U.S. patent application number 10/529294 was filed with the patent office on 2006-07-27 for method for producing a moulded body from sintered steel.
Invention is credited to Alexander Bouvier, Stefan Hartl, Peter Orth, Raimund Ratzi, Walter Regenfelder.
Application Number | 20060165548 10/529294 |
Document ID | / |
Family ID | 27792533 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060165548 |
Kind Code |
A1 |
Ratzi; Raimund ; et
al. |
July 27, 2006 |
Method for producing a moulded body from sintered steel
Abstract
The invention relates to a method for producing a molded body
made of sintered steel, with a sintering powder on the basis of
iron being mixed with a master alloy powder containing nickel,
boron and iron, and with the powder mixture being pressed into a
formed body before the formed body is sintered under the conditions
of a liquid-phase sintering with a volume share of liquid phase up
to 15%. In order to improve the impact strength, it is proposed
that the boron content of the powder mixture is between 0.03% and
0.2% by weight at a boron share of the master alloy powder of less
than 10% by weight, that the weight ratio between the nickel and
the boron share of the powder mixture exceeds 5 and that the master
alloy powder has an average particle size of between 10 and 90
.mu.m.
Inventors: |
Ratzi; Raimund; (Wels,
AT) ; Bouvier; Alexander; (Krumpendorf, AT) ;
Regenfelder; Walter; (Huttenberg, AT) ; Hartl;
Stefan; (Lolling, AT) ; Orth; Peter;
(Stadl-Paura, AT) |
Correspondence
Address: |
WILLIAM COLLARD;COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
27792533 |
Appl. No.: |
10/529294 |
Filed: |
September 30, 2003 |
PCT Filed: |
September 30, 2003 |
PCT NO: |
PCT/AT03/00292 |
371 Date: |
March 25, 2005 |
Current U.S.
Class: |
419/47 |
Current CPC
Class: |
B22F 3/1035 20130101;
C22C 33/0207 20130101; B22F 3/1035 20130101; C22C 33/0207 20130101;
B22F 2999/00 20130101; B22F 2999/00 20130101 |
Class at
Publication: |
419/047 |
International
Class: |
B22F 3/12 20060101
B22F003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2002 |
AT |
A 1480/2002 |
Claims
1. A method for producing a molded body made of sintered steel,
with a sintering powder on the basis of iron being mixed with a
master alloy powder containing nickel, boron and iron, and with the
powder mixture being pressed into a formed body before the formed
body is sintered under the conditions of a liquid-phase sintering
with a volume share of liquid phase up to 15%, wherein the boron
content of the powder mixture is between 0.03% and 0.2% by weight
at a boron share of the master alloy powder of less than 10% by
weight, that the weight ratio between the nickel and the boron
share of the powder mixture exceeds 5 and that the master alloy
powder has an average particle size of between 10 and 90 .mu.m.
2. A method according to claim 1, wherein the boron content of the
powder mixture lies between 0.10% and 0.15% by weight.
3. A method according to claim 1, wherein the powder mixture has a
carbon content of between 0.15% and 0.8% by weight.
Description
1. FIELD OF THE INVENTION
[0001] The invention relates to a method for producing a molded
body made of sintered steel, with a sintering powder on the basis
of iron being mixed with a master alloy powder containing nickel,
boron and iron and with the powder mixture being pressed into a
formed body before the formed body is sintered under the conditions
of a liquid-phase sintering with a volume share of liquid phase up
to 15%.
2. DESCRIPTION OF THE PRIOR ART
[0002] During the compacting of sintered steel by liquid-phase
sintering by using a master alloy powder made of nickel and boron,
the nickel diffuses into the iron powder at the latest after the
first occurrence of melt. The iron dissolves partly in the liquid
phase and any present nickel boride is converted into iron boride
which at least at temperatures above the iron-boron eutectic reacts
again with iron by forming a liquid phase, so that the liquid phase
increasingly encloses the body of the iron powder. The increase of
the liquid phase during the sintering leads to a reduction of the
pores and thus to a compacting of the sintered steel. Since the
quantity of the liquid phase is determined predominantly by the
content of iron in the liquid phase, it has already been proposed
(T. Nishida, T. Yamazaki, S. Chida, M. Yamamiya: Effect of B on the
Densification and the Mechanical Properties of Sintered Iron Powder
Compacts, J. Japan Inst. Metals, Vol. 54, No. 10 (1990), pp.
