Title of Invention

METHOD FOR TREATING FERROUS ALLOY PARTS BY SULPHURIZATION

Abstract According to this method, the parts are immersed in a bath of an aqueous solution, without passage of an electric current, comprising caustic soda at concentrations of between 4 00 and about 1000 g/1, sodium thiosulphate at concentrations of between 30 and about 300 g/1, and sodium sulphide at concentrations of between 60 and about 120 g/1, said solution being heated to a temperature between about l00°C and 140°C for a period of between 5 and about 30 minutes.
Full Text The invention relates to a method for treating
metal surfaces and, more generally, surfaces of ferrous
alloy parts, in order to improve their resistance to
jamming.
Such treatments are perfectly familiar to a person
skilled in the art and widely used in designing
mechanical elements, for example when parts have to rub
against one another under severe load and pressure
conditions. These treatments can also apply, or be
applied, both in cases of lubrication (with oil,
grease, etc.) and in cases of the absence of such
lubrication.
Various methods have been proposed to form, on the
surface of the ferrous alloy parts, compounds suitable
for improving interactions with the environment.
The various known treatment methods include
superficial oxidation methods which are suitable for
improving the corrosion resistance. Also known are
tool phosphatization methods which, by creating a
superficial layer of iron phosphate, are used to
improve the effects of lubrication in substantial
proportions.
Finally, sulphurization treatment methods are
known.
The invention relates more particularly to the
latter type of treatment.
The sulphurization of steels and the effects of a
superficial layer of iron sulphide on lubrication are
perfectly familiar to a person skilled in the art and,
for example, appear from the teaching of Patents FR 1
406 530 and FR 2 823 227.
According to the teaching of Patent FR 1 406 530,
the treated metal parts are immersed in a bath of
ionized molten salt. This electrolytic sulphurization
with molten salts can pose a threat to the environment.


According to the teaching of Patent FR 2 823 227,
an iron sulphide coating having an appropriate
thickness and Fe/S ratio is deposited on the part to be
treated, the coating being selected from those of which
the surface has a fractal dimension of at least 2.6.
Here also, the method employs electrolytic
sulphurization, v/hich can create technical constraints
limiting its productivity. It may also be observed
that the salts used are expensive.
Another solution appears from the teaching of
Patent US 6 139 973 which relates to a method used to
deposit iron sulphide by cathodic electrolysis of an
aqueous solution. Among the drawbacks, apart from the
limitations inherent in the electrolytic method
pertaining to the shape of the parts to be treated, it
appears that the Fe/S layer is not obtained by chemical
reaction, but deposited on the steel surface, and this
raises real problems of adhesion.
The problem that the invention proposes to solve
is to reduce the toxicity, on the one hand, and to
avoid the use of electrolysis, on the other, so that
the energy needed is limited to maintaining the aqueous
solution at a predetermined temperature.
It is also observed that the absence of current
flow makes it possible to control the composition,
thickness and continuity of the superficial layers with
great accuracy and high reproducibility, and also makes
it possible to treat parts of complex shape, including
those with cavities (bores, blind holes, gears, etc.).
To solve such a problem, a method has been
designed and developed for treating ferrous alloy parts
by sulphurization, whereby the parts are immersed in a
bath of an aqueous solution, without the passage of an
electric current, heated to a temperature between about
100°C and 140°C for a period of between 5 and abcut 30
minutes. The bath of aqueous solution has
concentrations of caustic soda, sodium thiosulphate and
sodium sulphide.


Caustic soda is corrosive to ferrous alloy parts
and' allows the liberation of Fe2+ and Fe3+ ions
necessary for the precipitation of a layer of iron
sulphide on the parts. The sulphur component of the
thiosulphate also allows the precipitation of this
layer of iron sulphide. Finally, iron sulphide is also
an important agent in the sulphurization method.
Advantageously, the sulphurizing power of the bath
requires the presence of caustic soda in concentrations
between 400 and 1000 g/1, of sodium thiosulphate in
concentrations between 30 and 300 g/1, and of sodium
sulphide in concentrations between 60 and 120 g/1.
Advantageously, the bath working temperature is
between about 120°C and 14 0°C. For the sake of
simplification, it is possible to work at the boiling
point, which depends on the composition of the aqueous
solution.
The resistance to jamming resulting from the
treatment method according to the invention is
evaluated by the test on the Faville Levally machine
according to standard ASTM-D-2170.
In a manner perfectly known to a person skilled in
the art, this test consists in treating a case-
hardened, quenched and ground 16NC6 steel cylindrical
test specimen 6.35 mm in diameter and 50 mm in height.
The specimen is clamped between two jaws cut in a
right-angled V to which a load is applied increasing
linearly as a function of time. The test is stopped
when jamming or flow of the specimen occurs. This test
is characterized by a quantity called the Faville
grade, which is the integral of the load applied with
respect to time, this grade being expressed in daN.s.
In this respect, it has appeared that, when the
specimen is treated by the method according to the
invention, the Faville grade must be higher than 12 000
daN.s and the specimen must have flowed and not jammed.
Reference is made below to the non-limiting
examples provided for information, which show the
results obtained with the features of the method


according to the invention, in comparison with
treatments according to the prior art.
Example 1
In this example, a comparison is made between the
Faville grade of test specimens of case-hardened,
quenched 16NC6 steel, in the case of an untreated
specimen (1), a phosphatized specimen (2), an oxidized
specimen (3), a specimen according to the method of the
invention (4) . The results are given in the table
below:

The specimen treated according to the invention is
quenched in an aqueous solution containing, on the
preparation of the bath, 775 g/1 of caustic soda,
200 g/1 of sodium thiosulphate and 90 g/1 of sodium
sulphide. The treatment is carried out at 13 0°C for 15
minutes.
It appears from this test that solutions 1, 2 and
3 do not impart any anti-jamming property to the part,
whereas solution 4, according to the invention, is
characterized by a high anti-jamming effect,
considering that the Faville grade is multiplied by 3.
Example 2:
In this example, a comparison is made between the
Faville test specimens of case-hardened, quenched 16NC6
steel, sulphurized by the method according to the
invention (1) and by the electrolytic method, as it
appears from the teaching of Patent FR 2 823 227. The
results are given in the table below:


The specimen according to the invention is treated
in an aqueous solution containing, on preparation of
the bath, 775 g/1 of caustic soda, 200 g/1 of sodium
thiosulphate and 90 g/1 of sodium sulphide.
The treatment was carried out at 13 0°C for 15
minutes.
It appears from these tests that solutions 1 and 2
have anti-jamming properties and that the specimen
sulphurized according to the method of the invention
(1) presents a 36% improvement in anti-jamming
behaviour.
Example 3:
In this example, all the specimens are treated in
aqueous solution by varying the temperature and initial
concentrations of caustic soda (NaOH), sodium
thiosulphate (Na2S2O3), sodium sulphide (Na2S) .
The results are given in the table below:


It appears from this table that:
- Solution 1 conforms to the desired features given
the preparation conditions and the grade of the
Faville test.
Solutions 2 and 3 do not conform, considering
their initial concentrations of sodium
thiosulphate and sodium sulphide. These two
examples illustrate the synergistic effect of
thiosulphates and sulphides for the treatment of
steels.
Solution 4, which is similar to solution 1 as
regards the composition of the aqueous solution,
does not conform because of the treatment
temperature, which is too low for reactions on the
specimen to take place effectively and to impart a
resistance to jamming.
Solution 5 yields a satisfactory result in terms
of anti-jamming properties, despite a different
bath composition to that of solution 1.
Solution 6 does not produce a satisfactory anti-
jamming response because the caustic soda
concentration is too low.
According to the features of the invention, it is
observed that the parts, treated according to the
claimed method, have oxygen in the different layers.
The advantages clearly appear from the
description, and the following features are emphasized
and repeated:
respect for the environment;
very accurate and highly reproducible control of
the composition, thickness and continuity of the
superficial layers;
the absence of current flow making it possible, in
particular, to treat parts of complex shape,
including those having cavities.

We claim :-
1. Method for treating ferrous alloy parts by-
sulphur izat ion, characterized in that the parts are
immersed in a bath of an aqueous solution, without the
passage of an electric current, comprising caustic soda
at concentrations of between 400 and about 1000 g/1,
sodium thiosulphate at concentrations of between 3 0 and
about 300 g/1, and sodium sulphide at concentrations of
between 60 and about 120 g/1, said solution being
heated to a temperature between about 100°C and 140°C
for a period of between 5 and about 3 0 minutes.
2. Method according to Claim 1, characterized in that
the bath working temperature is between about 12 0°C and
140°C and is preferably about 130°C.
3. Method according to Claim 1, characterized in that
the immersion time is preferably about 15 minutes.
4. Parts treated according to the method according to
any one of Claims 1 to 3.

According to this method, the parts are immersed
in a bath of an aqueous solution, without passage of an
electric current, comprising caustic soda at
concentrations of between 4 00 and about 1000 g/1,
sodium thiosulphate at concentrations of between 30 and
about 300 g/1, and sodium sulphide at concentrations of
between 60 and about 120 g/1, said solution being
heated to a temperature between about l00°C and 140°C
for a period of between 5 and about 30 minutes.

Documents:

00767-kolnp-2006-abstract.pdf

00767-kolnp-2006-claims.pdf

00767-kolnp-2006-description complete.pdf

00767-kolnp-2006-form 1.pdf

00767-kolnp-2006-form 3.pdf

00767-kolnp-2006-form 5.pdf

00767-kolnp-2006-international publication.pdf

00767-kolnp-2006-international search report.pdf

00767-kolnp-2006-others.pdf

767-kolnp-2006-granted-abstract.pdf

767-kolnp-2006-granted-claims.pdf

767-kolnp-2006-granted-correspondence.pdf

767-kolnp-2006-granted-description (complete).pdf

767-kolnp-2006-granted-examination report.pdf

767-kolnp-2006-granted-form 1.pdf

767-kolnp-2006-granted-form 18.pdf

767-kolnp-2006-granted-form 2.pdf

767-kolnp-2006-granted-form 26.pdf

767-kolnp-2006-granted-form 3.pdf

767-kolnp-2006-granted-form 5.pdf

767-kolnp-2006-granted-reply to examination report.pdf

767-kolnp-2006-granted-specification.pdf

767-kolnp-2006-granted-translated copy of priority document.pdf

767-KOLNP-2006-PRIORITY DOCUMENT.pdf


Patent Number 235988
Indian Patent Application Number 767/KOLNP/2006
PG Journal Number 37/2009
Publication Date 11-Sep-2009
Grant Date 10-Sep-2009
Date of Filing 30-Mar-2006
Name of Patentee H.E.F
Applicant Address RUE BENOIT FOURNEYRON F-42160 ANDREZIEUX BOUTHEON
Inventors:
# Inventor's Name Inventor's Address
1 HEAU, CHRISTOPHE 22 RUE VOLTAIRE F-42100 SAINT- ETIENNE
2 MAURIN-PERRIER, PHILIPPE 17 RUE ANTOINE DUPUY, F-42680 SAINT MARCELLIN EN FOREZ
PCT International Classification Number C23C 18/16
PCT International Application Number PCT/FR2004/050487
PCT International Filing date 2004-10-06
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 03/12,200 2003-10-14 France