U.S. patent application number 15/764090 was filed with the patent office on 2019-02-21 for ferritic stainless steel sheet.
This patent application is currently assigned to JFE STEEL CORPORATION. The applicant listed for this patent is JFE STEEL CORPORATION. Invention is credited to Mitsuyuki Fujisawa, Tomohiro Ishii, Chikara Kami, Shuji Nishida.
Application Number | 20190055634 15/764090 |
Document ID | / |
Family ID | 58423281 |
Filed Date | 2019-02-21 |
United States Patent
Application |
20190055634 |
Kind Code |
A1 |
Nishida; Shuji ; et
al. |
February 21, 2019 |
FERRITIC STAINLESS STEEL SHEET
Abstract
Provided is a ferritic stainless steel sheet excellent in terms
of corrosion resistance with which a decrease in the quantity of
surface defects and an improvement in toughness are realized at the
same time. The ferritic stainless steel sheet has a chemical
composition containing, by mass %, C: 0.020% or less, Si: 0.05% to
0.40%, Mn: 0.05% to 1.00%, P: 0.040% or less, S: 0.030% or less,
Al: 0.001% to 0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% to 0.80%, Cu:
0.30% to 0.80%, Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr:
0.005% to 0.150%, N: 0.020% or less, and the balance being Fe and
inevitable impurities, in which relational expression (1) below is
satisfied. Zr.ltoreq.Nb.ltoreq.Ti (1) (Here, each of Zr, Nb, and Ti
in relational expression (1) denotes the content (mass %) of the
corresponding chemical element.)
Inventors: |
Nishida; Shuji; (Chiyoda-ku,
Tokyo, JP) ; Ishii; Tomohiro; (Chiyoda-ku, Tokyo,
JP) ; Fujisawa; Mitsuyuki; (Chiyoda-ku, Tokyo,
JP) ; Kami; Chikara; (Chiyoda-ku, Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
58423281 |
Appl. No.: |
15/764090 |
Filed: |
September 26, 2016 |
PCT Filed: |
September 26, 2016 |
PCT NO: |
PCT/JP2016/004336 |
371 Date: |
March 28, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/60 20130101;
C22C 38/42 20130101; C21D 9/46 20130101; C22C 38/52 20130101; C22C
38/001 20130101; C22C 38/004 20130101; C21D 8/0236 20130101; C22C
38/002 20130101; C22C 38/50 20130101; C21D 6/005 20130101; C22C
38/54 20130101; C21D 8/0205 20130101; C22C 38/44 20130101; C22C
38/06 20130101; C22C 38/04 20130101; C22C 38/02 20130101; C22C
38/48 20130101; C21D 2211/005 20130101; C21D 6/007 20130101; C22C
38/00 20130101; C22C 38/008 20130101; C21D 6/004 20130101; C21D
6/008 20130101; C22C 38/46 20130101; C21D 8/0226 20130101; C21D
8/0263 20130101; C22C 38/005 20130101 |
International
Class: |
C22C 38/60 20060101
C22C038/60; C22C 38/54 20060101 C22C038/54; C22C 38/52 20060101
C22C038/52; C22C 38/50 20060101 C22C038/50; C22C 38/48 20060101
C22C038/48; C22C 38/46 20060101 C22C038/46; C22C 38/44 20060101
C22C038/44; C22C 38/42 20060101 C22C038/42; C22C 38/06 20060101
C22C038/06; C22C 38/04 20060101 C22C038/04; C22C 38/00 20060101
C22C038/00; C22C 38/02 20060101 C22C038/02; C21D 9/46 20060101
C21D009/46; C21D 8/02 20060101 C21D008/02; C21D 6/00 20060101
C21D006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2015 |
JP |
2015-192442 |
Claims
1. A ferritic stainless steel sheet having a chemical composition
containing, by mass %, C: 0.020% or less, Si: 0.05% to 0.40%, Mn:
0.05% to 1.00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001% to
0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% to 0.80%, Cu: 0.30% to 0.80%,
Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr: 0.005% to 0.150%, N:
0.020% or less, and the balance being Fe and inevitable impurities,
in which relational expression (1) below is satisfied:
Zr.ltoreq.Nb.ltoreq.Ti (1), where each of Zr, Nb, and Ti in
relational expression (1) denotes the content (mass %) of the
corresponding chemical element.
2. The ferritic stainless steel sheet according to claim 1, the
steel sheet having the chemical composition further containing, by
mass %, one, two, or more selected from Co: 0.01% to 0.50%, Mo:
0.01% to 0.30%, and W: 0.01% to 0.50%.
3. The ferritic stainless steel sheet according to claim 1, the
steel sheet having the chemical composition further containing, by
mass %, one, two, or more selected from V: 0.01% to 0.50%, B:
0.0003% to 0.0030%, Mg: 0.0005% to 0.0100%, Ca: 0.0003% to 0.0030%,
Y: 0.001% to 0.20%, and REM (rare-earth metal): 0.001% to
0.10%.
4. The ferritic stainless steel sheet according to claim 2, the
steel sheet having the chemical composition further containing, by
mass %, one, two, or more selected from V: 0.01% to 0.50%, B:
0.0003% to 0.0030%, Mg: 0.0005% to 0.0100%, Ca: 0.0003% to 0.0030%,
Y: 0.001% to 0.20%, and REM (rare-earth metal); 0.001% to
0.10%.
5. The ferritic stainless steel sheet according to claim 1, the
steel sheet having the chemical composition further containing, by
mass %, one or both selected from Sn: 0.001% to 0.50% and Sb:
0.001% to 0.50%.
6. The ferritic stainless steel sheet according to claim 2, the
steel sheet having the chemical composition further containing, by
mass %, one or both selected from Sn: 0.001% to 0.50% and Sb:
0.001% to 0.50%.
7. The ferritic stainless steel sheet according to claim 3, the
steel sheet having the chemical composition further containing, by
mass %, one or both selected from Sn: 0.001% to 0.50% and Sb:
0.001% to 0.50%.
8. The ferritic stainless steel sheet according to claim 4, the
steel sheet having the chemical composition further containing, by
mass %, one or both selected from Sn: 0.001% to 0.50% and Sb:
0.001% to 0.50%.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is the U.S. National Phase application of
PCT/JP2016/004336, filed Sep. 26, 2016, which claims priority to
Japanese Patent Application No. 2015-192442, filed Sep. 30, 2015,
the disclosures of these applications being incorporated herein by
reference in their entireties for all purposes.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to a ferritic stainless steel
sheet having excellent corrosion resistance, only a small quantity
of surface defects, and excellent toughness.
BACKGROUND OF THE INVENTION
[0003] A ferritic stainless steel sheet, which does not contain Ni
in a large amount, is a material having a lower price and more
excellent price stability than those of an austenitic stainless
steel sheet. In addition, ferritic stainless steel sheets are used
in various applications such as building materials, transport
machine, home electrical appliances, and kitchen appliances, since
they are excellent in terms of rust resistance.
[0004] The kind of ferritic stainless steel sheet which is used
particularly in a harsh corrosive environment is a SUS443J1-type
stainless steel sheet (JIS G 4305), which has excellent corrosion
resistance equivalent to that of a SUS304-type stainless steel
sheet (JIS G 4305, 18-mass %-Cr-8-mass %-Ni-based), which is an
austenitic stainless, steel, as a result of containing 20.0 mass %
to 23.0 mass % of Cr, 0.3 mass % to 0.8 mass % of Cu, and
sufficient amounts of stabilizing chemical elements (Ti, Nb, and
Zr).
[0005] The kind of SUS443J1-type stainless steel which is commonly
used is SUS443J1-type stainless steel containing mainly Ti as a
stabilizing chemical element. Such steel is excellent in terms of
workability because texture growth is promoted as a result of
containing Ti. Moreover, since such steel is sufficiently softened
even in the case where cold-rolled-sheet annealing is performed at
a lower temperature than that for steel containing Nb, it is
possible to manufacture such steel by using a cold-rolled-sheet
annealing and pickling line which is used for common steel, which
results in high productivity. However, in the case of Ti-containing
SUS443J1-type stainless steel, there may be a case where streaks
(surface defects), which deteriorate aesthetic appearance, occur on
the surface. It is known that the above-mentioned streaks are
caused by coarse TiN which is formed on the surface when casting is
performed. In addition, there is a problem of low toughness with
Ti-containing SUS443J1-type stainless steel. This is because coarse
TiN, which becomes a preferential starting point at which
fracturing occurs, is formed.
