CN114746565A

CN114746565A - Nickel-chromium-iron-aluminum alloy with good processability, creep property and corrosion resistance and application thereof

Info

Publication number: CN114746565A
Application number: CN202080083974.4A
Authority: CN
Inventors: H·哈坦多夫; B·诺瓦克
Original assignee: VDM Metals GmbH
Current assignee: VDM Metals GmbH
Priority date: 2019-12-06
Filing date: 2020-12-04
Publication date: 2022-07-12
Also published as: KR20220098789A; WO2021110217A1; EP4069874A1; DE102020132193A1; US20230002861A1; JP2023504842A

Abstract

The invention relates to a nickel-chromium-iron-aluminum alloy having in mass% from >17 to 33% chromium, from 1.8 to < 4.0% aluminum, from 0.10 to 15.0% iron, from 0.001 to 0.50% silicon, from 0.001 to 2.0% manganese, from 0.00 to 0.60% titanium, from 0.0002 to 0.05% magnesium and/or calcium, from 0.005 to 0.12% carbon, from 0.001 to 0.050% nitrogen, from 0.0001 to 0.020% oxygen, from 0.001 to 0.030% phosphorus, up to 0.010% sulfur, up to 2.0% molybdenum, up to 2.0% tungsten, the balance nickel with nickel > 50%, and process-related impurities common to applications in solar tower power stations using nitrate melts as heat transfer media, wherein the following relationships must be satisfied: fp ≦ 39.9 and (2a), Fp ═ Cr +0.272 × Fe +2.36 × Al +2.22 × Si +2.48 × Ti +0.374 × Mo +0.538 × W-11.8 × C (3a), wherein Cr, Fe, Al, Si, Ti, Mo, W and C are concentrations of the relevant elements in mass%.

Description

Nickel-chromium-iron-aluminum alloy with good processability, creep property and corrosion resistance and application thereof

The present invention relates to a nickel-chromium-iron-aluminum wrought alloy having outstanding high temperature corrosion resistance, good creep strength and improved workability.

Austenitic nickel-chromium-iron-aluminum alloys of varying nickel, chromium and aluminum contents have long been used in furnace construction and in the chemical and petrochemical industries. Good high temperature corrosion resistance and good high temperature strength/creep strength are required for such use.

Nickel alloys with different nickel, chromium and aluminium contents are also of great use in solar tower power stations due to their properties. These devices consist of a field of mirrors (heliostats) arranged around a tall tower. By means of a mirror, sunlight is concentrated on an absorber (solar receiver) mounted at the tip. The absorber consists of a tubular system in which a heat transfer medium is heated. The medium circulates in a circuit with an intermediate tank. The thermal energy is converted into electrical energy by means of a generator in a secondary circuit by means of a heat exchanger system. The heat transfer medium is primarily a Salt mixture of sodium Nitrate and potassium Nitrate Salt melts, which results in a maximum working Temperature of the Salt of about 700 deg.C (Kruizenga et al, Material Corrosion of High Temperature Alloys Immersed in 600 deg.C Binary Nitrate) depending on the alloy used for the component (Materials corporation of High Temperature Alloys in 600 deg.C Binary Nitrate Salt), Sandia Report, SAND 2013-.

At temperatures above 700 ℃, potassium nitrate salt melt can decompose significantly, which greatly increases corrosion to metal pipes. Thus, between 600 ℃ and 700 ℃ respectively, depending on the maximum working temperature of the material. The materials commonly used in the absorber were 800H alloy (material No. 1.4876, UNS N08810) or alloy 625 (material No. 2.4856, UNS N06625) (see table 1).

It is generally noted that the high temperature corrosion resistance of the alloys listed in table 1 increases with increasing chromium content. Alloy form containing aluminumTo have a more or less closed aluminium oxide layer (Al) thereunder₂O₃) Chromium oxide layer (Cr)₂O₃). The oxidation resistance can be improved by adding a small amount of high-affinity oxygen element, such as yttrium or cerium. The chromium content is slowly consumed during use of the application area to form the protective layer. A higher chromium content therefore increases the service life of the material, since a higher chromium content in the protective layer delays the chromium content falling below the critical limit and forms Cr-free layers₂O₃Point in time of an oxide other than iron and/or nickel, for example. The high temperature corrosion resistance can be further improved by adding aluminum and/or silicon. At a certain minimum content, these elements form a closed layer below the chromium oxide layer and reduce the consumption of chromium.

The high-temperature strength or creep strength at a given temperature is improved in particular by the high carbon content. However, high levels of mixed crystal strengthening elements such as chromium, aluminum, silicon, molybdenum, and tungsten may also improve high temperature strength. In the range of 500 ℃ to 900 ℃, aluminum, titanium and/or niobium may be added to improve strength by precipitating gamma' -and/or gamma "-phases.

Table 1 lists examples of these alloys according to the prior art.

Compared to alloy 600(N06600) or alloy 601(N06601), alloy 602CA (N06025), alloy 693(N06693), alloy 603(N06603), or alloy 214(N07208) is known to have excellent corrosion resistance due to its high aluminum content exceeding 1.8%. The 214 alloy exhibits excellent Corrosion resistance in a 60% sodium Nitrate/40% potassium Nitrate melt due to its High aluminum content (Kruizenga et al, Material correction of High Temperature Alloys Immersed in 600 ℃ Binary Nitrate Salt), Sandia Report, SAND 2013-2526, 2013). At the same time, alloy 602CA (N06025), alloy 693(N06693), alloy 603(N06603) or alloy 214(N07208) exhibit excellent high temperature strength or creep strength due to their high carbon content or high aluminum content in the temperature range in which nitrate melts are used. Alloys 602CA (N06025) and 603(N06603) themselves have excellent high temperature strength or creep strength at temperatures above 1000 ℃. However, for example, high aluminum content impairs processability, and higher aluminum content impairs greater damage (for example, alloy 693(N06693) and alloy 214 (N07208)). The same is true of the increased amount of silicon, which forms a low-melting intermetallic phase with nickel. In alloy 602CA (N06025) or alloy 603(N06603), cold formability is limited especially by the high proportion of primary carbides.

WO 2019/075177 a1 discloses a solar tower system, comprising absorption tubes, storage tanks and heat exchangers, all of which contain molten salts as heat transfer media at temperatures >650 ℃, wherein the disclosure includes at least one of the components of the absorber pipe, the storage tank and the heat exchanger being made of an alloy, it contains, in mass percent, 25 to 45% of Ni, 12 to 32% of Cr, 0.1 to 2.0% of Nb, up to 4% of Ta, up to 1% of V, up to 2% of Mn, up to 1.0% of Al, up to 5% of Mo, up to 5% of W, up to 0.2% of Ti, up to 2% of Zr, up to 5% of Co, up to 0.1% of Y, up to 0.1% of La, up to 0.1% of Cs, up to 0.1% of other rare earths, up to 0.20% of C, up to 3% of Si, 0.05 to 0.50% of N, up to 0.02% of boron and the balance iron and impurities.

