Low-yield-ratio seamless steel tube and manufacturing method thereof

Abstract

The invention relates to a low-yield-ratio seamless steel tube and a manufacturing method thereof. The chemical components of the seamless steel tube comprise, by mass, 0.30-0.40% of C, 0.25-0.5% of Si, 0.4-0.7% of Mn, 0.025% or less of P, 0.020% or less of S, 0.035-0.055% of Ti, 0.05-0.18% of RE, and the balance Fe and unavoidable impurities. The seamless steel tube is structurally characterizedin that the structure is a B-F composite structure or a B-F-M composite structure, wherein B is strip-like bainite, F is block-like or granular or strip-like ferrite, and M is martensite. The yield ratio of the seamless steel tube produced by means of the method can reach 0.85 or below, the yield strength reaches the steel grade of 650 MPa or above, and the low-yield-ratio seamless steel tube canbetter meet the requirements of oil and gas exploitation and other industries for tube products.

Description

technical field [0001] The invention relates to the technical field of seamless steel pipe production, in particular to a low yield ratio seamless steel pipe and a manufacturing method thereof. Background technique [0002] With the development of high-strength materials used in construction machinery, construction, containers, oil and gas exploration and other fields, the safety of materials has attracted more and more attention. The yield ratio reflects the cold deformation ability and plastic deformation ability of steel. Considering the safety of components, achieving a low yield ratio of materials has always been a goal pursued by the industry. [0003] As far as the industrial design of steel for oil and gas development is concerned, it has been successful to achieve a yield ratio of less than 0.85 for seamless pipes with a yield strength of less than 550 MPa. For example, the Chinese patent application number CN200710093884 discloses a K55 steel grade petroleum casi...

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Problems solved by technology

For example, the Chinese patent application number CN200710093884 discloses a K55 steel grade petroleum casing, the steel pipe yield ratio can be less than 0.85, but its disadvantage is that the upper limit of the yield strength is only 552MPa

At present, the mainstream strength steel grade of oil and gas exploitation has been upgraded from 55ksi steel grade to 80ksi steel grade or even higher. Therefore, the technical solution of this invention can no longer meet the requirements for the use of low yield ratio seamless steel pipes in current and future oil and gas exploitation projects. , the scope of application of its products is severely limited

[0004] The Chinese patent with the application number CN201010221546 discloses a seamless steel pipe of X70QS steel grade, which satisfies the technical indicators by adding a large number of types and quantities of alloying elements, but can only achieve a yield strength ratio of ≤0.9, and the upper limit of the yield strength cannot Breaking through 635MPa, the use safety is not high, and the application range is limited;

[0005] The Chinese patent application number CN201410175317 discloses a high-strength plastic vanadium microalloyed dual-phase steel seamless pipe, but because it mainly uses the principle of TRIP effect to obtain a low yield ratio, it is bound to sacrifice the yield strength of the material as a premise. As a result, the upper limit of the yield strength of the product failed to exceed 635MPa

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