Application of nickel-chromium-iron alloy

Abstract

The invention relates to the use of an alloy having the following composition (in% by weight): Ni 33.5 to 35.0%, Cr 26.0 to 28.0%, Mo 6.0 to 7.0%, Filt; the content of Mn is 1.0-4.0%, and the content of Silt is 33.5%; 0.1% of Cu, 0.5%-1.5% of Al, 0.01%-0.3% of Clt and the balance of Al; 0.01%, Plt; 0.015%, Slt; the raw materials comprise, by weight, 0.01% of sEgt, 0.1-0.25% of N, 0.001-0.004% of B, and 0.01% of 0-1.0%, as required Wlt; 0.2%, Colt; 0.5%, Nblt; , 0.2%, Tilt; the invention relates to a welding material for welding, in particular for welding and cladding, in particular for waste, biomass, sewage sludge and alternative fuel equipment in the field of heat recovery equipment, said welding and cladding material, after surfacing, in the working stress state in a fully austenitic structural matrix in the microstructure of the welding material, having a thickness of 0.1%, and impurities from the melting process, for use as a welding and cladding material in the field of heat recovery equipment, in particular for welding, in particular for welding, in a fully austenitic structural matrix. Sigma phase and other hard particles are formed in a targeted manner.

Description

[0001] This divisional application is a divisional application of the PCT patent application with the application date of March 22, 2021, the application number entering the Chinese national phase of 202180019731.9, and the invention title of "Use of Nickel-Chromium-Iron Alloy". Technical Field

[0002] The present invention relates to a new use of a nitrogen-alloyed nickel-chromium-iron alloy in the field of heat recovery. Background Art

[0003] EP 2 632 628 A1 discloses a workable homogeneous austenitic nickel alloy which has high corrosion resistance to corrosive liquid media under oxidation and reduction conditions and excellent resistance to local corrosion in acidic, chloride-containing media. The composition of the alloy is as follows (by mass percentage): chromium 26.0 - 28.0%, molybdenum 6.0 - 7.0%, iron at most 33.5%, manganese 1.0 - 4.0%, silicon at most 0.1%, boron 0.001 - 0.004%, copper 0.5 - 1.5%, aluminum 0.01 - 0.3%, magnesium 0.001 - 0.15%, carbon at most 0.01%, nitrogen 0.1 - 0.25%, nickel 33.5 - 35%, rare earth > 0 to 1.0% and other impurities related to smelting. This alloy is suitable as a material for components that must be resistant to chemical erosion.

[0004] As a cladding material for surfacing or flame spraying in heat recovery applications (such as in waste incineration equipment, alternative fuel equipment or biomass equipment), nickel alloys are mostly used at present. For example, FM 625 (UNS N06625), FM622 (UNS N06022) and FM 686 (UNS N06686).

[0005] The corrosion stresses of components of heat recovery equipment and surfaces in contact with flue gas are multifaceted and complex. Therefore, various types of high-temperature corrosion controlled by diffusion will occur, for example, corrosion caused by halogens containing chlorine and increasing bromine, sulfidation, carburization, molten salts or low-melting-point molten metals. In addition, below the dew point or during cleaning operations, during shutdown and maintenance, the materials used are also severely stressed by wet corrosion mechanisms. Another material stress is caused by alternating thermal loads during equipment startup and shutdown or by local and temporary "flame bundles" in the combustion chamber.

[0006] Although corrosion protection has been provided for heat exchanger tubes, heating surfaces, flue gas contact surfaces and other components by cladding with these known materials, respectively according to the materials used and working conditions, it is weakened on superheater tubes and other components subjected to thermal stress, thus forcing the operator to carry out shutdown and cost-intensive maintenance work and possibly necessary new construction.

[0007] So far, the materials described in EP 2 632 628 A1 have only been used in the field of wet corrosion, where an electrochemical reaction in combination with an electrolyte causes corrosion erosion. The known fields of application are: chemical processes involving phosphoric acid, sulfuric acid, seawater and brackish water applications, or pickling equipment using nitric acid / hydrofluoric acid.

[0008] A device for generating energy from biomass is known from DE 10 2007 062 810 A1. The components of this device can be composed of heat-resistant and corrosion-resistant materials, preferably stainless steel. Stainless steels with relatively high chromium and molybdenum contents are specified. However, the materials specified here are not suitable for surfacing, because these relatively low-alloyed materials form more residual δ-ferrite in the microstructure, especially in combination with the iron mixing that occurs during surfacing during the welding process, thus greatly limiting the general use under wet and high-temperature corrosion conditions. Summary of the Invention

[0009] The object of the present invention is to provide new fields of application for alloys that, according to the prior art, are only allowed for use at low temperatures up to a maximum of 450 °C.