EP 0508058 a1 discloses an austenitic nickel ferrochromium alloy consisting of, in mass percent: 0.12-0.3% of C, 23-30% of Cr, 8-11% of Fe, 1.8-2.4% of Al, 0.01-0.15% of Y, 0.01-1.0% of Ti, 0.01-1.0% of Nb, 0.01-0.2% of Zr, 0.001-0.015% of Mg, 0.001-0.01% of Ca, at most 0.03% of N, at most 0.5% of Si, at most 0.25% of Mn, at most 0.02% of P, at most 0.01% of S, and the balance of nickel, including inevitable impurities related to smelting.

US 4882125B 1 discloses a high chromium content nickel alloy characterized by excellent resistance to sulfidation and oxidation at temperatures above 1093 ℃, excellent creep strength for more than 200 hours at temperatures above 983 ℃ and voltages of 2000PSI, good tensile strength and good tensile elongation (both at room temperature and at elevated temperature), consisting of, in weight percent: 27-35% Cr, 2.5-5% Al, 2.5-6% Fe, 0.5-2.5% Nb, up to 0.1% C, 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 the balance Ni.

EP 0549286 discloses a high temperature resistant nickel-chromium alloy comprising the following: 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 one of the elements comprising the group Mg, Ca, Ce in total, < 0.5% Mg + Ca in total, < 1% Ce, 0.0001-0.1% B, 0-0.5% Zr, 0.0001-0.2% N, 0-10% Co, the balance iron and impurities.

A high-temperature-resistant nickel-base alloy is known from DE 60004737T 2, which comprises the following: 0.1% or less of C, 0.01 to 2% of Si, 2% or less of Mn, 0.005% or less of S, 10 to 25% of Cr, 2.1 to < 4.5% of Al, 0.055% or less of N, and 0.001 to 1% in total of at least one of the elements B, Zr, Hf, wherein the elements may be present in the following amounts: b is less than or equal to 0.03 percent, Zr is less than or equal to 0.2 percent, and Hf is less than 0.8 percent. 0.01-15% Mo, 0.01-9% W, wherein the total content of Mo + W may be 2.5-15%, 0-3% Ti, 0-0.01% Mg, 0-0.01% Ca, 0-10% Fe, 0-1% Nb, 0-1% V, 0-0.1% Y, 0-0.1% La, 0-0.01% Ce, 0-0.1% Nd, 0-5% Cu, 0-5% Co, the balance nickel. For Mo and W, the following formula must be satisfied:

2.5≤Mo+W≤15 (1)

DE 102015200881a1 describes a tubular body of austenitic steel for salt melts, in particular a solar receiver absorber tube using salt melt as a heat carrier, or other lines for transporting salt melt, which comprises, on a weight basis:

0% to 0.025% C, preferably 0.0095% to 0.024% C;

0.05% to 0.16% N;

2.4 to 2.6% Mo;

0.4% to 0.7% Si;

0.5% to 1.63% Mn;

0% to 0.0375% P;

0% to 0.0024% S;

17.15% to 18.0% Cr;

12.0% to 12.74% Ni;

0.0025% to 0.0045% of B;

with the balance being iron and possible common impurities.

DE 102012002514 describes a nichrome-aluminite alloy with, in mass percent, 12 to 28% chromium, 1.8 to 3.0% aluminum, 1.0 to 15% iron, 0.01 to 0.5% silicon, 0.005 to 0.5% manganese, 0.01 to 0.20% yttrium, 0.02 to 0.60% titanium, 0.01 to 0.2% zirconium, 0.0002 to 0.05% magnesium, 0.0001 to 0.05% calcium, 0.03 to 0.11% carbon, 0.003 to 0.05% nitrogen, 0.008 to 0.008% boron, 0.0001 to 0.010% oxygen, 0.001 to 0.030% phosphorus, at most 0.010% sulfur, at most 0.5% molybdenum, at most 0.5% tungsten, the balance nickel and the usual process-related impurities, wherein the following relationships must be satisfied: when PN >0, 7.7C-x a <1.0 and a is PN, or when PN ≦ 0, a is 0. Wherein x is (1.0Ti +1.06Zr)/(0.251Ti +0.132Zr) and PN is 0.251Ti +0.132Zr-0.857N and Ti, Zr, N, C are concentrations of the relevant elements in mass percent.

DE 102012013437B3 describes the use of a nickel chromium aluminum iron alloy for producing seamless tubes, which alloy has, in mass percent, > 25% to 28% chromium, > 2% to 3.0% aluminum, 1.0% to 11% iron, 0.01% to 0.2% silicon, 0.005% to 0.5% manganese, 0.01% to 0.20% yttrium, 0.02% to 0.60% titanium, 0.01% to 0.2% zirconium, 0.0002% to 0.05% magnesium, 0.0001% to 0.05% calcium, 0.03% to 0.11% carbon, 0.003% to 0.05% nitrogen, 0.0005 to 0.008% boron, 0.0001 to 0.010% oxygen, 0.001 to 0.030% phosphorus, maximum 0.010% sulfur, maximum 0.5% molybdenum, maximum 0.5% tungsten, maximum 0.5% nickel, the balance of the usual processes, wherein the following relationships have to be satisfied: 0<7.7C-x a <1.0(2) and a ═ PN, when PN >0(3a) or a ═ 0, when PN ≦ 0(3b) and x ═ 1.0Ti +1.06Zr)/(0.251Ti +0.132Zr) (3C), where PN ═ 0.251Ti +0.132Zr-0.857N (4) and Ti, Zr, N, C are the concentrations in mass percent of the relevant elements.

DE 102012011161a1 describes a nickel-chromium-aluminum alloy having, in mass percent, 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% magnesium and/or calcium, respectively, 0.005 to 0.12% carbon, 0.001 to 0.050% nitrogen, 0.0001 to 0.020% oxygen, 0.001 to 0.030% phosphorus, at most 0.010% sulfur, at most 2.0% molybdenum, at most 2.0% tungsten, the balance nickel and the usual process-related impurities, wherein the following relationships must be satisfied: cr + Al ≧ 28(2a) and Fp ≦ 39.9 and (3a) Fp ═ Cr +0.272Fe +2.36Al +2.22Si +2.48Ti +0.374Mo +0.538W +11.8C (4a), in which Cr, Fe, Al, Si, Ti, Mo, W and C are the concentrations of the relevant elements in mass%.

US 5,862,800 a discloses a solar tower power plant for bringing solar energy into molten salt, wherein tubes of alloy 625 of the same diameter and wall thickness are used. Alloy 625 has the following composition: 20-23% of Cr, less than or equal to 0.4% of Al, less than or equal to 5% of Fe, less than or equal to 0.5% of Si, less than or equal to 0.5% of Mn, less than or equal to 0.4% of Ti, 0.03-0.1% of C, less than or equal to 0.02% of P, less than or equal to 0.015% of S, 8-10% of Mo, 3.15-4.15% of Nb and the balance of Ni (more than or equal to 58%).

