WO2024110557A1 - Film d'acier au chrome pour la production de plaques bipolaires pour piles à combustible - Google Patents

Film d'acier au chrome pour la production de plaques bipolaires pour piles à combustible Download PDF

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WO2024110557A1
WO2024110557A1 PCT/EP2023/082753 EP2023082753W WO2024110557A1 WO 2024110557 A1 WO2024110557 A1 WO 2024110557A1 EP 2023082753 W EP2023082753 W EP 2023082753W WO 2024110557 A1 WO2024110557 A1 WO 2024110557A1
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chromium steel
steel foil
formula
chromium
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German (de)
English (en)
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Araz Ardehali Barani
Thomas Wegler
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Zapp Precision Metals Gmbh
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    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the invention relates to a chromium steel foil for producing bipolar plates for fuel cells, a method for producing a chromium steel foil, a bipolar plate and a use of a chromium steel foil according to the invention or a chromium steel foil produced by the method according to the invention for a bipolar plate.
  • PEMFC stacks Proton Exchange Membrane Fuel Cell Stacks (PEMFC stacks) consisting of several fuel cells are installed in hydrogen-powered vehicles.
  • the fuel cell consists of a proton-conducting membrane, a cathode, an anode and two bipolar plates.
  • the cathode and the anode are arranged on opposite sides of the proton-conducting membrane.
  • One bipolar plate is arranged on the cathode and one on the anode.
  • the fuel cells use bipolar plates to supply the electrochemically active components with hydrogen and oxygen and to remove the reaction product water and to dissipate the reaction heat.
  • These bipolar plates are made from metal strips or foils by forming, separating and joining different alloy classes. Rust, acid and Heat-resistant steels, nickel-based alloys or titanium are used. Pure titanium and a ferritic stainless steel are used for bipolar plates. Alternatively, austenitic stainless steels are used in cars and commercial vehicles due to their formability and corrosion resistance. However, these are always used together with a coating.
  • a metal strip can be coated before forming into a bipolar plate. Plates are then cut out of the strip and the flow profile is introduced into the plates to produce the bipolar plates. The bipolar plates are then assembled with other components to form fuel cells, which are then arranged in stacks (PEMFC). Alternatively, the coating can also be applied after forming, before or after separation.
  • the aim is to produce PEMFC stacks with a higher volumetric density.
  • the thickness of the bipolar plate can be reduced and the flow profile (flow field) can be structured more delicately and finely.
  • To produce thinner bipolar plates correspondingly thinner metal strips are used.
  • a decreasing thickness of the metal strips makes both continuous production and the uniform forming of the metal strips into bipolar plates without local micro-constrictions more difficult.
  • the formability of the metal strips is influenced by the structure and by impurities in the structure.
  • PREN the corrosion resistance
  • the PREN formula neglects the influence of the microalloying elements and the deoxidizers, which can bind both nitrogen and carbon. Therefore, the estimate using the PREN formula is inaccurate.
  • the object of the present invention is to provide a chromium steel foil that can be produced continuously and also has good formability and good corrosion resistance, while the chromium steel foil can be produced particularly thinly in order to enable PEMFC stacks with a high volumetric density. Furthermore, the object of the present invention is to propose a method for producing a chromium steel foil, a bipolar plate and a use of a chromium steel foil or for a bipolar plate.
  • the present object is achieved with a chromium steel foil for producing bipolar plates for fuel cells, wherein the chromium steel foil is austenitic and consists of the following alloy components in weight percent
  • the chromium steel foil according to the invention offers the advantage that it can be produced continuously and has good formability.
  • the chromium steel foil has a high corrosion resistance.
  • the chromium steel foil can be produced particularly thinly with a thickness of less than 0.1 mm, enabling PEMFC stacks with a high volumetric density.
  • the advantages of the invention result from the alloy in combination with the austenitic structure, the low thickness and the ratio of Niiceq according to formula 2 to Cr eq according to formula 3 between 0.4 and 2.0.
