LOW-ALLOYED STEEL PIPE FOR OIL WELL Russian patent published in 2018 - IPC C22C38/32 C22C38/28 

FIELD: metallurgy.

SUBSTANCE: pipe is made of steel having chemical composition including, wt %: C: not less than 0.15 and less than 0.30, Si: 0.05 to 1.00, Mn: 0.05 to 1.00, P: not more than 0.030, S: not more than 0.0050, Al: 0.005 to 0.100, O: not more than 0.005, N: not more than 0.007, Cr: not less than 0.10 and less than 1.00, Mo: more than 1.0 and not more than 2.5, V: 0.01 to 0.30, Ti: 0.002 to 0.009, Nb: 0 to 0.050, B: from 0 to 0.0050, Ca: from 0 to 0.0050, the rest is Fe and impurities. The chemical composition satisfies formula Mo/Cr≥2.0. The pipe has a yield point of not less than 758 MPa and the pipe steel microstructure has a crystal grain size number of a preceding austenite of not less than 7.0 according to ASTM E112, contains 50 or more particles of cementite with diameter of equivalent circle of not less than 200 nm, on the area of 100 mcm² matrices, as well as particles of carbide of alloying element of chemical formula M₂C in amount of not less than 25/mcm².

EFFECT: stable and high resistance to hydrogen sulfide cracking.

5 cl, 8 dwg, 3 tbl