U.S. patent application number 12/753974 was filed with the patent office on 2011-06-02 for alloy steel for low temperature vacuum carburizing.
This patent application is currently assigned to HYUNDAI MOTOR COMPANY. Invention is credited to Bong Lae Jo, Chang Won Kang.
Application Number | 20110129382 12/753974 |
Document ID | / |
Family ID | 43972461 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110129382 |
Kind Code |
A1 |
Jo; Bong Lae ; et
al. |
June 2, 2011 |
ALLOY STEEL FOR LOW TEMPERATURE VACUUM CARBURIZING
Abstract
The present invention relates to an alloy steel for low
temperature vacuum carburizing, and more particularly, to an alloy
steel for low temperature vacuum carburizing, wherein, where the
thermal processing of carburizing and quenching is performed at
810.degree. C. or so of an available minimum carburizing
temperature of a conventional vacuum carburizing furnace, it is
able to securing an adequate ferrite phase (.alpha.) to improve the
thermal distortion according to the thermal processing of an
annulus gear, and to satisfying shape restrictions such as a
roundness or a cylindricity of the annulus gear to be manufactured.
An alloy steel for a low temperature vacuum carburizing according
to the present invention, the alloy steel is composed of a chief
element of Fe, wherein the alloy steel is formed so that dissolved
oxygen (DO) is 10 ppm or less in an alloy system which comprises
0.17.about.0.24 weight percent of C, 0.8.about.1.2 weight percent
of Cr, 0.4.about.0.8 weight percent of Mn, 0.80.about.1.20 weight
percent of Si, 0.020 weight percent or less of P, 0.020 weight
percent or less of S, 0.015.about.0.045 weight percent of V, and
the remaining weight percent of Fe.
Inventors: |
Jo; Bong Lae; (Yongin,
KR) ; Kang; Chang Won; (Hwaseong, KR) |
Assignee: |
HYUNDAI MOTOR COMPANY
Seoul
KR
KIA MOTORS CORPORATION
Seoul
KR
|
Family ID: |
43972461 |
Appl. No.: |
12/753974 |
Filed: |
April 5, 2010 |
Current U.S.
Class: |
420/104 |
Current CPC
Class: |
C22C 38/04 20130101;
C22C 38/02 20130101; C22C 38/24 20130101 |
Class at
Publication: |
420/104 |
International
Class: |
C22C 38/24 20060101
C22C038/24; C22C 38/18 20060101 C22C038/18; C22C 38/02 20060101
C22C038/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2009 |
KR |
10-2009-0117993 |
Claims
1. An alloy steel for a low temperature vacuum carburizing, the
alloy steel being composed of a chief element of Fe, wherein the
alloy steel is formed so that dissolved oxygen (DO) is 10 ppm or
less in an alloy system which comprises 0.17.about.0.24 weight
percent of C, 0.8-1.2 weight percent of Cr, 0.4-0.8 weight percent
of Mn, 0.80-1.20 weight percent of Si, 0.020 weight percent or less
of P, 0.020 weight percent or less of S, 0.015-0.045 weight percent
of V, and the remaining weight percent of Fe.
2. An alloy steel for low temperature vacuum carburizing, the alloy
steel comprising 0.17.about.0.24 weight percent of C, 0.8-1.2
weight percent of Cr, 0.4-0.8 weight percent of Mn, 0.80-1.20
weight percent of Si, 0.020 weight percent or less of P, 0.020
weight percent or less of S, 0.015-0.045 weight percent of V, and
the remaining weight percent of Fe.
3. The alloy steel for low temperature vacuum carburizing of claim
2, wherein the alloy steel is formed so that dissolved oxygen (DO)
is 10 ppm or less.
4. An alloy steel for low temperature vacuum carburizing, the alloy
steel comprising Fe, wherein the alloy steel is formed so that
dissolved oxygen (DO) is 10 ppm or less.
