Method for increasing the strength and / or the hydrogen compatibility of a spring, spring, and valve having a spring

Abstract

The invention relates to a method for increasing the strength and the hydrogen compatibility of a spring, in which method the spring is manufactured from - an austenitic material, - a precipitation hardening rustproof material, - a duplex material or - a nickel-based alloy. According to the invention, after being manufactured, the spring is subjected to a thermochemical aftertreatment which comprises nitriding, nitrocarburizing and / or carburizing as process steps in order to form an austenitic edge layer. The invention also relates to a spring, and to a valve having a spring according to the invention.

Description

[0001] Description

[0002] Method for increasing the strength and / or hydrogen compatibility of a spring, spring and valve with spring

[0003] The present invention relates to a method for increasing the strength and / or hydrogen compatibility of a spring having the features of the preamble of claim 1. Furthermore, the invention relates to a spring and a valve having a spring according to the invention.

[0004] The preferred field of application of the invention is hydrogen applications, in particular fuel cell systems, electrolysis systems and systems in the field of hydrogen combustion engines and in the field of hydrogen filling stations.

[0005] State of the art

[0006] A variety of different valves are used in a fuel cell system or an electrolysis plant. In a hydrogen-based fuel cell system, for example, hydrogen must be supplied to the anode of at least one fuel cell via an anode subsystem. Typically, the hydrogen is extracted from a pressurized gas container and supplied to at least one fuel cell via a high-pressure, a medium-pressure, and a low-pressure section of the anode subsystem. All of these sections contain valves whose valve springs come into contact with hydrogen, or at least can come into contact with it. The valve springs, or the materials from which the valve springs are made, should therefore be compatible with hydrogen. In order to ensure the longevity of the springs, the material should also be sufficiently strong.In addition, the design freedom increases with the strength, since more installation space must be made available for components made of low-strength materials, so that certain design solutions are then no longer feasible.

[0007] Stable austenitic stainless steels exhibit comparatively low strengths. Even typical drawing operations cannot achieve the strengths achieved with higher-strength materials, such as precipitation-hardening stainless steel No. 1.4568. While higher strengths can be achieved with metastable austenitic materials, drawing operations usually introduce a significant amount of deformation martensite, which has a negative impact on hydrogen compatibility. Higher strengths can also be achieved with duplex steels, but due to the ferrite content in their microstructure, these are only suitable to a limited extent for applications in hydrogen atmospheres.

[0008] The present invention is concerned with the task of increasing the strength and hydrogen compatibility of a spring made of a low to medium strength material.

[0009] To achieve this objective, the method having the features of claim 1 and the spring having the features of claim 6 are proposed. Advantageous further developments of the invention can be found in the respective subclaims. Furthermore, a valve having a spring according to the invention is specified.

[0010] Disclosure of the invention

[0011] A method for increasing the strength and hydrogen compatibility of a spring is proposed, in which the spring is manufactured from an austenitic material, a precipitation-hardening stainless material, a duplex material, or a nickel-based alloy. According to the invention, after production, the spring is subjected to a thermochemical post-treatment, which includes nitriding, nitrocarburizing, and / or carburizing as a process step to form an austenitic surface layer.

[0012] The proposed thermochemical post-treatment of the spring leads to the formation of an austenitic surface layer, which effectively prevents the diffusion of hydrogen and thus hydrogen embrittlement. This allows the spring to be manufactured from a material that would have been only partially suitable for hydrogen applications without the proposed post-treatment.

[0013] The austenitic surface layer formed by the thermochemical post-treatment also exhibits significantly increased strength compared to the original material. This, in turn, enables the realization of particularly small springs, which can be used particularly in confined spaces.

[0014] With the help of the proposed process, an improvement in the hydrogen compatibility of the spring can be achieved while simultaneously increasing its strength.

[0015] The thermochemical post-treatment, in particular the process step of nitriding, nitrocarburizing, and / or carburizing, is preferably carried out in a temperature range of 350°C to 650°C using nitriding and / or carburizing process gases. The process time is preferably 1 to 24 hours. This process, which can also be referred to as a low-temperature process, allows for lower process temperatures but longer process times.

[0016] Alternatively or additionally, it is proposed that the thermochemical post-treatment, in particular the process step of nitriding, nitrocarburizing and / or carburizing, be carried out in a temperature range of 900°C to 1300°C using nitriding and / or carburizing process gases, with the process time preferably being between 1 minute and 12 hours. With the help of this process, which can also be referred to as a high-temperature process, the process times can be shortened. If necessary, both processes can also be combined, so that both the low-temperature process and the high-temperature process are used for thermochemical post-treatment. By combining both processes, for example, the penetration depth of the austenitic surface layer can be increased. To achieve greater penetration depths, however, the process time can also simply be extended.

