# Patent

## Title
Nickel-chromium-aluminum alloy having good processability, creep resistance and corrosion resistance

## Abstract

A nickel-chromium-aluminum-iron alloy includes (in wt.-%) 24 to 33% chromium, 1.8 to 4.0% aluminum, 0.10 to 7.0% iron, 0.001 to 0.50% silicon, 0.005 to 2.0% manganese, 0.00 to 0.60% titanium, 0.0002 to 0.05% each of magnesium and/or calcium, 0.005 to 0.12% carbon, 0.001 to 0.050% nitrogen, 0.0001 to 0.020% oxygen, 0.001 to 0.030% phosphorus, not more than 0.010% sulfur, not more than 2.0% molybdenum, not more than 2.0% tungsten, the remainder nickel and the usual process-related impurities, wherein the following relations must be satisfied: Cr+Al≧28 (2a) and Fp≦39.9 (3a) with Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C (4a), wherein Cr, Fe, Al, Si, Ti, Mo, W and C is the concentration of the respective elements in % by mass.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the National Stage of PCT/DE2013/000268 filed on May 15, 2013, which claims priority under 35 U.S.C. §119 of German Application No. 10 2012 011 161.4 filed on Jun. 5, 2012, the disclosure of which is incorporated by reference. The international application under PCT article 21(2) was not published in English.
The invention relates to a nickel-chromium-aluminum alloy with excellent high-temperature corrosion resistance, good creep resistance and improved processability.
Austenitic nickel-chromium-aluminum alloys with different nickel, chromium and aluminum contents have long been used in furnace construction and in the chemical as well as petrochemical industry. For this use, a good high-temperature corrosion resistance even in carburizing atmospheres and a good heat resistance/creep resistance are necessary.
In general, it may be remarked that the high-temperature corrosion resistance of the alloys listed in Table 1 increases with increasing chromium content. All these alloys form a chromium oxide layer (Cr2O3) with an underlying, more or less closed Al2O3 layer. Small additions of strongly oxygen-affine elements such as, e.g. Y or Ce improve the oxidation resistance. The chromium content is slowly consumed for build-up of the protecting layer in the course of use in the application zone. Therefore the lifetime of the material is prolonged by a higher chromium content, since a higher content of the element chromium forming the protective layer extends the time at which the Cr content lies below the critical limit and oxides other than Cr2O3 are formed, which are, e.g. iron-containing and nickel-containing oxides. A further increase of the high-temperature corrosion. resistance could be achieved by additions of aluminum and silicon. Starting from a certain minimum content, these elements form a closed layer under the chromium oxide layer and thus reduce the consumption of chromium.
In carburizing atmospheres (CO, H2, CH4, CO2, H2O mixtures), carbon may penetrate into the material, and so the formation of internal carbides may take place. These cause a loss of notch impact toughness. Also, the melting point may sink to very low values (down to 350° C.) and transformation processes may occur due to chromium depletion of the matrix.
A high resistance to carburization is achieved by materials with low solubility for carbon and low rate of diffusion of the carbon. In general, therefore, nickel alloys are more resistant to carburization than iron-base alloys, since both the diffusion of carbon and also the solubility of carbon in nickel are smaller than in iron. An increase of the chromium content brings about a higher carburization resistance by formation of a protecting chromium oxide layer, unless the oxygen partial pressure in the gas is not sufficient for the formation of this protecting chromium oxide layer. At very low oxygen partial pressure, it is possible to use materials that form a layer of silicon oxide or of the even more stable aluminum oxide, both of which are still able to form protecting oxide layers at much lower oxygen contents.
In the case that the carbon activity is >1, the so-called “metal dusting” may occur in alloys based on nickel, iron or cobalt. In contact with the supersaturated gas, the alloys may absorb large amounts of carbon. The segregation processes taking place in the alloy supersaturated with carbon leads to material destruction. In the process, the alloy decomposes into a mixture of metal particles, graphite, carbides and/or oxides. This type of material destruction takes place in the temperature range from 500° C. to 750° C.
Typical conditions for the occurrence of metal dusting are strongly carburizing CO, H2 or CH4 gas mixtures, such as occur in the synthesis of ammonia, in methanol plants, in metallurgical processes but also in hardening furnaces.
The resistance to metal dusting tends to increase with increasing nickel content of the alloy (Grabke, H. J., Krajak, R., Müller-Lorenz, E. M., Strauss, S.: Materials and Corrosion 47 (1996), p. 495), although even nickel alloys are not generally resistant to metal dusting.
The chromium and the aluminum content have a distinct influence on the corrosion resistance under metal dusting conditions (see FIG. 1). Nickel alloys with low chromium content (such as the Alloy 600 alloy, see Table 1) exhibit comparatively high corrosion rates under metal dusting conditions. The Alloy 602 CA (N06025) nickel alloy, with a chromium content of 25% and an aluminum content of 2.3% as well as Alloy 690 (N06690), with a chromium content of 30% (Hermse, C. G. M. and van Wortel, J. C.: Metal dusting: relationship between alloy composition and degradation rate. Corrosion Engineering, Science and Technology 44 (2009), p. 182-185), are much more resistant. The resistance to metal dusting increases with the sum of Cr+Al.
The heat resistance or creep resistance at the indicated temperatures is improved by a high carbon content among other factors. However, high contents of solid-solution-strengthening elements such as chromium, aluminum, silicon, molybdenum and tungsten improve the heat resistance. In the range of 500° C. to 900° C., additions of aluminum, titanium and/or niobium can improve the resistance, and specifically by precipitation of the γ′ and/or γ′′ phase.
Examples according to the prior art are listed in Table 1.
Alloys such as Alloy 602 CA (N06025), Alloy 693 (N06693) or Alloy 603 (N06603) are known for their excellent corrosion resistance in comparison with Alloy 600 (N06600) or Alloy 601 (N06601) by virtue of the high aluminum content of more than 1.8%. Alloy 602 CA (N06025), Alloy 693 (N06693), Alloy 603 (N06603) and Alloy 690 (N06690) exhibit excellent carburization resistance or metal dusting resistance by virtue of their high chromium and/or aluminum contents. At the same time, by virtue of the high carbon or aluminum content, alloys such as Alloy 602 CA (N06025), Alloy 693 (N06693) or Alloy 603 (N06603) have excellent heat resistance or creep resistance in the temperature range in which metal dusting occurs. Alloy 602 CA (N06025) and Alloy 603 (N06603) still have excellent heat resistance or creep resistance even at temperatures above 1000° C. Because of, for example, the high aluminum content, however, the processability is impaired, and the impairment becomes all the greater the higher the aluminum content is (For example, in Alloy 693-N06693). The same is true to a greater extent for silicon, which forms low-melting intermetallic phases with nickel. In Alloy 602 CA (N06025) or Alloy 603 (N06603), the cold formability in particular is limited by the high proportion of primary carbides.
U.S. Pat. No. 6,623,869 B1 discloses a metallic material that consists of not more than 0.2% C, 0.01-4% Si, 0.05-2.0% Mn, not more than 0.04% P, not more than 0.015% S, 10-35% Cr, 30-78% Ni, 0.005-<4.5% Al, 0.005-0.2% N and at least one of the elements 0.015-3% Cu or 0.015-3% Co, with the rest up to 100% iron. Therein the value of 40Si+Ni+5Al+40N+10(Cu+Co) is not smaller than 50, where the symbols of the elements denote the fractional content of the corresponding elements. The material has an excellent corrosion resistance in an environment in which metal dusting can occur and it may therefore be used for furnace pipes, pipe systems, heat-exchanger tubes and the like in petroleum refineries or petrochemical plants, and it can markedly improve the lifetime and safety of the plant.
EP 0 508 058 A1 discloses an austenitic nickel-chromium-iron alloy consisting of (in % by weight) C 0.12-0.3%, Cr 23-30%, Fe 8-11%, Al 1.8-2.4%, Y 0.01-0.15%, Ti 0.01-1.0%, Nb 0.01-1.0%, Zr 0.01-0.2%, Mg 0.001-0.015%, Ca 0.001-0.01%, N max. 0.03%, Si max. 0.5%, Mn max. 0.25%, P max. 0.02%, S max. 0.01%, Ni the rest, including unavoidable smelting-related impurities.
U.S. Pat. No. 4,882,125 B1 discloses a high-chromium-containing nickel alloy, which is characterized by an outstanding resistance to sulfurization and oxidation at temperatures higher than 1093° C., an outstanding creep resistance of longer than 200 h at temperatures above 983° C. and a stress of 2000 PSI, a good tensile strength and a good elongation, both at room temperature and elevated temperature, consisting of (in % by wt) 27-35% Cr, 2.5-5% Al, 2.5-6% Fe, 0.5-2.5% Nb, up to 0.1% C, respectively up to 1% Ti and Zr, up to 0.05% Ce, up to 0.05% Y, up to 1% Si, up to 1% Mn and Ni the rest.
EP 0 549 286 B1 discloses a high-temperature-resistant Ni—Cr alloy containing 55-65% Ni, 19-25% Cr, 1-4.5% Al, 0.045-0.3% Y, 0.15-1% Ti, 0.005-0.5% C, 0.1-1.5% Si, 0-1% Mn and at least 0.005%, of at least one of the elements of the group that contains Mg, Ca, Ce, <0.5% in total of Mg+Ca, <1% Ce, 0.0001-0.1% B, 0-0.5% Zr, 0.0001-0.2% N, 0-10% Co, 0-0.5% Cu, 0-0.5% Mo, 0-0.3% Nb, 0-0.1% V, 0-0.1% W, the rest iron and impurities.
From DE 600 04 737 T2 there has become known a heat-resisting nickel-base alloy containing ≦0.1% C, 0.01-2% Si, ≦2% Mn, ≦0.005% S, 10-25% Cr, 2.1-<4.5% Al, 0.055% N, in total 0.001-1% of at least one of the elements B, Zr, Hf, wherein the said elements may be present in the following contents: B≦0.03%, Zr≦0.2%, Hf<0.8%, Mo 0.01-15%, W 0.01-9%, wherein a total Mo+W content of 2.5-15% may be specified, Ti 0-3%, Mg 0-0.01%, Ca 0-0.01%, Fe 0-10%, Nb 0-1%, V 0-1%, Y 0-0.1%, La 0-0.1%, Ce 0-0.01%, Nd 0-0.1%, Cu 0-5%, Co 0-5%, the rest nickel. For Mo and W, the following formula must be satisfied:

