FIELD: metallurgy.
SUBSTANCE: pipe is fabricated by double sided one-layer hidden electric-arc welding on internal and external surface of basic material. Basic metal of the welded steel pipe and metal of welding seam have tensile strength 800 MPa or higher. Metal of the welding seam contains wt %, C: from 0.04 to 0.09, Si: from 0.30 to 0.50, Mn: from 1.4 to 2.0, Cu: less 0.5, Ni: over 0,9, but less 4.2, Mo: from 0.4 to 1.6, Cr: less 0.3, V: less 0.2 and the rest - Fe and unavoidable impurities. Value of CS calculated on assumption of composition of metal of welding seam by equation (1) is equal to zero or higher both on internal and internal surface, where CS=5.1+1.4[Mo]-[Ni]-0.6[Mn]-36.3[C] (l). Basic metal contains wt % C: from 0.03 to 0.12, Si: from 0.01 to 0.5, Mn: from 1.5 to 3.0, Al: from 0.01 to 0.08, Nb: from 0.01 to 0.08, Ti: from 0.0005 to 0.024, N: from 0.001 to 0.01, O: 0.004 or less, S: 0.002 or less, Ca: from 0.0005 to 0.01, at least one element chosen from group, including Cu: from 0.01 to 1.3, Ni: from 0.1 to 3.0, Mo: from 0.01 to 1.0, Cr: from 0.01 to 1.0, and V: from 0.01 to 0.1, and the rest: Fe and unavoidable impurities.
EFFECT: high strength steel pipe has tensile strength 800 MPa or higher, metal of welding seam of which has high resistance to cold cracking and high low temperature ductility.
2 cl, 2 dwg, 7 tbl, 17 ex