[0010] This object is achieved by using an alloy having the following composition (in mass %): Ni 33.5 - 35.0%

[0011] Cr 26.0 - 28.0%

[0012] Mo 6.0 - 7.0%

[0013] Fe < 33.5%

[0014] Mn 1.0 - 4.0%

[0015] Si ≤ 0.1%

[0016] Cu 0.5 - 1.5%

[0017] Al 0.01% - 0.3%

[0018] C ≤ 0.01%

[0019] P ≤ 0.015%

[0020] S ≤ 0.01%

[0021] N 0.1 - 0.25%

[0022] B 0.001 - 0.004%

[0023] sE > 0 - 1.0%

[0024] As required

[0025] W ≤ 0.2%

[0026] Co ≤ 0.5%

[0027] Nb ≤ 0.2%

[0028] Ti ≤ 0.1%,

[0029] and smelting-related impurities

[0030] The chromium content in the alloy is at least 26%, so high that chlorine or chlorine compounds from the flue gas atmosphere only cause slight corrosion of the protective layer.

[0031] As a welding-cladding material in the field of heat recovery equipment, especially for waste, biomass, sewage sludge and alternative fuel equipment, wherein after surfacing, the welding-cladding material forms σ-phase and other hard particles in the microstructure of the welding material in a fully austenitic structure matrix under working stress conditions.

[0032] The formation of the σ-phase causes the dispersion of hard particles in the microstructure of the weld metal, which leads to an increase in the hardness of the weld metal microstructure, thus achieving a protective top layer with unexpectedly high resistance to erosion-related damage. Due to the formation of the σ-phase, such a super-proportional increase in resistance to surfacing is achieved in heat recovery equipment under working stress conditions. Another contribution to erosion or corrosion promoting erosion is considered to be the formation of chromium carbide at the application temperature. Therefore, the weld metal can only obtain very high resistance to mechanical friction stress through the precipitation of intermetallic phases (such as the σ-phase) under working stress conditions, and thus can also resist dust and particle erosion.

[0033] Even when used for a very long time of over 10,000 hours, it is expected that under the changing conditions of heat recovery equipment, not only pure diffusion-controlled / electrochemical corrosion plays a role, but especially in combination with the material's resistance to mechanical stress, such as due to stray particles and smoke particles (erosion or erosion corrosion), this material has new performance characteristics.

[0034] In addition, the formation of iron(II) chloride or iron(III) chloride actually occurring in iron-containing materials is strongly inhibited, especially in the case of low oxygen partial pressure accompanied by the dissolution of the relevant materials.

[0035] In welding activities under various laboratory research and production conditions, this material has proven to have excellent weldability related to the welding cladding process - high crack resistance and good wetting properties - whether used in tungsten inert gas welding (WIG) or metal shielded gas welding (MSG). The application of the welding cladding layer can be carried out not only by surfacing, but also, for example, by flame or plasma spraying with powder or wire. Advantageously, the alloy is used as a cladding material in thermal recovery equipment (such as waste, biomass, sewage sludge, alternative fuel equipment) together with welding, flame spraying or plasma spraying techniques.

[0036] In the wet corrosion test of ASTM G 48C, the critical pitting temperature of the base material under the delivery conditions is usually higher than or equal to 85 °C. The formation of the σ phase reduces the pitting resistance, but the degree of alloying of the alloy is so high that the chromium content in the austenite matrix ensures passivation.

[0037] Advantageous further developments of the subject matter of the invention can be obtained from the dependent claims.

[0038] The alloy can be used in particular for coating steel by liquid phase, such as welding or flame spraying, and has high corrosion resistance to the erosive media that may form during the thermal recovery process.

[0039] The preferred chemical composition (in mass %) is listed as follows:

[0040] Ni 33.5 - 35.0%

[0041] Cr 26.0 - 28.0%

[0042] Mo 6.0 - 7.0%

[0043] Fe < 33.5%

[0044] Mn 1.8 - 3.0%

[0045] Si ≤ 0.1%

[0046] Cu 1.0 - 1.5%

[0047] Al 0.05% - 0.3%

[0048] C ≤ 0.01%

[0049] P ≤ 0.015%

[0050] S ≤ 0.01%

[0051] N 0.2 - 0.25%

[0052] B 0.001 - 0.004%

[0053] sE 0.020 - 0.060%

[0054] as required

[0055] W ≤ 0.2%

[0056] Co ≤ 0.5%

[0057] Nb ≤ 0.1%

[0058] Ti ≤ 0.5%,

[0059] and smelting-related impurities.

[0060] When studying the above materials by surfacing on 16Mo3 tubes, it was surprisingly and unexpectedly found that this can also be used advantageously within the temperature range of heat recovery and under specific conditions.

[0061] Detailed implementation and description of the drawings

[0062] The present invention will be described in more detail below by way of an example:

[0063] Figure 1 Shows a cross-section of a real heat exchanger tube, which can generally be used as a steam generator tube in waste incineration equipment. The inner tube is made of 16Mo3C steel, with a material thickness of 5 mm and a diameter of 38 mm. By means of the metal active gas shielded arc welding process (MSG), a surfacing material FM 31plus with a layer thickness of 2.0 - 2.4 mm is applied in a single layer under the rotation of the C-steel tube and the appropriate lateral movement of the welding torch, thereby forming the outer layer of the surfacing metal and the metallurgical bond between the C-steel tube and the weld metal. The following welding parameters are used for surfacing: having Welding current (pulse) = 108 A, welding voltage U = 26 V, overlap = 50%. A four-component gas containing argon, helium, hydrogen and carbon dioxide is used as the shielding gas. The wire diameter of FM 31plus from batch 118903 is 1.0 mm.