2.5≦Mo+W≦15  (1)

The task underlying the invention consists in designing a nickel-chromium-aluminum alloy which, with sufficiently high chromium and aluminum contents, assures an excellent metal dusting resistance, but which at the same time exhibits

    
    
        a good phase stability
        a good processability
        a good corrosion resistance in air, similar to that of Alloy 602 CA (N06025)
        a good heat resistance/creep resistance.
    
    


This task is accomplished by a nickel-chromium-aluminum alloy with (in % by wt) 24 to 33% chromium 1.8 to 4.0% aluminum, 0.10 to 7.0% iron, 0.001 to 0.50% silicon, 0.005 to 2.0% manganese, 0.00 to 0.60% titanium, respectively 0.0002 to 0.05% magnesium and/or calcium, 0.005 to 0.12% carbon, 0.001 to 0.050% nitrogen, 0.0001-0.020% oxygen, 0.001 to 0.030% phosphorus, max. 0.010% sulfur, max. 2.0% molybdenum, max. 2.0% tungsten, the rest nickel and the usual process-related impurities, wherein the following relationships must be satisfied:

Cr+Al≧28  (2a)

and Fp≦39.9 with  (3a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (4a)

where Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of the elements in question in % by mass.

Advantageous further embodiments of the subject matter of the invention are also described in the disclosure.
The spread for the element chromium lies between 24 and 33%, wherein preferred ranges may be adjusted as follows:

    
    
        >25-<30%
        25 to 33%
        26 to 33%
        27 to 32%
        27 to 31%
        27 to 30%
        27.5 to 29.5%
        29 to 31%
    
    


The aluminum content lies between 1.8 and 4.0%, wherein here also preferred aluminum contents may be adjusted as follows depending on the field of use of the alloy:

    
    
        1.8 to 3.2%
        2.0 to 3.2%
        2.0 to <3.0%
        2.0 to 2.8%
        2.2 to 2.8%
        2.2 to 2.6%
        2.4 to 2.8%
        2.3 to 2.7%
    
    


The iron content lies between 0.1 and 7.0%, wherein defined contents may be adjusted within the following spread depending on the area of application:

    
    
        0.1-4.0%
        0.1-3.0%
        0.1-<2.5%
        0.1-2.0%
        0.1-1.0%
    
    


The silicon content lies between 0.001 and 0.50%. Preferably Si may be adjusted in the alloy within the spread as follows:

    
    
        0.001-0.20%
        0.001-<0.10%
        0.001-<0.05%
        0.010-<0.20%
    
    


The same is true for the element manganese, which may be contained in proportions of 0.005 to 2.0% in the alloy. Alternatively, the following spread is also conceivable:

    
    
        0.005-0.50%
        0.005-0.20%
        0.005-0.10%
        0.005-<0.05%
        0.010-<0.20%
    
    


The titanium content lies between 0.0 and 0.60%. Preferably Ti may be adjusted within the spread as follows in the alloy:

    
    
        0.001-0.60%
        0.001-0.50%
        0.001-0.30%
        0.01-0.30%
        0.10-0.25%
    
    


Magnesium and/or calcium is also contained in contents of 0.0002 to 0.05%. Preferably the possibility exists of adjusting these elements as follows in the alloy:

    
    
        0.0002-0.03%
        0.0002-0.02%
        0.0005-0.02%
    
    


The alloy contains 0.005 to 0.12% carbon. Preferably this may be adjusted within the spread as follows in the alloy:

    
    
        0.01-0.10%
        0.02-0.10%
        0.03-0.10%
    
    


This is true in the same way for the element nitrogen, which is contained in contents between 0.001 and 0.05%. Preferred contents may be stated as follows:

    
    
        0.003-0.04%
    
    


The alloy further contains phosphorus in contents between 0.001 and 0.030%. Preferred contents may be stated as follows:

    
    
        0.001-0.020%
    
    


The alloy further contains oxygen in contents between 0.0001 and 0.020%, containing especially 0.0001 to 0.010%.
The element sulfur is specified as follows in the alloy:

    
    
        Sulfur max. 0.010%
    
    


Molybdenum and tungsten are contained individually or in combination in the alloy in a content of respectively at most 2.0%. Preferred contents may be stated as follows:

    
    
        Mo max. 1.0%
        W max. 1.0%
        Mo max. <0.50%
        W max. <0.50%
        Mo max. <0.05%
        W max. <0.05%
    
    


The following relationship between Cr and Al must be satisfied, so that a sufficient resistance to metal dusting is achieved:

Cr+Al≧28  (2a)

where Cr and Al are the concentrations of the elements in question in % by mass.

Preferred ranges may be adjusted with

Cr+Al≧29  (2b)

Cr+Al≧30  (2c)

Cr+Al≧31  (2d)

Furthermore the following relationship must be satisfied, so that a sufficient phase stability is achieved:

Fp≦39.9 with  (3a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (4a)

where Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of the elements in question in % by mass.

Preferred ranges may be adjusted with:

Fp≦38.4  (3b)

Fp≦36.6  (3c)

Optionally the element yttrium may be adjusted in contents of 0.01 to 0.20% in the alloy. Preferably Y may be adjusted within the spread as follows in the alloy:

    
    
        0.01-0.15%
        0.01-0.10%
        0.01-0.08%
        0.01-0.05%
        0.01-<0.045%
    
    


Optionally the element lanthanum may be adjusted in contents of 0.001 to 0.20% in the alloy. Preferably La may be adjusted within the spread as follows in the alloy:

    
    
        0.001-0.15%
        0.001-0.10%
        0.001-0.08%
        0.001-0.05%
        0.01-0.05%
    
    


Optionally the element Ce may be adjusted in contents of 0.001 to 0.20% in the alloy. Preferably Ce may be adjusted within the spread as follows in the alloy:

    
    
        0.001-0.15%
        0.001-0.10%
        0.001-0.08%
        0.001-0.05%
        0.01-0.05%
    
    


Optionally, in the case of simultaneous addition of Ce and La, cerium mixed metal may also be used, and specifically in contents of 0.001 to 0.20%. Preferably cerium mixed metal may be adjusted within the spread as follows in the alloy:

    
    
        0.001-0.15%
        0.001-0.10%
        0.001-0.08%
        0.001-0.05%
        0.01-0.05%
    
    


Optionally, the element Nb may be adjusted in contents of 0.0 to 1.10% in the alloy. Preferably Nb may be adjusted within the spread as follows in the alloy:

    
    
        0.001-<1.10%
        0.001-<0.70%
        0.001-<0.50%
        0.001-0.30%
        0.01-0.30%
        0.10-0.30%
        0.10-1.10%
        0.20-0.70%
        0.10-0.50%
    
    


If Nb is contained in the alloy, Formula 4a must be supplemented with a term for Nb as follows:

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.374*Mo+0.538*W−11.8*C  (4b)

where Cr, Fe, Al, Si, Ti, Nb, Mo, W and C are the concentrations of the elements in question in % by mass.

If necessary, zirconium may be used in contents between 0.01 and 0.20%. Preferably Zr may be adjusted within the spread as follows in the alloy:

    
    
        0.01-0.15%
        0.01-<0.10%
        0.01-0.07%
        0.01-0.05%
    
    


Optionally, zirconium may also be replaced completely or partly by

    
    
        0.001-0.2% hafnium.
    
    


Optionally, 0.001 to 0.60% tantalum may also be contained in the alloy.
Optionally, the element boron may be contained as follows in the alloy:

    
    
        0.0001-0.008%
    
    


Preferred contents may be stated as follows:

    
    
        0.0005-0.008%
        0.0005-0.004%
    
    


Furthermore, the alloy may contain between 0.0 and 5.0% cobalt, which furthermore may be limited even more as follows:

    
    
        0.01 to 5.0%
        0.01 to 2.0%
        0.1 to 2.0%
        0.01 to 0.5%
    
    


Furthermore, at most 0.5% Cu may be contained in the alloy.
The copper content may be further restricted as follows:

    
    
        Cu max. <0.05%
        Cu max. <0.015%
    
    


If Cu is contained in the alloy, Formula 4a must be supplemented with a term for Cu as follows:

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (4c)

where Cr, Fe, Al, Si, Ti, Cu, Mo, W and C are the concentrations of the elements in question in % by mass.

