Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0206—Metals or alloys
  • H01M8/0208—Alloys
  • H01M8/021—Alloys based on iron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0215—Glass; Ceramic materials
  • H01M8/0217—Complex oxides, optionally doped, of the type AMO3, A being an alkaline earth metal or rare earth metal and M being a metal, e.g. perovskites
  • H01M8/0219—Chromium complex oxides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0223—Composites
  • H01M8/0226—Composites in the form of mixtures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0223—Composites
  • H01M8/0228—Composites in the form of layered or coated products
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
  • H01M2008/1293—Fuel cells with solid oxide electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the invention relates to a creep-resistant ferritic steel for high-temperature-stressed components, in particular for use in high-temperature fuel cells.
• a solid oxide fuel cell converts chemical energy of a fuel, such as hydrogen, methane or carbon monoxide, directly into electrical energy by means of an oxidizing agent, such as oxygen or air.
• the fuel is separated from the oxidant by a solid electrolyte, such as yttria-stabilized zirconia.
• a solid electrolyte such as yttria-stabilized zirconia.
• the solid electrolyte passes oxygen ions from the oxygen side (cathode compartment) on the fuel side (anode compartment), where they react with the fuel. This releases electrons that can feed an external consumer.
• the solid electrolyte is coated with porous, catalytically active electrode materials.
• the anode on the fuel side consists of a cermet of metallic nickel and yttria-stabilized zirconia.
• the cathode on the oxygen side is usually made of a lanthanum-based perovskite.
• bipolar plate conducts the current from one cell into the neighboring cell and at the same time separates the cathode space of one cell in a gas-tight manner from the anode space of the other cell.
• the bipolar plate conducts the current from one cell into the neighboring cell and at the same time separates the cathode space of one cell in a gas-tight manner from the anode space of the other cell.
• the bipolar plate also the function of gas distribution in the cells and gives the cells their mechanical stability (EP 0338 823 Al). Therefore, in contrast to the electrolyte and to the electrodes, which are on the order of 100 ⁇ m thick, the bipolar plate is usually several millimeters thick. However, in recent SOFC concepts, especially for mobile applications in vehicles or aircraft, the bipolar plates are designed to be much thinner (0.3-1 mm) for reasons of weight saving.
• bipolar plate The requirements for a bipolar plate are manifold. It must have high oxidation resistance at high temperatures when exposed to fuel on one side and oxygen on the other side. In addition, it is mechanically firmly connected to the other components of the cell, which are partly made of ceramics.
• the bipolar plate must have a coefficient of thermal expansion adapted to the other components (approximately 10-12 * 10 -6 K -1 ).
• the respectively required exact value of the expansion coefficient depends on the respective cell concept. Generally, slightly higher coefficients of expansion are required for anodensubstrate-supported cells than for cell concepts based on an electrolyte-foil concept.
• Ferritic chromium steels can fulfill this requirement profile in principle. These materials form on their surface an oxide layer based on Cr 2 O 3 , which forms the interior of the material. protects against corrosion. However, these layers tend to be unstable at the high operating temperatures of high temperature fuel cells. They burst, whereby the fragments can clog the gas channels of the bipolar plate and obstruct the gas flow. In addition, they become thicker over time due to further corrosion, which increasingly reduces their electrical conductivity and thus the power output of the fuel cell stack.
• volatile chromium oxides or chromium hydroxides are also formed which act as a catalyst poison on the cathode or on the interface between the cathode and the electrolyte and thus further reduce the cell performance permanently.
• DE 44 10 711 C1 discloses a bipolar plate made of a chromium oxide-forming alloy, which is provided with a protective layer of aluminum in the area of the gas guide surfaces. At its operating temperature, the aluminum layer forms an Al 2 O 3 layer on its surface, which protects the chromium oxide layer against corrosion.
• the disadvantageous reduction in the electrical conductivity due to chromium oxide layers in the area of the contact surfaces between electrodes and bipolar plate must be accepted unchanged in this bipolar plate.
• EP 04 10 166 A1 discloses a component for conducting current for high-temperature fuel cells. This has a non-oxidizable metallic shell of gold, palladium or platinum, which has a high electrical conductivity and no material loses by evaporation. However, such a component is very expensive to manufacture and its long-term stability is not guaranteed.
