Tested steel 31CrMoV9 (/% : 0.28 ~0.33C

0.30 ~0.35Si

0.49 ~0.60Mn

0. 011 ~0.016P

0.027 ~ 0.031S

2.47 ~2.60Cr

0. 16 ~0.23Mo

0. 12 ~0. 19V) is melted by a 25 kg induction furnace

and the effect of binary basicity 2.5 ~ 3.5 of different ingredient refining slag (/% : 46.43 - 59. 89CaO

15.16 - 23.50Si0

2

10 〜20Al

2

O

3

6 〜 10MgO

2 ~5CaF

2

) on number

size and composition of inclusions in steel 31CrMoV9 has been studied

by orthogonal experiment method. Results show that the effect of binary basicity and alumina content in refining slag on inclusion content in this steel is obvious ； as the binary basicity of slag increases from 2.5 to 3.5

for per 0.3 mm

2

steel the average area of inclusions increases from 22.07 μm

2

to 25.67 μm

2

i. e. that increases by 16.31% and the number of inclusions decreases from 316.67/0.3 mm

2

to 255.00/0. 3 mm

2

i. e. that decreases by 19. 47%

it is available to form composite inclusions； as alumina content in slag increases from 10% to 20%

for per 0. 3 mm

2

steel the area of inclusions increases from 22. 57 μm

2

to 24. 28 μm

2

i. e. that increases by 7. 55% and the number of inclusions decreases from 292. 67/0.3mm

2

to 272.00/0.3 mm

2

i. e. that decreases by 7. 06%

it is available to form aluminium-magnesium spinal inclusions. With comprehensive analysis the refining slag contained 10% Al

2

O

3

10% MgO and 5% CaF

2

with binary basicity 3.5 has better refining effect.