Method for Producing at least One Component and Open-Loop and/or Closed-Loop Control Device

Abstract

The disclosure relates to a method for producing at least one, in particular metal, component, preferably a cylinder head, a nozzle body for a high-pressure injection pump, a component of a diesel injection engine, or a throttle disk, by means of low-pressure carbonitriding in at least one treatment chamber, which preferably can be evacuated, and an open-loop and/or closed-loop control device, which enables the setting of a specified ratio between a carbon concentration and a nitrogen concentration in a surface layer of the at least one component. In at least one treatment phase, a carbon-providing gas and a nitrogen-providing gas are simultaneously introduced into the treatment chamber. Based on a specified ratio between a carbon concentration and a nitrogen concentration to be absorbed by the at least one component in a surface layer of the component, a target value for the temperature and/or the pressure to be set in the treatment chamber is determined and is set in the treatment chamber for a specified time.

Description

The present invention relates to a method for producing at least one component and to an open-loop and/or closed-loop control device of the generic type of the independent claims.

PRIOR ART

The document DE 199 09 694 A1 describes a carbonitriding process in which the inward diffusion of the nitrogen takes place during the entire process or, if elemental nitrogen is used as the donor gas, preferably only in the last process phase. Molecular nitrogen, ammonia and other nitrogen-containing compounds are mentioned in particular as nitrogen donors. Carbon donors are not specified.

The document DE 101 18 494 C2 describes a low-pressure carbonitriding process in which steel parts are first carburized and subsequently nitrogenized with a nitrogen-donor gas. Acetylene, propane and ethylene are specified as carbon donors. A donor gas that contains ammonia is mentioned as the nitrogen donor. Nothing further is specified about the nitrogen donor.

The document DE 103 22 255 A1 describes a process for carburizing steel parts in which nitrogen-emitting gas is fed in both during the heating-up phase and during the diffusion phase. Ammonia and nitrous oxide are specified as nitrogen donors and acetylene, propane and ethylene are specified as carbon donors.

The mentioned documents DE 101 18 494 C2 and DE 103 22 255 A1 describe low-pressure carbonitriding processes in the pulsed mode, in which nitrogen compounds, such as for example ammonia or nitrous oxide, are used as the nitrogen donor gas and are introduced into the treatment chamber in the offering phases between the offers of carburization and/or when heating up the charge and/or in the final carbon diffusion phase, in order to introduce the nitrogen into the surface of the component.

Due to the alternating carbon and nitrogen offering phases, caused as a result of the process, it is not possible to ensure a continuous uptake of carbon and nitrogen. As a result of this, the process times become longer, since allowance has to be made for diffusion phases between the carbon and nitrogen offering phases in order to speed up the uptake of carbon or nitrogen in a subsequent offering phase.

Russian patent 1680798 describes a process for carbonitriding metallic components in which amine compounds, such as for example methyl amine, diethyl amine and dibutyl amine, are used as carbon and nitrogen donors, in order to introduce carbon and nitrogen simultaneously into the surface of the component. In the case of this process, amines are introduced into the treatment chamber at high temperatures (T=1100° C. to 1200° C.) in order to produce a carbon- and nitrogen-rich atmosphere. This process proceeds under atmospheric pressure.

In the case of this carbonitriding process, the high treatment temperatures of 1100 to 1200° C. and the atmospheric pressure are problematic. At these temperatures, the conversion of the amine compounds in the gas phase and on the surface of the component is so high that more complex geometries with interior surfaces, such as for example bores, or closely packed component charges are carbonitrided unevenly. In addition, the process gas pressure of 1 bar makes the diffusion of the donor gases within the charge and/or within interior geometries, such as for example blind-hole bores, considerably more difficult.

In technical terms, this temperature range together with the high process gas pressure must be rated as conditions necessitating a very high-maintenance plant. Furthermore, at these temperatures, low-cost metallic materials have a tendency to form coarse grains, which can have adverse effects on the durability of the component, as a result of which more expensive materials have to be used and/or an additional heat treatment step has to be carried out to make the grains fine.

A further important aspect is that, in the case of all the low-pressure carbonitriding processes described, no closed-loop control is provided for controlling the carbon and nitrogen uptake. The ratio between the carbon and nitrogen introduced in the outer layer is however decisive for the resultant properties of the material and the component.