• DE 44 22 624 A1 describes a process for the protection of bodies containing chromium, in which a protective layer of an oxidic chromate is applied. A disadvantage of these coating methods, however, is that they make the bipolar plates significantly more expensive. In addition, the own
• nektordicken only lower interconnector (approximately above 800 0 C) provide (about 0.3-1 mm), high operating temperatures and frequent temperature changes (such as several hundred or even several thousand changes in temperature during the operating time of the cell), makes a special property of ferritic steels is unfavorable. These steels have only low creep resistance at high temperatures. Under mechanical stress, caused for example by oxidation, they therefore tend to permanent plastic deformation. Thereby For example, the gas-tight seal between two fuel cells caused by the bipolar plate can break and the fuel cell stack completely fail.
• transition metals To increase the creep resistance transition metals, refractory metals or light metals are usually alloyed.
• transition metals often cause austenitization of the material, which increases the expansion coefficient and deteriorates the oxidation resistance.
• Refractory metals regularly additionally reduce the ductility of the material.
• Light metals Even if present in very low concentrations of 0.1-0.4% by mass, generally degrade the protective properties and electrical conductivity of Cr-based oxide overcoats. Creep-hardened steels are therefore unsuitable as construction material for the interconnector of a high-temperature fuel cell.
• the object of the invention is therefore to provide a ferritic steel which is suitable as a construction material for the interconnector of a high temperature fuel cell and at temperatures above 600 0 C has a better creep strength than the steel used for this purpose according to the prior art.
• a further object of the invention is to make available a permanently gas-tight bipolar plate of the abovementioned ferritic steel, even with frequent temperature changes, and a fuel cell stack with improved service life at high temperatures and frequent temperature changes.
• the ferritic steel comprises precipitates of an Fe 2 (M 7 Si) or Fe 7 (M, Si) 6 intermetallic phase with at least one metallic alloying element M.
• This intermetallic phase can already form during the production of the steel. However, it can also form after a subsequent heat treatment or during subsequent use of the steel at temperatures between 600 and 1000 0 C.
• any metal which together with iron forms the intermetallic phase of the Fe 2 M or Fe 7 M 6 type in particular niobium, molybdenum, tungsten or tantalum, is suitable as the alloying element M.
• the use of a combination of several metals M is possible.
• the metal M in the intermetallic phase is now partially substituted by silicon.
• the intermetallic phase then has a general chemical formula of the type Fe 2 (M 7 Si) or of the type Fe 7 (M 7 Si) 6 . It was over- surprisingly recognized that this significantly increases the oxidation resistance of said intermetallic phases at high temperatures, in particular in contact with the operating atmospheres of high-temperature fuel cells. At the same time, the disadvantageous incorporation of the metal M into the Cr oxide layer is suppressed.
• the silicon does not regularly unfold its disadvantageous effect known from the prior art as a light alloying element in the substitution of the metal M, since the silicon is dissolved in the intermetallic phase.
• the disadvantageous effect of the prior art was caused by the fact that the silicon internally oxidized at high temperatures.
• a ferritic steel with 22 percent by mass of chromium and 0.4 percent by mass of manganese called. At 700 0 C, the latter has under a load of 10 MPa after 1000 hours a consistent creep of 1.5%.
• the elements M such as niobium and / or tungsten, in an amount of only 1 percent by mass in combination with a silicon addition of 0.3 percent by mass, the permanent creep of the steel at the same chromium and manganese content is reduced to zero , 06%, about a factor of 25.
• the maximum permissible content of type Fe 2 M or Fe 7 M 6 type precipitates was very limited.
• the lack of oxidation resistance of the precipitates of the type Fe 2 M and Fe 7 M 6 meant that when the steel was used in the high-temperature fuel cell, rapidly growing oxide layers formed. This was particularly disadvantageous in the case of chromium-forming steels, since locally the formation of the protective oxidic
• the steel contains the metal M and silicon in concentrations such that an intermetallic phase of the type Fe 2 (M 7 Si) or Fe 7 (M x Si) 6 is able to form at temperatures between 700 ° C. and 900 ° C.
• This temperature range corresponds to the desired operating temperature of modern high-temperature fuel cells and is therefore particularly technologically relevant.
• the amount of metal M required for this is shown by the known phase diagrams.
• Nb 2 in the temperature range between 700 and 900 0 C a niobium content of at least about 0.2 weight percent niobium in the alloy is required to form the phase Fe.
• a tungsten content of at least about 3 mass% in the alloy is required.
• the intermetallic phase can thus be formed during the first use of the steel in a high-temperature fuel cell. However, as before, it can alternatively be formed directly during the production of the steel.
