EP1612290A1 - Process and apparatus for gaseous nitriding of a workpiece and workpiece. - Google Patents

Abstract

Method for gas nitriding a surface of a workpiece in a process chamber comprises varying the reducing pressure of the reducing gas in the chamber during the reducing phase according to a prescribed pressure scheme. Independent claims are also included for the following: (1) Gas nitriding device for carrying out the above method; and (2) Workpiece having a surface layer produced by the above method.

Description

The invention relates to a method for gas nitriding a surface of a workpiece, a gas nitriding apparatus for gas nitriding the workpiece according to a method according to the invention, and a workpiece having an upper surface layer comprising a diffusion layer with a hard layer according to the preamble of the independent claim of the respective category.

Processes and devices for gas nitriding of workpieces, for example by means of ammonia gas (NH ₃ ), are well known in the prior art in many variants.

The known methods, which serve primarily for tempering and hardening of the surfaces of the workpieces, raise particular disadvantages for specific applications, which are ultimately due to the manner of film formation during the various process steps in gas nitriding.

For example, it is well known to prepare the surfaces of the workpieces in a reducing step in which the surface is treated with a reducing gas for the actual nitriding process by continuously purging the process chamber in which the workpiece is treated with ammonia gas during the reducing step becomes. Although this gives you the advantage that constantly fresh ammonia is available, however, the concentration of hydrogen gas that is produced from the ammonia in a chemical reaction is reduced, so that too little hydrogen is available for reducing the surface area. In addition, a constant gas exchange creates turbulence and inhomogeneities in the gas atmosphere of the process chamber, which can adversely affect the reduction of the surface and the so-called "nitriding" of the material surface.

If, on the other hand, the ammonia is not exchanged during the reduction phase, on the one hand hydrogen accumulates in certain regions of the process chamber, so that there is no sufficient homogeneous mixing of the gases, which in turn reduces the surface area, ie, ridding the surface of oxides , such as of iron oxides, chromium oxides or the like adversely affected.

The consequence of insufficiently or unevenly reduced surfaces and insufficiently or unevenly nitrided surfaces leads in the subsequent actual nitriding process to the fact that the forming diffusion layers are less uniform and certain inhomogeneities in the formation and thus in the structural structure of the layer are the result. This leads inter alia to the fact that the resulting surface layers of the workpieces have correspondingly inferior properties, so that the layers in particular do not show the necessary hardness and wear resistance, resulting in particular under special loads, such as dynamic stresses for rapid wear or premature fatigue.

The object of the invention is therefore to provide a method and an apparatus for gas nitriding a workpiece, which allows a To treat the workpiece so that the workpiece receives a surface of the highest quality, which has in particular in terms of hardness and wear resistance significantly improved properties.

The objects of the invention which solve these objects in terms of process and apparatus are characterized by the features of the independent claim of the respective category.

The respective dependent claims relate to particularly advantageous embodiments of the invention.

The invention thus relates to a method for gas nitriding a surface of a workpiece in a process chamber with gas supply means for supplying fluids, in particular gases into the process chamber, which method comprises the following method steps: introducing the workpiece into the process chamber and supplying a process gas into the process chamber Generation of a gas atmosphere. Heating the workpiece in the gas atmosphere during a heating phase to a predetermined equilibrium temperature and holding the workpiece during an equilibrium phase at the equilibrium temperature. Further increasing the temperature in the process chamber during a Reduzierphase to a predetermined process temperature, wherein the process chamber during the Reduzierphase a reducing gas is supplied under a predetermined reducing pressure, and then in an activation phase of the process chamber, an activation gas is supplied. In this case, a predetermined activation pressure is set in the process chamber and activates the workpiece during a predetermined activation period at an activation temperature. Thereafter, the workpiece is gas nitrided in a nitriding phase in a nitriding gas atmosphere with a nitriding gas at a given nitriding pressure to form a diffusion layer, and the workpiece is hardened after gas nitriding in a hardening phase to produce a hard surface layer at a predetermined hardening pressure, the temperature during the Hardening phase is varied according to a predetermined temperature scheme and the workpiece is cooled after the hardening phase during a cooling phase to a final temperature. The reducing pressure of the reducing gas in the process chamber is thereby varied during the Reduzierphase according to a predetermined pressure scheme.

