U.S. patent application number 14/354418 was filed with the patent office on 2017-08-24 for method for low-pressure carbonitriding having an extended temperature range in an initial nitridation phase.
This patent application is currently assigned to ECM Technologies. The applicant listed for this patent is ECM Technologies. Invention is credited to Yves Giraud, Philippe Lapierre, Jerome Lardinois, Alfred Rallo.
Application Number | 20170241008 14/354418 |
Document ID | / |
Family ID | 47018193 |
Filed Date | 2017-08-24 |
United States Patent
Application |
20170241008 |
Kind Code |
A9 |
Lapierre; Philippe ; et
al. |
August 24, 2017 |
METHOD FOR LOW-PRESSURE CARBONITRIDING HAVING AN EXTENDED
TEMPERATURE RANGE IN AN INITIAL NITRIDATION PHASE
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.degree. C. to 750.degree. C. to a temperature between
860.degree. and 1000.degree. 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).
Inventors: |
Lapierre; Philippe;
(Valentigney, FR) ; Lardinois; Jerome; (Courcelles
Les Montbeliard, FR) ; Giraud; Yves; (Jarrie, FR)
; Rallo; Alfred; (Crolles, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ECM Technologies |
Grenoble Cedex |
|
FR |
|
|
Assignee: |
ECM Technologies
Grenoble Cedex
FR
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140238549 A1 |
August 28, 2014 |
|
|
Family ID: |
47018193 |
Appl. No.: |
14/354418 |
Filed: |
October 8, 2012 |
PCT Filed: |
October 8, 2012 |
PCT NO: |
PCT/EP2012/069888 PCKC 00 |
371 Date: |
April 25, 2014 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 8/32 20130101; C23C
8/02 20130101; C23C 8/34 20130101; C23C 8/80 20130101 |
International
Class: |
C23C 8/32 20060101
C23C008/32 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2011 |
FR |
1159878 |
Claims
1. A low-pressure carbonitriding method of steel parts,
particularly parts used to manufacture automobile vehicles,
comprising alternative cementation and nitriding steps, preceded by
a heating step comprising a simple heating phase followed by an
initial nitriding phase during which the heating is carried on, and
followed by a quenching step, wherein the initial nitriding phase
is carried out from a temperature in the range from 700.degree. C.
to 750.degree. C. and up to a temperature in the range from
860.degree. C. to 1,000.degree. C.
2. The low-pressure carbonitriding method of claim 1, wherein the
initial nitriding phase is immediately followed by a first
cementation step.
3. The low-pressure carbonitriding method of claim 1, wherein
during the initial nitriding phase, the heating is carried out with
a decreased temperature gradient as compared with the simple
heating phase.
4. The low-pressure carbonitriding method of claim 3, wherein
during the initial nitriding phase, the heating is carried out with
a temperature gradient in the range from 3.5.degree. C./min to
16.degree. C./min.
5. The low-pressure carbonitriding method of claim 3, wherein the
simple heating phase is carried out with a temperature gradient in
the range from 8.degree. C./min to 70.degree. C./min.
6. The low-pressure carbonitriding method of claim 3, wherein the
initial nitriding phase comprises a temperature stage.
7. The low-pressure carbonitriding method of claim 1, wherein it
comprises a final nitriding step accompanied by a cooling
immediately before the quenching.
8. The low-pressure carbonitriding method of claim 7, wherein the
cooling is carried out down to a temperature between 900.degree. C.
and 800.degree. C.
9. The low-pressure carbonitriding method of claim 7, wherein the
cooling is carried out with a temperature gradient between
10.degree. C./min and 1.degree. C./min.
10. The low-pressure carbonitriding method of claim 7, wherein the
final nitriding step comprises a temperature stage.
Description
[0001] The present invention claims priority of French application
1159875 filed on Oct. 31, 2011 having its content (text, drawings,
and claims) incorporated herein by reference.
[0002] The present invention relates to a method of low-pressure
carbonitriding of steel parts, particularly, although not
exclusively, parts used in the manufacturing of automobile
vehicles. In particular, the invention also applies to parts used
in the manufacturing of agricultural machines, machine tools, or
parts in the aeronautical field.