DISCLOSURE OF THE INVENTION

In comparison, the process according to the invention for producing at least one component and the open-loop and/or closed-loop control device according to the invention with the features of the independent claims have the advantage that, in at least one treatment phase, a carbon-emitting gas and a nitrogen-emitting gas are introduced simultaneously into the treatment chamber, that, depending on a specified ratio between a carbon concentration and a nitrogen concentration to be taken up by the at least one component in its outer layer, a target value for the temperature and/or the pressure to be set in the treatment chamber is determined and is adjusted in the treatment chamber for a specified time. In this way it is possible to ensure continuous carbon and nitrogen uptake. Carbon and nitrogen are offered simultaneously, and consequently without a change of process gas or diffusion phases between alternating carbon and nitrogen offering phases. As a result, the process times become shorter. Low-pressure carbonitriding additionally makes homogeneous carburizing and nitrogenizing possible, even in the case of closely packed charges or complex component geometries, such as for example bore geometries. The closed-loop control of the temperature and/or pressure allows a specified ratio between the carbon and nitrogen concentrations introduced in the outer layer to be set, and consequently the resultant properties of the material and component to be influenced.

Advantageous developments and improvements of the method specified in the main claim are possible by the measures presented in the dependent claims.

It is particularly advantageous if one and the same gas is introduced into the treatment chamber as the carbon-emitting gas and as the nitrogen-emitting gas. This considerably simplifies the method, since only one gas has to be introduced into the treatment chamber.

Advantageously chosen as such a gas is an amine compound, preferably aliphatic monoamine, as primary, secondary and tertiary compounds, or aliphatic diamine or a mixture of the two.

A further advantage is obtained here if a gas that emits carbon and nitrogen in a ratio of less than or equal to three is chosen as the carbon- and nitrogen-emitting gas. In this way, the desired ratios can be set in the carbon and nitrogen profiles while at the same time reducing the formation of soot in the furnace installation.

The same advantage is also obtained if, when using different gases for the emission of carbon and nitrogen in the treatment chamber, the amount, in particular the volumetric flow, of the carbon-emitting gas fed into the treatment chamber and the amount, in particular the volumetric flow, of the nitrogen-emitting gas fed into the treatment chamber in the ratio of the emission of carbon and nitrogen in the treatment chamber is chosen to be less than three.

It is advantageous for the closed-loop control if the pressure and/or the temperature in the treatment chamber is measured and as an actual value is corrected to the target value determined. This makes particularly simple and reliable closed-loop control to the specified ratio between the carbon concentration and the nitrogen concentration to be taken up by the at least one component in its outer layer possible.

The closed-loop control is also made particularly simple and convenient by the actual value for the temperature being corrected to the target value for the temperature by activating a heating device in the treatment chamber, the temperature of the heating device being increased if the actual value for the temperature is less than the target value for the temperature and the temperature of the heating device being lowered if the actual value for the temperature is greater than the target value for the temperature.

The closed-loop control is made correspondingly simple and convenient if the actual value for the pressure is corrected to the target value for the pressure by setting an amount of gas, in particular volumetric flow, discharged from the treatment chamber, the discharged amount of gas being lowered if the actual value for the pressure is less than the target value for the pressure and the discharged amount of gas being increased if the actual value for the pressure is greater than the target value for the pressure.

It is also advantageous if the target value for the temperature in the treatment chamber is changed at least once. This makes it possible to set different ratios between the carbon concentration and the nitrogen concentration used in different zones of depth of the outer layer.

A further advantage is obtained if a temperature-equalizing phase is arranged downstream of at least one heating-up phase or at least one cooling-down phase in the treatment chamber. In this way, the target value for the temperature can be adjusted as exactly as possible for all of the components within a charge.

It is advantageous that the target value for the pressure in the treatment chamber is changed at least once. This makes it possible to set different ratios between the carbon concentration and the nitrogen concentration used in different zones of depth of the outer layer.

A further advantage is that the target pressure in the treatment chamber is less than or equal to 100 mbar, preferably between two and 30 mbar. In this way, diffusion processes of the corresponding gas within a charge or within interior geometries, such as for example blind-hole bores, become considerably easier.

It is also advantageous that the target value for the temperature lies in a range from 650° C. to 1050° C., preferably in a range from 650° C. to 960° C. In this way, homogeneous carbonitriding of closely packed component charges or complex geometries with interior surfaces, such as for example with bore geometries, can be ensured.

In the case of the process gas being continuously offered, precipitates such as carbides, nitrides and carbonitrides may form in an unwanted and uncontrolled manner in the outer layer of the at least one component, in dependence on the temperature and the carbon and nitrogen depth profiles developing. It is therefore particularly advantageous in the case of the method according to the invention that a number of treatment phases are provided, respectively separated from one another by a diffusion phase. In this way, unwanted precipitates such as carbides, nitrides and carbonitrides in the outer layer of the at least one component can be avoided, and also a desired or specified carbon and nitrogen depth profile can be set in the outer layer of the at least one component.

Such a specified carbon and nitrogen depth profile can be produced particularly simply by the specified ratio between the carbon concentration and the nitrogen concentration to be taken up by the at least one component in its outer layer being chosen to be different in at least two of the treatment phases, depending on the specified carbon and nitrogen depth profile in the outer layer of the at least one component.

