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.