针对生产中出现的厚规格Q345B板材厚度中心分层缺陷进行了调查分析,结果表明：板材中心分层是由于连铸坯中较为严重的中心疏松在后期轧制过程中未能轧合所致。进一步对Q345B连铸坯轻压下工艺调查发现,实际凝固终点位置比模型计算值靠后,且凝固末端扇形段压下率低,不足以补偿其凝固收缩,从而形成较为严重的中心疏松缺陷。在调查分析基础上,通过将该规格连铸坯轻压下区间后延并加大轻压下量,增加了凝固末端压下率,降低了连铸坯中心疏松和中心偏析程度,从而彻底解决了板材中心分层问题。
Center separation defect of Q345B thick plates was investigated.The results show that the heavy center porosity carried over from continuous cast 320 mm thick mother slabs is the key reason for center separation defect.Analysis on soft reduction for the slabs indicates that the actual crater end is further down the strand than the calculated position from previous online solidification model,and hence,the reduction ratio is insufficient at the final stage of solidification to compensate the final solidification shrinkage.Based on the investigation and analysis,the soft reduction scheme is optimized by extending soft reduction range and increasing the reduction ratio at the final solidification stage.After the optimization,center porosity and center segregation in the slabs are alleviated,and the center separation defect in the thick Q345B plates is resolved.
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