亚包晶钢板坯纵裂成因与浸入式水口改型

Causes of longitudinal crack in hypo-peritectic steel slab and modification of submerged entry nozzle

针对某厂连铸机浇注亚包晶钢板坯表面纵裂纹发生率较高的问题,分析了双侧孔浸入式水口对裂纹形成的影响。在此基础上对浸入式水口结构进行优化,开发了新型浸入式水口。通过模拟研究和生产应用分析,对比了双侧孔浸入式水口与新型浸入式水口结构的差异以及两者对结晶器内流场和温度场的影响。结果表明,采用双侧孔水口浇注时,结晶器钢液流场和温度场分布不合理,导致结晶器内液渣层厚度不均匀,尤其是水口与结晶器壁之间位置液渣层厚度偏薄,从而诱发了板坯表面纵裂纹缺陷的大量发生,纵裂纹集中在板坯宽面中心400 mm范围,裂纹长度50~1 200 mm,深度2~12 mm;采用新型浸入式水口更有利于水口与结晶器壁间钢液流动,增加水口出入口钢液束流能力,使结晶器内钢液流场对称、温度场分布均匀、液渣层厚度均匀增加,亚包晶钢板坯表面纵裂纹改善显著,表面纵裂纹发生率由10.9%降低至1.5%。

The problem of high occurrence rate for surface longitudinal crack of hypo-peritectic steel slab casting by continous casting machine in a factory was studied,and the influence of submerged entry nozzle(SEN)with double side holes on crack formation was analyzed.On this basis,the structure of the SEN was optimized and a new-type SEN was developed.Through simulation research and production test,the differences in the structure of double side hole SEN and the new-type SEN,as well as their impact on the molten steel flow field and temperature field in the mold,were compared.The results show that the distribution of molten steel flow field and temperature field in the mold is unreasonable when using double side hole SEN,resulting in uneven thickness of liquid slag inside the mold,especially the thin thickness of liquid slag between the SEN and the mold wall,which induces a large number of sur-face longitudinal crack.The longitudinal cracks are concentrated in the 4oo mm range of the slab wide surface cen-ter,with the length of 50-1200 mm and the depth of 2-12 mm.The new-type SEN is more conducive to the flow of molten steel between the nozzle and the mold wall than the double side hole SEN,and is conducive to increasing the flow capacity of molten steel at the inlet and outlet of the SEN.The flow field of molten steel in the mold is symmet-rical,the temperature field distribution is uniform,the thickness of liquid slag is uniformly increased,and the longi-tudinal cracks on the surface of hypo-peritectic steel slab are significantly improved,the incidence of surface longitu-dinal cracks has decreased from 10.9%to 1.5%.