U.S. patent application number 15/751897 was filed with the patent office on 2018-08-23 for vibration-damping ferritic stainless steel material, and production method.
The applicant listed for this patent is NISSHIN STEEL CO., LTD.. Invention is credited to Yoshiaki HORI, Kazunari IMAKAWA, Satoshi SUZUKI.
Application Number | 20180237891 15/751897 |
Document ID | / |
Family ID | 58051723 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180237891 |
Kind Code |
A1 |
HORI; Yoshiaki ; et
al. |
August 23, 2018 |
VIBRATION-DAMPING FERRITIC STAINLESS STEEL MATERIAL, AND PRODUCTION
METHOD
Abstract
A ferritic stainless steel material excellent in vibration
damping capability has a composition containing, by mass %, from
0.001 to 0.03% of C, from 0.1 to 1.0% of Si, from 0.1 to 2.0% of
Mn, from 0.01 to 0.6% of Ni, from 10.5 to 24.0% of Cr, from 0.001
to 0.03% of N, from 0 to 0.8% of Nb, from 0 to 0.5% of Ti, from 0
to 2.0% of Cu, from 0 to 2.5% of Mo, from 0 to 1.0% of V, from 0 to
0.3% of Al, from 0 to 0.3% of Zr, from 0 to 0.6% of Co, from 0 to
0.1% of REM, from 0 to 0.1% of Ca, the balance of Fe and
unavoidable impurities, and has ferrite single phase matrix with
crystal grains of average crystal grain diameter of from 0.3 to 3.0
mm and a residual magnetic flux density of 45 mT or less.
Inventors: |
HORI; Yoshiaki; (Tokyo,
JP) ; IMAKAWA; Kazunari; (Tokyo, JP) ; SUZUKI;
Satoshi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISSHIN STEEL CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
58051723 |
Appl. No.: |
15/751897 |
Filed: |
August 10, 2016 |
PCT Filed: |
August 10, 2016 |
PCT NO: |
PCT/JP2016/073545 |
371 Date: |
February 12, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/42 20130101;
C22C 38/50 20130101; C22C 38/58 20130101; C21D 6/005 20130101; C22C
38/00 20130101; C21D 8/0273 20130101; C21D 2211/005 20130101; C21D
6/008 20130101; C21D 6/004 20130101; C21D 8/02 20130101; C22C
38/005 20130101; C22C 38/52 20130101; Y02P 10/20 20151101; C22C
38/46 20130101; C21D 6/00 20130101; C22C 38/44 20130101; Y02P
10/212 20151101; C22C 38/06 20130101; C21D 6/007 20130101; C22C
38/02 20130101; C22C 38/48 20130101; C22C 38/001 20130101 |
International
Class: |
C22C 38/58 20060101
C22C038/58; C22C 38/42 20060101 C22C038/42; C22C 38/44 20060101
C22C038/44; C22C 38/46 20060101 C22C038/46; C22C 38/48 20060101
C22C038/48; C22C 38/50 20060101 C22C038/50; C22C 38/52 20060101
C22C038/52; C22C 38/06 20060101 C22C038/06; C22C 38/02 20060101
C22C038/02; C22C 38/00 20060101 C22C038/00; C21D 6/00 20060101
C21D006/00; C21D 8/02 20060101 C21D008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2015 |
JP |
2015-160305 |
Claims
1. A vibration-damping ferritic stainless steel material having a
chemical composition containing, in terms of percentage by mass,
from 0.001 to 0.03% of C, from 0.1 to 1.0% of Si, from 0.1 to 2.0%
of Mn, from 0.01 to 0.6% of Ni, from 10.5 to 24.0% of Cr, from
0.001 to 0.03% of N, from 0 to 0.8% of Nb, from 0 to 0.5% of Ti,
from 0 to 2.0% of Cu, from 0 to 2.5% of Mo, from 0 to 1.0% of V,
from 0 to 0.3% of Al, from 0 to 0.3% of Zr, from 0 to 0.6% of Co,
from 0 to 0.1% of REM (rare earth element), from 0 to 0.1% of Ca,
and the balance of Fe, with unavoidable impurities, having a metal
structure containing a ferrite single phase as a matrix and ferrite
crystal grains having an average crystal grain diameter of from 0.3
to 3.0 mm, and having a residual magnetic flux density of 45 mT or
less.
