The X65 pipeline steel 13MnNbTi (% ： 0. 10 ~Q 16C

1.20 ~ 1.40Mn

0. 03 ~0. 05Nb

0.01 ~0. 02Ti

0.025 ~0. 05Al) is pilot-produced by 120 t top and bottom combined blown converter-100 t LF (VD) -5 strands Φ300 mm round bloom casting flow sheet at steelmaking plant

Baotou Steel Union Co Ltd. Production practice shows that it is available by desulphurization of hot metal ([S

]

≤0. 005% )

using slag stopper during converter tapping

basicity of refining slag ≥3. 0

VD treatment ≥13 min

to get [S

]

≤0. 005%

[P

]

≤0. 015% and [ H

]

≤1.5 x 10

-6

. With shielding casting in whole process and mold electromagnetic stirring

the oxygen content in steel is (13 ~21) x I0

-6

average oxygen content is 16. 44 x 10

-6

the surface quality of bloom is fine and the rating of macrostructure is 0 ~ 1.