FIELD: metallurgy.
SUBSTANCE: invention relates namely to flexible steel pipes and methods for manufacturing flexible steel pipes. The flexible steel pipe comprises steel strips end-to-end butt-welded with fillet welds and formed into a pipe by welding, each strip being made of C-Mn steel, B-Ti steel or Cr-Mo steel. The pipe has areas of the base metal, welds and their heat-affected zones. The pipe has a yield strength in excess of 80 ksi and a final microstructure containing a mixture of tempered martensite and bainite. At the same time, the final microstructure of the flexible pipe in all areas of the base metal, on welds and in heat-affected zones, consisting of tempered martensite more than 90% by volume, is homogeneous with a grain size of less than 20 mcm, and has a uniform distribution of fine-grained carbides.
EFFECT: resulting flexible pipes are characterized by high strength.
17 cl, 18 dwg, 6 ex
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