DRAWING

An exemplary embodiment of the invention is represented in the drawing and explained in more detail in the description that follows.

FIG. 1 shows a schematic representation of a plant for the low-pressure carbonitriding of at least one component,

FIG. 2 shows the influence of the temperature on the ratio between carbon and nitrogen set in the outer layer of a component,

FIG. 3 schematically shows a way of conducting a low-pressure carbonitriding process with a controlled temperature,

FIG. 4 schematically shows the buildup of the outer layer of the treated components that is achieved by the way in which the process is conducted as shown in FIG. 3 and

FIG. 5 shows a block diagram of an open-loop and/or closed-loop control device used for conducting the process.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1 shows a schematic representation of a plant 1 for the low-pressure carbonitriding of one or more components 2. In FIG. 1, five components 2 are represented by way of example. The components 2 are arranged on a support 3 in a treatment chamber 4. The components 2 can be heated by means of a heating device 5 represented in the lower region of the drawing. An inlet 6 with an associated flow control valve 7 allows the introduction of a carbon- and nitrogen-donor gas 8. A temperature sensor 9 and a pressure sensor 10 are arranged in the upper region of the drawing of the treatment chamber 4. An open-loop and/or closed-loop control device 11 shown above them receives the signals coming from the temperature sensor 9 and the pressure sensor 10. An outlet 12 of the treatment chamber 4 leads to the input of a pump 13, which may be formed for example as a vacuum pump. Arranged upstream of the pump 13 is a throttle 14, in particular for controlling the pressure.

During the operation of the plant 1, the carbon- and nitrogen-donor gas 8 is introduced simultaneously into the treatment chamber 4 in various process phases by means of the flow control valve 7. The open-loop and/or closed-loop control device 11 monitors and controls the process or the individual process phases, inter alia by means of the temperature sensor 9 and the pressure sensor 10. Of importance in particular is the temperature recorded by the temperature sensor 9, which is also referred to hereinafter as the treatment temperature. The treatment temperature is obtained in the atmosphere of the treatment chamber 4, as still to be explained in relation to the subsequent FIGS. 2 and 3. The pump 13 acts at the outlet 12 together with the throttle 14 like a valve. The degree of opening of the throttle 14 is controlled process-dependently by the open-loop and/or closed-loop control device 11, inter alia depending on the pressure recorded by the pressure sensor 10, which is also referred to hereinafter as the treatment pressure, in order to set the required treatment pressure in the treatment chamber 4, partially evacuate the treatment chamber 4 or let out or exchange the gases located in it. The heating device 5 is controlled by the open-loop and/or closed-loop control device 11, inter alia depending on the treatment temperature recorded by the temperature sensor 9. The flow control valve 7 is managed by the open-loop and/or closed-loop control device 11 in order to control the process-dependent throughputs of the process gas.

The carbon-donor gas, also referred to as the carbon-emitting gas, and the nitrogen-donor gas, also referred to as the nitrogen-emitting gas, may be different from one another. In this case, the different gases can be fed into the treatment chamber 4 in a desired mixing ratio in a mixing chamber (not represented in the drawing) upstream of the flow control valve 7 or by means of in each case a separate flow control valve. In this case, known gases can be chosen. For example, acetylene, propane or ethylene for the carbon-donor gas. For example, ammonia or nitrous oxide for the nitrogen-donor gas. The composition of the process gas for the treatment chamber 4 is set by way of the amounts of gas of the carbon-emitting gas and the nitrogen-emitting gas.

However, it has been found to be particularly advantageous if one and the same gas is chosen for the carbon-donor gas and for the nitrogen-donor gas, for example an amine compound, preferably aliphatic monoamine, as primary, secondary and tertiary compounds, or aliphatic diamine or a mixture of the two. This makes it considerably easier to conduct the process. A mixing chamber upstream of the flow control valve 7 or an additional flow control valve is not required in this case.

Instead of the way described on a temperature and pressure basis, the closed-loop control or open-loop control may alternatively be performed only on a temperature basis or only on a pressure basis, so that only one of the two sensors is required. In the case of temperature-based closed-loop control, only the temperature sensor is required, and in the case of pressure-based closed-loop control only the pressure sensor is required.