5. The alloy steel for low temperature vacuum carburizing of claim
4, wherein the alloy comprises 0.17.about.0.24 weight percent of C,
0.8-1.2 weight percent of Cr, 0.4-0.8 weight percent of Mn,
0.80-1.20 weight percent of Si, 0.020 weight percent or less of P,
0.020 weight percent or less of S, 0.015-0.045 weight percent of V,
and the remaining weight percent of Fe.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims under 35 U.S.C. .sctn.119(a)
to the benefit of Korean Patent Application Number
10.about.2009.about.0117993, filed on 1, Dec., 2009, the entire
contents of which is incorporated herein for all purposes by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates, generally, to an alloy steel
for low temperature vacuum carburizing, and more particularly, to
an alloy steel for low temperature vacuum carburizing, wherein,
when the thermal processing of carburizing and quenching is
performed at 810.degree. C. or so of an available minimum
carburizing temperature of a conventional vacuum carburizing
furnace, it is able to securing an adequate ferrite phase (.alpha.)
to suitably improve the thermal distortion according to the thermal
processing of an annulus gear, and to suitably satisfy shape
restrictions of the annulus gear to be manufactured, such as, but
not limited to, roundness or cylindricity.
[0004] 2. Description of Prior Art
[0005] In general, for gear-like components of a vehicle
transmission, a thermal processing of carburizing and quenching is
typically performed. When the thermal processing of carburizing and
quenching is performed, distortion of the components may occur. In
certain cases where the distortion is excessive, it may cause
problems with the assembly of the components, or unusual noise may
occur.
[0006] FIG. 1 shows an exemplary general annulus gear.
[0007] As shown in FIG. 1, an annulus gear is a cylindrical
component, wherein the annulus gear is a main component of a
planetary gear train applicable to an important power transmission
system of an automatic transmission. Preferably, the annulus gear
is an internal gear whose teeth are suitably processed through a
broaching processing. Since the annulus gear has a large diameter
and a thin thickness, it is very sensitive to thermal distortion.
Further, while teeth surface processing of a general external gear
is easily performed after the thermal processing such as grinding
or the like, the annulus gear is one of the components whose
processing is difficult after the thermal processing.
[0008] There are various thermal processing methods of the annulus
gear that encompass the thermal distortion.
[0009] For example, in order to minimize the thermal distortion of
the annulus gear, a series of methods of gas carburizing, furnace
cooling, high frequency heating and jig quenching have been used.
By performing the final jig quenching processing, that is, by
applying high frequency heating, jig assembling, and then
quenching, it is possible to satisfy the shape restrictions such as
the roundness, the cylindricity, and the like.
[0010] However, the above-described method involves long and
complex processing. Further, since the method is individually
performed by components, the operation efficiency may suitably
decrease. Further, when the jig is cooled, a shape of gear teeth
may suitably deform unevenly by a localized uneven cooling, and
accordingly, unusual noise may occur.
[0011] Recently, vacuum carburizing and gas quenching methods have
been applied, which have considerable productivity and uniform
cooling. It has been possible to improve the noise which is caused
by uneven deformation; however, aspects of the shape such as
roundness, cylindricity, or the like may still be improved.
[0012] Accordingly, new compositions and methods for low
temperature vacuum carburizing are needed.
[0013] The above information disclosed in this the Background
section is only for enhancement of understanding of the background
of the invention and therefore it may contain information that does
not form the prior art that is already known in this country to a
person of ordinary skill in the art.
BRIEF SUMMARY OF THE INVENTION
[0014] In one aspect, the present invention provides an alloy steel
for a low temperature vacuum carburizing, wherein, at 810.degree.
C. or so of an available minimum carburizing temperature of a
conventional vacuum carburizing furnace, it is able to reach an
adequate ferrite phase (.alpha.).
[0015] In preferred embodiments, the present invention provides an
alloy steel for a low temperature vacuum carburizing, the alloy
steel preferably being composed of a chief element of Fe, wherein
the alloy steel is formed so that dissolved oxygen (DO) is 10 ppm
or less in an alloy system which comprises 0.17.about.0.24 weight
percent of C, 0.8.about.1.2 weight percent of Cr, 0.4.about.0.8
weight percent of Mn, 0.80.about.1.20 weight percent of Si, 0.020
weight percent or less of P, 0.020 weight percent or less of S,
0.015.about.0.045 weight percent of V, and the remaining weight
percent of Fe.
[0016] Preferably, the alloy steel for a low temperature vacuum
carburizing of the present invention, in certain preferred
embodiments, where the thermal processing of carburizing and
quenching is performed at 810.degree. C. or so of an available
minimum carburizing temperature of a conventional vacuum
carburizing furnace, reaches an adequate ferrite phase (.alpha.) to
suitably improve the thermal distortion according to the thermal
processing of the annulus gear, and to suitably satisfies shape
restrictions such as a roundness or a cylindricity of the annulus
gear to be manufactured.
