The flow sheet for steelmaking steel 20CrMnTi

0. 45C

40Cr and GCrl5 at melting shop is 70 t BOF-LF- VD-220 mm x220 mm CC process. It is obtained by analysis of 22 heats of steel 20CrMnTi

40Cr and 0. 45C that the average nitrogen content in steel after BOF tapping- [N

]

is 21.70 x 10

-6

end LF refining the average [N

]

48. 95 x 10

-6

and in tundish the average [N

]

63. 62 x 10

-6

. With increasing hot metal ratio from original 85% to 92. 3%

controlling BOF end [P

]

≤0. 008%

ladle filling argon before tapping

quick forming foamed slag in LF refining with slag thickness 100 ~ 120 mm to prevent liquid absorbing nitrogen

using long nozzle and controlling

argon blowing rate

the results by melting 6 heats of steel GCrl5 show that the [N

]

at end LF refining is 51. 8 x 10

-6

~ 60. 2 x 10

-6

the [ N

]

at end VD is 29. 1 x 10

-6

~33. 9 x 10

-6

and the nitrogen content in products is 31. 8 x 10

-6

~40. 0 x 10

-6

all products meet the requirement for cold working.