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

Abstract

A seamless pipe of martensitic stainless steel for use as an oil well pipe. The seamless pipe is obtained by subjecting a seamless stainless-steel pipe having a composition containing, in terms of mass%, up to 0.020% carbon, 10-14% chromium, up to 3% nickel, up to 0.05% nitrogen, and 0.03-0.2% niobium, with the remainder being iron and inevitable impurities, to quenching in which the pipe is heated to a quenching temperature not lower than the Ac3 transformation point and then cooled to a temperature of 100 DEG C or lower at a cooling rate not lower than those of air cooling and, subsequently to the quenching, to tempering in which the pipe is heated to a tempering temperature not lower than 550 DEG C and then cooled. This seamless pipe has a tempered martensitic structure in which the amount of niobium precipitated is 0.020% or larger. The pipe combines high strength including a yield strength (YS) in the 95-ksi class (665-758 MPa) with excellent low-temperature toughness including a vTrs of -40 DEG C or lower. The seamless pipe can be subjected to warm straightening. Also provided is a process for producing the seamless pipe.

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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