Title of Invention

FERRITIC STAINLESS STEEL SHEET HAVING EXCELLENT CORROSION RESISTANCE AND METHOD OF MANUFACTURING THE SAME

Abstract A ferritic stainless steel sheet having excellent corrosion resistance and a method of manufacturing the steel sheet are provided. Specifically, the ferritic stainless steel sheet of the invention contains C of 0.03 or less mass%, Si of 0.03 to 1.0 mass%, Mn of 0.05 to 0.5 mass%, P of 0.04 or less mass%, S of 0.04 or less mass%, A1 of 0.005 to 0.1 mass%, Cr of 20.5 to 22.5 mass%, Cu of 0.3 to 0.8 mass%, Ni of 0.05 to 1.0 mass%, Ti of 4 x (C+N) to 0.35 mass%, Nb of 0.01 or less mass%, N of 0.03 or less mass% and C+N of 0.05 or less mass%, and has the remainder including Fe and inevitable impurities, wherein 240 + 35 X (Cr% - 20.5) + 280 x {Ti% - 4x (C% + N%) ≥ 280 is satisfied.
Full Text Description
FERRITIC STAINLESS STEEL SHEET HAVING EXCELLENT CORROSION
RESISTANCE AND METHOD OF MANUFACTURING THE SAME
Technical Field
The present invention relates to a ferritic
stainless steel sheet having excellent corrosion
resistance, and a method of manufacturing the steel sheet.
Background Art
Among various types of stainless steel, SUS304
(18%Cr-8%Ni) (Japanese Industrial Standards, JIS G 4305)
of austenitic stainless steel is widely used because of
excellent corrosion resistance of the steel. However,
this steel type is expensive because it contains a large
quantity of Ni. On the other hand, in ferritic stainless
steel that is not added with a large quantity of Ni,
SUS436L (18%Cr-l%Mo) (JIS G 4305) added with Mo is given
as a steel type having excellent corrosion resistance
equivalent to SUS304. However, again in the steel, since
Mo is an expensive element, cost is significantly
increased even if only 1% of Mo is added.
From a current situation as above, ferritic
stainless steel having corrosion resistance equivalent to
SUS304 or SUS436L is required with Mo being not added.

While SUS430J1L (19%Cr-0.5%Cu-0.4%Nb) (JIS G 4305) is
given as the ferritic stainless steel with Mo being not
added, it is inferior in corrosion resistance compared
with SUS304 or SUS436L.
On the contrary, JP-B-50-6167 discloses ferritic
stainless steel having a characteristic composition of Cr
of 9 to 30%, Cu of 0.1 to 0.6%, Ti of 5xC% to 15xC%, and
Sb of 0.02 to 0.2%; and JP-B-64-4576 (JP-A-60-46352)
discloses ferritic stainless steel having a characteristic
composition of Cr of 11 to 23%, Cu of 0.5 to 2.0%, at
least one of Ti, Nb, Zr and Ta in a ratio of 0.01 to 1.0%,
and V of 0.05 to 2.0%; and furthermore Japanese Patent No.
3420371 (JP-A-8-260104) discloses stainless steel having a
characteristic composition of Cr of 5 to 60%, Cu of 0.15
to 3.0%, Ti of 4x(C%+N%) to 0.5%, and Nb of 0.003 to
0.020% as a composition, respectively.
However, the JP-B-50-6167, JP-B-64-4576, and
Japanese Patent No. 3420371 do not show a composition that
combines highly efficient productivity by continuous
annealing of a hot-rolled sheet and high speed continuous
annealing of a cold-rolled sheet, with excellent corrosion
resistance equivalent to SUS304 or SUS436L.
It is necessary for manufacturing the steel at low
cost that expensive Mo is not added, in addition, the
steel can be mass-produced at high efficiency. While


corrosion resistance is improved with increase in addition
of Cr, toughness of a hot-rolled sheet is reduced.
While a hot-rolled sheet of high-Cr ferritic
stainless steel sheet needs to be subjected to annealing
and pickling in a continuous annealing and pickling line
before cold rolling, when the hot-rolled sheet has low
toughness, sometimes it can not be subjected to a
continuous process in the continuous annealing and
pickling line. Furthermore, in the light of highly
efficient productivity, it is necessary that a cold-rolled
sheet can be efficiently annealed in a high speed
continuous annealing line for cold-rolled sheet for
combined use with carbon steel.
In the light of such a circumstance, an object of
the invention is to provide a ferritic stainless steel
sheet that can be manufactured inexpensively and highly
efficiently, and has excellent corrosion resistance.
Disclosure of the Invention
To solve the problem, the inventors had conducted
earnest study on a method of obtaining a stainless steel
sheet having excellent corrosion resistance without
containing expensive Ni and Mo. As a result, they found
that Cr was limited in a range of 20.5% to 22.5% from a
viewpoint of corrosion resistance and productivity, and


