Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/053—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 30% but less than 40%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and W

Definitions

• High-temperature processes in petroleum chemistry require materials that are not only heat-resistant but also sufficiently corrosion-resistant and can withstand the stress caused by hot product and combustion gases.
• the tube coils of cracking and reformer furnaces are exposed to strongly oxidizing combustion gases with a temperature of up to 1100 ° C and more, while inside the cracking tubes at temperatures up to 1100 ° C a strongly carburizing and inside of reformer tubes at temperatures up to 900 ° C and high pressure there is a weakly carburizing and differently oxidizing atmosphere.
• Contact with the hot combustion gases also leads to nitriding of the pipe material and the formation of a scale layer, which is associated with an increase in the outer pipe diameter by a few percent and a reduction in the wall thickness by up to 10%.
• the carburizing atmosphere in the interior of the pipe causes carbon to diffuse into the pipe material and carbides such as il 23 C 6 are formed at temperatures above 900 ° C and, with increasing carburization, the carbon-rich carbide M 7 C 3 is formed.
• carbides such as il 23 C 6 are formed at temperatures above 900 ° C and, with increasing carburization, the carbon-rich carbide M 7 C 3 is formed.
• the consequence of this are internal tensions as a result of the increase in volume associated with carbide formation or conversion and a decrease in the strength.
• BESTATIGUNGSKOPIE speed and toughness of the pipe material Furthermore, graphite or fused carbon can arise in the interior of the tube material and, as a result, in connection with internal stresses, cracks can occur, which in turn cause more carbon to get into the tube material.
• High-temperature processes therefore require materials with a high creep resistance. Creep resistance, structural stability as well as carburization and oxidation resistance. This requirement is met - within limits - by alloys that contain 20 to 35% nickel, 20 to 25% chromium and to improve carburization resistance up to 1.5% silicon, such as the nickel-chromium steel alloy 35Ni25Cr-1 suitable for centrifugal cast iron pipes, 5Si, which is still resistant to oxidation and carburization even at temperatures of 1100 ° C.
• the high nickel content reduces the diffusion rate and the solubility of the carbon and thus increases the carburization resistance.
• the alloys form a top layer of Cr 2 O 3 at higher temperatures under oxidizing conditions, which acts as a barrier layer against the penetration of oxygen and carbon into the pipe material underneath.
• the Cr 2 0 3 becomes volatile, so that the protective effect of the cover layer is quickly lost.
• a further risk to carburization and oxidation resistance results from the limited creep strength and ductility of conventional nickel-chromium alloys, which lead to crevice cracks in the chromium oxide cover layer and the penetration of carbon and oxygen via the cracks into the pipe material.
• top layer cracks can occur and the top layer can also partially detach.
• the invention aims to contain the damage mechanism: carburization - reduction in creep resistance or creep resistance - internal oxidation with the further consequence of increased carburization and oxidation as well as to create a cast alloy which can also be used in carburizing and / or at extremely high operating temperatures oxidizing atmosphere still has a reasonable lifespan.
• the invention achieves this with the help of a nickel-chromium cast alloy with certain contents of aluminum and yttrium.
• the invention consists in a cast alloy up to 0.8% carbon up to 1% silicon up to 0.2% manganese
• the total nickel, chromium and aluminum content of the alloy should be 80 to 90%.
• the alloy preferably contains individually or side by side at most 0.7% carbon, up to 30% chromium, up to 12% iron, 2.2 to 6% aluminum, 0.1 to 2.0% niobium, 0.01 to 1.0% Titanium, up to 0.15% zirconium and - for a high creep resistance - up to 10% cobalt, at least 3% molybdenum and up to 5% tungsten, for example 4 to 8% cobalt, up to 4% molybdenum and 2 to 4% tungsten, if there is the high resistance to oxidation is not of primary importance.
• the contents of cobalt, molybdenum and tungsten must therefore be selected within the content limits according to the invention.
• Optimal results can be achieved if the chromium content alone or side by side at most 26.5%, the iron content at most 11%, the aluminum content 3 to 6%, the titanium content over 0.15%, the zirconium content over 0.05%, the The cobalt content is at least 0.2%, the tungsten content is more than 0.05% and the yttrium content is 0.019 to 0.089%.
• the high creep resistance of the alloy according to the invention for example a service life of 2000 hours at a load of 4 to 6 MPa and a temperature of 1200 ° C, guarantees the maintenance of a closed and firmly adhering oxide barrier layer in the form of a due to the high aluminum content of the alloy even supplementary or renewable AI 2 O 3 layer effective against carburization and oxidation.
