High strength thick welded steel pipe for line pipe superior in low temperature toughness and method of production of the same

摘要

The present invention provides high strength thick welded steel pipe for line pipe superior in low temperature toughness, and a method of production of the same. A base material steel plate containing C: 0.010 to 0.050%, Si: 0.01 to 0.50%, Mn: 0.50 to 2.00%, Al: 0.020% or less, Ti: 0.003 to 0.030%, and Mo: 0.10 to 1.50%, having a carbon equivalent Ceq of 0.30 to 0.53, having a crack susceptability parameter Pcm of 0.10 to 0.20, satisfying formula 3, comprised an area ratio of 20% or less of polygonal ferrite and an area ratio of 80% or more of bainite, and having an effective crystal grain size of 20 μm or less is formed into a pipe shape, then seam welded to make the effective crystal grain size of the heat affected zone 150 μm or less:10C+100Al+5Mo+5Ni3.3  formula 3.