EP3060692B1 - Method for producing a locally boronized or chromized component - Google Patents

Description

The invention relates to a method for producing a component from a low-alloyed steel material which is subjected to pressure and wear at least in a locally limited area.

The field of the invention extends to components of an injection system of an internal combustion engine.

State of the art

It is apparent from the well-known state of the art that components which are subjected to pressure and wear experience a bainitic or martensitic heat treatment to increase the high-pressure resistance. As a rule, the components are made of an alloyed material. The necessary geometric precision of these components is achieved by a machining hard machining, such as by grinding. If the set by the heat treatment material condition is not sufficient against wear, the surface of the components is coated to further increase the resistance to wear. In particular, nitriding, carbon and electroplated layers are suitable for this purpose. These layers are usually applied after a microstructural heat treatment. To improve the high pressure resistance, the toughness of the components is increased in the context of a further heat treatment. However, at the same time the hardness is reduced. The disadvantages of the prior art described above arise in particular due to the high temperatures during coating, which reduce the component strength in the base material. Due to the high temperatures namely the previously set by the heat treatment structure is changed. Due to the high-alloyed steel materials, the layer thickness produced is generally less than 25 μm. This is especially due to the limited diffusion of the coating atoms into the base material. Therefore, these thin layers do not provide sufficient protection under local load, such as particle impact. In the case of a soft basic structure, there are dents in the base material. Furthermore, the geometric precision must be prepared before the coating, since the layers are very thin and post-processing is therefore very difficult.

Disclosure of the invention

It is therefore an object of the present invention to provide a method for producing a component of an injection system of an internal combustion engine, whereby the component has areas with a relatively high hardness, wear and corrosion resistance as well as areas with a relatively high toughness and ductility.

The object is achieved on the basis of a method according to the preamble of claim 1 in conjunction with its characterizing features. Advantageous developments of the invention will become apparent from the following dependent claims.

According to the invention, the method comprises the following method steps. First, according to method step a), a machining of the component takes place in a non-heat-treated state. In particular, milling is suitable for cutting production or, in the case of rotationally symmetrical components, turning. As a result of which the component consists of a low-alloyed steel material which is not heat-treated and therefore in the soft state, the production is particularly gentle on tools and saves time.

In a further method step b), the component is locally covered with a powder having essentially either boron or chromium.

This is followed after process step c), the heat treatment of the locally covered with powder component. This leads to localized diffusion at the powder-covered areas, either boron atoms from the boron Diffusing powder or chromium atoms from the chromium-containing powder in the surface layer of the component diffuse. This is done at a first Temperature greater than the austenitizing temperature of the low alloy steel material. In other words, the component is either borated or chromated in a localized area. As a result, an iron boride or iron chromium layer is formed on the surface layer of the body.

Thereafter, according to method step d), the cooling of the component to room temperature and the removal of the powder from the surface of the body follows. Due to the powder properties and the coating process, the removal of the powder is particularly easy because it can be blown off, for example, with compressed air.

In accordance with process step e), a renewed heat treatment of the body takes place for the adjustment of either a martensitic or a bainitic structure at a second temperature, which is lower than the first temperature. The fact that the second temperature is lower than the first temperature, the generated boundary layer is not changed but only the basic structure. Particularly preferred is a bainitic structure is set, since this compared to the martensitic structure has a higher toughness and in the edge region, in other words both on the non-borated or chromed surfaces, as well as below the boron or chromium layer, compressive stresses.

Preferably, after process step e), a conversion treatment of the martensitic microstructure of at least one hour at a temperature of over 200 ° C is carried out. Furthermore, after process step e), preference is given to carrying out a conversion treatment of the bainitic structure of at least two to at most six hours at a temperature of at least 220 ° C. up to at most 260 ° C. The conversion treatment leads to a considerable increase in toughness.

According to a final process step, a fine machining of the component for the final shaping takes place. In particular, the grinding is suitable because the removal of very hard material is relatively low. The fine machining system precisely adjusts the geometry of the component and compensates for the distortion due to the heat treatment.

The first temperature is at least 890 ° C up to a maximum of 950 ° C. This temperature causes the boron atoms or the chromium atoms to diffuse into the surface layer of the body. The second temperature is temperature at least 840 ° C up to a maximum of 870 ° C. The temperature difference between the first and the second temperature causes the heat treatment has no influence on the borated or chromed edge layer of the component.

After process step f), surface refinement of the borated or chromated locally limited regions to increase the crack resistance is particularly preferably carried out. For surface refinement, mechanical polishing of the borated or chromed regions is particularly suitable.

According to a preferred embodiment, a valve body for an injection system of an internal combustion engine is machined in a first method step. According to a further preferred embodiment, a holding body for an injection system of an internal combustion engine is machined in a first method step.

In the case of the valve bodies, it is in particular the valve seats and, in the case of the holding bodies, in particular the guides which are exposed to high pressure and high wear and to a particle impact. The remaining areas of the valve body or the holding body are essentially exposed only to a compressive load, so that it is particularly advantageous here if stresses can be reduced by plastic deformation. In particular, areas with a ductile and tough structure are suitable for this purpose.

