The metallurgical flowsheet of steel 34CrNiMo6 (/% : 0. 30 ~0. 38C

0.50 〜0. 80Mn

≤0. 40Si

0.015 ~0.035S

≤0.035P

1.30 〜1.70Ni

1. 30 〜1.70Cr

0. 15 ~0. 30Mo) is 30 t EAF-LF-VD-casting  Φ70 mm electrode- 3. 6 t ESR ingot (Φ 610 mm)- forged to Φ280 mm round bar. Based on analysis the factors to influence rating of B-type inclusions in steel during steelmaking process

with using the measures including decreasing the oxygen content in electrode from original 20 x 10 to 11 x 10

-6

and increasing the S content in electrode from 0.035% to 0.045% to decrease the adding amount of FeS etc additives during ESR process

increasing the fluorite content in fluorite-Al

2

O

3

-SiO

2

-MgO ESR slag series from 45

% to 60% and decreasing the SiO

2

from 15% to 5%

the rating of B-type inclusions in round bar decreases from original 2. 5 to ≤ 1. 5 and the distribution of sulfur in steel uniform to insure the quality of ESR steel.