Main ingredients of test mould powder were ( % ) 35. 46CaO

32. 84SiO

2

7. 87Al

2

O

3

3. 04MnO

8. 48Na

2

O

7. 13F

2. 6C. Samples of mould molten slag and slag film during casting of stainless steel !Crl7 were taken to study the change of ingredients and properties of molten slag and performance of slag film. Results showed that at casting for less than 10 min

the Al

2

O

3

and Cr

2

O

3

content in molten slag definitely increased while basicity of molten slag slightly decreased

but for more than 10 min the contents were trending towards stability: as compared to fresh slag the melting temperature and viscosity of molten slag increased of which the change of solidification temperature was minor； the melting t

emperature of molten slag after change ingredient was still in suitable range

although the viscosity of molten slag increased by 0. 08 Pa

s； the slag film consisted of crystal layer and glassy layer

the crystallization ratio of slag film was about 71% and the main phases of film were cuspidite crystals with minor nepheline crystals.