2. The vibration-damping ferritic stainless steel material
according to claim 1, wherein the steel material has an oxidation
increase in quantity of 2.5 mg/cm.sup.2 or less on retaining at
900.degree. C. in the air for 200 hours.
3. A production method for a vibration-damping ferritic stainless
steel material, comprising subjecting a steel material having a
chemical composition containing, in terms of percentage by mass,
from 0.001 to 0.03% of C, from 0.1 to 1.0% of Si, from 0.1 to 2.0%
of Mn, from 0.01 to 0.6% of Ni, from 10.5 to 24.0% of Cr, from
0.001 to 0.03% of N, from 0 to 0.8% of Nb, from 0 to 0.5% of Ti,
from 0 to 2.0% of Cu, from 0 to 2.5% of Mo, from 0 to 1.0% of V,
from 0 to 0.3% of Al, from 0 to 0.3% of Zr, from 0 to 0.6% of Co,
from 0 to 0.1% of REM (rare earth element), from 0 to 0.1% of Ca,
and the balance of Fe, with unavoidable impurities, to final
annealing in a non-oxidative atmosphere under a condition of
retaining the steel material in a temperature range of from 900 to
1,250.degree. C. for 10 minutes or more, so as to make an average
crystal grain diameter of ferrite crystal grains of from 0.3 to 3.0
mm, and then cooling to a temperature of 200.degree. C. or less at
a maximum cooling rate of from a maximum attaining material
temperature to 200.degree. C. of 5.degree. C./sec or less and an
average cooling rate of from 850.degree. C. to 400.degree. C. of
0.3.degree. C./sec or more.
4. The production method for a vibration-damping ferritic stainless
steel material according to claim 3, wherein the final annealing is
performed in an air atmosphere instead of the non-oxidative
atmosphere, and acid cleaning is performed after the final
annealing.
5. The production method for a vibration-damping ferritic stainless
steel material according to claim 3, wherein the steel material
subjected to the final annealing is a steel material obtained by
working a steel sheet material.
6. The production method for a vibration-damping ferritic stainless
steel material according to claim 3, wherein the steel material
subjected to the final annealing is a steel material having a
chemical composition providing an oxidation increase in quantity of
2.5 mg/cm.sup.2 or less on retaining at 900.degree. C. in the air
for 200 hours.
Description
TECHNICAL FIELD
[0001] The present invention relates to a vibration-damping
ferritic stainless steel material that exhibits a ferromagnetic
vibration damping mechanism, and a production method therefor.
BACKGROUND ART
[0002] An exhaust gas flow pipe constituting an automobile exhaust
gas flow path member, and a heat shield cover therefor are demanded
to have salt corrosion resistance in addition to heat resistance,
and therefore a ferritic stainless steel excellent in heat
resistance has been frequently used. Vibrations from an engine
reach the exhaust gas flow pipe, and noises caused by the
vibrations may become a problem. In recent years, members of an
automobile are demanded to have light weights for improving the
fuel efficiency. The reduction in thickness of the exhaust gas flow
pipe for reducing the weight tends to further increase the noises
due to the vibrations. Furthermore, the vibrations from the engine
occurring in the heat shield cover may cause muffled sound, so as
to be an offensive noise source in some cases. There is a demand of
a heat resistant stainless steel material that is excellent in
capability of suppressing vibrations and noises from an exhaust gas
flow pipe. Furthermore, there is a large demand for improvement of
the vibration damping capability of a ferritic stainless steel
material not exclusively for the automobile heat resistant
member.
