Abstract: The metallurgical flowsheet of 160 angle steel Q420C with 18 mm thickness for power tower (/% : ≤0.20C, 1.00〜1.70Mn, ≤0.55Si, ≤0.035S, ≤0.035P, 0.02~0.20V, ≥0.015Als) is 80 t BOF-LF-CC-rolling process. The analysis on comer cracks of hot-rolled angle steel is carried out by optical microscope, scanning electron microscope and energy dispersive spectroscopy. The results show that there are decarburized layer and ferrite film around cracks, the S enrichment near cracks and the AIN precipitates at grain boundary are found that break the continuity of steel matrix. It is obtained that the slag inclusions at oscillation mark bottom, segregation, thermal stress and bending straightening stress lead to angle steel crack along grain boundary. With process measures including decreasing [N] to 0.0080% , controlling Als 0.017%~0.022% , [Mn]/[S] ≥80, liquid over heating extent ≤25°C , viscosity of mold powder 0.73 Pa·s, and straightening temperature ≥950°C , the quality cast billet increases to 85% from original 25.78% , it is available to decrease the occurrence of comer cracks of angle steel.

Key words: Steel Q420C, 180 mm x 180 mm Cast Billet, Angle Steel, Segregation, AIN, Corner Cracks

摘要： 电力铁塔用18 mm厚160角钢Q420C（/%:≤0.20C,1.00~1.70Mn,≤0.55Si,≤0.035S,≤0.035P,0.020.20V,≥0.015Als）的冶金流程为80 t BOF-LF-CC-车制工艺。利用光学显微镜、SEM以及能谱分析仪对热轧角钢角部裂纹进行了分析,结果表明,裂纹周围存在脱碳层及铁素体膜,裂纹处发现S富集及在晶界析出的AlN破坏了钢基体的连续性;得出连铸振痕谷底的夹渣、成分偏析,热应力和弯曲矫直应力导致了角钢沿晶界开裂。通过降低[N]至0.0080%,控制Als 0.017%~0.022%,Mn/S≥80,钢水过热度≤25℃,保护渣牯度0.73 Pa·s,矫直温度≥950℃等工艺措施,使连铸坯的优质品率由原25.78%提高至85%,有效地降低了角钢角部裂纹的发生。

关键词: Q420C钢, 180 mm x 180 mm连铸坯, 角钢, 偏析, AIN, 角部裂纹