U.S. patent application number 11/664272 was filed with the patent office on 2008-04-17 for induction heat treatment apparatus, induction heat treatment method, and worked product produced by method thereof.
Invention is credited to Takumi Fujita, Nobuyuki Suzuki.
Application Number | 20080087358 11/664272 |
Document ID | / |
Family ID | 36142566 |
Filed Date | 2008-04-17 |
United States Patent
Application |
20080087358 |
Kind Code |
A1 |
Fujita; Takumi ; et
al. |
April 17, 2008 |
Induction Heat Treatment Apparatus, Induction Heat Treatment
Method, And Worked Product Produced By Method Thereof
Abstract
In order to provide a heat treatment apparatus and method for
induction tempering through temperature control, the induction heat
treatment apparatus of the present invention conducts tempering
through high-frequency heating of a workpiece (1), and includes
temperature control means for adjusting the temperature of the
heating workpiece (1). The temperature control means includes
heating means (2) for high-frequency heating a workpiece (1),
temperature-control-dedicated temperature measuring means (3) for
measuring the temperature of the workpiece (1) heated by the
heating means (2), and temperature adjusting means connected to the
temperature measuring means (3) for providing a temperature control
signal to the heating means (2) based on temperature information
from the temperature measuring means (3). Further, the induction
heat treatment apparatus preferably includes tempering control
means, including tempering-dedicated temperature measuring means
(5) for measuring the tempering temperature of the workpiece (1)
heated by the heating means (2), and tempering time adjusting means
(6) connected to this temperature measuring means (5) for adjusting
the tempering time based on temperature information from the
temperature measuring means (5).
Inventors: |
Fujita; Takumi; (Mie,
JP) ; Suzuki; Nobuyuki; (Shizuoka, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
36142566 |
Appl. No.: |
11/664272 |
Filed: |
September 27, 2005 |
PCT Filed: |
September 27, 2005 |
PCT NO: |
PCT/JP05/17695 |
371 Date: |
March 30, 2007 |
Current U.S.
Class: |
148/400 ;
148/511; 266/249; 266/99 |
Current CPC
Class: |
C21D 1/42 20130101; C21D
11/00 20130101; Y02P 10/253 20151101; Y02P 10/25 20151101 |
Class at
Publication: |
148/400 ;
148/511; 266/249; 266/099 |
International
Class: |
C21D 1/42 20060101
C21D001/42; C21D 11/00 20060101 C21D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2004 |
JP |
2004-290314 |
Claims
1. An induction heat treatment apparatus for tempering through
high-frequency heating of a workpiece, comprising temperature
control means for adjusting a temperature of a heating
workpiece.
2. The induction heat treatment apparatus according to claim 1,
wherein said temperature control means comprises heating means for
high-frequency heating a workpiece, temperature-control-dedicated
temperature measuring means for measuring a temperature of the
workpiece heated by the heating means, and temperature adjusting
means connected to said temperature measuring means for providing a
temperature control signal to the heating means based on
temperature information from said temperature measuring means,
further comprising tempering control means including
tempering-dedicated temperature measuring means for measuring a
tempering temperature of the workpiece heated by the heating means,
and tempering time adjusting means connected to said temperature
measuring means for adjusting a tempering time based on temperature
information from said temperature measuring means.
3. The induction heat treatment apparatus according to claim 2,
wherein said tempering time adjusting means adjusts the tempering
time based on an equation of:
t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N (where t: tempering time, M.sub.0:
hardness after quenching, M.sub.f: hardness of raw material, M:
hardness after tempering, A: vibration factor term, Q: activation
energy, R: gas constant, T: tempering temperature, N: time
index).
4. The induction heat treatment apparatus according to claim 1,
wherein said workpiece includes steel.
5. An induction heat treatment method for tempering through
high-frequency heating of a workpiece, comprising a temperature
control step of adjusting a temperature of a heating workpiece, and
a tempering control step of measuring a tempering temperature to
adjust a tempering time, wherein said temperature control step
includes a heating step of high-frequency heating a workpiece, a
temperature-control-dedicated temperature measuring step of
measuring a temperature of a heated workpiece, and a temperature
adjusting step of providing a temperature control signal based on
measured temperature information for control of heating of the
workpiece, wherein said tempering control step includes a
tempering-dedicated temperature measuring step of measuring a
tempering temperature of a heating workpiece, and a tempering time
adjusting step of adjusting a tempering time based on measured
temperature information.
