WO2017009044A1

WO2017009044A1 - Method for nitriding a component

Info

Publication number: WO2017009044A1
Application number: PCT/EP2016/065124
Authority: WO
Inventors: Lothar Foerster; Thomas Krug; Jochen Schwarzer; Marcus Hansel; Thomas Waldenmaier
Original assignee: Robert Bosch Gmbh
Priority date: 2015-07-13
Filing date: 2016-06-29
Publication date: 2017-01-19
Also published as: BR112017028323A2; EP3322833B1; CN107849678A; DE102015213068A1; EP3322833A1

Abstract

The invention relates to a method for nitriding a component (6) composed of a metal material (W) that contains iron as a base metal, wherein, in a first nitriding phase (D1), the component (6) is heated to at least 450 °C and a nitrogen-delivering process gas and/or process gas mixture (7) is provided at the surface (8) of the component such that nitrogen diffuses through the surface (8), wherein a compound layer (V) containing iron nitride is formed in the first nitriding phase (D1), wherein the compound layer (V) is dissolved by heat treatment in a first decomposition phase (E1).

Description

Description Title:

Process for nitriding a component

The present invention relates to a method for nitriding a component made of a metallic material.

State of the art

To increase the fatigue strength of metallic components, it is known to nitride them in near-surface areas. By nitriding arise

Inclusions that pre-stress the near-surface areas with a compressive residual stress profile and in this way protect against notching and vibration loads in particular.

In addition to these inclusions, nitriding inevitably produces a hard, but brittle bonding layer in the areas closest to the surface, with a significantly higher nitrogen content. This layer can flake off in particular at notch loads, which can lead to failure of the component as well as consequential damage caused by released particles. In order to reduce this problem, it is known from DE 102005049534 AI to subsequently remove the compound layer electrochemically. For more complex part geometries this is not always possible.

Therefore, DE 102009045878 A1 discloses to limit the thickness of the bonding layer to an optimum already during the nitriding process

Part surface still sufficiently passivated against corrosion, but avoids the weakening of the fatigue strength by the bonding layer. (M. Sumida, "Surface Hardening and Microstructural Features of Chromium-Molybdenum Steel via Two-Stage Gas Nitriding with a Short Isothermal Time in Stage One", Materials Transactions 53 (8), 1468-1474 (2012)) is a two-stage Process known in which by changing the

Nitrogen supply an initially thick compound layer can be subsequently reduced again. Another prior art is DE 102009002985 AI to call.

It has been found that in the case of components with complicated geometries, nitration with a reduced bonding layer thickness often does not bring about the desired effect. Instead of being permanently resistant to vibration, the components fail with a large dispersion of the number of sustainable cycles.

Task and solution

It is therefore the object of the invention to provide a method for nitriding

Is provided with the dispersion of the number of sustainable cycles at d failures is reduced.

This object is achieved by a method according to the main claim. Further advantageous embodiments will be apparent from the dependent claims.

Disclosure of the invention

Within the scope of the invention, a method for nitriding a component to a metallic material containing iron as a base metal has been developed.

The component is heated in a first Nitrierphase to at least 450 ° C, and it is on its surface a nitrogen-emitting process gas and / or

Submitted process gas mixture. As a result, nitrogen diffuses through the

Surface. In the first nitration phase, an iron nitride-containing

Connecting layer formed. According to the invention, the bonding layer is dissolved in a first degradation phase by heat treatment.

It was recognized that the nitration measures with reduced bond layer thickness as a disturbing side effect reduce the nitrogen supply during the entire nitration. For components with complex geometries, this results in nitration becoming more uneven.

Imperfectly nitrided areas in the component surface develop during operation to weak points at which the component preferably fails under repeated vibration load. Due to the formation of the bonding layer, first of all the disadvantage is accepted that it has a significantly lower vibration resistance. By the subsequent dissolution of the compound layer in the mining phase, this disadvantage disappears.