If Nb and Cu are contained in the alloy, Formula 4a must be supplemented with a term for Nb and a term for Cu as follows:

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (4d)

where Cr, Fe, Al, Si, Ti, Nb, Cu, Mo, W and C are the concentrations of the elements in question in % by mass.

Furthermore, at most 0.5% vanadium may be contained in the alloy.
Finally, the elements lead, zinc and tin may be stated as impurities in contents as follows:

    Pb max. 0.002%
    Zn max. 0.002%
    Sn max. 0.002%


Furthermore, the following relationship, which assures a particularly good processability, may be optionally satisfied:

Fa≦60 with  (5a)

Fa=Cr+20.4*Ti+201*C  (6a)

where Cr, Ti and C are the concentrations of the elements in question in % by mass.

Preferred ranges may be adjusted with:

Fa≦54  (5b)

If Nb is contained in the alloy, Formula 6a must be supplemented with a term for Nb as follows:

Fa=Cr+6.15*Nb+20.4*Ti+201*C  (6b)

where Cr, Nb, Ti and C are the concentrations of the elements in question in % by mass.

Furthermore, the following relationship, which describes a particularly good heat resistance or creep resistance, may be optionally satisfied:

Fk≧45 with  (7a)

Fk=Cr+19*Ti+10.2*Al+12.5*Si+98*C  (8a)

where Cr, Ti, Al, Si and C are the concentrations of the elements in question in % by mass.

Preferred ranges may be adjusted with:

Fk≦49  (7b)

Fk≦53  (7c)

If Nb and/or B is contained in the alloy, Formula 8a must be supplemented with a term for Nb and/or B as follows:

Fk=Cr+19*Ti+34.3*Nb+10.2*Al+12.5*Si+98*C+2245*B  (8b)

where Cr, Ti, Nb, Al, Si, C and B are the concentrations of the elements in question in % by mass.

The alloy according to the invention is preferably smelted in an open system, followed by a treatment in a VOD or VLF system. However, a smelting and pouring in vacuum is also possible. Thereafter the alloy is cast in ingots or as continuous strand. If necessary, the ingot is then annealed for 0.1 h to 70 h at temperatures between 900° C. and 1270° C. Furthermore, it is possible to remelt the alloy additionally with ESU and/or VAR. Thereafter the alloy is worked into the desired semifinished product shape. For this it is annealed if necessary for 0.1 h to 70 h at temperatures between 900° C. and 1270° C., then hot-formed, if necessary with intermediate annealings for 0.05 h to 70 h between 900° C. and 1270° C. If necessary, the surface of the material may also be milled chemically and/or mechanically occasionally (even several times) and/or at the end for cleaning. After the end of hot shaping, cold shaping to the desired semifinished product shape with reduction ratios up to 98% may take place if necessary, with intermediate annealings for 0.1 min to 70 h between 700° C. and 1250° C. if necessary, under shielding gas, if necessary, such as argon or hydrogen, for example, followed by cooling in air, in the agitated annealing atmosphere or in the water bath. Thereafter a solution annealing takes place for 0.1 min to 70 h between 700° C. and 1250° C., under shielding gas, if necessary, such as argon or hydrogen, for example, followed by cooling in air, in the agitated annealing atmosphere or in the water bath. If necessary, chemical and/or mechanical cleanings of the material surface may take place occasionally and/or after the last annealing.
The alloy according to the invention can be readily manufactured and used in the product forms of strip, sheet, bar, wire, longitudinally seam-welded pipe and seamless pipe.
These product forms are manufactured with a mean grain size of 5 μm to 600 μm. The preferred range lies between 20 μm and 200 μm.
The alloy according to the invention will preferably be used in zones in which carburizing conditions prevail, such as, for example, in structural parts, especially pipes, in the petrochemical industry. Furthermore, it is also suitable for furnace construction.
Tests Performed:
The phases occurring at equilibrium were calculated for the different alloy variants with the JMatPro program of Thermotech. The TTNI7 database of Thermotech for nickel-base alloys was used as the database for the calculations.
The formability is determined in a tension test according to DIN EN ISO 6892-1 at room temperature. Therein the yield strength Rp0.2, the tensile strength Rm and the elongation A at break are determined. The elongation A is determined on the broken specimen from the elongation of the original gauge length L0:

A=(Lu−L0)/L0 100%=ΔL/L0100%

where Lu=measured length after break.

Depending on gauge length, the elongation at break is characterized by indices:
For example, for A5 the gauge length is L0=5·d0, where d0=initial diameter of a round specimen.
The tests were performed on round specimens with a diameter of 6 mm in the measurement zone and a gauge length L0 of 30 mm. The sampling took place transversely relative to the forming direction of the semifinished product. The deformation rate was 10 MPa/s for Rp0.2 and 6.7 10−3 l/s (40%/min) for Rm.
The magnitude of the elongation A in the tension test at room temperature may be taken as a measure of the deformability. A readily processable material should have an elongation of at least 50%.
The heat resistance is determined in a hot tension test according to DIN EN ISO 6892-2. Therein the yield strength Rp0.2, the tensile strength Rm and the elongation A at break are determined by analogy with the tension test at room temperature (DIN EN ISO 6892-1).
The tests were performed on round specimens with a diameter of 6 mm in the measurement zone and an initial gauge length L0 of 30 mm. The sampling took place transversely relative to the forming direction of the semifinished product. The deformation rate was 8.33 10−5 l/s (0.5%/min) for Rp0.2 and 8.33 10−4 l/s (5%/min) for Rm.
The respective specimen is mounted at room temperature in a tension testing machine and heated without loading by a tensile force to the desired temperature. After reaching the test temperature, the specimen is held without loading for one hour (600° C.) or two hours (700° C. to 1100° C.) for temperature equilibration. Thereafter the specimen is loaded with tensile force in such a way that the desired strain rates are maintained, and the test begins.
The creep resistance of a material improves with increasing heat resistance. Therefore the heat resistance is also used for appraisal of the creep resistance of the various materials.
The corrosion resistance at elevated temperatures was determined in an oxidation test at 1000° C. in air, wherein the test was interrupted every 96 hours and the dimensional changes of the specimens due to oxidation were determined. The specimens were placed in ceramic crucibles during the test, so that any oxide that may have spalled was collected and the mass of the spalled oxide can be determined by weighing the crucible containing the oxides. The sum of the mass of the spalled oxide and of the change in mass of the specimens corresponds to the gross change in mass of the specimen. The specific change in mass is the change in mass relative to the surface area of the specimens. Hereinafter these are denoted by mnet for the specific change in net mass, mgross for the specific change in gross mass, mspall for the specific change in mass of the spalled oxides. The tests were carried out on specimens of approximately 5 mm thickness. Three specimens were extracted from each batch, and the reported values are the mean values of these 3 specimens.


DESCRIPTION OF THE PROPERTIES
In addition to an excellent metal dusting resistance, the alloy according to the invention should also have the following properties:

    
    
        a good phase stability
        a good processability
        a good corrosion resistance in air, similar to that of Alloy 602CA (N06025)
        a good heat resistance/creep resistance.

Phase Stability

    
    


In the nickel-chromium-aluminum-iron system with additions of Ti and/or Nb, various embrittling TCP phases such as, for example, the Laves phases, sigma phases or the μ-phases or also the embrittling η-phase or ε-phases can be formed, depending on alloying contents (see, for example, Ralf Bürgel, Handbook of High-Temperature Materials Engineering [in German], 3rd Edition, Vieweg Verlag, Wiesbaden, 2006, page 370-374). The calculation of the equilibrium phase fractions as a function of temperature, for example of the batch 111389 of N06690, (see Table 2, typical compositions) shows theoretically the formation of ∝-chromium with a low content of Ni and/or Fe(BCC phase in FIG. 2) below 720° C. (Ts BCC) in large proportions. However, this phase is formed only with difficulty, because it is analytically very different from the base material. Nevertheless, if the formation temperature Ts BCC of this phase is very high, it can definitely occur, as is described, for example, in E. Slevolden, J. Z. Albertsen, U. Fink “Tjeldbergodden Methanol Plant: Metal Dusting Investigations,” Corrosion/2011, paper no. 11144 (Houston, Tex.: NACE 2011), p. 15′′ for a variant of Alloy 693 (UNS 06693). This phase is brittle and leads to an undesired embrittlement of the material. FIG. 3 and FIG. 4 show the phase diagrams of the Alloy 693 variants (from U.S. Pat. No. 4,882,125 Table 1) Alloy 3 and Alloy 10 from Table 2. Alloy 3 has a formation temperature Ts BCC of 1079° C., Alloy 10 of 639° C. 939° C. In E. Slevolden, J. Z. Albertsen, U. Fink “Tjeldbergodden Methanol Plant: Metal Dusting Investigations,” Corrosion/2011, paper no. 11144 (Houston, Tex.: NACE 2011), p. 15′′, the exact analysis of the alloy in which the ∝-chromium (BCC) occurs is not described. Nevertheless, it can be assumed that, among the examples presented in Table 2 for Alloy 693, ∝-chromium (BCC phase) can be formed in the analyses that theoretically have the highest formation temperatures Ts BCC(such as Alloy 10, for example). In a corrected analysis (with reduced formation temperature Ts BCC), ∝-chromium was observed only in the proximity of the surface in E. Slevolden, J. Z. Albertsen, U. Fink “Tjeldbergodden Methanol Plant: Metal Dusting Investigations,” Corrosion/2011, paper no. 11144 (Houston, Tex.: NACE 2011), p. 15′′. To avoid the occurrence of such an embrittling phase, the formation temperature in the alloys according to the invention should be Ts BCC lower than or equal to 939° C.—which is the lowest formation temperature Ts BCC among the examples for Alloy 693 in Table 2 (from U.S. Pat. No. 4,882,125 Table 1).
This is the case in particular when the following formula is satisfied:

Fp≦39.9 with  (3a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (4a)

where Cr, Al, Fe, Si, Ti, Mo, W and C are the concentrations of the elements in question in % by mass.

