U.S. patent application number 16/834836 was filed with the patent office on 2020-07-23 for rolled ferritic stainless steel sheet, method for producing the same, and flange part.
This patent application is currently assigned to NIPPON STEEL & SUMIKIN STAINLESS STEEL CORPORATION. The applicant listed for this patent is NIPPON STEEL & SUMIKIN STAINLESS STEEL CORPORATION. Invention is credited to Junichi HAMADA, Koji ITO.
Application Number | 20200232062 16/834836 |
Document ID | / |
Family ID | 54195715 |
Filed Date | 2020-07-23 |
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United States Patent
Application |
20200232062 |
Kind Code |
A1 |
HAMADA; Junichi ; et
al. |
July 23, 2020 |
ROLLED FERRITIC STAINLESS STEEL SHEET, METHOD FOR PRODUCING THE
SAME, AND FLANGE PART
Abstract
The present invention provides a rolled ferritic stainless steel
material excellent in corrosion resistance and toughness, in
particular suitable as a material for a flange and a method for
producing the same and flange part. The rolled ferritic stainless
steel material contains, by mass %, C: 0.001 to 0.08%, Si: 0.01 to
1.0%, Mn: 0.01 to 1.0%, P: 0.01 to 0.05%, S: 0.0002 to 0.01%, Cr:
10.0 to 25.0%, and N: 0.001 to 0.05%, has a balance of Fe and
unavoidable impurities, has a thickness of 5 mm or more, and has an
area ratio of crystal grains with a <011> direction within
15.degree. from the rolling direction of 20% or more in a
cross-section parallel to the rolling direction at any location
between the left and right ends of the steel sheet.
Inventors: |
HAMADA; Junichi; (Tokyo,
JP) ; ITO; Koji; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMIKIN STAINLESS STEEL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON STEEL & SUMIKIN
STAINLESS STEEL CORPORATION
Tokyo
JP
|
Family ID: |
54195715 |
Appl. No.: |
16/834836 |
Filed: |
March 30, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15128891 |
Sep 23, 2016 |
10648053 |
|
|
PCT/JP2015/059470 |
Mar 26, 2015 |
|
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16834836 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/44 20130101;
C22C 38/001 20130101; C22C 38/48 20130101; C22C 38/30 20130101;
C22C 38/26 20130101; C22C 38/52 20130101; C21D 8/0226 20130101;
C22C 38/005 20130101; C22C 38/002 20130101; C22C 38/46 20130101;
F16L 23/032 20130101; C21D 8/0263 20130101; C22C 38/32 20130101;
C22C 38/42 20130101; C21D 2201/05 20130101; C21D 2211/005 20130101;
C22C 38/06 20130101; C22C 38/20 20130101; C22C 38/40 20130101; C21D
8/02 20130101; C22C 38/008 20130101; C22C 38/18 20130101; C22C
38/02 20130101; C22C 38/54 20130101; C22C 38/28 20130101; C21D
6/002 20130101; C22C 38/00 20130101; C22C 38/004 20130101; C22C
38/04 20130101; C22C 38/50 20130101; C22C 38/24 20130101; C22C
38/22 20130101; C21D 9/46 20130101; C22C 38/60 20130101 |
International
Class: |
C21D 9/46 20060101
C21D009/46; C22C 38/60 20060101 C22C038/60; C22C 38/00 20060101
C22C038/00; C22C 38/02 20060101 C22C038/02; C22C 38/04 20060101
C22C038/04; C22C 38/06 20060101 C22C038/06; C22C 38/20 20060101
C22C038/20; C22C 38/22 20060101 C22C038/22; C22C 38/24 20060101
C22C038/24; C22C 38/26 20060101 C22C038/26; C22C 38/28 20060101
C22C038/28; C22C 38/30 20060101 C22C038/30; C22C 38/32 20060101
C22C038/32; 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 38/54 20060101
C22C038/54; C22C 38/18 20060101 C22C038/18; C21D 6/00 20060101
C21D006/00; C22C 38/40 20060101 C22C038/40; C21D 8/02 20060101
C21D008/02; C22C 38/42 20060101 C22C038/42; F16L 23/032 20060101
F16L023/032 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2014 |
JP |
2014-064779 |
Claims
1. A hot rolled annealed steel sheet or a hot rolled annealed steel
strip comprised of ferritic stainless steel material containing, by
mass %, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P:
0.01 to 0.05%, S: 0.0002 to 0.01%, Cr: 10.0 to 25.0%, and N: 0.001
to 0.05%, having a balance of Fe and unavoidable impurities, having
a thickness of 5 mm or more, and having an area ratio of crystal
grains with a <011> direction within 15.degree. from the
rolling direction of 20% or more in a cross-section parallel to the
rolling direction at any location between the left and right ends
of the steel sheet.
2. The hot rolled annealed steel sheet or the hot rolled annealed
steel strip comprised of ferritic stainless steel material
according to claim 1, wherein in a cross-section parallel to the
rolling direction at any location between the left and right ends
of the steel sheet, a sum of the lengths of low-angle grain
boundaries with a crystal misorientation of less than 15.degree. is
10% or more with respect to a sum of lengths of the crystal grain
boundaries.
3. The hot rolled annealed steel sheet or hot rolled annealed steel
strip comprised of ferritic stainless steel material according to
claim 1 or 2, further containing, by mass %, one type or two types
or more of Ti: 0.01 to 0.4%, Nb: 0.01 to 0.6%, B: 0.0002 to
0.0030%, A1: 0.005 to 0.3%, Ni: 0.1 to 1%, Mo: 0.1 to 2.0%, Cu: 0.1
to 3.0%, V: 0.05 to 1.0%, Mg: 0.0002 to 0.0030%, Sn: 0.01 to 0.3%,
Sb: 0.01 to 0.3%, Zr: 0.01 to 0.1%, Ta: 0.01 to 0.1%, Hf: 0.01 to
0.1%, W: 0.01 to 2.0%, Co: 0.01 to 0.2%, Ca: 0.0001 to 0.0030%,
REM: 0.001 to 0.05%, and Ga: 0.0002 to 0.1%.
4. The hot rolled annealed steel sheet or hot rolled annealed steel
strip comprised of ferritic stainless steel according to claim 1 or
2, used as a flange part.
Description
[0001] This application is a Divisional of copending application
Ser. No. 15/128,891 filed on Sep. 23, 2016, which is the U.S.
National Phase of PCT/JP2015/059470, filed Mar. 26, 2015, and which
claims priority under 35 U.S.C. .sctn. 119(a) to Application No.
2014-064779 filed in Japan, on Mar. 26, 2014, the entire contents
of all of which are expressly incorporated by reference into the
present application.
TECHNICAL FIELD
[0002] The present invention provides a rolled ferritic stainless
steel material of a thickness of 5 mm or more which prevents
cracking at the time of steel sheet production and is excellent in
corrosion resistance and toughness and which, in particular, is
suitable as a flange material.
BACKGROUND ART
[0003] The path of exhaust gas of an automobile is comprises an
exhaust manifold, muffler, catalyst, flexible tube, center pipe,
front pipe, and various other parts. When connecting these parts,
fastening parts called "flanges" are often used. In parts of
exhaust systems of automobiles, flange connections are being
positively employed since flanges enable reduction of the
processing steps and simultaneously enable reduction of the work
space. Further, from the viewpoint of the noise due to vibration
and securing rigidity, thick flanges of 5 mm thickness or more are
often used.
[0004] Flanges have in the past been produced by press-forming,
stamping, and otherwise processing ordinary steel sheet. However,
ordinary steel is inferior in corrosion resistance, so after
manufacture of the automobile, rust called "initial rust" occurs
and the beautiful appearance is ruined. Therefore, instead of
ordinary steel sheet, use of stainless steel sheet is being
positively promoted as a material for flange.