Advantageously, the metallic material contains at least one other

metallic element, and the nitrogen diffusing through the surface forms at least one special nitride with this further metallic element. The process then has the additional advantage that the formation of these special nitrides is made uniform.

The further metallic element may in particular be an alloying element of the metallic material. However, the invention expressly refers not only to higher alloyed materials, but also to low alloyed and unalloyed materials.

During the first nitriding phase, the duration of the first nitriding phase, the temperature of the component during the first nitriding phase and / or the supply of nitrogen on the surface of the component are advantageously selected such that the connecting layer has a thickness of at most 10 μm, preferably between 2 μm and 6 μηη, is formed. This range is preferred in the sense that the actual nitration is uniformed, but that no pore space is yet formed in the compound layer by the recombination of atomic to molecular nitrogen. These pores could not be removed by simply removing the iron nitride; they only could be removed by, for example mechanical or electrochemical, removal of the bonding layer.

In a particularly advantageous embodiment of the invention, a second nitration phase and a second degradation phase are connected to the first phase of degradation.

The parameters of the second nitriding phase do not have to match the parameters of the first nitriding phase. Likewise, the parameters of the second phase of dismantling do not have to match the parameters of the first stage of dismantling. Two (or more) nitration phases with intermediate decomposition phase have the advantage that overall a higher nitration depth can be achieved without being too thick at any time

Connecting layer is formed and thereby forms, for example, a pore space. The nitriding depth increases additively with each nitriding phase, while the thickness of the connecting layer always begins again at zero due to the preceding reduction phase.

By initially accepting the formation of a compound layer, higher temperature ranges are advantageously accessible for forming the special nitride. From the literature is known (for pure iron in the teacher diagram) that while maintaining the nitrogen supply tendency to form a

Bonding layer increases with increasing treatment temperature. The higher the temperature, the faster nitrogen diffuses to form the special nitride in the component surface. Advantageously, therefore, the component is heated to temperatures of up to 580 ° C for the formation of the special nitride. According to the prior art had to be worked at significantly lower temperatures, so as not to form a bonding layer

to promote disproportionately.

Experiments of the inventors have shown that already very thin

Compound layers of about 100-200 nm thickness, approximately below the

X-ray microscope or by means of energy-dispersive X-ray spectroscopy (EDX) are detectable, are correlated with early failures of the treated components. The connecting layer initially formed is therefore advantageously completely dissolved so that it is no longer recognizable at least in a light microscope. Advantageously, it is so completely dissolved that their phase shares by X-ray diffractometry (XRD) are no longer detectable. By observing the phase components, the dissolution can be observed in-situ.

For the ultimate vibration and notch strength of the component, it is only important that the bonding layer is completely dissolved. The general

Operation of the invention does not depend on how this is done in detail. In a particularly advantageous embodiment of the invention, the

Compound layer, however, dissolved by the concentration of atomic nitrogen and / or a nitrogen-emitting process gas is reduced and / or by the composition of a nitrogen donating

Process gas mixture is changed so that less nitrogen is offered for nitriding. This measure can be carried out, for example, for a batch of a variety of different components, which are in disordered form as bulk material in a treatment chamber, in one operation.

The nitrogen-emitting process gas may in particular be ammonia. It is also possible to use a mixture of, for example, ammonia with nitrogen and / or hydrogen. Then, by changing the

Mixture composition, the nitrogen supply for the nitration be changed without the pressure in the treatment chamber must be changed. However, the nitrogen supply at the component surface can also be reduced without changing the gas composition solely by further heating of the component and / or the gas or gas mixture: the higher the temperature, the faster ammonia dissociates at the component surface and the faster atomic nitrogen diffuses from the component surface path. If the gas composition is changed, then as an intermediate step, advantageously, the treatment chamber can be evacuated to the whole

Creating a treatment chamber defined conditions.

