Q345E钢Φ800 mm铸坯表面网状裂纹的分析及控制措施

Analysis on Surface Net Cracks of Φ800 mm Casting Bloom of Steel Q345E and Control Measures

采用金相显微镜和扫描电镜分析了Q345E钢Φ800 mm铸坯(/%:0.15C,0.27Si,1.37Mn,0.009P,0.001S,0.03Nb,0.04V,0.030A1,0.008 ON)表面网状裂纹,得出结晶器壁和凝固坯壳之间保护渣膜厚度不均匀,使坯壳局部受挤压,产生凹坑,冷却速度降低,产生热应力裂纹。通过将保护渣碱度(CaO)/(SiO_2)从1.03提高到1.15,熔点从1 235℃降至1 210℃,1 300℃粘度从0.87 Pa·s提高到1.10 Pa·s,使Φ800 mm连铸坯表面凹坑和网状裂纹的发生率从原60.5%降至0.5%以下。

The surface net cracks of Ф800 mm casting bloom of steel Q345E （/% ： 0. 15C, 0. 27Si, 1.37Mn, 0. 009P, 0. 001S, 0. 03Nb, 0.04V, 0. 030Al, 0.008 ON） have been analyzed by metallurgy and scanning electron microscope. It is obtained that the uneven thickness of flux film in between mold wall and solid shell leads to extruding local shell, forming depression, decreasing cooling rate and forming thermal stress cracks. With increasing basicity of mold powder （CaO）/（SiO2） from 1.03 to 1.15, decreasing melting point form 1 235 ℃ to 1 210 ℃, and increasing viscosity at 1 300 ℃ from 0. 87 Pa · s to 1.10 Pa ·s, the occurring rate of surface depression and net cracks of Ф800 mm casting bloom decreases from original 60. 5% to less than 0. 5%.