[0006] Patent Literature 1 and Patent Literature 2 describe the
prevention of surface defects and the improvement of toughness
regarding Ti-containing ferritic stainless steel.
[0007] Patent Literature 1 discloses a method for manufacturing
Ti-containing ferritic stainless steel having excellent roping
resistance and good surface quality. In Patent Literature 1, the
surface defect of a cold-rolled and annealed steel sheet is
prevented by controlling the solidifying temperature of the steel,
casting temperature, and TiN-precipitating temperature in the steel
so that a specified relationship is satisfied in order to control
the precipitation of TiN when the molten steel is cast.
[0008] Patent Literature 2 discloses a ferritic stainless steel
sheet which has excellent toughness and good corrosion resistance
and which is excellent in terms of productivity and economic
efficiency and a method for manufacturing the steel sheet. In
Patent Literature 2, the toughness of a hot-rolled and annealed
steel sheet and the toughness of a cold-rolled and annealed steel
sheet are improved by allowing nitrides in the steel to exist in
the form of ZrN.
CITATION LIST
Patent Literature
[0009] PTL 1: Japanese Unexamined Patent Application Publication
No. Hei 1-118341
[0010] PTL 2: Japanese Unexamined Patent Application Publication
No. 2011-214060
SUMMARY OF THE INVENTION
[0011] Nowadays, in response to the diversification of home
electrical appliances, there is a demand for a ferritic stainless
steel sheet with which a decrease in streaks on the surface and
excellent toughness are both realized at the same time in addition
to excellent corrosion resistance.
[0012] However, in the case of the method according to Patent
Literature 1, since TiN is purposefully precipitated in order to
obtain the effect of increasing the equiaxial crystal ratio of a
slab, it is not possible to achieve a sufficient effect of
improving toughness and reducing surface defects. In the case of
the method according to Patent Literature 2 also, since it is not
possible to sufficiently prevent the formation of TiN in steel, it
is not possible to obtain a sufficient effect of improving
toughness and reducing surface defects.
[0013] An object of aspects of the present invention is to provide
a ferritic stainless steel sheet excellent in corrosion resistance
in which a decrease in the quantity of surface defects and an
improvement in toughness are realized at the same time and which is
sufficiently softened even in the case where cold-rolled-sheet
annealing is performed at a temperature equivalent to that for
conventional Ti-containing SUS443J1-type stainless steel.
[0014] The present inventors, in response to the problems described
above, conducted comprehensive investigations in order to realize a
decrease in the quantity of surface defects and an improvement in
toughness at the same time and, as a result, found that it is
possible to improve the toughness of Ti-containing SUS443J1-type
stainless steel by adding appropriate amounts of Zr and Nb in
combination to Ti-containing SUS443J1-type stainless steel in order
to change the precipitation form of TiN, which causes a
deterioration in toughness, without an increase in
cold-rolled-sheet annealing temperature. Moreover, it was found
that, since it is possible to precipitate Ti-based inclusions in a
finely dispersed form by this effect, it is possible to decrease
the quantity of surface defects of a steel sheet caused by TiN.
[0015] Specifically, it was found that, by controlling the contents
of the stabilizing chemical elements (Ti, Nb, and Zr) in the
chemical composition of a SUS443J1-type ferritic stainless steel
sheet so that the content of Ti, which is the main stabilizing
chemical element, is 0.10 mass % to 0.50 mass %, the Nb content,
which is equal to or less than the Ti content, is 0.010 mass % to
0.150 mass %, and the Zr content, which is equal to or less than
the Nb content, is 0.005 mass % to 0.150 mass %, it is possible to
allow sufficient softening to occur even when cold-rolled-sheet
annealing is performed at a temperature equivalent to that for a
case where a stabilizing chemical element is limited to Ti, and it
is possible to realize a decrease in the quantity of surface
defects and a high toughness at the same time. The mechanism of
these is supposed to be as follows.
[0016] As a result of Nb and Zr being contained in combination in
steel, since complex carbonitrides of Ti, Zr, and Nb ((Ti, Zr,
Nb)(C,N)), whose particle size is smaller than that of TiN formed
in ferritic stainless steel containing only Ti, are dispersedly
precipitated, an improvement in toughness and a decrease in the
quantity of surface defects are realized.
[0017] Aspects of the present invention are based on the findings
described above, and the subject matter of aspects of the present
invention is as follows.
[0018] [1] A ferritic stainless steel sheet having a chemical
composition containing, by mass %, C: 0.020% or less, Si: 0.05% to
0.40%, Mn: 0.05% to 1.00%, P: 0.040% or less, S: 0.030% or less,
Al: 0.001% to 0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% to 0.80%, Cu:
0.30% to 0.80%, Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr:
0.005% to 0.150%, N: 0.020% or less, and the balance being Fe and
inevitable impurities, in which relational expression (1) below is
satisfied.
Zr.ltoreq.Nb.ltoreq.Ti (1)
[0019] (Here, each of Zr, Nb, and Ti in relational expression (1)
denotes the content (mass %) of the corresponding chemical
element.)
[0020] [2] The ferritic stainless steel sheet according to item
[1], the steel sheet having the chemical composition further
containing, by mass %, one, two, or more selected from Co: 0.01% to
0.50%, Mo: 0.01% to 0.30%, and W: 0.01% to 0.50%.
[0021] [3] The ferritic stainless steel sheet according to item [1]
or [2], the steel sheet having the chemical composition further
containing, by mass %, one, two, or more selected from V: 0.01% to
0.50%, B: 0.0003% to 0.0030%, Mg: 0.0005% to 0.0100%, Ca: 0.0003%
to 0.0030%, Y: 0.001% to 0.20%, and REM (rare-earth metal): 0.001%
to 0.10%.
[0022] [4] The ferritic stainless steel sheet according to any one
of items [1] to [3], the steel sheet having the chemical
composition further containing, by mass %, one or both selected
from Sn: 0.001% to 0.50% and Sb: 0.001% to 0.50%.
[0023] According to aspects of the present invention, it is
possible to obtain a ferritic stainless steel sheet having
excellent corrosion resistance, only a small quantity of surface
defects, and excellent toughness.
[0024] In addition, since sufficient softening occurs by performing
cold-rolled-sheet annealing at a temperature equivalent to that for
a case where a stabilizing chemical element is limited to Ti, there
is an improvement in the productivity of a ferritic stainless steel
sheet.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 is a diagram illustrating the influence of the
contents of Ti and Nb on toughness and the quantity of surface
defects under the condition of Zr.ltoreq.Nb.
[0026] FIG. 2 is a diagram illustrating the influence of the
contents of Nb and Zr on toughness and the quantity of surface
defects under the condition of Nb Ti.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0027] Hereafter, the embodiments of the present invention will be
described. Here, the present invention is not limited to the
embodiments described below.
[0028] The chemical composition of the ferritic stainless steel
sheet according to aspects of the present invention has a chemical
composition containing, by mass %, C: 0.020% or less, Si: 0.05% to
0.40%, Mn: 0.05% to 1.00%, P: 0.040% or less, S: 0.030% or less,
Al: 0.001% to 0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% to 0.80%, Cu:
0.30% to 0.80%, Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr:
0.005% to 0.150%, N: 0.020% or less, and the balance being Fe and
inevitable impurities, in which relational expression (1) below is
satisfied.
Zr.ltoreq.Nb.ltoreq.Ti (1)
[0029] Here, each of Zr, Nb, and Ti in relational expression (1)
denotes the content (mass %) of the corresponding chemical
element.
[0030] In addition, the chemical composition described above may
further contain, by mass %, one, two, or all selected from Co:
0.01% to 0.50%, Mo: 0.01% to 0.30%, and W: 0.01% to 0.50%.
[0031] In addition, the chemical composition described above may
further contain, by mass %, one, two, or more selected from V:
0.01% to 0.50%, B: 0.0003% to 0.0030%, Mg: 0.0005% to 0.0100%, Ca:
0.0003% to 0.0030%, Y: 0.001% to 0.20%, and REM (rare-earth metal):
0.001% to 0.10%.
[0032] In addition, the chemical composition described above may
further contain, by mass %, one or both selected from Sn: 0.001% to
0.50% and Sb: 0.001% to 0.50%.
