The steelmaking flowsheet of gear steel 8620RH ( K) (/% ： 0.18 ~0.22C

0. 17 ~0. 26Si

0.70 ~ 0. 90Mn

≤0.025P

0.015 ~ 0.025S

0.4 ~0.6Cr

0.4 ~0.7Ni

0.15 ~0.25Mo

0.015 ~ 0.045A1

≤0.0100N) is 60 t BOF-LF-VD-300 mm x360 mm casting bloom. The BOF end residual elements and tapping amount of steel

alloying adding amount in refining process

adding N method in VD process and carbon segregation of casting bloom in original process have been analyzed

it is obtained that the main causes of hardenability band width AHRC 4 〜5 being on low side in end-quench test are BOF liquid tapping amount not stable

higher superheating temperature extent of liquid in tundish

lower qualified rate of internal controlled compound of liquid and higher casting bloom carbon segregation index. With using the process measures including stabilizing BOF charging and tapping amount

blowing nitrogen to increase nitrogen in liquid in LF

idle hot ladle adding covering plate

controlling tundish liquid supeiheating temperature 15 ~25 ℃.

and optimizing casting electromagnetic stirring parameters

the qualified rate of internal-controlled end-quenched hardenability of steel 8620RH(K) increases from original <60% to 82.93%.