U.S. patent number 10,385,428 [Application Number 15/326,473] was granted by the patent office on 2019-08-20 for powder metallurgy wear-resistant tool steel.
This patent grant is currently assigned to ADVANCED TECHNOLOGY & MATERIALS CO., LTD, HEYE SPECIAL STEEL CO., LTD. The grantee listed for this patent is ADVANCED TECHNOLOGY & MATERIALS CO., LTD, HEYE SPECIAL STEEL CO., LTD. Invention is credited to Yucheng Fang, Chunjiang Kuang, Xiaoming Li, Xuebing Wang, Lizhi Wu, Hailin Zhong.
United States Patent |
10,385,428 |
Li , et al. |
August 20, 2019 |
Powder metallurgy wear-resistant tool steel
Abstract
A powder metallurgy wear-resistant tool steel includes chemical
components by mass percent of: V: 12.2%-16.2%, Nb: 1.1%-3.2%, C:
2.6%-4.0%, Si: .ltoreq.2.0%, Mn: 0.2%-1.5%, Cr: 4.0%-5.6%, Mo:
.ltoreq.3.0%, W: 0.1%-1.0%, Co: 0.05%-0.5%, N: 0.05%-0.7%, with
balance iron and impurities; wherein a carbide component of the
powder metallurgy wear-resistant tool steel is an MX carbide with a
NaCl type face-centered cubic lattice structure; wherein an M
element of the MX carbide comprises V and Nb, and an X element
comprises C and N.
Inventors: |
Li; Xiaoming (Beijing,
CN), Wu; Lizhi (Beijing, CN), Zhong;
Hailin (Beijing, CN), Wang; Xuebing (Beijing,
CN), Kuang; Chunjiang (Beijing, CN), Fang;
Yucheng (Beijing, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
HEYE SPECIAL STEEL CO., LTD
ADVANCED TECHNOLOGY & MATERIALS CO., LTD |
Shijiazhuang, Hebei
Beijing |
N/A
N/A |
CN
CN |
|
|
Assignee: |
HEYE SPECIAL STEEL CO., LTD
(Shijiazhuang, Hebel, CN)
ADVANCED TECHNOLOGY & MATERIALS CO., LTD (Beijing,
CN)
|
Family
ID: |
54027430 |
Appl.
No.: |
15/326,473 |
Filed: |
September 30, 2015 |
PCT
Filed: |
September 30, 2015 |
PCT No.: |
PCT/CN2015/091285 |
371(c)(1),(2),(4) Date: |
January 14, 2017 |
PCT
Pub. No.: |
WO2016/184009 |
PCT
Pub. Date: |
November 24, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170211167 A1 |
Jul 27, 2017 |
|
Foreign Application Priority Data
|
|
|
|
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May 15, 2015 [CN] |
|
|
2015 1 0250891 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F
3/15 (20130101); B22F 1/0003 (20130101); B22F
9/082 (20130101); C22C 38/26 (20130101); C22C
38/04 (20130101); C22C 38/30 (20130101); C22C
38/36 (20130101); C22C 38/22 (20130101); C22C
38/001 (20130101); C22C 33/0278 (20130101); C22C
38/002 (20130101); C22C 38/02 (20130101); C22C
38/24 (20130101); B22F 2009/0824 (20130101); B22F
2009/0848 (20130101); B22F 2009/0876 (20130101); B22F
2005/002 (20130101); B22F 2998/10 (20130101); B22F
2201/02 (20130101); B22F 2301/35 (20130101) |
Current International
Class: |
C22C
33/02 (20060101); C22C 38/24 (20060101); C22C
38/22 (20060101); C22C 38/30 (20060101); C22C
38/26 (20060101); C22C 38/00 (20060101); C22C
38/02 (20060101); C22C 38/10 (20060101); C22C
38/16 (20060101); C22C 45/02 (20060101); B22F
1/00 (20060101); H01F 1/147 (20060101); H01F
1/153 (20060101); H01F 1/20 (20060101); C22C
38/36 (20060101); C22C 38/04 (20060101); B22F
9/08 (20060101); B22F 3/15 (20060101); B22F
5/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
101487103 |
|
Jul 2009 |
|
CN |
|
103194685 |
|
Jul 2013 |
|
CN |
|
0515018 |
|
Nov 1992 |
|
EP |
|
H01152242 |
|
Jun 1989 |
|
JP |
|
Primary Examiner: Nguyen; Cam N.