  • the alloy with the ratio of Niiceq according to formula 2 to Cr eq according to formula 3 between 0.4 and 2.0 ensures that the chromium steel foil has an austenitic structure with good corrosion resistance.
  • the chromium steel foil has good formability due to the face-centered cubic, austenitic structure, so that the chromium steel foil can be produced continuously up to a thickness of less than 0.1 mm, preferably less than 0.075 mm, particularly preferably less than 0.05 mm: PEMFC stacks with a high volumetric density can therefore be produced from the chromium steel foil. As the thickness decreases, the chromium steel foil enables PEMFC stacks with increasing volumetric density to be produced.
  • Cr chromium
  • Cr is contained between 12 wt.% and 30 wt. Cr increases the corrosion resistance of the chromium steel foil. The corrosion resistance increases with increasing chromium content.
  • Ni nickel is contained between 0.1 wt.% and 20 wt.%, with nickel promoting the formation of austenite and increasing corrosion resistance under certain conditions.
  • Mn manganese is contained between 0.5 wt.% and 17 wt.%.
  • Manganese is an austenite-stabilizing alloying element and can substitute for nickel.
  • Cu copper
  • Cu is contained between 0.1 wt.% and 2 wt.%.
  • Cu is an austenite-stabilizing alloying element.
  • too high a Cu content leads to lower corrosion resistance.
  • C (carbon) is contained between 0.015 wt.% and 0.15 wt.% and is an austenite former.
  • N nitrogen
  • nitrogen is contained between 0.02 wt.% and 0.6 wt.%.
  • N is a particularly favorable austenite-stabilizing alloying element.
  • Mo mobdenum
  • Mo mobdenum
  • Mo increases corrosion resistance.
  • too high Mo contents prevent the formation of the austenitic phase.
  • Si silicon is contained between 0.2 wt.% and 1 wt.%. Si is a good deoxidizing element. Ti is present in amounts of between 0.001 wt.% and 0.25 wt.%. Titanium is very carbon and nitrogen-affine. By forming carbonitrides, it prevents the formation of chromium carbides. This keeps the concentration of dissolved chromium in the metal lattice high both locally and globally and improves corrosion resistance. This effect is used primarily in welding to prevent the local formation of chromium carbides at the grain boundaries and thus chromium depletion in the neighboring regions and thus increased sensitivity to intergranular corrosion or stress corrosion cracking. The following microalloying elements aluminum, niobium and vanadium have an analogous effect.
  • Nb (niobium) is contained between 0.01 wt.% and 0.5 wt.%
  • V vanadium
  • V vanadium
  • Al (aluminium) is contained between 0.003 wt.% and 1 wt.%. Aluminium is a deoxidising element.
  • the chrome steel foil has a ratio of Niiceq according to formula 2 to Cr eq according to formula 3 between 0.4 and 2.0. This means that the chrome steel foil meets the following ratio:
  • the ratio of Niiceq to Cr eq according to the invention takes into account the influence of the microalloying elements and the deoxidizers on the interstitial elements in the austenite formers.
  • the formula 2 for the Niiceq according to formula 2 only takes into account the dissolved interstitial elements carbon and nitrogen.
  • the chromium steel foil may comprise the following alloy components in weight percent
  • the chrome steel foil can continue to be produced continuously down to a thickness of less than 0.1 mm.
  • the chrome steel foil can enable PEM FC stacks with high volumetric density.
  • the proportion of austenitic structure can be at least 90%, preferably at least 95%, and particularly preferably at least 99%.
  • the formability and corrosion resistance can be improved due to the austenitic structure.
  • the chromium steel foil can continue to be produced continuously down to a thickness of less than 0.1 mm.
  • the chromium steel foil can therefore enable PEM FC stacks with a high volumetric density. The effect can improve with an increasing proportion of austenitic structure.