FIG. 2 shows the influence of the treatment temperature on the carbon and nitrogen introduced in the outer zone of the components 2, at a distance from the component surface of 50 μm after a carbonitriding period of 20 minutes at a set treatment pressure of the donor gas dimethyl amine (C₂H₆NH) of 10 mbar. In this case, FIG. 2 shows by way of example the experimentally determined influence of the treatment temperature on the ratio of the carbon concentration and the nitrogen concentration set in the outer zone of the components 2 for the two temperatures 800° C. and 850° C. The two temperatures were chosen for the representation in order to illustrate the change of the ratios of the amount of carbon and the amount of nitrogen taken up. At 800° C., the amount of nitrogen taken up predominates, whereas with a process of the same duration and a temperature of 850° C. more carbon is taken up. Generally, with increasing treatment temperature, it can be assumed that the ratio of the amount of carbon and the amount of nitrogen taken up is shifted toward higher carbon uptakes. With knowledge of the temperature influence on the ratio of the amount of carbon and the amount of nitrogen taken up, a controlled temperature regime can be followed, which, depending on the specified ratio between a carbon concentration and a nitrogen concentration to be taken up by the components 2 in their outer layer, necessitates a constantly controlled temperature and/or a lowering or raising of the treatment temperature.

It has also been experimentally demonstrated that, by increasing the treatment pressure, the ratio between carbon and nitrogen is shifted in favor of carbon.

Represented by way of example in FIG. 3 is a progression over time of the treatment temperature and the treatment pressure, also referred to as the process gas pressure, in the case of low-pressure carbonitriding. Schematically represented for purposes of illustration is the conduction of a low-pressure carbonitriding process with a controlled temperature, which is used for example in the case of the plant 1 shown in FIG. 1. The duration of the process t is represented on the x axis of the diagram, the temperature T is represented on the left-hand y axis and the pressure p of the atmosphere in the treatment chamber 4 is represented on the right-hand y axis. The low-pressure carbonitriding comprises a heating-up phase A, two temperature-equalizing phases B1, B2, two carbonitriding phases C1, C2, two diffusion phases D1, D2, a temperature change E and a cooling-off phase F.

An interruption on the x axis indicates that the process phases represented do not have to last for the periods of time respectively shown, but may also deviate from the representation of FIG. 3.

FIG. 3 shows that, during a heating-up phase A, the temperature is continuously increased with an approximately constant heating-up rate up to a treatment temperature of approximately 950° C. by means of the heating device 5. For this purpose, the heating device 5 is correspondingly activated by the open-loop and/or closed-loop control device 11 and the heating-up rate ΔT/Δt is controlled.

In a first temperature-equalizing phase B1, following the heating-up phase A, the treatment temperature is adjusted constantly to a first target value for the temperature of approximately 950° C. by the open-loop and/or closed-loop control device 11, by comparison of the temperature measured by means of the temperature sensor 9 with the first target value for the temperature of 950° C., by corresponding activation of the heating device 5. During the heating-up phase A and the first temperature-equalizing phase B, no carbon- or nitrogen-emitting gas is fed into the treatment chamber 4.

In a first treatment phase, following the first temperature-equalizing phase B1 and also referred to as the first carbonitriding phase C1, the treatment temperature continues to remain adjusted to its first target value. In addition, a carbon- and nitrogen-emitting gas, also referred to as the carbon- and nitrogen-donor gas, for example methyl amine, is fed into the treatment chamber 4 by way of the flow control valve 7. In this case, the treatment pressure, also referred to as the process gas pressure or donor gas pressure or partial pressure of the donor gas, is adjusted constantly to a first target value for the pressure of approximately 15 mbar by the open-loop and/or closed-loop control device 11, by comparison of the pressure measured by means of the pressure sensor 10 with the first target value for the pressure of 15 mbar, by corresponding activation of the degree of opening of the throttle 14.

The first target value for the treatment temperature and the first target value for the treatment pressure are determined in the open-loop and/or closed-loop control device 11, depending on the experimentally determined relationships described above, by means of correspondingly stored characteristic diagrams in order to obtain a first specified ratio between the amount of carbon and the amount of nitrogen taken up for the components 2 in their outer zone. The amount or depth of penetration of the carbon and nitrogen introduced into the components 2 according to the first specified ratio is determined by the chosen first treatment period Δt1 of the first carbonitriding phase C1. In this respect, a first treatment-period characteristic diagram is stored in the open-loop and/or closed-loop control device 11 and, for the chosen target value of the treatment temperature and the chosen target value for the treatment pressure and also the material composition of the components 2, describes an—experimentally or computationally—determined relationship between the treatment period and the amount of carbon and/or amount of nitrogen introduced into the components 2 or depth of penetration of the carbon and nitrogen into the outer layer. All of the components 2 treated in the treatment chamber should in this case have an identical material composition, in order that the desired result with respect to the carbon concentration and the nitrogen concentration to be introduced is achieved.

In the present example, the first carbonitriding phase C1 is subsequently followed optionally by a first diffusion phase D1, in which, by corresponding activation of the throttle 14 and the flow control valve 7 by the open-loop and/or closed-loop control unit 11, the treatment chamber 4 is evacuated by means of the pump 13, with the flow control valve 7 closed, or is purged with an inert gas, for example nitrogen or argon, which then is fed into the treatment chamber 4 instead of the carbon- and nitrogen-donor gas by way of the flow control valve 7 and is pumped away again by the pump 13.

