Method for heat treatment of chromium steel
Through a new heat treatment method, pre-oxidation, tempering and nitriding are directly carried out under a nitrogen atmosphere, solving the problems of cumbersome and high cost in traditional heat treatment steps, and achieving independent adjustment and efficiency improvement of the core hardness of high alloy chromium steel components.
Patent Information
- Application Number
- CN202380059501.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-08-15
- Filing Date
- 2023-08-10
- Publication Date
- 2025-03-28
AI Technical Summary
Prior art When heat treatment of high alloy chromium steels is performed, multiple steps are required including quenching, tempering, activation and nitriding, resulting in high time and cost and it is difficult to independently adjust the core hardness of the components.
Through a new heat treatment method, the traditional tempering and activation steps are eliminated and pre-oxidation, tempering and nitriding are performed directly under a nitrogen atmosphere, allowing the core hardness of the components to be independently adjusted.
This method can independently adjust the core hardness at a nitriding temperature between 480-600°C, making it between 620HV1-460HV1, and is suitable for a wider range of applications, reducing manufacturing costs and improving efficiency.
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Figure CN119731348A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for the heat treatment of chromium steel, in particular high-alloy chromium x steel, by gas nitriding and to a vehicle component, in particular, produced by such a production method.
[0002] The application area of the invention extends in particular to vehicle technology and tool manufacturing. Vehicle components that are subject to wear and vibration and are made of high-alloy chromium steel, i.e. steel materials with the main alloying component chromium, are usually tempered, activated and nitrided after forced martensitic hardening to achieve the desired component properties. Typically, such components are formed from special high-alloy chromium steels, such as X40CrMov5-1, X50CrMov5-1 and X90CrW18, and are used in the field of vehicle technology, which is of particular interest here, for example as components of valves, throttle devices or piston-cylinder assemblies in high-pressure applications. Background Art
[0003] According to the technical specification " According to the "Stahl-Nitrieren und Nitrocarburieren" (publisher: Stahl-Informations-Zentrum Düsseldorf, 2005 edition, ISSN 0175-2006), conventional gas nitriding of low-alloy and high-alloy steels of the type of interest here is carried out in multiple steps. First, a quenching process is carried out, then a number of tempering sequences are usually carried out at different temperatures and times, and then activation of the component surface is carried out as a separate process before the actual nitriding. In this case, several hours, days or even weeks may pass between the conditioning process consisting of quenching and tempering and the subsequent activation and (gas) nitriding process.
[0004] Low-alloy steels and high-alloy steels always have a natural oxide layer that is thin, a few nanometers, and which forms stably even at room temperature in normal air and / or at varying water vapor contents. This oxide layer consists of the oxygen-affinity alloying elements chromium, molybdenum, vanadium, silicon, aluminum and iron, as well as other oxidizable alloying elements of the steel.
[0005] As a result, these alloying elements are no longer dissolved in the crystal lattice and, as a thin oxide layer, completely impair the diffusion of atomic nitrogen at the subsequent nitriding temperatures in the range of 400 to 600° C. The result is an inhomogeneous connection layer and diffusion layer with undesirable different mechanical, electrical, magnetic and chemical functional properties. Usually, these thin oxide layers are removed chemically by pickling before the actual nitriding process, removed electrically by applying a voltage to decompose the oxide layer, or removed mechanically by surface processing, for example by brushing, grinding or polishing or the like. This processing intermediate step between conditioning and subsequent nitriding requires correspondingly high manufacturing and time costs. In addition, it is not possible to ensure that all surface areas have been processed accordingly.
[0006] During the entire heat treatment process, the core hardness of the component is adjusted by the tempering temperature in accordance with the functional requirements through at least one tempering step. In the framework of the tempering step of the metal heat treatment, the component is usually heated in a targeted manner in order to influence its properties and also reduce workpiece stresses.
[0007] The object of the present invention is to provide a method for the heat treatment of hardened chromium steel comprising tempering and gas nitriding, in which method the conventional tempering and activation are omitted and the core hardness of the component can be variably adjusted. Summary of the invention
[0008] This object is achieved by a method for heat treatment according to claim 1. The following dependent claims describe advantageous developments of the invention. The independent claim 10 defines the product resulting from the process of claim 1 as a specific vehicle component.
