HIGH-STRENGTH WELDED STEEL PIPE AND METHOD OF ITS PRODUCTION Russian patent published in 2014 - IPC C22C38/14 B21C37/08 

FIELD: metallurgy.

SUBSTANCE: steel sheet parent metal comprises the following components, in wt %: 0.010-0.080%, Si: 0.01-0.50%, Mn: 0.50-2.00%, S: 0.0001-0.0050%, Ti: 0.003-0.030%, Mo: 0.05-1.00%, B: 0.0003-0.0100%, O: 0.0001-0.0080%, N: 0.006-0.,0118%, P: at least 0,050% or smaller, Al: at least 0.008% or smaller, Fe and unavoidable impurities making the rest. Carbon equivalent (Ceq) makes 0.30 to 0.53, crack growth resistance in welding (Pcm) makes 0.10 to 0.20, while [N]-[Ti]/3.4 does not exceed 0.003. Mean size of primary γ-grains in thermal effects zone in steel sheet makes 250 mcm or smaller, while primary γ-grains include bainite and intragranular bainite.

EFFECT: sufficient low-temperature toughness.

9 cl, 3 dwg, 2 tbl, 1 ex