The object of the invention is to design a nickel alloy with a sufficiently high chromium and aluminum content to have

The stability of the phase is good and the phase stability is good,

good processability of the steel sheet, good workability,

good resistance to air corrosion, similar to alloy 602CA (N06025)

And good high temperature strength/creep strength,

in order to provide for other types of application scenarios.

This task is accomplished by a nickel-chromium-iron-aluminum alloy having, in mass percent, >17 to 33% chromium, 1.8 to < 4.0% aluminum, 0.10 to 15.0% iron, 0.001 to 0.50% silicon, 0.001 to 2.0% manganese, 0.00 to 0.60% titanium, 0.0002 to 0.05% 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, up to 0.010% sulfur, up to 2.0% molybdenum, up to 2.0% tungsten, the balance nickel having a nickel content of > 50%, and process-related impurities common for applications in solar tower power stations using nitrate melts as heat transfer media, wherein the following relationships must be satisfied:

fp is less than or equal to 39.9 and (2a)

Fp＝Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W-11.8*C (3a)

Wherein Cr, Fe, Al, Si, Ti, Mo, W and C are concentrations of the relevant elements in mass%.

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

Advantageous further developments of the subject matter of the invention can be taken from the dependent claims.

All alloy contents are stated in mass percent unless otherwise stated.

The distribution range of the element chromium is between > 17% and 33%, preferred ranges can be set as follows:

- >18 to 33%

-20% to 33%

-22 to 33%

-24 to 33%

-25% to 33%

-26 to 33%

-27 to 32%

-28 to 32%

- >28 to 32%

-29 to 31%

The aluminum content is between 1.8% and < 4.0%, wherein here too, depending on the field of application of the alloy, the preferred aluminum content can be set as follows:

-1.8 to 3.8%

-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%

-2.5% to < 4.0%

->3.0-<4.0％

->3.2-<4.0％

->3.2-3.8％

->3.0-<3.5％

The iron content is between 0.1% and 15.0%, wherein depending on the field of application, the preferred contents can be set within the following distribution ranges:

-0.1-12.0％

-0.1-10.0％

-0.1-7.5％

-0.1-4.0％

-0.1-3.0％

-0.1-<2.5％

-0.1-2.0％

-0.1-<2.0％

-0.1-1.0％

-0.1-<1.0％

-1.0-15.0％

-1.25-15.0％

->2.5-15.0％

->4.0-15.0％

->4.0-12.0％

->7.0-15.0％

->7.0-10.5％

-7.5-10.5％

the silicon content is between 0.001 and 0.50%. Preferably, the Si in the alloy may be provided in the following distribution range:

-0.001-<0,40％

-0.001-<0.25％

-0.001-0.20％

-0.001-<0.10％

-0.001-<0.05％

the same applies to the element manganese, which may be present in the alloy in an amount of 0.001% to 2.0%. Alternatively, the following distribution ranges are also conceivable:

-0.001-0.50％

-0001-<0.40％

-0.001-0.20％

-0.001-0.10％

-0.001-<0.05％

-0.005-<0.05％

the titanium content is between 0.00 and 0.60%. Preferably, Ti may be provided in the alloy in the following distribution ranges:

-0.001-0.60％

-0.001-0.50％

-0.001-0.30％

-0.001-0.10％

-0.01-0.30％

-0.01-0.25％

-0.00-<0.02％

magnesium and/or calcium are also contained at a content of 0.0002 to 0.05%. There is preferably the possibility of adjusting these elements in the alloy as follows:

-0.0002–0.03％

-0.0002–0.02％

-0.0005–0.02％

the alloy contains 0.005 to 0.12% carbon. Preferably, this can be provided in the alloy in the following distribution ranges:

-0.01-<0.12％

-0.005-0.10％

-0.005-<0.08％

-0.005-<0.05％

-0.01-0.03％

-0.01-<0.03％

-0.02-0.10％

-0.03-0.10％

in the same way applies to elemental nitrogen, which is contained in a content of between 0.001 and 0.05%. Preferred contents can be given as follows:

-0.003-0.04％

the alloy also contains between 0.001 and 0.030% phosphorus. Preferred contents can be given as follows:

-0.001-0.020％

the alloy also contains between 0.0001 and 0.020% oxygen, especially comprised between 0.0001 and 0.010%.

The elemental sulphur in the alloy is given as follows:

-sulphur at most 0.010%

Molybdenum and tungsten are contained in the alloy, individually or in combination, in amounts of up to 2.0% each. Preferred contents can be given as follows:

-Mo is at most 1.0%

-W is at most 1.0%

-Mo is at most < 0.50%

-W is at most < 0.50%

-Mo < 0.10% at most

-W is at most < 0.10%

-Mo < 0.05% at most

-W is at most < 0.05%

Furthermore, in order to provide sufficient phase stability, the following relationship must be satisfied:

fp is less than or equal to 39,9 and (2a)

Fp＝Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W-11.8*C (3a)

The preferred ranges may be set as:

Fp≤38.4 (2b)

Fp≤36.6 (2c)

the nickel content is greater than or equal to 50% or greater than 50%. Preferably, the following settings are possible:

-55% or more or 55%

-60% or more or 60% or more

- > 65% or more

- > 68% or more

Optionally, the content of the element yttrium in the alloy may be set to 0.001 to 0.20%. Preferably, Y may be provided in the alloy in the following distribution range:

-0.001-0.15％

-0.001-0.10％

-0.001-0.08％

-0001-<0.045％

-0.01-<0.045％

optionally, the content of the element lanthanum in the alloy may be set to 0.001 to 0.20%. Preferably, La may be disposed in the alloy in the following distribution range:

-0.001-0.15％

-0.001-0.10％

-0.001-0.08％

-0.001-0.04％

-0.01-0.04％

optionally, the content of the element cerium in the alloy may be set to 0.001 to 0.20%. Preferably, Ce may be provided in the alloy in the following distribution ranges:

-0.001-0.15％

-0.001-0.10％

-0.001-0.08％

-0.001-0.04％

-0.01-0.04％

optionally, a cerium mixed metal (a mixture of about 50% Ce, about 25% La, about 15% Pr, about 5% Nd, Sm, Tb, and Y) may also be used at a content of 0.001 to 0.20% in the case of simultaneous addition of cerium and lanthanum. Preferably, the cerium mixed metal in the alloy may be disposed in the following distribution range:

-0.001-0.15％

-0.001-0.10％

-0.001-0.08％

-0.001-0.04％

-0.01-0.04％

optionally, the content of elemental niobium in the alloy may be set between 0.00% and 1.10%. Preferably, the niobium may be disposed in the alloy in the following distribution range:

-0.001-<1.10％

-0.001-<0.70％

-0.001-<0.50％

-0.001-0.30％

-0.001-<0.30％

-0.001-<0.20％

-0.01-0.30％

-0.10-1.10％

-0.20-0.70％

if the alloy contains niobium, the formula (3a) must be supplemented with niobium 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 (3b)

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

Optionally, the zirconium content is between 0.001 and 0.20%. Preferably, the zirconium may be disposed in the alloy in the following distribution:

-0.001-0.15％

-0.001-<0.10％

-0.001-0.07％

-0.001-0.04％

-0.01-0.15％

-0.01-<0.10％

optionally, the hafnium content is between 0.001 and 0.20%. Preferably, hafnium may be present in the alloy in the following distribution ranges:

-0.001-0.15％

-0.001-<0.10％

-0.001-0.07％

-0.001-0.04％

-0.01-0.15％

-0.01-<0.10％

optionally, 0.001 to 0.60% tantalum may also be included in the alloy.

Preferably, Ta may be provided in the alloy in the following distribution:

-0.001-0.60％

-0.001-0.50％

-0.001-0.30％

-0.001-0.10％

-0.001-<0.02％

-0.01-0.30％

-0.01-0.25％

optionally, elemental boron may be included in the alloy as follows:

-00001-0008％

preferred contents can be given as follows:

-0.0005-0.008％

-0.0005-0.004％

in addition, the alloy may optionally contain 0.0% to 5.0% cobalt, which may also be limited as follows:

-0.001 to 5.0%

-0.01 to 5.0%

-0.01 to < 5.0%

-0.01 to 2.0%

-0.1 to 2.0%

-0.1 to < 2.0%

-0.001 to 0.5%

In addition, copper may be included in the alloy up to 0.5%.

The copper content may also be limited as follows:

-at most 0.20%

-at most 0.10%

-at most 0.05%

-<0.05％

-at most 0.015%

-<0.015％

If the alloy contains copper, then the formula (3a) must be supplemented with copper 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 (3c)

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

If the alloy contains niobium and copper, then formula (3a) must be supplemented with niobium plus one term and with copper plus one term 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 (3d)

In addition, up to 0.5% vanadium may be included in the alloy.

The vanadium content can also be limited as follows:

-at most 0.20%

-at most 0.10%

-at most 0.05%

Finally, for impurities, the elements lead, zinc and tin may be given in the following contents:

pb is 0.002% at most

Zn is 0.002% at most

Sn is at most 0.002%.

Further, the following relationship that may exhibit particularly good workability may be selectively satisfied:

fa is less than or equal to 60 and (4a)

Fa＝Cr+20.4*Ti+201*C (5a)

Wherein Cr, Ti and C are concentrations of the relevant elements in mass%.

The preferred ranges may be set as:

Fa≤54 (4b)

if the alloy contains niobium, then the formula (5a) must be supplemented with niobium plus one term:

Fa＝Cr+6.15*Nb+20.4*Ti+201*C (5b)

wherein Cr, Nb, Ti and C are concentrations of the relevant elements in mass%.

Further, the following relationship of high temperature strength or creep strength, which exhibits particularly good properties, can be selectively satisfied:

fk is more than or equal to 47 and (6a)

Fk＝Cr+19*Ti+10.2*Al+12.5*Si+98*C (7a)

Wherein Cr, Ti, Al, Si and C are concentrations of the relevant elements in mass%.

The preferred ranges may be set as:

Fk≥49 (6b)

Fk≥53 (6c)

if niobium and/or boron is included in the alloy, formula (7a) must be supplemented with niobium and/or boron additions as follows:

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

(7b)

wherein Cr, Ti, Nb, Al, Si, C and B are concentrations of the relevant elements in mass%.

The alloy according to the invention is preferably open-smelted and then processed in a VOD (Vacuum oxygen decarburization) or VLF (Vacuum Ladle Furnace) plant. But melting and casting in Vacuum (VIM) is also possible. After casting into blocks or as continuous casting, the alloy is annealed in the desired semifinished product form, optionally at a temperature between 900 ℃ and 1270 ℃ for 0.1 to 100 hours, and then thermoformed, optionally with intermediate annealing between 900 ℃ and 1270 ℃ for 0.05 to 100 hours. The surface of the material may optionally (also multiple times) be chemically and/or mechanically removed during and/or at the end of this period for cleaning. After the hot forming has ended, cold forming with a degree of forming of up to 98% can optionally be carried out to give the desired semifinished product, optionally with an intermediate annealing at 700 ℃ to 1250 ℃ for 0.1 min to 70 h, optionally under a protective gas, for example argon or hydrogen, and then cooling in air, in a moving annealing atmosphere or in a water bath. Solution annealing is then carried out at a temperature in the range of 700 ℃ to 1250 ℃ for 0.1 minutes to 70 hours, optionally under a protective gas, such as argon or hydrogen, and then cooling in air, in a moving annealing atmosphere or in a water bath. Thereafter, solution annealing is performed at a temperature ranging from 700 ℃ to 1250 ℃ for 0.1 minutes to 70 hours, if necessary. Optionally under a protective gas, such as argon or hydrogen, and then cooled in air, a moving annealing atmosphere, or a water bath. Optionally, chemical and/or mechanical cleaning of the material surface may be performed during and/or after the last anneal.

The alloy according to the invention can be produced and used very well in the form of products in the form of strips, sheets, bars, wires, longitudinal welded tubes and seamless tubes.

These product forms are produced with an average grain size of 5 μm to 600 μm. A preferred range is between 20 μm and 200 μm.

The alloy according to the invention is preferably used in solar tower power stations using nitrate melts as heat transfer medium.

It can be used for all parts in contact with molten salts.

It is particularly useful for absorbers (solar receivers) in solar power plant towers and/or for heat exchangers and/or storage and/or transport pipes of power generation circuits (for example by steam turbines).

The nitrate salt may preferably be a mixture of sodium nitrate and potassium nitrate salt.

The mixture may preferably consist of the following composition:

50-70% of sodium nitrate and 50-30% of potassium nitrate

55-65% of sodium nitrate and 45-35% of potassium nitrate

58-62% of sodium nitrate and 42-38% of potassium nitrate

Alternatively, a mixture of sodium nitrate, potassium nitrate and sodium nitride may be used.

If desired, the salt mixture may also be in pure CO₂The composition is used under an atmosphere.

The maximum working temperature is 800 ℃. The limitations can be as follows:

-up to 750 ℃ C

-up to 700 ℃ C

-up to 680 deg.C

-up to 650 deg.C

-<650℃

-up to 620 ℃ C

-up to 600 deg.C

-<600℃

The tests carried out

Phase stability

The equilibrium-occurring phases of the different alloy variants were calculated using the JMatPro program of Thermotech. The nickel-based alloy database TTNI7 of Thermotech is used as a data base for calculations.

