The production flow sheet for studied 0. 80% ~0. 82% C Steel for tire cord is 80 t BOF-CAS-LF-VD-150 mm x 150 mm CC process. With adding 300 kg manganese metal and 200 kg high purity silicon during top and bottom blown converter tapping to silicon-manganese combined deoxidize

during LF refining first slagging refining slag with basicity (CaO/SiO

2

)2. 04 then decreasing the basicity ( CaO/SiO

2

) to 0. 86 and maintaining -5% Al

2

O

3

content in slag to control the plasticity transformation of nonmetallic inclusions in steel. Results show that the average total oxygen content in casting billet is 16 X 10

-6

and the nitrogen content in billet is controlled about 50 x 10

-6

during CAS ( Composition adjustment by sealed argon bubbling) process the main inclusions in steel are MnO-Al

2

O

3

-SiO

2

in LF and VD process

and in casting billet the main inclusions are CaO-Al

2

O

3

-SiO

2

-MgO series

the size of that inclusion series is smaller i. e. 2 ~ 3

μm

which distribute near the 1 400 °C low melting zone.