U.S. patent application number 13/200933 was filed with the patent office on 2012-03-01 for martensitic stainless steel for disc brakes.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Osamu Furukimi, Junichiro Hirasawa, Yoshihiro Ozaki, Takumi Ujiro.
Application Number | 20120048662 13/200933 |
Document ID | / |
Family ID | 33410147 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120048662 |
Kind Code |
A1 |
Hirasawa; Junichiro ; et
al. |
March 1, 2012 |
Martensitic stainless steel for disc brakes
Abstract
A martensitic stainless steel for disc brakes, having high
temper softening resistance. The martensitic stainless steel is not
seriously softened by maintaining the steel at more than
600.degree. C. The martensitic stainless steel contains less than
0.050 mass % carbon, 1.0 mass % or less silicon, 2.0 mass % or less
manganese, 0.04 mass % or less phosphorus, 0.010 mass % or less
sulfur, 0.2 mass % or less aluminum, more than 11.5 mass % to 15.0
mass % chromium, 0.5 mass % to 2.0 mass % nickel, more than 0.50
mass % to 4.0 mass % copper, more than 0.08 mass % to 0.6 mass %
niobium, and less than 0.09 mass % nitrogen, the remainder being
iron and unavoidable impurities.
Inventors: |
Hirasawa; Junichiro; (Tokyo,
JP) ; Ozaki; Yoshihiro; (Tokyo, JP) ; Ujiro;
Takumi; (Tokyo, JP) ; Furukimi; Osamu; (Tokyo,
JP) |
Assignee: |
JFE STEEL CORPORATION
TOKYO
JP
|
Family ID: |
33410147 |
Appl. No.: |
13/200933 |
Filed: |
October 5, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10546248 |
Oct 5, 2005 |
|
|
|
PCT/JP04/05934 |
Apr 23, 2004 |
|
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13200933 |
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Current U.S.
Class: |
188/218XL |
Current CPC
Class: |
F16D 65/125 20130101;
C22C 38/48 20130101; F16D 2200/0017 20130101; C22C 38/001 20130101;
F16D 2069/004 20130101; C22C 38/42 20130101; F16D 2200/0021
20130101; F16D 2250/0007 20130101 |
Class at
Publication: |
188/218XL |
International
Class: |
F16D 65/12 20060101
F16D065/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2003 |
JP |
2003-124027 |
Claims
1. A brake disc for a disc brake system, the brake disc being in a
disc shape and made of a martensitic stainless steel, the steel
comprising: less than 0.050 mass % carbon, 1.0 mass % or less
silicon, 2.0 mass % or less manganese, 0.04 mass % or less
phosphorus, 0.010 mass % or less sulfur, 0.2 mass % or less
aluminum, chromium in a range of from more than 11.5 mass % to 15.0
mass %, nickel in a range of from 0.5 mass % to 2.0 mass %, copper
in a range of from more than 0.50 mass % to 4.0 mass %, niobium in
a range of from more than 0.08 mass % to 0.6 mass %, less than 0.09
mass % nitrogen, and 0.0005 mass % to 0.0050 mass % calcium, the
remainder being iron and unavoidable impurities, wherein the carbon
content, the nitrogen content, the niobium content, the chromium
content, the silicon content, the nickel content, the manganese
content, and the copper content satisfy the following relationships
(1) and (2): 0.03.ltoreq.[C]+[N]-13/93.times.[Nb].ltoreq.0.09 (1)
5.times.[Cr]+10.times.[Si]+30.times.[Nb]-9.times.[Ni]-5.times.[Mn]-3.time-
s.[Cu]-225.times.[N]-270.times.[C].ltoreq.40 (2), the steel sheet
being 90 percent or more martensite on a volume basis, and the
remainder of the volume of the steel being ferrite.
2. The brake disc according to claim 1, further containing 0.02
mass % to 0.3 mass % vanadium.
3. The brake disc according to claim 1, further containing one or
both of 0.02 mass % to 2.0 mass % molybdenum and 0.02 mass % to 2.0
mass % cobalt.
4. The brake disc according to claim 1, further containing one or
more of 0.02 mass % to 0.3 mass % titanium, 0.02 mass % to 0.3 mass
% zirconium, and 0.02 mass % to 0.3 mass % tantalum.
5. The brake disc according to claim 1, further containing 0.0005
mass % to 0.0050 mass % boron.
6. The brake disc according to claim 2, further containing one or
both of 0.02 mass % to 2.0 mass % molybdenum and 0.02 mass % to 2.0
mass % cobalt.
7. The brake disc according to claim 2, further containing one or
more of 0.02 mass % to 0.3 mass % titanium, 0.02 mass % to 0.3 mass
% zirconium, and 0.02 mass % to 0.3 mass % tantalum.
8. The brake disc according to claim 3, further containing one or
more of 0.02 mass % to 0.3 mass % titanium, 0.02 mass % to 0.3 mass
% zirconium, and 0.02 mass % to 0.3 mass % tantalum.
9. The brake disc according to claim 6, further containing one or
more of 0.02 mass % to 0.3 mass % titanium, 0.02 mass % to 0.3 mass
% zirconium, and 0.02 mass % to 0.3 mass % tantalum.
10. The brake disc according to claim 2, further containing 0.0005
mass % to 0.0050 mass % boron.
11. The brake disc according to claim 3, further containing 0.0005
mass % to 0.0050 mass % boron.
12. The brake disc according to claim 4, further containing 0.0005
mass % to 0.0050 mass % boron.
13. The brake disc according to claim 6, further containing 0.0005
mass % to 0.0050 mass % boron.
14. The brake disc according to claim 7, further containing 0.0005
mass % to 0.0050 mass % boron.
15. The brake disc according to claim 8, further containing 0.0005
mass % to 0.0050 mass % boron.
16. The brake disc according to claim 9, further containing 0.0005
mass %.to 0.0050 mass % boron.
17. The brake disc according to claim 1, wherein the martensitic
stainless steel is hot-rolled.
18. The brake disc according to claim 1, wherein the martensitic
stainless steel is cold-rolled.
19. The brake disc according to claim 1, wherein the martensitic
stainless steel has a hardness of 32 to 38 in HRC.
20. The brake disc according to claim 1, wherein the brake disc
comprises a circular opening in a center portion of the brake disc,
the circular opening being surrounded by a first circular portion
having a plurality of fixing holes, the first circular portion
being surrounded by a second circular portion having a plurality of
cooling holes, the second circular portion forming an outer
circumference of the brake disc.
21. The brake disc according to claim 20, wherein the second
circular portion having the plurality of cooling holes is a
friction section.