The formability was determined by tensile testing at room temperature according to DIN EN ISO 6892-1. The stretching limit Rp is determined in this way_0.2Tensile Strength R_mAnd a stretch ratio a to break. From the original measurement distance L on the broken sample₀And measuring the length L after fracture_uElongation of (b) determines the elongation a:

A＝(L_U-L₀)/L₀ 100％＝△L/L₀ 100％

the elongation at break has the following designation according to the measured length:

for example, for A₅Measuring the length L₀＝5·d₀And d is₀Round specimen initial diameter.

A diameter of 6mm and a measurement length L in the measurement range₀The test was performed on a circular sample of 30 mm. The samples were taken transversely to the direction of formation of the blanks. The forming speed is at R_p0.2Is 10MPa/s and is at R_mIs 6.710^-3 1/s(40％/min)。

The measurement of the elongation A in the room-temperature tensile test is taken as a measure of the plasticity. A well processable material should have a stretch of at least 50%.

The high-temperature strength is determined in a hot tensile test in accordance with DIN EN ISO 6892-2. The tensile limit R is determined here analogously to the tensile test at room temperature (DIN EN ISO 6892-1)_p0.2Tensile Strength R_mAnd a stretch ratio a to break.

A diameter of 6mm in the measuring range and an initial measuring length L₀The test was performed on a circular sample of 30 mm. The samples were taken transversely to the direction of formation of the blanks. The forming speed is at R_p0.2Is 8.3310^-51/s (0.5%/min) and R_m 8.33 10^-41/s (5%/min) (DIN EN ISO 6892-2).

The sample was mounted in a tensile tester at room temperature and heated to the desired temperature without applying a tensile force. After reaching the test temperature, temperature compensation was performed for one hour (600 ℃) or two hours (700 ℃ to 1100 ℃). Thereafter, the sample was loaded in tension to maintain the desired extension rate and the test was started.

The creep strength of the material can be increased with increasing high temperature strength. Therefore, high temperature strength is also used to evaluate creep strength of different materials.

Oxidation test was carried out in 1000 ℃ air and corrosion resistance at high temperature was measured, with the test being interrupted every 96 hours and the oxidation-induced corrosion being measuredThe sample mass changed. During the experiment, the samples were placed in a ceramic crucible in order to optionally collect any exfoliated oxide and thus the quality of the exfoliated oxide can be determined. The sum of the mass change of the sample (net mass change) and the mass of exfoliated oxide is the total mass change of the sample. The specific mass change is the mass change associated with the sample surface. M is as follows_NettoRepresenting the change in specific net mass, m_BruttoRepresents the specific total mass change, m_spallIndicating the change in specific mass of exfoliated oxide. The test was carried out on a sample having a thickness of about 5 mm. 3 samples were removed from each batch, where the values given are the average of these 3 samples.

Attribute description

Corrosion resistance in salt melts

Nickel alloy 625(N06625), alloy 120(N08120), alloy 230(N02230), alloy 242(N10242), alloy 214(N07208) (table 1) were investigated in particular for their corrosion resistance in a salt melt consisting of 60% sodium nitrate salt and 40% potassium nitrate salt, circulated with air, in Kruizenga et al (2013, corrosive material of high temperature alloys immersed in 600 ℃). The analysis of the alloys used is shown in table 2. After the test was completed, the weight of the oxide layer was determined by removing the oxide layer from the metal surface and weighing the sample before, after and after the removal of the oxide layer. This determines the weight loss (loss of scale removal) relative to the sample surface before the test.

Table 3 shows the corrosion rate after 3000 hours: once in mg/cm²The loss of scale removal was measured once as loss of metal in μm/year. The lowest corrosion rate is alloy 214 with a corrosion rate of 5.7 μm/year with an aluminum content of 4.5%, followed by alloy 224 with a corrosion rate of 8.3 μm/year with an aluminum content of 3.8%. All other nickel alloys tested (alloy 625, alloy 120, alloy 242, and alloy 230) had significantly higher corrosion rates of 16.8 μm/year, with higher aluminum contents below 0.5%. Alloy 214 and alloy 224 form an aluminum oxide layer that provides good protection against nitrate melts. If the aluminum content is too low, such as alloy 625, alloy 120, alloy 242, and alloy 230, no aluminum oxide layer will be formed, and thusResulting in an increased corrosion rate. It is therefore advantageous that the alloy used in the nitrate melt has a sufficiently large aluminium content to form a closed aluminium oxide layer.

In addition to having excellent corrosion resistance in nitrate melts, the alloy according to the invention has the following characteristics:

good phase stability

Good processability

Good resistance to air corrosion, similar to the 602CA alloy (N06025)

Good high temperature strength/creep strength

Stability of the phases

In nickel chromium iron aluminium systems with additions of Ti and/or Nb, depending on the alloy content, various brittle TCP (topologically close-packed) phases may form, such as Laves, Sigma or μ -phases or brittle h-or e-phases (see e.g. Ralf burgel, handbook of high temperature materials technology, 3 rd edition, Vieweg press, Wiesbaden, 2006, page 370-. For example, the calculation of the equilibrium phase ratio of N06690 of batch 111389 as a function of temperature (typical composition see Table 4) shows computationally that the temperature at 720 deg.C (T.sub._{s BCC}) Alpha-chromium (BCC phase in fig. 1) is formed in significant proportional amounts. The formation of this phase is very difficult because it is analytically very different from the base material. However, if the solvus temperature T of the phase_{s BCC}Very high, it appears with certainty, as E. "Slevilden, J.Z.Albertsen.U.Fink," Tjeldbergold Methanol Plant: Metal Dual investments, "corosion/2011, article No. 11144(Houston, TX: NACE 2011), page 15" describes a variant of alloy 693(UNS 06693). For alloy 3 or alloy 10 of table 4, fig. 2 and 3 show the phase diagrams of the alloy 693 variant (from US 4,88,125 table 1). This phase is brittle and therefore leads to unnecessary brittleness of the material. Formation temperature T of alloy 3_{s BCC}1079 deg.c and 939 deg.c as the forming temperature of alloy 10. No alpha-chromium (BCC phase) is described on "E.Slevilden, J.Z.Albertsen.U.Fink, Tjeldbergoden methane Plant: Metal Dual Investigations," corosion/2011, article No. 11144(Houston, TX: NACE 2011), page 15Precise analysis of the alloy under form, but it can be assumed that in the alloy 693 example given in Table 4, the highest solvus temperature T is computationally the highest_{s BCC}Alpha-chromium may be formed in the analysis of (e.g., alloy 10). Calibration analysis in "E.Slevolden, J.Z.Albertsen.U.Fink, Tjeldbergoden methane Plant: Metal Dual Investigations," corosion/2011, article No. 11144(Houston, TX: NACE 2011), page 15 "(using a reduced solvent temperature T. RTM_{s BCC}) Alpha-chromium is only detected near the surface. In order to avoid the occurrence of such brittle phases, in the alloys of the invention the solvus temperature T_{s BCC}939 ℃ or less, which corresponds to the lowest solvus temperature T in the example of alloy 693 in Table 4_{s BCC}(taken from table 1 of U.S. Pat. No. 4,88,125).

