USE OF A NICKEL-CHROMIUM-IRON ALLOY

Abstract

Alloy with the composition (in wt. %) 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>0-1.0%, if required W<0.2%, Co<0.5%, Nb<0.2%, Ti<0.1%, and impurities from the melting process, is used as a welding-plating material in the area of thermal processing systems, in particular rubbish, biomass, sewage sludge and substitute fuel systems, wherein, after the build-up welding, in the operationally stressed state in a fully austenitic structural matrix, the welding-plating material forms a sigma phase and other hard particles in the weld material microstructure in a targeted manner.

Claims

1. Use of an alloy with the 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>0-1.0% if necessary W≤0.2% Co≤0.5% Nb≤0.2% Ti≤0.1%, as well as smelting related impurities, as weld-cladding material in the field of thermal recycling systems, especially refuse, biomass, sewage sludge and substitute material incineration systems, wherein, after the build-up welding, the weld-cladding material selectively forms, in operationally-stressed condition, within a fully austenitic microstructure matrix, sigma phase and other hard particles in the weld-metal microstructure.

2. Use according to claim 1 with 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% if necessary W≤0.2% Co≤0.5% Nb≤0.1% Ti≤0.5%, as well as smelting related impurities.

3. Use according to claim 1, wherein the weld-cladding material is used in the field of heat exchanger tubes of refuse incineration systems.

4. Use according to claim 1, wherein the chromium content in the alloy, being at least 26%, is so high that chlorine or chlorine compounds from the flue-gas atmosphere lead to an only slight corrosion of the protective layer.

5. Use according to claim 1, wherein, due to the nickel content of at least 33.5% in the weld metal, the weld cladding material remains fully austenitic and no delta ferrite forms in corrosion-impairing proportions, even in the case of welding-related dilution with iron.

6. Use according to claim 1, wherein the weld cladding material is used for repairs.

7. Use according to claim 1, wherein the weld cladding material exists in the form of a wire.

8. Use according to claim 1, wherein the weld cladding material exists in the form of welding strips for submerged arc welding or electroslag welding.

9. Use according to claim 1, wherein the weld cladding material exists in the powder form.

Description

[0060] In the following, the invention will be explained in more detail on the basis of an example:

[0061] FIG. 1 shows a real heat-exchanger tube in cross section, which can typically be used as a steam-generator tube in a refuse incineration system. The inner tube consists of the 16Mo3 C-steel and has a material thickness of 5 mm and a diameter of 38 mm. By means of the metal active gas arc welding process (MSG), the build-up welding material FM 31 plus was applied with a layer thickness of 2.0-2.4 mm in a single layer under rotation of the C-steel tube and an adapted lateral movement of the welding torch, whereby an outer layer of build-up weld metal and a metallurgical bond between C-steel tube and weld metal were formed. The following welding parameters were used for production of the build-up weld: welding current (pulsed) with <I>=108 A, welding voltage U=26 V, overlap=50%. A four-component gas containing argon, helium, hydrogen and carbon dioxide was used as shield gas. The wire diameter of the FM 31 plus, from batch 118903, was 1.0 mm.

[0062] FIGS. 2 and 3 show metallographic microsections of this build-up weld, wherein FIG. 2 shows the transition from C-steel into the FM 31 plus weld metal and FIG. 3 shows the pure, finely dendritically solidified, fully austenitic weld metal of FM 31 plus.

[0063] FIG. 4 shows a comparison of the measured wasting away after an aging test of weld-clad heat-exchanger tubes, welded with FM 625 and FM 31 plus, after 1000 hours under real boiler room conditions of a refuse incineration system with maintenance of a defined temperature gradient between 360° C. and 540° C. steam temperature at the inner wall of the tube over the entire aging time. The temperature load relevant for cladding at the outside of the tube is much higher and lies mainly above 450° C. In the performed investigations, it was unexpectedly found that the build-up welding from FM 31 plus is basically as good as the build-up welding from FM 625 as regards the observed wasting away, and over a broad temperature range is even much better, even though the iron content, which otherwise under chlorinating conditions is particularly harmful, is higher by at least 28.5 mass-% in FM 31 plus than in FM 625.

[0064] In Table 1, the compositions are listed on the one hand for the build-up weld material according to the invention as well as for alternative materials used heretofore.

TABLE-US-00001 TABLE 1 Werkstoff FM 31plus FM 625 FM 622 Chg. Nr. 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 (Rest) 59.2 (Rest) 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 *)Smelting related impurities: Co, P, Nb, Ti Werkstoff = Material; Chg. Nr. = Batch no.; Rest = the rest Commas should be read as periods [.]

[0065] The material FM 31 plus as a weld-cladding material for component parts in thermal recycling systems is distinguished from the comparison materials by the autogenous development of property-improving microstructure phases in the range of the operating temperatures. Calculations with the J-MatPro software for Calphad in FIG. 5 and FIG. 6 describe that this effect is caused among other factors by the formation of intermetallic phases, such as, for example, the sigma phase. This can also be proved by metallographic investigations.