This is followed by a temperature-changing phase E for changing the treatment temperature to a second target value of approximately 850° C., by corresponding activation of the heating device 5, in order in the case of this exemplary embodiment to set the final ratio between the carbon and the nitrogen in the outer layer of the components 2.

In a second temperature-equalizing phase B2, following the temperature-changing phase E, the treatment temperature is adjusted constantly to the second target value for the temperature of approximately 850° C. by the open-loop and/or closed-loop control device 11, by comparison of the temperature measured by means of the temperature sensor 9 with the second target value for the temperature of 850° C., by corresponding activation of the heating device 5. During the temperature-changing phase E and the second temperature-equalizing phase B2, no carbon- or nitrogen-emitting gas is fed into the treatment chamber 4.

In a second treatment phase, following the second temperature-equalizing phase B2 and also referred to as the second carbonitriding phase C2, the treatment temperature continues to be adjusted to its second target value. In addition, a carbon- and nitrogen-emitting gas, for example methyl amine, is fed into the treatment chamber 4 by way of the flow control valve 7. In this case, the treatment pressure is adjusted constantly to a second target value for the pressure of approximately 10 mbar by the open-loop and/or closed-loop control device 11, by comparison of the pressure measured by means of the pressure sensor 10 with the second target value for the pressure of 10 mbar, by corresponding activation of the flow control valve 7.

The second target value for the treatment temperature and the second target value for the treatment pressure are determined in the open-loop and/or closed-loop control device 11, depending on the experimentally determined relationships described above, by means of correspondingly stored characteristic diagrams in order to obtain a second specified ratio between the amount of carbon and the amount of nitrogen taken up for the components 2 in their outer zone. The amount or depth of penetration of the carbon and nitrogen introduced into the components 2 according to the second specified ratio is determined by the chosen second treatment period Δt2 of the second carbonitriding phase C2. In this respect, a second treatment-period characteristic diagram, which is stored in the open-loop and/or closed-loop control device 11, is used and, depending on the chosen target value of the treatment temperature and the chosen target value for the treatment pressure and also the material composition of the components 2, describes the—experimentally or computationally —determined relationship between the treatment period and the amount of carbon and/or amount of nitrogen additionally introduced into the components 2 or, on the basis of the depth of penetration achieved in the first carbonitriding phase C1, the realizable additional depth of penetration of the carbon and nitrogen into the outer layer. If the treatment temperature and the treatment pressure of the second carbonitriding phase are chosen to correspond to the first carbonitriding phase, the first treatment-period characteristic diagram may also be used instead of the second treatment-period characteristic diagram.

In the case of the exemplary embodiment represented, the lowered second target value for the treatment temperature in comparison with the first carbonitriding phase C1 in the second carbonitriding phase C2 has the effect that the treatment chamber is adjusted to a temperature at which the nitrogen fraction taken up by the components 2 becomes greater and the carbon fraction taken up by the components 2 becomes less.

In the same way as the lowered treatment temperature, the lower treatment pressure in the second carbonitriding phase C2 in comparison with the first carbonitriding phase C1, represented in the exemplary embodiment, likewise has the effect that the ratio between the amount of carbon and the amount of nitrogen taken up by the components 2 is shifted in favor of nitrogen.

The second carbonitriding phase C2 may alternatively also follow on directly from the temperature-changing phase E, without a second temperature-equalizing phase B2.

As can be seen from FIG. 4, the amount of carbon and the amount of nitrogen taken up in the first carbonitriding phase C1 lies in a second zone 110 of the outer layer 125, which is at a further distance from the surface of the components 2 than the amount of carbon and the amount of nitrogen taken up during the second carbonitriding phase C2, which is in a first zone 105 of the outer layer 125, which on the one hand adjoins the second zone 110 and on the other hand is terminated by the surface 100 of the respective component 2.

Consequently, a corresponding depth profile of the carbon concentration and the nitrogen concentration taken up into the outer layer 125 of the components 2 is produced. In the present exemplary embodiment, the second treatment period Δt2 has been chosen to be shorter than the first treatment period Δt1. Therefore, the second zone 110 in the outer layer 125 of the components 2 has been formed thicker than the first zone 105. The first zone 105 has in this case a first thickness d1, which is less than a second thickness d2 of the second zone 110. Then, away from the first zone 105, the second zone 110 is adjoined by a core 115 of the respective component, into which no carbon or nitrogen has been taken up as a result of the treatment. The transition between the two zones 105, 110 is depicted in FIG. 4 in an ideally abrupt form, but in reality a gradual transitional region develops between the ratios of the corresponding carbon and nitrogen concentrations of adjacent zones.