1147-1153) to use a master alloy powder made of iron, nickel and
boron, thus providing additional iron boride through the prealloy,
leading to an acceleration of the reactions which leads to an
increase in the volume of the liquid phase. Netlike eutectic
structures are formed which increase the tensile strength of the
sintered steel, but have a serious negative effect on the impact
strength in particular. These connections were examined with a
master alloy powder with 20% by weight of iron, 70% by weight of
nickel and 10% by weight of boron as alloy components. The share of
the master alloy powder in the powder mixture made of master alloy
powder and iron powder was 3 to 7% by weight. Whereas the iron
powder had an average particle size of 80 .mu.m, the average
particle size of the master alloy powder was approximately 4 .mu.m
in order to obtain an improvement concerning the impact strength.
Apart from the fact that the production of such master alloy
powders is complex because the required prealloys are molten first
and then atomized and then fractured by exciting vibrations before
an average particle size of 4 .mu.m or finer is obtained by a
respective grounding process, the impact strength of the sintered
steels obtained with the help of these master alloy powders remains
unsatisfactory.
SUMMARY OF THE INVENTION
[0003] The invention is thus based on the object of providing a
method for producing a molded body made of sintered steel of the
kind mentioned above in such a way that especially the impact
strength of the sintered steel can be increased decisively.
[0004] This object is achieved by the invention in such a way that
the boron content of the powder mixture is between 0.03% and 0.2%
by weight at a boron share of the master alloy powder of less than
10% by weight, that the weight ratio between the nickel and the
boron share of the powder mixture exceeds 5 and that the master
alloy powder has an average particle size of between 10 and 90
.mu.m.
[0005] As a result of the cooperation of these measures, the
establishment of a continuous eutectic net structure can be
suppressed in a surprising manner, as is desirable for a
substantial compacting of the sintered steel. This means that the
molded body shows favorable values concerning the impact strength,
namely with respectively high tensile strengths as a result of the
higher density, even though a certain residual porosity needs to be
accepted due to the mutually delimited boride regions.
[0006] Although it can be assumed that the thickness of the boride
layers produced during the sintering will increase with coarser
particles of the master alloy powder and thus the probability of an
interconnected boride net will increase, it is possible to gain
advantages concerning the suppression of a marked boride network by
a mean fineness of the master alloy powder (average particle size
between 10 and 90 .mu.m) in comparison with fine powders because
they preferably comprise rounded edges through coarser master alloy
powder obtained through gas atomization, have a lesser tendency
towards agglomeration and can be mixed more evenly with the
sintering powder on the basis of iron. This fact leads in
connection with the limitation of the boron content in the entire
powder mixture to 0.03 to 0.2% by weight and to the thus following
delay in the grain growth at a respective choice of the sintering
temperature to a sufficient obstruction in the growing together of
local boride regions in order to prevent the formation of an
interconnected boride network. It is necessary to ensure a
sufficient nickel share in the powder mixture since nickel
ameliorates the effect of the boron concerning embrittlement of the
sintered steel. With a ratio between the nickel share and the boron
share in the powder mixture of at least 5, a respectively reduced
boron content can be used due to the sinter-supporting effect of
the nickel, which is of considerable relevance for the avoidance of
an interconnected boride network.
[0007] At a boron content of 0.03% in the powder mixture, it is
possible to notice a respective influence on the sintering with
respect to improved impact strength of the sintered steel under the
required conditions. Especially favorable conditions are obtained
in this connection when the boron content of the powder mixture is
between 0.10 and 0.15% by weight because the likelihood of an
interconnected boride network can be substantially excluded at
these boron contents.
