Method for manufacturing a hydrogen tank

Abstract

The invention relates to a method for manufacturing a hydrogen tank, comprising a hardened steel container (3) which has an inner liner (7), wherein the steel container (3) has a tubular cross-section and is tapered at its ends by forming, characterized in that the steel container (3) has a Vickers hardness greater than 370.

Description

[0001] The present invention further relates to a method for manufacturing a hydrogen tank according to the features in claim 1.

[0002] It is known from the prior art to manufacture pressurized gas cylinders or containers for storing and preserving media, particularly those in a gaseous state. Since high pressures often occur inside such a container, steel is the preferred material for its manufacture.

[0003] Hardenable steel alloys are used in this process. This allows for high tensile strengths, which in turn make it possible to store a suitable medium at high internal pressure.

[0004] A disadvantage of a steel alloy that has a high tensile strength is that, in this state of high strength, only limited deformation capacity is possible, or the forming forces are high in order to further form a semi-finished product made of such a steel alloy into a steel container or a pressurized gas tank.

[0005] The storage of hydrogen is further complicated by the fact that direct contact of the hydrogen with the steel alloy leads to a phenomenon known as hydrogen embrittlement.

[0006] The object of the present invention is therefore to demonstrate a hydrogen tank and a method for its production which is simple and cost-effective to manufacture, but at the same time can withstand a high internal pressure, thus exhibiting good resistance to high internal pressure and therefore good storage capacity.

[0007] The aforementioned problem is solved according to the invention by a method for manufacturing a hydrogen tank according to the features in claim 1.

[0008] Advantageous embodiments of the present invention are the subject of the dependent claims.

[0009] The hydrogen tank has a hardened steel container. The steel container is therefore made of a hardened steel alloy. An inner liner is provided. The liner is either inserted or applied as an internal coating. The liner shields the inner surface of the steel container from the hydrogen stored within, thus preventing hydrogen embrittlement. In cross-section, the steel container itself is tubular. The steel container is manufactured from a tubular semi-finished product. This tubular semi-finished product is formed at at least one end, preferably both ends. This means that the tubular semi-finished product is tapered at at least one, preferably both ends, thus providing a distinct container end. A closure or valve, for example, can be inserted into this container end.The respective container end can be machined after forming, for example by machining or milling; for instance, a thread can be cut. Preferably, however, no thermal joining process takes place at the formed end, so that no structural transformation occurs due to heat input.

[0010] The hydrogen tank according to the invention is thus manufactured from a tubular semi-finished product, which is already hardened. Therefore, the tubular semi-finished product has a tensile strength Rm preferably greater than 1600 MPa. The steel tank can then be manufactured according to the invention as follows: The tubular semi-finished product is tempered in a graduated process at its ends. This tempering is a heat treatment. This can be applied, for example, with a suitable heat source. However, the tempering is particularly preferably carried out only partially. Thus, the tubular semi-finished product is tempered, or more intensely tempered, in those areas where higher degrees of deformation will later occur. This is particularly the case at the outer ends, since this is where the greatest deformation or the highest degree of deformation takes place.

[0011] Following tempering, the specially graded semi-finished product is then cooled. A liner can then be inserted into the cooled semi-finished product, or an internal coating can be applied.

[0012] Following this, cold forming takes place, so that the graded and cooled semi-finished product is formed into the steel container. During this cold forming process, work hardening occurs, resulting in significantly improved formability and / or forming behavior in the previously tempered areas. Consequently, after cold forming, the steel container exhibits a Vickers hardness (HV 10) of at least 370, preferably higher, in all areas. Furthermore, a tensile strength (Rm) greater than 1,600 MPa is particularly preferred in at least the unformed areas. In the formed areas, a tensile strength (Rm) greater than 1,200 MPa, particularly greater than 1,300 MPa, and preferably greater than 1,400 MPa, is preferably present. The tensile strength should be limited to less than 3,000 MPa, particularly less than 2,500 MPa.