There subsequently follows a further diffusion phase D2, in which the treatment chamber 4 is evacuated or purged with an inert gas, for example nitrogen or argon. There subsequently follows a cooling-down phase F.

It goes without saying that numerous methods for carbonitriding are possible in this way, and the invention is not restricted to the sequence explained and the number of two temperature-equalizing phases B1, B2, two carbonitriding phases C1, C2, two diffusion phases D1, D2, one temperature change E and one cooling-down phase F.

Depending on the desired properties of the material and the component, such as for example the wear resistance and temperature resistance, and the ferrous material used for the components 2, a maximum outer concentration of carbon and nitrogen totalling 1.5 percent by mass should be maintained. It is desirable that the outer carbon concentration should lie between 0.5 and 0.8 percent by mass when there is an outer nitrogen concentration of between 0.2 and 0.7 percent by mass.

As described, to avoid unwanted precipitates of carbides, nitrides and carbonitrides and/or to set a specified carbon and nitrogen depth profile in the outer layer of the components 2, optionally one or more diffusion phases may be introduced between individual carbonitriding phases. The specified carbon and nitrogen depth profile in this case indicates at which distances from the surface of the components which ratio between the carbon concentration and the nitrogen concentration to be taken up by the component in its outer layer is intended to be present in the outer layer of the components. As described above, a corresponding carbonitriding phase is then provided for each of these zones of the outer layer with an individually specified ratio between the carbon concentration and the nitrogen concentration.

The desired distribution of the carbon concentration and the nitrogen concentration in the outer layer of the components 2 is consequently set by a controlled temperature regime and/or control of the donor gas pressure during the low-pressure carbonitriding and by suitable choice of the points in time and the treatment periods of the carbonitriding phases. In the case of carbonitriding phases in which the carbon- and nitrogen-donor gas is fed into the treatment chamber 4, the treatment temperature of the components is for this purpose advantageously controlled within a maximum deviation of +/−15° C., desirably within a maximum deviation of +/−8° C.

In addition, one advantage of the method according to the invention is that the process is carried out at low pressures less than or equal to 100 mbar, advantageously between 2 and 30 mbar, whereby the accessibility of bore geometries for the uptake of carbon and nitrogen increases. For this purpose, the process gas pressure of the carbon- and nitrogen-donor gas is advantageously controlled within a deviation of +/−8 mbar, even better within a deviation of +/−3 mbar. Lower temperatures of less than or equal to 1050° C., advantageously less than or equal to 960° C. and greater than or equal to 650° C., allow homogeneous carbonitriding of dense component charges or complex geometries, such as for example with bore geometries, to be carried out.

The characteristic diagrams described are developed from a simulation model, which calculates the diffusion of nitrogen and carbon in dependence on time, temperature, pressure and material composition.

FIG. 5 shows a block diagram of the open-loop and/or closed-loop control device 11 with the components that are provided for the activation of the flow control valve 7, the degree of opening of the throttle 14 and the heating device 5 for setting the carbonitriding phases. In this case, the degree of opening of the throttle 14 is set during the carbonitriding phases, with the vacuum pump 13 running, by the open-loop and/or closed-loop control device 11 in such a way that the treatment pressure in the treatment chamber 4 is controlled to the respective target value. The control of the treatment pressure by means of corresponding setting of the degree of opening of the throttle 14 takes place at the gas outlet from the treatment chamber 4 upstream of the pump 13. If the actual value of the treatment pressure, measured by the pressure sensor 10, exceeds the specified target value for the treatment pressure, the throttle 14 is opened further by corresponding activation on the part of the open-loop and/or closed-loop control device 11, so that the pump 13 can remove a greater volumetric flow from the treatment chamber 4 and the actual value for the treatment pressure is lowered. If the actual value of the treatment pressure, measured by the pressure sensor 10, does not reach the specified target value for the treatment pressure, the throttle 14 is closed further by corresponding activation on the part of the open-loop and/or closed-loop control device 11, whereby the volumetric flow that the pump 13 removes from the treatment chamber 4 is reduced and an increase in the actual value for the treatment pressure in the treatment chamber 4 is achieved.

The other components of the open-loop and/or closed-loop control device 11, as required for example for setting the heating-up phase A or the diffusion phases D1, D2, are not represented for reasons of overall clarity and can be formed in the way known to a person skilled in the art.