[0009] The invention includes the following teaching of process technology: the heat treatment of chromium steel, in particular high-alloy chromium x steel, by gas nitriding comprises the following process steps:
[0010] (A) A previously quenched component made of chrome steel is heated from ambient temperature T to U Heating to the material-specific pre-oxidation temperature T of the component V , for performing a pre-oxidation step;
[0011] (B) performing at least one tempering step with the addition of a nitriding process gas to the nitrogen atmosphere surrounding the component;
[0012] (C) The component is further heated to the material-specific tempering temperature T of the component. A and maintaining the tempering temperature preferably for at least one hour;
[0013] (D) Cooling the component to the material-specific nitriding temperature T of the component N for gas nitriding of components; and
[0014] (E) Cool the component further to ambient temperature T U superior.
[0015] The advantage of the solution according to the invention is in particular that the functionally important core hardness of the material can be freely adjusted independently of the nitriding temperature. This allows the method according to the invention to be used for a wider range of applications. The solution according to the invention enables the core hardness to be adjusted independently of the required nitriding temperature. This is because in the case of nitriding between 480-600° C., the core hardness is only between 620 HV1 and 460 HV1, corresponding to the nitriding temperature. An independent selection of the core hardness, for example 200-440 HV1, is not possible, because nitriding above the material-specific limits leads to a poorly functional microstructure.
[0016] Preferably, the preoxidation temperature of step (A) is selected in the range between 300 and 450° C., preferably in the range between 350 and 450° C. The range width results from the different material properties of the previously quenched steel components and depends to a certain extent on the alloying elements of the steel components. Experiments have shown that the mentioned preferred range with a higher lower range limit for the preoxidation temperature provides a higher energy efficiency, since the energy input for the subsequent further heating after the tempering step is reduced. In addition, the preoxidation temperature is used in accordance with the oxide that diffuses through to be formed. During heating, the nitrogen atmosphere prevents surface oxidation.
[0017] Preferably, the tempering of step (B) should be started directly after the end of the heating, that is, after the pre-oxidation temperature is reached, but at the latest when the component temperature is between 350 and 450° C. with the temperature distribution in the furnace as uniform as possible. The last-mentioned control parameters can be considered for simplified control of the temperature curve. The pre-oxidation can be carried out by synthetic air, atmospheric air or oxygen-containing gas. The start of the tempering step is preferably achieved by supplying a nitriding process gas after evacuation. As the nitriding process gas, an oxygen-friendly process gas, such as ammonia, an ammonia cracking gas mixture or the like, is suitable. The cracking gas is understood to be a gas mixture composed of gaseous nitrogen and hydrogen. It is not important during this tempering step whether the temperature remains constant or whether the temperature changes. However, starting from a critical process temperature of 450 to 550° C., the nitriding process gas can be removed by a vacuum process step, for example as an intermediate step B1, or by a flushing process with nitrogen.
[0018] After this tempering step, the component is further heated to the material-specific tempering temperature T A, preferably in nitrogen or, depending on the tempering temperature, also in ammonia or cracking gas, wherein the holding time is selected to be at least one hour, preferably 2 to 4 hours, more preferably 3+ / -0.5 hours. The duration of the holding time in turn depends on the type of chromium steel to be heat treated. In this case, process gas is also supplied, or pure nitrogen is supplied.
[0019] The heating of the component can preferably be carried out in a conventional chamber furnace with a corresponding gas exchange device. After the tempering step in step C, the component is cooled to the nitriding temperature T for gas nitriding. N After the material-specific cooling temperature has been reached, the nitrogen can be replaced by the nitriding process gas if necessary. After the nitriding temperature has been reached, the gas nitriding of the component is carried out in the conventional manner.
[0020] According to the above-described heat treatment method, vehicle components which are particularly subject to wear and vibrations can be produced from chrome steel, preferably high-alloy chrome x steel, in particular. These can be, for example, vehicle components such as nozzle bodies, valve blocks, valve plates, valve bodies, throttle plates, valve seats or pistons, which are mainly used in the high-pressure range of the fuel supply of vehicles. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The following is a detailed description of other measures to improve the present invention in conjunction with the description of the preferred embodiments of the present invention with reference to the accompanying drawings. The accompanying drawings show:
[0022] Figure 1 A flow chart of the method for heat treatment of chrome steel according to the invention, and
[0023] Figure 2 according to Figure 1 Graphic representation of the temperature-time curve of a heat treatment. DETAILED DESCRIPTION
[0024] according to Figure 1 The heat treatment of the quenched component made of chrome steel according to the invention comprises: firstly, in step A, heating the component from ambient temperature T to U Heated to a material specific pre-oxidation temperature T of approximately 350°C V The heating and the subsequent method steps are carried out in a conventional chamber furnace which is equipped with a gas exchange device.