Claims
What is claimed is:
1. A powder metallurgy wear-resistant tool steel, comprising
chemical components by mass percent of: V: 13.0%-16.0%, Nb:
1.2%-2.5%, C: 2.8%-3.7%, Si: .ltoreq.1.3%, Mn: 0.2%-1.5%, Cr:
4.8%-5.4%, Mo: .ltoreq.2.0%, W: 0.1%-0.5%, Co: 0.1%-0.4%, N:
0.05%-0.4%, O: .ltoreq.0.008%, with balance iron and impurities;
wherein a carbide component of the powder metallurgy wear-resistant
tool steel is an MX carbide with a NaCl type face-centered cubic
lattice structure; wherein an M element of the MX carbide comprises
V and Nb, and an X element comprises C and N; wherein in the
chemical components of the powder metallurgy wear-resistant tool
steel, a V equivalent is V.sub.eq: 13.0%-16.0%, wherein
V.sub.eq=V+0.65 Nb.
2. The powder metallurgy wear-resistant tool steel, as recited in
claim 1, wherein the impurities comprise S, wherein a S content is
no more than 0.1%.
3. The powder metallurgy wear-resistant tool steel, as recited in
claim 2, wherein the impurities comprise P, wherein a P content is
no more than 0.03%.
4. The powder metallurgy wear-resistant tool steel, as recited in
claim 3, wherein a volume fraction of the MX carbide is
16%-25%.
5. The powder metallurgy wear-resistant tool steel, as recited in
claim 4, wherein a size of at least 80% of the MX carbide is
0.5-1.3 .mu.m judging from volume percentage.
6. The powder metallurgy wear-resistant tool steel, as recited in
claim 5, wherein a maximum size of the MX carbide is no more than
5.0 .mu.m.
Description
CROSS REFERENCE OF RELATED APPLICATION
This is a U.S. National Stage under 35 U.S.C. 371 of the
International Application PCT/CN2015/091285, filed Sep. 30, 2015,
which claims priority under 35 U.S.C. 119(a-d) to CN
201510250891.0, filed May 15, 2015.
BACKGROUND OF THE PRESENT INVENTION
Field of Invention
The present invention relates to tool steel, and more particularly
to a powder metallurgy wear-resistant tool steel.
Description of Related Arts
Tool steel is widely used in manufacturing field. For a long
service life of a tool made of the tool steel, the tool steel
should be sufficient in wear resistance, impact toughness, bending
strength and hardness. Under normal conditions of use, wear
resistance determines the length of service life. Wear resistance
of the tool steel depends on the matrix hardness, as well as
content, morphology and particle size distribution of the second
hard phase in the steel. The second hard phase in the steel
comprises M.sub.6C, M.sub.2C, M.sub.23C.sub.6, M.sub.7C.sub.3 and
MX carbides, wherein microhardness of the MX carbides are higher
than other carbides, for providing better matrix protection during
operation, thereby reducing wear and improving the service life of
molds. Impact toughness and bending strength are key indicators of
toughness. Coarse carbides in the steel will cause stress
concentration, which reduces the toughness of the tool steel,
resulting in fracture under a relatively low external load. In
order to improve the toughness of the tool steel, it is important
to reduce or refine the carbides. In order to avoid plastic
deformation, hardness of the tool steel is usually required to be
HRC60 or more.
Conventionally, the tool steel is mainly casted and forged by
traditional production processes, wherein the tool steel prepared
by casting and forging processes is limited by liquid steel which
is slowly cooled during the processes. As a result, alloy
components are easy to be segregated during consolidation and to
form the coarse carbides. Even after subsequent forging and rolling
processes, such bad structure will still adversely affect the
performance of the alloy, resulting in low performances of the tool
steal in strength, toughness, wear resistance and grinding
performance, which is difficult to meet material performance and
life stability requirements of high-end manufacturing. Tool steel
prepared by a powder metallurgy method avoids the segregation
problem of alloy elements, wherein the powder metallurgy method
mainly comprises steps of: preparing powder by atomization, and
forming the powder by consolidation. In the step of preparing
powder by atomization, liquid steel is rapidly cooled into powder.
