HIGH-STRENGTH SEAMLESS STEEL PIPE FOR OIL-FIELD PIPE ARTICLES AND METHOD FOR MANUFACTURE THEREOF Russian patent published in 2018 - IPC C21D8/10 C22C38/00 C21D9/08 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy. To increase resistance to sulphide stress-corrosion cracking, seamless steel pipe contains, in wt%: C from 0.20 to 0.50, Si from 0.05 to 0.40, Mn from 0.3 to 0.9, Al from 0.005 to 0.1, N 0.006 or less, Cr from more than 0.6 to 1.7 or less, Mo from more than 1.0 to 3.0 or less, V from 0.02 to 0.3, Nb from 0.001 to 0.02, B from 0.0003 to 0.0030, O (oxygen): 0.0030 or less and Ti from 0.003 to 0.025, when the Ti/N ratio is satisfied: from 2.0 to 5.0, wherein the seamless steel pipe has a microstructure including a phase of tempered martensite with a volume fraction of 95 % or more, a primary austenite phase having a grain size of 8.5 or more, and in a cross section perpendicular to the rolling direction, the inclusion number on a nitride base with a particle size of 4 mcm or more and a number of 100 or less, calculated per 100 mm², inclusions on a nitride base with a particle size of less than 4 mcm and a number of 1,000 or less, calculated per 100 mm², inclusions on an oxide base with a particle size of 4 mcm or more and a number of 40 or less, per 100 mm² and inclusions on an oxide base with a particle size smaller than 4 mcm with a number of 400 or less, calculated per 100 mm².

EFFECT: higher resistance to sulphide stress corrosion cracking.

4 cl, 3 tbl