the amount of carbon or nitrogen as an impurity element
was decreased, and furthermore an appropriate amount of Ti
was added, thereby the stainless steel sheet having
excellent corrosion resistance equivalent to SUS304 or
SUS436L was obtained, and continuous annealing of a hot-
rolled sheet and annealing of a cold-rolled sheet in a
high speed continuous annealing line for cold-rolled sheet
were able to be performed, consequently, the cold-rolled
sheet was able to be produced highly efficiently.
The invention, which was made according to the
findings, is summarized as follows.
[1] A ferritic stainless steel sheet having
excellent corrosion resistance, the sheet containing C of
0.03% or less, Si of 1.0% or less, Mn of 0.5% or less, P
of 0.04% or less, S of 0.02% or less, Al of 0.1% or less,
Cr of 20.5% to 22.5%, Cu of 0.3% to 0.8%, Ni of 1.0% or
less, Ti of 4x(C%+N%) to 0.35%, Nb of less than 0.01%, N
of 0.03% or less, and C+N of 0.05% or less, and having the
remainder including Fe and inevitable impurities, wherein
the following equation (1) is satisfied,
240+35x(Cr%-20.5)+280x{Ti%-4x(C%+N%)}>280 (1),
here, C%, N%, Cr% and Ti% indicate the content (mass
percent) of C, N, Cr and Ti respectively.
[2] A method of manufacturing a ferritic stainless
steel sheet having excellent corrosion resistance, in


which a stainless steel sheet is used as a material, the
slab containing C of 0.03% or less, Si of 1.0% or less, Mn
of 0.5% or less, P of 0.04% or less, S of 0.02% or less,
Al of 0.1% or less, Cr of 20.5% to 22.5%, Cu of 0.3% to
0.8%, Ni of 1.0% or less, Ti of 4x(C%+N%) to 0.35%, Nb of
less than 0.01%, N of 0.03% or less, and C+N of 0.05% or
less, and having the remainder including Fe and inevitable
impurities, wherein the following equation (1) is
satisfied, and the material is hot-rolled, then a hot-
rolled material is subjected to continuous annealing for
hot-rolled sheet at a temperature of 800 to 1000°C and
then pickled, and then formed into a cold-rolled annealed
sheet through steps of cold rolling, finish annealing,
cooling and pickling;
24 0+35x(Cr%-20.5)+2 80x{Ti%-4x(C%+N%)}>280 (1),
here, C%, N%, Cr% and Ti% indicate the content of C,
N, Cr and Ti (mass percent) respectively.
In the specification, percent indicating a component
ratio of steel is mass percent without exception.
According to the invention, the ferritic stainless
steel sheet having excellent corrosion resistance
equivalent to SUS304 or SUS436L is obtained without adding
expensive Mo and the like. Moreover, the stainless steel
sheet of the invention can be produced highly efficiently,
and can be inexpensively manufactured because expensive Ni


or Mo is not added.
Furthermore, since the stainless steel sheet of the invention is decreased in the
quantity of impurity elements, and added with Ti as a stabilizing element for
fixing C or N in steel, it is excellent in weldability, workability of welding area,
and corrosion resistance of welding area.
Brief Description of the Accompanying Drawings
Fig.l is a view showing a relationship between Cr% and Ti%-4x(C%+N%), and a
result of neutral slat spray cycle testing.
Best Mode for Carrying Out the Invention
Hereinafter, the invention will be described in detail. First, a composition of the
invention is described.
. C: 0.03% or less, N: 0.03% or less, and C+N: 0.05% or less
The content of C and N is desirably low because they reduce toughness of a
hot-rolled sheet, and therefore limited to be 0.03% or less respectively, and
limited to be 0.05% or less even in total. Further preferably, the content of C is
0.015% or less, the content of N is 0.015% or less, and the content of C+N is
0.03% or less.