[0033] Hereafter, each of the constituent chemical elements will be
described. "%" used when describing the content of a constituent
chemical element means "mass %", unless otherwise noted.
[0034] C: 0.020% or less
[0035] C is a chemical element which is effective for improving the
strength of steel. Such an effect is obtained in the case where the
C content is 0.001% or more. However, in the case where the C
content is more than 0.020%, there is a significant deterioration
in corrosion resistance and workability. Therefore, the C content
is set to be 0.020% or less, preferably 0.015% or less, or more
preferably 0.010% or less.
[0036] Si: 0.05% to 0.40%
[0037] Si is a chemical element which is effective as a deoxidizing
agent. Such an effect is obtained in the case where, the Si content
is 0.05% or more. However, in the case where the Si content is more
than 0.40%, there is a deterioration in workability due to an
increase in the hardness of steel. In addition, in the case where
the Si content is more than 0.40%, since there is a decrease in the
amount of scale formed on the upper surface of a slab, which has a
lubrication effect when hot rolling is performed, there is an
increase in the quantity of surface defects. Therefore, the Si
content is limited to be in the range of 0.05% to 0.40%, or
preferably 0.05% to 0.25%. It is more preferable that the lower
limit of the Si content be 0.08% or more. It is more preferable
that the upper limit of the Si content be 0.15% or less.
[0038] Mn: 0.05% to 1.00%
[0039] Mn has a deoxidizing function. Such an effect of Mn is
obtained in the case where the Mn content is 0.05% or more. On the
other hand, in the case where the Mn content is more than 1.00%,
since the precipitation and coarsening of MnS are promoted, there
is a deterioration in corrosion resistance. Therefore, the Mn
content is limited to be in the range of 0.05% to 1.00%. It is
preferable that the lower limit of the Mn content be 0.10% or more,
or more preferably 0.15% or more. It is preferable that the upper
limit of the Mn content be less than 0.30%, or more preferably
0.25% or less.
[0040] P: 0.040% or less
[0041] P is a chemical element which deteriorates corrosion
resistance. In addition, there is a deterioration in hot
workability as a result of P being segregated at grain boundaries.
Therefore, it is desirable that the P content be as small as
possible, and the P content is set to be 0.040% or less, or
preferably 0.030% or less.
[0042] S: 0.030% or less
[0043] S combines with Mn to form a precipitate, that is, MnS.
Since the interface between such MnS and the base metal of
stainless steel becomes a starting point at which pitting corrosion
occurs, there is a deterioration in corrosion resistance.
Therefore, it is preferable that the S content be smaller, and the
S content is set to be 0.030% or less, or preferably 0.020% or
less.
[0044] Al: 0.001% to 0.15%
[0045] Al is a chemical element which is effective for deoxidation.
Such an effect is obtained in the case where the Al content is
0.001% or more. On the other hand, in the case where the Al content
is more than 0.15%, since there is a decrease in the amount of
scale formed on the surface of a slab, which has a lubrication
effect when hot rolling is performed, there is an increase in the
quantity of surface defects. Therefore, the Al content is limited
to be in the range of 0.001% to 0.15%. It is preferable that the
lower limit of the Al content be 0.005% or more, or more preferably
0.01% or more. It is preferable that the upper limit of the Al
content be 0.10% or less, or more preferably 0.05% or less.
[0046] Cr: 20.0% to 23.0%
[0047] Cr is a chemical element which improves corrosion resistance
by forming a passive film on the surface. It is not possible to
achieve sufficient corrosion resistance in the case where the Cr
content is less than 20.0%. On the other hand, in the case where
the Cr content is more than 23.0%, there is a tendency for
toughness to deteriorate due to a phase and 475.degree. C.
embrittlement. Therefore, the Cr content is set to be 20.0% to
23.0%. It is preferable the lower limit of the Cr content be 20.5%
or more. It is preferable that the upper limit of the Cr content be
22.0% or less, or more preferably 21.5% or less.
[0048] Ni: 0.01% to 0.80%
[0049] Ni is a chemical element which makes it possible to maintain
a passive state even at a lower pH by inhibiting an anode reaction
due to acid. That is, Ni improves corrosion resistance by markedly
inhibiting the progress of corrosion in an active dissolution state
as a result of increasing the effect of crevice corrosion
resistance. Such an effect of Ni is obtained in the case where the
Ni content is 0.01% or more. On the other hand, in the case where
the Ni content is more than 0.80%, there is a deterioration in
workability due to an increase in the hardness of steel. Therefore,
the Ni content is limited to be 0.01% to 0.80%. It is preferable
that the lower limit of the Ni content be 0.05% or more, or more
preferably 0.10% or more. It is preferable that the upper limit of
the Ni content be 0.40% or less, or more preferably 0.25% or
less.
[0050] Cu: 0.30% to 0.80%
[0051] Cu is a chemical element which improves corrosion resistance
by strengthening a passive film. On the other hand, in the case
where the Cu content is excessively large, since c-Cu tends to be
precipitated, there is a deterioration in corrosion resistance.
Therefore, the Cu content is set to be 0.30% to 0.80%. It is
preferable that the lower limit of the Cu content be 0.35% or more,
or more preferably 0.40% or more. It is preferable that the upper
limit of the Cu content be 0.60% or less, or more preferably 0.45%
or less.
[0052] Ti: 0.10% to 0.50%
[0053] Ti is a chemical element which improves corrosion resistance
by preventing sensitization due to Cr carbonitrides as a result of
fixing C and N. However, TiN, which is formed as a result of
containing Ti, causes a deterioration in toughness. In accordance
with aspects of the present invention, the above-mentioned
deterioration in toughness due to Ti is suppressed by the
combination effect of Nb and Zr as described below. The effect of
improving corrosion resistance through the use of Ti is obtained in
the case where the Ti content is 0.10% or more. On the other hand,
in the case where the Ti content is more than 0.50%, there is a
deterioration in workability due to an increase in the hardness of
a stainless steel sheet. In addition, in the case where the Ti
content is more than 0.50%, since it is difficult to control the
precipitation form of Ti-based inclusions even in the case where Nb
and Zr are contained, there is a deterioration in surface quality.
Therefore, the Ti content is set to be in the range of 0.10% to
0.50%. It is preferable that the lower limit of the Ti content be
0.15% or more, or more preferably 0.18% or more. It is preferable
that the upper limit of the Ti content be 0.35% or less, or more
preferably 0.26% or less.
[0054] Nb: 0.010% to 0.150%
[0055] Nb is, like Ti, a chemical element which improves corrosion
resistance by preventing sensitization due to Cr carbonitrides as a
result of fixing C and N. Moreover, Nb improves toughness and
inhibits a surface defect from occurring by the combination effect
with Zr described below. Such effects are obtained in the case
where the Nb content is 0.010% or more. On the other hand, in the
case where the Nb content is more than 0.150%, there is a
deterioration in workability due to an increase in the hardness of
a stainless steel sheet. In addition, in the case where the Nb
content is more than 0.150%, since there is an increase in
recrystallization temperature, there is a deterioration in
manufacturability. Therefore, the Nb content is set to be in the
range of 0.010% to 0.150%. It is preferable that the lower limit of
the Nb content be 0.030% or more, or more preferably 0.070% or
more. It is preferable that the upper limit of the Nb content be
less than 0.100%, or more preferably 0.090% or less.
[0056] Zr: 0.005% to 0.150%
[0057] Zr is, like Ti, a chemical element which improves corrosion
resistance by preventing sensitization due to Cr carbonitrides as a
result of fixing C and N. Moreover, Zr improves toughness and
inhibits a surface defect from occurring by the combination effect
with Nb described below. It is necessary that the Zr content be
0.005% or more in order to obtained such effects. On the other
hand, in the case where the Zr content is more than 0.150%, since
Zr-based inclusions are precipitated on the surface, there is an
increase in the quantity of surface defects. Therefore, the Zr
content is limited to be in the range of 0.005% to 0.150%. It is
preferable that the lower limit of the Zr content be 0.010% or
more, or more preferably 0.030% or more. It is preferable that the
upper limit of the Zr content be less than 0.100%, or more
preferably 0.080% or less.