[0003] The mechanisms attenuating vibration energy applied
externally to a metal single material are classified into a
eutectic type, a dislocation type, a ferromagnetic type, a
composite type, and others. A steel material having a ferrite phase
as the matrix (metal basis material) is a ferromagnetic material,
and thus various vibration damping materials utilizing a
ferromagnetic vibration damping mechanism have been proposed.
[0004] For example, PTL 1 shows an example, in which a vibration
damping capability is imparted to a steel material containing Cr.
There is described that Cr has a function of enhancing the
vibration damping characteristics, and the effect of the addition
thereof is increased up to 20.0% by weight (paragraph 0026).
However, the Cr content of the specific examples shown as the
examples is 3.08% at most.
[0005] PTL 2 shows a technique of imparting a vibration damping
capability by using a steel material containing large amounts of Si
and Co. It is taught that Cr has a significant effect of enhancing
the magnetostrictive, but decreases the loss factor when the
content thereof exceeds 9% (paragraph 0015).
[0006] PTL 3 describes a technique of imparting a vibration damping
capability by controlling the crystal grain diameter, the maximum
specific magnetic permeability, and the residual magnetic flux
density without addition of alloy elements, such as Al, Si, and Cr,
in large amounts. There is described that the crystal grain
diameter is 300 .mu.m or less in consideration of the surface
roughening in processing (paragraph 0023).
[0007] PTL 4 describes that a vibration damping capability is
imparted by using an iron alloy containing Cr and Ga in large
amounts.
CITATION LIST
Patent Literatures
[0008] PTL 1: JP-A-10-72643
[0009] PTL 2: JP-A-2002-294408
[0010] PTL 3: JP-A-2007-254880
[0011] PTL 4: JP-A-2011-241438
SUMMARY OF INVENTION
Technical Problem
[0012] As described in the patent literatures, it has been said
that Cr is effective for enhancing the vibration damping capability
of the steel material. However, no technique has been established
for improving the vibration damping capability in a steel material
using a high Cr content steel, such as a ferritic stainless
steel.
[0013] An object of the invention is to provide a ferritic
stainless steel material excellent in vibration damping
capability.
Solution to Problem
[0014] As a result of the detailed investigations made by the
present inventors, it has been found that for imparting an
excellent vibration damping capability by the ferromagnetic
vibration damping mechanism to a ferritic stainless steel material,
it is significantly effective that the steel material is worked
into a prescribed shape and then heated at a high temperature to
provide an extremely large average crystal grain diameter of 0.3 mm
or more in final annealing. It is important however that in the
cooling step subsequent to the final annealing, the cooling rate is
controlled in such a manner that the strain (dislocation) is
prevented from being introduced as much as possible, and compound
particles are prevented from being precipitated. The invention has
been accomplished based on the knowledge.
[0015] The object can be achieved by a vibration-damping ferritic
stainless steel material having a chemical composition containing,
in terms of percentage by mass, from 0.001 to 0.03% of C, from 0.1
to 1.0% of Si, from 0.1 to 2.0% of Mn, from 0.01 to 0.6% of Ni,
from 10.5 to 24.0% of Cr, from 0.001 to 0.03% of N, from 0 to 0.8%
of Nb, from 0 to 0.5% of Ti, from 0 to 2.0% of Cu, from 0 to 2.5%
of Mo, from 0 to 1.0% of V, from 0 to 0.3% of Al, from 0 to 0.3% of
Zr, from 0 to 0.6% of Co, from 0 to 0.1% of REM (rare earth
element), from 0 to 0.1% of Ca, and the balance of Fe, with
unavoidable impurities, having a metal structure containing a
ferrite single phase as a matrix and ferrite crystal grains having
an average crystal grain diameter of from 0.3 to 3.0 mm, and having
a residual magnetic flux density of 45 mT or less.
[0016] Herein, the elements, Nb, Ti, Cu, Mo, V, Al, Zr, Co, REM
(rare earth element), and Ca, each are an element that is
optionally added. The REM includes Sc, Y, and lanthanoid
elements.