It is essential that during the Reduzierphase the Reduzierdruck of the reducing gas is varied in the process chamber according to a predetermined pressure scheme, which is referred to as "pressure pulses" in the context of this application. In this case, during the reduction phase, the reduction pressure is varied, for example, alternately between a predetermined minimum reduction pressure and a maximum reduction pressure. For example, the pressure of the reducing gas with long pulse periods of the order of a few minutes, for example with a pulse period of 10 minutes, in particular with a pulse period between 3 minutes and 5 minutes, is periodically alternately alternated between a higher pressure and a lower pressure, the higher one Pressure still prefers well below atmospheric pressure, eg at about 300 millibar (mbar) to 700 millibar, more specifically between 400mbar and 500mbar, and preferably at about 450mbar. The lower pressure may, for example, be less than 300 mbar, in particular between 1 mbar and 100 mbar, and preferably about 50 mbar. By means of the pressure pulses according to the invention in the reduction phase, it can be achieved that the reducing action of a reducing gas is increased during the reduction phase. If the process chamber is charged with ammonia (NH ₃ ) in the reduction phase, for example, hydrogen (H, H ₂ ) can be formed from the ammonia, which as a reducing gas can have a reducing effect on the surface of the workpiece. The fact that the pressure of the gases is alternately increased and decreased in the process chamber, the formation of the reducing gas, for example, hydrogen from ammonia, significantly favored, so that the reducing effect during the Reduzierphase is significantly improved. It has been shown on the one hand that the reducing effect on the workpiece is additionally catalyzed by the presence of ammonia and on the other hand by the presence of ammonia during the Reduction phase already uses a nitriding of the surface, which is referred to in the context of this application as "nitriding".

The inventive method thus ensures that in the reduction phase by the pressure pulses always an optimal supply or an optimal mixture of reducing gas and nitriding gas, ie, for. of hydrogen and ammonia, is achieved in the process chamber, so that on the one hand, an optimal reduction of the surface of the workpiece takes place and on the other hand, a very uniform An-nitriding the surface of the workpiece is already achieved in the Reduzierphase. By using preferably very long pulse periods for the pressure pulses, e.g. Pulse periods of 10min, it is achieved that disturbing turbulence of the gases are largely avoided in the process chamber with good mixing of the gases, which favors an optimal and uniform process management in addition, especially but not only, the process of nitriding An.

By the above-described significant improvement of the reduction of the workpiece on the one hand and the optimization of the process of nitriding on the other hand during the Reduzierphase, the subsequent operations of gas nitriding are significantly influenced positively with hardening, that is, in particular in the nitration, in which in per se known As a result of diffusion, a diffusion layer is formed in the surface of the workpiece, the formation of the diffusion layer is significantly positively influenced. This means in particular that the diffusion layer has a much higher homogeneity than the diffusion layers known from the prior art, as a result of which, inter alia, the hardness of the surface of the workpiece is drastically increased. For example, By using the method according to the invention, the hardness (HRC) of the surface of workpieces made of X40CrMoV51 (1.2344 steel) can be easily increased to values of 1200 HCR and higher.

In a preferred embodiment of the method according to the invention, the nitriding pressure of the nitriding gas in the process chamber is also varied during the nitriding phase according to a predetermined pressure scheme.

In this case, the nitriding pressure is varied alternately between a predetermined minimum nitriding pressure and a maximum nitriding pressure during the nitriding phase.

This leads to a further improvement of the properties of workpieces which are treated according to the inventive method. It is thereby achieved that the diffusion layers have virtually no bonding layer, because in the nitration phase at relatively low pressures is also pressure pulsed, with the result that substantially no compound layer is formed on the outer edge of the diffusion layer. This means that e.g. in the treatment to high nitration depths (long treatment times), the connection layer growth is suppressed.

In this case, the pressure pulses may take place in analogy to the pressure pulses in the reducing phase, preferably in the rough vacuum between a higher pressure and a lower pressure, the higher pressure being e.g. at about 300 millibar (mbar) to 700 millibars, in particular between 400mbar and 500mbar, and preferably at about 450mbar. The lower pressure may e.g. be less than 300mbar, in particular between about 1 mbar and 100mbar and preferably be about 50mbar. Advantageously, e.g. the pressure of the nitriding gas with long pulse periods of the order of a few minutes, for example with a pulse period of 10 minutes, in particular with a pulse period between 3min and 5min varies periodically alternately between the higher pressure and the lower pressure.

In a specific exemplary embodiment of the method according to the invention, an oxidizing gas, preferably oxygen, is fed into the process chamber during the equilibrium phase in a manner known per se for the purpose of preparing the surface for the subsequent method steps for targeted pre-oxidation of the surface of the workpiece.

