U.S. patent application number 14/573280 was filed with the patent office on 2015-06-25 for method of manufacturing thin martensitic stainless steel sheet using strip caster with twin rolls and thin martensitic stainless steel sheet manufactured by the same.
The applicant listed for this patent is POSCO. Invention is credited to Ji-Woo Im, Seong-In Jeong, Jin-Ho Kim.
Application Number | 20150174648 14/573280 |
Document ID | / |
Family ID | 53399030 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150174648 |
Kind Code |
A1 |
Jeong; Seong-In ; et
al. |
June 25, 2015 |
Method of Manufacturing Thin Martensitic Stainless Steel Sheet
Using Strip Caster with Twin Rolls and Thin Martensitic Stainless
Steel Sheet Manufactured by the Same
Abstract
Provided is a method of manufacturing a THIN MARTENSITIC
STAINLESS STEEL SHEET by casting a thin cast strip using a strip
caster including a pair of rotating strip casting rolls and hot
rolling the thin cast strip, wherein any one of conditions (a) and
(b) is satisfied during the hot rolling, and a THIN MARTENSITIC
STAINLESS STEEL SHEET manufactured by the same: (a) Bending force
of rolling rolls: 30 to 500 kN (b) Size of crowns of rolling rolls:
50 to 250 .mu.m.
Inventors: |
Jeong; Seong-In; (Pohang-si,
KR) ; Kim; Jin-Ho; (Pohang-si, KR) ; Im;
Ji-Woo; (Pohang-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO |
Pohang-si |
|
KR |
|
|
Family ID: |
53399030 |
Appl. No.: |
14/573280 |
Filed: |
December 17, 2014 |
Current U.S.
Class: |
420/34 ;
164/463 |
Current CPC
Class: |
C22C 38/02 20130101;
C22C 38/40 20130101; B22D 11/0622 20130101; B22D 11/002 20130101;
B22D 11/1206 20130101; C22C 38/001 20130101; C22C 38/04
20130101 |
International
Class: |
B22D 11/00 20060101
B22D011/00; B22D 11/12 20060101 B22D011/12; C22C 38/00 20060101
C22C038/00; C22C 38/04 20060101 C22C038/04; C22C 38/02 20060101
C22C038/02; B22D 11/06 20060101 B22D011/06; C22C 38/40 20060101
C22C038/40 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2013 |
KR |
10-2013-0162513 |
Dec 9, 2014 |
KR |
10-2014-0176193 |
Claims
1. A method of manufacturing a THIN MARTENSITIC STAINLESS STEEL
SHEET by casting a thin cast strip using a strip caster comprising
a pair of rotating strip casting rolls and hot rolling the thin
cast strip, wherein any one of conditions (a) and (b) is satisfied
during the hot rolling: (a) Bending force of rolling rolls: 30 to
500 kN (b) Size of crowns of rolling rolls: 50 to 250%.
2. The method of claim 1, wherein the bending force of the rolling
rolls is 30 to 300 kN.
3. The method of claim 1, wherein the size of the crowns of the
rolling rolls is 50 to 200 .mu.m.
4. The method of claim 1, wherein the stainless thin steel sheet
comprises 0.3 wt % to 0.8 wt % of C, 12.0 wt % to 16.0 wt % of Cr,
0.2 wt % to 1.0 wt % of Si, 0.2 wt % to 1.0 wt % of Mn, 0.2 wt % to
1.0 wt % of Ni, 0.01 wt % to 0.1 wt % of N, 0.03 wt % or less of P,
and 0.03 wt % or less of S, and also includes Fe and other
inevitable impurities.
5. The method of claim 1, wherein a difference between reduction
ratios of the central part and the edge of the thin cast strip is
0.8% or less during hot rolling.