[0058] It was found that, in accordance with aspects of the present
invention, by containing Nb and Zr in combination to SUS443J1-type
stainless steel which contains only Ti as a stabilizing chemical
element, it is possible to allow sufficient softening to occur by
performing cold-rolled-sheet annealing even at a temperature
equivalent to that for the case where a stabilizing chemical
element is limited to Ti, and it is possible to realize a decrease
in the quantity of surface defects and a high toughness at the same
time. Specifically, it was found that, by controlling the contents
of the stabilizing chemical elements (Ti, Nb, and Zr) in the
chemical composition of a SUS443J1-type stainless steel so that the
Ti content is 0.10% to 0.50%, the Nb content is 0.010% to 0.150%,
and the Zr content is 0.005% to 0.150% under the condition
expressed by relational expression (1) below, it is possible to
allow sufficient softening to occur by performing cold-roiled-sheet
annealing even at a temperature equivalent to that for the case
where a stabilizing chemical element is limited to Ti, and it is
possible to realize a decrease in the quantity of surface defects
and a high toughness at the same time. The mechanism of these is
supposed to be as follows.
[0059] It is considered that, as a result of Nb and Zr being
contained in combination in steel, since complex carbonitrides of
Ti, Zr, and Nb ((Ti, Zr, Nb)(C,N)), whose particle size is smaller
than that of TiN formed in ferritic stainless steel containing only
Ti, are dispersedly precipitated, an improvement in toughness and a
decrease in the quantity of surface defects are realized. In order
to form the above-mentioned complex carbonitrides ((Ti, Zr,
Nb)(C,N)) in sufficient amounts, it is necessary that relational
expression (1) below be satisfied.
Zr.ltoreq.Nb.ltoreq.Ti (1)
[0060] Here, each of Zr, Nb, and Ti in relational expression (1)
denotes the content (mass %) of the corresponding chemical
element.
[0061] Regarding the relationship between Ti and Nb, it is
preferable that the relational expression Ti.gtoreq.1.5Nb, or more
preferably Ti.gtoreq.2Nb, be satisfied. Regarding the relationship
between Nb and Zr, it is preferable that the relational expression
Nb.gtoreq.1.3Zr, or more preferably Nb.gtoreq.1.5Zr, be
satisfied.
[0062] N: 0.020% or less
[0063] N is a chemical element which is inevitably mixed in steel.
However, in the case where the N content is more than 0.020%, there
is a significant deterioration in corrosion resistance and
workability. Therefore, the N content is set to be 0.020% or less,
or preferably 0.015% or less.
[0064] The basic constituent chemical elements are described above,
and the chemical elements described below may be appropriately
added in addition to the basic constituent chemical elements in
accordance with aspects of the present invention as described
above.
[0065] Co: 0.01% to 0.50%
[0066] Co is a chemical element which improves the crevice
corrosion resistance of stainless steel. Such an effect of Co is
obtained in the case where the Co content is 0.01% or more.
However, in the case where the Co content is more than 0.50%, such
an effect of Co becomes saturated, and there is a deterioration in
workability. Therefore, in the case where Co is contained, the Co
content is set to be 0.01% to 0.50%. It is preferable that the
lower limit of the Co content be 0.02% or more, or more preferably
0.03% or more. It is preferable that the upper limit of the Co
content be 0.30% or less, or more preferably 0.10% or less.
[0067] Mo: 0.01% to 0.30%
[0068] Mo is effective for improving the crevice corrosion
resistance of stainless steel. Such an effect is obtained in the
case where the Mo content is 0.01% or more. However, in the case
where the Mo content is more than 0.30%, such an effect of Mo
becomes saturated, and there is a deterioration in toughness due to
the formation of coarse intermetallic compounds. Therefore, in the
case where Mo is added, the Mo content is set to be 0.01% to 0.30%.
It is preferable that the lower limit of the Mo content be 0.02% or
more, or more preferably 0.03% or more. It is preferable that the
upper limit of the Mo content be 0.20% or less, or more preferably
0.10% or less.
[0069] W: 0.01% to 0.50%
[0070] W is a chemical element which improves the crevice corrosion
resistance of stainless steel. Such an effect of W is obtained in
the case where the W content is 0.01% or more. On the other hand,
in the case where the W content is more than 0.50%, such an effect
of W becomes saturated, and there is a deterioration in
workability. Therefore, in the case where W is contained, the W
content is set to be 0.01% to 0.50%. It is preferable that the
lower limit of the W content be 0.02% or more, or more preferably
0.03% or more. It is preferable that the upper limit of the W
content be 0.30% or less, or more preferably 0.10% or less.
[0071] V: 0.01% to 0.50%
[0072] V is a chemical element which improves the crevice corrosion
resistance of stainless steel. Such an effect of V is obtained in
the case where the V content is 0.01% or more. On the other hand,
in the case where the V content is more than 0.50%, such an effect
of V becomes saturated, and there is a deterioration in
workability. Therefore, in the case where V is added, the V content
is set to be 0.01% to 0.50%, preferably 0.01% to 0.30%, or more
preferably 0.01% to 0.10%.
[0073] B: 0.0003% to 0.0030%
[0074] Since B is a chemical element which improves hot workability
and secondary workability, it is effective to containing B to
Ti-containing steel. Such an effect of B is obtained in the case
where the B content is 0.0003% or more. On the other hand, in the
case where the B content is more than 0.0030%, there is a
deterioration in toughness. Therefore, in the case where B is
contained, the B content is set to be in the range of 0.0003% to
0.0030%. It is preferable that the lower limit of the B content be
0.0015% or more. It is preferable that the upper limit of the B
content be 0.0025% or less.
[0075] Mg: 0.0005% to 0.0100%
[0076] Mg functions as a deoxidizing agent along with Al by forming
Mg oxides in molten steel. Such an effect of Mg is obtained in the
case where the Mg content is 0.0005% or more. On the other hand, in
the case where the Mg content is more than 0.0100%, there is a
deterioration in manufacturability and a deterioration in the
toughness of steel. Therefore, in the case where Mg is contained,
the Mg content is limited to be in the range of 0.0005% to 0.0100%.
It is preferable that the lower limit of the Mg content be 0.0010%
or more. It is preferable that the upper limit of the Mg content be
0.0050% or less, or more preferably 0.0030% or less.
[0077] Ca: 0.0003% to 0.0030%
[0078] Ca is a chemical element which improves hot workability.
Such an effect of Ca is obtained in the case where the Ca content
is 0.0003% or more. On the other hand, in the case where the Ca
content is more than 0.0030%, there is a deterioration in the
toughness of steel, and there is a deterioration in corrosion
resistance due to the precipitation of CaS. Therefore, in the case
where Ca is added, the Ca content is limited to be in the range of
0.0003% to 0.0030%. It is preferable that the lower limit of the Ca
content be 0.001% or more. It is preferable that the upper limit of
the Ca content be 0.002% or less.
[0079] Y: 0.001% to 0.20%
[0080] Y is a chemical element which improves cleanliness by
inhibiting a decrease in the viscosity of molten steel. Such an
effect of Y is obtained in the case where the Y content is 0.001%
or more. On the other hand, in the case where the Y content is more
than 0.20%, such an effect of Y becomes saturated, and there is a
deterioration in workability. Therefore, in the case where Y is
added, the Y content is limited to be in the range of 0.001% to
0.20%, or preferably 0.001% to 0.10%.
[0081] REM (rare-earth metal): 0.001% to 0.10%
[0082] REM (rare-earth metal: one of the chemical elements having
atomic numbers of 57 through 71 such as La, Ce, or Nd) is a
chemical element which improves high-temperature oxidation
resistance. Such an effect of REM is obtained in the case where the
REM content is 0.001% or more. On the other hand, in the case where
the REM content is more than 0.10%, such an effect of REM becomes
saturated, and a surface defect occurs when hot rolling is
performed. Therefore, in the case where REM is contained, the REM
content is limited to be in the range of 0.001% to 0.10%. It is
preferable the lower limit of the REM content be 0.005% or more. It
is preferable that the upper limit of the REM content be 0.05% or
less.
[0083] Sn: 0.001% to 0.50%
[0084] Sn is effective for improving ridging resistance by
promoting the formation of a deformation zone when rolling is
performed. Such an effect is obtained in the case where the Sn
content is 0.001% or more. However, in the case where the Sn
content is more than 0.50%, such an effect of Sn becomes saturated,
and there is a deterioration in workability. Therefore, in the case
where Sn is added, the Sn content is set to be 0.001% to 0.50%. It
is preferable that the lower limit of the Sn content be 0.003% or
more. It is preferable that the upper limit of the Sn content be
0.20% or less.