•Si: 1.0% or less
Si is a necessary element as a deoxidizing agent.
To obtain the effect of Si, the Si content is preferably
0.03% or more. However, when a large quantity of Si is
added, toughness of a hot-rolled sheet is reduced.
Accordingly, the Si content is 1.0% or less. More
preferably, it is 0.3% or less.
•Mn: 0.5% or less
Mn has a deoxidizing effect. To obtain the effect,
the Mn content is preferably 0.05% or more. However,
since Mn forms sulfides in steel, which significantly
reduce corrosion resistance, the quantity of addition of
Mn is desirably low, and in the light of economic
efficiency in manufacturing, the Mn content is defined to
be 0.5% or less. More preferably, it is 0.3% or less.
•P: 0.04% or less
The P content is desirably low from a viewpoint of
workability in hot working, and it is defined to be 0.04%
or less.
•S: 0.02% or less
The S content is desirably low from a viewpoint of
workability in hot working and corrosion resistance, and
it is defined to be 0.02% or less. More preferably, it is
0.005% or less.
•Al: 0.1% or less


Al is an effective component for deoxidization. To
obtain the effect, the Al content is preferably 0.005% or
more. However, when Al is excessively added, surface
flaws are induced and workability is reduced due to
increase in Al-based nonmetallic inclusions. Accordingly,
the Al content is defined to be 0.1% or less. More
preferably, it is 0.01% to 0.05%.
•Cr: 20.5% to 22.5%
Cr is the most important element in the invention.
It is effective for improving corrosion resistance, and Cr
of 20.5% or more is necessary to be added to obtain the
corrosion resistance equivalent to SUS304 or SUS436L. On
the other hand, when Cr of more than 22.5% is added,
toughness of a hot-rolled sheet is reduced, consequently
continuous annealing of a hot-rolled sheet is difficult.
Accordingly, the Cr content is defined to be 20.5% to
22.5%. More preferably, it is 20.5% to 21.5%.
•Cu: 0.3% to 0.8%
Cu is an important element in the invention. It is
an element necessary for reducing crevice corrosion. For
the purpose, Cu of at least 0.3% needs to be added. On
the other hand, when the Cu content exceeds 0.8%,
workability in hot working is reduced. Accordingly, the
Cu content is defined to be 0.3% to 0.8%. More preferably,
it is 0.3% or more and less than 0.5%.


•Ni: 1.0% or less
Ni has an effect of preventing reduction in
workability in hot working due to addition of Cu. To
obtain the effect, the Ni content of 0.05% or more is
preferable. However, Ni is an expensive element, in
addition, even if Ni of more than 1.0% is added, the
effect is saturated. Accordingly, the Ni content is
defined to be 1.0% or less. More preferably, it is 0.1%
to 0.4%.
•Ti: 4x(C%+N%) to 0.35%
Ti is also the most important element in the
invention. It is an essential element to be added in the
invention, and necessary to be added for obtaining the
excellent corrosion resistance equivalent to SUS304 or
SUS436L in addition of Cr of 22.5% or less. Ti has been
recognized as an element having an effect that it forms
TiC or TiN with C or N, which is harmful for workability
or corrosion resistance of welding area, thereby makes C
or N harmless and thus improves corrosion resistance, and
the invention further found that Ti had an effect of
directly increasing pitting potential and thus improving
corrosion resistance. Furthermore, Ti is added for
preventing sensitization due to continuous annealing. To
obtain the effects, Ti of 4x(c%+N%) or more needs to be
added. On the other hand, when an excessive quantity of T


of more than 0.35% is added, toughness of a hot-rolled
sheet is reduced. Accordingly, the Ti content is defined
to be 4x(C%+N%) or more and 0.35% or less. More
preferably, it is 8x(C%+N%) or more and 0.30% or less.
•Nb: 0.01% or less
Nb increases the recrystallization temperature,
causing insufficient annealing in the high speed annealing
line for cold-rolled sheet, consequently certain
workability can not be ensured. Accordingly, the Nb
content is defined to be 0.01% or less. More preferably,
it is 0.005% or less.
•24 0+35x(Cr%-20.5)+280x{Ti%-4x(C%+N%)}>28 0
In the invention, Cr, Ti, C and N are defined to
satisfy the relationship of the equation (1) to obtain
excellent corrosion resistance equivalent to SUS304 or
SUS436L or more without containing Ni and Mo.
240 + 35x(Cr%-20.5)+280x{Ti%-4x(C%+N%)}≥280 (1) .
While Cr and Ti have the effect of increasing pitting
potential respectively, only addition of Cr of 20.5% or
more and the Ti of 4x(C%+N%) or more is insufficient for
obtaining the corrosion resistance equivalent to SUS304 or
SUS436L or more, and the Cr content and the Ti content
further need to satisfy the equation (1) with the C
content and the N content being considered. The equation
(1) is derived from a relationship between the Cr content