[0017] It is understood that the term "vehicle" or "vehicular" or
other similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like, and includes hybrid vehicles, electric vehicles, plug-in
hybrid electric vehicles, hydrogen-powered vehicles and other
alternative fuel vehicles (e.g. fuels derived from resources other
than petroleum).
[0018] As referred to herein, a hybrid vehicle is a vehicle that
has two or more sources of power, for example both gasoline-powered
and electric-powered.
[0019] The above features and advantages of the present invention
will be apparent from or are set forth in more detail in the
accompanying drawings, which are incorporated in and form a part of
this specification, and the following Detailed Description, which
together serve to explain by way of example the principles of the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above and other features of the present invention will
now be described in detail with reference to certain exemplary
embodiments thereof illustrated by the accompanying drawings which
are given hereinafter by way of illustration only, and thus are not
limitative of the present invention, and wherein:
[0021] FIG. 1 is a perspective view for illustrating a general
annulus gear of the prior art.
[0022] FIG. 2 is a view for explaining a concept of a low
temperature vacuum carburizing, and illustrates a state of Fe--C
(iron-carbon).
[0023] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the invention. The specific design features of
the present invention as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes will be
determined in part by the particular intended application and use
environment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] As described herein, the present invention features an alloy
steel for a low temperature vacuum carburizing. Preferably, the
alloy steel is comprised mainly of Fe.
[0025] In preferred aspects, the present invention features an
alloy steel for a low temperature vacuum carburizing, the alloy
steel being composed of a chief element of Fe, wherein the alloy
steel is formed so that dissolved oxygen (DO) is 10 ppm or less in
an alloy system which comprises 0.17.about.0.24 weight percent of
C, 0.8-1.2 weight percent of Cr, 0.4-0.8 weight percent of Mn,
0.80-1.20 weight percent of Si, 0.020 weight percent or less of P,
0.020 weight percent or less of S, 0.015-0.045 weight percent of V,
and the remaining weight percent of Fe.
[0026] An alloy-steel for a low temperature vacuum carburizing
according to preferred embodiments of the present invention will be
explained in detail.
[0027] A the low temperature carburizing method has been studied as
a substitute for the conventional jig quenching method in the
aspect of improving the shape such as roundness, cylindricity, or
the like, by applying the vacuum carburizing method. FIG. 2
illustrates an example of the low temperature vacuum carburizing
method, and illustrates a state of Fe--C (iron-carbon).
[0028] Referring to FIG. 2, the low temperature carburizing method
has carried out the carburizing processing at a temperature area
between dual phases A1.about.A3 in which an austenite phase
(.gamma.) and a ferrite phase (.alpha.) exist together.
Accordingly, the low temperature carburizing method improves the
thermal deformation, since a defined amount of the ferrite phase
(.alpha.) is suitably maintained without a phase change at a
temperature elevation process and carburizing process of products,
and it is also maintained in the quenching processing. However, in
case of the vacuum carburizing furnace which is being mass-produced
now, since it is possible to mass-produce in carburizing over a
temperature of 800.about.810.degree. C. according to the
characteristics of the equipment. Therefore, in case where a
carburizing material which is commonly used may be carburized and
quenched in an available carburizing temperature of 810.degree. C.,
it may not sufficiently improve the thermal deformation since the
ferrite phase (.alpha.) is secured not to enough.
[0029] As shown in the following Table 1, the alloy steel for the
low temperature vacuum carburizing according to preferred
embodiments of the present invention is composed of Fe, and
preferably a chief element of Fe, wherein the alloy steel is formed
so that dissolved oxygen (DO) is 10 ppm or less for a cleanliness
level of the alloy (in order to decrease a content of impurities)
in an alloy system which comprises 0.17.about.0.24 weight percent
of C, 0.8.about.1.2 weight percent of Cr, 0.4.about.0.8 weight
percent of Mn, 0.80.about.1.20 weight percent of Si, 0.020 weight
percent or less of P, 0.020 weight percent or less of S,
0.015.about.0.045 weight percent of V, and the remaining weight
percent of Fe.