[0017] For the purpose requiring heat resistance, such as an
automobile exhaust gas flow path member, a steal types having a
chemical composition controlled to provide an oxidation increase in
quantity of 2.5 mg/cm.sup.2 or less on retaining at 900.degree. C.
in the air for 200 hours is preferably applied. The temperature of
900.degree. C. for the oxidation test in the air is determined for
the condition for severely determining the oxidation resistance,
and the steel material according to the invention exhibits an
excellent vibration damping capability in a ferromagnetic region,
which is lower than that temperature.
[0018] As a production method for the vibration-damping ferritic
stainless steel material, there is provided a production method
containing subjecting a steel material having the chemical
composition to final annealing in a non-oxidative atmosphere under
a condition of retaining the steel material in a temperature range
of from 900 to 1,250.degree. C. for 20 minutes or more, so as to
make an average crystal grain diameter of ferrite crystal grains of
from 0.3 to 3.0 mm, and then cooling to a temperature of
200.degree. C. or less at a maximum cooling rate of from a maximum
attaining material temperature to 200.degree. C. of 5.degree.
C./sec or less and an average cooling rate of from 850.degree. C.
to 400.degree. C. of 0.3.degree. C./sec or more.
[0019] In the production method, the atmosphere for the final
annealing may be an air atmosphere instead of the non-oxidative
atmosphere. In this case, the steel material is subjected to acid
cleaning after the final annealing. The steel material subjected to
the final annealing may be a steel material obtained by working a
steel sheet material. In this case, the sheet thickness of the
steel sheet used (i.e., the thickness of the steel material
subjected to the final annealing) may be, for example, from 0.2 to
3.0 mm.
Advantageous Effects of Invention
[0020] According to the invention, a vibration damping capability
utilizing a ferromagnetic vibration damping mechanism can be
imparted to a ferritic stainless steel material. In particular, the
application of a ferritic type steel excellent in heat resistance
enables the vibration damping capability exhibited at up to a high
temperature range exceeding 700.degree. C. Metal materials
excellent in vibration dumping capability have been known for
non-ferrous alloys, such as a Cu--Mn-based alloy, which however
cannot be used at a high temperature. Furthermore, conventional
steel materials having a vibration damping capability imparted
thereto cannot be applied to the purposes, to which a ferritic
stainless steel material should be applied, from the standpoint of
the heat resistance and the corrosion resistance. The invention
contributes, for example, to vibration damping of an automobile
exhaust gas system.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is the optical micrograph of the metal structure of
Comparative Example No. 1.
[0022] FIG. 2 is the optical micrograph of the metal structure of
Example No. 3 of the invention.
[0023] FIG. 3 is the optical micrograph of the metal structure of
Example No. 6 of the invention.
DESCRIPTION OF EMBODIMENTS
Type of Steel Applied
[0024] In the invention, a ferritic stainless steel capable of
providing a matrix (metal basis material) formed of a ferrite
single phase at ordinary temperature is applied. The contents of
the alloy components may be determined within the aforementioned
ranges. While P and S are unavoidable impurities, the P content may
be allowed up to 0.040%, and the S content may be allowed up to
0.030%. In terms of the standard steel grades, for example, a steel
belonging to the ferritic stainless steel shown in Table 5 of JIS
G4305:2012 that has a chemical composition satisfying the
aforementioned composition can be used.
[0025] Examples of the steel types having high heat resistance
include the following compositional range (A).
[0026] (A) A steel containing, in terms of percentage by mass, from
0.001 to 0.03% of C, from 0.1 to 1.0% of Si, from 0.7 to 1.5% of
Mn, from 0.01 to 0.6% of Ni, from 17.5 to 19.5% of Cr, from 0.001
to 0.03% of N, from 0.3 to 0.8% of Nb, from 0 to 0.5% of Ti, from 0
to 1.0% of Cu, from 1.5 to 2.5% of Mo, from 0 to 1.0% of V, from 0
to 0.3% of Al, from 0 to 0.3% of Zr, from 0 to 0.6% of Co, from 0
to 0.1% of REM (rare earth element), from 0 to 0.1% of Ca, and the
balance of Fe, with unavoidable impurities.