This is especially true if the following equation is satisfied:

fp is less than or equal to 39.9 and (2a)

Wherein Cr, Al, Fe, Si, Ti, Nb, Cu, Mo, W and C are concentrations of the relevant elements in mass%. Table 4 of the alloys according to the prior art shows that the Fp of alloy 8, alloy 3 and alloy 2 is greater than 39.9 and that of alloy 10 is exactly 39.9. For T_{s BCC}All other alloys with the temperature less than 939 ℃ and the Fp less than or equal to 39.9.

Processability

Formability is considered here for example for processability.

The alloy may be hardened by a variety of mechanisms so that it has high temperature strength or creep strength. Thus, another element is added to the alloy, and the distribution, depending on the element, leads to a more or less increased strength (mixed grain hardening). A more effective method is to increase the strength by fine particles or precipitation (particle hardening). For example, carbides may be formed by adding a gamma' -phase of aluminum and other elements (e.g., Ti) to a nickel alloy or by adding carbon to a chromium-containing nickel alloy (see Ralf B ü rgel, handbook of high temperature materials, third edition, Vieweg Press, Wiesbaden, 2006, page 358-.

The increase in the content of the γ' -phase-forming element or the C content increases the high-temperature strength, but increasingly impairs the formability even in the solution-annealed state.

For very well formable materials, the target is the elongation A in the tensile test at room temperature₅50% or more and at least 45% or more.

This is achieved in particular when the following relationships are satisfied between the carbide-forming elements Cr, Nb, Ti and C:

fa ≤ 60 and (4a)

Fa＝Cr+6.15*Nb+20.4*Ti+201*C (5b)

Wherein Cr, Nb, Ti and C are concentrations of the relevant elements in mass%.

High temperature strength/creep Strength

At the same time the tensile limit or tensile strength should at least reach the value of alloy 601 at higher temperatures (see table 6).

The temperature is 600 ℃: ultimate elongation R_p0.2>150 Mpa; tensile Strength R_m>500MPa (8a,8b)

800 ℃ below zero: ultimate elongation R_p0,2>130 Mpa; tensile Strength R_m>135MPa (8c,8d)

Desirably, the tensile limit or tensile strength is within the tensile strength range of alloy 602CA (see table 6). At least three of the following four relationships should be satisfied:

the temperature is 600 ℃: ultimate elongation R_p0.2>250 MPa; tensile Strength R_m>570Mpa (9a,9b)

800 ℃ below zero: ultimate elongation R_p0.2>180 MPa; tensile Strength R_m>190Mpa (9c,9d)

The requirements 8a, 8b, 8c and 8d are particularly met when the following relationships are satisfied between the main hardening elements:

fk is more than or equal to 47 and (6a)

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

(7b)

-resistance to air corrosion:

the alloy according to the invention should have a good resistance to air corrosion similar to that of alloy 602CA (N06025).

The embodiment is as follows:

-production:

tables 5a and 5b show the analysis of laboratory-scale smelting batches, as well as some prior art large-scale smelting batches for comparison 602CA alloy (N06025), 690 alloy (N06690), 601 alloy (N06601). Batches according to the prior art are marked with T and batches according to the invention are marked with E. The laboratory-scale smelted batches were labeled with L and the large-scale smelted batches were labeled with G.

The alloy blocks in tables 5a and b, vacuum smelted on a laboratory scale, were annealed at between 900 ℃ and 1270 ℃ for 8 hours and hot rolled to a final thickness of 13mm or 6mm by means of hot rolling and further intermediate annealing at between 900 ℃ and 1270 ℃ for 0.1 to 1 hour. The resulting sheet was solution annealed at between 900 ℃ and 1270 ℃ for 1 hour. Samples required for the measurement were made from these sheets.

In the case of large-scale smelting of alloys, samples were taken from large-scale production from factory-made sheets of appropriate thickness. Samples required for the measurement were made from these sheets.

The grain size of all alloy variants is typically 70 to 505 μm.

For the sample batches in tables 5a and b, the following properties were compared:

corrosion resistance in nitrate melts

-phase stability

Formability based on tensile test at room temperature

High temperature strength/creep Strength by Hot tensile test

Corrosion resistance to air by means of oxidation test

Corrosion resistance in nitrate melts:

in the case of the laboratory-scale smelting batches 2301, 250129 to 250138 and 250147 to 250149, and batches 250164, 250311 and 250526, the content of aluminum was 1.8% or more. The aluminium content is sufficiently large that a closed aluminium oxide layer is formed below the chromium oxide layer. They therefore meet the requirements of corrosion resistance in salt melts.

-phase stability:

therefore, the solvus temperatures T calculated for the alloys selected according to the prior art in Table 4 and all laboratory batches (tables 5a and 5b) and entered in tables 4 and 5a are_{s BCC}The phase diagram of the selected alloy was calculated. For the compositions in tables 4 and 5a and b, the value of Fp was also calculated according to equation 3 d. The larger Fp is, the solidus temperature T_{s BCC}The larger. Solvus temperature T_{s BCC}Fp of all examples of N06693 higher than alloy 10>39.9. Therefore, Fp.ltoreq.39.9 (equation 2a) is required as a good criterion for obtaining sufficient phase stability in the alloy. All the laboratory batches in tables 5a and b meet the Fp ≦ 39.9 standard.

Formability (processability):

table 6 shows the tensile limits R at Room Temperature (RT) and 600 ℃_p0.2Tensile Strength R_mAnd elongation A₅Tensile strength R at 800 ℃_m. The values of Fa and Fk are also shown.

In Table 6, alloy sample lots 156817 and 160483 prepared according to prior art alloy 602CA had elongation A at room temperature₅Relatively small, 36 and 42%, respectively, below the requirement for good formability. Fa is greater than 60 and thus above the range characterizing good formability. All the alloys of the invention (E) have a elongation of more than 50%. They meet the requirements. For all alloys according to the invention, Fa is less than 60. Therefore, they are in a range having good formability. The elongation is particularly high when Fa is relatively small.

