The effect of ingredient and basicity ( 1.0 ~ 1.2 ) of (/% :) 38. 5 ~ 45. 8CaO-38. 2 〜42. 0SiO

2

-8 ~ 15 Al

2

O

3

-8MgO refining slag series on morphology of inclusions in spring steel 55SiCrA (/% : 0. 53C

1. 50Si

0. 70Mn

0. 69Cr

0. 008P

0. 003S

0. 005 Als) has been studied silicon-molybdenum tube furnace with Al

2

O

3

crucible in laboratory

and the thermodynamic calculation on ingredient of inclusions and the analysis on distribution of inclusions in ternary phase diagram a

re carried out by using thermodynamic software Factsage. Results show that with increasing Al

2

O

3

content in refining slag the Al

2

O

3

content in inclusions increases

as the basicity of slag is 1. 2 with 8% Al

2

O

3

the inclusions in steel are distributed at low melting point area in Al

2

O

3

-SiO

2

-MnO ternary phase diagram and the Al

2

O

3

content in inclusion is 30% ~40% . Thermodynamic calculation results show that as basicity of slag is 1.0 ~ 1. 2 the corresponding Als in steel is 0. 008% that meets the examination results. Therefore it is available to control the morphology of inclusions in spring steel by using low basicity 1.0 ~ 1. 2 and ≤8%Al

2

O

3

refining slag.