6. A THIN MARTENSITIC STAINLESS STEEL SHEET, comprising 0.3 wt % to
0.8 wt % of C, 12.0 wt % to 16.0 wt % of Cr, 0.2 wt % to 1.0 wt %
of Si, 0.2 wt % to 1.0 wt % of Mn, 0.2 wt % to 1.0 wt % of Ni, 0.01
wt % to 0.1 wt % of N, 0.03 wt % or less of P, and 0.03 wt % or
less of S, and also includes Fe and other inevitable impurities,
wherein a size of an edge crack is no more than 30 mm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 10-2013-0162513 filed on Dec. 24, 2013 and Korean
Patent Application No. 10-2014-0176193 filed on Dec. 9, 2014, with
the Korean Intellectual Property Office, the disclosures of which
are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present disclosure relates to a method of manufacturing
a THIN MARTENSITIC STAINLESS STEEL SHEET using a strip caster with
twin rolls and a THIN MARTENSITIC STAINLESS STEEL SHEET
manufactured by the same.
BACKGROUND OF THE INVENTION
[0003] Martensitic stainless steel is excellent in terms of
corrosion resistance, hardness, and wear resistance and is thus
used in various items and tools, and in particular, for razors,
scalpels, general kitchen knives, scissors, and the like.
Martensitic stainless steel is generally manufactured by forming
molten steel into ingots or slabs through a continuous casting
process, and reheating and hot rolling the ingots or slabs, while
the microstructures of the hot rolled steel may have a martensitic
phase, a tempered martensitic phase, a ferrite phase, and a
residual austenite phase. Such a hot rolled steel, formed as a
coil, may be transformed into ferrite and carbide and softened via
a batch annealing process for annealing hot rolled sheets, and the
soft material obtained by the hot rolling and annealing may undergo
a pickling process for removing scales formed during the hot
rolling and annealing. After the pickling, the soft material is
transformed into martensitic steel via a heat treatment process
after cold rolling and processing of a product.
[0004] A higher degree of hardness is required in steel used for
producing high quality metal tools, and such a high degree of
hardness may be realized by a martensitic microstructure formed in
steel used therefor. Martensitic microstructures are very hard
microstructures produced when high temperature austenite is rapidly
cooled. As the content of carbon dissolved in austenite of high
temperature increases, the content of carbon dissolved in
martensite increases, and thus the hardness of martensite also
increases. Accordingly, in order to manufacture martensitic
stainless steel having a high degree of hardness, as much carbon as
possible should be contained in steel.
[0005] However, in order to manufacture such martensitic steel, the
content of carbon therein should be increased, but in this case,
segregations may be severely generated and casting efficiency may
be reduced. For example, a solid-liquid region may be increased.
Further, ingot casting is mainly used to cast martensitic steel,
but ingot casting may lead to a reduction in quality in a
post-treatment process due to rough precipitates formed as
inter-granules and central segregations due to a slow cooling
speed, thereby causing many difficulties. In order to solve this
problem, a strip casting process is used instead of the ingot
casting, in which case, because central segregations are restrained
and chrome carbide precipitates are reduced in initial
inter-granules, the quality of steel may be improved and the strip
casting process is spotlighted as a remarkable process.
[0006] With reference to FIG. 1, in strip casting, molten steel 1
is accommodated in a ladle 2, the accommodated molten steel 1 is
introduced to a tundish 3, the molten steel 1 being supplied to a
sump, a space defined by strip casting rolls 5 and an edge dam 6,
through an entry nozzle 4, and the molten steel 1 passes between
the strip casting rolls 5 to allow a thin cast strip 7 to be
manufactured. Then, a meniscus shield 8 is provided above the strip
casting rolls 5 to prevent the oxidation of molten steel, and a
suitable gas is injected into the sump to maintain a predetermined
atmosphere. The thin cast strip 7 manufactured while being
withdrawn from a roll nip 9 at which the strip casting rolls 5 meet
is rolled by rolling rolls 10, and is wound by a winding device 11
via a cooling process and is manufactured into a thin steel
sheet.