[0064] Figure 2 and 3 shows the metallographic cross-section of this surfacing, where Figure 2 shows the transition from C-steel to FM 31plus weld metal, Figure 3 showing the fully austenitic weld metal of FM 31plus with pure, fine dendritic solidification.

[0065] Figure 4 shows the heat exchanger tubes with weld cladding welded using FM 625 and FM 31plus. After 1000 hours of service test (Auslagerungsversuch) under the real boiler room conditions of a waste incineration plant, with the steam temperature on the inner wall of the tube maintained at a temperature gradient defined between 360 °C and 540 °C throughout the service time (Auslagerungszeit), the comparison of the measured loss amounts. The external temperature load of the tube related to the cladding is significantly higher, basically above 450 °C. In the studies conducted, unexpectedly, it was found that the FM 31plus surfacing is basically equivalent to the FM 625 surfacing in terms of certain corrosion, and is even significantly superior in a wide temperature range, although the iron content of FM 31plus (which is generally considered particularly harmful under chlorinated conditions) is at least 28.5 mass% higher than that of FM 625.

[0066] Table 1 lists the compositions of the surfacing materials according to the present invention and the alternative materials used so far.

[0067] Material FM 31plus FM 625 FM 622 Batch number 118903*) 115949 122001 C 0.003 0.015 0.005 S 0.002 0.002 0.004 N 0.22 0.018 0.016 Cr 26.6 22.3 21.4 Ni 34.0 64.3 (balance) 59.2 (balance) Mn 1.94 0.01 0.16 Cu 1.24 0.01 0.01 Si 0.02 0.07 0.03 Mo 6.47 9.21 13.7 Fe 29.13 0.20 2.2 Al 0.07 0.06 0.11 B 0.0024 <0.001 0.001 V 0.03 <0.01 0.17 W 0.10 0.02 2.87 sE 0.04

[0068] * Smelting-related impurities: Co, P, Nb, Ti

[0069] Table 1

[0070] The difference between the FM 31plus material as the welding-cladding material for components in heat recovery equipment and the comparative materials is that a microstructure phase with improved properties will spontaneously form within the operating temperature range. The calculations using Calphad with J-MatPro software in Figure 5 and Figure 6 describe that this effect is caused by the formation of intermetallic phases (such as sigma phase). This can also be proven by metallographic investigation.

Claims

1. Use of an alloy having the following composition (in mass - %): Ni 33.5 - 35.0% Cr 26.0-28.0％ Mo 6.0 - 7.0% Fe < 33.5% Mn 1.0 - 4.0% Si ≤ 0.1% Cu 0.5 - 1.5% Al 0.01％-0.3％ C≤0.01％ P≤0.015％ S≤0.01％ N 0.1-0.25％ B 0.001-0.004％ sE > 0.02 - 1.0% as required W≤0.2％ Co ≤ 0.5% Nb ≤ 0.2% Ti ≤ 0.1%, and smelting - related impurities, which is used as a welding - cladding material in the field of heat recovery equipment, wherein the welding - cladding material, after surfacing and under working stress conditions, forms σ - phase and other hard particles in a targeted manner in the microstructure of the welding material in a fully austenitic structure matrix. Due to the nickel content in the welding metal being at least 33.5%, even when mixed with iron in relation to welding, the welding - cladding material remains fully austenitic and does not form δ - ferrite to the extent of corrosion damage.

2. The use according to claim 1, wherein the alloy has the following composition (in mass %): Ni 33.5 - 35.0% Cr 26.0-28.0％ Mo 6.0 - 7.0% Fe < 33.5% Mn 1.8 - 3.0% Si ≤ 0.1% Cu 1.0 - 1.5% Al 0.05％-0.3％ C≤0.01％ P≤0.015％ S≤0.01％ N 0.2-0.25％ B 0.001-0.004％ sE 0.020 - 0.060% as required W≤0.2％ Co ≤ 0.5% Nb ≤ 0.1% Ti ≤ 0.5%, and smelting - related impurities.

3. The use according to claim 1, wherein the heat recovery equipment is a waste, biomass, sewage sludge, and alternative fuel equipment.

4. Use according to any one of claims 1 to 3, characterized in that, The welding - cladding material is used for repair.

5. The use according to any one of claims 1 to 4, characterized in that, The welding - cladding material exists in the form of a wire.

6. The use according to any one of claims 1 to 4, characterized in that, The welding - cladding material exists in the form of a welding rod for submerged arc welding or electroslag welding.

7. Use according to any one of claims 1 to 4, characterized in that, The welding - cladding material exists in powder form.

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