TABLE-US-00001 TABLE 1 Alloy compositions of the steel of the
present invention and the conventional comparative steel (Unit of
the content: weight percent) O Classification C Cr Mn Si P S V
(ppm) Fe Steel of the 0.17~0.24 0.8~1.2 0.4~0.8 0.8~1.2 below below
0.015~0.045 below rest invention 0.02 0.02 10 Comparative 0.17~0.23
0.85~1.25 0.55~0.9 0.15~0.35 below below -- below rest Steel 0.03
0.03 25 (SCr420H)
[0030] In preferred exemplary embodiments, the alloy steel for the
low temperature vacuum carburizing according to the present
invention may be mainly designed as follows.
[0031] The alloy steel of the present invention is designed to
secure an adequate ferrite phase (.alpha.) at 810.degree. or so of
an available minimum carburizing temperature of a conventional
vacuum carburizing furnace. Preferably, since the alloy steel is
designed so that a temperature A3 of the alloy steel of the present
invention referring to FIG. 2, may secure over 850.degree. C., the
30.about.50% of the ferrite phase (.alpha.) may also exist in a
deep core of the alloy steel through the carburizing and quenching
of 810.degree. C..about.830.degree. C.
[0032] The alloy steel according to the present invention will be
explained in detail as follows.
[0033] In certain preferred embodiments, carbon (C) may comprise a
content of 0.17.about.0.24 weight percent so as to have an adequate
hardness of the core after the high frequency carburizing. In
certain preferred embodiments where the content is less than the
normal amount, the ferrite phase (.alpha.) is contained too much so
that the hardness of the core becomes lower, and accordingly, the
hardness of the alloy steel becomes lower. In certain examples
where the content is more than the normal amount, the ferrite phase
(.alpha.) is contained too little, and accordingly, it is deficient
in improving the thermal deformation.
[0034] Preferably, a chromium (Cr) which is an important element to
enhance a fatigue strength of a gear steel may comprise a content
of 0.8.about.1.2 weight percent. Preferably, since the chromium may
reduce the temperature of A3 as well as the temperature of A1
referring to FIG. 2, the amount of the chromium is suitably
restricted. In particular embodiments, the chromium is added more
than 0.8 weight percent in order to suitably reduce of the
temperature of A1 and to suitably secure the fatigue strength, and
it is restricted less than 1.2 weight percent because it may not
secure the adequate ferrite phase (.alpha.) according to the
temperature of A3 which is reduced.
[0035] According to further preferred embodiments, manganese (Mn)
may comprise a content of 0.4.about.0.8 weight percent to be
decreased in comparison with the conventional carburizing
steel.
[0036] Although the manganese (Mn) may suitably increase the
strength of the alloy steel, it is an element which may be a cause
of the uneven thermal deformation by suitably inducing the
segregation in steelmaking. In particular preferred embodiments,
the manganese (Mn) was added more than 0.4 weight percent to
decrease the temperature of A1, and the manganese (Mn) was
restricted less than 0.8 weight percent to reduce the
segregation.
[0037] Preferably, in order to secure the adequate amount of the
ferrite phase (.alpha.) by suitably increasing the temperature of
A3, the content of silicon (Si) was increased and the amount of
vanadium (V) was adequately added.
[0038] In further preferred embodiments, the silicon (Si)
preferably comprises 0.80.about.4.20 weight percent so as to
suitably increase the temperature of A3 and to suitably increase a
characteristic of the contact fatigue (pitting resistance) as well.
In certain exemplary embodiments, for example where the content of
the silicon (Si) is less than the normal amount, since the
temperature of A3 is not increased enough, it is difficult to
secure an adequate amount of the ferrite phase (.alpha.). Further,
in case where the content of the silicon (Si) is more than 1.2
weight percent, a known solid-solution strengthening is too much so
as to reduce exceedingly the formability, and accordingly, the
forging process and the manufacturing process may be suitably
difficult. Preferably, the alloy steel of the present invention is
suitable to the vacuum carburizing processing since the amount of
the silicon is very much in comparison with the conventional steel.
In certain preferred embodiments where the carburizing is suitably
performed in the conventional gas carburizing furnace, surface
oxide layers may be formed by the oxidizing atmosphere, and
accordingly, the durability of the alloy steel may be suitably
reduced.