[0007] Then, in a twin roll type strip casting process for directly
manufacturing a thin steel sheet having a thickness of 10 mm or
less from molten steel, supplying molten steel between interior
water cooled twin rolls rotating in opposite directions at a high
speed through an entry nozzle to manufacture a thin sheet having a
desired thickness without any crack and at an improved yield rate
is an important technological process.
[0008] In addition, in order to manufacture thin high carbon
martensitic stainless steel by applying a twin roll type strip
casting process, a casting technology is important, but it is more
important to reduce the incidence of edge cracks generated during
hot rolling, and the development of an economical casting method in
which edge quality can be improved by minimizing a tensile stress
causing edge cracks is necessary.
SUMMARY OF THE INVENTION
[0009] An aspect of the present disclosure may provide a method of
manufacturing a THIN MARTENSITIC STAINLESS STEEL SHEET having an
excellent edge quality by controlling a bending force of rolling
rolls in manufacturing a THIN MARTENSITIC STAINLESS STEEL SHEET
using a twin roll type strip caster and hot rolling rolls and a
THIN MARTENSITIC STAINLESS STEEL SHEET manufactured by the
same.
[0010] An aspect of the present disclosure may also provide a
method of manufacturing a THIN MARTENSITIC STAINLESS STEEL SHEET by
casting a thin cast strip using a strip caster including a pair of
rotating strip casting rolls and hot rolling the thin cast strip,
wherein any one of conditions (a) and (b) is satisfied during the
hot rolling:
[0011] (a) Bending force of rolling rolls: 30 to 500 kN
[0012] (b) Size of crowns of rolling rolls: 50 to 250 .mu.m.
[0013] Another aspect of the present disclosure provides a
stainless thin steel sheet, which comprises 0.3 wt % to 0.8 wt % of
C, 12.0 wt % to 16.0 wt % of Cr, 0.2 wt % to 1.0 wt % of Si, 0.2 wt
% to 1.0 wt % of Mn, 0.2 wt % to 1.0 wt % of Ni, 0.01 wt % to 0.1
wt % of N, 0.03 wt % or less of P, and 0.03 wt % or less of S, and
also includes Fe and other inevitable impurities, wherein the size
of an edge crack is 30 mm.
BRIEF DESCRIPTION OF DRAWINGS
[0014] The above and other aspects, features and other advantages
of the present disclosure will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0015] FIG. 1 is a schematic view showing a twin roll type strip
casting method;
[0016] FIG. 2 is a diagram illustrating rolling of a thin cast
strip;
[0017] FIG. 3 is a picture obtained by observing Invention Example
3 according to an embodiment of the present disclosure; and
[0018] FIG. 4 is a picture obtained by observing Comparative
Example 3 which departs from the scope of the present
disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Hereinafter, embodiments of the present disclosure will be
described in detail with reference to the accompanying drawings.
The disclosure may, however, be embodied in many different forms
and should not be construed as being limited to the embodiments set
forth herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the disclosure to those skilled in the art.
[0020] In the drawings, the shapes and dimensions of elements may
be exaggerated for clarity, and the same reference numerals will be
used throughout to designate the same or like elements.
[0021] An embodiment of the present disclosure provides a method of
manufacturing a THIN MARTENSITIC STAINLESS STEEL SHEET by casting a
thin cast strip using a strip caster comprising a pair of rotating
strip casting rolls and hot rolling the thin cast strip, wherein
any one of conditions (a) and (b) is satisfied during the hot
rolling:
(a) Bending force of rolling rolls: 30 to 500 kN (b) Size of crowns
of rolling rolls: 50 to 250 .mu.m.
