The IF steel that produced in Hanbao steelmaking plant was followed the procedure of combined blowing converter-RH refining-slab continuous casting. The number

size

composition and source of inclusions in different positions of the slab were systematically analyzed by means of SLIME

electrolytic extraction

filtration and separation

SEM and EDS. The results showed that the total oxygen and nitrogen contents of the head slab at 1. 5 m are 70 x 10

-6

47 x 10

-6

respectively

which is significantly higher than that of the mixed and the normal slab. The number of inclusions at 2. 5 m of head slab is 22. 1 mg/10 kg

which is 27 times as high as that of the normal slab. The main composition of the inclusions in the slab is the SiO

2

inclusion rich in K and Na

which is caused by the mould slag

and the size is mainly within 300 μm. It is necessary to optimize the composition of the slag

increase the viscosity to (0. 5 ±0. 1) Pa・s

improve the slag content of Al

2

0

3

and other means to reduce the risk of slag entrainment. By decreasing the amount of head and tail slab removal and flame cleaning

the degradation rate of hot strip caused by inclusions defects in deep drawing steel decreased from 0. 3% ~ 0. 4% to below 0. 2%.