The Table 2 with the alloys according to the prior art shows that Fp for Alloy 8, Alloy 3 and Alloy 2 is >39.9 and for Alloy 10 is exactly 39.9. For all other alloys with Ts BCC≦939° C., Fp is ≦39.9.
Processability
The formability will be considered here as an example of processability.
An alloy can be hardened by several mechanisms, so that it has a high heat resistance or creep resistance. Thus the alloying addition of another element brings about a more or less large increase of the strength (solid-solution hardening), depending on element. An increase of the strength by fine particles or precipitates (precipitation hardening) is far more effective. This may take place, for example, by the γ′-phase, which is formed by additions of Al and further elements, such as, for example: Ti to a nickel alloy, or by carbides, which are formed by addition of carbon to a chromium-containing nickel alloy (see, for example, Ralf Burgel, Handbook of High-Temperature Materials Engineering, 3rd Edition, Vieweg Verlag, Wiesbaden, 2006, page 358-369).
The increase of the content of elements forming the γ′-phase, or of the C content, indeed increases the heat resistance, but increasingly impairs the formability, even in the solution-annealed condition.
For a very readily formable material, elongations A5 of ≧50% but at least 45% are desired in the tension test at room temperature.
This is achieved in particular when the following relationship between the elements Cr, Nb, Ti and C forming the carbide is satisfied:

Fa≦60 with  (5a)

Fa=Cr+6.15*Nb+20.4*Ti+201*C  (6b)

where Cr, Nb, Ti and C are the concentrations of the elements in question in % by mass.

Heat resistance/creep resistance
At the same time, the yield strength or the tensile strength at higher temperatures should reach at least the values of Alloy 601 (see Table 4).

600° C.: yield strength Rp0.2>150 MPa; tensile strength Rm>500 MPa  (9a, 9b)

800° C.: yield strength Rp0.2>130 MPa; tensile strength Rm>135 MPa  (9c, 9d)

It would be desirable for the yield strength or the tensile strength to lie at least in the range of the values Alloy 602CA (see Table 4). At least 3 of the 4 following relationships should be satisfied:

600° C.: yield strength Rp0.2>230 MPa; tensile strength Rm>550 MPa  (10a, 10b)

800° C.: yield strength Rp0.2>180 MPa; tensile strength Rm>190 MPa  (10c, 10d)

This is achieved in particular when the following relationship between the mainly hardening elements is satisfied:

Fk≦45 with  (7a)

Fk=Cr+19*Ti+34.3*Nb+10.2*Al+12.5*Si+98*C+2245*B  (8b)

where Cr, Ti, Nb, Al, Si, C and B are the concentrations of the elements in question in % by mass.

Corrosion Resistance:

The alloy according to the invention should have a good corrosion resistance in air similar to that of Alloy 602CA (N06025).
EXAMPLES
Manufacture:
Tables 3a and 3b show the analyses of the batches smelted on the laboratory scale together with some industrially smelted batches, cited for comparison, according to the prior art, of Alloy 602CA (N06025), Alloy 690 (N06690), Alloy 601 (N06601). The batches according to the prior art are marked with a T, those according to the invention with an E. The batches corresponding to the laboratory scale are marked with an L, those smelted industrially with a G.
The ingots of the alloys smelted in vacuum on the laboratory scale in Table 3a and b were annealed for 8 h between 900° C. and 1270° C. and hot-rolled to a final thickness of 13 mm or 6 mm by means of hot rolls and further intermediate annealings for 0.1 to 1 h between 900° C. and 1270° C. The sheets produced in this way were solution-annealed for 1 h between 900° C. and 1270° C. The specimens needed for the measurements were prepared from these sheets.
For the industrially smelted alloys, a sample from the industrial production was taken from a commercially produced sheet of suitable thickness. The specimens needed for the measurements were taken from this sample.
All alloy variants typically had a grain size of 70 to 300
For the exemplary batches in Table 3a and 3b, the following properties were compared.

    
    
        Metal dusting resistance
        Phase stability
        Formability on the basis of the tension test at room temperature
        Heat resistance/creep resistance by means of hot tension tests
        Corrosion resistance by means of an oxidation test
    
    