[0022] In an example of a method of manufacturing the THIN
MARTENSITIC STAINLESS STEEL SHEET, as illustrated in FIG. 1, molten
steel 1 having undergone a refining process is accommodated in a
ladle 2, the accommodated molten steel 1 is introduced to a tundish
3, the molten steel 1 is supplied to a sump, a space defined by
strip casting rolls 5 and an edge dam 6 through an entry nozzle 4,
and the molten steel 1 passes between the strip casting rolls 5 to
manufacture a thin cast strip 7. The manufactured thin cast strip 7
is hot rolled by rolling rolls 10, and is wound by a winding device
11 via a cooling process and is manufactured into a thin steel
sheet.
[0023] In casting martensitic stainless steel using the twin roll
strip casting method, one of the main causes of increases in a
defect rate is the lowering of edge quality due to cracking of
edges. Martensitic steel has low high-temperature toughness because
of the generation of inter-granular carbides due to high carbon,
and so is sensitive to cracks. Accordingly, edge cracks are easily
generated in a process of rolling cast pieces using a strip casting
method, and when the shape of cast pieces is managed or wound into
a coil, a crack may be propagated by tensile force between a
rolling machine and a winding machine, causing a danger of strip
breakage.
[0024] The edge cracks are caused by discrepancies in the shape of
a thin cast strip, skulls due to locally overcooled metal, and a
rolling condition, and the present disclosure basically solves a
problem which may be caused by rolling in addition to a factor due
to a thin cast strip. In general, a rolling roll used for hot
rolling is provided with a bending unit for controlling a bending
change of the rolling roll. In addition, generally, when the
bending force of the bending unit is reduced, a reduction ratio of
an edge of the thin cast strip increases, and if the bending force
of the bending unit increases, the reduction ratio of the edge
decreases.
[0025] FIG. 2 is a view schematically illustrating a state in which
a thin cast strip is rolled, and according to the present
disclosure, a crown of a thin cast strip is uniformly rolled
widthwise through control of bending force as illustrated in FIG.
2. In more detail, a bending force of a rolling roll 10 is
controlled to 30 to 50 kN during hot rolling. When the bending
force is less than 30 kN, a reduction ratio applied to an edge is
excessively increased, such that an edge wave or a distortion is
generated, making rolling control unstable, and when the bending
force exceeds 500 kN, a small reduction ratio is applied to the
edge, a length of the edge is prolonged less than that of a central
portion of the thin case piece such that a tensile stress is
generated in the edge, easily causing edge cracks. Accordingly, it
is preferable that a bending force of the rolling roll 10 suggested
by the present disclosure range from 30 kN to 500 kN, and it is
preferable that a bending force of the rolling roll ranges from 30
kN to 300 kN to realize excellent edge quality through reduction of
edge cracks. More preferably, it is more preferable that a bending
force of the rolling roll range from 30 kN to 150 kN, and it is
most preferable that a bending force of the rolling roll range from
30 kN to 100 kN. Meanwhile, the above-mentioned edge wave means
that a length of the edge is elongated further than a central part
as high reduction ratio is applied to the edge and thus the edge
has a waveform, and the distortion refers to a defect generated by
a difference between rolling speeds of edges due to a difference
between the reduction ratios applied to the edges.
[0026] It is preferable that a uniform reduction ratio is applied
to the central part and the edges of the thin cast strip to control
the crown size of the rolling rolls 10 to 50 .mu.m to 250 .mu.m in
order to secure an excellent edge quality. When the crown size of
the rolling rolls is less than 50 .mu.m, edge cracks may be easily
generated, causing a reduction in a yield rate, and when the crown
size of the rolling rolls exceeds 250 .mu.m, the casting process
may be stopped because of generation of serpentine marks due to the
edge wave or distortion. The crown size of the rolling roll refers
to a height difference h between the edge and the center of the
thin cast strip. Accordingly, it is preferable that a crown size of
the rolling roll suggested by the present disclosure range from 50
.mu.m to 250 .mu.m, and it is preferable that a crown size of the
rolling roll range from 50 .mu.m to 200 .mu.m to realize an
excellent edge quality. More preferably, it is more preferable that
a crown size of the rolling roll 10 range from 50 .mu.m to 150
.mu.m, and it is most preferable that a crown size of the rolling
roll range from 50 .mu.m to 100 .mu.m.
