Seamless pipe of martensitic stainless steel for oil well pipe and process for producing same

Abstract

A seamless steel tube for OCTG which possesses both of high strength of yield strength YS of 95 ksi grade (665 to 758 MPa) and excellent low-temperature toughness, and a manufacturing method of the seamless steel tube are provided. To be more specific, to a stainless steel seamless tube having the composition which contains, by mass%, 0.020% or less C, 10 to 14% Cr, 3% or less Ni, 0.05% or less N, 0.03 to 0.2% Nb, and optionally further, 1.0% or less Si, 0.1 to 2.0% Mn, 0.020% or less P, 0.010% or less S, 0.10% or less Al, and Fe and unavoidable impurities as a balance, quenching in which the seamless tube is heated at a quenching temperature of A c3 transformation temperature or above and, thereafter, the seamless tube is cooled to a temperature range of 100°C or less at a cooling rate of air cooling or more, and tempering which follows the quenching and in which the seamless tube is heated at a tempering temperature of 550°C or above and is cooled are applied. Due to such treatment, a martensitic stainless steel seamless tube for country tubular goods which has the tempered martensitic structure where a precipitated Nb quantity is 0.020% or more, and possesses both of high strength at yield strength of 95 ksi grade and the excellent low-temperature toughness of fracture transition temperature vTrs of -40°C or below, and allows the hot straightening. In addition to the above-mentioned composition, the seamless steel tube may further contain one or two kinds of elements selected from Cu, Mo and / or one or two kinds selected from V, Ti, B in addition to the above-mentioned composition.

Description

technical field [0001] The present invention relates to a martensitic stainless steel seamless tube for Oil Country Tubular Goods, and in particular, to a high strength with a yield strength YS of 95 ksi (655 MPa) or more and excellent mechanical properties. A low-temperature toughness seamless steel tube for oil country tubular goods (seamless steel tube for OCTG) and a manufacturing method thereof. Background technique [0002] In recent years, from the perspective of rising crude oil prices and the expected exhaustion of petroleum resources in the near future, deep oil fields (oil wells) that have not been paid attention to before, carbon dioxide (carbon dioxide gas) ), chlorine ion (chlorine ion) and other severe corrosion environment (gas field) oil field or gas field (gas field), and alpine area (cold district) or seabed (seabed) and other oil fields with severe drilling environment (drilling environment), etc. Development gradually prevailed. Steel pipes for oil wel...

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Problems solved by technology

[0005] However, when tempering is performed at a low temperature of 450° C. or lower using the technique described in JP 2002-363708 A, since straightening after the tempering treatment is performed at a low temperature, Processing strain is introduced during straightening, and there is a problem that the variation in steel pipe properties, especially the yield strength YS increases

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