SEAMLESS STEEL PIPE AND METHOD OF ITS PRODUCTION Russian patent published in 2019 - IPC C22C38/58 C22C38/50 C21D8/10 C21D9/08 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to seamless steel pipe used as main pipe for oil and gas transportation. Pipe has the following chemical composition, wt%: C: from 0.02 to 0.15, Si: from 0.05 to 0.5, Mn: from 0.30 to 2.5, P: up to 0.03, S: up to 0.006, O: up to 0.004, Al: 0.01 to 0.10, Ti: 0.001 to 0.010, N: up to 0.007, Cr: 0.05 to 1.0, Mo: not less than 0.02 and less than 0.5, Ni: from 0.03 to 1.0, Cu: from 0.02 to 1.0, V: from 0.020 to 0.20, Ca: from 0.0005 to 0.005, Nb: from 0 to 0.05, the rest is iron and impurities. Main phase of microstructure from surface layer to middle in wall thickness is martensite of tempering or bainite tempering. Size of pre-urethane grains in microstructure according to scale of crystal grains ASTM E112-10 is less than 6.0. Part located between position spaced 1 mm from the inner surface and position spaced 1 mm from the outer surface has a Vickers hardness of 250 Hv or lower and a carbon equivalent of Ceq of not less than 0.430 % and less than 0.500 %.

EFFECT: pipe has yield point of not less than 555 MPa, as well as high resistance to sulphide cracking under stress.

6 cl, 9 dwg, 4 tbl