[0017] According to a preferred embodiment of the invention, the thermochemical post-treatment of the spring comprises the process step of nitrocarburizing at a temperature below 650°C, preferably below 500°C. In this way, a significant enrichment of the spring's surface layer with nitrogen and carbon can be achieved, with their total weight proportions being up to 18 wt.% based on the total weight of the surface layer materials. The enrichment with nitrogen and carbon, in turn, can significantly increase strength.

[0018] Furthermore, the spring is preferably made from a wire that is cold-drawn and / or wound several times. This process is therefore particularly suitable for producing a coil spring. This type of spring is frequently used in valves, especially as a coil compression spring.

[0019] Furthermore, the spring is preferably subjected to stress relief annealing after production and / or after the thermochemical post-treatment. For some materials, precipitation hardening can be achieved with the help of stress relief annealing. In combination with the proposed thermochemical post-treatment, the strength of the spring can thus be further increased.

[0020] Furthermore, a spring, in particular a helical spring, is proposed, which is made of an austenitic material, a precipitation-hardening stainless material, a duplex material, or a nickel-based alloy. According to the invention, the spring has a purely austenitic surface layer. The austenitic surface layer significantly reduces the diffusion of hydrogen into the material, thus improving the hydrogen compatibility of the spring. At the same time, the strength of the spring is increased.

[0021] The austenitic surface layer is preferably produced by a thermochemical post-treatment that includes nitriding, nitrocarburizing, and / or carburizing as a process step. This means that the austenitic surface layer is preferably produced according to the method according to the invention described above.

[0022] Furthermore, the austenitic surface layer preferably contains a total of at least 10 wt.%, preferably at least 15 wt.%, of nitrogen and / or carbon, based on the total weight of the surface layer materials. With such high nitrogen and / or carbon contents, the surface layer exhibits particularly high strength.

[0023] The proposed spring can, in particular, be manufactured or wound from a multiple cold-drawn wire. This is especially true if the spring is a helical spring. The spring can thus be manufactured largely using a conventional manufacturing process, followed by thermochemical post-treatment to increase the spring's strength and hydrogen tolerance.

[0024] Due to its properties, which are attributable to the proposed thermochemical post-treatment, a spring according to the invention is particularly suitable for applications under a hydrogen atmosphere.

[0025] In a further development of the invention, a valve for hydrogen applications is therefore proposed, which comprises a spring according to the invention. The valve can, in particular, be a high-pressure, medium-pressure, or low-pressure valve in a hydrogen-conducting path of an anode subsystem that serves to supply a fuel cell stack with hydrogen. Since the spring of such a valve comes into contact with hydrogen, or can come into contact with hydrogen, the advantages of the invention, in particular the increased hydrogen compatibility of the spring, are particularly effective here. The additionally increased strength of the spring enables a size reduction, thus saving installation space.

Claims

Claims 1 . A method for increasing the strength and hydrogen compatibility of a spring, in which the spring is manufactured from an austenitic material, a precipitation-hardening stainless material, a duplex material or a nickel-based alloy, characterized in that the spring is subjected to a thermochemical post-treatment after manufacture, which comprises nitriding, nitrocarburizing and / or carburizing as a process step to form an austenitic surface layer.

2. Process according to claim 1, characterized in that the thermochemical aftertreatment, in particular the process step of nitriding, nitrocarburizing and / or carburizing, is carried out in a temperature range of 350°C to 650°C using nitriding and / or carburizing process gases, wherein the process time is preferably 1 to 24 hours.

3. Process according to claim 1 and / or 2, characterized in that the thermochemical post-treatment, in particular the process step of nitriding, nitrocarburizing and / or carburizing, is carried out in a temperature range of 900°C to 1300°C using nitriding and / or carburizing process gases, wherein the process time is preferably 1 minute to 12 hours.

4. Method according to one of the preceding claims, characterized in that the spring is made from a wire which is cold-drawn and / or wound several times.

5. Method according to one of the preceding claims, characterized in that the spring is subjected to stress relieving treatment after manufacture and / or after thermochemical post-treatment.

6. Spring, in particular a helical spring, which is made of an austenitic material, a precipitation-hardening stainless material, a duplex material or a nickel-based alloy, characterized in that the spring has a purely austenitic surface layer which has preferably been produced by a thermo-chemical post-treatment which includes nitriding, nitrocarburizing and / or carburizing as a process step.

7. Spring according to claim 6, characterized in that the austenitic surface layer contains in total at least 10 wt.%, preferably at least 15 wt.%, nitrogen and / or carbon based on the total weight of the surface layer materials.

8. Spring according to claim 6 or 7, characterized in that the spring is made of a multiple cold-drawn wire, in particular wound.

9. A valve for hydrogen applications comprising a spring according to any one of claims 6 to 8.