# US 9,765,422 B2 · Method for low-pressure carbonitriding having an extended temperature range in an initial nitridation phase

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- Number: US 9,765,422 B2
- Document ID: US9765422B2
- Status: Granted
- Kind: B2
- Application number: 14/354,418
- Filed: 2012-10-08
- Published: 2014-08-28
- Granted: 2017-09-19
- Earliest claimed: 2011-10-31
- Assignees: ECM Technologies
- Applicants: ECM Technologies
- Inventors: Philippe Lapierre; Jerome Lardinois; Yves Giraud; Alfred Rallo
- Web page: https://patentgrep.com/patent/US9765422B2

## CPC

- C23C 8/32: of ferrous surfaces
- C23C 8/02: Pretreatment of the material to be coated (C23C8/04 takes precedence)
- C23C 8/34: more than one element being applied in more than one step
- C23C 8/80: After-treatment
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)

## Abstract

A method for the low-pressure carbonitriding of steel parts, in particular parts used in the manufacture of automobiles comprises a heating step that includes a simple heating phase (M) followed by an initial nitridation phase (Ni) from a temperature between 700° C. to 750° C. to a temperature between 860° C. and 1000° C. and carried out using a reduced temperature gradient relative to the simple heating phase. Additionally, alternate cementing (C1-Cn) and nitridation (N1-Nn) steps are performed at constant temperature, wherein the final nitridation step is accompanied with a decrease in temperature immediately before quenching (T).

## Claims

### Claim 1

A low-pressure carbonitriding method of steel parts comprising alternating cementation and nitriding steps, preceded by a step of increasing temperature comprising a continuously increasing temperature phase followed by an initial nitriding phase during which the increase of temperature is continued, and followed by a quenching step, wherein the initial nitriding phase is carried out from a first temperature in the range from 700° C. to 750° C. increasing up to a second temperature in the range from 860° C. to 1,000° C.

### Claim 2 (depends on 1)

The low-pressure carbonitriding method of claim 1, wherein the initial nitriding phase is immediately followed by a first cementation step.

### Claim 3 (depends on 1)

The low-pressure carbonitriding method of claim 1, wherein during the initial nitriding phase, the increase of temperature is carried out with a decreased temperature gradient as compared with the continuously increasing temperature phase.

### Claim 4 (depends on 3)

The low-pressure carbonitriding method of claim 3, wherein during the initial nitriding phase, the increase of temperature is carried out with a temperature gradient within a range of temperature gradients from 3.5° C./min to 16° C./min.

### Claim 5 (depends on 3)

The low-pressure carbonitriding method of claim 3, wherein the continuously increasing temperature phase is carried out with a temperature gradient within a range of temperature gradients from 8° C./min to 70° C./min.

### Claim 6 (depends on 3)

The low-pressure carbonitriding method of claim 3, wherein the initial nitriding phase comprises a temperature plateau.

### Claim 7 (depends on 1)

The low-pressure carbonitriding method of claim 1, wherein it comprises a final nitriding step accompanied by a cooling immediately before the quenching.

### Claim 8 (depends on 7)

The low-pressure carbonitriding method of claim 7, wherein the cooling is carried out down to a temperature between 900° C. and 800° C.

### Claim 9 (depends on 7)

The low-pressure carbonitriding method of claim 7, wherein the cooling is carried out with a temperature gradient within a range of temperature gradients from 10° C./min to 1° C./min.

### Claim 10 (depends on 7)

The low-pressure carbonitriding method of claim 7, wherein the final nitriding step comprises a temperature plateau.