The production flowsheet for 012 ~ 32 mm bars of gear steel 20CrMo (/%:0.19 〜0.23C

0.48 ~ 0.58Mn

0.24 〜0.28Si

0.009 -0.015P

0.003〜0.012S

0.87 ~1.08Cr

0.17 ~0.18Mo

0.024 ~ 0.046Als) is desulphurizing hot metal-120 t top and bottom combined blowing converter-LF-soft argon blowing-200 mm x 200 mm billet concasting-continuous rolling process. Results show that with using the process measures including controlling hot metal [S

]

≤0.030%

BOF end [C

]

5:0.08% and end [P

]

≤0.012%

adding 0.6 ~ 1.0kg/t aluminium pig for pre-deoxidizing at BOF tapping

controlling LF refining slag basicity 3.5 〜5.0

casting liquid overheating extent 20 ~30 ℃

casting rate 1. 1 ~ 1. 4 m/min

beginning r

olling at 1 060 ~ 1 100 °C and finishing rolling at ≤900 ℃，the total oxygen content and the nitrogen content in steel are respectively 12. 5 x 10

-6

〜22. 5 x 10

-6

and 33 x 10

-6

~40 x 10

-6

the rating of central and general porosity in rolled products is 0. 5 ~ 1. 0

the hot upset test and the mechanical properties of steel meet the requirement of standard

and the hardenability band width △J

9

HRC value is 3. 0 and the △J

15

HRC value is 4. 2.