Metal Structure
[0027] In the steel material according to the invention, it is
important that the average crystal grain diameter of the ferrite
recrystallized grains constituting the matrix (metal basis
material) is as extremely large as from 0.3 to 3.0 mm. The average
crystal grain diameter is more preferably 0.35 mm or more. A
ferromagnetic vibration damping material absorbs vibration energy
through migration of magnetic domain walls. The crystal grain
boundary becomes a barrier preventing the migration of magnetic
domain walls, and therefore it is generally said that a large
crystal grain diameter is advantageous for enhancing the vibration
damping capability. However, in the case of a ferritic stainless
steel material, a good vibration damping capability often cannot be
obtained with an average crystal grain diameter of approximately
100 .mu.m, and a measure for stably imparting a high vibration
damping capability has not been clarified. As a result of various
investigations by the inventors, it has been found that the
vibration damping capability of the ferritic stainless steel
material is enhanced by extremely increasing the average crystal
grain diameter thereof to 0.3 mm or more. While the mechanism
thereof is not clear at the present time, it is considered that the
ferrite recrystallized grains constituting the matrix of the
ferritic stainless steel material include grains having large sizes
and grains having small sizes mixed with each other, and the small
grains among these disadvantageously affect the migration of the
magnetic domain walls. It is estimated that the heat treatment is
performed to make the average crystal grain diameter as extremely
large as 0.3 mm or more, more preferably 0.35 mm or more, so as to
grow the recrystallized grains having small sizes to sizes that do
not prevent the migration of the magnetic domain walls, resulting
in the enhancement of the vibration damping mechanism over the
entire steel material.
[0028] The average crystal grain diameter can be measured by the
optical microscope observation of the cross section according to
the intercept method. According to the method described in JIS
G0551:2003, a straight line is drawn at an arbitrary position on
the image of the optical micrograph, and the number of the
intersection points of the straight line and the crystal grain
boundaries is counted, from which an average segment length is
calculated. The observation is performed for 20 or more in total of
straight lines with plural observation view fields. The ferritic
stainless steel material having an average crystal grain diameter
measured in this method that is 0.3 mm or more exhibits an
excellent vibration damping capability. The average crystal grain
diameter is more preferably 1.0 mm or more. The steel material
having been finished for the working to the shape of the member is
subjected to the final annealing described later to grow the
crystal grains, and thereby the adverse effect of the coarse
crystal grains to the workability can be avoided. The large crystal
grains are advantageous from the standpoint of the high temperature
creep resistance. However, an excessive increase of the crystal
grains may increase the load of the final annealing, which is
economically disadvantageous. The average crystal grain diameter
suffices to be in a range of 3.0 mm or less, and may be managed to
2.5 mm or less.
Magnetic Characteristics
[0029] For smoothly performing the migration of the magnetic domain
walls, it is also important that the ferrite crystal lattice has a
small strain. The extent of the strain in the crystal is reflected
to the residual magnetic flux density in the magnetic
characteristics. Specifically, assuming materials having the same
composition, it can be evaluated that a material having a smaller
residual magnetic flux density has a small strain of the crystal
lattice. According to the studies by the inventors, a good
vibration damping capability can be obtained in a ferritic
stainless steel material having a residual magnetic flux density
that is 45 mT (450 G) or less at ordinary temperature. The residual
magnetic flux density is more preferably 30 mT (300 G) or less. The
lower limit thereof is not particularly determined, and is
generally 12 mT (120 G) or more.
[0030] As other magnetic characteristics, the coercive force is
desirably 400 A/m (approximately 5 Oe) or less. The maximum
magnetic flux density is desirably 450 mT (4,500 G) or more, and
more preferably 520 mT (5,200 G) or more.
