中厚板Q235B表面纵裂原因分析及控制

ANALYSIS AND CONTROL OF SURFACE LONGITUDINAL CRACKS IN Q235B MEDIUM THICK PLATE

Q235B中厚板是敬业集团2022年的主流产品之一,但是自进入4月份以后,大批量Q235B板材表面出现纵裂缺陷,每月纵裂缺陷品占Q235B总产量的比例最高达到0.41%,造成了严重的经济损失。针对中厚板Q235B表面纵裂缺陷造成大量板材降级问题,通过跟踪Q235B板坯的炼钢连铸生产过程,对比纵裂缺陷品的工艺参数,研究了纵裂的原因并制定了相关控制措施。从钢水质量、浇注稳定性、铸坯凝固平衡性三方面入手,通过控制钢水冶炼成分碳含量0.15%~0.17%、硫含量小于0.012%,保证精炼软吹效果、减少钢中夹杂物,稳定铸坯拉速波动小于0.1 m/min,优化浇注工艺、水口插入深度115~125 mm,结晶器冷却制度、平衡铸坯宽窄面热流密度等措施,使Q235B板坯表面纵裂纹发生率得到明显控制,9月份纵裂缺陷品占比0.128%,较8月份减少0.283%。

Q235B medium thick plate is one of the mainstream products of Jingye Group in 2022.However,since April,a large number of Q235B plates have shown longitudinal crack defects on the surface,accounting for 0.41%of the total production of Q235B,causing serious economic losses to the company.In response to the problem of a large number of plate degradation caused by surface longitudinal cracks in medium and thick plate Q235B,by tracking the steelmaking and continuous casting production process of Q235B slab,comparing the process parameters of longitudinal crack defects,the causes of longitudinal cracks were studied,and relevant control measures were formulated.Starting from three aspects:steel quality,pouring stability,and solidification balance of the billet,the occurrence rate of longitudinal cracks on the surface of Q235B slab is significantly controlled by controlling the carbon content of the steel smelting component to be 0.15%~0.17%,and the sulfur content to be less than 0.012%,ensuring the refining soft blowing effect,reducing inclusions in the steel,stabilizing the fluctuation of casting speed to be less than 0.1 m/min,optimizing the pouring process,controlling the depth of water inlet insertion to be controlled between 115~125 mm,optimizing the cooling system of the crystallizer,and balancing the heat flux density of the wide and narrow surface of the slab.In September,the proportion of longitudinal crack defects was 0.128%,a decrease of 0.283%compared to August.