Description
[0001] This is a Division of application Ser. No. 10/546,248 filed
Oct. 5, 2005, which in turn is a National Phase of Application No.
PCT/JP2004/005934 filed Apr. 23, 2004. The disclosure of the prior
applications is hereby incorporated by reference herein in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to martensitic stainless
steels for brake discs (hereinafter referred to as discs) included
in disc brakes for motorcycles, motorcars, bicycles, and other
vehicles. An example of such disc brakes is shown in FIG. 1. The
present invention particularly relates to a martensitic stainless
steel for disc brakes which are hardly softened but have an initial
proper hardness after the disc brakes are maintained at high
temperature for a long time by friction heat during braking, that
is, which are superior in temper softening resistance (hereinafter
referred to as high-temperature softening resistance).
BACKGROUND ART
[0003] Disc brakes for motorcycles and other vehicles have a
function of slowing the rotation of wheels by the friction between
discs and pads. The temperature of the discs is greatly increased
due to friction heat generated during braking. In recent years, in
order to achieve high fuel efficiency to protect the Earth's
environment, vehicles have been reduced in weight and the discs
have been therefore reduced in thickness. Since a reduction in disc
thickness results in a reduction in heat capacity, the temperature
of the discs is greatly increased by friction during braking.
Therefore, there is a possibility that the discs are rapidly worn
away because the discs are tempered and softened.
[0004] In view of hardness and corrosion resistance, a low-carbon
martensitic stainless steel containing 12% chromium and 0.06%
carbon on a mass basis is used to manufacture discs of known disc
brakes. The stainless steel is usually machined so as to have a
predetermined shape, hardened, and then provided to users. The
composition of the stainless steel is designed such that the
stainless steel has a hardness of 32 to 38 in HRC (Rockwell C
hardness determined according to JIS Z 2245).
[0005] After a disc brake made of the martensitic stainless steel
is heated to high temperature, particularly 550.degree. C. or more,
by friction heat, the hardness thereof is seriously decreased due
to the relief of the strain of the disc brake and the precipitation
of carbonitrides. Therefore, the hardness of the disc brake can be
reduced to less than its lower limit, that is, less than 32 in HRC.
In particular, since the discs have been reduced in thickness as
described above, the discs need to have high-temper softening
resistance because the discs are heated to more than 600.degree. C.
in some cases.
[0006] In order to meet such a need, Japanese Unexamined Patent
Application Publication No. 2002-146482 discloses a steel sheet
used to improve the disc warpage caused by an increase in
temperature. However, the temperature disclosed in this document is
up to 600.degree. C. and no technique for improving temper
softening resistance, which is a key to prevent the hardness of
heated steel sheets from being reduced, is disclosed in the
document. Meanwhile, Japanese Unexamined Patent Application
Publication No. 2001-220654 discloses another steel sheet with high
temper softening resistance. This steel sheet has a hardness of 30
or more in HRC after the steel sheet is maintained at 530.degree.
C. or more. However, the hardness of this steel sheet is
insufficient because the following steel sheets have been recently
demanded: steel sheets that have high temper softening resistance
after they are heated to more than 600.degree. C.
[0007] It is an object of the present invention to provide a
martensitic stainless steel, having high temper softening
resistance, for disc brakes. The steel is slightly tempered and
softened if the steel is maintained at more than 600.degree. C.;
that is, the steel has a hardness of 32 or more or a hardness of 30
or more in HRC after the steel is tempered at 650.degree. C. or
670.degree. C., respectively.
DISCLOSURE OF INVENTION
[0008] In order to solve the above problems involved in the known
techniques, the inventors have investigated the effect of the
composition of martensitic stainless steels on the temper softening
resistance. As a result, the inventors have found that such steels
can be prevented from being softened due to the relief of strain by
adjusting the niobium content and the copper content to proper
values to form fine precipitates containing such elements at
500.degree. C. to 700.degree. C. to prevent the movement of
dislocation. The inventors have also found that if the steels are
maintained at more than 600.degree. C., the hardness of the steels
can be maintained high by adjusting the nitrogen content and the
nickel content to proper values to prevent carbide precipitates
from being formed at high temperature to keep the amount of
dissolved carbon to maintain the hardness of martensitic
structures.
[0009] The present invention, which has been made based on the
above findings, provides a martensitic stainless steel for disc
brakes. The steel contains less than 0.050 mass % carbon, 1.0 mass
% or less silicon, 2.0 mass % or less manganese, 0.04 mass % or
less phosphorus, 0.010 mass % or less sulfur, 0.2 mass % or less
aluminum, more than 11.5 mass % to 15.0 mass % chromium, 0.5 mass %
to 2.0 mass % nickel, more than 0.50 mass % to 4.0 mass % copper,
more than 0.08 mass % to 0.6 mass % niobium, and less than 0.09
mass % nitrogen, the remainder being iron and unavoidable
impurities. The carbon content, the nitrogen content, the niobium
content, the chromium content, the silicon content, the nickel
content, the manganese content, and the copper content satisfy the
following inequalities (1) and (2):
0.03.ltoreq.[C]+[N]-13/93.times.[Nb].ltoreq.0.09 (1)
5.times.[Cr]+10.times.[Si]+30.times.[Nb]-9.times.[Ni]-5.times.[Mn]-3.tim-
es.[Cu]-225.times.[N]-270.times.[C].ltoreq.40 (2).
[0010] Furthermore, the present invention provides another
martensitic stainless steel for disc brakes. This steel containing
less than 0.050 mass % carbon, 1.0 mass % or less silicon, 2.0 mass
% or less manganese, 0.04 mass % or less phosphorus, 0.010 mass %
or less sulfur, 0.2 mass % or less aluminum, more than 11.5 mass %
to 15.0 mass % chromium, more than 0.50 mass % to 2.0 mass %
nickel, more than 0.50 mass % to 4.0 mass % copper, more than 0.08
mass % to 0.6 mass % niobium, and less than 0.09 mass % nitrogen,
the remainder being iron and unavoidable impurities. The carbon
content, the nitrogen content, the niobium content, the chromium
content, the silicon content, the nickel content, the manganese
content, and the copper content satisfy the following inequalities
(1) and (2):
0.03.ltoreq.[C]+[N]-13/93.times.[Nb].ltoreq.0.09 (1)
5.times.[Cr]+10.times.[Si]+30.times.[Nb]-9.times.[Ni]-5.times.[Mn]-3.tim-
es.[Cu]-225.times.[N]-270.times.[C].ltoreq.40 (2).
The martensitic stainless steels preferably further contain 0.02
mass % to 0.3 mass % vanadium.
