The mechanical properties and micro structure of microalloying pipeline steel X70 ( % ：0. 04C

1. 54Mn

0. 05Nb

0. 04V

0. 01Ti

0.003 9N) of 14. 6 mm sheet continuous rolled from 150 mm casting slab have been tested and analyzed. Results show that with adding micro niobium and after breakdown with control rolling by deformation N70% at ≤950 °C

finishing rolling at 800 ℃

then cooling to 500 -550 °C with 20 ~30 ℃/s

the structure of X70 pipeline steel at ambient temperature is typical acicular ferrite with grain size 2 ~ 5 μm

which has excellent comprehensive mechanical properties i. e. σ

0.5

≥565 MPa

σ

b

≥655 MPa and Cv at -20℃≥212 J.