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  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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  • C22C19/03—Alloys based on nickel or cobalt based on nickel
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  • C22C—ALLOYS
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  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
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  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite

Definitions

• the present invention relates to an austenitic heat resistant alloy member.
• Austenitic heat resistant alloy members used as materials for superheater tubes and reheater tubes are required to have more excellent creep rupture strength.
• Patent Document 1 discloses an austenitic heat resistant alloy member that has both excellent hot workability and creep rupture strength, which are achieved by strictly controlling the content of S relative to the contents of Ca, Mg, and REM.
• the inventors have conducted detailed studies on the creep rupture strength and the creep rupture ductility, and as a result, obtained the following findings.
• the gist of the present invention which has been completed based on the above-described findings, is an austenitic heat resistant alloy member described below.
• C carbon stabilizes the austenite and forms fine carbide in a grain boundary, leading to the improvement of the creep rupture strength at high temperature.
• the content of C needs to be 0.010% or more.
• the carbide will be coarsened and precipitate in large amounts, leading to the degradation of ductility of the grain boundary and also the degradation of toughness and the creep rupture strength.
• the content of C is 0.010 to 0.150%.
• the content of C is preferably 0.030% or more, and more preferably 0.050% or more.
• the content of C is preferably 0.120% or less, and more preferably 0.100% or less.
• Si silicon
• Si has a deoxidation function and is an element that is effective for improving corrosion resistance and oxidation resistance at high temperature.
• the stability of the austenite degrades, leading to the degradation of toughness and the creep rupture strength. Accordingly, the content of Si is 2.00% or less.
• the content of Si is preferably 1.50% or less, and more preferably 1.00% or less.
• the content of Si is preferably 0.02% or more, and more preferably 0.05% or more.
• the content of Mn is preferably 0.005% or more, and more preferably 0.010% or more.
• S sulfur
• the content of S is 0.0100% or less.
• the content of S is preferably 0.0095% or less, and more preferably 0.0090% or less.
• Cr chromium
• Cr is dissolved in a matrix and is an element that significantly contributes to the improvement of the creep rupture strength at high temperature. Furthermore, Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperature.
• the content of Cr needs to be 20.00% or more. However, when the content of Cr exceeds 28.00%, the stability of the austenite at high temperature degrades, leading to the degradation of the creep rupture strength. Accordingly, the content of Cr is 20.00 to 28.00%.
• the content of Cr is preferably 21.00% or more, and more preferably 22.00% or more. Furthermore, the content of Cr is preferably 27.00% or less, and more preferably 26.00% or less.
• Ni nickel
• Ni nickel
• Ni is dissolved in a matrix and is an element that significantly contributes to the improvement of the creep rupture strength at high temperature.
• Ni is an element that is effective for obtaining the austenite and is an essential element for securing the stability of the microstructure when being used for a long time.
• the content of Ni needs to be 35.00% or more.
• Ni is an expensive element, and when contained in large amounts, leads to an increase in costs. Accordingly, the content of Ni is 35.00 to 50.00%.
• the content of Ni is preferably 37.00% or more, and more preferably 39.00% or more.
• the content of Ni is preferably 48.00% or less, and more preferably 46.00% or less.
• W tungsten
• W is dissolved in a matrix and is an element that significantly contributes to the improvement of the creep rupture strength at high temperature.
• the content of W needs to be 4.00% or more.
• excessively contained W leads only to the saturation of the effect, and what is worse, the creep rupture strength degrades.
• W is an expensive element, costs will increase when excessively contained. Accordingly, the content of W is 4.00 to 10.00%.
• the content of W is preferably 5.00% or more, and more preferably 6.00% or more.
• the content of W is preferably 9.00% or less, and more preferably 8.00% or less.
• Nb niobium
• C, or C and N precipitates in grains as fine carbide or carbo-nitride, and contributes to the improvement of the creep rupture strength at high temperature.
• the content of Nb needs to be 0.01% or more.
• an excessive content of Nb leads to the precipitation of a large amount of carbide carbo-nitride, and the degradation of the creep rupture ductility and toughness.
• the content of Nb is 0.01 to 1.00%.
• the content of Nb is preferably 0.05% or more, and more preferably 0.10% or more.
• the content of Nb is preferably 0.80% or less, and more preferably 0.60% or less.
• N nitrogen
• nitrogen is an element that is effective for stabilizing the austenite, whereas when excessively contained, a large amount of fine nitride precipitates in grains during the use at high temperature, leading to the degradation of the creep rupture ductility and toughness. Accordingly, the content of N is 0.0200% or less.
• the content of N is preferably 0.0180% or less, and more preferably 0.0150% or less.
• the content of N is preferably 0.0005% or more, and more preferably 0.0008% or more.
• Al (aluminum) is an element that has a deoxidation function, and therefore, the content of Al needs to be 0.010% or more. However, an excessive content of Al leads to a significant degradation of cleanliness of alloy, and the degradation of hot workability and ductility. Accordingly, the content of Al is 0.010 to 0.300%.
• the content of Al is preferably 0.030% or more, and more preferably 0.050% or more.
• the content of Al is preferably 0.250% or less, and more preferably 0.200% or less.
• B boron
• B is an element that is necessary to improve the creep rupture strength by segregating in a grain boundary during the use at high temperature to strengthen the grain boundary and finely dispersing grain boundary carbide.
• the content of B needs to be 0.0005% or more.
• an excessive content of B leads to the degradation of weldability and the degradation of hot workability.
• the content of B is 0.0005 to 0.0400%.
• the content of B is preferably 0.0010% or more, and more preferably 0.0020% or more.
• the content of B is preferably 0.0300% or less, and more preferably 0.0200% or less.
• the balance is Fe and impurities.
• impurities refer to components that are introduced due to various factors in raw materials such as ore and scrap and production processes when the alloy is industrially produced and that are acceptable to the extent that they do not adversely affect the present invention.
• the austenitic heat resistant alloy of the present invention may further contain one or more elements selected from Ca, Mg, REM, Co, Cu, Mo, and V to the extent indicated below. Note that since these elements are not essential for the member, the lower limit value of the content is 0%. The reason for limitation for each element will be described.
• an ingot or a cast piece that has the above-described chemical composition is subjected to hot working, followed by different types of hot working such as hot extrusion as necessary, and thereafter, a solution heat treatment is carried out. Furthermore, cold working may be carried out as necessary.
• the solution heat treatment temperature T was low, and therefore, recrystallization did not occur, leading to the degradation of the creep rupture ductility.
• Cr, W, Fe, and Ni could not sufficiently be dissolved, leading to the degradation of the creep rupture strength.
• the solution heat treatment time t r was short, and therefore, Cr, W, Fe, and Ni could not sufficiently be dissolved, leading to the degradation of the creep rupture strength.
• the austenitic heat resistant alloy member of the present invention is excellent in both the creep rupture strength and the creep rupture ductility for a long time. Accordingly, the austenitic heat resistant alloy member of the present invention is suitably used as a material for superheater tubes or reheater tubes of power generation boilers.

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