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