BACKGROUND OF THE INVENTION
[0003] A method of low-pressure carbonitriding of steel parts
comprises alternate steps of cementation and nitriding at constant
temperature, preceded by a heating step and by a temperature
equalization step, and followed by a quenching step, is known from
document EP 1885904. As a variation, it is provided to inject a
nitriding gas during the heating step and/or during the temperature
equalization step, from a 800.degree. C. temperature. Obiect of the
invention
[0004] The present invention aims at improving the method of the
previously-mentioned document, that is, improving the quality of
the obtained parts, preferably with a decrease of the treatment
time.
BRIEF DESCRIPTION OF THE INVENTION
[0005] To achieve this aim, the present invention provides a method
of low-pressure carbonitriding of steel parts, particular part used
in the manufacturing of automobile vehicles, comprising alternated
steps of cementation and nitriding at constant temperature,
preceded by a heating step comprising a simple heating phase
followed by an initial nitriding phase during which the heating is
carried on, and followed by a quenching step, wherein the initial
nitriding phase is carried out from a temperature in the range from
700.degree. C. to 750.degree. C. and up to a temperature in the
range from 860.degree. C. to 1,000.degree. C.
[0006] Thus, without increasing the duration of the heating step,
the nitrogen enrichment which is performed in conditions promoting
a good nitriding is increased, whereby it is possible to shorten or
to suppress one of the subsequent nitriding steps and to thus
decrease the total treatment time.
[0007] According to an advantageous version of the invention, the
initial nitriding phase is immediately followed by a first
cementation step. Thus, the total suppression of the temperature
equalization phase enables to lengthen the initial nitriding phase
in a temperature range optimal for nitriding.
[0008] According to another advantageous aspect of the invention,
during the initial nitriding step, the heating is carried out with
a decreased temperature gradient as compared with the simple
heating phase. Thus, the treatment time in a temperature range
optimal for nitriding is further increased.
[0009] According to still another advantageous aspect of the
invention, the method comprises a final nitriding step accompanied
by a cooling immediately before the quenching. Thus, the final
nitriding step is also carried out in an optimal temperature range,
so that the quality of the treatment is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing and other objects, features, and advantages
will appear on reading of the following description of different
specific non-limiting embodiments of the low-pressure
carbonitriding method according to the invention, in relation with
the 3 appended drawings which are simplified diagrams illustrating
the different steps of the method according to the invention
according to different embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Referring to FIG. 1, the method according to the invention
comprises a first heating step comprising a first simple heating
phase M, illustrated by a continuous straight line, from the
ambient temperature to a point at a 700.degree. C. temperature,
noted Nil in the drawing. According to the composition of the steel
to be treated, the simple heating phase may be carried out until a
temperature in the range from 700.degree. C. to 750.degree. C. is
reached, and has a duration in the range from 10 min to 90 min,
that is, the simple heating is carried out with a temperature
gradient in the range from 8.degree. C./min to 75.degree.
C./min.
[0012] The method then comprises an initial nitriding phase Ni
during which the heating is continued up to a 940.degree. C.
temperature in the illustrated example. In practice, the
940.degree. C. temperature corresponds to a compromise between a
860.degree. C. temperature, which enables to achieve a treatment of
better quality and a 1,000.degree. C. temperature, which enables to
perform a faster treatment.
[0013] In the embodiment of FIG. 1, corresponding to a first
embodiment of the initial nitriding phase, the heating carries on
regularly but with a temperature gradient in the range from
3.5.degree. C./min and 16.degree. C./min smaller than the
temperature gradient during the simple heating. The duration of the
initial nitriding phase is in the range from 15 min to 45 min,
according to the quantity of nitrogen which is desired to be fixed
in this initial step and to the composition of the steel to be
treated.
[0014] As known per se, the initial nitriding phase comprises
phases of injection of a nitriding gas such as ammonia alternating
with diffusion phases.
