The production flow sheet for pipeline steel X70 is KR metal pre-desulphuration-180 t BOF-LF-RH-slab CC process. With optimization of refining slag ingredient and slagging operation

and based on effect of bottom gas blowing rate (400-700 L/min) on end [S

]

the LF deep desulphurization process has been schemed. Pilot production results show that by controlling refining slag ingredient (/% ) 45-55CaO

30-40Al

2

O

3

≤10SiO

2

≤10Mgo

≤1.5(TFe + MnO)

with the technology measures including during slagging the lime being added in two separate batch (first in tapping

second at beginning of LF refining) or being added in multi-batch

during LF refining according to slag condition adjusting ingredient of slag

and bottom gas blowing rate 500-700 L/min during LF desulphurization period

the sulphur content in liquid-

[S

]

could be decreased to lower than 10 x 10

-6

in 40 min to meet the requirement of quick deep desulphurization for pipeline steel.