52CrMoV4弹簧扁钢连铸坯内部裂纹产生机理及预防

连铸坯的质量直接与后续的轧制过程以及中厚板的质量密切相关。通过低倍组织检验、显微组织观察、化学成分分析等方法对52CrMoV4弹簧扁钢连铸坯芯部裂纹产生的原因进行了分析。结果发现，该钢连铸坯中Cr、Mn、Mo等合金元素造成的中心偏析引起冷却过程中发生马氏体相变，产生了较大的拉应力，是导致52CrMoV4弹簧扁钢连铸坯出现芯部裂纹的主要原因。采取了提高钢水洁净度、降低浇注温度和拉坯速度、加大电磁搅拌力和冶炼时增加氮的质量分数等改进措施后，消除了52CrMoV4钢铸坯芯部裂纹缺陷，有效改善了铸坯芯部质量，最终轧制弹簧扁钢心部质量良好，完全满足客户使用需求。

Mechanism and prevention of internal crack generation of 52CrMoV4 continuous casting slab for spring flat steel

The quality of continuous casting slab is directly related to the subsequent rolling process and the quality of medium and heavy plates. In this paper, the causes of the internal crack of 52CrMoV4 continuous casting slab for spring flat steel were analyzed by means of macrostructure inspection, microstructure observation and composition analysis. The results showed that the central segregation of Cr, Mn and Mo in the continuous casting slab caused martensitic transformation and large tensile stress during the cooling process, which was the main reason for the central crack of the 52CrMoV4 continuous casting slab. After increasing the purity of molten steel, reducing the pouring temperature and casting speed, increasing the electromagnetic stirring force as well as increasing the mass fraction of N during smelting, the crack defects in the center of the 52CrMoV4 steel slab were eliminated and the quality of the center of the slab was effectively improved. As a result, the quality of the center in the hot-rolled spring flat steel was good and fully met the requirements of customers.