• the alloy should contain between 1 and 8 volume percent, preferably between 2.5 and 5 volume percent precipitates of Fe 2 (M, Si) and / or Fe 7 (M, Si) 6 . At levels below this range, the increase in creep resistance is not technologically significant. Shares above this range, however, regularly lead to an undesirable embrittlement of the alloy.
• the sum of precipitates of the Fe 2 (M, Si) phase and / or Fe 7 (M, Si) s should contain between 2 and 15 atomic percent silicon.
• a silicon content below 2 atomic percent in the Fe 2 (M 7 Si) or Fe 7 (M, Si) 6 phase the oxidation resistance of the intermetallic phase is poor.
• a silicon content above 15 atomic percent is the Solubility limit of silicon in the intermetallic phase exceeded, so that gradually the known disadvantages of silicon as alloying element reappear because the silicon oxidized internally.
• a silicon content in the proper intrinsic range between 2 and 15 atomic percent in the intermetallic phase is achieved, for example when using niobium as the only metal M, that the mass ratio of silicon to niobium between 0.08 and 1, but preferably between 0.1 and 0.4 is located.
• niobium as the only metal M
• the mass ratio of silicon to niobium between 0.08 and 1, but preferably between 0.1 and 0.4 is located.
• precipitates of the Fe 2 (Nb, Si) type are formed with silicon Share of about 7 atomic percent. The sum of all precipitates in steel accounts for about 1 percent by volume.
• the advantageous measures described below can also be used to optimize its suitability as a construction material for the interconnector of a high-temperature fuel cell, without the higher creep resistance achieved in accordance with the invention suffering as a result.
• the sum of the concentrations of nickel and cobalt in the alloy is greater than 0, but less than 4 percent by mass, preferably less than 1 percent by mass. This prevents the alloy from becoming an austenitic structure at high temperatures, such as those prevailing in a high-temperature fuel cell.
• the concentrations of carbon, nitrogen, sulfur, boron and phosphorus in the alloy are each greater than 0, but less than 0.1 mass percent, preferably less than 0.02 mass percent.
• These elements are among the accompanying elements and impurities commonly found in ferritic steels. Generally cause higher additions of these alloying elements embrittlement of the material, in particular at the alloy grain boundaries.
• the alloy contains between 12 and 28 mass percent, preferably between 17 and 25 mass percent, chromium.
• the steel then becomes a chromium oxide former.
• it forms a protective oxidic covering layer based on chromium.
• the cover layer protects the steel against corrosion, in particular in the oxidizing atmospheres of a fuel cell.
• the chromium content necessary for the formation of the cover layer depends on the operating temperature at which the steel is used, and can be determined by the skilled person in a reasonable number of experiments. Higher operating temperatures tend to require higher chromium contents.
• the cover layer is particularly advantageous in high-temperature fuel cells, since it spontaneously forms at normal operating temperatures between 600 and 1000 0 C. As a result, it automatically heals again for defects. This is particularly advantageous when the cell is exposed to frequent temperature changes by startup and shutdown. Under such conditions, thus increasing the life of the fuel cell.
• the chromium content can also be used to set the thermal expansion coefficient of the steel.
• an interconnector plate for the fuel cell stack is manufactured from the steel. Namely, in such a stack, one side of the plate is mechanically fixed to the cathode material of one cell and the other side of the plate is mechanically fixed to the anode material of the other cell. If the expansion coefficient of the bipolar plate differs too much from that of the cathode or anode material, strong ones will result mechanical stresses. These can cause rupture of the cathode, anode or solid electrolyte between the cathode and anode of a cell, resulting in failure of the cell.
• the thermal expansion coefficient of a ferritic steel containing chromium as a single, essential alloying element between 800 0 C and room temperature at a chromium content of 9% about 16 * 10 "6 K " 1 and with a chromium content of 22% about 13 * 10 ⁇ s K '1 .
• the alloy contains at least one oxygen affinity element, such as yttrium, lanthanum, zirconium, cerium or hafnium.
• the total concentration of oxygen affinity elements in the alloy may be between 0.01 and 1 mass%, preferably between 0.05 and 0.3 mass%.
• the addition of an oxygen-affine element or a combination of several oxygen-containing elements causes a reduction in the growth rate and an improvement in the adhesion of the chromium-based oxide overcoat. This is advantageous because high growth rates lead to a rapid reduction of the wall thickness of thin components. In addition, high growth rates cause the critical thickness that causes the oxide layers to flake already to be reached after short times, which unacceptably inhibits the gas flow in the narrow gas channels of a high-temperature fuel cell.
• the alloy may also contain the oxygen-affine element in the form of an oxide dispersion such as Y 2 O 3 , La 2 O 3 or ZrO 2 .