and the Ti content, and pitting potential (mV vs. S.C.E),
and shows minimum values of the Cr content and the Ti
content above which a value of pitting potential is at
least 280 mV that is a typical value of pitting potential
of SUS304 or SUS436L. Moreover, since dissolved Ti other
than Ti bound as TiC or TiN exhibits an effect of
increasing pitting potential, {Ti%-4x(C%+N%)}
corresponding to the quantity of dissolved Ti is used in
the equation (1).
•Mo: 0.2% or less
While Mo is an element for improving corrosion
resistance, it is an expensive element, in addition,
reduces toughness of a hot-rolled sheet, causing
difficulty in manufacturing, and furthermore increases
hardness of a cold-rolled annealed sheet, and therefore
reduces workability. Therefore, the Mo content is defined
to be 0.2% or less. More preferably, it is 0.1% or less.
In addition, the following elements can be added as
necessary.
•B: 0.0002 to 0.002%
B is an element effective for improving cold-work
embrittlement after deep drawing. The effect is not
obtained in the content of less than 0.0002%, and
excessive addition of B reduces workability in hot working
and deep drawability. Therefore, B is preferably added in


the quantity of 0.0002 to 0.002%.
•V: 0.01 to 0.5%, Zr: 0.01 to 0.5%
V and Zr have an effect of preventing occurrence of
intergranular corrosion in a welding area by making C or N
harmless. The effect is not exhibited in the content of V
and Zr of less than 0.005% respectively, and each of them
needs to be added in the quantity of 0.01% or more.
However, when V and Zr are added in the quantity of more
than 0.5% respectively, toughness of a hot-rolled sheet is
reduced, causing difficulty in manufacturing. Furthermore,
V and Zr bind with C, N or 0 (oxygen) to form inclusions,
leading to increase in surface defects. Therefore, they
are defined to be 0.5% or less respectively.
The remainder of the composition except for the
above components is Fe and inevitable impurities.
Next, a method of manufacturing the ferritic
stainless steel sheet having excellent corrosion
resistance of the invention is described.
As a highly efficient manufacturing method of the
steel of the invention, a method is recommended, in which
a slab is formed by continuous casting, then the slab is
heated to 1100 to 1250°C and hot-rolled to be formed into
a hot-rolled coil, which is then annealed at a temperature
of 800 to 1000°C and then pickled in a continuous


annealing and pickling line for hot-rolled sheet, and then
subjected to cold rolling to be formed into a cold-rolled
sheet, which is then efficiently annealed and pickled in a
high speed continuous annealing line for cold-rolled sheet
for combined use with carbon steel.
In particular, the method is described as follows.
First, molten steel is prepared, which is controlled
in the chemical composition range by secondary refining
using a converter, an electric furnace or the like,
together with a strong-stirring, vacuum oxygen
decarburization (VOD) process or an argon oxygen
decarburization (AOD) process. Then, a slab is ingoted
from the molten steel by continuous casting or ingot
casting. As a casting method, continuous casting is
preferable in the light of productivity and slab quality.
The slab obtained by casting is reheated to 1100 to
1250°C as necessary, then hot-rolled such that a thickness
of 2.0 mm to 6.0 mm is obtained, and then a hot-rolled
sheet is subjected to continuous annealing at a
temperature of 800 to 1000°C and then pickled.
A pickled hot-rolled sheet is sequentially subjected
each step of cold rolling, finish annealing, cooling, and
pickling, so that a cold-rolled annealed sheet having a
thickness of 0.03 mm to 5.0 mm is formed.
The reduction rate in cold rolling is preferably at


