包晶钢板坯纵裂纹分析及保护渣优化

Analysis of longitudinal cracks and optimization of mold flux for peritectic steel slab

在生产Q235B、Q345B等包晶钢时,铸坯表面产生了大量的纵裂纹,通过对该缺陷的宏观形貌、金相组织以及微观形貌分析,证实该类缺陷形成于结晶器内,根本原因在于δ相向γ相转变时体积收缩引起结晶器内初生坯壳生长不均,而保护渣是其关键的影响因素。为减缓铸坯向结晶器的传热,对现有保护渣进行了优化,将保护渣碱度由1.39增加到1.53,提高保护渣结晶性能以强化弯月面钢水的缓冷,同时将熔化温度由1 171降低到1 130℃,1 300℃时黏度保持在0.08Pa·s,确保保护渣消耗量以保证对铸坯的润滑。生产实践表明,采用优化的保护渣后,板坯表面质量明显改善,纵裂纹缺陷发生率由原来的10.58%降低到1.85%。

In the production of Q235 B、Q345 Bperitectic steel slabs,a variety of surface longitudinal cracks defects were found.According to the analysis of macroscopic morphology,metallurgical structure and microscopic morphology,it is confirmed that the surface longitudinal cracks are formed in the mold,the basic reason is the uneven growth of the composite shell in the mold caused by the volume shrinkage during the transformation fromδtoγphase,and the mold flux is the key factor.In order to reduce the heat transfer from the slab to the mold,the existing mold flux was optimized.The basicity of mold flux was increased from 1.39 to 1.53,and the crystallization property of mold flux was improved to enhance the slow cooling of molten steel at meniscus.At the same time,the melting temperature is reduced from 1 171 to 1 130℃,and the viscosity is kept at 0.08 Pa·s at 1 300℃,this can ensure the consumption of mold flux to ensure the lubrication of the billet.The production practice shows that the surface quality of the slab is improved obviously by using the optimized mold flux,and the proportion of longitudinal cracks is reduced from 10.58%to 1.85%.