High temperature strength/creep strength:

alloy sample lot 156656 of alloy 601 according to the prior art in table 6 is an example of the minimum requirements for tensile strength and ultimate elongation at 600 ℃ and 800 ℃. In contrast, sample batches 156817 and 160483 of alloy 602CA according to the prior art are examples of non-normal tensile limit and tensile strength values at 600 ℃ and 800 ℃. Alloy 601 represents a material that meets the high temperature strength or the minimum requirements for high temperature strength, which is described in relation 8a to 8 d. Alloy 602CA represents a material having excellent high temperature strength or creep strength, which is described in relation 9a to 9 d. The Fk value for both alloys is significantly higher than 47 and the Fk value for alloy 602CA is also significantly higher than that of alloy 601, reflecting the increase in strength values for alloy 602 CA. The alloy according to the present invention (E) exhibits a tensile limit and a tensile strength both at 600 ℃ and 800 ℃ in the range of the alloy 601 or much higher than the range of the alloy 601, and thus satisfies the relations 8a to 8 d. They are within the value range of alloy 602CA, and in addition to batch 250526 and batch 250311, also meet the ideal requirement of 3 of 4 relationships 9a through 9 d. Furthermore, for all alloys according to the invention in the examples in table 6, Fk is greater than 47 or greater than 54 and is thus in the range characterized by good high temperature strength or creep strength. In laboratory batches not according to the present invention, batches 2297 and 2300 are examples where the relationships 8a to 8d are not met and where Fk is less than 47.

-resistance to air corrosion:

table 7 shows the specific mass change after oxidation tests after 11 cycles of 96 hours (i.e. a total of 1056 hours) in air at 1100 ℃. Table 7 shows the specific total mass change, specific net mass change and specific mass change of the exfoliated oxides after 1056 hours. Sample batches of alloy 601 and alloy 690 according to the prior art showed significantly higher total mass change than alloy 602CA, with the total mass change of alloy 601 again being significantly greater than the total mass change of alloy 690. Both form a chromium oxide layer that grows faster than the aluminum oxide layer. Alloy 601 still contains about 1.3% aluminum. The aluminium content is too low to form a partially closed aluminium oxide layer, which is why aluminium is internally oxidised (internal oxidation) in the metal material below the oxide layer. This results in an increase in mass compared to alloy 690. Alloy 602CA has about 2.3% aluminum. Whereby the alloy is able to form a closed aluminium oxide layer below the chromium oxide layer. This significantly reduces the growth of the oxide layer and thus also the specific mass increase. All alloys (E) according to the invention contain at least 2% aluminium and therefore have a similarly low or lower overall mass increase as alloy 602 CA. All alloys according to the invention showed spalling similar to the sample batch of alloy 602CA within the accuracy of the measurement, whereas alloy 601 and alloy 690 showed large spalling.

Thus, the required definition of alloy "E" according to the invention can be specified as follows:

too low a chromium content means that when the alloy is used in a corrosive environment, the chromium concentration drops quickly below the critical limit, so that a closed chromium oxide layer can no longer be formed. Therefore, a chromium content of more than 17% is the lower limit. Too high a chromium content impairs the phase stability of the alloy, especially at high aluminum contents of > 1.8%. Therefore, 33% chromium is considered as the upper limit.

The formation of an alumina layer below the chromium oxide layer reduces the oxidation rate. When the aluminum content is less than 1.8%, the aluminum oxide layer is too full of cracks, and the function thereof cannot be fully exerted. Too high an aluminum content may affect the workability of the alloy. Therefore, an aluminum content < 4.0% constitutes the upper limit.

The cost of the alloy increases as the iron content decreases. Costs below 0.1% increase disproportionately because special raw materials must be used. Therefore, for cost reasons, 0.1% iron should be considered as a lower limit. Increasing the iron content reduces the phase stability (formation of brittle phases), especially at higher chromium and aluminium contents. Thus, 15% iron is a reasonable upper limit to ensure the phase stability of the alloy according to the invention.

Silicon is required in the production of the alloy. Therefore, a minimum content of 0.001% is necessary. Too much content in turn impairs processability and phase stability, especially in the case of high contents of aluminium and chromium. Therefore, the silicon content is limited to 0.50%.

A minimum content of 0.001% manganese is necessary to improve processability. Manganese is limited to 2.0% because this element reduces oxidation resistance.

Titanium can improve the high temperature resistance. Starting from 0.60%, the oxidation behavior worsens, which is why 0.60% is the maximum.

Even at low magnesium and/or calcium levels, processability is improved by incorporating sulfur, thereby avoiding low melting point nickel-sulfur eutectic. Therefore, the minimum content of magnesium and/or calcium is required to be 0.0002%. In the case of an excessively high content, an intermetallic compound nickel-magnesium phase or nickel-calcium phase may occur, which again significantly deteriorates workability. Therefore, the magnesium content and/or the calcium content is limited to at most 0.05%.

A minimum content of 0.005% carbon is necessary for good creep strength. The maximum content of carbon is limited to 0.12% because above this content the element reduces the workability due to excessive formation of primary carbides.

A minimum nitrogen content of 0.001% is required to improve the processability of the material. Since the formation of coarse carbonitrides reduces the workability, the maximum content of nitrogen is limited to 0.05%.

The oxygen content must be less than or equal to 0.020% to allow manufacturability of the alloy. Too low an oxygen content increases costs. Therefore, the oxygen content is 0.0001% or more.

The phosphorus content should be less than or equal to 0.030% because such interface activating elements impair the oxidation resistance. Too low a phosphorus content increases costs. Therefore, the phosphorus content is more than or equal to 0.001%.

The sulfur content should be set as low as possible, since such interface activating elements impair the oxidation resistance. Therefore, a maximum of 0.010% of sulfur was determined.

Molybdenum is limited to at most 2.0% because this element reduces oxidation resistance.

Tungsten is limited to at most 2.0% because this element also reduces oxidation resistance.

Nickel is the balance element. Too low a nickel content reduces the phase stability, especially at higher chromium contents. Therefore, nickel must be 50% or more.

fp is less than or equal to 39.9 and (2a)

Fp＝Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W-11.8*C (3a)

Wherein Cr, Fe, Al, Si, Ti, Mo, W and C are concentrations of the relevant elements in mass%. The previous text explains in detail the limitations of Fp and other elements that may be included.

If necessary, the oxidation resistance can be further improved by adding an oxophilic element, such as yttrium, lanthanum, cerium, or cerium mixed metal. These elements are incorporated together into the oxide layer, blocking the diffusion path of oxygen at the grain boundaries.

A minimum level of 0.001% yttrium is necessary to obtain the oxidation resistance enhancing effect of yttrium. For cost reasons, the upper limit is set to 0.20%.

A minimum level of 0.001% lanthanum is necessary to obtain the oxidation resistance enhancing effect of lanthanum. For cost reasons, the upper limit is set to 0.20%.

A minimum level of 0.001% cerium is necessary to obtain the antioxidant enhancing effect of cerium. For cost reasons, the upper limit is set to 0.20%.

A minimum level of 0.001% cerium mixed metal is necessary to achieve the oxidation resistance enhancing effect of the cerium mixed metal. For cost reasons, the upper limit is set to 0.20%.