• the concentration of the respective oxide dispersion in the alloy should then be between 0.1 and 2% by mass, preferably between 0.4 and 1% by mass.
• the advantage of the oxide dispersion over introduction in metallic form is that it increases the high-temperature strength.
• Steels containing oxide dispersions can be prepared for example by powder metallurgy.
• the alloy advantageously comprises an element E, which forms at temperatures above 500 0 C and the Cr 2 O 3 a spinel type ECr 2 O 4 on the surface of the steel.
• elements are manganese, nickel, cobalt and copper, with manganese being found to be particularly suitable.
• concentration of element E in the alloy should be between 0.05 and 2% by mass, preferably between 0.2 and 1% by mass. Due to the spinel formation that evaporates
• the alloy contains less than 0.5% by mass, preferably less than 0.15% by mass, of aluminum. This prevents the inclusion in the steel in the zone below the chromium-based oxide topcoat at high temperatures of inclusions of aluminum oxides, in particular at the alloy grain boundaries. These inclusions should be avoided as they adversely affect the mechanical properties of the steel and also cause the formation of metal inclusions in the chromium oxide layer by increasing the volume. These metal inclusions in turn affect the protective properties of the chromium oxide layer.
• Such oxide layers have a particularly disadvantageous effect if the bipolar plate for a fuel cell stack is manufactured from the steel.
• the power generated by the fuel cell stack must traverse all bipolar plates in the stack. Insulating layers on these plates therefore increase the internal resistance of the stack and significantly reduce the power output.
• the alloy contains a minor addition of titanium of less than 0.2 mass%, preferably less than 0.1 mass%.
• titanium preferably less than 0.1 mass%.
• the alloy contains a minor addition of titanium of less than 0.2 mass%, preferably less than 0.1 mass%.
• titanium At such low concentrations extremely fine particles of titanium oxide form below the chromium oxide topcoat at high temperatures. This causes a solidification of the material within this zone, whereby a bulging of the surface is suppressed by oxidation-induced stresses.
• Similar adverse effects occur as with excessively high aluminum contents.
• a bipolar plate of the steel according to the invention has particular advantages for use in a fuel cell stack and in particular for use in a bipolar plate for a fuel cell stack.
• the steel according to the invention can be tailored so that the plate is resistant to oxidation at typical operating temperatures of high-temperature fuel cells, has a good electrical conductivity (including the oxide layers forming on the surfaces) and has a low evaporation rate of volatile chromium compounds (chromium oxide or chromium oxy). hydroxide).
• the steel has a low thermal expansion coefficient (similar to that of the ceramic components in a high temperature fuel cell). It can be achieved by conventional methods hot and cold forming and mechanical processing. It has been recognized that due to these advantageous properties, the power output and lifetime of a fuel cell stack can be significantly increased by equipping it with bipolar plates of the steel of the present invention.
• the steel described here can also be used in other fields of technology in which a high oxidation / corrosion resistance and high creep resistance in combination with high electrical conductivity of the chromium oxide layer formed during operation, possibly with the additional requirement of low chromium evaporation, is required.
• it can be used for electrodes or for electrode holders in liquid metals and melts.
• the material is in oxygen detectors such. B. lambda probes applicable.
• Another field of application are steam-carrying lines in power plants.
• the new material can replace the ferritic 9-12% Cr steels used today, in particular if the operating temperatures are increased from the usual 500 to 550 ° C. to 600 to 700 ° C. in the interest of increased efficiency.
• FIG. 1 oxide layer 13 on an alloy 11 made of iron, Chromium, manganese and lanthanum.
• Figure 2 oxide layer 13 on an alloy 21 of iron, chromium, manganese and lanthanum with the addition of titanium.
• Figure 3 oxide layer 13 on an alloy 31 of iron, chromium, manganese and lanthanum with the addition of titanium and
• FIG. 4 oxide layer 13 on an alloy 41 made of iron,
• Figure 5 oxide layer 13 on an alloy 51 of iron, chromium, manganese, lanthanum, niobium and tungsten with substitution by silicon.
• FIG. 6 precipitations (56) of the type Fe 2 (M, Si) at alloying grain boundaries and precipitations (55) from
• Type Fe 2 (M, Si) in the alloy grain is Type Fe 2 (M, Si) in the alloy grain.
• compositions listed below for an interconnect alloy have proven to be particularly advantageous with regard to their expansion coefficient, creep resistance, oxidation resistance and the electrical conductivity of the oxide covering layer.