  • the proportion of austenitic structure results from the alloy components and can be determined using phase diagrams.
  • the proportion of recrystallized structure can be at least 90%, preferably at least 95%, and particularly preferably at least 99%.
  • the high proportion of recrystallized structure means that the formability of the chrome steel foil is particularly good.
  • the chrome steel foil can enable PEMFC stacks with a high volumetric density. The effect can improve with an increasing proportion of recrystallized structure.
  • the proportion of recrystallized structure can be determined using DIN ISO 643.
  • the average grain diameter can be greater than 1.5 pm and smaller than 10 pm, preferably smaller than 7.5 pm, and particularly preferably smaller than 5 pm, according to the line-cut method of Heyn (ASTM E112-13), wherein in particular the chromium steel foil can have a structure with equiaxial grains with an anisotropy index according to DIN-ISO 643 between 0.8 and 1.2, preferably between 0.9 and 1.1.
  • the chrome steel foil Due to the average grain diameter of more than 1.5 pm and less than 10 pm, the chrome steel foil can ensure good formability and corrosion resistance. Furthermore, the chrome steel foil can produce PEMFC stacks with high volumetric density With decreasing maximum mean grain diameter to 7.5 pm, and particularly preferably to 5 pm, the effect can be enhanced.
  • a structure with equiaxial grains with an anisotropy index according to DIN-ISO 643 between 0.8 and 1.2, preferably between 0.9 and 1.1, can further increase formability while at the same time ensuring good corrosion resistance. Furthermore, the chromium steel foils can enable PEMFC stacks with high volumetric density due to their good formability.
  • the chromium steel foil can have a microcleanliness level (MRZ) according to formula 4 less than or equal to 1,
  • WHERE MRZ (nNME1 + 2 X nNME2+3X nNME3 + 4 X ONME4+ 10 nNME10 + 10 nNMElarge)/130
  • ONMEI is the number of inclusions with a diameter of up to 1 pm
  • nNME2 is the number of inclusions with a diameter of up to 2 pm
  • ONME3 is the number of inclusions with a diameter of up to 3 pm
  • ONME4 is the number of inclusions with a diameter of up to 4 pm
  • nNMEio is the number of inclusions with a diameter between 4 and 10 pm
  • nNMElarge is the number of inclusions with a diameter greater than 10 pm.
  • Inclusions can become critical when manufacturing chrome steel foils with a thickness of less than 0.1 mm. During the rolling process, such inclusions can cause surface defects or even holes or cracks. If the latter reach a critical size, a strip tear during operation cannot be ruled out. Mechanical damage to the equipment and downtimes can result. Smaller inclusions of a few micrometers can also lead to tiny holes or cracks when forming bipolar plates. Such holes or cracks are not tolerable in bipolar plates and lead to leaks.
  • a chromium steel foil that has a micro-purity level of less than or equal to 1.
  • the chromium steel foils can therefore enable PEMFC stacks with high volumetric density.
  • corrosion resistance can be ensured due to the micro-purity level of less than or equal to 1.
  • the degree of micropurity can be determined using a scanning electron microscope and electron beam microanalysis. To do this, a sample can first be ground and polished. Then an analysis of the inclusions can be carried out in 130 adjacent and separate fields at 2500x magnification. (nominal resolution 0.1 pm/pixel). The 130 fields can correspond to an area of 1 mm 2 . The analysis can detect inclusions with a length greater than 0.9 pm. The inclusions can then be classified according to their size and composition. The micropurity level can then be calculated using formula 4 based on the number of inclusions in the various sizes.
  • the chromium steel foil can have a microcleanliness level (MRZ) according to formula 4 of less than or equal to 0.25.
  • MRZ microcleanliness level
  • a micro-purity level of less than or equal to 0.25 can ensure continuous production and improve the formability of the chrome steel foil. Furthermore, the improved formability allows the chrome steel foil to be made thin. This means that the chrome steel foil can enable PEMFC stacks with a high volumetric density. In addition, corrosion resistance can be ensured due to the micro-purity level of less than or equal to 0.25. Furthermore, the probability of freedom from cracks and pores can be increased due to the micro-purity level of less than or equal to 0.25.
