EP2430210A2

EP2430210A2 - Method for carbonitriding

Info

Publication number: EP2430210A2
Application number: EP10709725A
Authority: EP
Inventors: Lothar Foerster; Jochen Schwarzer; Laszlo Hagymasi; Thomas Waldenmaier
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2009-05-11
Filing date: 2010-03-18
Publication date: 2012-03-21
Anticipated expiration: 2030-03-18
Also published as: BRPI1014267A2; CN102439194A; CN102439194B; US20120103473A1; JP2012526203A; JP5930960B2; WO2010130484A3; DE102009002985A1; EP2430210B1; WO2010130484A2

Abstract

The invention relates to a method for carbonitriding at least one metal part in which the metal part is heated to a treatment temperature in a heating phase (1), is nitrided with a nitrogen donor gas in at least one nitriding phase (2a-2d) and is carburized with a carbon donor gas in at least one carburizing phase (3a-3d). Said method is characterised in that the first nitriding phase (2a) begins once the heating phase (1) has finished and prior to the beginning of the first carburizing phase (3a).

Description

5 description

title

Process for carbonitriding L O

The present invention relates to a process for carbonitriding at least one metal part.

Prior Art 15

Processes for the carbonitriding of metal parts are known from the publications DE 199 09 694 A1, DE 101 18 494 A1 and DE 103 22 255 A1.

The document DE 199 09 694 A1 describes a carbonitriding process, in which the diffusion of nitrogen throughout the process or at

Use of nitrogen as donor gas preferably takes place solely in the last process phase.

DE 101 18 494 C2 describes a low-pressure carbonitriding process in which steel parts are first carburized and then with a

Nitrogen donor gas to be embroidered.

The document DE 103 22 255 A1 describes a method for carburizing steel parts in which nitrogen-emitting gas is added both during the heating phase and during the diffusion phase.

However, by embroidering after or during the last carburizing phase, nitrogen is enriched only in a near-surface region having a smaller depth than the carburized region. As a result, the adhesion resistance, hardness, strength and wear resistance in the carburized

Range can not be increased sufficiently. On the other hand, nitriding during the heating phase leads to inhomogeneous tempering resistance, hardness, strength and / or wear resistance within the metal part or within a batch of metal parts. 5

The invention is therefore based on the object to provide a method for carbonitriding of metal parts, with which the tempering resistance and / or hardenability of a metal part can be improved and / or a depth of nitrogenation comparable to the carcass depth can be achieved. L O

Disclosure of the invention

This object is achieved by the process according to the invention for carbonitriding at least one metal part in which the metal part is heated to a treatment temperature in a heating phase, embroidered with a nitrogen donor gas in at least one nitriding phase and carburized in at least one carburizing phase with a carbon donor gas and characterized in that the first nitriding phase begins after the completion of the heating phase and before the beginning of the first carburizing phase.

The fact that the first nitriding phase begins only after the completion of the heating phase has the advantage that temperature gradients within the metal part or within a batch of several metal parts can be reduced and thus an inhomogeneous tempering resistance, hardness, strength and / or wear resistance within the metal part or within a batch of metal parts can be avoided.

The fact that the first carburizing phase is started only after the start of the nitriding phase has the advantage that the nitrogen introduced into the surface of the metal part can diffuse into the metal part over the entire further treatment period and increase the tempering resistance, hardness, strength and Wear resistance in the edge zone contributes.

35 In addition, the fact that the first carburizing phase starts only after the start of the nitridation phase involves nitrogen diffusion. accelerated carbon diffusion. This is because nitrogen atoms and carbon atoms can occupy the same interstices in the crystal lattice of the metal. By carrying out a carburizing phase following a nitriding phase, freed surface near-interstitial sites can be occupied by carbon atoms, thus making the effusion of nitrogen atoms and the associated nitrogen diffusion towards the surface more difficult. As a result, with the proposed process control, it is also possible to achieve a reduction in the known and known low-pressure nitrogen diffusion.

L O

Furthermore, the nitrogen can be introduced by the early supply of nitrogen relatively, for example, up to 1, 5 mm or even up to 6 mm, deep into the surface layer of the metal part. As a result, in metal parts, for example, with an operating temperature of up to 300 ⁰ C or even up to

15 350 ⁰ C, achieved an increase in tempering resistance in the edge region, sufficient hardness, strength and / or wear resistance achieved and / or a permanent function of the metal part can be ensured.

