中文摘要：

Q345B（含铌）钢是低合金高强度（HSLA）裂纹敏感性钢种。文中分析了C、Nb、二冷水量对其铸坯裂纹形成的影响和裂纹产生的原因。在此基础上结合工业试验对连铸二冷制度进行优化，提出弱冷却方式和均匀二次冷却，铸坯的矫直温度提高到950℃以上可有效控制裂纹的产生，降低了裂纹产生的几率，铸坯质量提高达80％。

英文摘要：

Q345B （containg Nb） is the sort of high strength low alloy （HSLA） steel which is sensitive to cracks. We analyzed the influences of C, Nb and the secondary cooling water flow rate on the cracks in the casting blank and the reasons for crack formation. Based on those results, we optimized the secondary cooling water distribution system in the process of continuous casting through industry tests and proposed a low cooling water distribution system and uniform cooling. The results show that when the temperature of a casting blank is above 950℃, it can prevent the cracks effectively, reduce the generation probability of cracks, and enhance the quality of casting blanks by 80%.