[0085] Sb: 0.001% to 0.50%
[0086] Sb is effective for improving ridging resistance by
promoting the formation of a deformation zone when rolling is
performed. Such an effect is obtained in the case where the Sb
content is 0.001% or more. However, in the case where the Sb
content is more than 0.50%, such an effect of Sb becomes saturated,
and there is a deterioration in workability. Therefore, in the case
where Sb is contained, the Sb content is set to be 0.001% to 0.50%.
It is preferable that the lower limit of the Sb content be 0.003%
or more. It is preferable that the upper limit of the Sb content be
0.20% or less.
[0087] The remainder which is other than the constituent chemical
elements described above is Fe and inevitable impurities.
Representative examples of the inevitable impurities described here
include H, O (oxygen), Zn, Ga, Ge, As, Ag, In, Hf, Ta, Re, Os, Ir,
Pt, Au, and Pb. Among these chemical elements, H and O (oxygen) may
be contained in an amount of 0.05% or less. Other chemical elements
may be contained in an amount of 0.3% or less.
[0088] Hereafter, a preferable method for manufacturing the
ferritic stainless steel sheet according to aspects of the present
invention will be described. Molten steel having the chemical
composition described above is prepared by using a known method
such as one which utilizes a converter, an electric furnace, or a
vacuum melting furnace and made into a steel material (slab) by
using a continuous casting method or an ingot casting-slabbing
method. This steel material is heated to a temperature of
1000.degree. C. to 1200.degree. C. and then subjected to hot
rolling so as to have a thickness of 2.0 mm to 5.0 mm under the
condition of a finishing temperature of 700.degree. C. to
1000.degree. C. The hot-rolled steel sheet, which has been obtained
as described above, is subjected to annealing at a temperature of
800.degree. C. to 1100.degree. C. followed by pickling, cold
rolling, and cold-rolled-sheet annealing at a temperature of
700.degree. C. to 1000.degree. C. After cold-rolled-sheet annealing
has been performed, pickling is performed in order to remove scale.
The cold-rolled steel sheet from which scale has been removed may
be subjected to skin pass rolling.
[0089] In addition, aspects of the present invention are effective
not only for the above-mentioned cold-rolled sheet product but also
for a hot-rolled sheet product.
Examples
[0090] After ferritic stainless steels having the chemical
compositions given in Table 1 (Table 1-1 and Table 1-2 are combined
to form Table 1), Table 2 (Table 2-1 and Table 2-2 are combined to
form Table 2), and Table 3 (Table 3-1 and Table 3-2 are combined to
form Table 3) had been made into steel ingots having a weight of
100 kg, the ingots were heated to a temperature of 1200.degree. C.
and subjected to hot rolling in order to obtain hot-rolled steel
sheets having a thickness of 4.0 mm. Subsequently, the hot-rolled
steel sheets were subjected to annealing at a temperature of
1100.degree. C. followed by pickling which utilized a commonly used
method and subjected to cold rolling so as to have a thickness of
2.0 mm followed by annealing at a temperature of 900.degree. C. and
pickling which utilized a commonly used method.
[0091] By determining the pitting potential (JIS G 0577) of the
obtained cold-rolled and annealed steel sheet, corrosion resistance
was evaluated. A case where the pitting potential was 290 mV (vs.
SCE) or more was judged as ".largecircle." (satisfactory), and a
case where the pitting potential was less than 290 mV (vs. SCE) was
judged as ".tangle-solidup." (unsatisfactory).
[0092] In addition, by performing a Charpy impact test on a test
piece (JIS B 7722, V notch) which had been taken from the obtained
cold-rolled and annealed steel sheet along the rolling direction,
the toughness of the steel sheet was evaluated. A case where the
Charpy impact value at 25.degree. C. was 200 J/cm.sup.2 or more was
judged as ".largecircle." (satisfactory), and a case where the
Charpy impact value at 25.degree. C. was less than 200 J/cm.sup.2
was judged as ".tangle-solidup." (unsatisfactory).
[0093] Moreover, by observing the surface of the cold-rolled and
annealed steel sheet in order to determine the density of streaks
on the surface, the quantity of surface defects was evaluated. By
preparing 10 steel sheets having each of the chemical compositions,
and by counting the number of streaks having a length in the
L-direction of more than 10 mm in a region having a width of 200 mm
and a length of 200 mm on the center portion of the upper surface
of each of the steel sheets, a case where the average of the
counted numbers was 1 or less was judged as ".largecircle."
(satisfactory), and a case where the average of the counted numbers
was more than 1 was judged as ".tangle-solidup."
(unsatisfactory).
[0094] Moreover, it was evaluated whether sufficient softening
occurred by performing annealing even at a temperature of
880.degree. C. for 20 seconds on the cold-rolled steel sheet which
had not yet been annealed. The evaluation was performed by
comparing the hardness (a) of a steel sheet in the cold-rolled
state or as cold-rolled, the hardness (b) of a steel sheet which
had been subjected to annealing at a temperature of 880.degree. C.
for 20 seconds, and the hardness (c) of a steel sheet which had
been subjected to annealing at a temperature of 1000.degree. C. for
20 seconds as an index of a case where sufficient softening
occurred. Three test pieces having a length of 15 mm and a width of
20 mm were taken from the cold-rolled steel sheet, and each of the
test pieces for respectively determining b and c was subjected to
the corresponding annealing. Subsequently, each of the three test
pieces were cut into pieces having a length of 15 mm and a width of
10 mm. Then, the Vickers hardness determined in the cross section
of the cut piece was used for the evaluation. As annealing
progressed, the harness of the steel sheet changed from a to c. A
case where 90% or more of such a softening process was completed
through annealing at a temperature of 880.degree. C. for 20
seconds, that is, a case where the relational expression
c+0.1.times.(a-c).gtoreq.b was satisfied, was judged as
".largecircle." (satisfactory), and other cases were judged as
".tangle-solidup." (unsatisfactory).
[0095] The obtained results are given in Tables 1, 2, and 3. In the
case of the steels of the examples of the present invention, all
the judgment results of the determined pitting potential, the
Charpy impact value, the surface defect, and the softening
temperature were ".largecircle.", which means that these steels had
good corrosion resistance and toughness, only a small quantity of
surface defects, and no manufacturing problem.
[0096] Comparative example No. 34, whose Cr content was lower than
the range according to aspects of the present invention, had poor
corrosion resistance.
[0097] Comparative example No. 35, whose Cr content was higher than
the range according to aspects of the present invention, had poor
toughness.
[0098] Comparative example No. 36, whose Ni content was lower than
the range according to aspects of the present invention, had poor
corrosion resistance.
[0099] Comparative example No. 37, whose Ti content was lower than
the range according to aspects of the present invention, had poor
corrosion resistance.
[0100] Comparative example No. 38, whose Ti content was higher than
the range according to aspects of the present invention, had poor
toughness and a large quantity of surface defects.
[0101] Comparative example No. 39, whose Nb content was lower than
the range according to aspects of the present invention, had poor
toughness and a large quantity of surface defects.
[0102] Comparative example No. 40, whose Nb content was higher than
the range according to aspects of the present invention, had poor
manufacturability due to a high softening temperature.
[0103] Comparative example No. 41, whose Zr content was lower than
the range according to aspects of the present invention, had poor
toughness and a large quantity of surface defects.
[0104] Comparative example No. 42, whose Zr content was higher than
the range according to aspects of the present invention, had a
large quantity of surface defects.
[0105] Comparative example No. 57, whose contents of Nb and Zr were
both lower than the range according to aspects of the present
invention, had poor toughness and a large quantity of surface
defects.
[0106] Comparative example No. 58, whose contents of Ti and Zr were
both lower than the ranges according to aspects of the present
invention, and whose contents of Al and Nb were both higher than
the ranges according to aspects of the present invention, had poor
toughness, a large quantity of surface defects, and poor
manufacturability due to a high softening temperature.
[0107] Here, comparative example Nos. 43 through 54, 67, and 68
will be described hereafter with reference to FIG. 1 and FIG.
2.