[0008] The carbon required for the hardening of a sintered steel is
usually added in the form of graphite. The carbon impairs the
advantageous effect of the boron on the sintering process, so that
it is recommended to limit the carbon content to a value of between
0.15 and 0.8% by weight.
[0009] The described effects of the measures in accordance with the
invention do not depend on the composition of the sintering powder
on the basis of iron, so that the composition of this sintering
powder can be chosen according to the respective requirements. The
master alloy powder is also not limited to a ternary alloy. The
master alloy powder can additionally contain manganese, chromium,
copper, molybdenum, vanadium, titanium, niobium, tungsten, carbon,
aluminum and/or at least one element from the group of the
lanthanides.
[0010] In one embodiment, a master alloy powder with 67% by weight
of nickel, 30% by weight of iron and 3% by weight of boron was
used. The average particle size was 40 .mu.m. This master alloy
powder was mixed with a weight share of 4% with a sintering powder
on the basis of iron having 0.3% by weight of carbon. The powder
mixture was pressed into a cylindrical formed body with a green
density of 7.160 g/cm3 and thereafter sintered at a temperature of
1250.degree. C. under a hydrogen atmosphere. After the sintering, a
density of 7.314 g/cm3 was measured. The impact strength was
measured with 78.24 J/cm2.
[0011] In a further embodiment, a master alloy powder with 63% by
weight of nickel, 30% by weight of iron and 7% by weight of boron
with an average particle size of 60 .mu.m were used, in a quantity
of 2% by weight in the entire powder mixture. The sintering powder
on the basis of iron had a carbon content of 0.3% by weight. In a
treatment corresponding to the above embodiment, a green density of
7.068 g/cm3 and a sintered density of 7.228 g/cm3 were measured.
The impact strength was 76.21 J/cm2.
[0012] In the stated mixture ratios, the nickel share in the
sintered steel was 2.68% by weight in the first embodiment and the
share of boron was 0.12% by weight, corresponding to a ratio of
nickel to boron of approximately 22:1. In the second embodiment,
the obtained share of nickel was 1.26% by weight and that of boron
was 0.14% by weight. The ratio of nickel to boron could thus be
stated with 9:1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The drawing shows the dependence of the impact strength on
the boron content in a method in accordance with the invention on
the basis of two master allow powders.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] Curve 1 relates to a master alloy powder with 67% by weight
of nickel, 30% by weight of iron and 3% by weight of boron. This
master alloy powder was added to the sintering powder in different
quantities. After sintering under the conditions of the
embodiments, the impact strength of the different molded bodies
having different boron shares was measured. Curve 1 shows the
principal progress of the impact strength depending on the values
of the boron content as entered in percent by weight on the
absciss. The magnitude of the impact strength is co-determined by
the composition of the sintering powder, so that the drawing only
shows the principal dependence of the impact strength on the boron
content, but no specific measured values for the impact strength.
It can be seen that the impact strength reaches a maximum in the
region of the boron content of between 0.13 and 0.15% by weight of
the sintered steel. Thereafter it drops strongly towards the higher
boron shares.
[0015] Curve 2 shows the measured values which are obtained in the
use of a master alloy powder with 63% by weight of nickel, 30% by
weight of iron and 7% by weight of boron according to the second
embodiment. In the determination of curves 1 and 2, merely the
weight shares of the master alloy powder in the powder mixture were
changed. All other parameters were left unchanged. It can be seen
from the two curves 1 and 2 that more favorable conditions
concerning the impact strength of the molded body are obtained over
a wider range for the master alloy powder with the higher nickel
and lower boron share. Both curves also show that at a boron
content of larger than 0.2% by weight the impact strength will
decrease rapidly and therefore only a boron content of up to 0.2%
by weight will lead to a respectively high impact strength.
* * * * *