MELANGE DE POUDRES METALLIQUES

METAL-POWDER BLEND

Abrégé anglais

The invention is based on the object to
provide a metal powder mixture which is simple to
manufacture and makes possible the manufacture of
high-strength.and wear-resistant cylinder parts with
low dimensional deviations. This metal powder
mixture is composed of a steel powder which is
obtained by atomizing a melt and is mixed with
0.3-0.7% by wt. graphite, wherein the steel alloy
powder is composed of (% by wt.)
max. ~0.02 ~% C
max. ~0.03 ~% Si
0.05 - 0.25 ~~% Mn
2.5 - 5.0 ~~% Ni
0.2 - 1.5 ~~% Mo
the remainder being iron and the usual
impurities
and the mixture contains finely particulate Cu in an
amount of 0.7-1.5% with the requirement that the
ratio of quantities of Cu:graphite is in the range
of 1.4-2.5.

Revendications

7
CLAIMS:
1. A method of manufacturing high-strength sintered
parts by sintering compacts which have been manufactured
from steel alloy powder containing Ni additionally
comprising (in % by wt.)
max. 0.02 % C
max. 0.03 % Si
0.05 - 0.25 % Mn
0.2 - 1.5 % Mo
the remainder being iron and the usual impurities wherein
(i) finely particulate Cu in an amount of 0.7-1.5% and
graphite in an amount of 0.3-0.7% have been added to the
steel alloy powder; (ii) the Ni content of the steel alloy
powder which was produced by spraying a steel melt with
water is greater than 2.5 to at most 5.0%; (iii) the ratio
of quantities of Cu:graphite is maintained in the range of
1.4-2.5; and (iv) the sintered parts undergo martensite full
hardening by being cooled in air or under a gas spray
without subsequent heat treatment following sintering.
2. A method according to claim 1, wherein the Ni
content is maintained in the range of 3.0-4.0%.
3. A metal powder mixture for use in the method
according to claim 1, manufactured from a steel alloy
containing Ni with (in % by wt.)
max. 0.02 % C
max. 0.03 % Si
0.05 - 0.25 % Mn

8
0.2 - 1.5 % Mo
the remainder being iron and the usual impurities, with an
addition of finely particulate Cu in an amount of 0.7-1.5%
and graphite in an amount of 0.3-0.7%, wherein the steel
powder produced by spraying with water has an Ni content of
greater than 2.5 to at most 5.0%, and wherein the ratio of
quantities of Cu:graphite is maintained in the range of 1.4-
2.5.
4. A metal powder mixture according to claim 3,
wherein the Mn content is limited to values of 0.10 to
0.20%.
5. A metal powder mixture according to claim 3 or 4,
wherein the Ni content is limited to 3.0-4.0%.
6. A metal powder mixture according to any one of
claims 3-5, wherein the Mo content is limited to values of
0.5-1.0%.
7. A metal powder mixture according to any one of
claims 3-6, wherein the graphite addition is limited to 0.5-
0.6%.
8. A metal powder mixture according to any one of
claims 3-7, wherein the ratio of Cu:graphite is 2.

Description

CA 02074193 2002-04-30
20337-414
1
METHOD OF MANUFACTURING HIGH-STRENGTH
SINTERED PARTS AND METAL POWDER MIXTURE
The invention relates to a method of manufacturing
high-strength sintered parts by sintering compacts which
have been manufactured from a steel alloy powder containing
Ni additionally comprising (in % by wt.)
max. 0.02 % C
max. 0.03 % Si
0.05 - 0.25 % Mn
0.2 - 1.5 % Mo
the remainder being iron and the usual impurities, wherein
(i) finely particulate Cu in an amount of 0.7-1.5% and
graphite in an amount of 0.3-0.7% have been added to the
steel alloy powder;(ii) wherein the Ni content of the steel
alloy powder which was produced by spraying a steel melt
with water is greater than 2.5 to at most 5.0%; (iii) the
ratio of quantities of Cu:graphite is maintained in the
range of 1.4-2.5; and (iv) the sintered parts undergo
martensite full hardening by being cooled in air or under a
gas spray without subsequent heat treatment following
sintering.
Additionally, the invention also relates to a
metal powder mixture for use in the method of the present
invention manufactured from a steel allay containing Ni with
(in % by weight)
max. 0.02 % C
max. 0.03 % Si