Furthermore, according to method step c), an iron boride or iron chromium layer having a layer thickness of at least 30 μm to at most 100 μm is preferably produced at the surface layer of the component. This layer, which is considerably thicker than the layer thickness of high-alloy steels, is caused by a low content of alloying elements of the low-alloyed steels. The boron atoms, when entering the surface layer of the body, essentially form Fe ₂ B iron boride with a hardness of 1500 to 2000HV. Preferably, 100Cr6 is used as the low-alloyed steel material.

Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

embodiments

Figur 1

eine vereinfachte schematische Schnittansicht eines Ventilkörpers, das die jeweiligen erfindungsgemäßen Verfahrensschritte durchläuft, und

Figur 2

ein nach dem Verfahren gemäß Figur 1 hergestellten Ventilkörper.

Show it:

FIG. 1

a simplified schematic sectional view of a valve body, which undergoes the respective process steps according to the invention, and

FIG. 2

a according to the method according to FIG. 1 manufactured valve body.

To FIG. 1 begins the inventive method with a first process step a, a machining production of a valve body 1 of the material 100Cr6 in a non-heat-treated state.

According to a method step b, the valve body 1 is covered locally with a powder 2 having essentially boron. The local coverage with powder is limited to the valve seat. 3

In a method step c, a heat treatment of the locally covered with the powder 2 valve body 1 at a first temperature of 910 ° C is made. This results in the localized diffusion of boron atoms from the powder 2 having boron into the surface layer of the valve body 1, in particular into the surface layer of the valve seat 3 to be borated. This results in an iron boride layer 5 with a layer thickness of up to 100 .mu.m at the surface layer of the valve body Valve seat 3 generated.

According to a next method step d, the valve body 1 is cooled to room temperature and the powder is removed.

After a method step e, the valve body 1 is heat treated again to adjust a bainitic structure 4. In this case, a second temperature is 840 ° C and is thus lower than the temperature required for boriding.

According to a process step f, a six hour conversion treatment is carried out at a temperature of 220 ° C to 260 ° C. This increases the toughness of the bainitic structure 4 to a greater degree than the hardness is lowered.

In a method step g, a fine machining is performed by grinding the valve body 1 for final shaping.

Finally, after process step h, a surface refinement of the locally delimited, borated regions is carried out. The surface refinement is produced by mechanical processing.

According to FIG. 2 For example, the valve body 1 produced by the method according to the invention has a tempered and thus tough bainitic base structure 4. The valve seat 3 of the valve body 1 is borated and has an iron boride layer 5 with a layer thickness of up to 100 μm. As a result, the valve body 1 has a first region, in the valve seat 3, with a high hardness, resistance to wear and corrosion as well as a second region with a relatively high toughness and ductility on the other hand.

The invention is not limited to the preferred embodiment described above. On the contrary, modifications are conceivable which are included in the scope of protection of the following claims. For example, it is also possible to produce other components instead of a valve body 1, in particular for an injection system of an internal combustion engine. It is also conceivable, for example, the production of a holding body. Furthermore, it is also conceivable to borate the components instead of chrome, to chromate. For this purpose, a chromium-containing powder is used which generates an iron chromium layer during the heat treatment of the component.

In addition, it should be noted that "encompassing" does not exclude other elements or steps, and "a" or "an" does not exclude a multitude. Further It should be understood that features or steps described with reference to any of the above embodiments may also be used in combination with other features or steps of other embodiments described above.

Claims (8)

1. Method for producing a component (1) of an injection system of an internal combustion engine of a low-alloy steel material that is exposed to pressure and wear at least in a localized region, comprising the following method steps:

   a) machining the component (1) in a state in which it has not been heat-treated, characterized by

   b) subsequently locally covering the component (1) with a powder (2) comprising essentially either boron or chromium,

   c) subsequently heat-treating the component (1) covered locally with powder (2) for the localized diffusion either of boron atoms from the boron-comprising powder (2) or of chromium atoms from the chromium-comprising powder (2) into the outer layer of the component (1) at a first temperature, which is greater than the austenitization temperature of the low-alloy steel material, the first temperature being at least 890°C to at most 950°C,

   d) subsequently cooling the component (1) to room temperature and removing the powder (2), and

   e) subsequently heat-treating the component (1) once again to set either a martensitic or a bainitic microstructure (4) at a second temperature, which is lower than the first temperature, the second temperature being at least 840°C to at most 870°C.
2. Method according to Claim 1, characterized in that, after method step e), a transformation treatment of the martensitic microstructure of at least one hour at a temperature of over 200°C is performed.
3. Method according to Claim 1, characterized in that, after method step e), a transformation treatment of the bainitic microstructure of at least two to at most six hours at a temperature of at least 220°C to at most 260°C is performed.
4. Method according to Claim 1, characterized in that, after method step e), to complete the method a precision machining of the component (1) for the final shaping is performed.
5. Method according to Claim 1, characterized in that, according to method step a), a valve body (1) for an injection system of an internal combustion engine is produced by machining.
6. Method according to Claim 1, characterized in that, according to method step a), a holding body (1) for an injection system of an internal combustion engine is produced by machining.
7. Method according to Claim 1, characterized in that, according to method step c), an iron-boride or iron-chromide layer (5) with a layer thickness of at least 30 µm to at most 100 µm is produced on the outer layer of the component (1).
8. Method according to Claim 1, characterized in that a 100Cr6 is used as the low-alloy steel material.

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