高碳钢矩形坯轻压下中心负偏析形成机理

高碳钢82A断面180 mm × 240 mm矩形坯轻压下试验中,铸坯心部碳元素产生了负偏析现象.将轻压下工艺与负偏析形成条件相结合,对中心负偏析形成机理进行了探讨.结果表明,轻压下消除了枝晶间富集溶质钢液向铸坯中心流动通道,铸坯中心受枝晶间富集溶质液体流动影响较小;凝固过程中心负偏析产生条件为vr/R＜-0.042 2,即液相流动速度vr和凝固速度R方向相反为形成中心负偏析的必要而非充分条件;轻压下易满足该条件并在此基础上提出了2种形成机理,即轻压下挤压作用导致心部钢液流动速度方向的改变或者脱落枝晶在铸坯心部先形核凝固导致凝固速度方向的改变都可能导致中心负偏析的形成.

Formation mechanism of center negative segregation in continuous casting of high carbon rectangular billet with soft reduction

Center negative segregation of carbon was generated with soft reduction in continuous casting of high carbon 82A rectangular billet with section size of 180mm??240mm. The formation mechanism of negative segregation was researched by combining the soft reduction process with the occurrence conditions of negative segregation. The results show that soft reduction can eliminate the segregation channel which interdendritic rich liquid of solutes flowed to center and the solidification in center may not influenced by the flow of interdendritic liquid. Center negative segregation will occur during solidification process under conditions of vx/R<-0. 0422. In other words, the formation of negative segregation must meet the conditions that the solidification velocity R and the liquid velocity vx are in opposite direction. The velocity of center liquid changes under the reduction force or the center solidification velocity changes by nucleation and growth of crystals are the two formation mechanisms of center negative segregation.