Half Value Width of X-Ray Diffraction Peak
[0031] For evaluating the strain of the crystal, a method of
measuring the half value width of the X-ray diffraction peak is
also effective. Specifically, in an X-ray diffraction pattern using
Co--K.alpha. line (with the diffraction angle 2.theta. for the
abscissa), the 1/2 half value width of the diffraction peak of the
(211) plane of the ferrite crystal can be used as an index.
According to the studies by the inventors, a good vibration damping
capability can be obtained in a ferritic stainless steel material
having a half value width of 0.160.degree. or less. As the index
for evaluating the strain of the crystal, the half value width of
the X-ray diffraction peak of the (211) crystal plane can be used
instead of or in addition to the residual magnetic flux
density.
Production Method
[0032] In the invention, the ferrite recrystallized grains are
grown in the final annealing of the ferritic stainless steel
material, so as to impart a vibration damping capability
thereto.
[0033] The process used for providing the steel material for being
subjected to the final annealing may be an ordinary production
process. For example, a cold rolled annealed acid-cleaned steel
sheet or a temper rolling finished steel sheet of a ferritic
stainless steel produced by an ordinary method as a raw material is
worked into a prescribed member. Examples of the working to the
member include various kinds of press work using a mold, bending
work, welding work, and the like.
[0034] The steel material having been worked into the member is
subjected to the final annealing. The material is heated and
retained in a temperature range of from 900 to 1,250.degree. C., so
as to grow the recrystallized grains to have an average crystal
grain diameter of the ferrite crystal grains of from 0.3 to 3.0 mm,
and more preferably from 0.35 to 3.0 mm. The retention time in the
aforementioned temperature range (i.e., the period of time where
the material temperature is in the temperature range) is ensured to
be such a period of time that is capable of growing the ferrite
crystal grains to the aforementioned average crystal grain
diameter, corresponding to the chemical composition and the degree
of working of the steel material subjected to the final annealing.
However, when the retention time is too short, the enhancement of
the vibration damping capability may be insufficient due to
shortage in homogenization in some cases. As a result of various
investigations, the retention time is preferably ensured to be 10
minutes or more. The retention time is more preferably 50 minutes
or more, and further preferably 100 minutes or more. However, a too
long retention time is economically disadvantageous. The retention
time at the aforementioned temperature may be set in a range of 300
minutes or less, and may also be a range of 200 minutes or less.
The appropriate retention temperature and retention time can be
comprehended in advance by a preliminary experiment corresponding
to the chemical composition and the degree of working of the steel
material.
[0035] In the cooling step after retaining in the aforementioned
temperature range, quenching is necessarily avoided to prevent
strain in the crystal due to thermal contraction associated with
cooling from being introduced. As a result of various
investigations, it has been found that it suffices that the maximum
cooling rate of from the maximum attaining temperature, which is in
a range of from 900 to 1,250.degree. C., to 200.degree. C. is
controlled to 5.degree. C./sec or less. When the cooling rate is
too slow, on the other hand, aging precipitation may occur in a
temperature range during cooling in some cases, and the
precipitated phase may be a factor impairing the migration of the
magnetic domain walls through the formation of a strain field in
the crystal. Therefore, it is necessary to avoid excessively slow
cooling. As a result of various investigations, the harmful effect
due to the formation of the precipitated phase can be avoided by
making the average cooling rate of from 850.degree. C. to
400.degree. C. of 0.3.degree. C./sec or more.
[0036] The final annealing is desirably performed in a
non-oxidative atmosphere. Examples thereof include vacuum
annealing. In this case, the interior of the furnace is vacuumed to
a depressurized state (vacuum atmosphere), for example, of
approximately 1.times.10.sup.-2 Pa or less, and therein, the steel
material is heated to and retained in the aforementioned
temperature range. In the cooling step, the cooling rate can be
controlled, for example, by controlling the introduction amount of
an inert gas, and the like. The final annealing may be performed in
a reductive atmosphere containing hydrogen. The final annealing may
be performed in an air atmosphere, and in this case, a
post-treatment, such as acid cleaning, is necessarily performed for
removing oxidized scale.