[0011] The martensitic stainless steels preferably further contain
one or more of the following elements: [0012] (1) one or both of
0.02 mass % to 2.0 mass % molybdenum and 0.02% to 2.0 mass % cobalt
on a mass basis; [0013] (2) one or more of 0.02 mass % to 0.3 mass
% titanium, 0.02% to 0.3 mass % zirconium, and 0.02 mass % to 0.3
mass % tantalum on a mass basis; and [0014] (3) one or both of
0.0005 mass % to 0.0050 mass % boron and 0.0005 mass % to 0.0050
mass % calcium.
[0015] The present invention provides a hot-rolled sheet or
cold-rolled sheet made of one of the martensitic stainless
steels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an illustration showing an example of a brake
disc, including a sheet of steel according to the present
invention, for motorcycles.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] The martensitic stainless steel according to the present
invention has the above composition and therefore has high temper
softening resistance. That is, the steel has a hardness of 32 to 38
in HRC after the steel is hardened and the steel has a hardness of
32 or more or a hardness of 30 or more in HRC after the steel is
tempered at 650.degree. C. or 670.degree. C., respectively.
Furthermore, the steel has high toughness and corrosion
resistance.
[0018] The reason for limiting the composition of the steel having
the above features to the above range will now be described.
Carbon Content of Less than 0.050 Percent by Mass
[0019] Carbon as well as nitrogen is an element useful in enhancing
the hardness of the steel by hardening. In order to achieve such an
advantage, the steel preferably contains 0.015 percent or more
carbon on a mass basis. When the steel is maintained at more than
600.degree. C., carbon bonds to chromium to form coarse
Cr.sub.23C.sub.6 precipitates; hence, carbon is useless in
enhancing the hardness and deteriorates the corrosion resistance
because carbon creates rust. An excessive increase in carbon
content leads to a reduction in toughness. Therefore, it is
necessary to limit the carbon content to less than 0.050 percent by
mass. In particular, in order to enhance the toughness and the
corrosion resistance, the carbon content is preferably less than
0.05 percent by mass and more preferably less than 0.045 percent by
mass.
Nitrogen Content of Less than 0.09 Percent by Mass
[0020] Nitrogen as well as carbon is an element useful in enhancing
the hardness of the steel by hardening. In particular, nitrogen
forms fine Cr.sub.2N precipitates at 500.degree. C. to 700.degree.
C.; hence, the temper softening resistance is improved by the
effect of hardening due to precipitation. Therefore, the use of
nitrogen rather than carbon is effective in enhancing the temper
softening resistance. In order to achieve such an advantage, the
steel preferably contains 0.015 percent or more nitrogen on a mass
basis. In order to further enhance the temper softening resistance,
the nitrogen content is more than 0.03 percent by mass. On the
other hand, an excessive increase in nitrogen content leads to a
reduction in toughness; hence, the nitrogen content must be limited
to less than 0.09 percent by mass. Silicon content of 1.0 percent
by mass or less
[0021] Since an excessive increase in silicon content leads to a
reduction in toughness, the silicon content is limited to 1.0
percent by mass or less. The silicon content is preferably 0.3
percent by mass or less.
Manganese Content of 2.0 Percent by Mass or Less
[0022] Manganese bonds to sulfur to form MnS, which causes a
reduction in corrosion resistance. Therefore, the manganese content
is limited to 2.0 percent by mass or less. The manganese content is
preferably less than 1.0 percent by mass and more preferably less
than 0.5 percent by mass.
Phosphorus Content of 0.04 Percent by Mass or Less
[0023] Phosphorus is an element that causes a reduction in hot
workability. Therefore, in view of production, it is preferable
that the phosphorus content be minimized. However, since an
excessive reduction in phosphorus content leads to an increase in
steel making cost, the upper limit of the phosphorus content is
0.04 percent by mass. In view of hot workability, the phosphorus
content is preferably 0.02 percent by mass or less.
Sulfur Content of 0.010 Percent by Mass or Less
[0024] Since an increase in sulfur content leads to a reduction in
hot workability, the sulfur content as well as the phosphorus
content is preferably low. In consideration of the desulfurization
cost in steel making steps, the sulfur content is 0.010,percent by
mass or less. In view of hot workability, the sulfur content is
preferably 0.005 percent by mass or less.
Aluminum Content of 0.2 Percent by Mass or Less
[0025] Since an excessive increase in aluminum content leads to a
reduction in toughness, the aluminum content is limited to 0.2
percent by mass or less. The aluminum content is preferably 0.20
percent by mass or less and more preferably 0.05 percent by mass or
less.
Chromium Content of More than 11.5 to 15.0 Percent by Mass
[0026] Chromium is an element essential to achieve corrosion
resistance which is an advantage of the stainless steel. In order
to achieve high corrosion resistance, it is necessary that the
chromium content be more than 11.5 percent by mass. In order to
achieve higher corrosion resistance, the chromium content is
preferably 12.0 percent by mass or more. On the other hand, an
increase in chromium content leads to a reduction in workability
and a reduction in toughness. In particular, when the chromium
content is more than 15.0 percent by mass, the stainless steel has
seriously low toughness. Therefore, the upper limit of the chromium
content is limited to 15.0 percent by mass. In order to achieve
high toughness, the chromium content is preferably less than 14.0
percent by mass and more preferably less than 13.0 percent by
mass.
Nickel Content of 0.5 to 2.0 Percent by Mass
[0027] Nickel inhibits chromium carbonitride from precipitating at
high temperature more than 600.degree. C. to maintain the hardness
of martensitic structures supersaturatedly containing dissolved
carbon, thereby enhancing the temper softening resistance.
Furthermore, nickel is useful in enhancing the corrosion resistance
which is an advantage of the stainless steel and also useful in
enhancing the toughness. In order to achieve such advantages, it is
necessary that the nickel content be 0.5 percent by mass or more.
The nickel content is preferably more than 0.50 percent by mass and
more preferably 0.55 percent by mass or more. Furthermore, in order
to achieve high temper softening resistance, the nickel content is
preferably more than 1.0 percent by mass. On the other hand, when
the nickel content is more than 2.0 percent by mass, the increase
in temper softening resistance is saturated and raw material cost
is increased. Therefore, the nickel content is limited to 2.0
percent by mass or less.
Copper Content of More than 0.50 to 4.0 Percent by Mass
[0028] Copper forms fine .epsilon.-Cu precipitates at about
600.degree. C. and the temper softening resistance is improved by
the effect of the precipitates. In order to achieve such an
advantage, the copper content is more than 0.50 percent by mass and
preferably more than 0.5 percent by mass. In order to achieve high
temper softening resistance, the copper content is preferably 1.0
percent by mass or more and more preferably 1.5 percent by mass or
more. On the other hand, when the copper content is more than 4.0
percent by mass, the temper softening resistance is saturated and
raw material cost is increased. Therefore, the copper content is
limited to 4.0 percent by mass or less.