[0013] Because cold forming takes place, the liner or inner coating inside the steel container is not negatively affected or even destroyed by subsequent thermal exposure or, conversely, by hot forming. Due to the cold forming process, the properties of the liner or the inner coating remain unaffected. This would be different if the liner or inner coating were exposed to heat, for example, through hot forming. After the cold forming process is complete, the steel container, and thus the pressure vessel, is manufactured and simultaneously suitable for containing hydrogen, since a suitable liner or inner coating is present inside the steel container, preventing hydrogen embrittlement.A closure or valve can then be inserted into the respective formed ends, so that the entire hydrogen tank is ready for assembly and for filling and storing hydrogen.

[0014] A steel or steel alloy is particularly preferred which contains the alloying elements described below, expressed in weight percent; furthermore, the alloy contains iron as a residue and impurities resulting from the melting process: My. Max. C 0,18 % 0,50 % Mn 0,2 % 4,0 % Si 0,05 % 2% P 0,05 % S 0,05 % Al 0,001 % 0,25 % Cr 2,0 % You 3,0 % Mo 0,9 % Nb 0,3 % V 0,3 % W 1,0 % Take 0,2 % Hf 0,2 % Cu 1,0 % B 0,01 % Ten 0,1 % Approx. 0,005 % O 0,01 % N 0,03 % H 0,001 %

[0015] The sum of other alloying and accompanying elements as well as impurities is less than 1%. The remaining amount is iron.

[0016] The finished steel container then exhibits a characteristic Vickers HV hardness. Specifically, this is Vickers HV10 hardness. The Vickers hardness is determined according to DIN EN ISO 5407-1. In the unformed areas, it is at least 370, preferably greater than 390, and particularly greater than 400. In the unformed areas, the steel container has a Vickers HV hardness greater than 490, and particularly greater than 500. Overall, with regard to the pressure resistance of the entire hydrogen tank to be manufactured, the Vickers HV hardness value will deviate by less than 20%, i.e., from the formed area to the unformed area. The Vickers HV10 hardness should not exceed 700, preferably less than 680, and particularly less than 660.

[0017] Thus, an open, tubular section of the semi-finished product can be used for the steel container or shell material to be manufactured later, which in this state contains at least 95% martensite. Before an internal coating or liner is applied, the previously described graded tempering takes place. For example, the semi-finished product may only be formed at one end later. Therefore, only one end of the semi-finished product is open. The other end may be closed. In this case, the graded tempering is preferably applied only to this single open end.

[0018] Preferably, steel alloys containing less than 1 wt.% silicon can be used. The temperature of the unformed area should be below 250 °C, preferably below 220 °C. Optionally, the area not to be formed in the subsequent cold forming process can be actively cooled to generally prevent a temperature increase in the unformed area. The highest tempering temperatures of the graded-heated or tempered area depend on the degree of deformation in the subsequent cold forming process. The area to be most deformed or most tapered is preferably tempered at a temperature below 600 °C, particularly below 550 °C. For heat-treatable steels that have a secondary hardening maximum, the highest tempering temperature of the graded-heated area should be below this secondary hardening maximum temperature, particularly more than 50 °C below it.In particular, the tempering temperature should be at least 200 °C, preferably at least 220 °C, and most preferably at least 250 °C.

[0019] For steels containing more than 1 wt% silicon, the most tapered area should be below 650 °C. The non-formable areas can also have a temperature below 300 °C, preferably below 220 °C, since silicon suppresses carbide formation and thus counteracts softening. Generally, these areas can also be cooled. However, the non-formable areas should be at least at room temperature.

[0020] Optionally, the tubular semi-finished product can be heated to a temperature below 250 °C before and / or after the graded thermal treatment of the end sections described above. This results in a bake-hardening effect, which further increases the yield strength (Rp 0.2).

