Ferritic heat-resistant steel
a heat-resistant steel and ferritic technology, applied in the field of ferritic heat-resistant steel, can solve the problems of high thermal stress applied easy damage to headers and piping, material cost and process cost, etc., to improve oxidation resistance, increase si, and improve the effect of steam oxidation resistan
Inactive Publication Date: 2011-01-27
FUJITA TOSHIO +1
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Benefits of technology
The steel exhibits significantly improved long-term creep rupture strength and steam oxidation resistance, enabling reliable operation at 650°C with reduced material costs and enhanced durability, thus improving thermal power plant efficiency and reducing fuel consumption and CO2 emissions.
Problems solved by technology
Therefore, when the plant starts or stops, a great thermal stress is applied to these header and piping and the header and piping are easily damaged due to thermal fatigue.
In addition, the increase in material cost and process cost causes an economic problem.
Therefore, it has been found that the creep rupture strength lowers during long-term use for several tens of thousands of hours or longer.
Particularly, at a high temperature around 650° C. much higher than 600° C., so-called fluting that involves sudden lowering in creep strength after about several tens of thousands of hours is a great obstacle in the development of a high-Cr steel (for example, Non-Patent Document 1).
To solve these problems, a special method by addition of noble metals (Non-Patent Document 2) has also been proposed, however, this greatly increases the material cost, so that it has not been made practicable.
Method used
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[0050]Hereinafter, examples / embodiments of the present invention will be described by using actual examples.
[0051]The heat-resistant steels having the chemical compositions shown in Table 1 of the present examples and comparative steels were molten in a vacuum induction melting furnace, and forged into 50 kg ingots, respectively. The comparative steel A is nominal 9Cr1MoNbV steel, comparative steels B and C are nominal 9Cr0.5Mo1.8WNbV steels, and all of these have been made practicable as boiler steels. After forming steel sheets with a thickness of 20 millimeters by hot forging, the steel sheets were normalized at 1,050° C. for 60 minutes and tempered at 780° C. for 60 minutes, and then subjected to a creep rupture test. In addition, small-sized sheet-like test specimens were processed from the steel sheets, and subjected to an oxidation test by using steam at 650° C.
TABLE 1(wt %)CSiMnPSCrMoWVNbNiSteel A of the present invention0.0430.510.500.0030.0018.90.451.800.190.0510.005Steel ...
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Abstract
Disclosed is a ferritic heat-resistant steel which has the following chemical composition (by weight): C: from 0.01% to less than 0.08%; Si: 0.30-1.0%; P: 0.02 or less; S: 0.010% or less; Mn: 0.2-1.2%; Ni: 0.3% or less; Cr: 8.0-11.0%; Mo: 0.1-1.2%; W: 1.0-2.5%; V: 0.10-0.30%; Nb: 0.02-0.12%; Co: 0.01-4.0%; N: 0.01-0.08%; B: not less than 0.001% and less than 0.010%; Cu: 0.3% or less; and Al: 0.010% or less, provided that the chemical composition satisfies the following equations: Mo (%)+0.5×W (%)=1.0-1.6, and C (%)+N (%)=0.02-0.15%, and which comprises a tempered martensite single-phase tissue produced by thermal refining and contains 30% by weight or less of δ ferrite.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The present application is a continuation of U.S. patent application Ser. No. 12 / 278,306, which is a National Stage of International Application No. PCT / JP2007 / 051968, filed Feb. 6, 2007, which claims priority under 35 U.S.C. §119 of Japanese Patent Application 2006-029009, filed Feb. 6, 2006. The entire disclosure of the parent application is expressly incorporated by reference herein.TECHNICAL FIELD[0002]The present invention relates to a ferritic heat-resistant steel, and more specifically, to a high-strength steel for boiler steel pipes suitable for an ultra supercritical pressure thermal power plant with improved power generation efficiency.BACKGROUND ART[0003]Recently, in thermal power plants, the temperature and pressure of steam conditions have been raised for improvement in plant efficiency in view of global environmental issues such as CO2 emissions reduction. Now, plants which can raise the steam temperature from the current ma...
Claims
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IPC IPC(8): C22C38/22C22C38/32C22C38/24C22C38/26C22C38/30C22C38/44C22C38/54
CPCC21D8/105C22C38/54C21D9/085C21D2211/005C21D2211/008C22C38/001C22C38/02C22C38/04C22C38/22C22C38/24C22C38/26C22C38/30F22B37/04F22B37/10C22C38/46C22C38/44C22C38/42C22C38/06C22C38/52C22C38/48C21D9/08
InventorSATO, TAKASHITAMURA, KOHJIFUJITA, TOSHIO
OwnerFUJITA TOSHIO