[0025] After heating and preoxidation, in step B, a tempering frequency is started with the addition of a nitriding process gas, which in this embodiment is ammonia, for tempering the heated component. Once the critical process temperature has been reached, the ammonia is removed again according to an intermediate step B1. The further heating in step B1 is carried out until a material-specific tempering temperature T of more than 550° C. is reached. AIn this example, the tempering temperature is maintained for about 3 hours.
[0026] After the tempering in step C, the nitriding is carried out in such a way that in step D the component is cooled to the material-specific nitriding temperature of the component, so that the gas nitriding begins. Then, in step E the component is further cooled to the ambient temperature T U superior.
[0027] Figure 2 The temperature-time curve of the above method flow is explained. In the method flow, in the heating step A, the temperature of the heating element is increased from the ambient temperature T U Starting at any heating time t A The heating of the component is carried out in a nitrogen atmosphere. Then, in step B, after the pre-oxidation, a tempering step is started with the addition of process gas ammonia, wherein first the pre-oxidation temperature T of about 400° caused by the heating is brought to a temperature of 100 °C. V Remains constant. From the critical process temperature T of about 500°C k Initially, in an intermediate step B1, the process gas ammonia is removed again and cracking gas is introduced instead. Further heating in step C to the tempering temperature T A The tempering temperature is maintained in a nitrogen atmosphere for about 3 hours until time t K , until the tempering is completed. Then, in step D, the nitriding temperature T is cooled again in the presence of ammonia and cracking gas. N After the gas nitriding is completed, in step E, from time t N Start to execute the component to the ambient temperature T U Further cooling on.
[0028] The present invention is not limited to the above-mentioned preferred embodiments. In fact, variants of these embodiments can also be considered, which are included in the scope of protection of the subsequent claims. For example, it is also possible to omit the intermediate step B1. The specific temperature, especially the pre-oxidation temperature T V , tempering temperature T A And the nitriding temperature T N , depends on the specific composition of the chromium steel to be heat treated, especially its alloying elements.
Claims
1. A method for the heat treatment of chromium steel, in particular high-alloy chromium x steel, by gas nitriding, comprising the following process steps: (A) A previously quenched component made of chromium steel was heated from ambient temperature (T U ) is heated to the material-specific pre-oxidation temperature (T V ) for performing a pre-oxidation step; (B) performing at least one tempering step with the addition of a nitriding process gas to the nitrogen atmosphere surrounding the component; (C) further heating the component to a material-specific tempering temperature (T A ) and maintaining the tempering temperature for a duration; (D) Cooling the component to a material-specific nitriding temperature (T N ) for gas nitriding of the component; (E) further cooling the component to the ambient temperature (T U )superior.
2. The method according to claim 1, It is characterized in that The pre-oxidation temperature (T V ) is adjusted in the range between 300°C and 450°C, preferably in the range between 350°C and 450°C.
3. The method according to claim 1, It is characterized in that The tempering step in step (B) which is initiated directly after the heating is completed begins with reaching the pre-oxidation temperature, but at the latest with a component temperature of between 350° C. and 450° C.
4. The method according to claim 1, It is characterized in that The nitriding process gas is selected from the group of oxygen-philic process gases, the group comprising: ammonia, ammonia cracking gas mixture.
5. The method according to claim 1, It is characterized in that In step (B), the nitriding process gas is removed in an intermediate step (B1) or replaced by pure nitrogen starting from reaching a critical process temperature of 450° C. to 550° C.
6. The method according to claim 1, It is characterized in that In step (C), the component is further heated to a tempering temperature of between 550° C. and 700° C.
7. The method according to claim 1, It is characterized in that The holding time of the tempering temperature in step (C) is at least 1 hour, preferably between 2 and 4 hours, particularly preferably 3+ / -0.5 hours.
8. The method according to claim 1, It is characterized in that The component contains at least 2% chromium as an alloy metal.
9. The method according to claim 1, It is characterized in that The components are heated in a chamber furnace which has a gas exchange device.
10. A vehicle component made of a chrome steel, in particular a high-alloy chrome x steel, tempered according to the production method of any of the preceding claims.
11. The component according to claim 10, It is characterized in that The component is selected from the group of vehicle components subject to wear and vibration, the group comprising a nozzle body, a valve block, a valve plate, a valve body, a throttle plate, a valve seat, a piston.