Niobium may be added if desired, as it also increases the high temperature resistance. Higher levels can add significant cost. Therefore, the upper limit is determined to be 1.10%.

The alloy may also contain tantalum if desired, as tantalum may also improve high temperature resistance and oxidation resistance. Higher levels can add significant cost. Therefore, the upper limit is determined to be 0.60%. A minimum level of 0.001% is required to be effective.

The alloy may also contain zirconium, if desired. A minimum level of 0.001% zirconium is necessary to obtain the high temperature strength and oxidation resistance enhancing effect of zirconium. For cost reasons, the upper limit of zirconium is set at 0.20%.

The alloy may also contain hafnium, if desired. A minimum level of 0.001% hafnium is necessary to obtain the high temperature strength and oxidation resistance enhancing effect of hafnium. For cost reasons, the upper limit of hafnium is set at 0.20%.

Boron may be added to the alloy if desired, as it improves creep strength. Therefore, a content of at least 0.0001% should be present. Meanwhile, such interface activating elements may reduce oxidation resistance. Therefore, a maximum of 0.008% boron was determined.

The cobalt content of such alloys can be up to 5.0%. Higher levels significantly reduce oxidation resistance.

Copper is limited to at most 0.5% because this element reduces oxidation resistance.

Vanadium is limited to at most 0.5% because this element reduces oxidation resistance.

Lead is limited to at most 0.002% because this element reduces oxidation resistance. As are zinc and tin.

Furthermore, the following relationship of the carbide-forming elements chromium, titanium and carbon can optionally be satisfied, which describes a particularly good processability:

fa ≤ 60 and (4a)

Fa＝Cr+20.4*Ti+201*C (5a)

Wherein Cr, Ti and C are concentrations of the relevant elements in mass%. The limitations of Fa and other elements that may be included are explained in detail above.

Furthermore, the following relationship between the strength increasing elements, which describes a particularly good high temperature strength or creep strength, can optionally be satisfied:

fk is not less than 47 and (6a)

Fk＝Cr+19*Ti+10.2*Al+12.5*Si+98*C (7a)

Wherein Cr, Ti, Al, Si and C are concentrations of the relevant elements in mass%. The limitations of Fa and other elements that may be included are explained in detail above.

Claims

1. A nichrome alloy having in mass% between >17 and 33% chromium, 1.8 and < 4.0% aluminum, 0.10 and 15.0% iron, 0.001 and 0.50% silicon, 0.001 and 2.0% manganese, 0.00 and 0.60% titanium, 0.0002 and 0.05% magnesium and/or calcium, 0.005 and 0.12% carbon, 0.001 and 0.050% nitrogen, 0.0001 and 0.020% oxygen, 0.001 and 0.030% phosphorus, maximum 0.010% sulfur, maximum 2.0% molybdenum, maximum 2.0% tungsten, the balance nickel with > 50% nickel, and process related impurities common for use in solar tower power stations using melt nitrate as the heat transfer medium, wherein the following relationships must be satisfied:

fp is less than or equal to 39.9 and (2a)

Fp＝Cr+0.272*Fe+2.36*Al+2.22*Si+2.48*Ti+0.374*Mo+0.538*W-11.8*C (3a)

2. Alloy according to claim 1, in particular for all parts in contact with molten salts.

3. An alloy according to claim 1 or 2, wherein the alloy is usable at temperatures up to 800 ℃.

4. An alloy according to one of claims 1 to 3 having a chromium content of more than 18% to 33%.

5. Alloy according to one of claims 1 to 4, having an aluminium content of 1.8 to 3.8%.

6. An alloy according to any one of claims 1 to 5 having an iron content of 0.1 to 12.0%.

7. Alloy according to one of claims 1 to 6, having a silicon content of 0.001 to < 0.40%.

8. Alloy according to one of claims 1 to 7, having a manganese content of 0.001 to 0.50%.

9. Alloy according to one of claims 1 to 8, having a titanium content of 0.001 to 0.50%.

10. Alloy according to one of claims 1 to 9, having a carbon content of 0.01 to 0.10%.

11. An alloy according to one of claims 1 to 10, optionally having a yttrium content of 0.001 to 0.20%.

12. Alloy according to one of claims 1 to 11, optionally having a lanthanum content of 0.001 to 0.20%.

13. Alloy according to one of claims 1 to 12, optionally having a cerium content of 0.001 to 0.20%.

14. An alloy according to one of claims 1 to 13, optionally having a cerium mixed metal content of 0.001 to 0.20%.

15. Alloy according to one of claims 1 to 14, optionally with 0.0 to 1.1% niobium, wherein formula (3a) is supplemented by a Nb-containing term:

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 (3b)

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

16. The alloy according to one of claims 1 to 15, optionally having a zirconium content of 0.001 to 0.20%.

17. Alloy according to one of claims 1 to 16, optionally having a hafnium content of 0.001 to 0.20%.

18. The alloy according to one of claims 1 to 17, optionally having a boron content of 0.0001 to 0.008%.

19. An alloy according to any one of claims 1 to 18, optionally containing 0.0% to 5.0% cobalt.

20. The alloy according to one of claims 1 to 19, further containing up to 0.5% copper, wherein formula (3a) is supplemented by a term with copper:

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 (3c)，

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

21. An alloy according to one of claims 1 to 20, further containing up to 0.5% vanadium.

22. The alloy according to one of claims 1 to 21, wherein the content of impurities is set to at most 0.002% lead, at most 0.002% zinc, at most 0.002% tin.

23. Alloy according to one of claims 1 to 22, wherein the following formula is satisfied and thereby particularly good machinability is achieved: -60 (4a) for Nb-free alloys Fa ≦ and Fa ═ Cr +20.4 × Ti +201 × C (5a) in which Cr, Ti and C are the concentrations in mass% of the relevant elements, or-5 b for alloys with Nb in which Cr, Nb +20.4 × Ti +201 × C (5b) in which Cr, Nb, Ti and C are the concentrations in mass% of the relevant elements.

24. Alloy according to one of claims 1 to 23, wherein the following formula is satisfied and thus a particularly good high temperature strength/creep strength is achieved: fk ≧ 47 (6a) and Fk ═ Cr +19 × Ti +10.2 × Al +12.5 × Si +98 × C (7a) for alloys not containing B and Nb, where Cr, Ti, Al, Si and C are the concentrations in mass percent of the relevant elements, or Fk ═ Cr +19 × Ti +34.3 Nb +10.2 × Al +12.5 × Si +98 × C +2245 × B (7B) for alloys with B and/or Nb, where Cr, Ti, Nb, Al, Si, C and B are the concentrations in mass percent of the relevant elements.

25. Use of the alloy according to one of claims 1 to 24 as strip, sheet, wire, bar, longitudinally welded pipe and seamless pipe.

26. Use of the alloy according to one of claims 1 to 24 for the production of strips, sheets, wires, rods, longitudinally welded pipes and seamless pipes.