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Martensitic Creep Resistant Steel Strengthened by Z-Phase

a martensitic or martensiticferritic steel alloy technology, applied in the field of martensitic or martensiticferritic steel alloys, can solve the problems of unexpected breakdown of creep strength to strength levels below those of the currently available steels, high temperature properties of materials used in boilers, steam lines and turbines, etc., to achieve the effect of improving long-term creep properties

Inactive Publication Date: 2010-04-15
DANMARKS TEKNISKE UNIV +1
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  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0009]It is an object of the present invention to provide a martensitic or martensitic-ferritic steel alloy with improved long-term creep properties compared to presently known materials.
[0011]It is an object of preferred embodiments of the present invention to provide a martensitic or martensitic-ferritic steel alloy in which the good creep properties can be combined with a high corrosion resistance.

Problems solved by technology

A main limiting factor is the high temperature properties of materials used in the boilers, steam lines and turbines.
However, prolonged testing showed unexpected breakdowns in creep strength to strength levels below those of the currently available steels.

Method used

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Embodiment Construction

[0026]Components for use in power plants should be designed to operate at high temperatures and stresses for very long times, preferably more than 30 years. It is not practical to test new materials for so long, and therefore long-term properties are estimated by extrapolating results from shorter-term tests. Double logarithmic plots of test stress vs. rupture time normally show smooth curves, but many 11-12% Cr steels suffer a breakdown in long-term strength and the curves bend after several thousand hours of testing. An example of such bent curves is given in FIG. 1, showing creep test results for a steel with 0.1% C, 11% Cr, 3% Co, 3% W, and minor contents of V, Nb and N.

[0027]High long-term creep strength of steel alloys has recently been obtained by compositions resulting in precipitation of fine MX nitride particles in the form (V,Nb)N in addition to coarser M23C6 carbide particles. An example of such an alloy is given in FIG. 2, which shows particles in a steel with 0.1% C, 9...

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Abstract

The present invention relates to steel alloys having a martensitic or martensitic-ferritic structure and comprising Z-phase (CrXN) particles, where X is one or more of the elements V, Nb, Ta, and where the Z-phase particles have an average size of less than 400 nm. The alloy comprises by wt % the following components: 9 to 15% Cr, 0.01-0.20% N, C in an amount less than 0.1%, one or more of: 0.01-0.5% V, 0.01-1% Nb, 0.01-2% Ta, and a balance being substantially iron and inevitable impurities. The invention further relates to a method of manufacturing such a steel alloy, a component comprising such a steel alloy, and to the use of such a steel alloy for high temperature components.

Description

FIELD OF THE INVENTION[0001]The present invention relates to martensitic or martensitic-ferritic steel alloys and in particular to creep resistant alloys to be used for high temperature components. The invention further relates to manufacturing of such steels.BACKGROUND OF THE INVENTION[0002]In the field of steam power plants there is strong focus on improving the efficiency of the plants by increase of operating steam temperature and pressure. A main limiting factor is the high temperature properties of materials used in the boilers, steam lines and turbines. These materials have to be designed to operate at high temperatures and stresses for prolonged times, so high creep strength and oxidation resistances are needed in order to keep degradation to a minimum. Tempered martensitic steel alloys offer the best combination of creep strength, oxidation resistance, thermal expansion coefficient and yield strength.[0003]Over the last two decades, several 9% Cr martensitic steel alloys wi...

Claims

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Application Information

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IPC IPC(8): C21D6/00C22C38/26
CPCC22C1/02C22C38/18C22C38/001
Inventor DANIELSEN, HILMARHALD, JOHN
Owner DANMARKS TEKNISKE UNIV
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