[0005] Ferritic stainless steel sheet has less of a content of Ni
and is lower in cost than austenitic stainless steel sheet, so
mainly ferritic stainless steel sheet is often used for flanges,
but there was a problem of inferior toughness. If steel sheet is
low in toughness, the problem arises that plate fracture ends up
occurring when running steel strip or uncoiling steel strip at a
steel sheet production line. Further, in flange-making, cracks
sometimes occur at the time of cutting, stamping, and other
processing. Furthermore, when impacted in a low temperature
environment in the winter, the problem arises that a flange ends up
cracking and the automobile exhaust pipe ends up breaking. 5 mm or
more thick ferritic stainless steel sheet is particularly low in
toughness in some cases, so there was the issue that the
reliability for use of the thick ferritic stainless steel sheet for
the production of a flange was too low.
[0006] Therefore, to use the thick ferritic stainless steel sheet
to produce a flange, the toughness of the steel sheet, in
particular the toughness of the hot rolled steel sheet or hot
rolled annealed and pickled steel sheet has to be improved. Several
attempts have been made to solve the problems relating to the
toughness of ferritic stainless steel sheet.
[0007] For example, PLTs 1 and 2 disclose manufacturing conditions
for mass production of thickness 5 to 12 mm ferritic stainless
steel hot rolled coil or hot rolled annealed coil. PLT 1 relates to
Ti-containing ferritic stainless steel and shows the method of
adjusting the hardness and Charpy impact value by making the
coiling temperature 570.degree. C. or more and dipping the coil in
water. Further, PLT 2 relates to Nb-containing ferritic stainless
steel and shows the method of adjusting the hardness and Charpy
impact value by making the hot rolling finishing temperature
890.degree. C. or more, coiling at 400.degree. C. or less, and
dipping the coil in water. The arts disclosed in PLTs 1 and 2
define the hot rolling conditions from the viewpoint of improvement
of the toughness of the hot rolled plate or hot rolled annealed
steel sheet, but control of the total length of a coil to the above
conditions was difficult and the factors in metal structure for
improvement of toughness were unknown.
[0008] Further, PLT 3 discloses ferritic stainless steel excellent
in cold crack resistance obtained by making the length of subgrain
boundaries with a small crystal misorientation of the ferrite phase
a constant value or more. This ferritic stainless steel is obtained
by the method of making the hot rolling finishing temperature 800
to 1000.degree. C., making the coiling temperature over 650.degree.
C. to 800.degree. C., and dipping in a water tank after coiling.
Further, PLT 4 discloses ferritic stainless steel sheet excellent
in toughness defining the ratio of the precipitates at the grain
boundaries. The arts disclosed in PLTs 3 and 4 control the
properties of the crystal grain boundaries and precipitates on the
crystal grain boundaries so as to try to improve the toughness, but
a level of toughness sufficient for a material for a flange has not
necessarily been realized.
CITATION LIST
Patent Literature
[0009] PLT 1. Japanese Patent Publication No. 2012-140687A
[0010] PLT 2. Japanese Patent Publication No. 2012-140688A
[0011] PLT 3. WO2013/085005A
[0012] PLT 4. Japanese Patent Publication No. 2009-263714A
SUMMARY OF INVENTION
Technical Problem
[0013] An object of the present invention is to solve the problem
of the existing art and efficiently produce rolled ferritic
stainless steel material for flange excellent in toughness.
Solution to Problem
[0014] To solve this problem, it is necessary to control the
factors having an effect on toughness other than the above. In the
present invention, the inventors proceeded with intensive research
on this point. That is, the inventors engaged in detailed research
relating to the low temperature toughness of ferritic stainless
steel sheet from the viewpoints of the structure and
crystallography in the components and process of production. As a
result, they discovered to improve the toughness of for example 5
mm or more thick ferritic stainless steel sheet, in particular hot
rolled steel sheet or hot rolled annealed steel sheet, it is
extremely effective to control the direction of the crystal
orientation of the matrix phase.
[0015] The gist of the present invention to solve the above
problems lies in:
(1) A rolled ferritic stainless steel material containing, by mass
%, C: 0.001 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.01
to 0.05%, S: 0.0002 to 0.01%, Cr: 10.0 to 25.0%, and N: 0.001 to
0.05%, having a balance of Fe and unavoidable impurities, having a
thickness of 5 mm or more, and having an area ratio of crystal
grains with a <011> direction within 15.degree. from the
rolling direction of 20% or more in a cross-section parallel to the
rolling direction at any location between the left and right ends
of the steel sheet. (2) The rolled ferritic stainless steel
material according to (1), wherein in a cross-section parallel to
the rolling direction at any location between the left and right
ends of the steel sheet, a sum of the lengths of low-angle grain
boundaries with a crystal misorientation of less than 15.degree. is
10% or more with respect to a sum of lengths of the crystal grain
boundaries. (3) The rolled ferritic stainless steel material
according to (1) or (2), further containing, by mass %, one type or
two types or more of Ti: 0.01 to 0.4%, Nb: 0.01 to 0.6%, B: 0.0002
to 0.0030%, Al: 0.005 to 0.3%, Ni: 0.1 to 1%, Mo: 0.1 to 2.0%, Cu:
0.1 to 3.0%, V: 0.05 to 1.0%, Mg: 0.0002 to 0.0030%, Sn: 0.01 to
0.3%, Sb: 0.01 to 0.3%, Zr: 0.01 to 0.1%, Ta: 0.01 to 0.1%, Hf:
0.01 to 0.1%, W: 0.01 to 2.0%, Co: 0.01 to 0.2%, Ca: 0.0001 to
0.0030%, REM: 0.001 to 0.05%, and Ga: 0.0002 to 0.1%. (4) A method
of production of rolled ferritic stainless steel material
comprising smelting molten steel containing, by mass %, C: 0.001 to
0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.01 to 0.05%, S:
0.0002 to 0.01%, Cr: 10.0 to 25.0%, and N: 0.001 to 0.05% and
having a balance of Fe and unavoidable impurities, performing a hot
rolling process having a hot rolling finishing temperature of
800.degree. C. to 900.degree. C., and performing a coiling process
at a coiling temperature of 500.degree. C. or less. (5) The method
of production of rolled ferritic stainless steel material according
to (4), wherein the molten steel further contains, by mass %, one
type or two types or more of Ti: 0.01 to 0.4%, Nb: 0.01 to 0.6%, B:
0.0002 to 0.0030%, Al: 0.005 to 0.3%, Ni: 0.1 to 1%, Mo: 0.1 to
2.0%, Cu: 0.1 to 3.0%, V: 0.05 to 1.0%, Mg: 0.0002 to 0.0030%, Sn:
0.01 to 0.3%, Sb: 0.01 to 0.3%, Zr: 0.01 to 0.1%, Ta: 0.01 to 0.1%,
Hf: 0.01 to 0.1%, W: 0.01 to 2.0%, Co: 0.01 to 0.2%, Ca: 0.0001 to
0.0030%, REM: 0.001 to 0.05%, and Ga: 0.0002 to 0.1%. (6) The
method of production of rolled ferritic stainless steel material
according to (4) or (5), further comprising, after hot rolling,
heating by a heating rate of 10.degree. C./sec or more to
800.degree. C. to 1000.degree. C., then annealing, then cooling by
a cooling rate of 10.degree. C./sec or more. (7) The rolled
ferritic stainless steel material according to any one of (1) to
(3) characterized by being used as a flange part. (8) A ferritic
stainless steel flange part comprised of a flange part made of the
rolled ferritic stainless steel material according to any one of
(1) to (3) wherein an impact energy at -20.degree. C. is 125 J or
more.
Advantageous Effects of Invention
[0016] According to the present invention, it is possible to
efficiently produce rolled ferritic stainless steel material for
flange excellent in toughness without requiring new facilities.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a view showing the relationship between the
<011> oriented grain ratio and Charpy impact value.
[0018] FIG. 2 is a front view of the flange part.
[0019] FIG. 3 is a schematic view showing a low temperature drop
weight test method of a flange part of FIG. 2.
