In order to reduce inclusions in steel and modify inclusions to prevent nozzle clogging during casting process

the equilibrium theimodynamic calculations of Ca-Al

Al-O

Al-S and Ca-S

and the analysis of oxygen and nitrogen of 5 heats 100 t LF of cold heading steel SWRCH22A (/% ： 0.18 ~0. 20C

0. 44 ~0. 62Si

0. 85 ~0. 89 Mn

0.012 ~ 0. 015P

0. 006 ~ 0. 009S

0 ~ 0. 004Ca

0.000 7 -0.001 0B

0. 011 ~ 0. 088Als) by calcium treatment on inclusions in steel have been carried out. The equilibrium curves of [Ca

]

-[Al

]

a[O

]

-[Al

]

and [S

]

-[Al

]

at 1 873 K and [ Ca

]

-[ S

]

at 1 823 ~ 1 923 K are obtained and compared to corresponding measured data of 5 heats. By analysis the op

timized LF refining process: (1) end refining slag- MgO = 6%

SiO

2

<

6% and CaO/Al

2

O

3

=1.6 ~1.8; (2) amount of BOF tapping slagging being about 700kg

amount of end refining slag being about 2 000 kg; (3) according to the aim end refining slag with CaO/Al

2

O

3

= 1. 6 ~ 1. 8 to define the amount of charging slag materials; and (4) avoiding the boiling of liquid steel during feeding calcium wire process and the oxidation of liquid during process of end refining to tundish.