SEAMLESS HIGH-STRENGTH PIPE OF STEEL OF MARTENSITE GRADE FOR CASING STRINGS AND ITS PRODUCTION METHOD Russian patent published in 2022 - IPC C21D8/10 B21C37/06 C22C38/46 

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely to the production of high-strength seamless steel pipes of steel of a martensite grade for construction of casing strings and related products of pipe workpieces in commercial production of hydrocarbons and their transportation. A steel workpiece contains components in the following ratio, wt.%: carbon 0.04-0.08, manganese 0.30-0.80, chrome 12.0-14.0, nickel 3.80-4.50, silicon 0.15-0.50, vanadium 0.010-0.110, molybdenum 0.80-1.30, aluminum 0.010-0.050, iron and unavoidable impurities is the rest, while satisfying following conditions: 13.0≤([Cr]+[Mo]+1.5×[Si])≤16.05 and 4.7≤([Ni]+20×[C]+0,3×[Mn]+1.5×[V])≤6.5, where Cr, Mo, Si, Ni, C, Mn, V are a content in steel of chrome, molybdenum, silicon, nickel, carbon, manganese, and vanadium, respectively, wt.%. The workpiece is subjected to hot deformation at a temperature of 900÷1250°C to obtain a pipe with a molded single-phase austenite microstructure and to subsequent thermal processing of the pipe. During thermal processing, heating for austenitization, cooling on air or in a water-air mixture, and subsequent release are carried out. Heating for austenitization is carried out to a temperature of Ac₃+(180÷230°C). As release, high release is carried out with heating to a temperature of Ac₁-(20÷150)°C with exposure at this temperature for at least 6 min per 1 mm of a thickness of a pipe wall and subsequent cooling on calm air to form a thin-dispersed microstructure consisting of released martensite and residual austenite with a content not exceeding 5 vol.%.

EFFECT: required strength and viscoelastic characteristics of pipes and increase in their quality.

2 cl, 2 dwg