6. The induction heat treatment method according to claim 5,
wherein said tempering time adjusting step adjusts the tempering
time based on an equation of:
t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N (where t: tempering time, M.sub.0:
hardness after quenching, M.sub.f: hardness of raw material, M:
hardness after tempering, A: vibration factor term, Q: activation
energy, R: gas constant, T: tempering temperature, N: time
index).
7. A worked product produced by the induction heat treatment method
defined in claim 5.
Description
TECHNICAL FIELD
[0001] The present invention relates to an induction heat treatment
method of steel, more particularly, to an induction tempering
method of steel. Furthermore, the present invention relates to an
apparatus therefor, and a worked product produced by a method
thereof.
BACKGROUND ART
[0002] The tempering process of steel is applied to a quenched item
for the purpose of improving the toughness and stabilization in
dimension. The conditions for tempering are often defined by the
temperature for each type of steel, and the holding time is
generally altered more or less depending upon the thickness of the
product. This is because the effect of tempering is governed by the
effect of temperature than the effect of the holding time. A
possible approach to reduce the steps in the tempering process is
to carry out tempering in a short period of time at high
temperature. It is conventionally known to estimate the effect of
tempering based on the temperature T of tempering and the time t
for tempering using a tempering parameter P expressed by the
equation set forth below (refer to J. H. Hollomon and L. D. Jaffe,
Trans. Met. soc. Aime, 162, 1945, p. 223 (Non-Patent Document 1)).
P=T{log(t)+C}
[0003] This equation represents the temperature and time required
to obtain the same tempering effect. For practical usage, there is
known the following equation representing the relationship of the
material strength, tempering temperature, and tempering time (refer
to Japanese Patent Laying-Open No. 10-102137 (Patent Document 1)).
X=1-exp{-(kt).sup.N} k=A exp(-Q/RT)
M=M.sub.0-(M.sub.0-M.sub.f)X
[0004] (where X: rate of change in mechanical property, k: reaction
rate coefficient, t: tempering time, N: time index, A: vibration
factor term, Q: activation energy, R: gas constant, T: tempering
temperature, M: hardness after tempering, M.sub.0: hardness after
quenching, M.sub.f: hardness of raw material).
[0005] Although the effect of tempering can be known based on
temperature and time by the equations set forth above, tempering at
a high temperature for a short period of time is not generally
carried out in practice. This is to avoid generation of unevenness
in tempering in the furnace for tempering. Tempering is often
carried out to treat many target objects at one time. Therefore,
the tempering state in the furnace may be uneven depending upon the
shape (thickness), the amount of objects to be treated, and the
like. Thus, the treatment conditions in treating a large amount of
objects at one time will correspond to a process carried out for a
long period of time at a relatively low temperature less, likely to
cause unevenness in the tempering state.
[0006] A treatment method suitable for tempering at a high
temperature in a short period of time includes an induction heat
treatment method that allows heat treatment individually on each
product. It is reported that a substance of high efficiency can be
obtained by rapid-heating tempering based on induction tempering,
as compared to tempering using a normal controlled atmosphere
furnace (refer to "Iron and Steel", Volume 74, 1998, p. 334
(Non-Patent Document 2) and p. 342 (Non-Patent Document 3) by
Kawasaki et al.). However, induction tempering is not a common
process. This may be due to the fact that identifying the heat
treatment conditions is complicated since temperature control is
difficult.
[0007] Patent Document 1: Japanese Patent Laying-Open No.
10-102137
[0008] Non-Patent Document 1: J. H. Hollomon and L. D. Jaffe,
Trans. Met. soc. Aime, 162, 1945, p. 223.
[0009] Non-Patent Document 2: Kawasaki et al., "Iron and Steel"
Volume 74, 1988, p. 334
[0010] Non-Patent Document 3: Kawasaki et al., "Iron and Steel"
Volume 74, 1988, p. 342
DISCLOSURE OF THE INVENTION
Subject of the Invention
[0011] The subject of the present invention is to provide a heat
treatment apparatus for induction tempering by temperature control,
a treatment method thereof, and a worked product produced by the
method thereof.
