In order to study the control of 90 t BOF-RH-LF-CC flowsheet produced ultra-low carbon steel AISI 1006 inclusions

the sample was taken at different sampling point at cross section of 200 mm×200 mm cast bloom to analyze inclusions

the analysis results show that the ratio of inclusions of small particles in the steel are relatively large

and the inclusions with size of5- 10 μm accounted for90. 1%

3.6% of the 10- 13 μm

and5.4% above 13 μm

and the larger size inclusions are mainly distributed in the center

of the casting bloom. The largest distribution of inclusions is at the length of side 1/4 of the cast billet

followed by the near center

and the least inclusions near the surface of the cast bloom. The inclusions in the casting bloom are mainly Al

2

O

3

Al

2

O

3

·CaO · (CaS ·MnS)

Al

2

O

3

·CaO ·MgO · (CaS ·MnS)

MgO · Al

2

O

3

· (CaS ·MnS)composite inclusions

which are endogenous inclusions. The process optimization is carried out

RH high vacuum holding time is controlled for more than 15 minutes

Deoxygenation slagging and desulfurization be controlled well during LF refining

the refining time is controlled for within 90 minutes

the alkalinity of the refining final slag is 6 to 7

the silicon calcium line is fed before leaving the station for modification treatment

the soft blowing time is controlled for more than 25 minutes

the continuous casting is well protected

the tundish large argon flow is purged for more than 10 minutes to avoid the secondary oxidation

the inclusions are controlled in the direction of calcium aluminate

and the T.O content of molten steel is reduced

after process optimization

T.O content of mloren steel ≤20×10

-6

rate of B 、D 、Ds inclusion≤1.0.