DESCRIPTION OF EMBODIMENTS
[0020] Below, the reasons for limitation of the present invention
will be explained. The crystal grain refinement and the precipitate
refinement and softening contribute to improvement of the
toughness, but large amounts of additional elements are required
and it was difficult to secure sufficient toughness for using
thickness 5 mm or more thick ferritic stainless hot rolled plate or
hot rolled annealed steel sheet for the production of flanges.
[0021] In the present invention, the crystal orientation of the
matrix phase comprised of the ferrite phase was focused on and the
relationship between the crystal orientation of the matrix phase
and the toughness was investigated in detail. As a result, the
inventors discovered that the toughness of the steel sheet is
improved by forming crystal grains with a stable orientation of
crystal grains of the <011> direction of within 15.degree.
from the rolling direction (below, also referred to as the
"<011> oriented grain") by an area ratio of 20% or more.
[0022] FIG. 1 shows the relationship between the <011>
oriented grain ratio of the hot rolled plate or hot rolled annealed
steel sheet of steel with a different thickness produced by various
processes (17% Cr-0.34% Nb-0.005% C-0.01% N) and the Charpy impact
value. Here, the crystal orientation was measured using EBSP
(electron back-scattering diffraction pattern), by which the
orientation for every crystal grain per unit area from the
cross-section of all thicknesses parallel to the rolling direction
between the two ends of the left and right of the hot rolled steel
sheet or hot rolled annealed steel sheet was measured, and the area
ratio of crystal grains with a <011> direction per unit area
of the cross-section within 15.degree. from the rolling direction
(below, also referred to as the "<011> oriented grain ratio")
was measured. Further, the Charpy impact value was measured using a
V-notch test piece taken from hot rolled annealed steel sheet
(giving V-notch in width direction) and measuring the value based
on JISZ2242 at 0.degree. C.
[0023] As shown in FIG. 1, if the <011> oriented grain ratio
is 20% or more, the Charpy impact value is improved and the
toughness becomes excellent. Here, "excellent toughness" means
having an impact value at 0.degree. C. of 7 J/cm.sup.2 or more and
no brittle fracture at the time of uncoiling a hot rolled coil and
at the time of running the plate. The cleavage surface of ferrite
steel is the {100} plane. It is known that brittle fracture occurs
along this plane, but if <011> oriented grains grow, the
angle formed by the crack propagation direction and cleavage
surface becomes greater, so the resistance to cleavage fracture
becomes larger and the toughness value is improved.
[0024] Furthermore, in the present invention, it was discovered
that the ratio of the sum of the lengths of low-angle grain
boundaries with a crystal misorientation of less than 15.degree.
with respect to the sum of the lengths of the crystal grain
boundaries has an effect on the toughness. This feature is an
important structural feature for improving the toughness along with
the above-mentioned <011> oriented grain ratio. In general,
the dislocations introduced by the processing (for example,
hot-rolling) are rearranged in the processes of restoration of the
dislocations and recrystallization of the material. In the stage of
restoration, crystal grains surrounded by low-angle grain
boundaries with a crystal misorientation of less than 15.degree.
(below, referred to as the subgrains") are formed, while coarse
crystal grains surrounded by high angle grain boundaries of
15.degree. or more are formed in the recrystallation process.
Usually, due to recrystallization heat treatment, the ratio of high
angle grain boundaries is increased and the low-angle grain
boundaries are decreased, but the high angle grain boundaries move
and grow remarkably fast, so the toughness falls due to the
coarsening of the grain size.
[0025] In the present invention, it was discovered that by forming
the subgrains so that the sum of the lengths of the low-angle grain
boundaries becomes 10% or more of the sum of the lengths of the
crystal grains at the cross-section, this suppresses movement and
growth of the grain boundaries and effectively acts as resistance
to brittle cracking. That is, they discovered that when the
<011> oriented grain ratio is 20% or more, and subgrains are
formed so that the sum of the lengths of the low-angle grain
boundaries becomes 10% or more of the sum of lengths of crystal
grain boundaries at the cross-section, it is possible to improve
the Charpy impact value at 0.degree. C. to 11 J/cm.sup.2 or more.
By improving the Charpy impact value at 0.degree. C. to 11
J/cm.sup.2 or more, it is possible to secure a toughness whereby no
cracking occurs at the time of flange-making.
[0026] The ratio of the lengths of the low-angle grain boundaries
of less than 15.degree. with respect to the sum of the lengths of
crystal grain boundaries at the cross-section can be measured by
the above EBSP orientation analysis and can be measured by a method
similar to the above method of measurement of the <011>
oriented grain ratio. Further, the measurement of the <011>
oriented grain ratio and the ratio of low-angle grain boundaries of
less than 15.degree. performed using EBSP is desirably performed
over the cross-section of the entire thickness of a length 1.0 mm
parallel to the rolling direction at any location between the two
left and right ends of the hot rolled steel sheet or hot rolled
annealed steel sheet. Further, if considering the ductility of the
steel sheet, 20% or more is desirable.
[0027] Next, the ranges of components of the steel will be
explained. The % of the contents of the components means the mass
%. [0028] C causes degradation of the toughness by the hardening by
solid solution C and precipitation of carbides, so the smaller the
content the better. Further, if the content of C is over 0.08%,
randomness of the crystal orientation occurs due to the formation
of carbides and the growth of <011> oriented grains is
suppressed, so the upper limit is made 0.08%. However, excessive
reduction leads to an increase of the refining costs, so the lower
limit of the content of C is made 0.001%. Furthermore, if
considering the manufacturing cost, corrosion resistance, and
toughness of hot rolled sheet, 0.002% to 0.015% is desirable.
[0029] Si is sometimes added as a deoxidizing element and also
gives rise to improvement of the oxidation resistance, but is a
solution strengthening element, so from the viewpoint of the
toughness, the smaller the better. Further, if the content of Si is
over 1.0%, due to the changes in the slip system, growth of
<011> oriented grains is suppressed, so the upper limit is
made 1.0%. On the other hand, to secure oxidation resistance, the
lower limit is made 0.01%. However, excessive reduction of the
content of Si leads to an increase in the refining costs, so
considering the material quality and initial rust resistance, 0.05%
to 0.9% is desirable. [0030] Mn, like Si, is a solution
strengthening element, so in terms of material quality, the smaller
the content the better. Further, if over 1.0%, the formation of
precipitates of MnS etc. causes randomness in crystal orientation
and suppresses growth of <011> oriented grains, so the upper
limit of Mn content is made 1.0%. On the other hand, excessive
reduction of the Mn content leads to an increase in refining costs,
but addition of a trace amount of Mn has the effect of improvement
of scale removal, so the lower limit is made 0.01%. Furthermore, if
considering the material quality and manufacturing costs, 0.1% to
0.5% is desirable. [0031] P, like Mn and Si, is a solution
strengthening element and causes the material to harden, so from
the viewpoint of the toughness, the smaller the content the better.
Further, if the content of P is over 0.05%, the formation of
phosphides causes randomness in the crystal orientation and
suppresses growth of <011> oriented grains, so the upper
limit is made 0.05%. However, excessive reduction leads to an
increase in the cost of materials, so the lower limit is made
0.01%. Furthermore, if considering the manufacturing costs and
corrosion resistance, 0.015% to 0.03% is desirable. [0032] S is an
element degrading the corrosion resistance, so the smaller the
content the better. Further, if the content of S is over 0.01%,
randomness of the crystal orientation occurs due to the MnS,
Ti.sub.4C.sub.2S.sub.2, and other precipitates and growth of the
<011> oriented grains is suppressed, so the upper limit is
made 0.01%. On the other hand, S bonds with the Mn or Ti and has
the effect of improving the stampability in flange-making. This
effect is expressed from a content of S of 0.0002%, so the lower
limit is made 0.0002%. Furthermore, if considering the refining
costs and the suppression of crevice corrosion at a time when the
stainless steel is made into a fuel part, the content of S is
desirably 0.0010% to 0.0060%. [0033] Cr is an element for improving
the corrosion resistance and oxidation resistance. If considering
the salt damage resistance demanded from a flange, 10.0% or more is
necessary. On the other hand, excessive addition of Cr results in
hardening and causes the formability and toughness to deteriorate.
