WO2015058932A1

WO2015058932A1 - Method for producing a locally boronized or chromized component

Info

Publication number: WO2015058932A1
Application number: PCT/EP2014/070881
Authority: WO
Inventors: Karl-Otto Englert
Original assignee: Robert Bosch Gmbh
Priority date: 2013-10-22
Filing date: 2014-09-30
Publication date: 2015-04-30
Also published as: EP3060692B1; DE102013221403A1; EP3060692A1

Abstract

The invention relates to a method for producing a component (1) which is made of a low-alloyed steel material and is exposed to pressure and wear at least in a locally limited region, said method comprising the following method steps: a) machining the component (1) in a state in which it has not been heat-treated, b) locally covering the component (1) with a powder (2) comprising essentially either boron or chromium, c) heat-treating the component (1) covered locally with powder (2) for the locally limited diffusion either of boron atoms from the boron-comprising powder or of chromium atoms from the chromium-comprising powder (2) into the marginal layer of the component (1) at a first temperature, which is greater than the austenitization temperature of the low-alloyed steel material, d) cooling the component (1) to room temperature and removing the powder (2), and e) heat-treating the component (1) again to set either a martensitic or a bainitic microstructure (4) at a second temperature, which is lower than the first temperature.

Description

description

Title:

Process for producing a locally borated or chromated component

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 primarily to components of a

Injection system of an internal combustion engine.

State of the art

From the well-known prior art it is apparent that components which are subjected to pressure and wear to increase the

High pressure resistance experienced a bainitic or martensitic heat treatment. 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 to stand against wear is not sufficient, the other

Increasing the resistance against wear the surface of the components coated. 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 increases the toughness of the components during 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 the coating, the

Reduce 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 usually less than 25μη "ΐ 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 the object of the present invention, a method for

To provide a component, 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. For machining, in particular, the milling or rotationally symmetrical

Components rotate. The fact that the component of a low-alloy steel material, which is not heat-treated and thus is in the soft state exists, the production is particularly gentle on tools and

time-saving.

In a further method step b), the component is provided with a

Substantially either boron or chromium-containing powder covered locally.

This is followed after process step c), the heat treatment of the locally covered with powder component. This results in localized diffusion at the powder-covered areas, with either boron atoms diffusing from the powder comprising the boron or chromium atoms diffusing from the chromium powder into the surface layer of the component. 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

educated.

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 preferably, a bainitic structure is set, since this compared to the martensitic structure a higher toughness and in the

Border area, in other words both to the non-bored or

chromed surfaces, and below the boron or chromium layer, residual 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

Finishing precisely adjusts the geometry of the component and compensates for the distortion due to the heat treatment. More preferably, the first temperature is at least 850 ° C up to the highest 950 ° C. This temperature causes the boron atoms or the chromium atoms to diffuse into the surface layer of the body. Further preferably, the second temperature is at least 840 ° C up to at most 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, in particular, the mechanical polishing of the borated or chromated is suitable

Areas.

According to a preferred embodiment is in a first

Process step, a valve body for an injection system a

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

machined.

In the valve bodies, it is in particular the valve seats and in the

Holding body in particular the guides that are exposed to high pressure and high wear and 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 with a layer thickness of at least 30 μm up to at most 2 μm is preferably produced at the surface layer of the component. This, compared to the layer thickness of high-alloy steels, significantly thicker layer is due to a low content of alloying elements of the low alloyed

Steels evoked. 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, 10006 is used as 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

Show it:

Figure 1 is a simplified schematic sectional view of a

Valve body, the respective invention

Goes through process steps, and

FIG. 2 shows a method produced according to the method according to FIG

Valve body.

According to FIG. 1, the method according to the invention begins with a first method step a, a machining of a valve body 1 made of the material 10006 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 locally limited 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 surface of the valve seat 3 to be bored. This results in an iron boride layer 5 having a layer thickness of up to Ι ΟΟμηη at the surface layer the 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 that required for boriding

Temperature.

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. Here is the

Surface finishing produced by mechanical processing.

According to FIG. 2, the valve body 1 produced by the process according to the invention has a tempered and thus tough bainitic basic structure 4. The valve seat 3 of the valve body 1 is borated and has a

Iron boride layer 5 with a layer thickness of up to Ι ΟΟμηη on. 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, instead of a valve body 1, other components, in particular for an injection system of a

Internal combustion engine to manufacture. 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 during the heat treatment of the component a

Iron chromium layer generated.

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

Embodiments can be used. Reference signs in the claims are not to be considered as limiting.

Claims

claims

1 . Method for producing a component (1) from a low-alloyed steel material which is subjected to pressure and wear at least in a locally limited area, comprising the following method steps:

a) machining production of the component (1) in a not

heat treated condition,

marked by:

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

c) heat treatment of locally with powder (2) covered component (1) for localized diffusion of either boron atoms from the boron-containing powder (2) or chromium atoms from the chromium-containing powder (2) in the surface layer of the component (1) at a first temperature greater than the austenitizing temperature of the low-alloyed steel material; d) cooling the component (1) to room temperature and removing the powder

(2), and

e) reheating the component (1) to set either a martensitic or a bainitic structure (4) at a second temperature lower than the first temperature.

2. The method according to claim 1,

characterized in that after process step e) a

Conversion treatment of the martensitic structure of at least one hour at a temperature of about 200 ° C is made.

3. The method according to claim 1,

characterized in that after process step e) a

Conversion treatment of the bainitic structure of at least two to a maximum of six hours at a temperature of at least 220 ° C up to at most 260 ° C is made.

4. The method according to claim 1, characterized in that after step e) to complete the process, a fine machining of the component (1) is carried out for the final shaping.

5. The method according to claim 1,

characterized in that the first temperature is at least 890 ° C up to at most 950 ° C.

6. The method according to claim 1,

characterized in that the second temperature is at least 840 ° C up to at most 870 ° C.

7. The 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 machined.

8. The 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 machined.

9. The method according to claim 1,

characterized in that according to method step c) a Eisenborid- or Eisenchromidschicht (5) is produced with a layer thickness of at least 30μηι up to at most Ι ΟΟμηη at the edge layer of the component (1).

10. The method according to claim 1,

characterized in that a 10006 is used as the low-alloyed steel material.