Niobium Content of More than 0.08 to 0.6 Percent by Mass
[0029] Niobium strongly bonds to carbon or nitrogen to form niobium
carbide precipitates or niobium nitride precipitates, respectively.
These precipitates have no influence on the hardness of the
hardened stainless steel but inhibit a strain introduced into
martensitic structures by hardening from being relieved; thereby
enhancing the temper softening resistance of the stainless steel
maintained at about 600.degree. C. In order to achieve such an
advantage, it is necessary that the niobium content be more than
0.08 percent by mass. The niobium content is preferably 0.10
percent by mass or more. On the other hand, when the niobium
content is more than 0.6 percent by mass, the temper softening
resistance is saturated and the toughness is reduced; hence, the
niobium content is limited to 0.6 percent by mass or less. In view
of toughness, the niobium content is preferably 0.4 percent by mass
or less and more preferably 0.2 percent by mass or less.
Inequality 0.03.ltoreq.[C]+[N]-13/93.times.[Nb].ltoreq.0.09 (1)
[0030] Carbon and nitrogen are elements essential to enhance the
hardness of the steel by hardening. However, niobium carbide
produced by the reaction between carbon and niobium and niobium
nitride produced by the reaction between nitrogen and niobium are
useless in increasing the hardness. Therefore, in order to control
the hardness of the steel by hardening, the effects of carbon and
nitrogen must be estimated using the middle term
[C]+[N]-13/93.times.[Nb] of inequality (1), wherein the middle term
represents the remainder obtained by subtracting the carbon and
nitrogen content of the precipitates from that of the steel. When
the middle term is less than 0.03, the hardness is less than 32 in
HRC. In contrast, when the middle term is more than 0.09, the
hardness is more than 38 in HRC. Therefore, in order to allow the
hardened steel to have a hardness of 32 to 38 in HRC, which is
suitable for disc brake uses, the middle term of inequality (1) is
limited to 0.03 to 0.09.
Inequality
5.times.[Cr]+10.times.[Si]+30.times.[Nb]-9.times.[Ni]-5.times.[Mn]-3.time-
s.[Cu]-225.times.[N]-270.times.[C].ltoreq.40 (2)
[0031] Inequality (2) is useful in evaluating the hardenability. In
order to allow a disc material to have high hardenability, it is
necessary that 90 percent or more austenite be formed on a volume
basis by heating the disc material at 900.degree. C. to
1000.degree. C. and transformed into martensite by air-cooling the
heated disc material. In ordinary martensitic stainless steels, the
amount of austenite is maximized at about 1000.degree. C. and
decreased at higher than or lower than 1000.degree. C. When the
left side of inequality (2) is more than 40, a temperature range in
which 90 percent or more austenite is formed on a volume basis is
small. Hence, the steel can hardly be sufficiently hardened, that
is, the hardness of the steel is outside a proper hardness range if
the hardening temperature is fluctuated in a manufacturing step. In
view of productivity, the hardening temperature is preferably low
because an increase in hardening temperature increases heating cost
and heating time. From this view, it is critical that the steel
hardened from 900.degree. C. have a hardness of 32 or more in HRC.
Therefore, in order to achieve high hardenability, it is necessary
that the left side of inequality (2) be limited to 40 or less.
[0032] In the present invention, the steel preferably contains
components below in addition to the above essential elements.
Vanadium content of 0.02 to 0.3 percent by mass
[0033] Vanadium as well as niobium is an element useful in forming
fine carbonitride precipitates to enhance the temper softening
resistance. The vanadium content is preferably 0.02 percent by mass
or more and more preferably 0.10 percent by mass or more. However,
when the vanadium content is more than 0.3 percent by mass, the
toughness is low. Therefore, the upper limit of the vanadium
content is preferably 0.3 percent by mass.
One or Both of Molybdenum Content of 0.02 to 2.0 Percent by Mass
and Cobalt Content of 0.02 to 2.0 Percent by Mass
[0034] Molybdenum and cobalt are elements useful in enhance the
corrosion resistance; hence, the steel may 0.02 percent or more
molybdenum and/or 0.02 percent or more cobalt on a mass basis as
needed. Molybdenum as well as nickel inhibits chromium carbonitride
from precipitating to maintain the hardness of martensitic
structures supersaturatedly containing carbon, thereby enhancing
the temper softening resistance. In order to enhance the corrosion
resistance, the steel preferably contains 0.5 percent or more of
each element on a mass basis. When the molybdenum content and the
cobalt content are 1.5 percent by mass or less respectively, the
steel has sufficiently high corrosion resistance. In contrast, when
the molybdenum content and the cobalt content are more than 2.0
percent by mass respectively, the effect of improving the corrosion
resistance is saturated and the toughness is decreased. Therefore,
the upper limit of the molybdenum content and that of the cobalt
content are preferably 2.0 percent by mass respectively.
One or More of Titanium Content of 0.02 to 0.3 Percent by Mass,
Zirconium Content of 0.02 to 0.3 Percent by Mass, and Tantalum
Content of 0.02 to 0.3 Percent by Mass
[0035] Titanium, zirconium, and tantalum as well as niobium are
elements useful in creating fine carbonitride precipitates to
enhance the temper softening resistance. The steel may contain 0.02
percent or more of each element on a mass basis as needed. However,
when the content of the element is more than 0.3 percent by mass,
the toughness is low. Therefore, the upper limit of the content of
the element is preferably 0.3 percent by mass.
One or Both of Boron Content of 0.0005 to 0.0050 Percent by Mass
and Calcium Content of 0.0005 to 0.0050 Percent by Mass
[0036] Boron and calcium are useful in enhancing the toughness of
the steel if the boron or calcium content is small. Hence, the
steel preferably contains 0.0005 percent or more boron and/or
0.0005 percent or more calcium on a mass basis. However, when the
boron or calcium content is more than 0.0050 percent by mass
respectively, the effect is saturated and the corrosion resistance
is decreased. Therefore, the upper limit of the boron or calcium
content is preferably 0.0050 percent by mass respectively.
[0037] The martensitic stainless steel of the present invention
contains iron and avoidable impurities in addition to the above
components. Examples of the impurities (0.01 percent or less by
mass) include alkali metals, alkaline-earth metals, rare-earth
element, and transition metals, for example, sodium, barium,
lanthanum, yttrium, and hafnium. The impurities do not reduce the
advantages of the present invention.