Further, if the content of Cr is over 25.0%, randomness of the
crystal orientation occurs due to the precipitation of coarse Cr
carbides and nitrides and other precipitates and growth of the
<011> oriented grains is suppressed, so the upper limit is
made 25.0%. Further, if considering the manufacturing costs and
plate fracture at the time of production due to deterioration of
the toughness, 10.0% to 18.0% is the desirable content of Cr.
[0034] N, like C, causes the toughness and corrosion resistance to
deteriorate, so the smaller the content the better. Further, if the
content of N is over 0.05%, randomness of the crystal orientation
occurs due to the formation of nitrides and growth of <011>
oriented grains is suppressed, so the upper limit is made 0.05%.
However, excessive reduction of the content of N leads to an
increase in the refining costs, so the lower limit is made 0.001%.
Furthermore, if considering the manufacturing costs and workability
and the initial rusting, 0.005 to 0.02% is desirable.
[0035] Furthermore, the present invention preferably optionally
contains the elements shown below.
[0036] Ti bonds with C, N, and S and is an element added according
to need so as improve the corrosion resistance, grain-boundary
corrosion resistance, and toughness. The action of fixing C and N
appears from 0.01%, so the lower limit is made 0.01%. Further,
addition of over 0.4% of Ti causes hardening and also leads to
precipitation of coarse Ti(C,N) compounds and remarkable
deterioration of the toughness and also suppresses the growth of
the <011> oriented grains. Therefore, the upper limit of the
content of Ti is made 0.4%. Furthermore, if considering the
manufacturing costs etc., 0.05% to 0.25% is desirable.
[0037] Nb is added as necessary for improving the high temperature
strength and also, like Ti, bonding with C or N to improve the
corrosion resistance, grain-boundary corrosion resistance, and
toughness. This action is expressed when the content of Nb is 0.01%
or more, so the lower limit is made 0.01%. However, if excessively
adding Nb, the steel sheet is hardened and the formability of the
steel sheet is degraded. In addition, coarse Nb(C,N) compounds and,
depending on the heat history, (Fe,Nb).sub.6C and Fe.sub.2Nb
precipitate and cause remarkably deterioration of the toughness of
the steel sheet. Also, growth of the <011> oriented grains to
be suppressed. Therefore, the upper limit is made 0.6%. Further, if
considering the material costs and crevice corrosion ability, 0.1%
to 0.45% is desirable.
[0038] B is an element segregating at the grain boundaries and
thereby improving the secondary workability of the product. To
improve the stampability of the flange, it is added according to
need. This action is expressed when the content of B is 0.0002% or
more, so the lower limit of the content of B is made 0.0002%.
However, excessive addition of B causes borides to precipitate and
degrades the toughness of the steel sheet and, in addition,
suppresses the growth of <011> oriented grains, so the upper
limit is made 0.0030%. Furthermore, if considering the cost and the
drop in ductility, 0.0003% to 0.0010% is desirable.
[0039] Al is sometimes added as a deoxidizing element. Its action
is expressed from a 0.005% or more Al content, so the lower limit
is made 0.005%. Further, addition of 0.3% or more of Al causes a
drop in the toughness of the steel sheet and degrades the
weldability and surface quality and also suppresses the growth of
<011> oriented grains, so the upper limit is made 0.3%.
Furthermore, if considering the refining costs, 0.01% to 0.1% is
the desirable content of Al.
[0040] Ni suppresses crevice corrosion and promotes repassivation
to thereby improve the initial rust resistance, so is added as
required. This action is expressed when the content of Ni is 0.1%
or more, so the lower limit is made 0.1%. However, excessive
addition causes hardening and degrades the formability. In
addition, it suppresses the growth of <011> oriented grains
and makes stress corrosion cracking occur more easily, so the upper
limit is made 1%. Further, if considering the material cost, 0.1%
to 0.5% is desirable.
[0041] Mo is an element improving the corrosion resistance and high
temperature strength. In particular, it is an element necessary for
suppressing crevice corrosion when a flange part has a gap
structure. This action is expressed when the content of Mo becomes
0.1% or more, so the lower limit is made 0.1%. Further, if the Mo
content exceeds 2.0%, the formability remarkably deteriorates, the
toughness at the time of manufacture deteriorates, and the growth
of <011> oriented grains is suppressed, so the upper limit is
made 2.0%. Furthermore, if considering the manufacturing costs,
0.1% to 1.2% is desirable.
[0042] Cu is added as needed not only to improve the high
temperature strength, but also to suppress crevice corrosion and
promote repassivation. This action is expressed when the content of
Cu becomes 0.1% or more, so the lower limit is made 0.1%. However,
excessive addition, by precipitation of .epsilon.-Cu, hardens the
steel sheet and degrades the formability and toughness of the steel
sheet and, further, suppresses the growth of <011> oriented
grains, so the upper limit is made 3.0%. Further, if considering
the pickling ability etc. at the time of manufacture, 0.1% to 1.2%
is desirable.
[0043] V is added not only to suppress the crevice corrosion, but
also to contribute to improvement of toughness by addition in a
small amount. This action is expressed from a content of V of 0.05%
or more, so the lower limit is made 0.05%. However, excessive
addition of V not only hardens the steel sheet and degrades the
formability of the steel sheet but also causes the precipitation of
coarse V(C,N) compounds which lead to a deterioration of the
toughness of the steel sheet and suppression of growth of
<011> oriented grains, so the upper limit is made 1.0%.
Further, if considering the material costs and initial rusting,
0.07% to 0.2% is desirable.
[0044] Mg is an element which sometimes is added as a deoxidizing
element and, in addition makes the structure of the slab finer and
contributes to improvement of the formability. Further, Mg oxides
form sites for precipitation of Ti(C,N) compounds, Nb(C,N)
compounds, and other carbonitrides. Mg oxides have the effect of
causing fine dispersion and precipitation of these. This action is
expressed with a content of V of 0.0002% or more and contributes to
improvement of the toughness, so the lower limit is made 0.0002%.
However, excessive addition leads to deterioration of the
weldability and corrosion resistance. In addition, excessive
addition leads to the formation of coarse precipitates which lead
to suppression of <011> oriented grains, so the upper limit
is made 0.0030%. If refining the refining costs, 0.0003% to 0.0010%
is desirable.
[0045] Sn and Sb contribute to improvement of the corrosion
resistance and high temperature strength, so 0.01% or more is added
in accordance with need. By adding over 0.3%, sometimes the slab
cracks at the time of production of the steel sheet and, in
addition, the growth of <011> oriented grains is suppressed,
so the upper limit is made 0.3%. Furthermore, if considering the
refining costs or manufacturability, 0.01% to 0.15% is
desirable.
[0046] Zr, Ta, and Hf bond with C and N and are added in 0.01% or
more in accordance with need to contribute to improvement of the
toughness. However, addition over 0.1% results in an increase in
costs and also leads to remarkable deterioration of the
manufacturability and suppression of growth of the <011>
oriented grains, so the upper limit is made 0.1%. Furthermore, if
considering the refining costs and manufacturability, 0.01% to
0.08% is desirable.
[0047] W contributes to the improvement of the corrosion resistance
and high temperature strength, so is added in 0.01% in accordance
with need. Adding over 2.0% leads to deterioration of the toughness
at the time of production of the steel sheet and to suppression of
growth of the <011> oriented grains and increase of costs, so
the upper limit is made 2.0%. Furthermore, if considering the
refining costs and manufacturability, 0.01% to 1.0% is
desirable.
[0048] Co contributes to improvement of the high temperature
strength, so is added in 0.01% or more in accordance with need.
Addition of over 0.2% leads to deterioration of the toughness at
the time of production of the steel sheet and to suppression of
growth of <011> oriented grains and increased costs, so the
upper limit is made 0.2%. Furthermore, if considering the refining
costs and manufacturability, 0.01% to 0.1% is desirable.
