Q235B和Q345B钢中厚板表面纵裂纹的成因分析和工艺优化

Q235B钢（/%:0.14~0.17C,0.30~0.60Mn,0.010~0.040Als）和Q345B钢（/%:0.15~0.18C,1.30~1.60Mn,0.010~0.040Als）100 mm厚板的生产流程为铁水预处理-120 t转炉-LF-200 mm板坯连铸-轧制工艺。通过分析得出中厚板表面纵裂纹源于铸坯裂纹。通过保护渣碱度由1.16提高至1.26,1300℃黏度由0.80Pa·s提高至0.97 Pa·s,软搅拌时间不低于10 min,拉速控制在1.0 m/min左右,液面上下波动≤5 mm,保持结晶器锥度9.0 mm,钢水过热度20~25℃,二冷水为0.662 L/kg等工艺措施,使Q235B和Q345B钢中厚板纵裂率由2.17%下降至1.08%,板材综合合格率由原94.78%提高到98.16%。

Analysis on Formation of Surface Longitudinal Crack of Steel Q235B and Q345B Medium-Heavy Plate and Process Optimization

The flowsheet of 100 mm heavy plate of steel 235B (/% : 0.14 ~0.17C, 0. 30 ~ 0.60Mn, 0.010 ~ 0. 040Als) and steel Q345B (/% : 0. 15 ~0.18C, 1. 30 ~1. 60Mn, 0. 010 ~ 0. 040Als) is hot metal pretreatment-120 t converter-LF-220 mm slab casting- rolling process. By analysis it is obtained that the surface cracks of medium-heavy plate originate from cracks of casting slab. With using the process measures including increasing basicity of mold shielding slag from 1.16 to 1. 26, increasing its viscosity at 1 300 °C from 0. 80 Pa·s to 0. 97 Pa·s, soft stirring time no-less than 10 min, controlling casting speed about 1. 0 m/min； liquid surface up and down ≤5 mm； maintaining mold cone 9. 0 mm； liquid superheat extent 20 ~25 °C and secondary water rate 0. 662 L/kg, the ratio of longitudinal cracks of steel Q235B and Q345B medium-heavy plate decreases from original 2.17% to 1. 08% , and the comprehensive qualified ratio of plate products increases to 98. 16% from original 94. 78%.