Advantageously, the component for dissolving the connecting layer to not more than 1000 ° C, preferably not more than 600 ° C, further heated. Above about 600 ° C is to be expected that the metallic material of the component is austenitic by the nitrogen introduced on its surface. This is not desirable in nitriding because the component warps, its core is too high annealed and / or its lattice structure could be changed at the edge. Furthermore, many nitriding are limited to operating temperatures up to 700 ° C; at higher temperatures, the service life of the furnace materials can be greatly reduced, which can cause more distortion. Niobium nitride and chromium nitride are examples of special nitrides, which are up to about 1000 ° C

are temperature resistant.

The inclusions from the special nitride, which are for the advantageous

Compressive stresses are metastable. Advantageously, therefore, the component temperature is kept below the temperature at which

Dissolve inclusions from the special nitride spontaneously. The compressive residual stresses then remain as it were in the structure of the component.

In particular, for dissolving the bonding layer, the supply of atomic nitrogen at the component surface can not only be reduced but completely reduced to zero, for example by evacuating the treatment chamber or by introducing only an inert gas, such as, for example, molecular nitrogen or argon, onto the component surface. However, there is a material-dependent optimum here: the combination of the concentration of the nitrogen and / or process gas or of the composition of the

Process gas mixture on the one hand and the component temperature on the other hand is in a particularly advantageous embodiment of the invention from a

Map area selected in which a diffusion of in the

Bonding layer bound nitrogen is driven from the surface of the component.

For nitrided pure iron as the simplest material system, the well-known teacher diagram exemplifies in which combinations of temperature, nitriding index and nitrogen supply an iron nitride layer forms or dissolves or whether the iron will transform into an austenitic structure.

Advantageously, the combination of the concentration of the nitrogen and / or process gas or of the composition of the process gas mixture on the one hand and the component temperature on the other hand selected from a map area in which the iron nitride of the connecting layer thermodynamically is unstable. The process that led to the formation of the compound layer then preferably proceeds backwards. In a further particularly advantageous

Embodiment is in this map area the Sonderitrid thermodynamically stable. It then remains in full.

In a further particularly advantageous embodiment, the combination of the concentration of nitrogen and / or process gas or from the composition of the process gas mixture on the one hand and the

On the other hand, the component temperature is selected from a characteristic field range in which the nitrogen, which is more strongly bound in the special nitrides, remains in the surface of the component. Then the decisive for the fatigue strength actual nitriding is fully retained, and it is only the

Compound layer regressed.

In a further advantageous embodiment of the invention, the

Part surface oxidized before at least one nitration phase and / or after at least one degradation phase in an additional oxidation phase. As a result, iron oxide is formed, whereby the nitriding effect is improved. However, since this also favors the formation of the bonding layer at the same time, the degradation phase provided according to the invention in this embodiment is particularly advantageous with respect to the vibration resistance.

The process gases or process gas mixtures can, for example

nitriding characteristic and / or oxidation index and / or

are supplied to the treatment chamber controlled by the coefficient of coal control. But you can also be supplied as a solid gas amount of the treatment chamber, for example. The general functioning of the invention does not depend on the fact that the process gases or process gas mixtures are supplied regulated in a certain way. By carbon number controlled feed, the component can be simultaneously nitrided and carburized. This changes the structure of the connection layer. Alternatively or in combination with this, the nitration effect can be increased by means of oxidation-parameter-controlled feed.

Furthermore, such a scheme is advantageous if the component consists of a highly alloyed with chromium steel. Advantageously, the process is carried out under atmospheric pressure. Then the treatment chamber does not have to be pressure-resistant. Advantageously, the method but also in low pressure, ie with a lower pressure than that

Atmospheric pressure, be performed. Already at a low

Pressure difference can be prevented, for example, escape process gases in case of a leak from the treatment chamber. In addition, the mean free path for diffusion at a lower pressure is greater.