Therefore, the alloy elements in the liquid steel are completely
consolidated before segregation. A structure is fine and even after
powder consolidation, wherein compared with casting and forging,
alloy performance is significantly improved. Conventionally, only
the powder metallurgy method is able to satisfy extremely high
performance requirements of high alloy tool steel. Tool steel
prepared by powder metallurgy has been reported, but components of
some kinds of steel are not reasonably designed, so structure and
performance should be further improved.
SUMMARY OF THE PRESENT INVENTION
An object of the present invention is to solve at least one of the
above technical problems to some extent. Therefore, the present
invention provides a powder metallurgy wear-resistant tool steel
with excellent performances.
Accordingly, in order to accomplish the above objects, the present
invention provides a powder metallurgy wear-resistant tool steel,
comprising chemical components by mass percent of: V: 12.2%-16.2%,
Nb: 1.1%-3.2%, C: 2.6%-4.0%, Si: .ltoreq.2.0%, Mn: 0.2%-1.5%, Cr:
4.0%-5.6%, Mo: .ltoreq.3.0%, W: 0.1%-1.0%, Co: 0.05%-0.5%, N:
0.05%-0.7%, with balance iron and impurities; wherein a carbide
component of the powder metallurgy wear-resistant tool steel is an
MX carbide with a NaCl type face-centered cubic lattice structure;
wherein an M element of the MX carbide comprises V and Nb, and an X
element of the MX carbide comprises C and N.
According to the powder metallurgy wear-resistant tool steel of an
embodiment of the present invention, alloy components are designed
for preparing a high wear-resistant tool steel, which is sufficient
in impact toughness, bending strength and hardness. By adding a
large amount of vanadium and carbon alloy elements, the MX carbide
is formed, which improves wear resistance. Meanwhile, a certain
amount of alloy elements such as chromium, molybdenum and silicon
is added for strengthening a matrix and increasing a precipitation
amount of the MX carbide. In the embodiment of the present
invention, besides the alloy elements above, a certain amount of
niobium and nitrogen alloy elements is added and solid dissolved in
the MX carbide, so as to form a composite MX carbide comprising C,
N, V and Nb. A type of the MX carbide is (V, Nb) (C, N), which
increases a nucleation rate of the MX carbide, in such a manner
that the MX carbide precipitated is finer and a toughness of the
tool steel is improved. Adding amounts of niobium and nitrogen
should be controlled within a proper range for preventing formation
of highly stable carbides such as NbC, VN and NbN.
Preferably, in the chemical components of the powder metallurgy
wear-resistant tool steel, a V equivalent is V.sub.eq: 13.0%-16.0%,
wherein V.sub.eq=V+0.65 Nb.
Preferably, the impurities comprise O, wherein an O content is no
more than 0.01%.
Preferably, the powder metallurgy wear-resistant tool steel
comprises the chemical components by mass percent of: V:
13.0%-16.0%, Nb: 1.2%-2.5%, C: 2.8%-3.7%, Si: .ltoreq.1.3%, Mn:
0.2%-1.5%, Cr: 4.8%-5.4%, Mo: .ltoreq.2.0%, W: 0.1%-0.5%, Co:
0.1%-0.4%, N: 0.05%-0.4%, O: .ltoreq.0.008%, with balance iron and
impurities.
Preferably, the impurities comprise S, wherein an S content is no
more than 0.1%.
Preferably, the impurities comprise P, wherein a P content is no
more than 0.03%.
Preferably, a volume fraction of the MX carbide is 16%-25%.
Preferably, a size of at least 80% of the MX carbide is 0.5-1.3
.mu.m judging from volume percentage.
Preferably, a maximum size of the MX carbide is no more than 5.0
.mu.m.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Preferred embodiments of the present invention are illustrated as
follows. Examples of the embodiments are shown in drawings. The
same or similar elements and the elements having same or similar
functions are denoted by like reference numerals throughout the
descriptions. The embodiments described herein with reference to
drawings are explanatory, and used to generally understand the
present disclosure, and not intended to be limiting.
