Effects of B2O3 on melting temperature of two CaO-based refining slag series with low basicity [ ( CaO)/ (SiO

2

)=3 ~4

]

and high basicity [ (CaO)/(SiO

2

)= 5 〜7. 5

]

have been studied. Results indicate that B

2

O

3

is more available than Al

2

O

3

and CaF

2

to decrease the melting temperature of CaO-based refining slag

for low basicity slag

it is effective to decrease melting temperature of slag with replacing CaF

2

Al

2

O

3

or SiO

2

partly by B

2

O

3

for high basicity slag

with replacing CaF

2

by B

2

O

3

the extra-low melting temperature CaO

-based refining slag with high ( CaO) /( SiO

2

) and high (CaO)/( Al

2

O

3

) could be got

it is available to increase the slag forming rate

the ability of slag for desulfurization and dephosphorization

and the ability of slag to absorb deoxidation products by silicon and aluminium.