WO2006018348A1 - Method for producing a temperature-resistant and anticorrosion fuel injector body - Google Patents

Abstract

The invention relates to a method for producing components for fuel injectors from a ferritic or martensitic, rust-resistant material. The inventive method comprises the following steps: first, once the component has been previously softened, it is subjected to a treatment in a N<sub

Description

Method for producing a temperature and corrosion resistant fuel injector body

Technical area

Fuel injector or nozzle body in fuel injection systems for self-igniting internal combustion engines are subjected to increasing thermal stress due to the ever-increasing power density. On the one hand, the pressure level with which fuel injectors in particular are subjected to fuel injectors increases continuously; on the other hand, owing to the restricted installation space, it is desirable to design fuel injectors so that they are installed in the most space-saving manner possible. the fuel injectors are getting smaller and smaller. In addition to the thermal stress is significant that the fuel injector are exposed to corrosion stress. The high thermal stress and the stress caused by corrosion phenomena of the fuel injector body result in failures, especially in the shaft region of the fuel injector body due to stress corrosion cracking.

State of the art

In currently formed fuel injectors for fuel injection systems for Verbren¬ nungskraftmaschinen, be it high-pressure accumulator injection systems (common rail), be it pump-nozzle units (PDE) or pump-line nozzle units (PLDE) wer¬ the injector or Nozzle body made of case-hardened 18CrNi8. This material can be used up to a temperature of 300 ° C. With a hitching temperature of 360 ° C, case-hardened X40CrMoV5-1 is used and at temperatures up to 450 ° C nitrided X40CrMoV5-1 is used.

The enumerated case-hardened materials have the disadvantage that they either are not or only slightly resistant to corrosion. The corrosion resistance, which is present only to a small extent, is further enhanced by the heat treatment, carburized carbide or chromium nitrite precipitate are further reduced. The heat treatment, however, is essential for producing a sufficient hardness of the material.

Presentation of the invention

According to the invention, an injector or nozzle body made of a corrosion-resistant steel, preferably a ferritic or martensitic, stainless steel having the composition C 0.06-0.4%, Cr 11-25% and Mo <1.5 % to manufacture. Furthermore, nickel, silicon and manganese can be contained up to 1.5%.

In the soft pre-machined state, a fuel injector or nozzle body is subjected to an embroidery treatment in a vacuum oven, the following treatment parameters being considerable:

The treatment temperature within the vacuum furnace is between 1000 ° C - 1150 ° C; The atmosphere prevailing inside the vacuum furnace is a nitrogen atmosphere with a pressure of between 0.1 and 2 bar, whereby the duration of the nitrogenizing process within the vacuum furnace may be between 0.5 and 8 hours. After the as-embossing treatment of the jet engine body, which is a virtually dimensionally accurate component which is merely to be reground for adjusting the exact dimensions of tolerances, the treatment temperature is set at between 1000 ° C. and 1150 ° C. to room temperature. Quenching is preferably carried out with nitrogen at a pressure of 2-10 bar. Preferably, the quenching of the injector or nozzle body should be done directly from the make-up atmosphere to provide denitration, i. a decrease in the nitrogen content in the edge region of the workpiece or workpiece blank to avoid.

The temperatures, the atmosphere and the duration of the sticking process within the vacuum furnace depend on the nitrogen profile to be achieved. Preferably, marginal nitrogen contents are adjusted between 0.3 and 0.6%, the depths of injection varying between 0.3 and 1.5 mm, depending on the load and size of the nozzle body. The Auf¬ embroidery depths depend to a considerable extent on the duration of the embroidery treatment within the vacuum furnace.

After embroidering, the workpiece is deep-frozen within a temperature range of -60 ° C. to -196 ° C. in order to convert the retained austenite. Thereafter, one or possibly several tempering treatments of the parts takes place at temperatures between 400 ° C - 550 ° C to reduce further retained austenite while maintaining a high toughness.

By the inventively proposed treatment of the injector or the nozzle body of a fuel injector, a significantly higher corrosion resistance of this component can be achieved. Compared with the production of temperature-resistant nozzle body by annealing and nitriding, can be due to the proposed method according to the invention as a result of shorter process times and less complex equipment a kosten¬ favorable alternative for the production of temperature-resistant nozzle body. Due to the material composition, a better machinability of the fuel injector body or nozzle body obtained can be achieved, in comparison to through-hardening stainless steels, which are characterized by high carbon or high nitrogen contents. Furthermore, in comparison to these steels, a higher mechanical strength of the workpiece treated as proposed according to the invention sets in, since as a result of a difference between the edge hardness and the core hardness of the fuel injector or nozzle body, residual stress of the drains builds up in their boundary layer ,

The core hardness of the workpieces subjected to an embossing treatment, as proposed according to the invention, depends on the carbon content of the base material. Since the core hardness is lower in comparison to the edge hardness after the pinch-off treatment and the subsequent Ab¬, the workpieces treated as proposed according to the invention have better toughness properties than through-hardening stainless steels that are carbon and nitrogen-alloyed. A further advantage is that the workpieces proposed as proposed according to the invention are distinguished by high resistance to cavitation.

drawing

Reference to the drawings, the invention will be described below in more detail.