For example, the method may also be performed under plasma nitriding conditions with or without active screen support. This will be the

Nitration accelerates overall. At any time, an oxygen and / or carbon emitting process gas or gas mixture may be added to effect nitrocarburization. The freedom of the finished component surface from a hard iron nitride-containing

Bonding layer has the side effect that tools with which this surface is subsequently machined mechanically, less quickly

wear out. To model the overall process, simulation models can be used that calculate the diffusion of nitrogen and the formation of the special nitrides as a function of time, temperature and material composition. Otherwise, the process parameters can be fine tuned in a known manner by making a series of coupons and inspecting metallographic cuts.

Whether a given component with the inventive method

has been heat treated, may show a denitration at the nitriding temperature. Compared to a component which, for example by a reduced supply of ammonia, nitriding bond layer-free from the outset, from a treated with the inventive method component less nitrogen

as the concentration of unbound nitrogen atoms in the

Iron matrix is already greatly reduced during nitriding by effusion and diffusion in the edge region. How much nitrogen is allowed to

for example, by weighing the component, by analyzing the Determination of the composition of the exhaust gas or by measuring the pressure increase in a temperature-controlled measuring chamber. In addition, the originally formed, later dissolved compound layer is detectable metallographically by a modified Anätzverhalten.

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

It shows:

Figure 1: Course of the temperature T over the time t in one embodiment of the method according to the invention.

FIG. 2: micrograph of a sample nitrated according to the prior art (a) and a sample (b) nitrided by the process according to the invention.

FIG. 3: GDOES depth profile analysis of the nitrogen concentration n over the edge distance d for the sample according to FIG. 2a (curve a) and the sample according to FIG. 2b (curve b).

Figure 4: Effect of nitration with bonding layer thicknesses of <1 μηη and 5 μηη on the fatigue strength.

Figure 5: Effect of nitration according to an embodiment of the invention on the fatigue strength.

Figure 1 shows an example of the process control for an embodiment of the method according to the invention. The continuous curve indicates the course of the temperature T over the time t. Along the time axis sections AI to F are defined in which different activities take place. In the heating phase AI, the component 6 is first brought from room temperature to a temperature of 420 ° C. The heating rate is constant. The treatment chamber in which the process is carried out is filled with an inert gas, such as nitrogen or argon, with an overpressure of 20 to 100 mbar above atmospheric pressure.

In the subsequent to the heating phase AI

Temperature equalization phase Bl, the treatment temperature is kept constant at about 420 ° C. During the heating phase AI and the temperature equalization phase Bl is thereby no oxygen-containing

Process gas or nitrogen donor gas 7 supplied.

The temperature equalization phase Bl is followed by a

Preoxidation phase C with an oxygen-containing process gas. For this purpose, the treatment chamber, for example, air, nitrous oxide, synthetic

Air or a nitrogen-steam mixture isobaric supplied.

After the pre-oxidation phase C, an inert gas such as nitrogen or argon is fed isobarically to the treatment chamber to exchange the gas atmosphere. This is followed by the heating phase A2 with a constant

Heating rate until a treatment temperature of about 540 ° C is reached. The heating phase A2 is followed by the second

Temperature equalization phase B2 on. In the subsequent nitriding phase Dl the treatment chamber is the

Exchange of the gas atmosphere isobar supplied with a nitrogen donor gas 7, for example, an ammonia-nitrogen mixture or an ammonia-nitrogen-hydrogen mixture. Due to a sufficiently high supply of ammonia, the metallic components 6 contained in the treatment chamber are nitrided, and a bonding layer V is formed.

In the subsequent degradation phase El, the nitrogen supply is lowered by the treatment chamber isobaric an ammonia-nitrogen mixture or an ammonia-nitrogen-hydrogen mixture with a lower

Ammonia content is supplied. As a result, the binding of nitrogen in the Compound layer V thermodynamically unstable. On the one hand, the nitrogen diffuses deeper into the component and forms special nitrides N. On the other hand, it also passes from the surface of the bonding layer into the atmosphere of the treatment chamber. The connection layer is dissolved. The surface area of the component loses its hard, brittle

Character.

