With 100 t LF original refining end slag (/% : 53. 8CaO

8. 16MgO

16. 6SiO2

17. 45Al

2

O

3

1. 44TFe

1. 26S

ZG. 08) to improved refining end slag (/% : 51.3CaO

6. 36MgO

25. 0SiO

2

6. 73Al

2

O

3

2. 96TFe

0. 76S

R2. 05) by decreasing the basicity and Al

2

O

3

content in slag

the equivalent number of inclusions in steel 65Mn (/% : 0. 63 ~ 0. 65C

0. 19 ~ 0. 22Si

0. 92 ~ 0. 9

6Mn

0. 005 ~ 0.006S

0. 021 ~ 0. 022P

0.003 5 ~ 0.003 7T [O

]

) decreases from 18. 4 incluisons/mm

2

to 11. 3 inclusions/mm

2

and the average diameter of inclusions reduces from 8. 4 μm to 4.5 μm. As compared with original refining slag by using optimized refining slag the number of Al

2

O

3

per mm

2

in steel 65 Mn at LF end refining decreases from 5. 9 to 1. 7; and the Al

2

O

3

content in CaO-SiO

2

-Al

2

O

3

and CaO-SiO

2

-Al

2

O

3

-MgO compound inclusions decreases from 38. 3% ~ 44. 7% to 17. 5% ~ 28. 7% ； and the reject rate of coil due to unqualified B series Al

2

O

3

inclusion decreases from 6% to 3%.