At an input unit 200 of the open-loop and/or closed-loop control device 11, a user can input a number of parameters for a desired treatment of the components 2 in the treatment chamber 4. Thus, by corresponding input, the user can specify one or more ratios between the carbon concentration and the nitrogen concentration to be taken up by the components 2 in their outer layer 125. A first ratio specified in this way is identified in FIG. 5 as the first ratio data record 205; an nth specified ratio, where n may be chosen as greater than or equal to one, is identified as the nth ratio data record 215. If n=1, then there is only one ratio data record for the specified ratio, which corresponds to the first ratio data record 205. If more than one ratio is specified, there is the corresponding number of ratio data records. The entirety of all the specified ratio data records is identified by 220. For each ratio data record, an assigned carbonitriding phase is intended to be set here in order to implement the specified ratio in the outer layer 125. If only one ratio data record is specified here, there will also only be one zone of the outer layer 125 with the corresponding specified ratio; if there are a number of ratio data records, a carbonitriding phase is set for each ratio data record, in the time sequence in which they are input or in the sequence in which they are numbered. Then there forms in the outer layer 125 a zone with the corresponding ratio of the carbon concentration and the nitrogen concentration for each ratio data record, and consequently for each carbonitriding phase, the zones being formed in relation to the surface 100 of the respective component 2 in accordance with the time sequence of the input of the associated specified ratio, and consequently in the sequence of their numbering. In this case, the first ratio data record sets the carbon and nitrogen concentrations at the greatest distance from the outer surface 100 of the respective component 2 and the last data record used sets the carbon and nitrogen concentrations nearest the surface. An example of two such zones, and consequently two such specified ratios, has been described with reference to FIG. 4. In this case, the second zone 110 with the thickness d2 was set in the outer layer of the component 2 with a first ratio data record and the first zone 105 with the thickness d1 was set with a second ratio data record.

For each specified ratio, a desired amount or depth of penetration should also be indicated, in other words an associated thickness of the assigned zone. Correspondingly, a first specified thickness data record is identified in FIG. 5 by 225 and an nth specified thickness data record is indicated by 235. The entirety of the thickness data records is identified by 240. In the time sequence in which they are input, for each required carbonitriding phase, the corresponding ratio data record is fed as an input variable to a temperature-pressure characteristic diagram 250 and the assigned thickness data record is fed as an input variable to the treatment-period characteristic diagram 255. The temperature-pressure characteristic diagram was in this case determined experimentally and, for each ratio between the carbon concentration and the nitrogen concentration to be taken up by the components 2 in their outer layer 125 that is specified at its input, emits at its output a target value ST for the assigned treatment temperature and a target value SD for the assigned treatment pressure. The result of such an experimental evaluation for the treatment temperature and the treatment pressure has been stated by way of example with reference to FIG. 2. The target value ST for the treatment temperature and the target value SD for the treatment pressure are likewise fed as input variables to the treatment-period characteristic diagram 255. The target value ST for the treatment temperature is also fed as an input variable to a first comparing element 265. The target value SD for the treatment pressure is also fed as an input variable to a second comparing element 260.

Furthermore, at the input unit 200, a material composition, for example of the case-hardening steel 20MnCr5, is selected from a proposed set that characterizes the material composition of the components 2. In this case, a material-composition data record 245 is generated and likewise fed as an input variable to the treatment-period characteristic diagram 255. The treatment-period characteristic diagram 255 was in this case likewise determined experimentally and indicates which treatment period is required in order in the case of a component of the selected material composition with the specified target value ST for the treatment temperature and the specified target value SD for the treatment pressure to form the specified thickness of the zone to be formed with carbon and nitrogen taken up according to the specified ratio of the carbon concentration and the nitrogen concentration in the outer layer 125 of the respective component 2. For the treatment period thus determined at the output of the treatment-period characteristic diagram 255, a corresponding enabling signal is sent to the flow control valve 7, so that this valve is open during the determined treatment period for the assigned carbonitriding phase. Outside the determined treatment period, the flow control valve 7 is closed or is only opened for purging with an inert gas, for example nitrogen or argon, in a way known to a person skilled in the art, for diffusion phases that are possibly provided.

As a further input variable, an actual value IT for the treatment temperature, which is determined by the temperature sensor 7, is fed to the first comparing element 265. The first comparing element 265 compares the target value ST of the treatment temperature with the actual value IT of the treatment temperature and, depending on the difference between the target value ST for the treatment temperature and the actual value IT for the treatment temperature, emits a control signal to the heating device 5, in order to minimize the control deviation and correct the actual value IT for the treatment temperature to the target value ST for the treatment temperature.

As a further input variable, an actual value ID for the treatment pressure, which is determined by the pressure sensor 10, is fed to the second comparing element 260. The second comparing element 260 compares the target value SD of the treatment pressure with the actual value ID of the treatment pressure and, depending on the difference between the target value SD for the treatment pressure and the actual value ID for the treatment pressure, emits a control signal to the throttle 14, in order to minimize the control deviation and correct the actual value ID for the treatment pressure to the target value SD for the treatment pressure.