[0037] In the case where a flat plate member is to be provided,
such a method may be employed that a cold rolled annealed steel
sheet in a coil form is directly placed in an annealing furnace and
subjected to the final annealing, and then cut into a prescribed
dimension.
EXAMPLES
[0038] The steels shown in Table 1 were made, from which cold
rolled annealed acid-cleaned steel sheets having a sheet thickness
of 2 mm were obtained according to an ordinary method. Specimens
collected from the steel sheets were subjected to final annealing
under the conditions shown in Table 2 except for a part of
Comparative Examples (Nos. 1 and 2). The method of the final
annealing was vacuum annealing, and performed in the following
manner. The specimen was placed in a sealable vessel, and in the
state where the interior of the vessel was vacuumed to a pressure
of approximately 1.times.10.sup.-2 Pa or less, the specimen was
heated and retained at the temperature (i.e., the maximum attaining
temperature) shown in Table 2. Thereafter, except for a part of
Comparative Examples (No. 5), after decreasing the temperature to
900.degree. C., the specimen was cooled to a temperature of
400.degree. C. or less by introducing argon gas to the vessel up to
a pressure of approximately 90 kPa, and then exposed to the air
after the temperature reached 200.degree. C. or less. In the
specimen of No. 5, a thermal history of retaining at 700.degree. C.
for 60 minutes was added to the cooling step from the maximum
attaining temperature. The cooling rate conditions after the final
annealing are shown in Table 2 according to the following
standard.
Maximum Cooling Rate Condition
[0039] .largecircle.: The maximum cooling rate from the maximum
attaining temperature to 200.degree. C. was 5.degree. C./sec or
less.
[0040] .times.: The maximum cooling rate from the maximum attaining
temperature to 200.degree. C. exceeded 5.degree. C./sec.
Average Cooling Rate Condition in Intermediate Temperature
Region
[0041] .largecircle.: The average cooling rate from 850.degree. C.
to 400.degree. C. was 0.3.degree. C./sec or more.
[0042] .times.: The average cooling rate from 850.degree. C. to
400.degree. C. was less than 0.3.degree. C./sec.
[0043] In a part of the specimens shown in Table 2 were applied
with a 10% tensile strain in the rolling direction as a
post-treatment. The specimens were obtained in the aforementioned
manners.
TABLE-US-00001 TABLE 1 Chemical composition (% by mass) Steel C Si
Mn Ni Cr Nb Cu Mo Al N E 0.010 0.28 1.00 0.17 18.42 0.65 0.15 2.02
0.006 0.010 M 0.008 0.63 0.29 0.23 11.16 -- 0.07 0.05 0.040
0.008
TABLE-US-00002 TABLE 2 Final Annealing Maximum Average cooling rate
Temperature Time cooling rate condition in intermediate Class No.
Steel Atmosphere (.degree. C.) (min) condition temperature range
Post-treatment Comparative 1 E -- -- -- -- -- -- Example
Comparative 2 E -- -- -- -- -- 10% strain applied Example Example
of 3 E vacuum 1200 120 .largecircle. .largecircle. -- invention
Comparative 4 E vacuum 1100 30 .largecircle. .largecircle. 10%
strain applied Example Comparative 5 E vacuum 1100 30 .largecircle.
X -- Example (Retain at 700.degree. C. for 60 min) Example of 6 M
vacuum 950 120 .largecircle. .largecircle. -- invention
[0044] The specimens were evaluated as follows.
Measurement of Average Crystal Grain Diameter
[0045] The metal structure of the cross section in parallel to the
rolling direction and the sheet thickness direction (L cross
section) was observed with an optical microscope, and the average
crystal grain diameter was measured by the intercept method
described previously.