For the batches 2297 to 2308 and 250060 to 250149 smelted on the laboratory scale, but especially for the batches according to the invention marked with E (2301, 250129, 250132, 250133, 250134, 250137, 250138, 250147, 250148), the Formula (2a) Al+Cr≧28 is satisfied. They therefore satisfy the requirement that has been imposed on the metal dusting resistance.
For the selected alloys according to the prior art in Table 2 and for all laboratory batches (Tables 3a and 3b), the phase diagrams were therefore calculated and the formation temperature Ts BCC was entered in Tables 2 and 3a. For the compositions in Tables 2 as well as 3a and 3b, the value for Fp according to Formula 4a was also calculated. Fp is larger the higher the formation temperature Ts BCC. All examples of N06693 with a formation temperature Ts BCC higher than that of Alloy 10 have an Fp>39.9. The requirement Fp≦39.9 (Formula 3a) is therefore a good criterion for obtaining an adequate phase stability in an alloy. All laboratory batches in Table 3a and 3b satisfy the criterion Fp≦39.9.
The yield strength Rp0.2, the tensile strength Rm and the elongation A5 for room temperature RT and for 600° C. are entered in Table 4, as is the tensile strength Rm for 800° C. The values for Fa and Fk are also entered.
Exemplary batches 156817 and 160483 of the alloy according to the prior art, Alloy 602 CA in Table 4, have a comparatively small elongation A5 at room temperature of 36 or 42%, which fall short of the requirements for good formability. Fa is >60 and therefore above the range that characterizes good formability. All alloys according to the invention (E) exhibit an elongation >50%. Thus they satisfy the requirements. Fa is <60 for all alloys according to the invention. They therefore lie in the range of good formability. The elongation is particularly high when Fa is comparatively small.
The exemplary batch 156658 of the alloy according to the prior art, Alloy 601 in Table 4, is an example of the minimum requirements on yield strength and tensile strength at 600° C. and 800° C., whereas the exemplary batches 156817 and 160483 of the alloy according to the prior art, Alloy 602 CA, are examples of very good values of yield strength and tensile strength at 600° C. and 800° C. Alloy 601 represents a material that exhibits the minimum requirements on heat resistance and creep resistance, which are described in Formulas 9a to 9d, Alloy 602 CA a material that exhibits an outstanding heat resistance and creep resistance, which are described in the Formulas 10a to 10d. For both alloys, the value of Fk is much larger than 45, and for Alloy 602 CA it is additionally even much higher than the value of Alloy 601, which reflects the elevated strength values of Alloy 602 CA. The alloys according to the invention (E) all exhibit a yield strength and tensile strength at 600° C. and 800° C. in the range of or considerably above that of Alloy 601, and have therefore satisfied the Formulas 9a to 9d. They lie in the range of the values of Alloy 602 CA and also satisfy the desirable requirements, in other words 3 of the 4 Formulas 10a to 10d. Fk is also greater than 45 for all alloys according to the invention in the examples in Table 4, and in fact is even mostly greater than 54 and thus in the range which is characterized by a good heat resistance and creep resistance. Among the laboratory batches not according to the invention, batches 2297 and 2300 are an example wherein the Formulas 9a to 9d are not satisfied and also an Fk<45 is obtained.
Table 5 shows the specific changes in mass after an oxidation test at 1100° C. in air after 11 cycles of 96 h, i.e. a total of 1056 h. The specific gross change in mass, the specific net change in mass and the specific change in mass of the spalled oxides after 1056 h are indicated in Table 5. The exemplary batches of the alloys according to the prior art, Alloy 601 and Alloy 690, exhibited a much higher gross change in mass than Alloy 602 CA, that of Alloy 601 being even many times greater than that of Alloy 690. Both form a chromium oxide layer that grows faster than an aluminum oxide layer. Alloy 601 still contains approximately 1.3% Al. This content is too low yet to form an aluminum oxide layer that is even only partly closed, and so the aluminum in the interior of the metallic material underneath the oxide layer oxidizes (internal oxidation), which results in a greater mass increase in comparison with Alloy 690. Alloy 602 CA has approximately 2.3% aluminum. Thus an at least partly closed aluminum oxide layer can form underneath the chromium oxide layer in this alloy. This reduces the growth of the oxide layer markedly and thus also the specific increase in mass. All alloys according to the invention (E) contain at least 2% aluminum and therefore have a gross increase in mass that is small, similar to that of Alloy 602 CA, or smaller. Also, all alloys according to the invention, similarly to the exemplary batches of Alloy 602 CA, exhibit spallings in the range of the measurement accuracy, while Alloy 601 and Alloy 690 exhibit great spallings.
The claimed limits for the alloy “E” according to the invention can therefore be substantiated in detail as follows:
Too low Cr contents mean that the Cr concentration at the oxide-metal interface sinks very rapidly below the critical limit during use of the alloy in a corrosive atmosphere, and so a closed pure chromium oxide can no longer be formed in case of a damage to the oxide layer, although other less protective oxides can form. Therefore 24% Cr is the lower limit for chromium. Too high Cr contents impair the phase stability of the alloy, especially at the high aluminum contents of ≧1.8%. Therefore 33% Cr must be regarded as the upper limit.
The formation of an aluminum oxide layer underneath the chromium oxide layer reduces the rate of oxidation. Below 1.8% Al, the aluminum oxide layer being formed has too many gaps in order to develop its effect completely. Too high Al contents impair the processability of the alloy. Therefore an Al content of 4.0% constitutes the upper limit.
The costs for the alloy rise with the reduction of the iron content. Below 0.1%, the costs rise disproportionately, since special raw material must be used. For cost reasons, therefore, 0.1% Fe must be regarded as the lower limit. With increase of the iron content, the phase stability decreases (formation of embrittling phases), especially at high chromium and aluminum contents. Therefore 7% Fe is a practical upper limit for ensuring the phase stability of the alloy according to the invention.
Si is needed during the manufacture of the alloy. Thus a minimum content of 0.001% is necessary. Too high contents again impair the processability and the phase stability, especially at high aluminum and chromium contents. The Si content is therefore limited to 0.50%.
A minimum content of 0.005% Mn is necessary for the improvement of the processability. Manganese is limited to 2.0%, since this element reduces the oxidation resistance.
Titanium increases the high-temperature resistance. From 0.60%, the oxidation behavior can be greatly impaired, and so 0.60% is the maximum value.
Even very low Mg and/or Ca contents improve the processability by binding sulfur, whereby the occurrence of low-melting NiS eutectics is prevented. Therefore a minimum content of respectively 0.0002% is necessary for Mg and or Ca. At too high contents, intermetallic Ni—Mg phases or Ni—Ca phases may form, which again greatly impair the processability. The Mg and/or Ca content is therefore limited to at most 0.05%.
A minimum content of 0.005% C is necessary for a good creep resistance. C is limited to a maximum of 0.12%, since above that content this element reduces the processability due to the excessive formation of primary carbides.
A minimum content of 0.001% N is necessary, whereby the processability of the material is improved. N is limited to at most 0.05%, since this element reduces the processability by the formation of coarse carbonitrides.
The oxygen content must be 0.020%, in order to ensure manufacturability of the alloy. A too low oxygen content increases the costs. The oxygen content is therefore 0.001%.
The content of phosphorus should be lower than or equal to 0.030%, since this surface-active element impairs the oxidation resistance. A too low P content increases the costs. The P content is therefore 0.0001%.
The contents of sulfur should be adjusted as low as possible, since this surface-active element impairs the oxidation resistance. Therefore 0.010% S is set as the maximum.
Molybdenum is limited to at most 2.0%, since this element reduces the oxidation resistance.
Tungsten is limited to at most 2.0%, since this element also reduces the oxidation resistance.
The following relationship between Cr and Al must be satisfied, in order that sufficient resistance to metal dusting is achieved:

Cr+Al≧28  (2a)

where Cr and Al are the concentrations of the elements in question in % by mass. Only then is the content of oxide-forming elements high enough to ensure a sufficient metal dusting resistance.

Furthermore, the following relationship must be satisfied, in order that sufficient phase stability is achieved:

Fp≦39.9 with  (3a)

Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W−11.8*C  (4a)

where Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of the elements in question in % by mass. The limits for Fp as well as possible incorporation of further elements have been substantiated in detail in the foregoing text.

If necessary, the oxidation resistance may be further improved with additions of oxygen-affine elements. They achieve this by being incorporated in the oxide layer and blocking the diffusion paths of the oxygen at the grain boundaries therein.
A minimum content of 0.01% Y is necessary, in order to obtain the oxidation-resistance-increasing effect of the Y. For cost reasons, the upper limit is set at 0.20%.
A minimum content of 0.001% La is necessary, in order to obtain the oxidation-resistance-increasing effect of the La. For cost reasons, the upper limit is set at 0.20%.
A minimum content of 0.001% Ce is necessary, in order to obtain the oxidation-resistance-increasing effect of the Ce. For cost reasons, the upper limit is set at 0.20%.
A minimum content of 0.001% cerium mixed metal is necessary, in order to obtain the oxidation-resistance-increasing effect of the cerium mixed metal. For cost reasons, the upper limit is set at 0.20%.
If necessary, niobium may be added, since niobium also increases the high-temperature resistance. Higher contents raise the costs very greatly. The upper limit is therefore set at 1.10%.
If necessary, the alloy may also contain tantalum, since tantalum also increases the high-temperature resistance. Higher contents raise the costs very greatly. The upper limit is therefore set at 0.60%. A minimum content of 0.001% is necessary in order to achieve an effect.
If necessary, the alloy may also contain Zr. A minimum content of 0.01% Zr is necessary, in order to obtain the high-temperature-resistance-increasing and oxidation-resistance-increasing effect of the Zr. For cost reasons, the upper limit is set at 0.20% Zr.
If necessary, Zr may be replaced completely or partly by Hf, since this element, just as Zr, increases the high-temperature resistance and the oxidation resistance. The replacement is possible starting from contents of 0.001%. For cost reasons, the upper limit is set at 0.20% Hf.
If necessary, boron may be added to the alloy, since boron increases the creep resistance. Therefore a content of at least 0.0001% should be present. At the same time, this surface-active element impairs the oxidation resistance. Therefore 0.008% boron is set as the maximum.
Cobalt may be present in this alloy up to 5.0%. Higher contents reduce the oxidation resistance markedly.
Copper is limited to at most 0.5%, since this element reduces the oxidation resistance.
Vanadium is limited to at most 0.5%, since this element likewise reduces the oxidation resistance.
Pb is limited to at most 0.002%, since this element reduces the oxidation resistance. The same is true for Zn and Sn.
Furthermore, the following relationship, which describes a particularly good processability, may be optionally satisfied for carbide-forming elements Cr, Ti and C:

Fa≦60 with  (5a)

Fa=Cr+20.4*Ti+201*C  (6a)

where Cr, Ti and C are the concentrations of the elements in question in % by mass. The limits for Fa and the possible incorporation of further elements have been substantiated in detail in the foregoing text.

Furthermore, the following relationship, which describes a particularly good heat resistance or creep resistance, with respect to the strength-increasing elements may be optionally satisfied:

Fk≧45 with  (7a)

Fk=Cr+19*Ti+10.2*Al+12.5*Si+98*C  (8a)

where Cr, Ti, Al, Si and C are the concentrations of the elements in question in % by mass. The limits for Fa and the possible incorporation of further elements have been substantiated in detail in the foregoing text.