In this way, the respectively specified ratio between the carbon concentration and the nitrogen concentration in the outer layer 125 of the respective component 2 is set in the desired thickness in the corresponding zone for the treatment period determined. If a number of such ratios are specified, then a carbon and nitrogen depth profile specified by the ratio data records 205, . . . , 215 and the thickness data records 225, . . . , 235 is set in the outer layer 125 by the carbonitriding phases that are assigned and optionally separated from one another in each case by a diffusion phase.

Claims

1. A method for producing at least one metallic component in at least one treatment chamber, the method comprising:

introducing, in at least one treatment phase, a carbon-emitting gas and a nitrogen-emitting gas simultaneously into the at least one treatment chamber

determining, in the at least one treatment phase, a target value for at least one of a temperature and a pressure to be set in the at least one treatment chamber, the target value depending on a specified ratio between a carbon concentration and a nitrogen concentration to be taken up by the at least one metallic component in an outer layer of the at least one metallic component; and

adjusting, in the at least one treatment phase, the target value in the at least one treatment chamber for a specified time.

2. The method as claimed in claim 1, wherein the carbon-emitting gas is a first gas and the nitrogen-emitting gas is the first gas.

3. The method as claimed in claim 2, wherein the first gas is an amine compound.

4. The method as claimed in claim 2, wherein the first gas emits carbon and nitrogen in a ratio of less than or equal to three.

5. The method as claimed in claim 1, wherein a ratio between a volumetric flow of the carbon-emitting gas introduced into the at least one treatment chamber and a volumetric flow of the nitrogen-emitting gas introduced into the at least one treatment chamber is less than three.

6. The method as claimed in claim 1, further comprising:

measuring the at least one of the temperature and the pressure in the at least one treatment chamber; and

correcting the at least one of the temperature and the pressure to match the target value.

7. The method as claimed in claim 1, further comprising:

activating a heating device in the treatment chamber to adjust the temperature to match the target value for the temperature the activating comprising: increasing the temperature of the heating device in response to the temperature being less than the target value for the temperature; and decreasing the temperature of the heating device in response to the temperature being greater than the target value for the temperature.

8. The method as claimed in claim 1, further comprising:

setting a volumetric flow discharged from the at least one treatment chamber to adjust the pressure to match the target value for the pressure, the setting comprising: decreasing the volumetric flow in response to the pressure being less than the target value for the pressure; and increasing the volumetric flow in response to the pressure being greater than the target value for the pressure.

9. The method as claimed in claim 1, further comprising:

changing the target value for the temperature in the treatment chamber at least once.

10. The method as claimed in claim 1, further comprising:

at least one of heating up the temperature and cooling down the temperature; and

equalizing the temperature after the at least one of the heating up and cooling down.

11. The method as claimed in claim 1, further comprising:

changing the target value for the pressure in the treatment chamber at least once.

12. The method as claimed in claim 1, wherein the target value for the pressure in the treatment chamber is less than or equal to 100 millibar.

13. The method as claimed in claim 1, wherein the target value for the temperature is between 650 degrees Celsius and 1050 degrees Celsius.

14. The method as claimed in claim 1, wherein a plurality of treatment phases are performed, the plurality of treatment phases each being respectively separated from one another by a diffusion phase.

15. The method as claimed in claim 14, wherein a specified ratio between a carbon concentration and a nitrogen concentration to be taken up by the at least one metallic component in an outer layer of the at least one metallic component is different in at least two of the plurality of treatment phases, depending on a specified carbon and nitrogen depth profile in the outer layer of the at least one metallic component.

16. At least one of an open-loop control device and a closed loop control device for producing at least one metallic component in at least one treatment chamber, comprising:

a controller configured to: introduce, in at least on treatment phase, a carbon-emitting gas and a nitrogen-emitting gas simultaneously into the treatment chamber; determine, in at least one treatment phase, a target value for at least one of a temperature and a pressure in the at least one treatment chamber, the target value depending on a specified ratio between a carbon concentration and a nitrogen concentration to be taken up by the at least one metallic component in an outer layer of the at least one metallic component; and adjust, in at least one treatment phase, the target value in the at least one treatment chamber for a specified time.

17. The method as claimed in claim 1, wherein the at least one metallic component is at least one of a cylinder head, a nozzle body for a injection pump, a component of a diesel injection engine and a throttle plate.

18. The method as claimed in claim 3, wherein the amine compound is at least one of an aliphatic monoamine, as primary, secondary and tertiary compounds, an aliphatic diamine, and a mixture of an aliphatic monoamine and an aliphatic diamine.

19. The method as claimed in claim 12, wherein the target value for the pressure in the treatment chamber is between 2 millibar and 30 millibar.

20. The method as claimed in claim 13, wherein the target value for the temperature is between 650 degrees Celsius and 960 degrees Celsius.