least 25% to secure mechanical properties such as
toughness and workability as the object of the invention.
More preferably, it is at least 50%. Moreover, the cold
rolling may be performed one time or at least two times
including intermediate annealing. Respective steps of the
cold rolling, finish annealing, and pickling may be
repeatedly performed. Furthermore, a method is
recommended, in which a cold-rolled sheet is efficiently
annealed and pickled in the high speed continuous
annealing line for cold-rolled sheet for combined use with
carbon steel. Moreover, while productivity is reduced,
the cold-rolled sheet may be annealed and pickled in a
typical annealing and pickling line for cold-rolled sheet
of stainless steel. Moreover, the cold-rolled sheet may
be subjected to bright annealing in a bright annealing
line as necessary.
In the case of welding the steel sheet of the
invention as described hereinbefore, all the typical
welding methods can be used, such as arc welding including
TIG (tungsten inert gas welding) and MIG (metal inert gas
welding), resistance welding such as seam welding and spot
welding, and laser welding.
Example 1
Ferritic stainless steel having compositions as


shown in Table 1 was ingoted into 30 kg steel ingots, then
the ingots were heated to a temperature of 1150°C and hot
rolled, thereby hot-rolled sheets having a thickness of
2.5 to 2.8 mm were obtained. Here, the addition of Mo was
controlled in a level of being expected to be mixed as an
impurity in real operation. Test pieces (JIS B 7722 V
notch) were taken out from obtained hot-rolled sheets in a
rolling direction and subjected to the Charpy impact test.
A comparative example 11 having a high Cr content of 22.8%
that is out of the range of the invention, and a
comparative example 12 having a high Ti: content of 0.39%
that is out of the range of the invention were low in
toughness and thus hard to be subjected to continuous
annealing for hot-rolled sheet in real operation,
therefore they were not subjected to subsequent tests.
Specimens other than comparative examples 11 and 12
were annealed at 950°C, then cold-rolled, so that cold-
rolled sheets 0.8 mm in thickness were prepared. Then,
the cold-rolled sheets were annealed at 880°C in the air.
In a comparative example 13 having a high Nb content of
0.15% that is out of the range of the invention, steel was
insufficiently annealed at the temperature and therefore
elongation was less than 20%, consequently sufficient
workability was not able to be secured in cold-rolled-
sheet annealing in the high speed continuous annealing


line for cold-rolled sheet, therefore subsequent tests
were not performed.
Test pieces taken from specimens (examples of the
invention 1 to 8, and 21 to 25) other than the comparative
examples 11 to 13 obtained according to the above, and
test pieces taken from cold-rolled annealed sheets 0.8 mm
in thickness of SUS304, SUS436L and SUS430J1L were
subjected to measurement of pitting potential at 30°C in
3.5% NaCl solution according to JIS G 0577, and subjected
to neutral salt spray cycle testing. The neutral salt
spray cycle testing was performed 45 cycles to specimens
(20 mm x 30 mm in size) having a polished surface using a
No. 600 abrasive paper with steps of neutral salt spray
(5% NaCl, 35°C, and spray time of 2 hr), drying (60°C, 4 hr,
and relative humidity of 40%), and wetting (50°C, 2 hr,
and relative humidity of 95% or more) as one cycle.
Obtained results were collectively shown in Table 1.
Next, crevice corrosion testing was performed to
specimens (examples of the invention 1 to 8, and 21 to 25),
SUS304, and SUS436L other than the comparative examples 11
to 15 and SUS430J1L. In the testing, flat plates of 60 mm
wide and 80 mm long, and 20 mm wide and 30 mm long taken
out from each of specimens were used, wherein surfaces of
them were polished using No. 600 abrasive paper, then the
flat plate of 20 mm wide and 30 mm long was placed on the


flat plate of 60 mm wide and 80 mm long such that
respective diagonals were overlapped, and then respective
center points were bonded by spot welding to form a
crevice structure. Such test pieces were subjected to 90
cycles of the neutral salt spray cycle testing, then spot
welding areas were removed and crevice portions were
opened, so that depth of corrosion pitting was measured by
a laser microscope. Results obtained from the above are
collectively shown in Table 1.
In Table 1, a criterion of each test is as follows.
(1) Charpy impact test: a test piece having absorbed
energy at 25°C of 50 J/cm2 or more was determined as O
(pass), and a test piece having the energy of less than 50
J/cm2 was determined as x (reject).
(2) Cold-rolled sheet annealing: a test piece having
elongation after annealing at 880°C of 20% or more was
determined as O (pass), and a test piece having elongation
after annealing at 880°C of less then 20% was determined
as x (reject).
(3) Neutral salt spray cycle testing: with respect
to one side (60 x 80 mm) of a test piece, a test piece
having rust area of less than 20% was determined as O
(pass) , and a test piece having rust area of 20% or more
was determined as x (reject).
(4) Crevice corrosion testing result: in corrosion