The present invention provides a powder metallurgy wear-resistant
tool steel with significant performances. According to the present
invention, the powder metallurgy wear-resistant tool steel
comprises chemical components by mass percent of: V: 12.2%-16.2%,
Nb: 1.1%-3.2%, C: 2.6%-4.0%, Si: .ltoreq.2.0%, Mn: 0.2%-1.5%, Cr:
4.0%-5.6%, Mo: .ltoreq.3.0%, W: 0.1%-1.0%, Co: 0.05%-0.5%, N:
0.05%-0.7%, with balance iron and impurities; wherein a carbide
component of the powder metallurgy wear-resistant tool steel is an
MX carbide with a NaCl type face-centered cubic lattice structure;
wherein an M element of the MX carbide comprises V and Nb, and an X
element of the MX carbide comprises C and N.
According to the embodiments of the present invention, alloy
components are designed for preparing a high wear-resistant tool
steel, which is sufficient in impact toughness, bending strength
and hardness.
Utilization of V is a key to improve wear resistance. V is a main
element for forming the MX carbide, whose content is controlled
between 12.2%-16.2%.
Nb and V have similar functions, both of which are involved in
forming the MX carbide. According to the present invention, Nb is
solved in the MX carbide for increasing a nucleation rate when the
MX carbide is precipitated, so as to improve precipitating and
refining of the MX carbide, and improve the wear resistance. An Nb
adding limit prevents Nb-enriched MX carbide from precipitation.
According to the present invention, a Nb content is controlled at
1.1%-3.2%.
C is one of the forming elements of the MX carbide, whose content
is no less than 2.6% for ensuring that alloy elements are fully
involved in carbide precipitation. A maximum C content is no more
than 4.0% for avoiding that excessive C is solved in the matrix.
When the above C content is controlled within 2.6%-4.0%, an
optimized cooperation of wear resistance and toughness is
obtained.
Si is not involved in carbide formation, but as a deoxidizing agent
and a strengthening element of the matrix. Excessive Si will lower
the toughness of the matrix, so a Si content is controlled at
Si.ltoreq.2.0%.
Mn is added as a deoxidizing agent, for fixing sulfur and reducing
hot brittleness. In addition, manganese increases a quenching
degree. According to the present invention, a Mn content is
controlled within 0.2%-1.5%.
On one hand, Cr is solved in the matrix for improving hardness
thereof, on the other hand, a small amount of Cr is solved in the
MX carbide for promoting MX carbide precipitation. Therefore, a Cr
content is 4.0%-5.6%.
Functions of Mo and W are similar to that of Cr. According to the
embodiment of the present invention, a Mo content is
Mo.ltoreq.3.0%, and a W content is 0.1%-1.0%.
Co is mainly solved in the matrix for promoting carbide
precipitation and refining particle size of the carbide. A Co
content is 0.05%-0.5%.
N is involved in MX carbide formation. Under a rapid cooling
condition, N promotes nucleation precipitation of the MX carbide
while the MX carbide never excessively grows, which is conducive to
improvement of the wear resistance. An N content is limited within
0.05%-0.7%.
According to the powder metallurgy wear-resistant tool steel of the
embodiments of the present invention, by adding a large amount of
vanadium and carbon alloy elements, the MX carbide is formed, which
improves wear resistance. Meanwhile, a certain amount of alloy
elements such as chromium, molybdenum and silicon is added for
strengthening a matrix and increasing a precipitation amount of the
MX carbide, so as to form a composite MX carbide comprising C, N, V
and Nb. A type of the MX carbide is (V, Nb) (C, N), which increases
a nucleation rate of the MX carbide, in such a manner that the MX
carbide precipitation is finer and a toughness of the tool steel is
improved. Adding amounts of niobium and nitrogen should be
controlled within a proper range for preventing formation of highly
stable carbides such as NbC, VN and NbN.
Preferably, in the chemical components of the powder metallurgy
wear-resistant tool steel, a V equivalent is V.sub.eq: 13.0%-16.0%,
wherein V.sub.eq=V+0.65 Nb.
Preferably, the impurities comprise O, wherein an O content is no
more than 0.01%. Excessive O will lower the toughness of the tool
steel. According to the embodiments of the present invention, the O
content is no more than 0.01% for ensuring an outstanding steel
performance.