Means for Achieving the Subject
[0012] An induction heat treatment apparatus of the present
invention corresponds to a heat treatment apparatus for tempering
through high-frequency heating of a workpiece, and is characterized
by including temperature control means for adjusting the
temperature of the heating workpiece. The temperature control means
includes heating means for high-frequency heating a workpiece,
temperature-control-dedicated temperature measuring means for
measuring the temperature of the workpiece heated by the heating
means, and temperature adjusting means connected to this
temperature measuring means for providing a temperature control
signal to the heating means based on temperature information from
the temperature measuring means. Further, the induction heat
treatment apparatus further includes tempering control means
including tempering-dedicated temperature measuring means for
measuring the tempering temperature of the workpiece heated by the
heating means, and tempering time adjusting means connected to this
temperature measuring means for adjusting the tempering time based
on the temperature information from the temperature measuring
means. The tempering time adjusting means preferably adjusts the
tempering time by t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N
[0013] (where, t: tempering time, M.sub.0: hardness after
quenching, M.sub.f: hardness of raw material, M: hardness after
tempering, A: vibration factor term, Q: activation energy, R: gas
constant, T: tempering temperature, N: time index). Steel is
preferable as the workpiece.
[0014] An induction heat treatment method of the present invention
effects tempering through high-frequency heating of a workpiece.
The method includes a temperature control step of adjusting the
temperature of a heating workpiece, and a tempering control step of
measuring the tempering temperature for adjusting the tempering
time. The temperature control step includes a heating step of
high-frequency heating a workpiece, a temperature-control-dedicated
temperature measuring step of measuring the temperature of the
heated workpiece, and a temperature adjusting step of providing a
temperature control signal based on the measured temperature
information to control heating of the workpiece. The tempering
control step includes a tempering-dedicated temperature measuring
step of measuring the tempering temperature, of the heating
workpiece, and a tempering time adjusting step of adjusting the
tempering time based on the measured temperature information. The
tempering time adjusting step preferably adjusts the tempering time
by t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N.
[0015] The worked product of the present invention is produced by
such an induction heat treatment method.
EFFECT OF THE INVENTION
[0016] According to the present invention, a tempering process of a
short period of time at high temperature through high-frequency
heating is allowed. The number of tempering steps can be reduced
and a worked product of high efficiency can be obtained. Further, a
predetermined heat treatment quality can be achieved whatever the
type of material treated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic diagram of a configuration of a
typical induction heat treatment apparatus of the present
invention.
[0018] FIG. 2 is a condition diagram of SUJ2 material representing
the relationship between the tempering temperature and tempering
time of the present invention.
[0019] FIG. 3 is a diagram to describe the relationship between the
tempering temperature and tempering time of the present
invention.
DESCRIPTION OF REFERENCE CHARACTERS
[0020] 1 workpiece, 2 heating means, 3
temperature-control-dedicated temperature measuring means, 4
temperature adjusting means, 5 tempering-dedicated temperature
measuring means, 6 tempering time adjusting means
BEST MODES FOR CARRYING OUT THE INVENTION
[0021] An induction heat treatment apparatus of the present
invention includes temperature control means for adjusting the
temperature of a workpiece, allowing tempering through
high-frequency heating of a workpiece. Therefore, processing of a
short period of time at high temperature is allowed for a workpiece
such as steel, and the number of treatment steps can be reduced.
Furthermore, rapid-heating tempering is effected for each
individual material, allowing reduction in unevenness in the heat
treatment quality. A worked product of high efficiency can be
produced.
[0022] Typically as shown in FIG. 1, the temperature control means
preferably includes heating means 2 for high-frequency heating a
workpiece 1, temperature-control-dedicated temperature measuring
means 3 for measuring the temperature of workpiece 1 heated by
heating means 2, and temperature adjusting means 4 connected to
temperature-control-dedicated temperature measuring means 3 for
providing a temperature control signal to heating means 2 based on
temperature information from the temperature measuring means.