Furthermore, with the process according to the invention, an edge carbon concentration of ≥ 0.3 mass% to <0.7 mass% or even up to 1 mass%, and an edge nitrogen concentration of ≥ 0.1 mass% to <0.35 mass% or even from to to 0.5 mass percent can be achieved. In order to increase the tempering resistance, hardness, strength and / or wear resistance, in the area of carburizing steels, for example up to 1.5 mm or even up to 6 mm deep, advantageously a nitrogen concentration of at least 0.05% by mass, optionally of at least 0 , 15 percent by mass, to be achieved.

In particular, the method according to the invention can be used for carbonitriding the edge layer of a metal part. The inventive method can also be used for carbonitriding of several metal parts. For example, the method according to the invention can be used for carbonitriding one or more metallic workpieces.

The metal of the metal part can be both a metal and a metal alloy, for example steel. - A -

Within the scope of a further embodiment of the method according to the invention, the first nitriding phase ends, in particular directly before the first carburizing phase or during the first carburizing phase or with the first carburizing phase or after the first carburizing phase. In that the first

After the carburization phase directly adjoins the first nitridation phase or at least partially proceeds simultaneously with the first nitridation phase, the nitrogen effusion can be reduced or prevented during further carburizing phases, further nitriding phases or diffusion phases.

L O

Furthermore, the method according to the invention can have at least one second nitriding phase. This can occur, for example, after the first carburization phase. In particular, the second nitriding phase may begin following the first carburizing phase.

15

In the context of a further embodiment of the method according to the invention, the method has a temperature equalization phase between the heating phase and the first nitriding phase, in which the treatment temperature for equalizing the temperature in the metal part or

20 between a plurality of metal parts, in particular at a constant atmosphere, is kept constant. In this case, a constant atmosphere can be understood as meaning both a vacuum and a, preferably inert, gas atmosphere having a constant pressure and a constant composition. In particular, the temperature equalization phase subsequent to the heating phase may

25 se expire. The first nitriding phase can in turn follow the

Run off temperature equalization phase. The temperature uniformity phase may, for example, last at least 5 minutes, in particular 30 minutes. A temperature equalization phase has the advantage that temperature gradients within the metal part or within a batch of several me-

30 tallteilen can be further reduced and thus inhomogeneous tempering resistance, hardness, strength and / or wear resistance within the metal part or within a batch of metal parts can be further avoided.

35 In the phases following the temperature equalization phase, for example, nitriding phases, carburization phases and / or diffusion phases. sen, the treatment temperature can continue to be kept constant, in particular at the same treatment temperature as in the Temperaturvergleichfahrigungspha- se. An increase or decrease in the temperature in a subsequent treatment phase is conceivable, however. 5

Within the scope of a further embodiment of the method according to the invention, the method is carried out in a, in particular evacuable, treatment chamber.

In the context of a further embodiment of the method according to the invention, the method has at least one diffusion phase in which the treatment chamber is evacuated and / or filled with an inert gas, for example argon. The first diffusion phase may, for example, be between the first nitriding phase and the first carburizing phase or between the first

15 carburizing phase and the second nitriding phase.

Within the scope of a further embodiment of the method according to the invention, in addition to the first nitriding phase, the method has at least one further nitriding phase and / or at least one of the first carburizing phase

20, a further carburizing phase and / or at least one further diffusion phase in addition to the first diffusion phase. The further nitriding phases and / or further carburization phases can take place both in particular directly, one behind the other, for example alternately, as well as partially or completely simultaneously. By concurrent or consecutive succession of

25 ckungsphasen and Aufkohlungsphasen the carbon and nitrogen diffusion in the structure of the metal part can be advantageously increased. In addition, further diffusion phases can take place between the further nitriding phases and / or further carburizing phases. For example, a further carburizing phase may take place during or subsequent to another nitriding phase.

30 seconds or begin another nitriding phase during or after a carburizing phase. After completing these two phases, for example, another diffusion phase can then begin.

In the context of a further embodiment of the method 35 according to the invention, the nitrogen donor gas comprises a compound selected from the group consisting of ammonia, nitrogen and mixtures thereof, in particular amines. monia. In particular, the nitrogen donor gas may consist of a compound selected from the group consisting of ammonia, nitrogen and mixtures thereof, in particular ammonia.