  • the chromium steel foil can have the following mechanical properties in the longitudinal direction determined according to DIN EN ISO 6892 using the sample shape type H according to DIN 50125:
  • the chrome steel foil can be produced continuously.
  • the formability of the chrome steel foil can be improved by the breaking elongation Aso between 30 and 65%.
  • the improved formability means that the chrome steel foil can be made thinner.
  • the chrome steel foils can have good formability, making them particularly suitable for the production of bipolar plates. The chrome steel foils can therefore enable PEMFC stacks with a high volumetric density.
  • the chromium steel foil can have the following mechanical properties transverse to the rolling direction determined according to DIN EN ISO 6892 using the sample shape type H according to DIN 50125:
  • the chrome steel foil can be produced continuously.
  • the elongation at break Aso between 40 and 70% can improve the formability of the chrome steel foil.
  • the improved formability means that the chrome steel foil can be made thinner. This means that the chrome steel foils can enable PEMFC stacks with a high volumetric density.
  • the chrome steel foils can have good formability, making them particularly suitable for the production of bipolar plates.
  • the present object is achieved by a method for producing a chromium steel foil, in particular a chromium steel foil according to the invention, comprising the steps
  • heat treatment of the cold strip preferably in a continuous furnace, under protective gas, preferably hydrogen or argon, wherein the heat treatment is carried out at a temperature between 900 °C and 1050 °C, preferably between 925 °C and 1025 °C, and particularly preferably between 950 °C and 1000 °C, and wherein the heat treatment is carried out for 5 to 300 s, preferably 5 to 200 s.
  • protective gas preferably hydrogen or argon
  • the process is used to produce a chromium steel foil simply, efficiently and continuously. Due to the high degree of deformation in step (d) and the subsequent heat treatment (e), the chromium steel foil produced using the process has a fine-grained, recrystallized structure. As a result, the process produces a chromium steel foil that has good formability. In addition, the chromium steel foil produced using the process has a high corrosion resistance. Furthermore, the chromium steel foil produced using the process can be produced particularly thinly with a thickness of less than 0.1 mm, enabling PEMFC stacks with a high volumetric density.
  • Hot rolling can be rolling of the chromium steel foil at a temperature above the recrystallization temperature of the chromium steel foil.
  • Cold rolling can be the rolling of metal strips, such as chrome steel foil, below their recrystallization temperature between two or more rotating rollers. Cold rolling can usually take place at room temperature without prior heating.
  • Intermediate annealing can be an annealing without phase change of the chromium steel foil at a temperature in the recrystallization range after cold forming. Intermediate annealing can take place between the individual forming stages during cold rolling of the chromium steel foil.
  • the chrome steel foil can be straightened, in particular by means of stretch bending, to a flatness of at least ⁇ 5 I-unit, preferably ⁇ 2 I-unit.
  • the process can be used to produce a chrome steel foil particularly easily, efficiently and continuously, whereby the chrome steel foil can be particularly suitable for PEMFC stacks with high volumetric density.
  • Stretch-bend leveling is a technology for increasing the flatness of strips. With this technology, the strip is stretched in a defined way by tension on the one hand and bent simultaneously between various rollers on the other.
  • the flatness of surfaces is the maximum height deviation of the chrome steel foil from a flat surface. Based on the ASTM standard A1030/A1030M-2016, the flatness is measured in the longitudinal direction in sections of 1 cm. The ratio of the length of the measured line of the chrome steel foil in relation to a projected length on the flat basis is converted into I-units as described in the aforementioned ASTM and must not be greater than 5, preferably not greater than 2 I-units.
  • the chrome steel foil can be ground before the first cold rolling, whereby a thickness variance of less than 0.5% can be set.