TABLE-US-00001 TABLE 1-1 Test Chemical Composition (mass %) No. C
Si Mn P S Al Cr Ni Cu Ti Nb Zr N Other Chemical Element Note 1
0.010 0.09 0.21 0.025 0.002 0.020 20.2 0.29 0.43 0.19 0.075 0.031
0.009 Example 2 0.012 0.12 0.17 0.021 0.002 0.026 21.1 0.30 0.44
0.24 0.071 0.034 0.007 Example 3 0.011 0.11 0.19 0.029 0.003 0.027
21.2 0.28 0.42 0.19 0.089 0.012 0.008 Example 4 0.012 0.10 0.22
0.027 0.002 0.035 22.7 0.18 0.41 0.20 0.088 0.011 0.013 Example 5
0.009 0.11 0.20 0.021 0.002 0.029 20.6 0.02 0.44 0.22 0.095 0.034
0.008 Example 6 0.008 0.12 0.16 0.028 0.002 0.037 20.6 0.21 0.44
0.21 0.076 0.021 0.008 Example 7 0.010 0.12 0.20 0.028 0.003 0.032
21.4 0.79 0.41 0.24 0.069 0.023 0.010 Example 8 0.010 0.09 0.16
0.028 0.003 0.024 20.9 0.27 0.41 0.11 0.055 0.036 0.013 Example 9
0.011 0.10 0.22 0.020 0.002 0.035 20.9 0.29 0.45 0.22 0.075 0.020
0.010 Example 10 0.007 0.10 0.16 0.027 0.001 0.031 20.7 0.23 0.42
0.48 0.079 0.023 0.010 Example 11 0.012 0.12 0.18 0.023 0.003 0.028
20.5 0.19 0.43 0.20 0.012 0.007 0.008 Example 12 0.011 0.12 0.19
0.030 0.001 0.026 20.9 0.13 0.40 0.21 0.077 0.040 0.013 Example 13
0.010 0.11 0.19 0.026 0.003 0.031 20.9 0.12 0.43 0.32 0.147 0.032
0.012 Example 14 0.011 0.11 0.18 0.026 0.002 0.033 21.2 0.24 0.42
0.24 0.094 0.006 0.013 Example 15 0.008 0.09 0.19 0.028 0.003 0.033
20.7 0.11 0.41 0.23 0.081 0.047 0.010 Example 16 0.012 0.08 0.17
0.030 0.002 0.036 21.4 0.18 0.43 0.40 0.148 0.146 0.012 Example 17
0.009 0.09 0.16 0.029 0.002 0.032 21.4 0.24 0.41 0.12 0.072 0.051
0.007 Example 18 0.013 0.08 0.21 0.021 0.002 0.024 20.9 0.25 0.45
0.17 0.092 0.065 0.008 Example 19 0.007 0.10 0.20 0.022 0.002 0.148
20.6 0.15 0.42 0.21 0.123 0.090 0.008 Example 20 0.008 0.08 0.17
0.027 0.002 0.026 21.3 0.21 0.45 0.11 0.099 0.092 0.008 Example 21
0.009 0.12 0.20 0.026 0.002 0.023 20.8 0.25 0.41 0.16 0.112 0.095
0.012 Example 22 0.009 0.11 0.15 0.026 0.003 0.037 21.1 0.26 0.43
0.21 0.147 0.118 0.012 Example 23 0.009 0.10 0.16 0.029 0.002 0.034
20.7 0.18 0.43 0.21 0.061 0.014 0.007 Co: 0.07, Mo: 0.05, W: 0.08
Example 24 0.007 0.10 0.20 0.021 0.003 0.029 20.7 0.14 0.45 0.19
0.070 0.011 0.010 V: 0.07, Ca: 0.0012, La: 0.03 Example 25 0.012
0.09 0.20 0.028 0.002 0.023 20.8 0.27 0.43 0.21 0.065 0.019 0.011
Sn: 0.05, Sb: 0.08 Example 26 0.007 0.09 0.23 0.029 0.002 0.020
20.8 0.18 0.40 0.22 0.074 0.025 0.013 Co: 0.47, Mg: 0.0005 Example
27 0.012 0.08 0.21 0.021 0.002 0.023 21.1 0.22 0.42 0.25 0.085
0.027 0.010 Co: 0.25, V: 0.28, Sn: 0.16 Example 28 0.009 0.08 0.18
0.029 0.002 0.038 21.4 0.15 0.41 0.20 0.099 0.036 0.011 Mo: 0.28,
B: 0.0018, Ca: 0.0023 Example 29 0.008 0.11 0.16 0.024 0.002 0.035
21.0 0.27 0.42 0.26 0.071 0.033 0.010 W: 0.45, Mg: 0.0025, Sb: 0.04
Example 30 0.013 0.12 0.22 0.024 0.002 0.021 20.9 0.24 0.41 0.18
0.088 0.031 0.009 Co: 0.04, Y: 0.003, La: 0.007 Example 31 0.008
0.11 0.20 0.026 0.001 0.037 21.3 0.11 0.44 0.24 0.077 0.029 0.011
Mo: 0.17, Ce: 0.05, Sn: 0.001 Example 32 0.008 0.10 0.17 0.026
0.002 0.021 21.3 0.11 0.41 0.21 0.094 0.020 0.013 Sn: 0.005 Example
33 0.009 0.11 0.22 0.021 0.003 0.039 20.8 0.22 0.42 0.24 0.078
0.031 0.010 Sb: 0.13 Example
TABLE-US-00002 TABLE 1-2 Test Corrosion Surface Softening No.
Ti--Nb Nb--Zr Resistance Charpy Defect Temperature Note 1 0.12
0.044 .largecircle. .largecircle. .largecircle. .largecircle.
Example 2 0.17 0.037 .largecircle. .largecircle. .largecircle.
.largecircle. Example 3 0.10 0.077 .largecircle. .largecircle.
.largecircle. .largecircle. Example 4 0.11 0.077 .largecircle.
.largecircle. .largecircle. .largecircle. Example 5 0.13 0.061
.largecircle. .largecircle. .largecircle. .largecircle. Example 6
0.13 0.055 .largecircle. .largecircle. .largecircle. .largecircle.
Example 7 0.17 0.046 .largecircle. .largecircle. .largecircle.
.largecircle. Example 8 0.06 0.019 .largecircle. .largecircle.
.largecircle. .largecircle. Example 9 0.15 0.055 .largecircle.
.largecircle. .largecircle. .largecircle. Example 10 0.40 0.056
.largecircle. .largecircle. .largecircle. .largecircle. Example 11
0.19 0.005 .largecircle. .largecircle. .largecircle. .largecircle.
Example 12 0.13 0.037 .largecircle. .largecircle. .largecircle.
.largecircle. Example 13 0.17 0.115 .largecircle. .largecircle.
.largecircle. .largecircle. Example 14 0.15 0.088 .largecircle.
.largecircle. .largecircle. .largecircle. Example 15 0.15 0.034
.largecircle. .largecircle. .largecircle. .largecircle. Example 16
0.25 0.002 .largecircle. .largecircle. .largecircle. .largecircle.
Example 17 0.05 0.021 .largecircle. .largecircle. .largecircle.
.largecircle. Example 18 0.08 0.027 .largecircle. .largecircle.
.largecircle. .largecircle. Example 19 0.09 0.033 .largecircle.
.largecircle. .largecircle. .largecircle. Example 20 0.01 0.007
.largecircle. .largecircle. .largecircle. .largecircle. Example 21
0.05 0.017 .largecircle. .largecircle. .largecircle. .largecircle.
Example 22 0.06 0.029 .largecircle. .largecircle. .largecircle.
.largecircle. Example 23 0.15 0.047 .largecircle. .largecircle.
.largecircle. .largecircle. Example 24 0.12 0.059 .largecircle.
.largecircle. .largecircle. .largecircle. Example 25 0.15 0.046
.largecircle. .largecircle. .largecircle. .largecircle. Example 26
0.15 0.049 .largecircle. .largecircle. .largecircle. .largecircle.
Example 27 0.17 0.058 .largecircle. .largecircle. .largecircle.
.largecircle. Example 28 0.10 0.063 .largecircle. .largecircle.
.largecircle. .largecircle. Example 29 0.19 0.038 .largecircle.
.largecircle. .largecircle. .largecircle. Example 30 0.09 0.057
.largecircle. .largecircle. .largecircle. .largecircle. Example 31
0.16 0.048 .largecircle. .largecircle. .largecircle. .largecircle.