[0038] The structure of a sheet made of the martensitic stainless
steel for disc brakes according to the present invention will now
be described.
[0039] In the steel of the present invention, in order to achieve
sufficiently high hardenability, it is necessary that 90 percent or
more austenite be formed on a volume basis by heating the steel at
900.degree. C. to 1000.degree. C. and transformed into martensite
by air-cooling the heated steel. Therefore, the steel preferably
contains 90 percent or more martensite on a volume basis, the
remainder being ferrite. When the volume of martensite is less than
90%, the volume of ferrite, which is soft, is large; hence, desired
hardness can hardly be achieved.
[0040] A method for manufacturing the martensitic stainless steel
according to the present invention will now be described.
[0041] The method for manufacturing the steel is not particularly
limited and any known method for manufacturing an ordinary
martensitic stainless steel may be used.
[0042] The method preferably includes a step of preparing molten
steel containing the above essential components and additional
components used as needed in a converter or an electric furnace and
a step of subjecting the molten steel to secondary smelting by a
smelting process such as a vacuum degassing process (an RH
process), VOD (vacuum oxygen decarburization), or AOD (argon oxygen
decarburization). The molten steel may be formed into a steel
material (a slab) by a known process such as a continuous casting
process or a slabbing process. In view of productivity and quality,
the continuous casting process is preferably used. The obtained
steel material is heated at 1100.degree. C. to 1250.degree. C.,
hot-rolled at a finishing temperature of 800.degree. C. to
1100.degree. C., and then coiled at 600.degree. C. to 900.degree.
C., whereby a hot-rolled steel strip with a thickness of 3 to 8 mm
is prepared. The hot-rolled steel strip is annealed at 650.degree.
C. to 900.degree. C. for four to 20 hours in a batch-type furnace
such as a box annealing furnace and then rolled into a sheet as
needed, whereby a disc material is prepared. The hot-rolled steel
strip may be descaled by pickling or shot blast.
[0043] The disc material obtained as described above is stamped
into pieces having a disc shape. Each piece is heated at
900.degree. C. to 1000.degree. C., hardened by an air-cooling
process or another process by which the piece can be cooled at a
cooling rate of air-cooling or higher, and then subjected to
descaling and/or coating as needed. Friction faces of the resulting
piece that are rubbed with brake pads are mechanically polished
such that the piece is improved in beauty and thickness accuracy,
whereby a disc product having a configuration shown in FIG. 1 is
obtained.
[0044] The martensitic stainless steel, manufactured as described
above, according to the present invention can be used to
manufacture brake discs for motorcycles, bicycles, motorcars, and
snow mobiles. Since discs for bicycle disc brakes have a thickness
of about 2 mm, the hot-rolled steel strip annealed and then pickled
is cold-rolled with a tandem mill or a reverse mill such as a
Sendzimir mill, annealed at 600.degree. C. to 900.degree. C. as
needed, and then pickled as needed, whereby a material for such
discs is prepared. This disc material can be processed into
products by the same procedure as that for manufacturing the former
product using the hot-rolled steel strip.
EXAMPLE 1
[0045] Steel samples (Nos. 1 to 67) containing chemical components
shown in Tables 1 to 4 were prepared in a small-sized vacuum
melting furnace. Each steel sample was cast into an ingot with a
weight of 50 kgf. The ingot was hot-rolled into a sheet with a
thickness of 5 mm at a finishing temperature of 900.degree. C. The
hot-rolled sheet was annealed at 700.degree. C. for eight hours in
an argon atmosphere, gradually cooled, and then pickled in such a
manner that the sheet was immersed in an acid mixture (an aqueous
solution containing 10 mass % nitric acid and 3 mass % hydrofluoric
acid) maintained at 60.degree. C. such that scale on the sheet is
removed, whereby a test specimen investigated as described below
was prepared.
(Hardenability)
[0046] Two test pieces were prepared by cutting each test specimen.
The test pieces were 30 mm square and had a thickness equal to the
sheet thickness. One of the pieces was heated at 900.degree. C. for
ten minutes and the other one was heated at 1000.degree. C. for ten
minutes. The resulting pieces were hardened by air-cooling. Scale
was removed from surfaces of the pieces by pickling. The surface
hardness in HRC (JIS Z 2245) was measured at five points per test
piece and obtained measurements were averaged. It is necessary for
steel for discs to have a hardness of 32 to 38 in HRC after the
steel is hardened at 900.degree. C. or 1000.degree. C. as described
above. Hence, if one of the test pieces hardened at the above
temperature has a hardness outside the above range, the test
specimen can be evaluated to be inferior in stability of
hardenability; that is, there is a possibility that the test
specimen has an insufficient hardness due to fluctuations in
heat-treating temperature.
(Temper Softening Resistance)
[0047] Other two test pieces were prepared by cutting each test
specimen. These test pieces were 30 mm square and had a thickness
equal to the sheet thickness. The test pieces were heated at
1000.degree. C. for ten minutes and then hardened by air-cooling.
One of the test pieces was tempered at 650.degree. C. for one hour
and the other one was tempered at 670.degree. C. for one hour.
Scale was removed from surfaces of the pieces by pickling. The
surface hardness (HRC) was measured at five points per test piece
and obtained measurements were averaged, whereby the temper
softening resistance of the test pieces tempered at 650.degree. C.
and 670.degree. C. was evaluated. If the test piece tempered at
650.degree. C. has a hardness of 32 or more in HRC and the test
piece tempered at 670.degree. C. has a hardness of 30 or more in
HRC, the test specimen can be evaluated to have sufficiently high
temper softening resistance.
(Corrosion Resistance)
[0048] A corrosion resistance test was performed as follows: each
test specimen was heated at 1000.degree. C. for ten minutes,
hardened by air-cooling, and then tempered at 650.degree. C. for
one hour; a test piece having a width of. 70 mm, a length of 150
mm, and a thickness equal to the sheet thickness was prepared by
cutting the resulting test specimen; a test face (a test face of
the test piece) was wet-polished with a sheet of #800 emery
polishing paper; the resulting test piece was subjected to a salt
spray test for eight hours according to JIS Z 2371; and the number
of rust spots was counted. The corrosion resistance was evaluated
as follows: a rating of .largecircle. was given to the test pieces
having no rust spot, a rating of .DELTA. was given to the test
pieces having one to four rust spots, and a rating of .times. was
given to the test pieces having five or more rust spots. The test
pieces having five or more rust spots can be evaluated to be
inferior in corrosion resistance and are not therefore suitable for
practical use.
