The φ140 mm of steel(0.21C

1.45Mn

1.44Cr

1.21Ni

0.49Mo

0.07Nb)for R4 of fshore mooring chain was produced at Daye  Steel by 60 t EBT are fumnace -70 t LF refining + RH vacuum degassing -3 strand 350mm×470 mm billet caster -850 primary mill blooming -750 semi-continuous mill rolling process. The re-  sults showed that with LF refining for 45 min

feeding Al wire and Ca-Si wire deoxidizing

then ≤66.65 Pa RH vacuum degassing for 20min + soft argon blowing for ≥10 min

the oxygen content in finished products of steel for off shore mooring chain was 14.8×10

-6

nitrogen content 69.8×10

-6

hydrogen content 1.2×10

-6

segregation porosity rating were 0.5

inclnsion rating 0～1

impact energy at -40 ℃≥100 and each index met the require ment of standard.