As already mentioned, especially hydrogen and / or ammonia are used as reducing gases, both as activating gas in the Activation phase as well as nitriding gas in the nitration phase, ammonia is advantageously used.

In a further embodiment, during the Reduzierphase and / or during the activation phase, the reducing gas and / or the activation gas further comprises an additional gas, preferably CO ₂ or N ₂ O. It is understood that the aforementioned gases used advantageously during the various process steps can be understood only as an example. That is, the list of usable fluids in the context of the inventive method is by no means exhaustive. Rather, all fluids, in addition to all suitable gases may include liquids such as water, which are known in the art for performing the method steps, are used.

In a further embodiment of the method according to the invention, a gas is ionized by means of an ionizing agent, preferably in the reducing phase and / or in the nitration phase. The ionization of one or more gases present in the process chamber can be achieved, for example, by providing in the process chamber a suitable electrode assembly which is connected to an electrical energy source which is connected between the electrodes e.g. generates a pulsed direct or alternating voltage, which, inter alia, alternately values between 100V and 1000V, preferably values between 350V and 600V can take. The pulsed electrical voltage can have frequencies between a few hertz (Hz) and 30 kHz, in particular between 500 Hz and 20 kHz, preferably between 1 kHz and 15 kHz.

Preferably, but not exclusively, an ionization of the gases is carried out in the reduction phase and / or in the nitration phase. In particular, while hydrogen, nitrogen, carbon dioxide (CO ₂ ), or methane (CH ₄ ), methane, especially in the nitration phase, ionized.

The ionization of the gases in the Reduzierphase causes an improvement in the Reduzierprozesse, while in the nitration phase above all it is possible to nitride the workpiece only on selected surfaces, which are directly accessible to the plasma, ie the ionized particles of the gases, while the area of the surface of the workpiece covered by suitable measures is substantially not nitrided.

It goes without saying that all of the method steps described above can also be used advantageously in all possible combinations, and the exemplary embodiments described above are to be understood merely as examples.

Furthermore, the invention relates to a gas nitriding apparatus for gas nitriding a workpiece according to one of the above-described gas nitriding methods according to the invention. The erfindungsgemässe gas nitriding apparatus comprises a process chamber for receiving the workpiece, and gas supply means for supplying the process chamber with gases and a gas exhaust means for withdrawing the gases from the process chamber, wherein for generating a negative pressure in the process chamber, the gas exhaust means comprises a shut-off device. In this case, a pressure control device with a gas extraction device and gas flow control devices are provided so that a gas pressure and / or a mixing ratio of gases in the process chamber can be varied according to a predefinable pressure scheme.

In a preferred embodiment of the gas nitriding device according to the invention, a control unit is provided for controlling and / or regulating the gas pressure in the process chamber.

In addition, a measuring device may be provided for detecting and controlling and / or regulating the gas pressure and / or a gas temperature and / or the composition of gases in the process chamber.

In a further embodiment, the gas nitriding device comprises an ionization agent, which preferably has a plasma generator, for the ionization of a gas located in the process chamber.

It goes without saying that form all combinations of the aforementioned embodiments further advantageous embodiments of a novel gas nitriding device.

A workpiece produced by a gas nitriding method according to the invention has a surface layer comprising a diffusion layer with a hard layer.

In this case, in a particular embodiment, the workpiece on the hard layer having an additional outer end layer, which is preferably applied by means of a PVD method, CVD method, or an arc evaporation method or a thermal spraying method.

The invention will be explained in more detail with reference to the drawing.

Fig. 1

ein Zeit-Temperatur Schema eines erfindunggemässen Verfahrens;

Fig. 2

ein Ausführungsbeispiel einer erfindungsgemässen Gasnitriervorrichtung;

Fig. 3

ein Ausführungsbeispiel gemäss Fig. 2 mit lonsisierungsmittel;

Fig. 4

ein erfindungsgemässes Werkstück.

Show it:

Fig. 1

a time-temperature diagram of a method according to the invention;

Fig. 2

an embodiment of a gas nitriding device according to the invention;

Fig. 3

an embodiment according to FIG. 2 with lonsisierungsmittel;

Fig. 4

a workpiece according to the invention.

