Q345B连铸坯表面夹渣缺陷的形成原因及控制

摘要

描述了Q345B铸坯表面夹渣缺陷的宏观形貌,并通过扫描电镜及能谱仪对缺陷形貌进行观察和能谱分析.结果表明,缺陷内主要为氧化铁皮并含有保护渣成分.分析了铸坯表面夹渣缺陷的形成原因主要有以下4个方面:浸入式水口设计不合理引起的结晶器液面波动卷渣、结晶器内弯月面受冲击夹渣、保护渣成分不均匀引起的分熔现象及结晶器振动负滑脱时间长导致的下渣不均匀.并提出优化措施:1)优化浸入式水口的结构,将侧孔角度为25°减小至18°;2)改善结晶器流场,板间的氩气流量由原来的5 L/min减少至3 L/min以下,SEN的插入深度控制在90 ～ 130 mm;3)优化保护渣成分和性能,将保护渣熔点由原来的1 050℃提高至1 150℃,碱度大于1,黏度0.12～0.2 Pa·s,降低了保护渣的消耗;4)调整结晶器振动参数,使负滑脱时间由原来的0.207 s减至0.165 s.22炉的现场试验结果表明,优化后的工艺由于铸坯缺陷引起的中厚板表面裂纹发生率控制在1％以下,并实现了铸坯、中厚板表面质量的稳定控制.%This paper describes the macroscopic morphology of the slag pit on the surface of microalloyed steel Q345B.The morphology and composition of the defects were analyzed by SEM and energy spectrometer.The results show that the slag pit in the casting slab was mainly iron oxide scale and contains a small amount of protection residue.The reason for the formation of slab surface slag defects was analyzed which basically has the following 4 aspects:slag entrapment caused by surface fluctuation due to the unreasonable design of the submerged nozzle,wrapped slag caused by the hit on meniscus in the mold,the fractional melting caused by the uneven composition of the mold fluxes,and the long time of the mold vibration with negative slip.Thus the following optimization measure are proposed:Firstly,optimize the structure of the submerged nozzle by reducing the angle of the side hole form 25°to 18°.Secondly,improve the flow vectors in the mold,the argon flow rates between the plates being reduced from 5 L/min to less than 3 L/min and the insertion depth of SEN controlled between 90 and 130 mm.Thirdly,optimize the composition and performance of mold slag,the melting point of the protection residue being increased from 1 050 ℃ to 1 150 ℃,the basicity should be greater than 1 and the viscosity between 0.12 Pa · s and 0.2 Pa · s.Fourthly,reduce the negative slip time from 0.207s to 0.165s by adjusting the vibration coefficient of the mold.The results of 22 field tests show that the surface crack of the plate caused by slag pit was controlled below 1％,and the surface quality control of the casting slab and plate is realized.