HIGH-STRENGTH SEAMLESS STEEL PIPE FOR USE IN OIL WELL, HIGH RESISTANCE TO CRACKING UNDER STRESSES IN SULPHIDE-BEARING MEDIUM Russian patent published in 2017 - IPC C22C38/32 C21D8/10 C21D9/08 C22C38/54 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to a high-strength seamless steel pipe suitable for use in oil wells. Seamless steel pipe is made from steel containing in wt%: C 0.15–0.50, Si 0.1–1.0, Mn 0.3–1.0, P 0.015 or less, S 0.005 or less, Al 0.01–0.1, N 0.01 or less, Cr 0.1–1.7, Mo from 0.40–1.1, V from 0.01–0.12, Nb 0.01–0.08, Ti 0.03 or less, B 0.0005–0.003, Fe and inevitable impurities – the rest. Structure of the steel pipe consists of a tempered martensite phase as the main phase and a former austenitic grain with the grain size of 8.5 or more. On four sections located at 90° from each other on a circumference hardness as per Vickers scale HV10 measured at the load of 10 kgf is equal to 295 HV10 or less in each of the three areas: in the area on the inner surface side at a distance from 2.54 to 3.81 mm from the inner surface of the pipe in the direction of its thickness, in the area on the outer surface side at a distance from 2.54 to 3.81 mm from the outer surface of the pipe in the direction of its thickness, and in the area in the center of the pipe wall thickness.

EFFECT: pipe is characterized by high resistance to cracking under stresses in a sulphide-bearing medium.

16 cl, 1 dwg, 3 tbl