In the subsequent second nitration phase D2, the nitrogen supply is increased again to the level of the nitration phase Dl. In the interior of the component, further Sonderitride form, while again forms a connecting layer in its surface next to the surface. This is completely degraded in the subsequent mining phase E2, in which the nitrogen supply is lowered back to the level of the first degradation phase El.

At the end of the second phase of degradation E2, an inert gas such as nitrogen or argon is supplied isobarically to the treatment chamber to exchange the gas atmosphere. As a result, the nitriding of the metallic components 6 is terminated. The treatment chamber and the metallic components 6 are then cooled to room temperature.

It goes without saying that in this way numerous methods for nitriding can be realized and the invention is not limited to the illustrated sequence and number of two heating phases AI, A2, two temperature equalization phases B1, B2 of a preoxidation phase C, two high-nitration phases

Nitrogen supply Dl, D2, two degradation phases with lower nitrogen supply El, E2 and a cooling phase F is limited.

The division into two nitration phases D 1 and D 2 with intermediate degradation phase E 1 has the advantage that the connection layer V does not reach a very great thickness, in which it forms pores P. These would not be removed in the degradation phase El.

FIG. 2 illustrates the comparison of a sample nitrided according to the prior art (FIG. 2 a) with a sample nitrided in accordance with the process procedure shown in FIG. 1 (FIG. 2 b) in a sectional drawing. The nitrogen donor gas 7 was in each case on the surface 8 of the component 6 from the metallic

Material W submitted.

In the production of the sample outlined in FIG. 2a, the degradation phases E1 and E2 had been omitted in comparison to the process control illustrated in FIG. As a result, an 8 μηη thick bonding layer V remained on the actual nitriding layer N, whose 4 μηη thicker upper region P was additionally penetrated by pores. The sample sketched in FIG. 2 b was made in accordance with FIG

Process management produced. The 8 μηη thick connecting layer was not about removed, but it was during the degradation phases El and E2 each incurred in the previous nitration Dl or D2 compound layer thickness of 4 μηη by removing the nitrogen from the iron nitride

Compound layer V regressed. The iron was always at his

Space. As a result, the normal structure is also in the area that is closest to the surface 8 of the component 6, continued without breakage. in the

In comparison with FIG. 2 a, the undesired pores P which extend in FIG. 2 a to a depth of approximately 4 μm are absent in the surface 8 of the component 6.

The re-formed connection layer V shows a stronger Anätzverhalten compared to a connection layer-free nitration from the outset and therefore appears darker on microscope images of metallographic cuts.

The material of the samples sketched in FIG. 2 is X40CrMoV5-l, which in addition to iron as the base metal contains the following further alloying elements in the following percentages by mass: carbon 0.39, silicon 1.10, manganese 0.4, chromium 5.20, molybdenum 1.40 , Vanadium 0.95.

FIG. 3 shows a GDOES depth profile analysis of the components 6 shown in FIG. 2. Curve a relates to the component 6 sketched in FIG. 2a. Curve b relates to the component 6 sketched in FIG. 2b. The nitrogen concentration n is plotted in mass percent M in each case % over the edge distance (depth) d in μηη. In curve a, the approximately 8 μηη thick compound layer is clearly too detect. According to curve b, in the case of the component 6 sketched in FIG. 2b, the entire surface 8 near its surface is nitrided very uniformly. With increasing depth d, the nitrogen concentration n in the component 6 according to FIG. 2a also converges to the nitrogen concentration n in the component 6 according to FIG. 2b.

