Steel member and its manufacturing method
A manufacturing method and technology of steel components, applied in the direction of manufacturing tools, furnace types, furnaces, etc., can solve problems such as difficulty in practical use and reduced productivity of rolling lines, and achieve the effects of cost reduction, alloy element suppression, and resource conservation
Inactive Publication Date: 2016-04-27
KOBE STEEL LTD
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Problems solved by technology
However, in this technique, if an extremely thick material with a plate thickness of more than 100 mm is produced, the above-mentioned controlled rolling will significantly reduce the productivity of the rolling line, so it is difficult to say that it is practical.
Method used
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[0047] In order to obtain a steel member, the inventors of the present invention are composed of Cr-Mo steel (for example, 1.25Cr-0.5Mo grade steel) whose alloy element amount is suppressed compared with the above-mentioned 2.25Cr-1.0Mo steel, and use a plate thickness of It is assumed that a thick steel plate of 90 mm or more (hereinafter referred to simply as "steel plate") is a steel member that is excellent in toughness (low temperature toughness) and strength at the central part of the plate thickness even when PWHT is performed for a particularly long time on this thick steel plate, And repeated painstaking research.
[0048] As a result, in order to ensure the high toughness of the central part of the plate thickness of the steel member, it was found that it is particularly effective based on the following points:
[0049] · Become a fine tissue. Specifically, (a) it is at least one of tempered bainite and tempered martensite, and (b) the grains are surrounded by high-...
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Abstract
Provided is a steel member which is obtained using a thick steel plate and in which the inner zone (thicknesswise central zone) of the steel material exhibits high strength and high toughness even in a case where the steel member has undergone high-temperature and long-time post-welding heat treatment. The steel member has a prescribed composition and is characterized in that the texture of a thicknesswise central zone of the plate satisfies all the requirements (a) to (d): (a) the texture is tempered bainite and / or tempered martensite; (b) the mean equivalent circle diameter of grains that are each surrounded by a large-angle grain boundary where the misorientation between two adjacent grains is 15 or more is 20 µm or less; (c) the maximum diameter of grain-boundary carbides is 0.8 µm or less; and (d) the fraction of grain-boundary carbides is 1.0% by area or more.
Description
technical field [0001] The present invention relates to steel components and methods for their manufacture. Specifically, the present invention relates to a steel member obtained by performing welding and post-weld heat treatment (PWHT) on a thick steel plate, and particularly relates to a steel member having excellent strength and toughness at the central part of the plate thickness even if the PWHT is at a high temperature for a long time. its method of manufacture. Background technique [0002] For the purpose of improving operation efficiency, medium and high temperature pressure vessels used in the chemical industry including petroleum refining tend to require further high temperature and high pressure resistance. Therefore, steel sheets used for steel members such as the pressure vessels described above are required to be thicker and stronger. In addition, from the viewpoint of safety, a high level of toughness is also required for the above-mentioned steel members. ...
Claims
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IPC IPC(8): C22C38/00C21D6/00C21D9/50C22C38/54
CPCC22C38/54C21D6/00C21D9/50C21D2211/002C21D2211/008C22C38/00C22C38/001C22C38/02C22C38/04C22C38/06C22C38/42C22C38/44C22C38/46
Inventor 山口彻雄
Owner KOBE STEEL LTD