TABLE 1







Alloys according to ASTM B 168-11 All values in % by mass


























Alloy
Ni
Cr
Co
Mo
Nb
Fe
Mn
Al
C
Cu
Si
S
Ti
P
Zr
Y
B
N
Ce





Alloy 600-
72.0
14.0-



 6.0-
1.0

0.15
 0.5 max
0.5
0.015









N06600
min
17.0



10.0
max

max
 
max
max









Alloy 601-
58.0-
21.0-



Rest
1.0
1.0-
0.10
 0.5 max
0.5
0.015









N06601
63.0
25.0




max
1.7
max
 
max
max









Alloy 617-
44.5
20.0-
10.0-
 8.0-

 3.0
1.0
0.8-
0.05-
 1.0 max
0.5
0.015
0.6



0.006




N06617
min
24.0
15.0
10.0

max
max
1.5
0.15
 
max
max
max



max




Alloy 690-
58.0
27.0-



 7.0-
0.5

0.05
 0.5 max
1.0
0.015









N06690
min
31.0



11.0
max

max
 
max
max









Alloy 693-
Rest
27.0-


0.5-
 2.5-
1.0
2.5-
0.15
 0.5 max
0.5
0.01
1.0








N06693

31.0


2.5
 6.0
max
4.0
max
 
max
max
max








Alloy 
Rest
24.0-



 8.0-
0.15
1.8-
0.15-
 0.1 max
0.5
0.010
0.1-
0.020
0.01-
0.05-





602CA-

26.0



11.0
max
2.4
0.25
 
max
max
0.2
max
0.10
0.12





N06025





















Alloy 45-
45
26.0-



21.0-
1.0

0.05-
 0.3 max
2.5-
0.010

0.020




0.03-


N06046
min
29.0



25.0
max

0.12

3.0
max

max




0.09


Alloy 603-
Rest
24.0-



 8.0-
0.15
2.4-
0.20-
0.50 max
0.5
0.010
0.01-
0.020
0.01-
0.01-





N06603

26.0



11.0
max
3.0
0.40

max
max
0.25
max
0.10
0.15





Alloy 696-
Rest
28.0-

 1.0-

 2.0-
1.0

0.15
1.5-3.0
1.0-
0.010
1.0








N06696

32.0

 3.0

 6.0
max

max

2.5
max
max






















TABLE 2





Typical compositions of some alloys according to ASTM B 168-11


(prior art). All values in % by mass


*) Alloy composition from U.S. Pat. No. 4,882,125 Table 1


























Alloy
Batch
C
S
Cr
Ni
Mn
Si
Mo
Ti
Nb
Cu





Alloy 
164310
0.07
0.002
15.75
73.77
0.28
0.32

0.2

0.01


600













N06600













Alloy 
156656
0.053
4.0016
22.95
59.58
0.72
0.24

0.47

0.04


601













N06601













Alloy 
111389
0.022
0.002
28.45 
61.95
0.12
0.32

0.29

0.01


690













N06690













Alloy
Alloy 
0.015
≦0.01
29.42
60.55
0.014
0.075

0.02
1.04
0.03


693
10 *)












N06693













Alloy 
Alloy 
0.007
≦0.01
30.00
60.34
0.11
0.38

0.23
1.13
0.03


693
8 *)












N06693













Alloy 
Alloy 
0.009
≦0.01
30.02
57.79
0.01
0.14

0.02
2.04
0.03


693
3*)












N06693













Alloy 
Alloy 
0.006
≦0.01
30.01 
60.01
0.12
0.14

0.01 
0.54
0.03


693
2 *)












N06693













Alloy 
163968
0.170
≦0.01
25.39 
62.12
0.07
0.07

0.13

0.01


602













N06025













Alloy 
52475
0.225
0.002
25.20 
61.6
0.09
0.03

0.16 
0.01
0.01


603













N06603













Alloy 
UNS
0.080
≦0.01
30.00 
61.20
0.1
1.5 
2
0.1

2


696
average












N06696














Ts BCC
Cr +




Alloy
Batch
Fe
P
Al
Zr
Y
B
in ° C.
Al
Fp






Alloy 
164310
9.42
0.009
0.16


0.001

15.9 
19.1



600













N06600













Alloy 
156656
14.4
0.008
1.34
0.015
0  
0.001
669
24.3
31.2



601













N06601













Alloy 
111389
8.45
0.005
0.31

0  
0
720
28.8 
32.7



690













N06690













Alloy
Alloy 
5.57

3.2


0.002
939
32.6
39.9



693
10 *)












N06693













Alloy 
Alloy 
4.63

3.08


0.002
979
33.1 
41.3



693
8 *)












N06693













Alloy 
Alloy 
5.57

4.3 


0.002
1079
34.3
44.5



693
3*)












N06693













Alloy 
Alloy 
5.80

3.27


0.002
948
33.3 
40.3



693
2 *)












N06693













Alloy 
163968
9.47 
0.008
2.25
0.08
0.08 
0.005
690
27.6 
31.8



602













N06025













Alloy 
52475
9.6
0.007
2.78
0.07
0.08 
0.003
707
28.0 
32.2



603













N06603













Alloy 
UNS
3





792
30.0 
35.1



696
average












N06696
















TABLE 3a





Composition of the laboratory batches, Part 1. All values in % by mass


(T: alloy according to the prior art. E: alloy according to the invention, L:


smelted on the laboratory scale: G: industrially smelted)




