FIG. 4 shows results of a durability test of notched, cylindrical components 6 (tensile specimens) with respect to the fatigue strength. All components 6 were remunerated. A part of the components 6 was not further heat-treated while the rest of the components 6 were nitrided. Before the zugschwellenden claim all components 6 were reworked in the clamping area. The notches were not reworked. Non-nitrided components 6, components 6 with an approximately 5 μm thick bonding layer V and components 6 with a bonding layer V thicker than 1 μm were tested.

The amplitude q of the voltages applied to the components 6 is plotted in N / mm ² over the number z of vibrations to which the components 6 were exposed. At each point, the type of symbol indicates whether component 6 passed the test (hollow symbol) or failed (filled symbol). With the different symbol shapes is indicated in each case, on soft sample, the measurements refer. A square lying on its edge indicates a measured value which was obtained on a non-nitrided component 6. A square standing on a point indicates a measuring point which has been recorded on a component 6 with 5 μηη thick bonding layer V. A circle indicates a measuring point which thickens on a component 6 with a diameter of less than 1 μm

Connecting layer was recovered. By the measuring points in each case a compensation curve (la, 2a, 3a) is set, indicating for which combinations of voltage amplitudes q and repetition numbers z each one

Default probability of 50% is expected. These compensation curves (1a, 2a, 3a) are respectively surrounded by dashed curves (1b, 2b, 3b) and (1c, 2c, 3c), which indicate for which combinations of voltage amplitudes q and number z of repetitions failure rates of 10% or 90% are expected. Curves denoted by the number 1 refer to components 5 nitrided with a 5 μm thick compound layer V. Curves denoted by the number 2 refer to non-nitrided components 6. Curves designated by the number 3 are referred to with a less than 1 μηη thick compound layer V nitrided components 6. The letter a denotes the respective

Compensation curve corresponding to 50% probability of failure. The letter b indicates the curve corresponding to 90% failure probability. The letter c indicates the curve corresponding to 10% failure probability.

The non-nitrided components 6 cut the worst from a failure probability of 50%. The components 6 with a less than 1 μηη thick compound layer V show the highest sustainable voltage amplitude based on a failure probability of 50%. However, the negative effects of the thin compound layer V in the scattering 1 / T _{N of} the repetition numbers z become clear: While non-nitrided components 6 have a dispersion of 1 / T _N = 2.72 and the components 6 have a thickness of 5 μηη

Compound layer V have a dispersion of 1 / T _N = 1.44, the scattering in the components 6 with a less than 1 μηη thick compound layer V with 1 / T _N = 16.2 is significantly higher. Remarkable are still differences in the

Eckschwingzahl, so the point on the axis of the repetition number z, where the compensation curve (la, 2a, 3a) for 50% probability of failure in a horizontal course kinkickt. While the Eckschwingzahlen the non-nitrided components 6 and the components 6 with a thickness of less than 1 μηη

Connection layer V are in a comparable range, is the

Eckschwingzahl the components 6 with a 5 μηη thick compound layer V clearly shifted to the left to a low value of about 5000 load changes. This shows that with nitride-thick compound layer V nitrided components

6 at this stress based on 50% probability of failure can be very early, but with little variance. The nitrided with a less than 1 μηη thick bonding layer V components 6 show in this

Stress based on 50% probability of failure comparable to the non-nitrided components 6 corner vibrating number, but the dispersion is massive elevated. Due to the increasing scattering 6 higher security surcharges must be taken into account in the design of the components, whereby the benefits of the heat treatment significantly relativized.

The material of the samples investigated in FIG. 4 is 50CrMo4, which, in addition to iron as the base metal, has the following further alloying elements in the following

Contains percentages by mass: carbon 0.50, chromium 1.05, molybdenum 0.23.