[0021] The steel container or hydrogen tank described above is manufactured in particular by a process with the following process steps: • Provision of a tubular semi-finished product made of a hardened steel alloy with a tensile strength Rm greater than 1600 MPa • Area-by-area tempering of the semi-finished product in areas that will later be reshaped, • Cooling of the partially graded tempered semi-finished product and optional application of a liner or internal coating, • Cold forming of the semi-finished product in the tempered areas, whereby cold forming results in work hardening, such that a Vickers HV10 hardness greater than 370 is achieved in all areas of the formed steel container.

[0022] The process is particularly characterized by the fact that the semi-finished product is partially and, in this case, graduated tempering. Graduated tempering means that a specific section of the tubular semi-finished product is heated to a different intensity or temperature. The temperature and intensity of the heat treatment depend primarily on the expected degree of deformation. A high degree of deformation is achieved with a correspondingly high temperature. However, these temperatures are generally below 650 °C, preferably below 600 °C, and particularly below 550 °C, as described above.

[0023] The areas not to be formed are tempered or held at temperatures below 300 °C, preferably below 250 °C, and most preferably below 220 °C. It is also possible to actively cool the areas not to be formed so that their temperature does not differ significantly from room temperature.

[0024] Further advantages, features, and properties of the present invention are the subject of the following description. Preferred embodiments are illustrated in the schematic figures. These serve to facilitate understanding of the invention. They show Fig. 1a to c a manufacturing process according to the invention for a steel container of a hydrogen tank, Fig. 2 a longitudinal section through an end area of ​​a manufactured steel container for a hydrogen tank and Fig. 3a and b are an alternative design variant.

[0025] The same reference numerals are used in the figures for identical or similar components, even if repeated representation in the description is omitted for the sake of simplicity. The embodiments described above and below can be combined with one another as desired without departing from the scope of the invention.

[0026] According to Fig. 1a A tubular semi-finished product 1 made of a hardened steel alloy is provided. According to section line AA, the tubular semi-finished product 1 has a round cross-section. The tubular semi-finished product 1 preferably has a uniform tensile strength Rm distributed over its entire length 2 and over its entire cross-section, preferably greater than 1600 MPa, particularly greater than 1700 MPa, and most preferably greater than 1800 MPa.

[0027] According to Fig. 1b The tubular semi-finished product 1 is now tempered, i.e., subjected to heat treatment. The temperature profile over the length 2 is shown in Fig.Figure 1b shows a schematic representation. The later end regions 4, 6, which are expected to undergo the greatest deformation, are heat-treated at the relatively highest temperature. This is preferably below 650 °C. The regions expected to undergo moderate deformation, i.e., from the outer end region 4 to an inner longitudinal section, are heat-treated at a relatively lower temperature. This is, in the sense of the invention, a graded heat treatment. A central longitudinal section 5, which does not undergo any deformation, has a significantly lower temperature and is heat-treated at a maximum of 300 °C. This section can also be actively cooled so that, for example, a temperature of approximately room temperature is maintained.

[0028] The graded heat-treated semi-finished product is then cooled. The strength is reduced in the end regions 4 and 6, which simultaneously increases the formability. The resulting steel container 3 is then formed by a mechanical forming process (not shown in detail), either axial or radial pressure forming. Fig. 1c is provided. The outer end sections 4 are heavily deformed and are merely optional. A central longitudinal section 5 has not been deformed at all. End sections 4 and 6 of the steel container 3 have a bell-shaped profile. A sealing plug and / or a valve, for example, can be inserted into the respective end sections 4 and 6, so that a gaseous medium (not shown) can be filled and stored in the steel container 3. The steel container 3 is then a hydrogen tank.

[0029] After completion of the heat treatment and cooling of the heat-treated semi-finished product, and before forming, a coating is applied or a liner 7 is inserted into an interior space. This is shown in the cross-sectional view according to [reference]. Fig.2. The inner coating, or liner 7, thus separates a hydrogen-filled interior space 8 from the wall 9, or wall thickness, of the hardened steel alloy. Hydrogen embrittlement is therefore effectively prevented. The liner 7, or inner coating, extends into the outer end section 4 and is fitted with a valve (not shown). The outer end section 4, or end section 6, is then cold-formed with the liner, or inner coating 7. During cold forming, work hardening occurs, resulting in a Vickers HV hardness greater than 370 across the entire wall 9, or wall thickness. At the same time, no further heat treatment is necessary, so the liner, or inner coating 7, remains undamaged.