It shows:

Figure 1 shows a hardness / depth profile of the material X6Cr17 at 1050 ° C, a treatment lungsdauer of 5 h, an N ₂ pressure of 1 bar, a freezing at -196 ° C and after an eight-hour tempering at 420 ° C and

FIG. 2 shows a micrograph of the material whose hardness / depth profile is shown in FIG. 1, with the treatment parameters mentioned therein (without tempering). variants

Following the method proposed according to the invention, an injector body or a nozzle body for a fuel injector or a nozzle holding body is produced from a ferritic or martensitic stainless steel of the following composition. The ferritic or martensitic stainless steel contains between 0.06 and 0.4% carbon, as well as chromium between 11 and 25%, and molybdenum with a content of <1.5%. Furthermore, nickel, silicon and manganese can contain up to 1.5% in the steel. An injector body or a nozzle body is produced from a ferritic or martensitic stainless steel of this type, which in the soft pre-processed state is subjected to an embroidery treatment within a vacuum furnace with the following treatment parameters:

The treatment temperature to which the injector body or the nozzle body of the fuel injector or a nozzle holding body is exposed is between 1000 ° C. and 1150 ° C. The atmosphere which prevails within the vacuum furnace and which is exposed to the nozzle body or the injector body for the duration of the treatment time contains nitrogen, at a pressure between 0.2 and 2 bar. The achievable Aufsticktiefen in the edge regions of the nozzle body or Injektorkörpers depend on the treatment time of the component, i. from the contact time of the prevailing in the vacuum furnace Stickstoffatmo¬ sphere on the component contained in the vacuum furnace. The treatment periods can be between 0.5 h and 8 h.

During the embroidery treatment of the injector or the nozzle body within the vacuum furnace, the surface of the injector or the nozzle body is exposed to the nitrogen atmosphere prevailing inside the vacuum furnace. The nitrogen thus diffuses into the surface of the nozzle body or injector body so that its edge region has an increased nitrogen concentration.

After the injector or nozzle body has been embossed within the vacuum furnace, the component is quenched from the treatment temperature, which is between 1000 ° C. and 1150 ° C., to room temperature, for which purpose preferably nitrogen is used under a pressure of between 2 and 10 bar , This quenching of the component contained in the vacuum furnace is preferably carried out directly in the supercharging atmosphere prevailing inside the vacuum furnace, ie in the presence of nitrogen, in order to avoid edge desorption of the edge areas of the injector body or the nozzle body previously subjected to an embossing treatment. Depending on which nitrogen profile is desired in the edge regions of the injector body or the nozzle body of a fuel injector or a nozzle holding combination, the temperatures, the atmosphere and the duration of the treatment of the Aufstick- process is selected It has proved to be advantageous if in Randbreich one Nozzle contents between 0.3% and 0.6% be set ein¬ nozzle body or an injector body. The depth, ie the Aufsticktiefen in the edge regions of the injector body or nozzle body, depending on the stress and size of the injector body and the nozzle body can be between 0.3 mm and 1.5 mm. The Aufsticktiefen until the depth of the workpiece relative to the nitrogen enrichment takes place, depend essentially on the stress of the component, ie of its thermal stress, of its mechanical stress by Drackbeaufschlagung and of its size.

After embroidering the injector or nozzle body within the vacuum furnace, the workpiece is frozen within a temperature range between -60 ° C to -196 ° C to convert the retained austenite. Thereafter, the workpieces at temperatures between 400 ° C to 550 ° C for several hours one or more ange¬ let.

The illustration according to FIG. 1 shows, as an exemplary embodiment, the hardness / depth profile of the materials X6Cr17, which has undergone an embroidery treatment at 1050 ° C. for a treatment time of 5 hours. The nitrogen atmosphere inside the vacuum furnace was under a pressure of 1 bar. After quenching the previously embroidered workpiece, deep-freezing took place at a temperature of -196 ° C. (curve 6), followed by tempering of the workpiece over a period of 8 hours at a tempering temperature of 420 ° C. (curve 7). Curve 6 shows the resulting hardness in the surface region of the workpiece toward the core during a Aufstickbehandlung and a subsequent deep freezing, while the curve 7 the self-adjusting hardness from the surface of the materials to the core after an embroidery treatment the deep freezing and a tempering at a temperature of 420 ° C over 8 h. The workpiece embroidered in accordance with this treatment parameter has an attachment depth 9 in an edge region 2, which can be divided into a first subregion 3 and into a second subregion 4. A third subregion 5 represents the core of the workpiece.