(Toughness)
[0049] The toughness was measured as follows: each test specimen
was heated at 1000.degree. C. for ten minutes, hardened by
air-cooling, and then tempered at 650.degree. C. for one hour;
three subsize Charpy impact test pieces (a thickness of 10 mm, a
width of 5 mm (equal to the thickness of the hot-rolled sheet), and
a length of 55 mm) were prepared by cutting the resulting test
specimen according to JIS Z 2202; the Charpy impact value of the
test pieces was measured by performing the Charpy impact test at
25.degree. C. (JIS Z 2242); and obtained measurements were then
averaged. If the test specimen has an average Charpy impact value
of 50 J/cm.sup.2 or more, the specimen can be evaluated to be
suitable for practical use.
[0050] Tables 1 to 4 show the results of the above tests. The steel
samples (Nos. 1 to 49) shown in Tables 1, 2, and 3 comply with the
standards of the present invention. For the steel samples, the test
pieces hardened from 900.degree. C. and 1000.degree. C. have a
proper hardness, that is, a hardness of 32 to 38 in HRC. The test
pieces hardened from 1000.degree. C. and then tempered at
650.degree. C. have a hardness of 32 or more in HRC. The test
pieces hardened from 1000.degree. C. and then tempered at
670.degree. C. have a hardness of 30 or more in HRC. The test
pieces subjected to the impact test have a Charpy impact value of
50 J/cm.sup.2 or more. The test pieces subjected to the salt spray
test have high corrosion resistance. In contrast, the steel samples
(Nos. 50 to 67) shown in Tables 4 do not comply with the standards
of the present invention. For these steel samples, the test pieces
have low hardness, low Charpy impact value, and/or low corrosion
resistance after they have been hardened from 900.degree. C. or
1000.degree. C. or tempered at 650.degree. C. or 670.degree. C. As
is clear from the above results, the hot-rolled sheets prepared
using the steel samples having the same composition as that of the
martensitic stainless steel of the present invention have
satisfactory properties and are suitable for disc brakes.
EXAMPLE 2
[0051] Properties of a cold-rolled steel sheet were investigated.
An annealed cold-rolled sheet was obtained by the following
procedure: the test specimen prepared by processing the annealed
hot-rolled sheet, prepared using Steel Sample 1 shown in Table 1 of
Example 1, having a thickness of 5 mm was cold-rolled, whereby a
cold-rolled sheet with a thickness of 1.5 mm was prepared; the
cold-rolled sheet was annealed in such a manner that the sheet was
heated at 750.degree. C. for one minute and then air-cooled; the
resulting cold-rolled sheet was descaled in such a manner that the
sheet was immersed in an acid mixture (10% nitric acid and 3%
hydrofluoric acid on a mass basis) maintained at 60.degree. C. The
annealed cold-rolled sheet was tested in the same manner as that
described in Example 1. A subsize Charpy impact test piece had a
width of 1.5 mm (the thickness of the cold-rolled sheet). Results
obtained by testing the cold-rolled sheet were as follows: test
pieces hardened from 900.degree. C. had a hardness of 37 in HRC,
test pieces hardened from 1000.degree. C. had a hardness of 37 in
HRC, test pieces hardened from 1000.degree. C. and then tempered at
650.degree. C. had a hardness of 34 in HRC, and test pieces
hardened from 1000.degree. C. and then tempered at 670.degree. C.
had a hardness of 32 in HRC. The subsize Charpy impact test piece
had a Charpy impact value of 85 J/cm.sup.2. Test pieces subjected
to the salt spray test had no rust spot; that is, these test pieces
had high corrosion resistance. As is clear from these results, the
cold-rolled steel sheet prepared using the steel sample having the
same composition as that of the martensitic stainless steel of the
present invention has satisfactory properties and are suitable for
disc brakes.
INDUSTRIAL APPLICABILITY
[0052] As described above, according to the present invention, a
martensitic stainless steel, having high temper softening
resistance, for disc brakes can be manufactured by properly
controlling the composition thereof. In particular, the martensitic
stainless steel is not seriously softened by maintaining the steel
at more than 600.degree. C. The steel has a hardness of 32 or more
or a hardness of 30 or more in HRC after the steel is tempered at
650.degree. C. for one hour or tempered at 670.degree. C. for one
hour, respectively.
TABLE-US-00001 TABLE 1 Composition (percent by mass) Steel Other
Samples C Si Mn P S Al Cr Ni Cu Nb N Elements 1 0.041 0.24 0.33
0.01 0.004 0.012 12.2 1.21 1.65 0.17 0.057 -- 2 0.048 0.23 0.18
