| 摘要 |
The present invention provides high strength welded steel pipe for line pipe inexpensive in cost and superior in low temperature toughness, and a method of production of the same, produced by forming a base material steel plate containing, by mass %, C: 0.010 to 0.050%, Si: 0.01 to 0.50%, Mn: 0.50 to 2.00%, S: 0.0001 to 0.0050%, and Ti: 0.003 to 0.030%, limiting Al to 0.020% or less and Mo to less than 0.10%, having a carbon equivalent Ceq of 0.30 to 0.53 and a crack susceptibility parameter Pcm of 0.10 to 0.20, comprised of polygonal ferrite and residual bainite of an area rate of 20% or less, and having an effective crystal grain size of 20 μm or less, into a pipe shape, then seam welding it and making the effective crystal grain size of the heat affected zone 150 μm or less. |