[0023] The tempering control means preferably includes
tempering-dedicated temperature measuring means 5 for measuring the
tempering temperature of workpiece 1 heated by heating means 2, and
tempering time adjusting means 6 connected to tempering-dedicated
temperature measuring means 5 for adjusting the tempering time
based on temperature information from the temperature measuring
means. Preferably, a plurality of temperature measuring means
(thermometer) for measuring the tempering temperature are provided.
By providing a plurality of thermometers, unevenness in temperature
in a workpiece can be reduced, and the quality of tempering can be
monitored at a plurality of sites on the workpiece. The type of the
thermometer includes, but not limited to, a radiation thermometer.
A contact-type thermometer may be used, depending upon the layout
of the apparatus.
[0024] An induction heat treatment apparatus of the present
invention will be described specifically, based on an example of a
6206 type outer ring made of SUJ2 as the workpiece. This workpiece
has been quenched at 850.degree. C. in an RX gas atmosphere
furnace. With regards to the heat treatment standard of the SUJ2
material, the hardness after tempering is set to at least 58 HRC
and not more than 62 HRC.
[0025] The following relationship is established for the material
strength, tempering temperature, and tempering time, as indicated
in Patent Document 1. X=1-exp{-(kt).sup.N} k=A exp(-Q/RT)
M=M.sub.0-(M.sub.0-M.sub.f)X
[0026] (where X: rate of change in mechanical property, k: reaction
rate coefficient, t: tempering time, N: time index, A: vibration
factor term, Q: activation energy, R: gas constant, T: tempering
temperature, M: hardness after tempering, M.sub.0: hardness after
quenching, M.sub.f: hardness of raw material).
[0027] From these equations, the equation set forth below can be
derived for tempering time t.
t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N
[0028] Hardness after quenching M.sub.0 and hardness of raw
material M.sub.f in the equation can be obtained from actually
measured values. Further, N, A, and Q can be determined
empirically. Therefore, by inserting the value of tempering
temperature T, tempering time t can be calculated by the present
equation. The tempering time adjusting means of the present
invention is directed to adjusting tempering time t based on the
present equation. Since the present equation corresponds to the
relationship between the heat treatment temperature and the holding
time with respect to the standard and quality of the object
subjected to heat treatment, this equation can be employed
effectively for all types of workpieces.
[0029] According to the present equation for obtaining tempering
time t, a condition diagram representing the relationship between
tempering temperature T and tempering time t, as shown in FIG. 2,
can be produced. Referring to FIG. 2, region A corresponds to the
range of at least 62 HRC, region B corresponds to the range of 58
HRC at most, and region C corresponds to the range of 58-62 HRC.
The tempering conditions can be obtained roughly from FIG. 2. A
tempering process of a shorter time is allowed as the tempering
temperature becomes higher. Therefore, it is desirable to set a
higher tempering temperature from the standpoint of reducing the
number of steps of heat treatment. In consideration of unevenness
being facilitated in tempering caused by unevenness in temperature,
however, it is preferable to determine the tempering temperature in
view of the balance between the number of steps and unevenness in
tempering.
[0030] Upon determining the tempering conditions, they are input to
temperature adjusting means 4 such as a personal computer shown in
FIG. 1. Temperature adjusting means 4 is connected to
temperature-control-dedicated temperature measuring means 3 and
heating means 2 to provide a temperature control signal under PID
control to heating means 2, based on the temperature information
from temperature-control-dedicated temperature measuring means 3,
for control of the heat pattern of workpiece 1. At the same time,
the temperature information from tempering-dedicated temperature
measuring means 5 is provided to tempering time adjusting means 6
that is a personal computer or the like. Determination is made
whether heating is sufficient based on that heat pattern to
identify the tempering end timing. Since the temperature
information from tempering-dedicated temperature measuring means 5
changes from moment to moment, it is desirable to accumulate the
values of M (hardness after tempering), as shown in FIG. 3. At the
end of tempering, cooling is effected by coolant injecting means 7.
It is to be noted that temperature adjusting means 4 and tempering
time adjusting means 6 may be implemented by the same personal
computer.
