The process flow sheet to melt microalloying pipeline steel X80 is 300 t top and bottom combined blowing converter-ladle argon blowing and microalloying-LF-RH. With converter gas-dynamic slag stopper to control tapping slag a- mount ≤4 kg/t； ladle top and bottom blowing argon blowing for 6 min with aluminium bullet shooting； controlling LF top slag CaO/Al

2

O

3

= 1. 7 -1.9

basicity of slag (CaO/SiO

2

) = 4. 5 ~6 and (FeO + MnO) ≤l. 0% ； with feeding FeCa wire 0. 8 kg/t during RH refining process

the T [O

]

is decreased to 13 x 10

-6

the inclusion size ≤10 μm and the ≤5 μm inclusions account for 98. 93% of the total inclusions

and the A1

2

O

3

spinel inclusions are modified to CaO-MgO-Al

2

O

3

series ternary inclusions. The inclusion amount

size

morphology and ingredient

of inclusions during melting process are analyzed to get the modification regulation of inclusions in pipeline steel.