In Figure 5 are analogously with a method according to a

Embodiment of the invention nitrided components 6 (circles as symbols, curves designated by number 4) and other non-nitrided components 6 (squares as symbols, curves designated by number 5) compared. The inclination of the curves 4a, 4b and 4c in the time-strength range is comparable to the inclination of the curves 5a, 5b and 5c. Moreover, the curves 4a, 4b and 4c approach the curves 5a, 5b and 5c in the time-strength range. This can be spoken of a comparable time stability. The voltage amplitude is increased by about 24% based on a failure probability of 50%. The advantage of the method according to the invention manifests itself in particular in the fact that the scattering of the components 6 nitrided according to this method is similar in comparison with the non-nitrided components 6 and no early failures occur with small numbers z of load changes.

The material of the samples investigated in FIG. 5 is 8CrMol6, which, in addition to iron as the base metal, has the following further alloying elements in the following

Contains percentages by mass: carbon 0.09, chromium 3.90, molybdenum 0.50.

Claims

claims

1. A method for nitriding a component (6) of a metallic material (W) containing iron as a base metal, wherein the component (6) in a first nitration phase (Dl) heated to at least 450 ° C and at its

Surface (8) a nitrogen-emitting process gas and / or

Process gas mixture (7) is presented so that nitrogen diffuses through the surface (8), wherein in the first nitration (Dl) an iron nitride-containing compound layer (V) is formed,

characterized in that

the connecting layer (V) in a first phase of degradation (El)

Heat treatment is dissolved.

2. Method according to claim 1, characterized in that the metallic material (W) contains at least one further metallic element and that the nitrogen diffusing through the surface (8) forms at least one special nitride (N) with this further metallic element.

3. The method according to any one of claims 1 to 2, characterized

in that the duration of the first nitriding phase (D1), the temperature of the component (6) during the first nitriding phase (D1) and / or the supply of nitrogen on the surface (8) of the component during the first nitriding phase (D1) are so selected be that the connecting layer (V) with a thickness of at most 10 μηη, preferably with a thickness of 2 μηη to 6 μηη, is formed.

4. The method according to any one of claims 1 to 3, characterized

characterized in that at the first mining phase (El) a second

Connect the nitration phase (D2) and a second phase (E2).

5. The method according to any one of claims 1 to 4, characterized

in that the component (6) is heated to temperatures of up to 580 ° C to form the special nitride (N).

6. The method according to any one of claims 1 to 5, characterized

in that the connecting layer (V) is dissolved by reducing the concentration of atomic nitrogen and / or a nitrogen-emitting process gas (7) and / or changing the composition of a nitrogen-emitting process gas mixture (7).

7. The method according to any one of claims 1 to 6, characterized

characterized in that the component (6) for dissolving the connecting layer (V) is further heated.

8. The method according to claim 7, characterized in that the

Component (6) to not more than 1000 ° C, preferably to not more than 600 ° C, is further heated.

9. The method according to any one of claims 7 to 8, characterized

characterized in that the temperature of the component (6) below the

Temperature is kept at which the inclusions from the Sonderitrid (N) spontaneously dissolve.

10. The method according to any one of claims 6 to 9, characterized

in that the combination of the concentration of the nitrogen and / or process gas (7) or of the composition of the

Process gas mixture (7) on the one hand and the temperature of the component (6) on the other hand is selected from a map range in which a diffusion of bound in the connecting layer (V) nitrogen from the surface of the component (6) is driven.

11. The method according to any one of claims 6 to 10, characterized

Process gas mixture (7) on the one hand and the temperature of the component (6) on the other hand is selected from a map area in which the iron nitride of the bonding layer (V) is thermodynamically unstable.

12. The method according to any one of claims 10 to 11, characterized

Process gas mixture (7) on the one hand and the temperature of the component (6) on the other hand is selected from a map area in which the in

Special nitrides (N) more strongly bound nitrogen in the surface of the component (6) remains.

13. The method according to any one of claims 1 to 12, characterized

in that the surface (8) of the component (6) is oxidized before at least one nitration phase (D1, D2) and / or after at least one degradation phase (El, E2) in an additional oxidation phase (C).