Preferably, the powder metallurgy wear-resistant tool steel
comprises the chemical components by mass percent of: V:
13.0%-16.0%, Nb: 1.2%-2.5%, C: 2.8%-3.7%, Si: .ltoreq.1.3%, Mn:
0.2%-1.5%, Cr: 4.8%-5.4%, Mo: .ltoreq.2.0%, W: 0.1%-0.5%, Co:
0.1%-0.4%, N: 0.05%-0.4%, O: .ltoreq.0.008%, with balance iron and
impurities.
For obtaining a better combination performance, the chemical
components of the powder metallurgy wear-resistant tool steel
should be controlled within a certain range.
Preferably, the impurities comprise S, wherein a S content is no
more than 0.1%.
Preferably, the impurities comprise P, wherein a P content is no
more than 0.03%.
Preferably, a volume fraction of the MX carbide is 16%-25%.
Preferably, a size of at least 80% of the MX carbide is 0.5-1.3
.mu.m judging from volume percentage.
Preferably, a maximum size of the MX carbide is no more than 5.0
.mu.m.
According to the embodiments of the present invention, the powder
metallurgy wear-resistant tool steel is prepared by a method
comprising steps of:
a) preparing a liquid tool steal with the above components and
loading the liquid tool steal into a ladle;
b) electrically heating covering slag at a top surface of the
liquid steel in the ladle for maintaining superheat, injecting an
inert gas from a hole at a bottom of the ladle for stirring the
liquid steel;
c) moving the liquid steel into a tundish which is pre-heated
through the guiding tube at the bottom of the ladle, adding
covering slag to the top surface of the liquid steel when the
liquid steel enters into the tundish and buries a bottom end face
of the guiding tube;
d) continuously additional heating the tundish for maintaining the
superheat;
e) moving the liquid steel into an atomization chamber from the
tundish for atomization with an inert gas, wherein metal powder
obtained is subsided at a bottom of the atomization chamber; then
entering a powder storage with a protective atmosphere; after
atomization, screening with a protective screening device before
storing in the powder storage; and
f) loading the metal powder in the powder storage into a hot
isostatic pressing capsule with inert gas protection; after fully
vibration filled, evacuate-degassing the hot isostatic pressing
capsule; and then sealing welding a capsuling end; finally
providing a hot isostatic pressing treatment, in such a manner that
the metal powder is fully consolidated, and completing powder
metallurgy.
The above powder metallurgy comprises non-vacuum melting
atomization and hot isostatic pressing processes with full-process
protection to control the oxygen content and carbide morphology,
and optimize a tool steel performance. The covering slag of the
ladle is able to cut off the air and conductively heat. The inert
gas is injected into the bottom of the ladle through the hole, so
that temperatures at different positions of the liquid steel equals
to each other, and harmful inclusions rapidly floats, thus being
removed. The guiding tube at the bottom of the ladle guides the
liquid steel as well as reduces turbulence fluid generated during
flowing, so as to keep slag and inclusion out. Furthermore, the
guiding tube prevents the liquid steel from being exposed to air,
avoiding increase of an oxygen content of the liquid steel. The
covering slag of the tundish prevents the liquid steel from being
exposed to air when the liquid steel flows through the tundish,
avoiding increase of the oxygen content. The tundish is pre-heated
before the liquid steel enters, so as to avoid local condensation
or early precipitation of a second phase when the liquid steel
enters into the tundish. The powder storage has the protection
atmosphere inside and a forced cooling function. The protective
screening device protects a screening process and prevents the
powder from flying. The powder storage is connected to the hot
isostatic pressuring capsule in a sealed form, and the inert gas is
injected into the hot isostatic pressing capsule before loading
powder for discharging air, so as to control the oxygen
content.
In summary, according to the present invention, a powder metallurgy
tool steel with high wear resistance is obtained, which is also
sufficient in impact toughness, bending strength and hardness.
According to the embodiments of the present invention, the tool
steel adapts certain chemical components and rapid
cooling-consolidation process of the powder metallurgy, wherein a
type of the MX carbide is (V, Nb) (C, N), in such a manner that the
MX carbide precipitated is finer and a toughness of the tool steel
is improved. After heat treatment, the hardness is more than HRC60,
so as to satisfy different application requirements with a wide
range of uses. The tool steel of the present invention is prepared
according to the powder metallurgy, wherein a plurality of
effective protection methods are used for keeping the liquid steel
and the powder clean. Compared with conventional powder metallurgy
tool steel, with a similar content of the MX carbide, the MX
carbide of the tool steel of the present invention is finer and the
tool steel is tougher.
