区域也随之增大；最大形核密度控制晶粒尺寸，该值越大晶粒的尺寸则越小。连铸拉坯速度波动在±0.5m/min时，最终铸态组织特征并没有明显变化，而浇注温度对于最终铸坯组织结构具有较大的影响，晶粒平均半径由15℃的1.555mm增加到45℃的1.721mm，并且中心等轴晶比例逐渐减小。因此，连铸生产过程中，在满足钢液顺利浇注的条件下，降低浇注钢液的过热度会很大程度上改善重轨钢内部组织结构，提高铸坯内部质量。

Numerical Simulation on Solidification Microstructure of Bloom During Continuously Casting Process

The solidification microstructure plays an important role in controlling bloom quality during continuous casting. A numerical model was established to study the effect of CA model parameters and casting conditions on final solidification microstructure based on the production of heavy rail steel U71Mn. It can be concluded that the mean nucleation undercooling and maximum nucleation density affects the columnar crystal zone and crystal size, respectively. When the casting speed fluctuation is lower than 0.5m/min, the final solidification microstructure is less changed. Nevertheless, the casting temperature greatly affects the solidification microstructure. When the temperature increases from 15℃ to 45℃, the mean grain diameter increases from 1.555mm to 1.721mm, meanwhile the equiaxed grain ratio gradually decreases. Therefore, at the casting temperature meeting the requirement of normal production, the bloom quality will be improved as the casting temperature is properly decreased.