SEAMLESS HIGH-STRENGTH MARTENSITIC STEEL PIPE FOR CASING AND ITS MANUFACTURING METHOD Russian patent published in 2023 - IPC C21D8/10 B21C37/06 C22C38/50 

FIELD: metallurgy.

SUBSTANCE: invention is related to production of high-strength seamless steel pipes from high-alloy martensitic steel for construction of casing strings and related products from pipe billets in commercial production of hydrocarbons and their transportation. The pipe is obtained from steel containing components in the following ratio, in % by weight: carbon 0.04-0.08, manganese 0.30-0.80, chromium 12.0-14.0, nickel 3.80-4.50, silicon 0.15-0.50, vanadium 0.010-0.110, molybdenum 0.80-1.30, aluminium 0.010-0.050, titanium 0.01-0.06, nitrogen 0.01-0.04, the rest being iron and inevitable impurities. The pipe has a finely dispersed microstructure consisting of tempered martensite with uniformly distributed carbonitride precipitates and residual austenite with a content not exceeding 5% of volume. The content of chemical elements in steel simultaneously meets the following conditions: 13.0≤([Cr]+[Mo]+1.5×[Si])≤16.05, 4.7≤([Ni]+20×[C]+0.3×[Mn]+1.5×[V])≤6.5, 1.25≤([Ti]+[C])/[N]≤14.0, where Cr, Mo, Si, Ni, C, Mn, V, Ti, N are the content of chromium, molybdenum, silicon, nickel, carbon, manganese, vanadium, titanium and nitrogen in steel, respectively, in % by weight.

EFFECT: required strength and viscoplastic characteristics of pipes are ensured by obtaining a finely dispersed microstructure of tempered martensite with uniformly distributed carbonitride precipitates and residual austenite and improving the quality of pipes.

2 cl, 1 dwg