For better understanding by the skilled person in the art,
preferred embodiments of the present invention are illustrated as
follows.
Preferred Embodiment 1
The preferred embodiment 1 refers to a group of powder metallurgy
wear-resistant tool steels, whose chemical components are listed in
Table 1.1:
TABLE-US-00001 TABLE 1.1 chemical components of powder metallurgy
wear-resistant tool steels in the preferred embodiment 1 C Si Mn Cr
Mo W V Nb Co S N O embodiment 1.1 2.98 1 0.6 4.57 1.3 0.1 12.4 3
0.3 0.001 0.08 0.008 embodiment 1.2 3.38 0.89 0.3 5.26 1.8 0.1 13.1
1.15 0.3 0.001 0.06 0.0078 embodiment 1.3 3.98 1.5 1.3 5.45 2.4 0.7
15.9 2.6 0.4 0.005 0.5 0.008 embodiment 1.4 3.50 0.6 1.0 4.86 1.5
0.5 14.5 1.8 0.24 0.003 0.3 0.008
The powder metallurgy wear-resistant tool steels are prepared with
a method comprising steps of:
a) loading liquid tool steal of the present invention into a
smelting ladle with a load weight of 1.5-8 ton;
b) electrically heating covering slag at a top surface of the
liquid steel in the smelting ladle by graphite electrodes,
injecting argon or nitrogen gas from a hole at a bottom of the
smelting ladle for stirring the liquid steel, opening a guiding
tube when a liquid steel overheated temperature is 100.degree.
C.-200.degree. C.;
c) moving the liquid steel into a tundish, which is pre-heated to
800.degree. C.-1200.degree. C., through the guiding tube at the
bottom of the smelting ladle, controlling a size of an inlet of the
guiding tube, in such a manner that a flow rate of the liquid steel
is 10 kg/min-50 kg/min, adding a covering slag when the liquid
steel enters into the tundish and buries a bottom end face of the
guiding tube;
d) forming powder by atomization while continuously additional
heating the tundish for maintaining the liquid steel temperature at
100.degree. C.-200.degree. C.;
e) moving the liquid steel into an atomization chamber through an
opening at a bottom of the tundish, opening an atomizing gas
nozzle, using nitrogen as an atomizing gas for atomization, wherein
a nitrogen purity is .gtoreq.99.999%, an oxygen content is
.ltoreq.2 ppm, a gas pressure is 1.0 MPa-5.0 MPa; cracking the
liquid steel into drops by impact of an inert gas, while rapidly
cooling into metal powder and depositing at a bottom of the
atomization chamber; then entering a powder storage through the
bottom of the atomization chamber; after atomization, waiting until
the powder in the powder storage is cooled to a room temperature,
and screening with a protective screening device; wherein an inert
protective gas with a positive pressure is injected into a
screening device chamber, and the powder storage has a protective
atmosphere with a positive pressure inert gas; and
f) loading the metal powder in the powder storage into a hot
isostatic pressing capsule, firstly injecting an inert gas into the
hot isostatic pressing capsule for excluding air, then connecting
the hot isostatic pressuring capsule and the powder storage in a
sealed form; providing a vibration operation during loading for
increasing filling density of the metal powder; then
evacuate-degassing the hot isostatic pressing capsule while keeping
a temperature at 200.degree. C.-600.degree. C.; degassing to 0.01
Pa and continuously heating for .gtoreq.2 h, and then sealing
welding a capsuling end; finally providing a hot isostatic pressing
treatment, with a temperature of 1100.degree. C.-1160.degree. C.,
and keeping a pressure of .gtoreq.1001 MPa for .gtoreq.1 h,
naturally cooling after the metal powder is fully consolidated.