[0049] Ca is sometimes added for desulfurization. The effect
appears at a content of Ca of 0.0001% or more, so the lower limit
is made 0.0001%. However, addition of over 0.0030% causes coarse
CaS to be formed, the toughness and corrosion resistance to
deteriorate, and the growth of <011> oriented grains to be
suppressed, so the upper limit is made 0.0030%. Furthermore, if
considering the refining costs and manufacturability, 0.0003 to
0.0020% is desirable.
[0050] An REM (rare earth metal) is sometimes added as needed from
the viewpoint of improvement of the toughness or improvement of the
oxidation resistance due to refinement of various precipitates.
This effect appears with an REM content of 0.001% or more. However,
addition of over 0.05% causes the casting ability to remarkably
deteriorate and, further, suppresses the growth of <011>
oriented grains, so the upper limit is made 0.05%. Furthermore, if
considering the refining costs and manufacturability, 0.001 to
0.01% is desirable. Further, in the present invention, REM, in
accordance with the general definition, is the general term for the
two elements of scandium (Sc) and yttrium (Y) and the 15 elements
(lanthanoids) of lanthanum (La) to lutetium (Lu). These may be
added alone or may be mixtures.
[0051] Ga may be added in 0.1% or less for improving corrosion
resistance and suppressing hydrogen embrittlement. From the
viewpoint of the formation of sulfides or hydrides, the lower limit
of content of Ga is made 0.0002%. Preferably, it is 0.0010% or
more. Furthermore, from the viewpoint of the manufacturability and
cost and from the viewpoint of the growth of <011> oriented
grains, 0.0040% or less is preferable.
[0052] The other components are not particularly prescribed in the
present invention, but in the present invention, Bi etc. may be
added in accordance with need to 0.001% to 0.1%. Note that, As, Pb,
and other generally harmful elements or impurity elements are
preferably reduced as much as possible.
[0053] Next, the method of production will be explained. The rolled
steel material of the present invention is produced by a
steelmaking-hot rolling, steelmaking-hot rolling-pickling, or
steelmaking-hot rolling-annealing-pickling process. In steelmaking,
the method of smelting steel containing the above essential
components and components added in accordance with need in a
converter then secondarily smelting the steel is suitable. The
smelted molten steel is made into a slab in accordance with a known
casting method (continuous casting). The slab is heated to a
predetermined temperature and hot rolled to a predetermined
thickness by continuous rolling.
[0054] In the present invention, the finishing temperature in hot
rolling and the coiling temperature are prescribed. The higher
temperature the finishing temperature of the hot rolling becomes,
the more the deformation strain of the ferrite phase is removed
after final rolling and the more restoration of the structure is
promoted. Subgrains are formed so that the <011> direction
changes from the rolling direction to within 15.degree., and the
toughness of the steel sheet is improved. On the other hand, with a
finishing temperature of less than 800.degree. C., the crystal
grains having an orientation other than the <011> oriented
grains (<001> direction etc.) end up being formed due to the
hot rolling shear strain. By making the finishing temperature
800.degree. C. or more, the formation and growth of crystal grains
of other orientations are suppressed and subgrains comprised of
<011> oriented grains can be formed so that the area ratio of
the subgrains with respect to the cross-section of the entire plate
thickness becomes 20% or more, so the finishing temperature is made
800.degree. C. or more. However, an excessive increase in the
finishing temperature suppresses the growth of <011> oriented
grains and also leads to a drop in the pickling ability, so the
upper limit of the finishing temperature is made 900.degree. C.
Furthermore, if considering the surface defects, 810 to 880.degree.
C. is desirable.
[0055] After the final rolling in the hot rolling process, a
coiling process is performed at 500.degree. C. or less. If
performing the coiling process at an over 500.degree. C. high
temperature, precipitates causing a drop in toughness are formed,
embrittlement occurs at 475.degree. C., and the steel strip is made
a low toughness, so the upper limit of the initial process is made
500.degree. C. Further, to suppress the rotation of the crystal
orientation of the <011> oriented grains as subgrains formed
at the time of the final rolling performed at a finishing
temperature of 800.degree. C. or more and prevent formation of a
recrystallized structure, it is necessary to make the upper limit
of the temperature of the coiling process 500.degree. C. However,
excessive decrease in the temperature of the coiling process causes
poor coil shape, so the lower limit of the temperature of the
coiling process is made 200.degree. C. Furthermore, if considering
the shape stability and pickling ability, the coiling process is
desirably performed at 300.degree. C. to 450.degree. C. Further,
the thickness of the hot rolled plate is made the 5 mm or more,
which is usually used for flanges, but if excessively made thicker,
the toughness sharply falls, so preferably 5 mm to 20 mm is
desirable. Furthermore, 6 mm to 15 mm is desirable.
[0056] If running the plate through an annealing-pickling process
after hot rolling, the annealing conditions are defined. Along with
the rise of the annealing temperature, restoration and
recrystallization proceed and <011> oriented grains are
reduced. To suppress this action, the steel is heated to 800 to
1000.degree. C. If the annealing temperature is less than
800.degree. C., the worked structure at the time of the hot rolled
process remains, restoration does not sufficiently proceed, and the
steel sheet becomes hard, so the toughness of the steel sheet
becomes poor. Further, if the annealing temperature is over
1000.degree. C., the grain growth after the end of
recrystallization remarkably proceeds and randomness of the crystal
orientation proceeds resulting in the reduction of the <011>
oriented grains, so the toughness of the steel sheet remarkably
deteriorates. Further, from the viewpoint of formation of solid
solutions of the precipitates, suppression of coarsening of the
crystal grains, and remaining presence of <011> oriented
grains, annealing at 850 to 950.degree. C. is desirable.
[0057] When heating the steel sheet or steel strip to the annealing
temperature, the heating rate is made 10.degree. C./sec or more. If
the heating rate is slower than this, recrystallization proceeds
resulting in subgrains being consumed and crystal grains become
coarser. The <011> oriented grains are reduced and the
toughness of the steel sheet is degraded. When the heating rate is
less than 10.degree. C./sec, the <011> oriented grains
decrease because other oriented grains end up being formed during
the heating and the <011> oriented grains are corroded along
with the growth of the other orientations. In particular, the
<112> and <100> oriented grains grew and it became
difficult to make the ratio of <011> oriented grains present
20% or more.
[0058] Further, the cooling rate is made 10.degree. C./sec or more,
but this suppresses the formation of precipitates causing the
deterioration of toughness in the cooling process. Further, if the
cooling rate is less than 10.degree. C./sec, a change occurring in
the crystal orientation in the cooling process reduces the
<011> oriented grain ratio. Furthermore, if considering the
productivity, the heating rate is preferably 15.degree. C./sec or
more and the cooling rate is preferably 15.degree. C./sec or more.
Note that, if the chemical composition of the present invention, a
sufficient effect is exhibited by the above cooling rate. Even if
cooling by a cooling rate faster than the above rate (for example,
by 50.degree. C./sec or more), the effect of the present invention
becomes saturated. In the present invention, if considering the
surface quality, the shape of the steel sheet, and manufacturing
costs, the cooling rate is preferably made less than 50.degree.
C./sec.
[0059] The hot rolled steel sheet or hot rolled steel strip of the
present invention is formed of the rolled ferritic stainless steel
material having the components of the present invention and
produced by the hot rolling process. The hot rolled annealed steel
sheet or hot rolled annealed steel strip of the present invention
is formed of the rolled ferritic stainless steel material having
the components of the present invention and annealed after the hot
rolling. The hot rolled steel sheet or hot rolled steel strip of
the present invention or the hot rolled annealed steel sheet or hot
rolled annealed steel strip of the present invention each have a
Charpy impact value measured at 0.degree. C. based on JISZ2242 of
11 J/cm.sup.2 or more and secures a toughness by which no cracking
occurs at the time of flange-making.