1 shows a schematic representation of a time t temperature T schema of a method according to the invention. After a workpiece 2 has been introduced into a process chamber 3, is used to produce a Gas atmosphere, a process gas 4, in the present example nitrogen (N ₂ ), introduced into the process chamber 3. Then, the process chamber 3 is heated, so that the process gas 4 and the workpiece 2 is heated to a predetermined equilibrium temperature GT under a predetermined gas pressure. The workpiece 2 is then held during an equilibrium phase G substantially at the equilibrium temperature GT, which may for example be between 200 ° C and 600 ° C, preferably in the vicinity of 350 ° C, held for a predetermined period of time t. Subsequently, the temperature T is increased in the process chamber 3 during a Reduzierphase R to a predetermined process temperature PT, the process chamber 3 during the Reduzierphase R a reducing gas 5 at a predetermined Reduzierdruck RP, which is pressure-cycled as described in detail above. Depending on the workpiece and other requirements, the process temperature PT can be between 300 ° C and 1000 ° C, for example; Preferably, the process temperature PT is about 600 ° C.

Subsequently, in an activation phase AK of the process chamber 3, an activation gas 6 is supplied, so that a predetermined activation pressure AP is set, which is preferably but not necessarily at normal pressure, so for example. is about 1000mbar. During the activation phase AK, the workpiece 2 is activated in a manner known per se during a predetermined activation period at an activation temperature AT. The activation temperature AT may be substantially the same as the process temperature PT as in the present example; However, it can also deviate significantly up or down from it.

Subsequently, the workpiece 2 in a Nitrierphase N at a nitriding temperature NT, which may be here as for example the activation temperature AT and / or the process temperature PT, in a Nitriergasatmosphäre, as the nitriding gas such as ammonia (NH ₃ ), methane (CH ₄ ), Hydrogen (H, H ₂ ), nitrogen (N, N ₂ ), and all other suitable Nitriding gases and / or additional gases, which have already been mentioned in part above, gas nitrided at a given nitriding pressure NP to produce a diffusion layer 200. Preferably, but not necessarily, the method is carried out pressure pulsed as described above. The higher pressure during the pressure pulses is well below the normal pressure of about 1000mbar. As a result, it is achieved that the diffusion layer 200 has no bonding layer, which is why in this case the process can also be referred to as "bonding layer free nitriding". If, in contrast, a significantly higher nitriding pressure NP is selected in the nitration phase N. For example, a nitriding pressure NP of about 1000mbar, creating a bonding layer that has some negative properties that are extremely disturbing for many applications. Thus, the bonding layer is relatively brittle, so that it tends to cracking or chipping, especially in dynamic loads of the workpiece 2, for example, when the workpiece 2 is a coil spring 2 or a leaf spring 2. In addition, it is difficult, as will be described later, a hard layer 201 sufficient hardness produced and difficult to an additional outer terminating layer 202 are applied.

Subsequent to the nitriding phase N, the workpiece 2 is hardened in a hardening phase H to produce a surface layer 201 at a predetermined hardening pressure HP, the temperature T being varied during the hardening phase H according to a predetermined pattern. That is, in the present specific embodiment, the temperature T is initially maintained at a substantially constant value for a certain period of time t. In this particular example, the temperature T in the first part of the hardening phase H equal to the process temperature PT or equal to the activation and nitriding temperature AT, NT was chosen constant. Of course, it is possible that the temperature T in this part of the hardening phase H also higher or lower at a constant value is selectable, or the temperature profile is also varied in a first phase according to any suitable temperature scheme.

In the example shown in FIG. 1, the temperature T is thus initially substantially constant during a first part of the hardening phase H and is then lowered to a lower temperature T, wherein the temperature reduction does not have to be linear with time t, but rather a specific scheme can follow, or in between even rise again.

The hardening pressure HP is preferably chosen in the vicinity of normal pressure, ie at about 1000 mbar, but depending on the workpiece 2 and other requirements may also deviate more or less strongly to higher or lower pressures.

Finally, after the hardening phase H during a cooling phase K, the workpiece 2 is heated to an end temperature ET, which is e.g. may correspond to room temperature, cooled.

FIG. 2 schematically shows an exemplary embodiment of a gas nitriding device according to the invention for carrying out the gas nitriding process described in detail above by way of example.

The gas nitriding device comprises a process chamber 3 for receiving a workpiece 2, and gas supply means 9, 91 for supplying the process chamber 3 with gases. The process chamber _{3 can be} supplied with ammonia (NH ₃ ) via the gas supply means 9, here configured as a gas supply line 9.

