Abstract: With sampling analysis on defects of Q355 series steel medium plate defect by ultrasonic inspection and heat-transferring simulation for slab solidification process, it is disclosed that the biconical liquid core appearing at slab solidifying front and C/Mn/H gathering in this zone are the cause of the medium plate two side ultrasonic inspection defect. Through process improvement and strict control, the RH vacuum degassing time ≥20 min, the whole process of continuous casting protecting, and hydrogen content of steel in mold ≤2 x 10^-6 and superheat of continuous casting less than 30 °C ,the center carbon segregation of slab is better than 1.0 rating, combining slow cooling of slab and medium plate, the qualification rate of medium plate inspection is 99. 6% .

摘要： 通过对Q355系钢中板探伤缺陷进行取样分析，结合板坯连铸凝固传热计算，揭示了板坯凝固末端呈现双锥形液芯的凝固特性，双液芯区域由于C、Mn与H富集，成为中板两侧探伤缺陷的根源。通过工艺改进并严格控制，RH真空脱气时间≥20 min，连铸全程保护，结晶器钢液H含量≤2×10^-6；连铸过热度≤30 ℃，板坯中心碳偏析优于1.0级；结合执行板坯、中板缓冷处理，中板探伤正品率达到99.6%。