• this layer consists of ⁇ - Al 2 0 3 and at most contains mixed oxides that do not change the character of the ⁇ - Al 2 0 3 layer; at higher temperatures, in particular above 1050 ° C., given the rapidly decreasing resistance of the Cr 2 0 3 layer of conventional materials at these temperatures, it increasingly takes on the protection of the alloy according to the invention against carburization and oxidation.
• NiO nickel oxide
• Ni (Cr, Al) 2 0 4 mixed oxides
• the structure of the alloy according to the invention contains inevitably ⁇ '-phase above 4% aluminum, which has a strengthening effect at low and medium temperatures, but also reduces the toughness or elongation at break. In individual cases, it may therefore be necessary to make a compromise between the toughness and the resistance to oxidation / carburization.
• the barrier layer according to the invention from ⁇ -Al 2 O 3, the stable Al 2 0 3 - modification is stable at all oxygen concentrations.
• the table contains the comparative alloys 5 and 7 as an example of two wrought alloys with a comparatively low carbon content and a very fine-grained structure with a grain size of ⁇ 10 ⁇ m, which are not covered by the invention, while all other test alloys are cast alloys.
• Yttrium is a strong oxide former, the effect of which in the alloy according to the invention is that the conditions of formation and the adhesiveness of the ⁇ -Al 2 O 3 layer improve significantly.
• the aluminum content of the alloy according to the invention has an important task in that aluminum leads to the formation of a ⁇ '-precipitation phase, which brings about a considerable increase in the tensile strength.
• the yield strength and the tensile strength of the three alloys 13, 19, 20 to 900 ° C. according to the invention are considerably higher than the strength values of the four comparative alloys.
• the elongation at break of the alloys according to the invention essentially corresponds to that of the comparison alloys; It increases sharply above about 900 ° C., as can be seen from the diagram in FIG. 3, while the strength reaches the level of the comparative alloys (FIGS. 1, 2). This is explained by the fact that the ⁇ '-phase goes into solution from about 900 ° C and is completely dissolved above about 1000 ° C.
• the creep behavior of alloys according to the invention with different contents of aluminum is shown in the Larson-Miller diagram in FIG. 4.
• the deterioration in carburization resistance at lower aluminum contents can be explained by the fact that the protective oxide layer tears open during cooling after the annealing or also (partially) flakes off, so that carburization occurs in the area of the cracks and flaking. With higher aluminum contents, the Al 2 0 3 barrier layer mentioned forms under the oxide layer (top layer).
• the line in the diagram in FIG. 13 separates the area of the alloys with a sufficiently protective ⁇ -aluminum oxide layer above the straight line from the area of the alloys with a resistance to carburization or catalytic coking impaired by mixed oxides.
• FIG. 14 illustrates the superiority of the steel alloy according to the invention using six exemplary embodiments 21 to 26 in comparison with the conventional comparative alloys 1, 3, 4 6 and 7.
• the compositions of the test alloys 21 to 26 are shown in the table.
• FIGS. 15 and 16 show the service life of the alloy 13 according to the invention with 2.4% aluminum as a reference variable with service life 1 in each case at 1100 ° C. (FIG. 15 ) and 1200 ° C (Fig. 16) for three load cases (15.9 MPa; 13.5 MPa; 10.5 MPa) the related service lives of the alloys 19 (3.3% aluminum) and 20 (4.8 % Aluminum).
• the diagram in FIG. 15 shows that for alloy 19 with an average aluminum content of 3.3%, the reduction in the service life increases with increasing load, while for alloy 20 with its high aluminum content of 4.8% it increases for all load cases results in a strong but roughly equal reduction in the relative tool life.
• the diagram for 1200 ° C shows a reduction in the service life with an increase in the aluminum content from 2.4% (alloy 13) to 3.3% (alloy 19) for all three load cases, a decrease in the relative service life to about two thirds.
• the two diagrams show that the service life until the break in the creep test decreases with increasing aluminum content. Furthermore, the negative influence of aluminum on the creep life decreases with increasing temperature and increasing stress duration or with decreasing stress.
• the high aluminum alloys are particularly suitable for long-term use at temperatures for which no cast or centrifugal cast materials could previously be used.
• the cast alloy according to the invention is particularly suitable as a material for furnace parts, radiant tubes for heating furnaces, rollers for annealing furnaces, parts of continuous casting and strip casting plants, hoods and muffle for glow furnaces, parts of large diesel engines, containers for catalysts as well as for crack and reformer tubes.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Mold Materials And Core Materials (AREA)
• Catalysts (AREA)
• Laminated Bodies (AREA)
• Powder Metallurgy (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Ceramic Products (AREA)
• Soft Magnetic Materials (AREA)
• Coating By Spraying Or Casting (AREA)
• Exhaust Silencers (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Furnace Housings, Linings, Walls, And Ceilings (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Supercharger (AREA)

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