[0039] According to other further embodiments, the vanadium (V)
preferably comprises 0.015.about.0.045 weight percent so as to
suitably increase the temperature of A3 and to further maximize a
grain refinement. Preferably, since the vanadium (V) is an element
for a fine precipitation strengthening, in further preferred
embodiments, the amount of the vanadium (V) was restricted to be
more than 0.015 weight percent to suitably improve the hardness of
the core according the fine precipitation strengthening, and to
increase the temperature of A3 as well. Further, the amount of the
vanadium (V) was restricted to be less than 0.045 weight percent
since the price of the vanadium (V) is very expensive.
[0040] According to further exemplary embodiments, dissolved oxygen
(DO) was formed to be 10 ppm or less. Since a hardness of the core
in the alloy-steel of the present invention is comparatively low in
comparison with those of the conventional alloy steel for
carburizing, the requisite characteristics of a surface layer (a
carburizing layer) are considered, and accordingly, the dissolved
oxygen was suitably restricted to be 10 ppm or less. Preferably, if
the dissolved oxygen is more than 10 ppm, it may affect the
performance for surface contact fatigue.
EXAMPLES
[0041] In the following Table 2, the chemical compositions and the
important phase deformation temperature of the alloy steel of the
present invention and the comparative steel are illustrated.
TABLE-US-00002 TABLE 2 Phase deformation Available temperature
carburizing Chemical component (weight percent) (.degree. C.)
Temperature Classification C Cr Mn Si P S V O (ppm) Fe Al A3
(.degree. C.) Steel of 0.22 1.0 0.6 1.1 0.015 0.01 0.04 8 rest 761
852 770~840 invention Comparative 0.2 1.1 0.8 0.2 0.015 0.015 -- 17
rest 743 803 755~790 steel (SCr42OH)
[0042] In case of the comparative steel as the conventional steel,
when it is carburized at 810.degree. or so of an available minimum
carburizing temperature of a conventional vacuum carburizing
furnace, it may predict that the amount of the ferrite phase
(.alpha.) is not in existence since it is carburized at a single
phase area of the austenite phase (.gamma.) over the temperature of
A3. In case of the alloy steel of the present invention, t may
secure the adequate amount of the ferrite phase (.alpha.) and thus
improve the thermal deformation.
[0043] The comparative examples are illustrated in the following
Table 3, wherein they are carburized at the actual temperature of
810.degree., respectively.
TABLE-US-00003 TABLE 3 Physical properties for thermal processing
Hardness (Hv) the a Average size after (surface/ amount of thermal
processing Thermal processing deep the core (.mu.m) Classification
condition (%) Roundness Cylindricity Remarks Embodiment Vacuum
carburizing 750/340 about 35 38 42 Low (steel of the
(810.quadrature.) temperature invention) .quadrature. High pressure
carburizing gas cooling of steel of (130 bar, Helium) the invention
Comparative 1 760/390 about 2 53 72 Low example temperature
(conventional carburizing steel) of the conventional steel 2 Gas
carburizing 750/400 0 36 40 Jig (920.quadrature.) quenching
.quadrature. Furnace cooling .quadrature. High frequency heating
.quadrature. Jig quenching (Oil cooling) Used test component: Rear
annulus gear for 6-speed automatic transmission (the inside
diameter of gear IBD: 122.45 mm (Gear of FIG. 1) Average size after
thermal processing is a mean value of 20 test products indicates
data missing or illegible when filed
[0044] In certain examples where the alloy steel of the present
invention was suitably performed in low temperature vacuum
carburizing at the temperature of 810.degree., it was shown that
the thermal deformation was considerably improved after the thermal
processing, in comparison with the conventional steel which is
performed in the same thermal processing. In case of the
conventional carburizing material, the ferrite phase (.alpha.) was
not adequately secured at the deep core in carburizing at this
temperature. In case of the alloy steel of the present invention,
the ferrite phase (.alpha.) was adequately secured.
[0045] Further, the result was almost equal in comparison with the
conventional jig quenching method.
[0046] As the above-described, in case where the thermal processing
of carburizing and quenching is performed at 810.degree. or so of
an available minimum carburizing temperature of a conventional
vacuum carburizing furnace, the alloy steel for the low temperature
vacuum carburizing according to the present invention is able to
secure an adequate ferrite phase (.alpha.) to improve the thermal
distortion according to the thermal processing of an annulus gear,
and to satisfy shape restrictions such as the roundness or the
cylindricity of the annulus gear to be manufactured.
* * * * *