In order to develop magnesium-containing resulfurized free-cutting steel

the formation and evolution of inclusions are investigated by high temperature simulation experiments and thermodynamic calculations. The effect of sulfur addition on the inclusions in liquid after magnesium treatment and mechanism are specially discussed. The experimental results show that the addition of sulfur causes the transformation of magnesium inclusions in liquid steel along the path of MgO

（1）

一 2MgO • SiO2

2（s）

^ MgO-SiO

2

-MnO

(1)

. The results of thermodynamic calculation show that as a sufficient amount of sulfur is added to the molten steel

the [ Mg

]

in liquid is determined by the eq

uilibrium of [ Mg

]

-[ S

]

instead of [ Mg

]

- [0

]

. When [ S

]

≤0. 12%

the equilibrium [ Mg

]

exceeds 0.00078% and the equilibrium product is MgO； as 0. 12% ≤ [S

]

≤0. 46%

the equilibrium [Mg

]

is in the range of 0.000 15% ~0.00078% and the equilibrium product is solid solution (2MgO • SiO

2

) and (Mg

Mn)S; as [S

]

>0.46%

the equilibrium [Mg

]

is lower than 0.00015% and the equi¬librium product is liquid inclusions (MgO-SiO

2

-MnO) and (Mg

Mn)S.