The production process flowsheet of wind power gear ring of steel F42CrMo4 is hot metal-100 t EAF-LF- VD-Φ500 mm CCM-slow cooling-forged to Φ2000 ~ 3900 mm ring forgings. The analysis on sampling at wind power gear ring defect region by ultrasonic positioning shows that the main causes for some batch of wind power gear ring of steel F42CrMo4 unqualified by detection test are aluminum oxide inclusions and porosity defects of casting bloom. With the process measures including controlling EAF end carbon >0. 15%

the end point of LF was fed with 0.5 kg/t calcium wire

and after fed with calcium

argon was blown soft >10 min

after VD the argon blowing rate increasing to 2 X30 L/min from original 2x25 L/min

and controlling liquid super-extent 10 ~ 18 ℃，th

e nitrogen

hydrogen and oxygen content in steel decrease respectively from ≤80 x 10

-6

≤ l. 5 x 10

-6

and≤ 20 x 10

-6

to ≤ 75 x 10

-6

≤ 1.2 x 10

-6

and ≤ 15 x 10

-6

and the detection qualified rate of forgings increases to more than 98.95%.