  • the thickness variance can be calculated as follows, for example.
  • the thickness can be measured from the edge of the strip at intervals of 1/20 of the strip width.
  • the median can be calculated from these measured values. The minimum and maximum measured value should not deviate from the median by more than 0.5%.
  • the present object is achieved with a bipolar plate comprising a flow profile, wherein the bipolar plate consists of a chromium steel foil according to the invention or from a chromium steel foil produced by the process according to the invention.
  • the bipolar plate according to the invention offers the advantage that it can be produced efficiently because the chromium steel foil can be produced continuously.
  • the chromium steel foil according to the invention or the chromium steel foil produced according to the method according to the invention has good formability, high corrosion resistance and a thickness of less than 0.1 mm.
  • the bipolar plate also has a particularly good flow profile due to the good formability and is not damaged during forming. Due to the good flow profile, fuel cells with the bipolar plate according to the invention are particularly efficient.
  • the bipolar plate is very corrosion-resistant.
  • the bipolar plate also has a low thickness, so that PEMFC stacks with a high volumetric density are possible.
  • the method according to the invention and the chromium steel foil according to the invention are intermediate products for the bipolar plate.
  • the bipolar plate is produced directly by a simple forming step from the chromium steel foil produced using the method according to the invention or the chromium steel foil according to the invention.
  • the chromium steel foil produced using the method according to the invention or the chromium steel foil according to the invention thus brings its good formability and corrosion resistance to the bipolar plate. Furthermore, due to the small thickness of the chromium steel foil, the bipolar plate can also be very thin.
  • the bipolar plate can have a particularly efficient flow profile, so that fuel cells with the bipolar plate according to the invention can be particularly efficient due to the good flow profile.
  • the bipolar plate can have a maximum permissible height Sz according to DIN ISO 25178 at the surface of the flow profile of less than 2 pm.
  • the bipolar plate Due to the low development of topographies on the surface, the chrome steel foils are particularly suitable for subsequent coating. Smaller maximum Roughnesses require both less time for coating and a smaller layer thickness for complete coverage of the surface.
  • the bipolar plate can also have a particularly efficient flow profile. Due to the maximum permissible height Sz surface of the flow profile being less than 2 pm, the flow profile can ensure a particularly efficient distribution of the fluids. Thus, due to the good flow profile, fuel cells with the bipolar plate according to the invention can be particularly efficient.
  • the present object is achieved by using a chromium steel foil according to the invention or a chromium steel foil produced by the method according to the invention for a bipolar plate.
  • a chromium steel foil according to the invention or a chromium steel foil produced according to the method according to the invention for a bipolar plate offers the advantage that the bipolar plate is produced efficiently because the chromium steel foil is produced continuously.
  • the chromium steel foil according to the invention or the chromium steel foil produced according to the method according to the invention has good formability, high corrosion resistance and a thickness of less than 0.1 mm.
  • the bipolar plate also has a particularly good flow profile due to the good formability and is not damaged during forming. Due to the good flow profile, fuel cells with the bipolar plate according to the invention are particularly efficient.
  • the bipolar plate is very corrosion-resistant.
  • the bipolar plate also has a low thickness, enabling PEMFC stacks with a high volumetric density.
  • the term “comprise” includes, in addition to its literal meaning, the terms “consist essentially of” and “consist of” and refers specifically to these.
  • the term “comprise” refers both to embodiments in which the subject matter “comprises” specifically listed elements does not comprise any further elements, and to embodiments in which the subject matter “comprises” specifically listed elements may and/or actually comprises further elements.
  • the term “have” is to be understood as the term “comprise” which also includes and refers to the terms “consist essentially of” and “consist of”.