[0060] Further, as shown in the later explained examples, the
flange part produced from the rolled ferritic stainless steel
material of the present invention is excellent in low temperature
toughness without cracking due to being given a 125 J or less
impact energy at -20.degree. C.
Examples
[0061] Molten steels of the chemical compositions shown in Table
1-1 and Table 1-2 were smelted and cast into slabs. The slabs were
hot rolled to 5 mm thicknesses or more to produce hot rolled coils.
The hot rolled coils were produced by controlling the hot rolling
finishing temperature to 810 to 880.degree. C. and the coiling
temperature to 300 to 450.degree. C. After that, as shown in Table
1-1 and Table 1-2, annealed coils were produced. As conditions of
the annealing process, the annealing temperature was made 850 to
950.degree. C. and the heating rate and cooling rate were both made
15.degree. C./sec. The samples for evaluation of the crystal
orientation and the test pieces for Charpy impact tests were taken
from these hot rolled plates or hot rolled annealed steel sheets.
Between the two left and right ends of the hot rolled steel sheets
or hot rolled annealed steel sheets, cross-sections of lengths 1.0
mm parallel to the rolling direction and entire thicknesses were
exposed as specimens. The exposed cross-sections were measured for
orientation for each crystal grain using EBSP and measured for area
ratio of crystal grains with a <011> direction within
15.degree. from the rolling direction (<011> oriented grain
ratio) (area %). Further, the ratio of the lengths of the low-angle
grain boundaries having a crystal misorientation of less than
15.degree. at the cross-section measured for the <011>
oriented grain ratio and the sum of the crystal grain boundaries at
the cross-section of the entire thickness. The Charpy impact test
was conducted by the above method based on JISZ2242. Further, in
Table 1-2, the notation "*" denotes outside the present
invention.
TABLE-US-00001 TABLE 1-1 Composition (mass %) No. C Si Mn P S Cr N
Ti Nb B Al Ni Mo Cu Inven- A1 0.005 0.43 0.32 0.023 0.0006 10.7
0.008 0.18 -- -- -- -- -- -- tion A2 0.062 0.35 0.51 0.032 0.0046
16.2 0.035 -- -- -- -- -- -- -- exmple A3 0.075 0.25 0.42 0.030
0.0021 16.5 0.033 -- -- -- 0.08 -- -- -- A4 0.011 0.33 0.13 0.023
0.0007 17.3 0.018 -- 0.42 -- 0.03 -- -- -- A5 0.004 0.06 0.07 0.025
0.0008 17.2 0.011 0.21 -- 0.0005 -- -- -- -- A6 0.005 0.07 0.03
0.026 0.0010 17.4 0.013 -- 0.38 0.0003 0.06 -- 0.8 -- A7 0.008 0.91
0.35 0.030 0.0005 13.9 0.009 -- 0.42 -- 0.03 0.1 -- -- A8 0.005
0.07 0.09 0.024 0.0010 17.2 0.013 0.21 -- 0.0010 0.09 -- 1.1 -- A9
0.009 0.45 0.15 0.021 0.0007 21.1 0.019 -- 0.43 -- 0.07 0.3 -- 0.4
A10 0.013 0.22 0.27 0.022 0.0007 18.9 0.016 0.09 0.35 0.0007 0.12
0.2 -- 0.3 A11 0.006 0.23 0.96 0.031 0.0008 17.6 0.014 0.07 0.46
0.0005 0.06 -- 1.8 -- A12 0.005 0.42 0.38 0.015 0.0019 17.1 0.006
0.13 0.42 0.0004 0.03 -- -- 1.2 A13 0.006 0.44 0.15 0.030 0.0009
11.6 0.006 0.17 -- 0.0004 0.07 0.1 0.1 0.1 A14 0.005 0.06 0.16
0.031 0.0025 11.5 0.013 0.15 -- 0.0006 0.05 0.7 -- A15 0.014 0.16
0.23 0.026 0.0016 14.5 0.009 0.08 0.22 0.0006 0.05 -- -- -- A16
0.012 0.13 0.33 0.036 0.0009 17.6 0.012 -- 0.36 0.0006 0.07 0.2 --
0.4 A17 0.013 0.15 0.22 0.026 0.0011 17.5 0.010 -- 0.29 -- -- --
0.3 -- A18 0.055 0.41 0.45 0.032 0.0035 16.1 0.025 -- -- -- 0.11 --
-- 0.2 A19 0.006 0.35 0.09 0.025 0.0009 19.5 0.017 0.17 0.22 0.0004
0.07 0.13 1.5 0.1 A20 0.008 0.09 0.13 0.032 0.0017 17.1 0.015 --
0.33 -- 0.03 -- -- -- Composition (mass %) Hot rolled plate/ No. V
Mg Sn Sb Zr Ta Hf W Co Ca REM Ga Hot rolled annealed plate Inven-
A1 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed plate
tion A2 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate exmple A3 -- -- -- -- -- -- -- -- -- -- -- -- hot rolled
plate A4 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate A5 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate A6 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate A7 0.07 -- -- -- -- -- -- -- -- 0.0005 -- -- Hot rolled
annealed plate A8 0.10 0.0006 -- -- -- -- -- -- -- -- -- -- Hot
rolled annealed plate A9 -- -- -- -- -- -- -- -- -- -- -- -- Hot
rolled annealed plate A10 0.12 0.0004 -- -- -- -- -- -- -- 0.0007
-- -- hot rolled plate A11 -- -- -- -- -- -- -- -- -- -- -- -- Hot
rolled annealed plate A12 -- -- -- -- -- -- -- -- -- -- -- -- Hot
rolled annealed plate A13 0.13 0.0003 -- -- -- -- -- -- -- -- -- --
Hot rolled plate A14 0.18 0.0005 -- -- -- -- 0.06 -- -- 0.0018 0.01
-- Hot rolled annealed plate A15 -- -- 0.12 -- -- -- -- -- -- --
0.02 -- hot rolled plate A16 -- -- -- 0.15 -- -- -- -- -- -- -- --
Hot rolled annealed plate A17 -- -- -- -- -- -- -- 1.50 -- -- -- --
hot rolled plate A18 0.15 0.0005 -- -- 0.09 -- -- -- 0.09 -- -- --
Hot rolled annealed plate A19 0.13 0.0003 0.06 0.05 0.07 0.05 0.05
0.06 0.05 0.0011 0.008 -- Hot rolled annealed plate A20 -- -- -- --
-- -- -- -- -- -- -- 0.010 Hot rolled annealed plate
TABLE-US-00002 TABLE 1-2 Composition (mass %) No. C Sr Mn P S Cr N
Ti Nb B Al Ni Mo Cu Comparative B1 0.092* 0.24 0.37 0.020 0.0009
10.7 0.011 -- -- -- -- -- -- -- Examples B2 0.005 1.56* 0.25 0.020
0.0009 17.3 0.006 0.18 -- 0.0009 0.09 -- -- -- B3 0.013 0.32 1.43*
0.020 0.0012 14.5 0.010 -- 0.35 -- -- -- -- -- B4 0.003 0.42 0.43
0.06* 0.0002 16.3 0.010 0.12 -- 0.0007 0.05 -- -- -- B5 0.007 0.26
0.32 0.019 0.0125* 18.8 0.013 0.16 -- -- -- -- -- -- B6 0.012 0.31
0.34 0.040 0.0026 25.3* 0.005 -- -- 0.0005 -- -- -- -- B7 0.004
0.25 0.36 0.020 0.0015 17.5 0.06* 0.22 -- -- -- -- -- -- B8 0.003
0.26 0.12 0.030 0.0053 14.1 0.015 0.46* -- -- -- -- -- -- B9 0.008
0.39 0.12 0.032 0.0035 16.2 0.005 -- 0.65* 0.0100* -- -- -- -- B10