CA 02074193 2002-04-30
20337-414
la
0.05 - 0.25 % Mn
0.2 - 1.5 % Mo
the remainder being iron and the usual impurities, with an
addition of finely particulate Cu in an amount of 0.7-1.5%
and graphite in an amount of 0.3-0.7%, wherein the steel
powder produced by spraying with water has an Ni content of
greater than 2.5 to at most 5.0%, and wherein the ratio of
quantities of Cu: graphite is maintained in the range of 1.4-
2.5.
A steel alloy powder for manufacturing high-
strength sintered parts is known from EP 0 136 169 B1. The
steel alloy powder is composed of (% by wt.)
max. 0.02 % C
max. 0.1 % Si
0.4 - 1.3 % Ni
0.2 - 0.5 % Cu
0.1 - 0.3 % Mo
max. 0.3 % Mn
max. 0.01 % N
the remainder being iron and the usual impurities.

2~~t~~.~
(~:f r. _ 2 _
1 This alloy powder is to be inexpensive to
2 manufacture and to process, is to have good pressing
3 properties, and is to ensure a high strength in the
4 sintered finished part. The reference does not
discuss in detail the properties of the finished
6 part with respect to the obtainable accuracy to size
7 of the finished part.
8 When a compact manufactured of steel
9 powder is sintered, its geometry usually changes.
This is called shrinkage due to sintering. This
11 effect is counteracted by martensitic hardening
12 essentially because of the attendant increase in
13 volume due to structural transformation. Of course,
14 a volumetric change of the finished part compared
to
the compact used for sintering can also be taken
16 into consideration when dimensioning the pressing
17 die, i.e., it is attempted to anticipate the
18 dimensional deviations and to compensate the
19 deviations by changing the dimensions of the compact
from the beginning. However, this was only very
z1 incompletely achieved in the past, not only because
22 the relative dimensional deviations depend on the
23 respective wall thicknesses of the compact, but also
24 because the relative dimensional deviations are
significantly influenced by the density obtained in
26 the compact which is subject to significant
27 variations within the same compact and also between
28 individual compacts which are otherwise the same.
29 Consequently, the efforts for obtaining a
dimensional constancy in the sintered finished part
31 of finished alloy materials have in the past only
32 resulted in a reproducible limitation of the
33 dimensional deviations in the most favorable case
to
34 values of approximately 0.1%. Such deviations are
no longer tolerable for many parts. For this
36 reason, sintered parts are frequently subjected to
37 a final calibration procedure which is very
38 expensive. However, this calibration procedure
39 cannot even be carried out in hardened parts because
of the hardness of the sintered parts.
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r.:.
,. . ., -2A-
1 A sinter alloy in which the Ni content is at most
2 2.5% is known from EP 0 042 654. This content is of
3 significance in connection with the Mo content for
4 the possibility of air hardening. However, the
highest limit of 0.7% Mo disclosed in this reference
6 cannot be carried out. In this alloy, the improved
7 strength is obtained by a special heat treatment
8 after sintering.
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CA 02074193 2000-11-14
3
It is the object of the invention to provide a metal
powder mixture which is as simple as possible to manufacture
and permits the manufacture of high-strength and wear-resistant
sintered parts whose dimensional deviations can be kept within
a tolerance range having a width of at most tD.05% without
requiring additional structural measures in the pressing tool
for the manufacture of compacts to be sintered. Accordingly,
it should be a property of the metal powder not to result in
significant shrinkage or growth when compacts manufactured by
conventional compacting are sintered.
This object is met by a method and a metal powder
mixture having the features recited above. Advantageous
further developments of this mixture are the preferred Mn
content of the mixture is 0.10 to 0.20%, the preferred Ni
content of the mixture ~is 3.0 to 4.0%, the preferred Mo content
of the mixture is 0.5 to 1.0%, the preferred graphite content
is 0.5 to 0.6% and the preferred ratio of Cu:graphite is 2.
Contrary to the steel alloy powder known from EP 0
136 169 B1, the present invention provides that the Cu content
is not already introduced in the alloy used for atomizing, but
is admixed in finely distributed form to the steel powder. In
addition, in accordance with the invention, the quantitative
contents of the individual alloy elements are maintained within
different limits than in the known steel powder. It is
25~ particularly important that the ratio of the Cu content
relative to the graphite content which is also introduced into
the metal powder mixture in powder form as carbon is maintained
in the range of 1.4-2.5, preferably 2Ø When observing all
requirements of the invention, it is surprisingly possible to
manufacture compacts by using the usual compressing procedures
of powder metallurgy which, again under the usual sintering