  • Fig. 2 Light microscopic image of the structure of a chrome steel foil
  • FIG. 7 Section through the flow profile shown in Fig. 6;
  • FIG. 8 schematic representation of a cross section through a bipolar plate
  • FIG. 11 Surface topography of the flow profile from Fig. 10 after forming
  • Table 1 shows various compositions for chromium steel foil for the production of bipolar plates for fuel cells. Due to the alloy, the chromium steel foils are austenitic. The chromium steel foils consist of the following alloy components in weight percent
  • Remainder Fe and unavoidable impurities individually maximum 0.05%, in total maximum 0.15% in weight percent.
  • the chrome steel foils in Table 1 have a thickness of less than 0.1 mm, preferably less than 0.075 mm, particularly preferably less than 0.05 mm and a width of greater than 100 mm, preferably greater than 300 mm.
  • Fig. 1 shows the ratio of interstitially corrected nickel equivalent Niiceq to chromium equivalent Cr eq as well as the PREN number plotted against Niiceq. From Fig. 1 it can be seen that a high corrosion resistance is achieved with a ratio of Niiceq to Cr eq between 0.4 and 2.0. The high corrosion resistance is evident from the high PREN number.
  • chrome steel foils have the following alloy components in weight percent:
  • microalloying elements Al, Nb, Ti and V serves to prevent a pronounced precipitation of chromium carbides at the grain boundaries during or after welding of the bipolar plates. This reduces the susceptibility to intergranular corrosion or stress corrosion cracking to a minimum.
  • the proportion of austenitic structure is at least 99% and the proportion of recrystallized structure is at least 99%.
  • the chromium steel foils have an average grain diameter of greater than 1.5 pm and less than 10 pm, preferably less than 7.5 pm, and particularly preferably less than 5 pm, according to the Heyn line cut method (ASTM E112-13).
  • the chromium steel foils have a structure with equiaxial grains.
  • Fig. 2 shows a light micrograph of the structure of a chromium steel foil.
  • the average grain diameter is greater than 1.5 pm and smaller than 10 pm, preferably smaller than 7.5 pm, and particularly preferably smaller than 5 pm, according to the Heyn line-section method (ASTM E112-13).
  • the chromium steel foil also has a structure with equiaxial grains.
  • Fig. 2 also shows how the mean grain diameter is determined using the line intersection method by Heyn (ASTM E112-13).
  • the intersection points of the line with the grain boundaries are shown as points.
  • the mean grain diameter is calculated by dividing the measured line length by the number of these points.
  • the Heyn line intersection method (ASTM E112-13) is also used to determine the equiaxiality of the grains. For this, a vertical line is drawn through the light microscopic image in addition to a horizontal line. The intersection points with the grain boundaries are determined for both the horizontal line and the vertical line. The grain shape can be determined from the ratio of intersection points with the horizontal line to the intersection points with the vertical line.
  • the ratio for equiaxial grains is between 0.8 and 1.2, preferably between 0.9 and 1.1.
  • Fig. 3 shows the relationship of the relative formability depending on the mean grain diameter for different chromium steel foil thicknesses.
  • the degree of deformation was determined in hydraulic cupping tests according to DIN EN ISO 16808.
  • Relative formability ji / jStd x 100 (Formula 7) ji is the degree of thickness deformation measured on foils (25, 50, 75 and 100 micrometer thickness) with an increased crystallographic forming capacity jStd is the degree of thickness deformation measured on foils (25, 50, 75 and 100 micrometer thickness) with an average grain diameter of 25 micrometers
  • MRZ microcleanliness level
  • the chrome steel foil has a microcleanliness level (MRZ) according to formula 4 of less than or equal to 0.25.
  • MRZ microcleanliness level
  • Fig. 4 shows the method for determining the MRZ purity level.
  • the micro-purity level is determined using a scanning electron microscope and electron beam microanalysis. To do this, a sample is first ground and polished. The inclusions are then analyzed in 130 adjacent and separate fields at 2500x magnification (nominal resolution 0.1 pm/pixel). The 130 fields correspond to an area of 1 mm 2 . The analysis detects inclusions with a length greater than 0.9 pm. The inclusions are then classified according to their size and composition. The micro-purity level is then calculated using formula 4 based on the number of inclusions in the various sizes.