[0031] The induction heat treatment method of the present invention
includes a temperature control step of adjusting the temperature of
the heating workpiece, and a tempering control step of measuring
the tempering temperature to adjust the tempering time. The
temperature control step includes a heating step of high-frequency
heating a workpiece, a temperature-control-dedicated temperature
measuring step of measuring the temperature of the heated
workpiece, and a temperature adjusting step of providing a
temperature control signal based on the measured temperature
information to control heating on the workpiece. The tempering
control step includes a tempering-dedicated temperature measuring
step of measuring the tempering temperature of a heating workpiece,
and a tempering time adjusting step of adjusting the tempering time
based on the measured temperature information.
[0032] The tempering time adjusting step allows the tempering time
to be adjusted through
t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N.
[0033] According to the induction heat treatment method of the
present invention, tempering of a short period of time at high
temperature through high-frequency heating of a workpiece such as
steel is allowed. The number of tempering steps can be reduced.
Furthermore, a worked product of high efficiency can be provided.
In addition, a predetermined heat treatment quality can be achieved
whatever the type of material treated.
EXAMPLE 1
[0034] An induction tempering process was conducted using the
induction heat treatment apparatus of FIG. 1. The present apparatus
includes temperature control means and tempering control means. The
temperature control means includes a coil qualified as heating
means 2 for high-frequency heating a workpiece 1, a radiation
thermometer qualified as temperature-control-dedicated temperature
measuring means 3 for measuring the temperature of workpiece 1
heated by heating means 2, and a personal computer qualified as
temperature adjusting means 4 connected to the radiation
thermometer to output a temperature control signal to heating means
2 based on the temperature information from the radiation
thermometer.
[0035] The tempering control means includes a radiation thermometer
qualified as tempering-dedicated temperature measuring means 5 for
measuring the tempering temperature of workpiece 1 heated by
heating means 2, and a personal computer qualified as tempering
time adjusting means 6 connected to this radiation thermometer to
adjust the tempering time based on the temperature information from
the radiation thermometer. Tempering time adjusting means 6 adjusts
tempering time t through
t=[ln{(M.sub.0-M.sub.f)/(M-M.sub.f)}.times.{A
exp(-Q/RT)}.sup.-N].sup.1/N.
[0036] In the present example, a 6206 type outer ring made of SUJ2
was taken as the workpiece, quenched at 850.degree. C. in an RX gas
atmosphere furnace. With regards to the heat treatment standard of
the SUJ2 material, the hardness after tempering was set to at least
58 HRC and not more than 62 HRC. Further, a radio-frequency power
supply of 80 kHz was employed for the coil. Although
temperature-control-dedicated temperature measuring means 3 and
tempering-dedicated temperature measuring means 5 are indicated as
separate units for the sake of description in FIG. 1, the same
radiation thermometer was used therefor in the present example. The
tempering time corresponds to the period of the hardness of the
temperature measured region arriving at 60 HRC. The determined
conditions were input to the personal computer, and the heat
pattern of workpiece 1 was controlled under PID control. At the
same time, the measured temperature information of workpiece 1 was
input into the personal computer for adjustment of the tempering
time.
[0037] The results of the induction tempering corresponding to
different heat treatment conditions are shown in Table 1. It is
appreciated from Table 1 that, although the processing time could
be shortened in proportion to a higher tempering temperature,
unevenness in tempering (unevenness in hardness) became more
significant. However, a worked product that is within the range of
the quality and standard set (at least 58 HRC and not more than 62
HRC) could be obtained under each of these conditions by the
current process. TABLE-US-00001 TABLE 1 Heat Treatment Condition
Highest Rate of Increase Processing Hardness (HRC) Temperature in
Temperature Time Measured (.degree. C.) (.degree. C./sec.) (sec.)
Value Unevenness 300 100 95 59.5-60.8 1.3 270 100 1500 59.8-60.3
0.5 240 100 5100 59.9-60.1 0.2
[0038] It should be understood that the embodiments and examples
disclosed herein are illustrative and non-restrictive in every
respect. The scope of the present invention is defined by the terms
of the claims, rather than the description above, and is intended
to include any modification within the scope and meaning equivalent
to the terms of the claims.
INDUSTRIAL APPLICABILITY
[0039] Induction tempering can be conducted by the least number of
steps, and a heat treated product of high quality can be
provided.
* * * * *