Name
Batch
C
N
Cr
Ni
Mn
Si
Mo
Ti





T
G
Alloy 602 CA
156817
0.171
0.036
25.2
62.1
0.06
0.07
0.01
0.17


T
G
Alloy 602 CA
160483
0.172
0.025
25.7
62.0
0.06
0.05
0.02
0.14


T
G
Alloy 601
156656
0.053
0.018
23.0
59.6
0.72
0.24
0.04
0.47


T
G
Alloy 690
80116
0.010
0.025
27.8
62.8
0.18
0.15
0.01
0.31


T
G
Alloy 690
111389
0.022
0.024
28.5
62.0
0.12
0.32
<0.01
0.29



L
Cr30Al1La
2297
0.018
0.023
29.9
68.0
0.25
0.09
<0.01
<0.01



L
Cr30Al1LaT
2300
0.019
0.021
30.2
67.5
0.25
0.08
<0.01
<0.01



L
Cr30Al1TiLa
2298
0.018
0.022
29.9
67.5
0.25
0.08
<0.01
0.3



L
Cr30Al1TiNbLa
2308
0.017
0.028
30.1
67.1
0.25
0.08
<0.01
0.31



L
Cr30Al1CLaTi
2299
0.060
0.021
30.1
67.6
0.25
0.09
<0.01
0.01



L
Cr30Al1CLa
2302
0.049
0.02
30.1
67.1
0.26
0.09
<0.01
<0.01


E
L
Cr30Al2La
2301
0.015
0.021
30.2
66.6
0.25
0.08
<0.01
<0.01



L
Cr30Al1Ti
250060
0.017
0.027
29.6
67.9
0.24
0.11
<0.01
0.31



L
Cr30Al1Ti
250063
0.017
0.024
29.9
67.4
0.25
0.10
<0.01
0.31



L
Cr30Al1TiNb
250066
0.016
0.022
29.9
67.1
0.24
0.09
<0.01
0.31



L
Cr30Al1TiNb
250065
0.017
0.025
30.3
67.1
0.24
0.10
0.01
0.3



L
Cr30Al1TiNbZr
250067
0.019
0.020
29.7
67.2
0.25
0.10
0.02
0.31



L
Cr30Al1TiNb
250068
0.017
0.024
29.8
66.6
0.25
0.09
0.01
0.31


E
L
Cr28Al2
250129
0.018
0.025
28.2
68.3
0.25
0.10
<0.01
<0.01


E
L
Cr28Al2Y
250130
0.022
0.022
28.1
68.6
0.25
0.07
<0.01
<0.01


E
L
Cr28Al2YC1
250132
0.059
0.022
28.3
68.2
0.27
0.06
<0.01
<0.01


E
L
Cr28Al2Nb.5C1
250133
0.047
0.022
28.3
67.7
0.25
0.06
0.01
<0.01


E
L
Cr28Al2Nb.5C1
250148
0.049
0.019
27.9
67.9
0.26
0.07
<0.01
<0.01


E
L
Cr28Al2Nb1C1
250134
0.048
0.026
28.2
67.1
0.26
0.09
0.02
<0.01


E
L
Cr28Al2Nb1C1
250147
0.045
0.017
28.4
67.5
0.27
0.07
0.02
<0.01


E
L
Cr28Al2Nb1C1Y
250149
0.054
0.020
27.9
67.2
0.27
0.06
0.01
<0.01


E
L
Cr28Al2TiC1
250137
0.063
0.024
28.2
67.7
0.27
0.09
<0.01
0.15


E
L
Cr28Al2TiC1
250138
0.053
0.018
28.3
68.4
0.27
0.05
<0.01
0.16














Ts BCC
Cr +





Name
Batch
Nb
Cu
Fe
Al
W
in ° C.
Al
Fp





T
G
Alloy 602 CA
156817
<0.01
0.01
9.6
2.36
—
683
27.6
31.9


T
G
Alloy 602 CA
160483
0.01
0.01
9.4
2.17
—
683
27.8
31.8


T
G
Alloy 601
156656
0.01
0.04
14.4
1.34
0.01
669
24.3
31.2


T
G
Alloy 690
80116
<0.01
0.01
8.5
0.14
—
683
27.9
31.4


T
G
Alloy 690
111389
0.01
0.01
8.5
0.31
—
720
28.8
32.7



L
Cr30Al1La
2297
<0.01
<0.01
0.56
1.04
<0.01
737
30.9
32.5



L
Cr30Al1LaT
2300
<0.01
<0.01
0.54
1.3
<0.01
737
31.5
33.3



L
Cr30Al1TiLa
2298
<0.01
<0.01
0.55
1.28
<0.01
759
31.2
33.8



L
Cr30Al1TiNbLa
2308
0.28
<0.01
0.53
1.25
0.01
772
31.4
34.3



L
Cr30Al1CLaTi
2299
<0.01
<0.01
0.54
1.25
0.01
730
31.3
32.7



L
Cr30Al1CLa
2302
<0.01
<0.01
0.57
1.65
<0.01
730
31.8
33.6


E
L
Cr30Al2La
2301
<0.01
<0.01
0.54
2.25
<0.01
809
32.4
36.6



L
Cr30Al1Ti
250060
<0.01
<0.01
0.54
1.16
0.01
759
30.8
33.3



L
Cr30Al1Ti
250063
<0.01
<0.01
0.53
1.39
<0.01
759
31.3
34.2



L
Cr30Al1TiNb
250066
0.31
<0.01
0.50
1.42
0.01
772
31.3
34.6



L
Cr30Al1TiNb
250065
0.31
<0.01
0.05
1.41
0.01
768
31.7
34.8



L
Cr30Al1TiNbZr
250067
0.31
<0.01
0.53
1.47
0.01
776
31.1
34.4



L
Cr30Al1TiNb
250068
0.88
<0.01
0.53
1.43
0.02
799
31.2
35.2


E
L
Cr28Al2
250129
<0.01
0.01
0.57
2.51
<0.01
740
30.7
34.3


E
L
Cr28Al2Y
250130
<0.01
<0.01
0.51
2.61
<0.01
766
30.7
34.3


E
L
Cr28Al2YC1
250132
0.01
0.02
0.60
2.61
0.02
762
30.9
34.1


E
L
Cr28Al2Nb.5C1
250133
0.50
0.02
0.52
2.76
0.02
800
31.1
35.2


E
L
Cr28Al2Nb.5C1
250148
0.56
0.03
0.48
2.62
0.01
779
30.5
34.5


E
L
Cr28Al2Nb1C1
250134
1.06
0.03
0.48
2.64
0.02
830
31.1
36.1


E
L
Cr28Al2Nb1C1
250147
0.90
0.02
0.43
2.15
0.02
774
30.5
34.3


E
L
Cr28Al2Nb1C1Y
250149
1.04
0.03
0.45
2.64
<0.01
800
30.6
35.1


E
L
Cr28Al2TiC1
250137
<0.01
0.03
0.5
2.88
<0.01
788
31.0
34.9


E
L
Cr28Al2TiC1
250138
<0.01
0.03
0.45
2.62
0.01
774
30.9
34.5
















TABLE 3b





Composition of the laboratory batches, Part 2. All values in %


by mass (The following values apply for all alloys: Pb: max. 0.002%, Zn:


max. 0.002%, Sn: max. 0.002%) (see Table 3a for meanings of T, E, G, L)



























Name
(Batch
S
P
Mg
Ca
V
Zr
Co





T
G
Alloy 602 CA
156817
0.002
0.005
0.004
0.001
0.03
0.08
0.05


T
G
Alloy 602 CA
160483
<0.002
0.007
0.010
0.002
—
0.09
0.04


T
G
Alloy 601
158656
0.002
0.008
0.012
<0.01
0.03
0.015
0.04


T
G
Alloy 690
80116
0.002
0.006
0.030
0.0009
—
<0.002
0.02


T
G
Alloy 690
111389
0.002
0.005
<0.001
0.0005
—
—
0.01



L
Cr30Al1La
2297
0.004
0.003
0.015
<0.01
<0.01
<0.002
—



L
Cr30Al1LaT
2300
0.003
0.002
0.014
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1TiLa
2298
0.004
0.002
0.016
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1TiNbLa
2308
0.002
0.002
0.014
<0.01
<0.01
<0.002
—



L
Cr30Al1CLaTi
2299
0.003
0.002
0.015
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1CLa
2302
0.003
0.002
0.013
<0.01
<0.01
<0.002
0.001


E
L
Cr30Al2La
2301
0.003
0.002
0.015
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1Ti
250060
0.003
0.002
0.009
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1Ti
250063
0.003
0.003
0.012
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1TiNb
250066
0.002
0.002
0.012
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1TiNb
250065
0.002
0.002
0.012
<0.01
<0.01
<0.002
<0.001



L
Cr30Al1TiNbZr
250067
0.003
0.002
0.010
<0.01
<0.01
0.069
<0.001



L
Cr30Al1TiNb
250068
0.002
<0.002
0.010
<0.01
<0.01
<0.002
<0.001


E
L
Cr28Al2
250129
0.004
0.003
0.011
0.0002
<0.01
<0.002
—


E
L
Cr28Al2Y
250130
0.003
0.003
0.013
<0.0002
<0.01
<0.002
—


E
L
Cr28Al2YC1
250132
0.003
0.004
0.009
0.0012
0.01
0.003
<0.01


E
L
Cr28Al2Nb.5C1
250133
0.005
0.003
0.009
0.0012
<0.01
0.004
0.01


E
L
Cr28Al2Nb.5C1
250148
0.004
0.004
0.010
0.0005
0.01
—
<0.01


E
L
Cr28Al2Nb1C1
250134
0.006
0.002
0.009
0.0009
<0.01
0.006
0.01


E
L
Cr28Al2Nb1C1
250147
0.002
0.002
0.010
0.0005
<0.01
0.01
0.01


E
L
Cr28Al2Nb1C1Y
250149
0.004
0.005
0.013
<0.0005
<0.01
0.006
<0.01


E
L
Cr28Al2TiC1
250137
0.005
0.004
0.008
0.0002
<0.01
0.004
<0.01


E
L
Cr28Al2TiC1
250138
0.005
0.004
0.010
0.0002
<0.01
0.003
0.01







Name
(Batch
Y
La
B
Hf
Ta
Ce
O





T
G
Alloy 602 CA
156817
0.060
—
0.003
—
—
—
0.001


T
G
Alloy 602 CA
160483
0.070
—
0.003
—
—
—
0.001


T
G
Alloy 601
158656
—
—
0.001
—
—
—
0.0001


T
G
Alloy 690
80116
—
—
0.002
—
—
—
0.0005


T
G
Alloy 690
111389
—
—
—
—
—
—
0.001



L
Cr30Al1La
2297
<0.001
0.062
<0.001
<0.001
<0.005
0.001
0.0001



L
Cr30Al1LaT
2300
<0.001
0.051
<0.001
<0.001
<0.005
0.001
0.0001



L
Cr30Al1TiLa
2298
<0.001
0.058
<0.001
<0.001
<0.005
0.001
0.002



L
Cr30Al1TiNbLa
2308
<0.001
0.093
<0.001
<0.001
<0.005
0.001
0.002



L
Cr30Al1CLaTi
2299
<0.001
0.064
<0.001
<0.001
<0.005
0.001
0.002



L
Cr30Al1CLa
2302
<0.001
0.057
<0.001
<0.001
<0.005
0.001
0.0001


E
L
Cr30Al2La
2301
<0.001
0.058
<0.001
<0.001
<0.005
0.001
0.002



L
Cr30Al1Ti
250060
<0.001
<0.001
<0.001
<0.001
<0.005
<0.001
0.003



L
Cr30Al1Ti
250063
<0.001
<0.001
<0.001
<0.001
<0.005
<0.001
0.003



L
Cr30Al1TiNb
250066
<0.001
<0.001
<0.001
<0.001
<0.005
<0.001
0.004



L
Cr30Al1TiNb
250065
<0.001
<0.001
<0.001
<0.001
<0.005
<0.001
0.005



L
Cr30Al1TiNbZr
250067
<0.001
<0.001
<0.001
<0.001
<0.005
<0.001
0.003



L
Cr30Al1TiNb
250068
<0.001
<0.001
<0.001
<0.001
<0.005
<0.001
0.004


E
L
Cr28Al2
250129
—
—
<0.0005
—
—
—
0.001


E
L
Cr28Al2Y
250130
0.063
—
<0.0005
—
—
—
0.001


E
L
Cr28Al2YC1
250132
0.07
—
0.001
—
—
—
0.001


E
L
Cr28Al2Nb.5C1
250133
0.01
—
—
—
—
—
0.001


E
L
Cr28Al2Nb.5C1
250148
<0.01
—
—
—
—
—
0.003


E
L
Cr28Al2Nb1C1
250134
0.01
—
<0.0005
—
—
—
0.003


E
L
Cr28Al2Nb1C1
250147
0.01
—
0.0012
—
—
—
0.001


E
L
Cr28Al2Nb1C1Y
250149
0.08
—
0.0012
—
—
—
0.002


E
L
Cr28Al2TiC1
250137
<0.01
—
0.0012
—
—
—
0.001


E
L
Cr28Al2TiC1
250138
<0.01
—
0.0012
—
—
—
0.004
















TABLE 4







Results of the tension tests at room temperature (RT), 600° C. and


800° C. The deformation rate was 8.33 10−5 1/s (0.5%/min) for Rp0.2 and 8.33


10−4 1/s (5%/min) for Rm; KG = grain size.