  • Fig. 5 shows the production of crack- and hole-free bipolar plates depending on the purity level MRZ and the thickness of the chrome steel foil used.
  • the lower the purity level the more bipolar plates show no cracks or holes after Therefore, a lower degree of purity leads to a higher proportion of defect-free bipolar plates even with decreasing thickness of the chrome steel foil.
  • the chromium steel foil has a yield strength Rp0.2 between 250 and 800 MPa, a tensile strength between 500 and 1200 MPa, and an elongation at break A80 between 30 and 65% in the longitudinal direction, determined using the tensile method.
  • the chromium steel foil has a yield strength Rp0.2 between 300 and 800 MPa, a tensile strength between 400 and 1200 MPa, and an elongation at break A80 between 35 and 70%, determined transversely to the rolling direction using the tensile method.
  • Fig. 6 shows a bipolar plate with an incorporated flow profile 2 for determining the forming capacity.
  • the bipolar plate 2 is made from a chromium steel foil according to the invention.
  • Bipolar plates 1 are manufactured using various forming processes.
  • the flow profiles 2 for the media flow are individually designed for the application and forming process.
  • the filigree is defined in order to be able to better estimate and compare different bipolar plates 1 and the requirements for the material. In addition, this value offers a suitable target value for material development and for evaluating the results.
  • FIG. 7 shows a section through the flow profile shown in Fig. 6.
  • Fig. 8 shows a schematic representation of a cross section through a bipolar plate 1.
  • the parameter TK (channel depth) and the parameter BK (channel width) are shown.
  • the filigree is defined. It is determined from the channel width and channel depth as well as the thickness of the bipolar plate according to formula 8.
  • the chromium steel foils made of steel 9 and 10 listed in Table 1 were produced according to the process according to the invention and tested in forming tests until failure.
  • Fig. 9 shows the dependence of the filigree on the average grain diameter for chrome steel foils of different thicknesses. As the average grain diameter decreases, the achievable filigree also increases for the respective thickness of the chrome steel foil.
  • the bipolar plate 1 has a maximum permissible height Sz according to DIN ISO 25178 at the surface of the flow profile 2 of less than 2 pm.
  • Fig. 10 shows the surface of bipolar plates 1 after forming chromium steel foils with different average grain diameters.
  • the maximum height was determined according to ISO 25178 “Geometric product specification - Surface texture: Planar” and is shown in Fig. 11.
  • Fig. 11 shows the surface topography of the flow profile from Fig. 10 after forming.
  • the measurement with a larger average grain diameter shows a larger maximum height, as can be seen in the left image of Fig. 11.
  • the maximum height decreases, as can be seen in the right image of Fig. 11.
  • Fig. 12 shows the maximum height Sz on the surface as a function of the average grain diameter.
  • the maximum height Sz was determined according to ISO 25178. As can be seen from Fig. 12, the maximum height is influenced by the average grain diameter. The smaller the average grain diameter, the lower the maximum height after forming. Consequently, a small average grain diameter is not only beneficial for high filigree, but also for smooth surfaces with a low maximum height in the flow profile.
  • the coating to be applied for the electrical contact resistance can then preferably be made thinner. Erosion phenomena and flow disturbances in the channels are thus minimized.
  • Fig. 13 shows the influence of the holding time on the grain size at different temperatures.
  • the chromium steel foils were annealed at different temperatures and holding times after cold forming.
  • the resulting average grain diameters were shown for alloys 7, 9 and 11 as a function of the strip temperature and holding time in a laboratory furnace.
  • the strip thickness should preferably be reduced by at least 70% of the thickness by cold rolling.
  • the stored energy is a necessary prerequisite for the subsequent recrystallization.
  • a furnace room temperature of preferably 900 to 1050°C should be set.