Within the first portion 3 of the edge portion 2, which may correspond to an insertion depth between 0 and 0.5 mm, for example, the hardness measured in Vickers hardness is 0.30, in a range of about 600 at a constant level. At the In the second subarea (see reference numeral 4 of the attachment depth 9), the holding of 600 HV falls to the core hardness. The second portion 4 extends in the edge region 2 of the component 1 between 0.5 mm and 1 mm; to the second portion 4, the portion 5 connects, which extends approximately from 1 mm to 1.5 mm in Richtimg on the core of the workpiece to be treated. Within the third portion 5, there is substantially a Vickers hardness (HV) of about 200, which remains substantially constant over the third portion 5, which corresponds to the core of the component 1.

The illustration according to FIG. 2 shows a microsection which corresponds to the heat treatment state of the workpiece shown in its hardness / capping profile in FIG.

The illustration according to FIG. 2 shows that a martensitic microstructure is present in the edge region 2 of the material 1, which leads to the high hardness shown in the edge region 10 of the component 1. In the area of hardening waste, apart from martensitic grains, there are also ferritic areas, which are shown in white in the illustration according to FIG.

By the method proposed according to the invention, a significantly higher corrosion resistance of injector body or nozzle body components can be achieved. The method proposed according to the invention represents a cost-effective alternative for the. Production of temperature-resistant nozzle or injector bodies in comparison to the hardening and nitriding of stainless steels. It has a much shorter process time and is also characterized by a less expensive system technology. The resulting workpieces, which have undergone the inventively proposed Stitch treatment and quenching and subsequent tempering, are characterized by better machinability compared to through-hardening stainless steels, which can be carbon and nitrogen alloyed. The materials obtained with the method proposed according to the invention have a higher mechanical resistance compared with the abovementioned steels, since due to the difference between the edge and the core hardness (compare curve according to FIG. 1) compressive stresses in the surface layer build up. Due to a lower core hardness in the range between 150 and 200 HV (hardness Vickers) lying and prevailing in the edge region hardness of about 600 to 700 HV (hardness Vickers), the workpieces we¬ considerably better toughness properties. The workpieces obtained are further characterized by a high resistance to cavitation and are relatively insensitive to collapse. menstruating, formed in the fluid vapor bubbles, which claim the materials me¬ mechanically significant, as soon as the fluid pressure drops below its vapor pressure.

LIST OF REFERENCE NUMBERS

1 core material injector / nozzle body

2 edge area 3 1st area (outside)

4 2nd subarea

5 3rd section (inside)

6 Workpiece treatment Embroidering and freezing

7 Workpiece treatment Embroidering, freezing and tempering 8 Hardness curve

9 stitching depth

10 micrographs

Claims

claims 1. Failure to produce fuel injector components from a ferritic or martensitic stainless material with the following steps: the component is subjected to a treatment in N ₂ atmosphere at a treatment temperature between 1000 ° C. and 1150 ° C. in the soft preprocessed state, the component is quenched from the treatment temperature to room temperature, - After quenching of the component to room temperature, a deep cooling of the component and - The component is started one or more times at medium tempering temperatures. 2. The method according to claim 1, characterized in that the ferritic or martensite, rust-resistant material has a carbon content between 0.06% and 0.4%, a chromium content between 11% and 25% and a molybdenum content of <1.5% having. 3. The method according to claim 2, characterized in that each NickeL silicon and / or manganese are included up to a proportion of 1.5%. 4. The method according to claim 1, characterized in that the treatment of the Bau¬ part in N ₂ atmosphere at an N ₂ pressure between 0.2 bar to 2 bar is performed. 5. The method according to claim 1, characterized in that the quenching of the component from the treatment temperature to room temperature with N ₂ at pressures zwi¬ rule 2 bar and 10 bar immediately after the treatment of the component with treatment temperature in N ₂ - atmosphere. 6. The method according to claims 1 to 5, characterized in that in components in the edge region (2) N ₂ contents between 0.3% and 0.6% and Aufsticktiefen (9) zwi¬ rule 0.3 mm and 1, 5 mm are generated. 7. The method according to claim 1, characterized in that the component is cooled after quenching to a temperature between -60 ° C and -196 ° C. 8. The method according to claim 1, characterized in that the treatment of Bau¬ part in N ₂ - atmosphere at treatment temperatures between 1000 ° C and 1150 ° C for a period between 0.5 h and 8 h is performed. 9. The method according to claim 1, characterized in that the tempering temperature between 400 ° C and 550 ° C is selected. 10. The method according to claim 9, characterized in that the component is started once or several times. 11. The method according to claim 1, characterized in that in the edge region (2) of the component within a first portion (3) a Vickers hardness (HV) is set between 800 and 600, with a difference to the third portion 5, the Core of the component corresponds, of at least 100 HV.