Example 32 0.12 0.074 .largecircle. .largecircle. .largecircle.
.largecircle. Example 33 0.16 0.047 .largecircle. .largecircle.
.largecircle. .largecircle. Example *[Corrosion Resistance] A case
where the pitting potential was 290 mV (vs. SCE) or more was judged
as ".largecircle." (satisfactory), and a case where the pitting
potential was less than 290 mV (vs. SCE) was judged as
".tangle-solidup." (unsatisfactory). *[Charpy Impact Value] A case
where the Charpy impact value (of a steel sheet having a thickness
of 2 mm) at 25.degree. C. was 200 J/cm.sup.2 or more was judged as
".largecircle." (satisfactory), and a case where the Charpy impact
value (of a steel sheet having a thickness of 2 mm) at 25.degree.
C. was less than 200 J/cm.sup.2 was judged as ".tangle-solidup."
(unsatisfactory). *[Surface Defect] A case where the number of
streaks in a region of 200 mm.sup.W .times. 200 mm.sup.L was 1 or
less was judged as ".largecircle." (satisfactory), and a case where
the above-described number was more than 1 was judged as
".tangle-solidup." (unsatisfactory). *[Softening Temperature] A
case where the relational expression c + 0.1 .times. (a - c)
.gtoreq. b was satisfied was judged as ".largecircle."
(satisfactory), and other cases were judged as ".tangle-solidup."
(unsatisfactory), where the Vickers hardness of a steel sheet in
the cold-rolled state was defined as a, the Vickers hardness of a
steel sheet which had been subjected to a heat treatment at a
temperature of 880.degree. C. for 20 seconds was defined as b, and
the Vickers hardness of a steel sheet which had been subjected to a
heat treatment at a temperature of 1000.degree. C. for 20 seconds
was defined as c.
TABLE-US-00003 TABLE 2-1 Chemical Composition (mass %) Other
Chemical Test No. C Si Mn P S Al Cr Ni Cu Ti Nb Zr N Element Note
34 0.008 0.10 0.15 0.023 0.002 0.039 19.6 0.29 0.43 0.20 0.090
0.021 0.010 Comparative Example 35 0.012 0.09 0.19 0.025 0.001
0.022 23.2 0.12 0.40 0.20 0.087 0.017 0.009 Comparative Example 36
0.010 0.11 0.18 0.025 0.001 0.034 21.0 -- 0.43 0.25 0.063 0.021
0.012 Comparative Example 37 0.008 0.11 0.17 0.022 0.001 0.039 20.8
0.11 0.45 0.09 0.036 0.018 0.013 Comparative Example 38 0.011 0.12
0.19 0.025 0.002 0.030 20.7 0.14 0.44 0.52 0.079 0.018 0.012
Comparative Example 39 0.011 0.11 0.21 0.028 0.002 0.023 20.8 0.28
0.45 0.24 0.008 0.005 0.010 Comparative Example 40 0.007 0.09 0.19
0.025 0.002 0.037 21.4 0.28 0.40 0.42 0.153 0.033 0.013 Comparative
Example 41 0.011 0.09 0.21 0.030 0.003 0.030 20.7 0.12 0.43 0.20
0.097 0.003 0.009 Comparative Example 42 0.009 0.11 0.20 0.027
0.003 0.037 20.7 0.24 0.41 0.25 0.071 0.157 0.012 Comparative
Example 43 0.008 0.09 0.20 0.025 0.002 0.034 20.9 0.19 0.44 0.13
0.141 0.138 0.010 Comparative Example 44 0.013 0.11 0.21 0.027
0.002 0.035 21.5 0.14 0.45 0.11 0.125 0.094 0.012 Comparative
Example 45 0.009 0.11 0.16 0.025 0.002 0.039 21.5 0.13 0.40 0.13
0.147 0.107 0.009 Comparative Example 46 0.008 0.10 0.16 0.024
0.002 0.026 21.1 0.19 0.41 0.10 0.148 0.109 0.008 Comparative
Example 47 0.011 0.10 0.16 0.022 0.002 0.039 21.3 0.23 0.42 0.11
0.123 0.018 0.008 Comparative Example 48 0.007 0.11 0.22 0.021
0.001 0.025 21.3 0.22 0.41 0.13 0.148 0.033 0.009 Comparative
Example 49 0.009 0.11 0.21 0.030 0.001 0.022 21.4 0.24 0.40 0.11
0.085 0.098 0.010 Comparative Example 50 0.009 0.09 0.15 0.028
0.001 0.026 21.4 0.27 0.44 0.12 0.103 0.132 0.009 Comparative
Example 51 0.011 0.12 0.19 0.021 0.002 0.027 20.6 0.25 0.43 0.10
0.064 0.071 0.010 Comparative Example 52 0.012 0.10 0.19 0.023
0.002 0.029 21.0 0.26 0.42 0.13 0.074 0.144 0.009 Comparative
Example 53 0.013 0.08 0.17 0.029 0.001 0.021 21.5 0.24 0.43 0.23
0.032 0.051 0.008 Comparative Example 54 0.013 0.11 0.16 0.020
0.002 0.021 20.9 0.29 0.42 0.11 0.051 0.142 0.010 Comparative
Example 55 0.010 0.10 0.20 0.020 0.002 0.037 21.4 0.24 0.44 0.12
0.132 0.145 0.008 Comparative Example 56 0.008 0.11 0.20 0.028
0.002 0.024 20.8 0.24 0.43 0.10 0.118 0.133 0.008 Comparative
Example 57 0.011 0.10 0.16 0.022 0.001 0.038 21.0 0.23 0.44 0.31
0.001 0.002 0.009 Comparative Example 58 0.009 0.12 0.16 0.022
0.002 0.035 20.6 0.13 0.40 0.02 0.256 0.003 0.011 Comparative
Example
TABLE-US-00004 TABLE 2-2 Test Corrosion Surface Softening No.
Ti--Nb Nb--Zr Resistance Charpy Defect Temperature Note 34 0.11
0.069 .tangle-solidup. .largecircle. .largecircle. .largecircle.
Comparative Example 35 0.11 0.070 .largecircle. .tangle-solidup.
.largecircle. .largecircle. Comparative Example 36 0.19 0.042
.tangle-solidup. .largecircle. .largecircle. .largecircle.
Comparative Example 37 0.05 0.018 .tangle-solidup. .largecircle.
.largecircle. .largecircle. Comparative Example 38 0.44 0.061
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 39 0.23 0.003 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 40 0.27 0.120
.largecircle. .largecircle. .largecircle. .tangle-solidup.
Comparative Example 41 0.10 0.094 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 42 0.18 -0.086
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 43 -0.01 0.003 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 44 -0.02 0.031
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 45 -0.02 0.040 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 46 -0.05 0.039
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 47 -0.01 0.105 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 48 -0.02 0.115
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 49 0.03 -0.013 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 50 0.02 -0.029
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 51 0.04 -0.007 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 52 0.06 -0.070
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 53 0.20 -0.019 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 54 0.06 -0.091
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 55 -0.01 -0.013 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 56 -0.02 -0.015
.largecircle. .tangle-solidup. .tangle-solidup. .largecircle.
Comparative Example 57 0.31 -0.001 .largecircle. .tangle-solidup.
.tangle-solidup. .largecircle. Comparative Example 58 -0.24 0.253
.largecircle. .tangle-solidup. .tangle-solidup. .tangle-solidup.
Comparative Example *[Corrosion Resistance] A case where the
pitting potential was 290 mV (vs. SCE) or more was judged as
".largecircle." (satisfactory), and a case where the pitting
potential was less than 290 mV (vs. SCE) was judged as
".tangle-solidup." (unsatisfactory). *[Charpy Impact Value] A case
where the Charpy impact value (of a steel sheet having a thickness
of 2 mm) at 25.degree. C. was 200 J/cm.sup.2 or more was judged as
".largecircle." (satisfactory), and a case where the Charpy impact
value (of a steel sheet having a thickness of 2 mm) at 25.degree.
C. was less than 200 J/cm.sup.2 was judged as ".tangle-solidup."
(unsatisfactory). *[Surface Defect] A case where the number of
streaks in a region of 200 mm.sup.W .times. 200 mm.sup.L was 1 or
less was judged as ".largecircle." (satisfactory), and a case where
the above-described number was more than 1 was judged as
".tangle-solidup." (unsatisfactory). *[Softening Temperature] A
case where the relational expression c + 0.1 .times. (a - c)
.gtoreq. b was satisfied was judged as ".largecircle."