0.009 0.29 0.26 0.010 0.0015 19.5 0.005 -- -- 0.0035* -- -- -- --
B11 0.006 0.36 0.33 0.040 0.0033 11.1 0.007 -- -- -- 0.36* -- -- --
B12 0.002 0.42 0.42 0.020 0.0032 13.8 0.006 -- -- -- -- 1.5* -- --
B13 0.003 0.17 0.26 0.030 0.0013 16.5 0.012 -- 0.25 -- 0.04 -- 2.6*
-- B14 0.011 0.25 0.27 0.020 0.0023 11.9 0.006 -- -- -- -- -- --
3.3* B15 0.005 0.31 0.21 0.010 0.0016 13.5 0.010 -- -- -- 0.03 --
-- -- B16 0.009 0.39 0.12 0.040 0.0022 14.5 0.013 -- -- 0.0005 --
-- -- -- B17 0.006 0.21 0.33 0.030 0.0007 17.3 0.016 -- -- -- -- --
-- -- B18 0.005 0.32 0.17 0.050 0.0011 13.6 0.013 -- -- -- 0.06 --
-- -- B19 0.005 0.21 0.25 0.010 0.0025 16.3 0.009 -- -- -- 0.13 --
-- -- B20 0.056 0.13 0.65 0.016 0.0046 11.5 0.035 -- -- -- -- -- --
-- B21 0.043 0.96 0.95 0.025 0.0056 10.9 0.045 -- -- -- -- -- -- --
B22 0.055 0.85 0.35 0.035 0.0076 16.5 0.033 -- -- -- -- -- -- --
B23 0.063 0.65 0.64 0.019 0.0009 17.5 0.035 -- -- -- -- -- -- --
B24 0.042 0.43 0.56 0.037 0.0016 17.6 0.039 -- -- -- -- -- -- --
B25 0.009 0.33 0.13 0.015 0.0016 10.8 0.015 0.12 -- -- -- -- -- --
B26 0.008 0.13 0.31 0.025 0.0013 14.5 0.015 0.12 -- -- -- -- -- --
Composition (mass %) hot rolled plate/ No. V Mg Sn Sb Zr Ta Hf W Co
Ca REM Ga Hot rolled annealed plate Comparative B1 -- -- -- -- --
-- -- -- -- -- -- -- Hot rolled/annealed plate Examples B2 -- -- --
-- -- -- -- -- -- -- -- -- hot rolled plate B3 -- -- -- -- -- -- --
-- -- -- -- -- Hot rolled annealed plate B4 -- -- -- -- -- -- -- --
-- -- -- -- Hot rolled annealed plate B5 -- -- -- -- -- -- -- -- --
-- -- -- Hot rolled annealed plate B6 -- -- -- -- -- -- -- -- -- --
-- -- Hot rolled annealed plate B7 -- -- -- -- -- -- -- -- -- -- --
-- Hot rolled annealed plate B8 -- -- -- -- -- -- -- -- -- -- -- --
Hot rolled annealed plate B9 -- -- -- -- -- -- -- -- -- -- -- --
hot rolled plate B10 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled
annealed plate B11 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled
annealed plate B12 -- -- -- -- -- -- -- -- -- -- -- -- hot rolled
plate B13 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate B14 -- -- -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate B15 1.2* -- -- -- -- -- -- -- -- -- -- -- hot rolled plate
B16 -- 0.0042* -- -- -- -- -- -- -- -- -- -- Hot rolled annealed
plate B17 -- -- 0.45* -- -- -- -- -- -- -- -- -- Hot rolled
annealed plate B18 -- -- -- 0.36* -- -- -- -- -- -- -- -- Hot
rolled annealed plate B19 -- -- -- -- 0.2* -- -- -- -- -- -- -- Hot
rolled annealed plate B20 -- -- -- -- -- 0.3* -- -- -- -- -- -- Hot
rolled annealed plate B21 -- -- -- -- -- -- 0.2* -- -- -- -- -- Hot
rolled annealed plate B22 -- -- -- -- -- -- -- 2.3* -- -- -- -- Hot
rolled annealed plate B23 -- -- -- -- -- -- -- -- 0.3* -- -- -- Hot
rolled annealed plate B24 -- -- -- -- -- -- -- -- -- 0.0045* -- --
Hot rolled annealed plate B25 -- -- -- -- -- -- -- -- -- -- 0.06*
-- Hot rolled annealed plate B26 -- -- -- -- -- -- -- -- -- -- --
0.5* Hot rolled annealed plate Notations "*" show outside present
invention.
TABLE-US-00003 TABLE 2-1 Ratio of low- <011> angle grain Hot
rolled oriented boundary of Impact plate/Hot rolled grain less than
15.degree. value No. annealed plate ratio (%) (%) (J/cm.sup.2) Inv.
A1 Hot rolled 27 21 15 ex. annealed plate A2 Hot rolled 33 45 15
annealed plate A3 Hot rolled plate 21 20 12 A4 Hot rolled 42 53 29
annealed plate A5 Hot rolled 22 23 15 annealed plate A6 Hot rolled
56 59 21 annealed plate A7 Hot rolled 72 62 20 annealed plate A8
Hot rolled 43 46 15 annealed plate A9 Hot rolled 35 39 19 annealed
plate A10 Hot rolled plate 20 22 11 A11 Hot rolled 26 25 16
annealed plate A12 Hot rolled 21 23 13 annealed plate A13 Hot
rolled plate 20 18 14 A14 Hot rolled 26 35 15 annealed plate A15
Hot rolled plate 21 26 16 A16 Hot rolled 35 39 17 annealed plate
A17 Hot rolled plate 20 19 12 A18 Hot rolled 53 69 26 annealed
plate A19 Hot rolled 45 56 27 annealed plate A20 Hot rolled 25 23
16 annealed plate
TABLE-US-00004 TABLE 2-2 Ratios of low- <011> angle grain Hot
rolled oriented boundary of Impact plate/Hot rolled grain less than
15.degree. value No. annealed plate ratio (%) (%) (J/cm.sup.2)
Comp. B1 Hot rolled 16* 9* 6 Ex. annealed plate B2 Hot rolled plate
18* 9* 9 B3 Hot rolled 15* 7* 7 annealed plate B4 Hot rolled 11* 8*
5 annealed plate B5 Hot rolled 16* 6* 7 annealed plate B6 Hot
rolled 14* 9* 6 annealed plate B7 Hot rolled 15* 9* 8 annealed
plate B8 Hot rolled 13* 8* 4 annealed plate B9 Hot rolled plate 5*
3* 2 B10 Hot rolled 18* 2* 10 annealed plate B11 Hot rolled 6* 6* 6
annealed plate B12 Hot rolled plate 5* 4* 5 B13 Hot rolled 4* 3* 4
annealed plate B14 Hot rolled 10* 9* 8 annealed plate B15 Hot
rolled plate 11* 9* 9 B16 Hot rolled 16* 9* 7 annealed plate B17
Hot rolled 18* 9* 10 annealed plate B18 Hot rolled 5* 7* 6 annealed
plate B19 Hot rolled 2* 4* 3 annealed plate B20 Hot rolled 2* 4* 1
annealed plate B21 Hot rolled 3* 3* 2 annealed plate B22 Hot rolled
4* 4* 4 annealed plate B23 Hot rolled 5* 5* 6 annealed plate B24
Hot rolled 6* 4* 5 annealed plate B25 Hot rolled 12* 9* 6 annealed
plate B26 Hot rolled 10* 9* 3 annealed plate Notations "*" show
outside present invention.
[0062] Table 2-1 and Table 2-2 show the results. In Table 2-2, the
notation "*" shows outside the present invention. Further, "the
ratio of the low-angle grain boundary of less than 15.degree." is
the ratio of sum of the length of the low-angle grain boundary
having a difference in crystal orientation of less than 15.degree.
at the cross-section at which the <011> oriented grain ratio
was measured and the sum of the length of the crystal grain
boundaries at the cross-section.