[0015] According to a second embodiment of the initial nitriding
phase, illustrated in FIG. 2, the heating carries on with the same
temperature gradient as during the simple heating up to a point at
a temperature in the range from 750.degree. C. to 850.degree. C.,
here 800.degree. C., noted Ni2 in FIG. 2. The temperature is then
maintained at a stage until a time noted Ni3 in FIG. 2, from which
a strong heating is achieved to reach the cementation temperature.
The stage temperature is selected in a way known per se to perform
the initial nitriding phase in optimal conditions given the
composition of the parts to be treated. It should be noted, on this
regard, that given the stage, the final heating may be performed
very rapidly, for example from 80.degree. C./min to 100.degree.
C./min without submitting the parts to inacceptable stress.
[0016] According to a third embodiment of the initial nitriding
phase, illustrated by means of FIG. 3, the heating carries on from
point Ni1 with a lower temperature gradient than in the first
embodiment, preferably in a range from 2.degree. C./min to
8.degree. C./min, until a time noted Ni4, here corresponding to a
850.degree. C. temperature, from which a strong heating is achieved
to reach the cementation temperature, according to a gradient
similar to that of the second embodiment.
[0017] Whatever the embodiment used for the initial nitriding
phase, the method then comprises n cementation phases alternating
with nitriding phases. As known per se, the cementation and
nitriding steps comprise phase of injection of a treatment gas
alternating with diffusion phases, not shown in the drawings. In
the drawing, the diagram has been interrupted between nitriding
step N1 and last cementation step Cn. At the end of this last
cementation step Cn, the method comprises a final nitriding step Nn
accompanied by a cooling immediately before quenching T.
[0018] According to a first embodiment of last nitriding step Nn,
illustrated by a short-dashed line in the drawing, the cooling is
achieved continuously down to a temperature in the optimal
temperature range for the nitriding while remaining sufficiently
high to allow an efficient quenching. In the illustrated example,
the final temperature before quenching is 840.degree. C. In
practice, satisfactory results are obtained for a final temperature
before quenching in the range from 900.degree. C. to 800.degree. C.
It has been observed that such a limited temperature decrease
decreases the stress on parts during the quenching.
[0019] The final nitriding step has a duration preferably between
15 min and 60 min, which corresponds to a temperature gradient in
the range from 10.degree. C./min to 1.degree. C./min. In the same
way as for the initial nitriding phase, the final nitriding step
preferably comprises phases of injection of a nitriding gas
alternating with diffusion phases.
[0020] According to a second embodiment of last nitriding step Nn,
illustrated in FIG. 2 by a long-dashed line in the drawing, the
cooling is first strong, with as large a gradient as possible
without generating undue stress in the steel down to the optimal
nitriding temperature for the steel being treated, noted Nnl in the
drawing, here 840.degree. C., after which the temperature is
maintained at a stage until the beginning of the quenching.
[0021] In practice, the method according to the invention may be
implemented by combining any of the embodiments of the initial
nitriding phase with any of the embodiments of the final nitriding
phase, or even ending the treatment cycle conventionally, that is,
with a quenching performed directly from the cementation
temperature.
[0022] It should be noted that due to the increased efficiency of
the nitriding phases according to the invention, it is possible to
replace at least one nitriding step comprised between two
cementation steps with a simple diffusion step. Such a step is
shorter than a nitriding step so that the total treatment time is
shortened.
[0023] Of course, the invention is not limited to the described
embodiment and alternative embodiments may be applied thereto
without departing from the framework of the invention such as
defined in the claims. In particular, the initial heating may be
carried out according to a constant gradient, as illustrated by a
dotted line in the drawing. In this case, it should however be
noted that the nitriding phase has a shortened duration, as
illustrated by a stripe-dot line in the drawing.
[0024] Due to the small temperature gradient during the initial
nitriding phase, it has been experienced that the temperature of
the parts to be treated has time to equalize so that it is possible
to suppress the equalizing step provided in the
previously-mentioned document. If necessary, for example, due to a
specific configuration of the parts to be treated, a short
temperature equalization step may however be provided between the
initial nitriding phase and the first cementation step.
* * * * *