(satisfactory), and other cases were judged as ".tangle-solidup."
(unsatisfactory), where the Vickers hardness of a steel sheet in
the cold-rolled state was defined as a, the Vickers hardness of a
steel sheet which had been subjected to a heat treatment at a
temperature of 880.degree. C. for 20 seconds was defined as b, and
the Vickers hardness of a steel sheet which had been subjected to a
heat treatment at a temperature of 1000.degree. C. for 20 seconds
was defined as c.
TABLE-US-00005 TABLE 3-1 Chemical Composition (mass %) Other
Chemical Test No. C Si Mn P S Al Cr Ni Cu Ti Nb Zr N Element Note
59 0.009 0.08 0.16 0.027 0.002 0.029 20.6 0.28 0.32 0.13 0.118
0.038 0.013 Mo: 0.09 Example 60 0.009 0.10 0.17 0.026 0.003 0.029
21.4 0.30 0.33 0.15 0.139 0.022 0.010 V: 0.11 Example 61 0.012 0.11
0.21 0.027 0.002 0.024 21.1 0.21 0.44 0.16 0.146 0.029 0.009 Mo:
0.26 Example 62 0.010 0.11 0.23 0.026 0.003 0.031 20.9 0.23 0.41
0.22 0.056 0.050 0.010 Ca: 0.0024 Example 63 0.008 0.12 0.20 0.029
0.001 0.021 21.0 0.14 0.44 0.26 0.091 0.082 0.011 W: 0.33 Example
64 0.012 0.10 0.18 0.025 0.003 0.038 21.3 0.22 0.43 0.25 0.113
0.105 0.011 B: 0.0015 Example 65 0.009 0.11 0.23 0.026 0.003 0.037
20.7 0.19 0.57 0.22 0.126 0.102 0.012 Co: 0.18 Example 66 0.010
0.12 0.23 0.025 0.001 0.022 20.9 0.22 0.78 0.23 0.128 0.119 0.010
La: 0.08 Example 67 0.009 0.09 0.22 0.022 0.002 0.020 21.2 0.27
0.41 0.25 0.116 0.120 0.007 Comparative Example 68 0.008 0.10 0.15
0.029 0.002 0.023 21.5 0.20 0.45 0.21 0.129 0.141 0.013 Comparative
Example
TABLE-US-00006 TABLE 3-2 Test Corrosion Surface Softening No.
Ti--Nb Nb--Zr Resistance Charpy Defect Temperature Note 59 0.01
0.080 .largecircle. .largecircle. .largecircle. .largecircle.
Example 60 0.01 0.117 .largecircle. .largecircle. .largecircle.
.largecircle. Example 61 0.01 0.117 .largecircle. .largecircle.
.largecircle. .largecircle. Example 62 0.16 0.006 .largecircle.
.largecircle. .largecircle. .largecircle. Example 63 0.17 0.009
.largecircle. .largecircle. .largecircle. .largecircle. Example 64
0.14 0.008 .largecircle. .largecircle. .largecircle. .largecircle.
Example 65 0.09 0.024 .largecircle. .largecircle. .largecircle.
.largecircle. Example 66 0.10 0.009 .largecircle. .largecircle.
.largecircle. .largecircle. Example 67 0.13 -0.004 .largecircle.
.tangle-solidup. .tangle-solidup. .largecircle. Comparative Example
68 0.08 -0.012 .largecircle. .tangle-solidup. .tangle-solidup.
.largecircle. Comparative Example *[Corrosion Resistance] A case
where the pitting potential was 290 mV (vs. SCE) or more was judged
as ".largecircle." (satisfactory), and a case where the pitting
potential was less than 290 mV (vs. SCE) was judged as
".tangle-solidup." (unsatisfactory). *[Charpy Impact Value] A case
where the Charpy impact value (of a steel sheet having a thickness
of 2 mm) at 25.degree. C. was 200 J/cm.sup.2 or more was judged as
".largecircle." (satisfactory), and a case where the Charpy impact
value (of a steel sheet having a thickness of 2 mm) at 25.degree.
C. was less than 200 J/cm.sup.2 was judged as ".tangle-solidup."
(unsatisfactory). *[Surface Defect] A case where the number of
streaks in a region of 200 mm.sup.W .times. 200 mm.sup.L was 1 or
less was judged as ".largecircle." (satisfactory), and a case where
the above-described number was more than 1 was judged as
".tangle-solidup." (unsatisfactory). *[Softening Temperature] A
case where the relational expression c + 0.1 .times. (a - c)
.gtoreq. b was satisfied was judged as ".largecircle."
(satisfactory), and other cases were judged as ".tangle-solidup."
(unsatisfactory), where the Vickers hardness of a steel sheet in
the cold-rolled state was defined as a, the Vickers hardness of a
steel sheet which had been subjected to a heat treatment at a
temperature of 880.degree. C. for 20 seconds was defined as b, and
the Vickers hardness of a steel sheet which had been subjected to a
heat treatment at a temperature of 1000.degree. C. for 20 seconds
was defined as c.
[0108] FIG. 1 illustrates the evaluation results of Charpy impact
values and surface defects of the examples of the present invention
and comparative examples (Nos. 43 through 48), whose chemical
compositions were within the range according to aspects of the
present invention, and in which the relational expression Nb Zr was
satisfied and the relational expression Ti Nb was not satisfied, in
a form of graph in which the horizontal axis indicates the Ti
content and the vertical axis indicates the Nb content. Here, for
all the steel sheets illustrated in FIG. 1, in a case where the
evaluation result regarding a Charpy impact value was satisfactory,
the evaluation regarding a surface defect was satisfactory, and in
a case where the evaluation result regarding a Charpy impact value
was unsatisfactory, the evaluation regarding a surface defect was
unsatisfactory. As FIG. 1 indicates, it is necessary that the
relational expression Ti.gtoreq.Nb be satisfied in order to realize
excellent toughness and a decrease in the quantity of surface
defects at the same time within the range of the chemical
composition according to aspects of the present invention.
[0109] FIG. 2 illustrates the evaluation results of Charpy impact
values and surface defects of the examples of the present invention
and comparative examples (Nos. 49 through 54, 67, and 68), whose
chemical compositions were within the range according to aspects of
the present invention, and in which the relational expression Ti Nb
was satisfied and the relational expression Nb Zr was not
satisfied, in a form of graph in which the horizontal axis
indicates the Nb content and the vertical axis indicates the Zr
content. As FIG. 2 indicates, it is necessary that the relational
expression Nb.gtoreq.Zr be satisfied in order to realize excellent
toughness and a decrease in the quantity of surface defects at the
same time within the range of the chemical composition according to
aspects of the present invention. Moreover, as FIG. 1 and FIG. 2
indicate, it is clarified that it is necessary that both the
relational expression Ti.gtoreq.Nb and the relational expression
Nb.gtoreq.Zr, that is, the relational expression
Zr.ltoreq.Nb.ltoreq.Ti, be satisfied in order to realize excellent
toughness and a decrease in the quantity of surface defects at the
same time within the range of the chemical composition according to
aspects of the present invention.
[0110] Here, comparative example Nos. 55 and 56, whose chemical
compositions were within the range according to aspects of the
present invention, and in which the relational expression
Ti.gtoreq.Nb. or the relational expression Nb.gtoreq.Zr was not
satisfied, were unsatisfactory in the evaluations both regarding a
Charpy impact value and regarding a surface defect.
INDUSTRIAL APPLICABILITY
[0111] The ferritic stainless steel sheet according to aspects of
the present invention, which has excellent toughness and only a
small quantity of surface defects, can preferably be used not only
for parts which are required to have satisfactory corrosion
resistance but also for parts which are required to have
satisfactory toughness and surface quality including the inner
panels of elevators, interiors, duct hoods, muffler cutters,
lockers, the parts of home electrical appliances, the parts of
office appliances, the interior parts of automobiles, the exhaust
pipes of automobiles, building materials, the lids of drainage
channel, maritime containers, house wares, kitchen appliances, the
interior and exterior materials of buildings, automobile parts,
escalators, railway vehicles, the chassis of electrical apparatuses
and the like.
* * * * *