0.02 0.003 0.003 12.7 1.18 1.62 0.21 0.042 -- 3 0.042 0.23 0.32
0.02 0.003 0.013 12.2 1.20 0.58 0.18 0.053 -- 4 0.044 0.22 0.44
0.03 0.001 0.003 12.5 1.32 1.14 0.18 0.043 -- 5 0.018 0.86 0.38
0.02 0.004 0.013 12.3 1.58 1.58 0.18 0.053 -- 6 0.043 0.24 0.43
0.02 0.003 0.003 12.9 1.77 1.61 0.09 0.055 -- 7 0.011 0.21 0.34
0.02 0.003 0.002 12.4 1.12 1.92 0.19 0.085 -- 8 0.043 0.18 0.78
0.02 0.005 0.003 12.7 1.68 1.62 0.15 0.045 Ti: 0.15 9 0.043 0.17
0.35 0.01 0.002 0.008 14.4 1.58 1.75 0.38 0.071 -- 10 0.041 0.19
1.75 0.02 0.003 0.003 12.3 1.57 1.60 0.18 0.036 -- 11 0.033 0.12
0.42 0.02 0.004 0.015 11.8 1.51 3.65 0.23 0.046 -- 12 0.042 0.21
0.42 0.02 0.003 0.003 12.3 0.57 2.04 0.16 0.043 -- 13 0.037 0.29
0.41 0.02 0.004 0.013 12.5 1.17 1.85 0.55 0.082 -- 14 0.042 0.22
0.42 0.01 0.003 0.005 12.3 1.07 2.05 0.19 0.024 -- 15 0.042 0.23
0.25 0.02 0.003 0.018 12.3 1.88 1.50 0.33 0.063 Mo: 0.85 16 0.033
0.15 1.55 0.02 0.003 0.003 12.3 0.47 1.08 0.15 0.045 -- 17 0.037
0.23 0.45 0.02 0.004 0.016 12.8 1.94 1.55 0.25 0.035 Mo: 1.43 18
0.039 0.22 0.33 0.02 0.003 0.023 12.9 1.17 1.62 0.15 0.048 Mo: 1.05
19 0.044 0.21 0.25 0.02 0.003 0.017 12.2 1.10 2.12 0.23 0.054 Mo:
0.12 20 0.043 0.15 0.18 0.02 0.003 0.022 12.1 1.13 2.07 0.39 0.052
Mo: 1.75 21 0.039 0.23 0.35 0.02 0.003 0.002 12.2 1.22 1.61 0.17
0.055 V: 0.05 22 0.041 0.23 0.33 0.02 0.002 0.002 12.3 1.22 0.59
0.18 0.053 V: 0.13 23 0.042 0.23 0.34 0.02 0.003 0.003 12.8 1.47
1.14 0.09 0.044 V: 0.12 24 0.040 0.18 1.55 0.02 0.002 0.003 12.2
0.51 1.11 0.18 0.035 V: 0.13 25 0.041 0.23 0.35 0.02 0.002 0.003
12.4 0.46 2.54 0.16 0.044 V: 0.19 26 0.035 0.30 0.45 0.03 0.004
0.003 12.4 1.15 1.55 0.55 0.085 V: 0.30 Value of Value of Hardness
of Hardened Hardness of Hardness of Middle Left Side Test Pieces
(HRC) Test Pieces Test Pieces Charpy Term of of Quenching Quenching
Temperature Temperature Salt Impact Steel Inequality Inequality
Temperature Temperature at 650.degree. C. at 670.degree. C. Spray
Value Samples (1) (2) at 900.degree. C. at 1000.degree. C. (HRC)
(HRC) Test (J/cm.sup.2) Remarks 1 0.074 27 37 37 35 32 78 Example 2
0.061 33 34 35 33 31 .DELTA. 58 Example 3 0.070 31 35 36 32 30 68
Example 4 0.062 31 35 35 33 30 73 Example 5 0.046 38 33 34 32 30 56
Example 6 0.085 23 37 37 32 30 74 Example 7 0.069 30 34 35 33 31 73
Example 8 0.067 24 34 35 33 31 .DELTA. 68 Example 9 0.061 36 33 35
32 30 52 Example 10 0.052 22 34 35 33 30 .DELTA. 83 Example 11
0.047 21 33 33 32 30 .DELTA. 72 Example 12 0.063 34 35 35 32 30 79
Example 13 0.042 35 33 34 32 30 52 Example 14 0.039 35 33 34 32 30
86 Example 15 0.059 26 34 34 33 31 73 Example 16 0.06 33 35 35 32
30 70 Example 17 0.037 32 33 33 32 30 74 Example 18 0.066 33 33 35
32 30 75 Example 19 0.066 28 34 34 33 31 75 Example 20 0.040 33 33
33 32 30 81 Example 21 0.070 28 36 36 34 32 80 Example 22 0.069 32
35 36 32 30 70 Example 23 0.073 29 36 36 32 30 75 Example 24 0.050
34 35 35 33 31 .DELTA. 65 Example 25 0.063 35 34 34 32 30 53
Example 26 0.043 38 33 34 32 30 52 Example
TABLE-US-00002 TABLE 2 Composition (percent by mass) Steel Other
Samples C Si Mn P S Al Cr Ni Cu Nb N Elements 27 0.042 0.28 0.12
0.02 0.003 0.003 11.8 1.12 1.73 0.22 0.066 V: 0.12, B: 0.0015 28
0.048 0.25 0.18 0.02 0.003 0.003 12.8 1.15 1.62 0.23 0.043 -- 29
0.043 0.23 0.34 0.02 0.003 0.023 12.1 1.20 1.11 0.18 0.054 Co:
0.12, B: 0.0009 30 0.044 0.31 0.44 0.03 0.001 0.003 12.5 0.52 1.04
0.15 0.043 Co: 0.30 31 0.038 0.16 0.28 0.02 0.004 0.003 12.2 0.58
1.68 0.18 0.043 Ca: 0.0011 32 0.043 0.21 0.43 0.02 0.003 0.003 12.9
1.87 1.61 0.09 0.055 Co: 1.2, Ca: 0.0006 33 0.012 0.21 0.33 0.02
0.003 0.012 12.5 1.12 1.82 0.19 0.084 Mo: 0.8, V: 0.05 34 0.043
0.15 0.28 0.02 0.005 0.003 12.7 1.66 1.62 0.16 0.015 B: 0.0045 35
0.042 0.17 0.34 0.01 0.002 0.003 12.8 1.08 1.64 0.58 0.071 Mo: 0.7,
V: 0.08 36 0.041 0.09 1.55 0.02 0.003 0.003 12.3 0.54 1.10 0.15
0.041 Ca: 0.0046 37 0.036 0.12 0.43 0.02 0.002 0.003 12.1 1.51 1.65
0.23 0.046 Co: 0.8, Ta: 0.08 38 0.042 0.29 0.42 0.02 0.003 0.003
12.2 1.07 2.04 0.16 0.042 Mo: 1.5, V: 0.12 39 0.018 0.29 0.43 0.02
0.004 0.003 12.5 0.97 1.95 0.15 0.082 Co: 0.03, B: 0.0019 Value of
Value of Hardness of Hardened Hardness of Hardness of Middle Left
Side Test Pieces (HRC) Test Pieces Test Pieces Charpy Term of of
Quenching Quenching Temperature Temperature Salt Impact Steel
Inequality Inequality Temperature Temperature at 650.degree. C. at
670.degree. C. Spray Value Samples (1) (2) at 900.degree. C. at
1000.degree. C. (HRC) (HRC) Test (J/cm.sup.2) Remarks 27 0.077 26
37 37 34 32 .DELTA. 68 Example 28 0.058 35 33 35 33 30 .DELTA. 55
Example 29 0.072 29 35 36 33 31 67 Example 30 0.66 39 33 35 33 30
