The thermodynamic calculation on deformation of inclusions in tested steel GS35C-A (/% : 0. 34 ~0. 35C

0. 20 ~0. 22Si

0. 69Mn

0. 013 ~0. 016P

0. 026 ~0. 045S

0.027 〜0. 046Al

0.000 8 - 0.001 9Ca) has been carried out

and the morphology and amounts of inclusions in steel produced by corresponding process 1[ BOF-LF ( sulphur alloying)-RH-calcium treatment-CC

]

and optimized process 2 [BOF-LF-RH-calcium treatment- sulphur alloying- CC

]

are studied. Results show that (a) with increasing [S

]

in liquid the balancing calcium content in steel to form CaS decreases； and in process of forming low point melting inclusions modified by calcium treatment the [Al

]

in liquid gradually decreases； (b)

with decreasing end RH Ca and S content in liquid respectively from 0. 001 9% and 0. 045% ( process 1) to 0. 000 8% and 0. 026% ( optimized process 2)

the average continuous-continuous casting heats increases respectively from 2. 5 heats to 8 heats; ( c) before optimization by process 1 the typical inclusion in liquid in tundish consists of sulphide around magnesia aluminium spinel

while after optimization by process 2 the inclusion in liquid in tundish is calcium aluminate; and as compared with before optimization

after optimization the number of inclusions per mm

2

in steel at end RH and in tundish decreases respectively from 9.09 and 6.23 to 5.06 and 3.76.