pitting produced in a crevice portion of a test piece,
when ten points of the pitting having large depth have an
average value of depth of less than 300 µm, the test piece
was determined as O (pass), and when they have the average
value of depth of more than 300 µm, the test piece was
determined as x (reject). Depth of the corrosion pitting
was measured by the laser microscope.
It is known from Table 1 that the examples of the
invention have pitting potential equivalent to SUS304 or
SUS436L or more, and shows excellent results of the
neutral salt spray cycling testing, that is, the examples
have excellent corrosion resistance. Moreover, they show
average depth of corrosion pitting of less than 300 µm in
the crevice corrosion testing, that is, they further have
excellent crevice corrosion resistance.
On the other hand,- in the comparative example 14
having the low Cr content of 20.1% that is out of the
range of the invention, and the comparative example 15
that does not satisfy the equation (1), pitting potential
was low compared with SUS304 or SUS436L, in addition, rust
area was large in the neutral salt spray testing, that is,
corrosion resistance was bad.
Fig. 1 shows a relationship between pitting
potential, and Cr% and Ti%-4x (C%+N%) in the examples of
the invention 1 to 8, and 21 to 25 and the comparative


examples 14, 15 and 16. As clearly seen from Fig. 1, to
obtain the pitting potential of 280 mV corresponding to
SUS304 or SUS436L or more, it is obviously necessary to
satisfy the equation (1), 240+35x(Cr%-20.5)+280x{Ti%-
4x(C%+N%)}>280.
Furthermore, in the comparative example 16 that is
not added with Cu, average depth of corrosion pitting in
the crevice corrosion testing is 300 |xm or more, that is,
crevice corrosion resistance is bad compared with the
examples 1 to 8 and 21 to 25, SUS304, and SUS436L.
It was known from the above that, in the examples of
the invention, a hot-rolled sheet was able to be subjected
to continuous annealing, and elongation at 880°C was 20%
or more and therefore the cold-rolled sheet was able to be
annealed in the high speed continuous annealing line for
cold-rolled sheet, consequently the cold-rolled sheet was
able to be produced at high efficiency. Moreover, it was
found that the examples of the invention had excellent
corrosion resistance equivalent to SUS304 or SUS436L.
Industrial Applicability
The invention is preferable for members required to
have corrosion resistance, mainly including containers for
marine transportation, vessels, kitchen instruments,
interior and exterior building materials, automobile parts,


elevators, escalators, railcars, and outer panels of
electric apparatus.



WE CLAIM
1. A ferritic stainless steel sheet having excellent corrosion resistance,
comprising;
C of 0.03 or less mass%
Si of 0.03 to 1.0 mass%
Mn of 0.05 to 0.5 mass%
P of 0.04 or less mass%
S of 0.04 or less mass%
A1 of 0.005 to 0.1 mass%
Cr of 20.5 to 22.5 mass%
Cu of 0.3 to 0.8 mass%
Ni of 0.05 to 1.0 mass%
Ti of 4 x (C+N) to 0.35 mass%
Nb of 0.01 or less mass%
N 0f 0.03 or less mass%
C+N of 0.05 or less mass% and
the steel sheet having
the remainder including Fe and inevitable impurities;
wherein the following equation (1) is satisfied,
240 + 35 X (Cr% - 20.5) + 280 x {Ti% - 4x (C% + N%) > 280 (1)

here, C%, N%, Cr% and Ti% indicate the content (mass percent) of C,N, Cr and
Ti respectively.
2. A method of manufacturing a ferritic stainless steel sheet having
excellent corrosion resistance:
wherein a stainless steel is used as a material, the steel sheet containing
C of 0.03 or less mass%
Si of 0.03 to 1.0 mass%
Mn of 0.05 to 0.5 mass%
P of 0.04 or less mass%
S of 0.04 or less mass%
A1 of 0.005 to 0.1 mass%
Cr of 20.5 to 22.5 mass%
Cu of 0.3 to 0.8 mass%
Ni of 0.05 to 1.0 mass%
Ti of 4 x (C+N) to 0.35 mass%
Nb of 0.01 or less mass%
N Of 0.03 or less mass%
C+N of 0.05 or less mass% and
the steel sheet having