[0063] The Invention Examples A1 to A20 are hot rolled plates or
hot rolled annealed steel sheets having the components of the
present invention and produced by the method of production of the
present invention. The Invention Examples A1 to A20 all have
<011> oriented grain ratios of 20% or more, have ratios of
the low-angle grain boundary of less than 15.degree. of 10% or
more, and impact values at 0.degree. C. of 11 J/cm.sup.2 or more.
If steel having an impact values at 0.degree. C. of 7 J/cm.sup.2 or
more, brittle fracture does not occur when the hot rolled coil is
uncoiled and the plate is run, so it will be understood that the
rolled ferritic stainless steel sheet of the present invention has
sufficient toughness. As opposed to this, Comparative Examples B1
to B26 are hot rolled plates or hot rolled annealed steel sheets
having some of the components outside the scope of the present
invention. Comparative Examples B1 to B26 have <011> oriented
grain ratios of less than 20%, ratios of the low-angle grain
boundary of less than 15.degree. of less than 10%, and impact
values at 0.degree. C. failing to reach 7 J/cm.sup.2 in many
cases.
[0064] The steels having the components of the present invention
were used to manufacture coils while changing the hot rolling
conditions and the annealing conditions as shown in Table 3. The
results of evaluation are shown. The notations shown in the column
of "Steel No." of Table 3 correspond to the numbers of the steel
sheets shown in the "No." column of Table 1. That is, the steel
sheets shown in Table 3 have the same compositions as the steel
sheets of the corresponding numbers of Table 1 corresponding to the
numbers shown in the "Steel No." column of Table 3 and were
produced by the methods of production described in Table 3. The
steel sheets of Invention Examples C1 to C24 of Table 3 are
produced by the manufacturing conditions of the present invention
and have excellent toughness. On the other hand, the steel sheets
of Comparative Examples D1 to D6 have some of the manufacturing
conditions outside the scope of the present invention. The
<011> oriented grain ratios are less than 20%, the ratios of
the low-angle grain boundary of less than 15.degree. are less than
10%, and the impact values at 0.degree. C. fail to reach 7
J/cm.sup.2.
[0065] Further, the steel sheets of the Invention Examples C1 to
C24 and the steel sheets of Comparative Examples D1 to D6 were used
as materials to produce flange parts 1 of shapes symmetric to the
left and right as shown in FIG. 2. Each flange part 1 was provided
with a hole 11 having an inside diameter of a diameter of 55 mm at
center thereof and holes 12 for passing bolts and other fastening
hardware at the left and right of the hole 11. Above and below the
hole 11, the thinnest edge parts 11a and 11b were formed
symmetrically to the top and bottom about the center of the hole
11. Further, the ratio of the inside diameter of the hole 11 to the
short axis of the oval 5 circumscribing the flange part was 0.65,
while the ratio of the thickness of the edge parts 11a and 11b to
the short axis of the oval 5 was 0.18 in each case.
[0066] The flange part 1 was tested by a low temperature drop
weight test using the low temperature drop weight test apparatus 2
shown in FIG. 3. The low temperature drop weight test was conducted
using the drop weight test apparatus 2. First, a flange part 1
cooled to -20.degree. C. was stood up and fastened on a fastening
table 4 so that the thinnest parts 11a and 11b became the top end
and bottom end. Next, a weight 3 of 16 kg was freely dropped on the
side surface of the thin part 11a from a height 80 cm and the
presence of any cracks of the flange part 1 was visually examined.
In this case, the energy given to the flange part became 125 J. The
flange part was cooled to -20.degree. C. using a temperature and
humidity testing chamber or using alcohol and liquid nitrogen to
adjust the temperature, the sample was held at -20.degree. C. for
10 minutes, then impact was applied.
[0067] The results of the low temperature dropping weight test are
shown in Table 3. In Table 3, the notation "*" indicates outside
the present invention. From Table 3, it will be understood that the
flange parts produced by the Invention Examples C1 to C24 do not
crack when given a 125 J or less impact energy at -20.degree. C. In
this way, according to the present invention, it is possible to
provide a flange part excellent in low temperature toughness. As
opposed to this, the hot rolled plates or hot rolled annealed
plates produced by manufacturing conditions outside the scope of
the present invention in Comparative Examples D1 to D6 cracked due
to the impact energy and did not have sufficient toughness.
TABLE-US-00005 TABLE 3 Characteristics Ratio of Cracking in less
than low Hot rolling conditions Annealing conditions <011>
5.degree. low- temperature Finishing Coiling Thick- Heating Heating
Cooling orientation angle grain Impact impact test Steel temp.
temp. ness temp. rate rate ratio boundaries value of flange No. no
(.degree. C.) (.degree. C.) (mm) (.degree. C.) (.degree. C./sec)
(.degree. C./sec) (%) (%) (j/cm.sup.2) part Invention C1 A1 830 470
8 880 16 20 27 21 15 No example C2 A1 830 470 8 No annealing 35 33
21 No C3 A2 810 450 8 820 12 19 33 35 15 No C4 A2 810 450 13 820 15
21 31 34 14 No C5 A2 810 450 13 No annealing 42 49 30 No C6 A4 840
350 5 1000 15 16 45 59 31 No C7 A4 840 350 8 970 17 18 42 53 29 No
C8 A4 840 350 13 950 16 25 40 46 27 No C9 A4 840 350 8 No annealing
53 68 35 No C10 A5 820 400 13 940 19 15 22 29 16 No C11 A5 820 400
13 No annealing 35 38 23 No C12 A6 860 400 5 990 20 17 60 73 25 No
C13 A6 860 400 8 970 20 23 56 66 21 No C14 A6 860 400 13 950 18 19
50 59 18 No C15 A6 860 400 5 No annealing 67 86 36 No C16 A7 805
420 5 1000 18 21 75 81 24 No C17 A7 805 420 8 960 15 20 72 82 20 No
C18 A7 805 420 13 940 15 16 60 66 16 No C19 A7 805 420 8 No
annealing 75 80 39 No C20 A8 860 330 8 970 25 15 43 40 15 No C21 A8
860 330 8 No annealing 52 38 25 No C22 A9 880 330 5 970 23 30 26 26
24 No C23 A9 880 330 5 No annealing 33 30 29 No C24 A10 880 300 8
970 20 24 20 25 11 No Comparative D1 A1 750* 470 8 880 16 20 15* 9*
6 Yes example D2 A2 810 550* 8 820 12 19 18* 9* 5 Yes D3 A4 840 350
8 750* 17 18 10* 8* 4 Yes D4 A5 820 400 13 1050* 19 15 8* 7* 3 Yes
D5 A6 860 400 5 990 5* 17 18* 9* 6 Yes D6 A8 60 330 8 970 25 5* 10*
9* 4 Yes
[0068] Note that, the other conditions in the manufacturing
apparatus or manufacturing process may be suitably selected. For
example, the hot rolling apparatus may be a continuous type tandem
mill or reverse type mill. A Steckel mill having a heating device
may also be used in the middle of rolling. The slab thickness, hot
rolled plate thickness, etc. may also be suitably designed. After
hot rolling and coiling, the steel may also be dipped in a water
cooling pool. For the pickling after hot rolling or after hot
rolling and annealing, the shot blast, bending, brush, or other
mechanical descaling method may be suitably selected. For the acid
solution, sulfuric acid, nitrofluoric acid, or other existing acid
solution may be used. Furthermore, after this, coil grinding, shot
blasting, painting, plating, or other various surface treatments
may be applied.
INDUSTRIAL APPLICABILITY
[0069] As clear from the above explanation, the rolled ferritic
stainless steel material of the present invention is excellent in
manufacturability and secures toughness at the time of
flange-making and at the time of use. That is, by using the
material applying the present invention in particular for an
automobile or motorcycle part, reliability is secured and the
degree of social contribution can be raised. The invention is
extremely beneficial to industry.
REFERENCE SIGNS LIST
[0070] 1. flange part [0071] 2. drop weight test apparatus [0072]
3. weight [0073] 4. fastening table [0074] 11. hole [0075] 11a,
11b. edge parts [0076] 5. circumscribing oval
* * * * *