• the percentages are in each case percent by mass.
• iron base 21-23% chromium, 0.2-0.6% manganese, 0.05- 0.15% lanthanum, 0.4-1% niobium, 0.3-0.6% silicon, less than 0.1% aluminum, 0.001-0.02% carbon.
• Iron base 21-23% chromium, 0.2-0.6% manganese, 0.05- 0.15% lanthanum, 0.4-1% niobium, 0.3-0.6% silicon, 0.04-0.1% titanium, less than 0.1% aluminum, 0.001-0.04% carbon.
• Iron base 21-23% chromium, 0.2-0.6% manganese, 0.05- 0.15% lanthanum, 0.2-0, 6% niobium, 1.5-3.5% Tungsten, 0.3- 0.6% silicon, less than 0.05% aluminum.
• Iron base 21-23% chromium, 0.2-0.6% manganese, 0.05- 0.15% lanthanum, 0.2-0.6% niobium, 1.5-3.5% Tungsten, 0.3-0.6% silicon, 0.04-0.1% titanium, less than 0.08% aluminum, 0.001-0.01% carbon.
• Iron base 21-23% chromium, 0.2-0.6% manganese, 0.05- 0.15% lanthanum, 3.0-5.0% tungsten, 0.1-0.6% Silicon, 0.02-0.1% titanium, less than 0.08% aluminum, 0.001-0.01% carbon.
• Iron base 21-23% chromium, 0.2-0.6% manganese, 0.05-
• FIG. 1 shows an oxide layer 13 on an iron-based alloy 11 with 21-23% chromium, 0.2-0.6% manganese and 0.05-0.15% lanthanum with alloy grain boundaries 12.
• the oxide layer 13 of Cr 2 O 3 and Cr 2 MnO 4 is formed at 800 ° C. in air.
• FIG. 2 shows the oxide layer 13 on an alloy 21 to which 0.02-0.1% of titanium has been added compared to the alloy 11 from FIG. As a result, fine inner oxidation particles of Ti oxide form below the Cr 2 O 3 layer.
• FIG. 3 shows the oxide layer 13 on an alloy 31 which, in addition to the alloy 21 from FIG. 2, additionally contains 0.3-0.6% silicon.
• silicon precipitates of SiO 2 are formed at and in the vicinity of the alloy / oxide interface. These undesirably cause the image fertilizing metallic inclusions 34 and increasing the oxidation rate.
• the oxide layer is thus significantly thicker than in FIGS. 1 and 2.
• the formation of metallic inclusions and the increase in the oxidation rate also occur when 0.3-0.6% of silicon is added to a titanium-free alloy (cf. FIG. 1).
• FIG. 4 shows the oxide layer 13 on an alloy 41 to which 0.2-0.6% of niobium and 1.5-3.5% of tungsten have been added compared to the alloy 11 of FIG.
• a niobium-rich oxide layer 47 Between the oxide layer 13 and the alloy 41 is a niobium-rich oxide layer 47.
• the additions of niobium and tungsten form precipitates 45 of the Fe 2 M type in the alloy grain.
• precipitations 46 of the Fe 2 M type are formed the alloy receives a higher creep resistance.
• the disadvantage is that the oxidation rate is greatly increased.
• the oxide layer on alloy 41 is significantly thicker than on alloy 11. Additional doping with 0.02-0.1% titanium would cause fine internal oxidation particles as shown in FIGS. 2 and 3.
• Figure 5 shows the inventive design with the Oxidschic ⁇ it 13 on an alloy 51, compared to the alloy 11 of Figure 1 0.2-0.6% niobium, 1.5-3.5% tungsten and 0.3-0.6 % Silicon were added.
• precipitations 55 of the type Fe 2 (M 7 Si) are formed in the alloy grain.
• precipitates 56 of type Fe 2 (M, Si) are formed.
• the precipitates 55 and 56 give the alloy a higher creep resistance.
• the rate of oxidation is increased by the additions of elements Nb and W compared to alloy
• the oxide layer on the alloy 51 from FIG. 5 has a similar thickness to that on the alloy 11 from FIG. Additional doping with 0.02-0.1% titanium would cause fine internal oxidation particles as shown in FIGS. 2 and 3.
• FIG. 6 shows a scanning electron micrograph of the precipitates 55 and 56 from FIG. 5.

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• 2006
  • 2006-02-18 DE DE102006007598A patent/DE102006007598A1/de not_active Withdrawn
• 2007
  • 2007-01-31 US US12/223,949 patent/US20090104494A1/en not_active Abandoned
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