According to requirements, the tool steel of the present invention
are further forged for obtaining certain shapes and sizes, and are
treated with different heat treatments for obtaining different
performances, wherein the heat treatments comprises annealing,
quenching and tempering. Annealing comprises steps of heating a
forging piece to 870.degree. C.-890.degree. C. and keeping the
temperature for 2 h; cooling to 530.degree. C. with a rate of
.ltoreq.15.degree. C./h; then cooling to below 50.degree. C. by
furnace cooling or static air cooling. Quenching comprises steps of
pre-heating the forging piece after annealing at a temperature at
815.degree. C.-845.degree. C.; keeping the temperature at
1000.degree. C.-1200.degree. C. for 15-40 min after the temperature
is even, then quenching to 530.degree. C.-550.degree. C., and
cooling to below 50.degree. C. Tempering comprises steps of heating
the forging piece after quenching to 540.degree. C.-670.degree. C.
and keeping the temperature for 1.5-2 h, then air-cooling to below
50.degree. C.; repeating for 2-3 times.
According to embodiments 1.1-1.4, the powder metallurgy
wear-resistant tool steels are obtained, wherein an increase of the
oxygen content during process is .ltoreq.30 ppm. After hot working,
a fully dense tool steel with a relative density of 100% is
obtained, which is prepared into bars with a diameter of 50 mm.
Preferred Embodiment 2
The preferred embodiment 2 proves heat treatment hardness, impact
toughness, bending strength, wear resistance, carbide content and
particle size of the powder metallurgy wear-resistant tool steel of
the preferred embodiment 1, wherein the carbide content and the
particle size is analyzed based on structure images obtained by
scanning electron microscope; and the heat treatment hardness, the
impact toughness, the bending strength and the wear resistance are
tested referring to GB/T 230.1, GB/T 229, GB/T 14452-93, and GB/T
12444-2006.
The powder metallurgy wear-resistant tool steel of the embodiments
1.1 and 1.2 are compared with a powder metallurgy tool steel (alloy
A) and a forged tool steel (alloy B) bought, wherein results are as
follows:
TABLE-US-00002 TABLE 2.1 components comparison between embodiment
1.1, embodiment 1.2, alloy A, and alloy B C Si Mn Cr Mo W V Nb Co S
N O embodiment 1.1 2.98 1 0.6 4.57 1.3 0.1 12.4 3 0.3 0.001 0.08
0.008 embodiment 1.2 3.38 0.89 0.3 5.26 1.8 0.1 13.1 1.15 0.3 0.001
0.06 0.0078 embodiment 1.3 3.98 1.5 1.3 5.45 2.4 0.7 15.9 2.6 0.4
0.005 0.5 0.008 embodiment 1.4 3.50 0.6 1.0 4.86 1.5 0.5 14.5 1.8
0.24 0.003 0.3 0.008
According to the powder metallurgy wear-resistant tool steel of the
embodiments 1.1 and 1.2, the oxygen content is 50-60 ppm before
preparing and 60-80 ppm after preparing, which means the increase
of the oxygen content is .ltoreq.30 ppm.
TABLE-US-00003 TABLE 2.2 heat treatment hardness, impact toughness
and bending strength comparison between embodiment 1.1, embodiment
1.2, alloy A, and alloy B heat treatment impact bending quenching
tempering hardness toughness strength method method (HRC) a.sub.k
(J/cm.sup.2) .sigma..sub.bb (MPa) embodiment 1.1 1150.degree. C.
for 550.degree. C. .times. 1.5 h .times. 3 61 20 3790 30 min
embodiment 1.2 1150.degree. C. for 550.degree. C. .times. 1.5 h
.times. 3 62 19 4430 30 min A 1150.degree. C. for 550.degree. C.
.times. 1.5 h .times. 3 62 13 3860 30 min B 1000.degree. C. for
200.degree. C. .times. 1.5 h .times. 2 60 22 2600 15 min
According to Table 2.2, the powder metallurgy wear-resistant tool
steels of the present invention have best combinations of strength
and toughness.
TABLE-US-00004 TABLE 2.3 wear resistance comparison between
embodiment 1.1, embodiment 1.2, alloy A, and alloy B quenching
tempering hardness alloy mass method method HRC loss (mg)
embodiment 1150.degree. C. for 550.degree. C. .times. 1.5 h .times.
3 61 15.7 1.1 30 min embodiment 1150.degree. C. for 550.degree. C.