the remainder including Fe and inevitable impurities;
in which the following equation (1) is satisfied, and
the material is hot-rolled
then a hot-rolled material is subjected to continuous annealing for hot-rolled
sheet at a temperature of 800 to 1000°c and then pickled, and then formed into
a cold-rolled annealed sheet through steps of cold rolling, finish annealing,
cooling and pickling;
240 + 35 X (Cr% - 20.5) + 280 x {Ti% - 4x (C% + N%) ≥ 280 (1)
here, C%, N%, Cr% and Ti% indicate the content of C, N, Cr and Ti (mass
percent) respectively.


A ferritic stainless steel sheet having excellent corrosion resistance and a
method of manufacturing the steel sheet are provided. Specifically, the ferritic
stainless steel sheet of the invention contains C of 0.03 or less mass%, Si of
0.03 to 1.0 mass%, Mn of 0.05 to 0.5 mass%, P of 0.04 or less mass%, S of
0.04 or less mass%, A1 of 0.005 to 0.1 mass%, Cr of 20.5 to 22.5 mass%, Cu of
0.3 to 0.8 mass%, Ni of 0.05 to 1.0 mass%, Ti of 4 x (C+N) to 0.35 mass%, Nb
of 0.01 or less mass%, N of 0.03 or less mass% and C+N of 0.05 or less mass%,
and has the remainder including Fe and inevitable impurities, wherein 240 +
35 X (Cr% - 20.5) + 280 x {Ti% - 4x (C% + N%) ≥ 280 is satisfied.

Documents:

03994-kolnp-2007-abstract.pdf

03994-kolnp-2007-claims.pdf

03994-kolnp-2007-correspondence others.pdf

03994-kolnp-2007-description complete.pdf

03994-kolnp-2007-drawings.pdf

03994-kolnp-2007-form 1.pdf

03994-kolnp-2007-form 2.pdf

03994-kolnp-2007-form 3.pdf

03994-kolnp-2007-form 5.pdf

03994-kolnp-2007-international publication.pdf

03994-kolnp-2007-international search report.pdf

03994-kolnp-2007-others.pdf

03994-kolnp-2007-pct priority document notification.pdf

03994-kolnp-2007-pct request form.pdf

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3994-kolnp-2007-CORRESPONDENCE OTHERS 1.1.pdf

3994-KOLNP-2007-CORRESPONDENCE-1.2.pdf

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3994-kolnp-2007-examination report.pdf

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3994-KOLNP-2007-FORM-27.pdf

3994-kolnp-2007-granted-abstract.pdf

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3994-kolnp-2007-granted-specification.pdf

3994-KOLNP-2007-OTHER PATENT DOCUMENT.pdf

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3994-KOLNP-2007-PA.pdf

3994-kolnp-2007-reply to examination report.pdf

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Patent Number 246207
Indian Patent Application Number 3994/KOLNP/2007
PG Journal Number 08/2011
Publication Date 25-Feb-2011
Grant Date 21-Feb-2011
Date of Filing 16-Oct-2007
Name of Patentee JFE STEEL CORPORATION
Applicant Address 2-3, UCHISAIWAI-CHO 2-CHOME, CHIYODA-KU TOKYO
Inventors:
# Inventor's Name Inventor's Address
1 TOMOHIRO ISHII C/O INTELLECTUAL PROPERTY DEPT., JFE STEEL CORPORATION 2-3, UCHISAIWAI-CHO 2-CHOME, CHIYODA-KU TOKYO 100-0011
2 KAZUHIDE ISHII C/O INTELLECTUAL PROPERTY DEPT., JFE STEEL CORPORATION 2-3, UCHISAIWAI-CHO 2-CHOME, CHIYODA-KU TOKYO 100-0011
3 OSAMU FURUKIMI C/O INTELLECTUAL PROPERTY DEPT., JFE STEEL CORPORATION 2-3, UCHISAIWAI-CHO 2-CHOME, CHIYODA-KU TOKYO 100-0011
PCT International Classification Number C22C 38/00,C21D 9/46
PCT International Application Number PCT/JP2006/315540
PCT International Filing date 2006-07-31
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2005-236861 2005-08-17 Japan