According to the issues for the steel 10B21 (/% : 0.19-0.22C

≤0.08Si

0.8-1.0Mn

≤0.020P

≤0.020S

0.010-0.040Al

0.001-0.005B) during steelmaking process including silicon content in liquid going beyond the limit of standard

poor castability and exiting cracked comer of cast billet

with analysis on production data and inclusions in steel

and cast billet macro-examination

it is obtained that after LF white slagging

the SiO

2

in slag is reduced by Al led to [Si

]

going beyond the limit； the castability of steel 10B21 decreases by Al

2

O

3

in liquid depositing in nozzle

and during casting solidification process the boron nitride and oxide precipitate at grain boundary ca

using cast billet cracked comer. With using the process measures including increasing BOF end [C

]

to 0.10%-0.14%

controlling tapping liquid temperature 1640-1660℃

decreasing BOF aluminium iron adding amount from 1.82 kg/t to 1.36 kg/t

decreasing LF refining aluminium iron adding amount from 2.8 to 1.6 kg/t

increasing feeding calcium amount from 1.23 kg/t to 2.05 kg/t

adding micro fixed nitrogen element Ti and optimizing casting process

the ratio of [Si

]

≤0.08% increases from 65.62% to 89.50%

single tundish continuous-continuous casting heats in crease from 4 heats to 12 heats and the casting bloom cracked comer is effectively controlled

and the yield of qualified cast billet increases from 88.23% to 97.44%.