CA 02074193 2000-11-14
3a
conditions, have almost complete dimensional constancy
independently of the wall thicknesses of the compacts. The
dimensional deviations are less than ~0.05.

. .
... ;
When the sintered parts are cooled in air
or by means of a gas shower (for example, inert gas
supplied under pressure) arranged in the cooling
zone of a sintering =urnace, a completely
martensitic structure is obtained in the sintered
parts which imparts a high-strength (more than
750 N/mmZ) to the parts without requiring a
subsequent heat treatment.
The invention shall be described in more
detail with the aid of the following example.
A steel powder having the following
composition (% by wt.) was produced by water
atomizing of a melt.
0.01 % C
0.02 % Si
0.10 % Mn
4.0 % Ni
0.5 % Mo
0.020 % P
0.010 % S
the remainder being iron and the usual
impurities.
After water atomizing of the melt, the
steel powder was dried and subjected at
approximately 1,000°C to reduction annealing in an
Hz atmosphere. After cooling, the resulting
agglomerate was ground into fine particles. The
residual oxygen content of the steel powder was
approximately 0.15% and its apparent density was
approximately 3 g/cm3.
Subsequently, added to this steel powder
were 0.60% graphite powder and 1.0% finely
G:\MJM\3245158P.PAT

._,
particulate Cu as well as about 1% conventional
lubricants. After these components were uniformly
mixed, compacts were produced by cold pressing in
the conventional manner, wherein the density of the
compacts was approximately 7 g/em3.
After the compacts were sintered at
approximately 1,120°C, the finished parts had
dimensional deviations of less than ~0.03% relative
to the dimensions of the compact. When cooled under
a nitrogen shower after sintering, the parts were
completely martensitically hardened and had a
tensile strength of more than 820 N/mm2 with a
hardness of approximately 400 HB.
In another test with the metal powder
mixture according to the invention, the compacts
were subjected to a two-fold pressing and sintering
procedure with temperature stages of 800°C and
1,120°C. Again, the two sintering procedures
resulted in dimensional deviations of less than
0.03%. The tensile strength was approximately
900 N/mm2, and the hardness approximately 450 HB.
The advantages of the metal powder mixture
according to the invention are to be seen
particularly in the fact that dimensionally constant
sintered parts can be manufactured which do not
require any complicated mechanical, deforming, or
thermal after-treatment after sintering, and wherein
the steel powder can be manufactured inexpensively.
This is because the selected alloy according to the
invention can be water atomized with subsequent
reduction under H2 atmosphere. Expensive vacuum
annealing, as it is required in other finished-
G:\MJM\324515$P.PAT

,:-
r..; . ,
1 alloy, water-atomized metal powders for the same
2 use, is not required. Also, in addition to the
3 inexpensive manufacture, the metal powder mixture
4 results in excellent strength and wear properties.
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