In a further embodiment of the method according to the invention, the carbon donor gas comprises a compound selected from the group consisting of acetylene, ethylene, propane, propene, methane and mixtures thereof. In particular, the carbon donor gas may be a compound selected from the group consisting of acetylene, ethylene, propane, propene, L-O methane, and mixtures thereof.

Within the scope of a further embodiment of the process according to the invention, the process is a low-pressure carbonitriding process.

In the context of a further embodiment of the method according to the invention, the treatment temperature is in a range of ≥ 780 ⁰ C to <1050 ⁰ C, in particular from ≥ 780 ⁰ C to <950 ⁰ C.

Within the scope of a further embodiment of the process 20 according to the invention, a nitrogen donor gas partial pressure of less than 500 mbar, for example less than 100 mbar, in particular less than or equal to 50 mbar, for example less than 20 mbar, is present during the nitridation phases. During the carburizing phases, for example, a carbon donor gas partial pressure of less than 300 mbar, in particular less than 20 mbar, for example less than 10 mbar, may be present.

To compensate for nitrogen losses by nitrogen during a diffusion sequence, during or before, in particular the diffusion phase upstream, nitriding the temperature, for example, a

30 temperature which is within a range of 850 ⁰ C to 950 ⁰ C adapted / increased; and / or the nitrogen supply, for example by increasing the nitrogen donor gas partial pressure, for example to 50 mbar or 30 mbar, and / or the nitrogen donor gas volume flow rate, for example to 3000 l / h, are increased. In this way, the nitrogen concentration

35 in the near-surface region, for example from ≥ 0.1 mm to ≤ 0.2 mm or even up to 0.3 mm, higher than in the final product and a nitrogen be compensated. If the nitrogen concentration in a subsequent diffusion phase is now reduced due to nitrogen effusion and decreases, for example, to an edge nitrogen concentration of up to 0.5% by mass or, for example, 0.1% by mass to ≦ 0.35% by mass, an increase in tempering resistance and Hardenability on the surface advantageously still be guaranteed.

Another object of the present invention is a metal part, for example a metallic workpiece, in which the nitriding depth is greater than that

Carburizing depth is. Such a metal part can be produced by a method according to the invention. The advantage here is that the component can have a deep-reaching support effect under mechanical stress at elevated operating temperatures.

Another object of the present invention is a metal part, for example a metallic workpiece, produced by a method according to the invention. In particular, in such a metal part, the nitriding depth may be greater than the carburizing depth.

drawings

Further advantages and advantageous embodiments of the objects according to the invention are illustrated by the drawing and explained in the following description. It should be noted that the drawing has only descriptive character and is not intended to limit the invention in any way.

Fig. 1 shows a graph for schematically illustrating an embodiment of the method according to the invention.

In the context of the embodiment shown in FIG. 1, the method comprises a heating phase 1, a temperature equalization phase 4, four elevations. tion phases 2a, 2b, 2c, 2d, four carburization phases 3a, 3b, 3c, 3d and two diffusion phases 5a, 5b.

FIG. 1 shows that, during the heating phase 1, the temperature is maintained continuously at a constant heating rate, up to a treatment temperature of approx

950 ⁰ C is increased.

In the subsequent to the heating phase 1 temperature equalization phase 4, the treatment temperature is kept constant at about 950 ⁰ C. During the heating phase 1 and the temperature equalization phase 4, neither a nitrogen donor gas nor a carbon donor gas is supplied.

In the first nitriding phase 2a adjoining the temperature equalization phase 4, a nitrogen donor gas, for example ammonia, is supplied with a nitrogen donor gas partial pressure of about 50 mbar. The treatment temperature is kept constant at about 950 ^° C., as in the following nitriding phases 2b, 2c, 2d, carburizing phases 3a, 3b, 3c, 3d and diffusion phases 5a, 5b. The first nitriding phase 2 a is followed by a first carburizing phase 3 a in which the nitrogen donor gas partial pressure is reduced again to 0 mbar and the carbon donor gas partial pressure is increased to about 10 mbar. The first carburization phase 3a is followed by a first diffusion phase 5a, in which the carbon donor gas partial pressure is lowered again to 0 mbar. This can be done, for example, by evacuating the treatment chamber or filling the treatment chamber with an inert gas.