[0030] Fig.Figures 3a and b show an alternative design variant. Here, the tubular semi-finished product 1 is closed at one end by a base 10. This already exhibits a tensile strength greater than 1600 MPa. A graded heat treatment then takes place only on the right side, relative to the plane of the image. After the heat treatment and cooling, a liner or an internal coating 7 can be inserted.

[0031] According to Fig. 3b is then formed on the right side of the steel container 3, as seen in the image plane, so that a steel container 3 is formed which in turn has a Vickers HV10 hardness greater than 370 in its wall 9. A valve (not shown in detail) can then be inserted into the outer end region 4 on the right side, as seen in the image plane. Reference symbol: 1 tubular semi-finished product 2 length to 1 3 steel containers 4 outer end area 5 middle length section 6 End section or end area 7 Interior coating / liner 8 Interior 9 wall 10 Floor QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] DIN EN ISO 5407-1

[0016]

Claims

[1] Method for manufacturing a hydrogen tank, preferably with the features of claim 1, characterized by the following process steps: • Providing a tubular semi-finished product (1) made of a hardened steel alloy with a tensile strength Rm greater than 1600 MPa • Area-by-area tempering of the semi-finished product in areas that will later be reshaped, • Cooling of the tempered semi-finished product and optional insertion of a liner (7) or an internal coating, • Cold forming of the semi-finished product in the tempered areas, whereby cold forming results in work hardening such that a Vickers HV10 hardness greater than 370 is achieved in all areas of the formed steel container (3). [2] Method according to claim 1, characterized by , that the end areas (4, 6) of the semi-finished product are tempered. [3] Method according to claim 1 or 2, characterized bythat the tempering takes place in a graded manner, in particular with different temperatures, preferably tempering at a temperature below 650 °C, in particular below 600 °C and most preferably below 550 °C. [4] Method according to any one of claims 1 to 3, characterized by that the areas not to be transformed are tempered below 300 °C, in particular below 250 °C, and most preferably below 220 °C. [5] Method according to any one of the preceding claims, characterized by , that for the production of the steel container (3) at least one end area (4), in particular both end areas (4, 6) of the semi-finished product (1) are tapered during cold forming. [6] Method according to any of the preceding claims, characterized by , that the steel container (3) is manufactured in its end regions (4, 6) having the shape of a pressurised gas cylinder. [7] Method according to any of the preceding claims, characterized by , that a steel is used which contains the following alloying elements, expressed in wt.%, with the remainder being iron and smelting-related impurities of less than 1%: Min. Max. C 0,18 % 0,50 % Mn 0,2 % 4,0 % Si 0,05 % 2% P 0,05 % S 0,05 % Al 0,001 % 0,25 % Cr 2,0 % Ni 3,0 % Mon 0,9 % Note 0,3 % V 0,3 % W 1,0 % Ta 0,2 % Hf 0,2 % Cu 1,0 % B 0,01 % Ti 0,1 % Approx 0,005 % O 0,01 % N 0,03 % H 0,001 % [8] Method according to any one of the preceding claims, characterized by , that the inner liner is drawn in as a liner (7) or applied as an inner coating, the drawing in or application taking place particularly after cooling and before cold forming. [9] Method according to any one of the preceding claims, characterized by , that the steel container (3) has a Vickers HV hardness of at least 370 in at least some areas, particularly in formed areas, and that, furthermore preferably, the Vickers HV hardness is greater than 490 in non-formed areas. [10] Method according to any of the preceding claims, characterized by, that the steel container (3) has a tensile strength RM greater than 1,200 MPa in all areas, in particular greater than 1,300 MPa, preferably greater than 1,400 MPa.

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