含铌微合金钢连铸坯角部裂纹控制二冷新工艺

New secondary cooling process for transverse corner crack control of Nb micro-alloyed steel slab

基于唐钢中厚板厂含铌钢板坯连铸生产实际,采用数值模拟方法研究了Q345B-Nb含铌钢板坯连铸过程实施铸坯角部二冷高温区角部组织多相变晶粒细化控冷工艺的可行性。结果表明,通过在结晶器窄面足辊下方增加6组针对铸坯角部强喷淋冷却的喷嘴结构,可使铸坯角部温度下降至约600℃,而后减少立弯段中下部3区与4区冷却水量,可使铸坯角部温度回升至900℃以上,满足铸坯角部多相变温度控制条件。在此基础上,将新控冷工艺应用于现场实际,实施铸坯二冷高温区多相变控冷新工艺后,铸坯角部距表面0~20mm范围内的组织均可由传统工艺下＂奥氏体＋先共析铁素体膜＂结构转变成＂铁素体＋珠光体＂结构,且晶粒细化至不大于20μm,铸坯抗裂纹能力大幅提高,含铌钢连铸坯角部裂纹率由原工艺的5.89%稳定控制在小于0.1%水平。

The implementation feasibility of the Q345 B-Nb steel slab corners grains refinement by cyclic phase transformations at high temperature was studied by mathematical simulation according to the practical Nb micro-alloyed steel continuous casting in Tangshan Iron and Steel Plate.The simulation result showed that the corner temperature could be cooled below to 600 ℃ by setting six groups of the nozzles for the strong spray cooling of the slab corners under the mold narrow face foot rollers,and then the temperature may rise to 900 ℃ by reducing the water cooling consumption of cooling zone 3 and zone 4 in bending segment.Thus,the temperature of slab corners could meet the need of cyclic phase transformations.Based on this,the new process was applied to the practical continuous casting.The application results showed that the slab corners microstructure transferred from the austenite ＋ ferrite film structure to the ferrite＋pearlite structure,and the grains were greatly refined to≤20μm by using the new technology in the range of 0~20 mm under the slab corner surface,and the cracking rate of the Nb micro-alloyed steel slab corner reduced from 5.89% of using traditional cooling process to0.1%.