The extent of modification of Al

2

O

3

inclusion and factor of CaS inclusion formation in refining liquid of steel 20CrMnTiHl after calcium treatment have been studied by thermodynamics equilibrium calculation between liquid steel and inclusions. Calculated results show that with calcium treatment of liquid steel containing 0. 020% ~ 0. 035% [S

]

and 0. 02% 〜0. 04% [ Al

]

the stable CaS forms easily and the aluminum deoxidizing product Al

2

0

3

is not easily modified to low-melting calcium aluminate 12( CaO)

7( Al

2

0

3

). In order to completely modify the Al

2

O

3

to low-melting calcium aluminate (CaO) • ( Al

2

0

3

) and 12( CaO) *7( Al

2

O

3

)

in refining process the calcium treatment of liquid steel should carry out in conditions of low [S

]

and ≥1 600℃

and the sulfur wire feeding operation carries out after soft argon stirring

it is available to obviously decrease the occurrence of nozzle blocking.