53 Example 31 0.056 36 33 35 33 31 66 Example 32 0.085 22 37 37 33
30 74 Example 33 0.069 31 34 35 34 32 63 Example 34 0.036 34 33 34
33 30 68 Example 35 0.032 39 32 34 34 32 54 Example 36 0.061 31 34
35 32 30 .DELTA. 64 Example 37 0.050 28 35 35 34 31 62 Example 38
0.062 30 35 35 34 32 69 Example 39 0.079 30 37 37 32 30 72
Example
TABLE-US-00003 TABLE 3 Composition (percent by mass) Steel Other
Samples C Si Mn P S Al Cr Ni Cu Nb N Elements 40 0.042 0.25 0.42
0.02 0.003 0.005 12.4 1.07 2.05 0.16 0.044 Mo: 1.1, V: 0.28 41
0.041 0.91 0.15 0.02 0.003 0.003 12.3 1.88 1.60 0.33 0.063 Mo: 0.2,
Ti: 0.05 42 0.036 0.12 0.12 0.02 0.002 0.003 12.1 1.12 1.88 0.25
0.048 Mo: 1.9, V: 0.04 43 0.036 0.23 0.33 0.04 0.008 0.003 12.8
1.94 1.52 0.25 0.038 Mo: 0.7, Zr: 0.14 44 0.039 0.23 1.87 0.02
0.003 0.023 12.9 1.11 1.62 0.26 0.045 V: 0.2, Ca: 0.0012 45 0.043
0.21 0.28 0.01 0.003 0.003 12.2 1.10 2.03 0.47 0.054 V: 0.11 46
0.043 0.12 0.18 0.02 0.002 0.152 12.1 1.12 2.07 0.48 0.056 Mo: 1.3,
V: 0.03 47 0.041 0.26 0.65 0.02 0.003 0.022 12.3 1.06 1.85 0.22
0.047 V: 0.14, B: 0.0012 48 0.043 0.12 0.31 0.02 0.002 0.003 12.1
1.71 0.58 0.25 0.058 Co: 0.08, Ca: 0.0036 49 0.044 0.30 0.05 0.03
0.005 0.003 14.3 1.1 20.05 0.15 0.055 Mo: 0.7, V: 0.13 Value of
Value of Hardness of Hardened Hardness of Hardness of Middle Left
Side Test Pieces (HRC) Test Pieces Test Pieces Charpy Term of of
Quenching Quenching Temperature Temperature Salt Impact Steel
Inequality Inequality Temperature Temperature at 650.degree. C. at
670.degree. C. Spray Value Samples (1) (2) at 900.degree. C. at
1000.degree. C. (HRC) (HRC) Test (J/cm.sup.2) Remarks 40 0.064 30
35 35 34 32 63 Example 41 0.058 33 34 35 34 32 53 Example 42 0.049
32 35 35 34 32 74 Example 43 0.039 32 33 34 34 32 69 Example 44
0.048 30 33 34 34 32 .DELTA. 71 Example 45 0.031 36 32 34 34 32 50
Example 46 0.032 35 32 34 34 32 53 Example 47 0.057 31 34 35 34 32
.DELTA. 72 Example 48 0.066 26 35 35 32 30 68 Example 49 0.078 38
35 37 34 32 55 Example
TABLE-US-00004 TABLE 4 Composition (percent by mass) Steel Other
Samples C Si Mn P S Al Cr Ni Cu Nb N Elements 50 0.051 0.14 0.12
0.02 0.003 0.003 12.2 1.05 2.03 0.15 0.043 -- 51 0.033 1.12 0.16
0.02 0.002 0.005 12.3 1.68 1.88 0.30 0.065 Mo: 0.7, Zr: 0.12 52
0.043 0.21 2.12 0.02 0.003 0.006 12.1 1.22 1.80 0.43 0.064 Ti: 0.25
53 0.049 0.13 1.78 0.03 0.008 0.005 12.2 0.10 1.23 0.26 0.018 -- 54
0.080 0.02 0.25 0.02 0.005 0.031 12.2 0.85 0.35 0.04 0.011 -- 55
0.050 0.25 2.12 0.02 0.003 0.001 12.5 0.86 0.01 0.25 0.030 -- 56
0.046 0.32 1.52 0.02 0.002 0.007 12.3 0.27 0.01 0.13 0.037 -- 57
0.040 0.12 0.31 0.03 0.002 0.022 11.2 1.43 1.88 0.23 0.055 Ta: 0.12
58 0.043 0.23 0.44 0.02 0.002 0.009 12.2 0.44 3.21 0.25 0.055 -- 59
0.043 0.29 0.43 0.03 0.003 0.009 12.4 1.06 1.89 0.62 0.084 V: 0.06
60 0.043 0.19 0.34 0.01 0.003 0.005 12.5 1.72 0.41 0.19 0.059 Co:
0.08, Ca: 0.0023 61 0.008 0.16 0.21 0.02 0.002 0.006 13.3 1.14 1.63
0.00 0.092 -- 62 0.023 0.14 0.19 0.02 0.005 0.221 12.2 1.65 2.23
0.16 0.076 -- 63 0.043 0.12 0.34 0.02 0.002 0.012 12.1 1.18 1.56
0.08 0.035 -- 64 0.033 0.23 0.34 0.01 0.003 0.003 12.1 1.46 1.66
0.34 0.043 B: 0.0025 65 0.038 0.13 0.08 0.03 0.002 0.013 12.8 1.08
1.58 0.16 0.077 Mo: 1.3, V: 0.03 66 0.033 0.21 0.12 0.02 0.003
0.005 12.8 1.13 1.54 0.31 0.044 Mo: 1.9, V: 0.04 67 0.039 0.22 0.33
0.02 0.002 0.033 15.4 1.93 1.51 0.20 0.058 -- Value of Value of
Hardness of Hardened Hardness of Hardness of Middle Left Side Test
Pieces (HRC) Test Pieces Test Pieces Charpy Term of of Quenching
Quenching Temperature Temperature Salt Impact Steel Inequality
Inequality Temperature Temperature at 650.degree. C. at 670.degree.
C. Spray Value Samples (1) (2) at 900.degree. C. at 1000.degree. C.
(HRC) (HRC) Test (J/cm.sup.2) Remarks 50 0.073 27 35 35 33 31 X 15
Comparative Example 51 0.056 37 32 35 33 31 23 Comparative Example
52 0.047 23 34 34 32 30 X 65 Comparative Example 53 0.031 39 32 33
24 21 X 16 Comparative Example 54 0.085 28 37 37 22 19 X 14
Comparative Example 55 0.045 34 32 34 24 21 X 22 Comparative
Example 56 0.065 38 33 35 21 18 X 19 Comparative Example 57 0.063
21 35 35 33 31 X 65 Comparative Example 58 0.063 31 34 35 28 25 X
29 Comparative Example 59 0.040 36 32 34 32 30 23 Comparative
Example 60 0.075 27 36 36 26 23 69 Comparative Example 61 0.100 29
39 40 20 16 18 Comparative Example 62 0.077 21 36 36 33 31 16
Comparative Example 63 0.067 28 35 35 23 20 69 Comparative Example
64 0.028 35 28 29 25 22 65 Comparative Example 65 0.093 28 39 40 38
35 64 Comparative Example 66 0.034 42 30 33 32 30 69 Comparative
Example 67 0.069 38 33 36 32 30 25 Comparative Example Note:
Underlined values are outside the scope of the present
invention.
* * * * *