The first diffusion phase 5a is followed by a second carburizing phase 3b having a carbon donor gas partial pressure of about 10 mbar and a second nitriding phase 2b having a nitrogen donor gas partial pressure of about

50 mbar. Figure 1 shows that the second carburizing phase 3b and the second nitriding phase 2b start simultaneously. However, the second carburizing phase 3b is longer than the second nitriding phase 2b and thus ends only after the nitriding phase 2b. In the period in which both phases 2b, 3b proceed simultaneously, a carbon donor gas partial pressure of about 10 mbar and a

Nitrogen donor gas partial pressure of about 50 mbar ago. After completion of the second nitridation phase 2b, however, the nitrogen donor gas partial pressure is lowered to 0 mbar and the carbon donor gas partial pressure of about 10 mbar is maintained until the end of the second carburizing phase 3b. The second carburization phase 3b is followed by a second diffusion phase 5b in which the carburizing donor gas partial pressure is lowered again to 0 mbar.

The second diffusion phase 5b in turn is followed by a third carburizing phase 3c with a carbon donor gas partial pressure of about 10 mbar. Upon completion of the third carburizing phase 3c, the carbon donor gas

Lowered partial pressure to 0 mbar and it runs a third nitriding phase 2c with a nitrogen donor gas partial pressure of about 50 mbar. This is in turn followed by a fourth carburizing phase 3d, in which the nitrogen donor gas partial pressure is lowered to 0 mbar and the carbon donor gas partial pressure is increased to about 10 mbar. After completing the fourth carburizing phase 3d, the carbon donor gas partial pressure is lowered back to 0 mbar and a fourth nitridation phase 2d proceeds with a nitrogen donor gas partial pressure of about 50 mbar, which is very long compared to the previous nitriding phases 2a-2c , After this final nitriding phase 2d, the treatment temperature of 950 ^° C. is no longer maintained and quenching is carried out to room temperature to set the desired microstructural composition.

It goes without saying that numerous methods for carbonitriding are possible in this way and the invention is not based on the sequence described and

Number of four nitriding phases 2a, 2b, 2c, 2d, four carburization phases 3a, 3b, 3c, 3d and two diffusion phases 5a, 5b is limited.

Claims

5 claims

1. A method for carbonitriding at least one metallic metal part, in which the metal part

heated in a heating phase (1) to a treatment temperature L O,

- In at least one nitriding phase (2a-2d) is embroidered with a nitrogen donor gas, and

- is carburized in at least one carburizing phase (3a-3d) with a carbon donor gas,

15 characterized in that the first nitriding phase (2a) begins after completion of the heating phase (1) and before the start of the first carburizing phase (3a).

2. The method according to claim 1, characterized in that the first startup phase (2a) before the first carburizing phase (3a) or during the first carburizing phase (3a) or with the first carburizing phase (3a) or after the first carburizing phase (3a ) ends.

3. The method according to claim 1 or 2, characterized in that the drive 25 between the heating phase (1) and the first nitriding a Temperaturvergleichmäßigungsphase (4), in which the treatment temperature to equalize the temperature within the metal part or between a plurality of metal parts , especially at a constant atmosphere, is kept constant.

30

4. The method according to any one of claims 1 to 3, characterized in that the method is carried out in a, in particular evacuated, treatment chamber.

5. The method according to claim 4, characterized in that the method comprises at least one diffusion phase (5a, 5b), in which the treatment chamber is evacuated and / or filled with an inert gas.

5 6. The method according to claim 5, characterized in that the method in addition to the first nitriding phase (2a) at least one further Aufsti- ckungsphase (2b-2d) and / or next to the first carburizing phase (3a) at least one further carburizing phase (3b-3d ) and / or at least one further diffusion phase (5b) has LO in addition to the first diffusion phase (5a).

7. The method of claim 1, wherein the nitrogen donor gas comprises a compound selected from the group consisting of ammonia, nitrogen and mixtures thereof.

15

8. The method according to any one of claims 1 to 7, characterized in that the carbon donor gas comprises a compound selected from the group consisting of acetylene, ethylene, propane, propene, methane and mixtures thereof.

20

9. The method according to any one of claims 1 to 8, characterized in that the method is a low-pressure carbonitriding method.

10. The method according to any one of claims 1 to 9, characterized in that the treatment temperature is in a range of ≥ 780 ⁰ C to ≤ 1050 ⁰ C.

1 1. A method according to any one of claims 1 to 10, characterized in that during the nitriding phase (2a-2d) a nitrogen donor gas

30 partial pressure of less than 500 mbar is present.

12. Metal part where the nitriding depth is greater than the carburizing depth.

13. Metal part, produced by a method according to one of claims 1 to

35 1 1.