Via the gas supply means 91 of the process chamber further gases, such as process gases, additional gases and all other in the context of this application etähnten fluids and gases are supplied, wherein the supply the various gases separated by the gas control devices 122 controllable and / or adjustable sit.

The gas control devices 121, 122, which in the present case preferably comprise an electrically controllable and / or controllable valve, make it possible to suitably control the inflow of ammonia and all other gases into the process chamber 3.

Furthermore, the gas control device comprises a pump, e.g. a vacuum pump 120 with which the process chamber 3 can be evacuated to a predeterminable pressure.

In addition, a gas extraction means 10 is provided, so that the process chamber 3 gases can be withdrawn, which can be flared in the gas vent 10, if the gases are combustible. The gas removal means 10 has a shut-off device 11, which is configured, for example, but not necessarily, as an electrically controllable and / or controllable valve 11, so that the withdrawal of gases from the process chamber can be controlled.

As a result of the previously described means for supplying and removing gases from the process chamber 3, virtually any desired value of a gas pressure in the process chamber 3 can be set. So from the fine vacuum, i. Press the much smaller than e.g. are 1 mbar, up to gas pressures that are well above normal pressure, ie above 1000mbar.

In addition, and in particular, the pressure pulses described in detail above can be carried out in the process chamber 3. For this purpose, the shut-off device 11 is closed in the operating state and by suitable control and / or regulation of the pump 120 and the gas control devices 121, 122, the pressure pulses can be controlled as desired.

For controlling and / or regulating all physical and chemical processes, in particular for controlling and / or regulating the gas pressure in the process chamber 3, as shown in FIG. 2, a control unit 123 may be provided which, for example, comprises a data processing system and thus all processes , including data acquisition by means of suitable sensors, coordinated. In the present example a measuring device 131, e.g. a vacuum gauge 131 is provided, which among other things allows the measurement of the gas pressure or the measurement of the hydrogen content or other gases in the process chamber 3. In addition, at least one thermocouple 130 is provided with which the temperature T in the process chamber 3 can be determined.

It goes without saying that additional measuring devices 130, 131 can additionally be provided for recording important process data and the acquisition of all data in one or more control units 123 can be coordinated and further processed for process control.

Further important features of the gas nitriding device according to the invention, such as the furnace heater 15 or the ventilation device 16, which serves to circulate the gases in the process chamber, are inherently from AT 408 994 B known and therefore need not be explained in detail here.

In Fig. 3, an embodiment according to FIG. 2 with lonsisierungsmittel 13 is shown in a schematic drawing. For reasons of clarity, the process chamber 3 is shown only hinted. In the present embodiment, the workpiece 3 is arranged on a cathode plate 14, wherein the cathode plate 14 is electrically connected in a known manner with a plasma generator 17. The process chamber itself is also electrically connected to the plasma generator 17 and forms the anode in the present arrangement. This is between process chamber 3 and workpiece 2 or cathode plate 14 an electrical ionisierungsspannung applied, so that the gas located in the process chamber is ionizable to a predetermined part and in a predeterminable manner. Of course, the ionization means 13 can be controlled by the control unit.

Finally, FIG. 4 shows a workpiece 2 according to the invention. The workpiece 2 has a surface layer comprising a diffusion layer 200 with a hard layer 201, which was produced by the method according to the invention described above in a gas nitriding device according to the invention. In this case, the diffusion layer 200 connection layer is free, so it has essentially no connection layer.

The workpiece 2 itself is preferably a dynamically loaded workpiece 2, such as e.g. a spring 2.

In addition, the workpiece 2, which is produced by a method according to the invention without a connecting layer, as shown in FIG. 4, can be provided with an additional finishing layer 202 in a particularly advantageous manner. The additional termination layer 202 is e.g. by a PVD method, e.g. by sputtering, a CVD method, an arc evaporation method or a thermal spraying method. All of the aforementioned methods for applying the additional capping layer 202 are well known, so that explanation at this point can be omitted.

Since the diffusion layer connecting layer is free, the additional finishing layer shows particularly good adhesive properties on the diffusion layer, so that in particular the hardness of the surface of the inventive treated workpiece, but also the wear resistance and thus Related properties are significantly improved compared to the prior art.

