Q235B热轧板表面纵裂成因分析及工艺控制

Q235B钢(0. 11% ~0. 17%C)10~20 mm热轧板的生产流程为铁水预处理-50 t转炉-吹氧-(2。0 ~ 230)mm x(900 ~ 1 600)mm板坯连铸-热轧工艺。分析表明.Q235B钢热轧板表面裂纹来源于铸坯纵裂。统计分 析了成分、钢水过热度、拉速、连铸二冷水量、保护渣等对连铸坯纵裂的影响。通过控制Mn/S≥40,钢水过热度 15-35 °C,拉速1. 15 m/min,按季节调节二冷水量，釆用熔点≥1 100 °C，粘度0.20 ~0. 32 Pa .s,碱度≥1. 10的保 护渣等措施，使Q235B钢热轧板表面纵裂纹由3.51%降至W0. 96%。

Analysis on Forming Cause of Surface Longitudinal Crack of Steel Q235B Hot-Rolled Plate and Controlling Process

The flowsheet for 10 ~20 mm hot-rolled plate of Q235B steel (0. 11% ~0. 17% C) is hot metal pretreatment-50 t converter-argon blowing-(200 ~230)mm x (900 ~ 1 600) mm slab casting-hot rolling process. The analysis results show that the surface crack of hot-rolled plate stems from casting slab longitudinal cracks of steel Q235B. The effect of composition, liquid overheat extent, casting speed, casting secondary water rate and mold powder on longitudinal crack of casting slab has been statistically analyzed. With the measures including controlling Mn/S ≥40, liquid overheat extent 15 ~35 °C , casting speed 1. 15 m/min, adjusting secondary water rate according to season and using mold powder with melting point ≥1 100°C , viscosity 0. 20 ~ 0. 32 Pa .s and basicity ≥1. 10, the ratio of occurrence of steel Q235B hot- rolled plate surface longitudinal crack decreases to ≤0. 96% from original 3. 51% .