Q420B铁塔角钢裂纹的成因分析和工艺优化

Q420B铁塔角钢（/%:0.12~0.17C,0.15~0.35Si,1.25~1.60Mn,≤0.035P,≤0.035S,0.06~0.09V）的生产流程为60 t转炉-LF-220 mm×290 mnm坯连铸-型钢轧制。铁塔角钢成品酸洗后发现部分批次出现裂纹和表面夹杂,分析表明,裂纹深度达1 mm,有夹杂物和氧化、脱碳现象。通过保护渣碱度从0.97降至0.79,粘度由0.236 Pa·s提高至0.450 Pa·s,连铸坯矫直温度从900℃提高至1 000℃,二冷比水量从0.9 L/kg降至0.7L/kg等工艺措施,铸坯的合格率由93%提高到97%,并有效地避免了角钢裂纹的形成。

Analysis on Forming Cause for Crack of Anger Steel Q420B for Tower and Process Optimization

The production flowsheet for angle steel Q420B for tower (/% : 0. 12~0. 17C, 0. 15 ~ 0.35Si, 1.25 ?1.60Mn, ≤0.035P, ≤0. 035S, 0. 06~0. 09V) is 60 t BOF-LF-220 mm x 290 mm bloom casting-section steel rolling. The surface cracks and inclusions occur at partial batches of finished tower anger steel products after pickling and the analysis results show that the depth of cracks is up to 1 mm with inclusions, oxidation and decarburization phenomenon. With the process measures including decreasing the basicity of mould shielding powder from 0. 97 to 0. 79 and increasing its viscosity from 0. 236 Pa·s to 0.450 Pa·s, increasing the straightening temperature casting slag from 900 to 1 000 and decreasing the secondary cooling water rate from 0. 9 L/kg to 0. 7 L/kg, the qualified rate of casting bloom increases from 93% to 97% and it is available to avoid the formation of crack of angle steel.