Claims (16)

Process for gas nitriding a surface of a workpiece (2) in a process chamber (3) with gas supply means (31) for supplying fluids, in particular gases into the process chamber (3), which method comprises the following method steps: - Introducing the workpiece (2) in the process chamber (3) and supplying a process gas (4) in the process chamber (3) for generating a gas atmosphere; - Heating the workpiece (2) in the gas atmosphere during a heating phase (A) to a predetermined equilibrium temperature (GT); - Holding the workpiece (2) during an equilibrium phase (G) at the equilibrium temperature (GT); - Increasing the temperature (T) in the process chamber (3) during a Reduzierphase (R) to a predetermined process temperature (PT), wherein the process chamber (3) during the Reduzierphase (R) a reducing gas (5) under a predetermined reducing pressure (RP ) is supplied, - And then in an activation phase (AK) of the process chamber (3) an activation gas (6) is supplied, in the process chamber (3) a predetermined activation pressure (AP) is set and the workpiece (2) during a predetermined activation period at an activation temperature ( AT) is activated, - And then the workpiece (2) in a Nitrierphase (N) in a Nitriergasatmosphäre with a nitriding gas (7) at a given nitriding pressure (NP) to produce a diffusion layer (200) is gas-nitrided, - And the workpiece (2) after the gas nitriding in a hardening phase (H) for producing a hard surface layer (201) at a given curing pressure (HP) is hardened, wherein the temperature T is varied during the hardening phase (H) according to a predetermined temperature scheme, and - The workpiece (2) after the hardening phase (H) during a cooling phase (K) is cooled to an end temperature (ET)
characterized in that the reducing pressure (RP) of the reducing gas (5) in the process chamber (3) during the Reduzierphase (R) is varied according to a predetermined pressure scheme. A method according to claim 1, wherein the nitriding pressure (NP) of the nitriding gas (7) in the process chamber (3) during the nitriding phase (N) is varied according to a predetermined printing scheme. A method according to claim 1 or 2, wherein the reducing pressure (RP) is alternately varied between a predetermined minimum reducing pressure and a maximum reducing pressure during the reducing phase (R). A method according to any one of the preceding claims, wherein the nitriding pressure (NP) is alternately varied between a predetermined minimum nitriding pressure and a maximum nitriding pressure during the nitriding phase (N). Method according to one of the preceding claims, wherein in the process chamber (3) during the equilibrium phase (G), an oxidizing gas, preferably oxygen, for pre-oxidation of the surface of the workpiece (2) is supplied. Method according to one of the preceding claims, wherein the reducing gas (5) is hydrogen or ammonia. Method according to one of the preceding claims, wherein the activation gas (6) and / or the nitriding gas (7) is ammonia. Method according to one of the preceding claims, wherein during the reduction phase (R) and / or the activation phase (AK), the reducing gas and / or the activation gas (6) comprises an additional gas, preferably CO ₂ or N ₂ O. Method according to one of the preceding claims, wherein a gas is ionized by means of an ionizing agent (13), preferably in the reduction phase (R) and / or in the nitration phase (N). Gas nitriding device for gas nitriding a workpiece (2) according to a method for gas nitriding (1) according to one of claims 1 to 9, comprising a process chamber (3) for receiving the workpiece (2), and gas supply means (9, 91) for supplying the process chamber (3 ) with gases and a gas removal means (10) for removing gases from the process chamber (3) for generating a negative pressure in the process chamber, the gas exhaust means (10) comprises a shut-off device (11), characterized in that a pressure control device (12) with a Gas exhaust device (120) and gas flow control means (121, 122) is provided, so that a gas pressure and / or a mixing ratio of gases in the process chamber (3) is variable according to a predeterminable pressure scheme. Gas nitriding apparatus according to claim 10, wherein a control unit (123) for controlling and / or regulating the gas pressure in the process chamber (3) is provided. Gas nitriding apparatus according to claim 10 or 11, wherein a measuring device (130, 131) is provided for detecting and controlling and / or regulating the gas pressure and / or a gas temperature and / or the composition of gases in the process chamber (3). Gas nitriding apparatus according to any one of claims 10 to 12, wherein an ionization means (13), preferably comprising a plasma generator, is provided for the ionization of a gas located in the process chamber (3). A workpiece having a surface layer comprising a diffusion layer (200) having a hard layer (201) produced by a gas nitriding method according to any one of claims 1 to 9. The workpiece according to claim 14, which has on the hard layer (201) an additional outer terminating layer (202) which is preferably applicable by means of a PVD method, CVD method, an arc evaporation method or a thermal spraying method. Workpiece according to one of claims 14 or 15, wherein the workpiece is a dynamically loaded component, in particular a spring.

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