[0046] The micrographs of the metal structures of Nos. 1, 3, and 6
are exemplified in FIGS. 1, 2, and 3, respectively.
Magnetism Measurement
[0047] A test piece of 250 mm.times.20 mm.times.t (t: sheet
thickness, approximately from 1.8 to 2 mm) with a longitudinal
direction directed in the rolling direction was subjected to a
magnetism measurement with a direct current magnetism measurement
device (B-H Curve Tracer, produced by Riken Denshi Co., Ltd.). The
coil used was a solenoidal coil of 62.5 mm in diameter.times.160 mm
and 100 turns. The maximum magnetic flux density Bm, the residual
magnetic flux density Br, and the coercive force Hc were obtained
from the resulting B-H curve.
X-Ray Diffraction
[0048] The X-ray diffraction pattern was measured with an X-ray
diffraction apparatus (RINT 2500H, produced by Rigaku Corporation)
under condition of a Co tube, 40 kV, and 200 mA, and the 1/2 half
value width (degree) of the diffraction peak of the (211) plane of
the ferrite crystals was obtained.
Measurement of Loss Factor .eta.
[0049] A test piece of 250 mm.times.20 mm.times.t (t: sheet
thickness, approximately from 1.8 to 2 mm) with a longitudinal
direction directed in the rolling direction was measured for the
frequency response function at ordinary temperature by the central
exciting method according to JIS K7391:2008, the half value width
was read at the position decreased by 3 dB from the resonance peak
of the resulting frequency response function, from which the value
.eta. was calculated according to the expression (1) of JIS
K7391:2008, and the average value of the values .eta. obtained for
various frequencies was designated as the loss factor .eta. of the
material.
[0050] The results are shown in Table 3.
TABLE-US-00003 TABLE 3 Magnetic characteristics Maximum Residual
Average magnetic magnetic X-ray diffraction crystal grain flux
density flux density Coercive force (211) diameter Bm Br Hc Half
value width Loss Class No. Steel (mm) (mT) (mT) (Oe) (A/m) (degree)
factor .eta. Comparative 1 E 0.025 534.5 30.23 3.414 271.7 0.141
0.0008 Example Comparative 2 E 0.030 388.8 66.75 11.02 876.9 0.241
0.0003 Example Example of 3 E 1.52 543.0 25.40 2.802 223.0 0.131
0.0023 invention Comparative 4 E 2.13 370.4 50.48 8.528 678.6 0.230
0.0004 Example Comparative 5 E 1.95 493.9 76.73 9.039 719.3 0.176
0.0004 Example Example of 6 M 0.94 593.1 17.53 1.846 146.9 0.154
0.0041 invention
[0051] It is understood that the materials of the invention
obtained by performing the final annealing under the aforementioned
appropriate condition have a small strain of the crystal lattice
since the residual magnetic flux density is small, and the half
value width of the X-ray diffraction peak is also small. The
average crystal grain diameter thereof is significantly large.
These materials have a loss factor .eta. that is largely higher
than Comparative Examples, and exhibit an excellent vibration
damping capability with a loss factor .eta. of 0.0020 or more at
ordinary temperature by the central exciting method according to
JIS K7391:2008.
[0052] On the other hand, No. 1 as Comparative Example has a small
average crystal grain diameter since the material is an ordinary
cold rolled annealed acid cleaning finished material, and thus is
inferior in vibration damping capability. No. 2 is an ordinary cold
rolled annealed acid cleaning finished material, to which a work
strain is applied, and thus is more inferior in vibration damping
capability than No. 1. No. 4 has a considerably large average
crystal grain diameter by performing the appropriate final
annealing, but is applied with a work strain thereafter, and thus
has a low vibration damping capability. No. 5 is considered to have
aged precipitation formed due to the retention at 700.degree. C. on
cooling in the final annealing, and thus has a low vibration
damping capability.
* * * * *