The evolution of inclusions in steel Q235

SPA-H and DC01 treated by feeding silicon-calcium wire and calcium-aluminium wire after LF refining in metal pretreatment-150 t BOF-ladle argon blowing-LF-CSP flowsheet and the effect of refining slag on inclusions are studied by thermodynamic calculation and scanning electron microscope. The results show that during refining process before Ca treatment the greater part of Al

2

O

3

in steel is modified to MgO·Al

2

O

3

by refining slag (/%： 52.97 ~55.63CaO

4.11 ~12.78SiO2

5.11~9.87MgO

22.93 ~31.72Al

2

O

3

0. 58 ~1.27FeO

0. 01 ~0. 07MnO) ; based on

the Mg-Al-O predominant forming diagram

with micro-amount Mg in steel the Al

2

O

3

may modify to MgO· Al

2

O

3

spinel

the calcium treatment is mainly to modify the MgO· Al

2

O

3

spinel

therefore it is need to feeding sufficient amount of calcium for high melting point aluminium-magnesium and aluminium-magnesium-calcium inclusion modifying to low melting point region; in order to avoid forming high melting point CaS inclusions

before calcium treatment with [Al

]

=0. 02% ~0. 04% the [S

]

should be less than 0.001 4%.