.times. 1.5 h .times. 3 62 13.5 1.2 30 min A 1150.degree. C. for
550.degree. C. .times. 1.5 h .times. 3 62 13.4 30 min B
1000.degree. C. for 200.degree. C. .times. 1.5 h .times. 2 60 320
15 min
According to Table 2.3, wear resistances of the powder metallurgy
wear-resistant tool steels of the preferred embodiments of the
present invention are similar to that of the alloy A, and are far
better than that of the alloy B.
TABLE-US-00005 TABLE 2.4 particle size comparison between
embodiment 1.1, embodiment 1.2, alloy A, and alloy B MX carbide
M.sub.7C.sub.3 carbide quenching tempering particle size volume
particle volume method method .mu.m vol % size .mu.m vol %
embodiment 1.1 1150.degree. C. for 550.degree. C. .times. 0.5-1.3
16-25 NA NA 30 min 1.5 h .times. 3 embodiment 1.2 1150.degree. C.
for 550.degree. C. .times. 0.5-1.3 16-25 NA NA 30 min 1.5 h .times.
3 A 1150.degree. C. for 550.degree. C. .times. 0.8-2.0 16-25 NA NA
30 min 1.5 h .times. 3 B 1000.degree. C. for 200.degree. C. .times.
NA NA 5-30 <16 15 min 1.5 h .times. 2
Referring to Table 2.4, the carbide particle size refers to a size
of carbide with at least 80% of volume content.
According to carbide analysis of the tool steel, carbide components
of the powder metallurgy wear-resistant tool steels of the present
invention and the alloy A are MX carbide. The type of the MX
carbide of the present invention is (V, Nb) (C, N), which is mainly
formed by V, Nb, C, N and a few alloy elements such as Fe and Cr.
According to Table 2.4, the volume fraction of the MX carbide of
the tool steel of the present invention is up to 16%-25%. Different
from the alloy B, a huge amount of the MX carbide is conducive to a
high wear resistance. The carbide particle sizes according to the
present invention are really small, most of which is less than 1.3
.mu.m while a biggest one is no more than 5 .mu.m, which is
conducive to a high toughness of the tool steel.
In summary, the powder metallurgy wear-resistant tool steels
according to the present invention have excellent wear resistance,
which are also sufficient in impact toughness, bending strength and
hardness. After heat treatment, the hardness is more than HRC60, so
as to satisfy different application requirements with a wide range
of uses. For example, the tool steel is applicable to plastic
machinery parts such as hard powder pressing, stamping die cutting,
industrial cutting blades, wood cutting tools, wear parts, screws,
screw sleeves, screw head. Compared with the conventional casting
and forging tool steel, the present invention has advantages such
as sufficient wear resistance and great increase of service life.
Compared with the conventional powder metallurgy tool steel, with a
similar content of the carbide, the tool steel of the present
invention is tougher due to finer carbide. The powder metallurgy
process of the present invention adapts a plurality of effective
protection methods for keeping the liquid steel and the powder
clean during preparation. The increase of the oxygen content during
process is .ltoreq.30 ppm for ensuring a high-performance alloy
material.
During description, words such as "first" and "second" are
describing only without indicating importance or numbers of
technical features. Therefore, "first" or "second" may refer to one
or more features. During description, "a plurality of" refers to no
less than two except for detailed illustration.
During description, references such as "one embodiment", "some
embodiments", "an example", "specific example", or "some examples"
mean that a particular feature, structure, material, or
characteristic of the described embodiments or examples are
included in at least one embodiment or example of the present
invention. In the specification, the terms of the above schematic
representation is not necessarily for the same embodiment or
example. Furthermore, the particular features, structures,
materials, or characteristics described in any one or more of the
embodiments or examples are able to be combined in a suitable
manner. One skilled in the art will understand that features in
different embodiments or examples may be combined if not
conflicting to each other.
One skilled in the art will understand that the embodiment of the
present invention as shown in the drawings and described above is
exemplary only and not intended to be limiting. It will thus be
seen that the objects of the present invention have been fully and
effectively accomplished. Its embodiments have been shown and
described for the purposes of illustrating the functional and
structural principles of the present invention and is subject to
change without departure from such principles. Therefore, this
invention includes all modifications encompassed within the spirit
and scope of the following claims.
* * * * *