  • the strip temperature should preferably be set so that the holding time in the furnace atmosphere is a maximum of 300s. The thinner the foils, the lower the temperature and the shorter the time should be.

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Abstract

L'invention concerne un film d'acier au chrome pour la production de plaques bipolaires pour piles à combustible, le film d'acier au chrome étant austénitique ; le film d'acier au chrome étant constitué des composants d'alliage suivants en pourcentage en poids : 0 % < Fe < 80 %, 12 % < Cr < 30 %, 0,1 % < Ni < 20 %, 0,5 % < Mn < 17 %, 0,1 % < Cu < 2 %, 0,015 % < C < 0,15 %, 0,02 % < N < 0,6 %, 0,05 % < Mo < 3 %, 0,2 % < Si < 1 %, 0,001 % < Ti < 0,25 %, 0,01 % < Nb < 0,5 %, 0,05 % < V < 0,2 %, 0,003 % < AI < 1 %, le reste étant du Fe, et comprend des contaminations inévitables d'au plus 0,05 % et au total d'au plus 0,15 % en pourcentage en poids ; le film d'acier au chrome présente une épaisseur inférieure à 0,108 mm, de préférence inférieure à 0,075 mm, de manière particulièrement préférable inférieure à 0,05 mm et une largeur supérieure à 100 mm, de préférence supérieure à 300 mm ; le film d'acier au chrome présente un rapport de NiICeq (valeur équivalente de nickel corrigée de manière interstitielle) selon la formule 2 à Creq (équivalent de chrome) selon la formule 3 comprise entre 0,4 et 2,0 ; NiICeq = N + 0,5xMn + Cu + 30x (N - 0,29xTi - 0,15xNb - 0,27xV - 0,483xAl) + 30x(C - 0,25 x Ti - 0,13xNb-0,24xV - 0,41xAI) (formule (2)), et Creq = Cr + 1,5 x Si + Mo (formule (3)), la teneur en éléments d'alliage étant donnée en pourcentage en poids.
PCT/EP2023/082753 2022-11-22 2023-11-22 Film d'acier au chrome pour la production de plaques bipolaires pour piles à combustible WO2024110557A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180034070A1 (en) * 2015-03-03 2018-02-01 Nippon Steel & Sumitomo Metal Corporation Stainless steel sheet for polymer electrolyte fuel cell separator
WO2021172381A1 (fr) * 2020-02-27 2021-09-02 日鉄ステンレス株式会社 Acier inoxydable pour feuilles métalliques, feuille d'acier inoxydable, procédé de production d'acier inoxydable pour feuilles métalliques, et procédé de production de feuille d'acier inoxydable
EP3916136A1 (fr) * 2019-01-21 2021-12-01 JFE Steel Corporation Tôle d'acier inoxydable austénitique destinée à un séparateur de pile à combustible et procédé de production d'une telle tôle d'acier inoxydable austénitique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180034070A1 (en) * 2015-03-03 2018-02-01 Nippon Steel & Sumitomo Metal Corporation Stainless steel sheet for polymer electrolyte fuel cell separator
EP3916136A1 (fr) * 2019-01-21 2021-12-01 JFE Steel Corporation Tôle d'acier inoxydable austénitique destinée à un séparateur de pile à combustible et procédé de production d'une telle tôle d'acier inoxydable austénitique
WO2021172381A1 (fr) * 2020-02-27 2021-09-02 日鉄ステンレス株式会社 Acier inoxydable pour feuilles métalliques, feuille d'acier inoxydable, procédé de production d'acier inoxydable pour feuilles métalliques, et procédé de production de feuille d'acier inoxydable
EP4112751A1 (fr) * 2020-02-27 2023-01-04 NIPPON STEEL Stainless Steel Corporation Acier inoxydable pour feuilles métalliques, feuille d'acier inoxydable, procédé de production d'acier inoxydable pour feuilles métalliques, et procédé de production de feuille d'acier inoxydable

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