KG in
Rp0,2 in 
Rm in 
A5 in 
Rp0,2 in MPa
Rm in MPa
A5 in %
Rp0,2 in MPa
Rm in MPa





Name
Batch
μM
MPa RT
MPa RT
% RT
600° C.
600° C.
600° C.
800° C.
800° C.
Fa
Fk























T
Alloy 602 CA
156817
76
292
699
36
256
578
41
186
198
63.0
76.9


T
Alloy 602 CA
160483
76
340
721
42
254
699
69
186
197
62.2
79.6


T
Alloy 601
156656
136
238
645
53
154
509
54
133
136
43.3
56.3


T
Alloy 690
80116
92
279
641
56
195
469
48
135
154
36.2
41.6


T
Alloy 690
111389
72
285
630
50
188
465
51
—
—
36.8
43.6



Cr30Al1La
2297
233
221
637
67
131
460
61
134
167
33.5
43.4



Cr30Al1LaT
2300
205
229
650
71
131
469
65
132
160
33.9
46.3



Cr30Al1TiLa
2298
94
351
704
59
228
490
31
149
161
39.7
51.5



Cr30Al1TiNbLa
2308
90
288
683
55
200
508
39
174
181
41.6
61.0



Cr30Al1CLaTi
2299
253
258
661
62
212
475
59
181
185
42.3
50.0



Cr30Al1CLa
2302
212
353
673
59
233
480
59
189
194
40.0
52.9


E
Cr30Al2La
2301
155
375
716
66
298
504
49
275
277
33.2
55.6



Cr30Al1Ti
250060
114
252
662
67
183
509
62
143
154
39.3
60.4



Cr30Al1Ti
250063
118
252
659
70
176
510
57
148
152
39.6
52.9



Cr30Al1TiNb
250066
121
240
666
67
186
498
66
245
255
41.4
63.6



Cr30Al1TiNb
250065
132
285
685
61
213
521
58
264
265
41.8
64.0



Cr30Al1TiNbZr
250067
112
287
692
67
227
532
65
280
280
41.6
64.2



Cr30Al1TiNb
250068
174
261
666
69
205
498
65
297
336
44.9
83.2


E
Cr28Al2
250129
269
334
674
66
—
—
—
191
224
31.8
56.8


E
Cr28Al2Y
250130
167
322
693
63
252
522
53
220
244
32.6
57.9


E
Cr28Al2YC1
250132
189
301
669
65
—
—
—
226
226
40.2
64.0


E
Cr28Al2Nb.5C1
250133
351
399
725
67
334
522
33
285
353
40.8
78.9


E
Cr28Al2Nb.5C1
250148
365
353
704
60
284
523
58
259
344
41.2
79.5


E
Cr28Al2Nb1C1
250134
384
448
794
59
410
579
28
343
377
44.4
99.4


E
Cr28Al2Nb1C1
250147
350
372
731
57
306
547
49
309
384
43.0
89.1


E
Cr28Al2Nb1C1Y
250149
298
415
784
53
339
528
27
340
400
45.1
99.2


E
Cr28Al2TiC1
250137
142
379
745
59
327
542
29
311
314
44.0
70.4


E
Cr28Al2TiC1
250138
224
348
705
61
278
510
46
247
296
42.2
66.5
















TABLE 5







Results of the oxidation tests at


1000° C. in air after 1056 h

















mgross
mnet in
uumspell



Name
Batch 
Test No.
in g/m2 
g/m2
in g/m2
















T
Alloy 602 CA
160483
412
8.66
7.83
0.82


T
Alloy 602 CA
160483
425
5.48
5.65
−0.18


T
Alloy 601
156125
403
51.47
38.73
12.74


T
Alloy 690
111389
412
23.61
7.02
16.59


T
Alloy 690
111389
421
30.44
−5.70
36.14


T
Alloy 690
111389
425
28.41
−0.68
29.09



Cr30Al1La
2297
412
36.08
−7.25
43.33



Cr30Al1LaT
2300
412
41.38
−2.48
43.86



Cr30Al1TiLa
2298
412
49.02
−30.59
79.61



Cr30Al1TiNbLa
2306
412
40.43
16.23
24.20



Cr30Al1CLaTi
2308
412
42.93
−15.54
58.47



Cr30Al1CLa
2299
412
30.51
0.08
30.44



Cr30Al2La
2302
412
27.26
9.57
17.68


E
Cr30Al1Ti
2301
412
8.43
6.74
1.69



Cr30Al1Ti
250060
421
43.30
−19.88
63.17



Cr30Al1TiNb
250063
421
32.81
−22.15
54.96



Cr30Al1TiNb
250066
421
26.93
−16.36
43.28



Cr30Al1TiNbZr
250065
421
25.85
−24.27
50.12



Cr30Al1TiNb
250067
421
41.59
−15.56
57.16



Cr28Al2
250068
421
42.69
−39.26
61.95


E
Cr28Al2Y
250129
425
3.72
3.55
−0.16


E
Cr28Al2YC1
250130
425
4.68
4.90
−0.23


E
Cr28Al2Nb.5C1
250132
425
3.94
5.01
−1.07


E
Cr28Al2Nb.5C1
250133
425
2.56
3.98
−1.42


E
Cr28Al2Nb1C1
250148
425
3.16
3.21
−0.07


E
Cr28Al2Nb1C1
250134
425
3.34
4.23
−0.89


E
Cr28Al2Nb1C1Y
250147
425
2.72
2.62
0.10


E
Cr28Al2TiC1
250149
425
3.44
3.84
−0.40


E
Cr28Al2TiC1
250137
425
3.62
4.24
−0.62


E
Cr30Al1La
250138
425
3.87
4.28
−0.41









LIST OF REFERENCE NUMBERS


    FIG. 1 Metal loss due to metal dusting as a function of the aluminum and chromium content in a strongly carburizing gas with 37% Co, 9% H2O, 7% CO2, 46% H2, which has ac=163 and p(O2)=2.5·10−27. (from Hermse, C. G. M. and van Wortel, J. C.: Metal dusting: relationship between alloy composition and degradation rate. Corrosion Engineering, Science and Technology 44 (2009), p. 182-185).
    FIG. 2 Proportions of the phases in thermodynamic equilibrium as a function of the temperature of Alloy 690 (N06690) on the example of the typical batch 111389.
    FIG. 3 Proportions of the phases in thermodynamic equilibrium as a function of the temperature of Alloy 693 (N06693) on the example of Alloy 3 from Table 2.
    FIG. 4 Proportions of the phases in thermodynamic equilibrium as a function of the temperature of Alloy 693 (N06693) on the example of Alloy 10 from Table 2.

## Claims

1. Nickel-chromium-aluminum alloy with (in % by wt) greater than 25 to less than 30% chromium, 1.8 to 3.2% aluminum, 0.10 to 7.0% iron, 0.001 to 0.50% silicon, 0.005 to 2.0% manganese, 0.00 to 0.60% titanium, 0.10 to 1.10% niobium, respectively 0.0002 to 0.05% magnesium and/or calcium, 0.005 to 0.12% carbon, 0.001 to 0.050% nitrogen, 0.0001-0.020% oxygen, 0.001 to 0.030% phosphorus, max. 0.010% sulfur, max. less than 0.5% molybdenum, max. less than 0.5% tungsten, the rest nickel and the usual process-related impurities, wherein the following relationships must be satisfied:


Cr+Al≧28  (2a)



and Fp≦36.6 with  (3a)



Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.374*Mo+0.538*W−11.8*C  (4a)

where Cr, Fe, Al, Si, Ti, Nb, Mo, W and C are the concentrations of the elements in question in % by wt.

2. Alloy according to claim 1, with an iron content of 0.1 to 4.0%.

3. Alloy according to claim 1, with a silicon content of 0.001-0.20%.

4. Alloy according to claim 1, with a manganese content of 0.005 to 0.50%.

5. Alloy according to claim 1, with a titanium content of 0.001-0.60%.

6. Alloy according to claim 1, with a carbon content of 0.01 to 0.10%.

7. Alloy according to claim 1, further containing yttrium with a content of 0.01 to 0.20%.

8. Alloy according to claim 1, further containing lanthanum with a content of 0.001 to 0.20%.

9. Alloy according to claim 1, further containing cerium with a content of 0.001 to 0.20%.

10. Alloy according to claim 1, further containing cerium mixed metal with a content of 0.001 to 0.20%.

11. Alloy according to claim 1, further containing zirconium with a content of 0.01 to 0.20%.

12. Alloy according to claim 1, in which the zirconium is substituted completely or partly by 0.001 to 0.2% hafnium.

13. Alloy according to claim 1, further containing boron with a content of 0.0001 to 0.008%.

14. Alloy according to claim 1, further containing 0.0 to 5.0% cobalt.

15. Alloy according to claim 1, further containing at most 0.5% copper, wherein Formula 4a is supplemented by a term with Cu:


Fp=Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+1.26*Nb+0.477*Cu+0.374*Mo+0.538*W−11.8*C  (4b)

and Cr, Fe, Al, Si, Ti, Nb, Cu, Mo, W and C are the concentrations of the elements in question in % by wt.

16. Alloy according to claim 1, further containing at most 0.5% vanadium.

17. Alloy according to claim 1, wherein the impurities are adjusted in contents of max. 0.002% Pb, max. 0.002% Zn, max. 0.002% Sn.

18. Alloy according to claim 1, wherein the following formulas are satisfied:


Fa≦60  (5a)



with Fa=Cr+6.15*Nb+20.4*Ti+201*C  (6a),

where Cr, Nb, Ti and C are the concentrations of the elements in question in % by wt.

19. Alloy according to claim 1, wherein the following formula is satisfied:


Fk≧45  (7a)



with Fk=Cr+19*Ti+34.3*Nb+10.2*Al+12.5*Si+98*C+2245*B  (8a)

where Cr, Ti, Nb, Al, Si, C and B are the concentrations of the elements in question in % by wt.