FIELD: metal industry.
SUBSTANCE: invention relates to metal industry, in particular to a welded steel pipe used in oil and natural gas transportation pipelines. The pipe is obtained by forming a 6-20 mm thick steel sheet in cylindrical by welding both ends in direction of steel sheet width and performing a single layer submerged arc welding both on inside and outside surface. The steel plate has a chemical composition containing, in wt%: C: 0.030-0.080, Si: 0.10-0.50, Mn: 1.00-2.00, P: 0.010 or less, S: 0.005 or less, Cu: 0.05 or less, Ni: 0.05 or less, Cr: 0.50 or less, Mo: 0.20 or less, Nb: 0.05 or less, V: 0.100 or less, Ti: 0.050 or less, Al: 0.01-0.05, Ca: 0.0005-0.0050, Mg: 0.0003-0.0100, REM: 0.020 or less, the rest Fe and inevitable impurities. The weld metal on the inside of the surface has a chemical composition containing, in wt%: C: 0.030-0.060, Si: 0.50 or less, Mn: 0.80-1.80, Cu: 0.05 or less, Ni: 0.05 or less, Cr: 0.30 or less, Mo: 0.10 or less, Nb: 0.040 or less, V: 0.010 or less, Ti: 0.010-0.040, B: 0.0015-0.0040, Al: 0.030 or less, O: 0.020-0.040, N: 0.007 or less, the rest Fe and inevitable impurities, the index indicating the weld metal (Pcm) hardenability is 0.140-0.180. The weld metal on the outer surface has a chemical composition containing, in wt%: C: 0.030-0.060, Si: 0.50 or less, Mn: 0.80-1.80, Cu: 0.05 or less, Ni: 0.05 or less, Cr: 0.30 or less, Mo: 0.20 or less, Nb: 0.040 or less, V: 0.010 or less, Ti: 0.010-0.040, B: 0.0015-0.0060, Al: 0.030 or less, O: 0.020-0.040, N: 0.007 or less, and remaining Fe and inevitable impurities, the Pcm is 0.140-0.185.
EFFECT: pipe has the required mechanical properties.
6 cl, 5 dwg, 9 tbl, 1 ex