[0027] Meanwhile, according to the present disclosure, the alloy
composition of the stainless thin steel sheet is not specifically
limited as long as the stainless thin steel sheet has fine
martensitic microstructures, but it is preferable that the
stainless thin steel sheet include 0.3 wt % to 0.8 wt % of C, 12.0
wt % to 16.0 wt % of Cr, 0.2 wt % to 1.0 wt % of Si, 0.2 wt % to
1.0 wt % of Mn, 0.2 wt % to 1.0 wt % of Ni, 0.01 wt % to 0.1 wt %
of N, 0.03 wt % or less of P, and 0.03 wt % or less of S, and also
includes Fe and other inevitable impurities. Hereinafter, the alloy
composition suggested by the present disclosure will be
described.
[0028] C: 0.3 wt % to 0.8 wt %
[0029] Carbon (C) is an element which increases hardness of
martensitic stainless steel, and 0.3 wt % or more of carbon is
included to secure a hardness of 600 Hv or more required by razor
steel. As the content of carbon increases, the hardness of
martensite produced through heat treatment, but the content of
carbide also increases and thus corrosion resistance and cooling
processing efficiency are lowered, such that it is preferable that
0.8 wt % or less of carbon is included.
[0030] Cr: 12.0 wt % to 16.0 wt %
[0031] Chrome (Cr) is an element which is added to improve
corrosion resistance of martensitic stainless steel, and a chrome
oxide film may be densely formed to improve corrosion resistance
only in a case in which the content of chrome of a matrix
microstructure is 12 wt % or more. In addition, by preventing a
large amount of carbide from being formed to lower the content of
chrome, it is preferable that 12.5 wt % or more of Cr is added to
further improve corrosion resistance due to formation of a chrome
oxide film. Meanwhile, because corrosion resistance is improved but
the hardness of martensite produced by heat treatment is lowered
when the content of chrome exceeds 16 wt %, it is preferable that
the content of the chrome be 16 wt % or less.
[0032] Si: 0.2 wt % to 1.0 wt %
[0033] Silicon (Si) is an element which is added for the purpose of
deoxidation, and because such a deoxidation effect cannot be
sufficiently obtained when the content of silicon is 0.2 wt % or
less, it is preferable that the content of silicon be 0.2 wt % or
more. Meanwhile, because cooling processing efficiency is
significantly low when the content of silicon exceeds 1.0 wt %, it
is preferable that the content of silicon be 1.0 wt % or less.
[0034] Mn: 0.2 wt % to 1.0 wt %
[0035] Manganese (Mn) is an element which is added for the purpose
of deoxidation and to increase dissolution of nitrogen, and because
a deoxidation effect is not sufficient when the content of
manganese is 0.2 wt % or less, it is preferable that the content of
manganese be 0.2% or more. Meanwhile, because corrosion resistance
is low when the content of manganese is 1.0 wt %, it is preferable
that the content of manganese be 1.0 wt % or less.
[0036] Ni: 0.2 wt % to 1.0 wt %
[0037] Nickel (Ni) is an element which is added to martensitic
stainless steel to improve the corrosion resistance of the basis
material without forming carbide. It is preferable that 0.2 wt % or
more of nickel be added to sufficiently obtain corrosion
resistance. Meanwhile, when the content of nickel (Ni) exceeds
1.0%, an excessive amount of residual austenite is formed after
reinforcing heat treatment so that high degree of hardness cannot
be obtained. Although the corrosion resistance of the
microstructures of martensitic stainless steel according to the
related art is remarkably changed after the reinforcing heat
treatment by austenitization temperature and time conditions during
the reinforcing heat treatment, but according to the present
disclosure, addition of 0.2 wt % to 1.0 wt % of Ni supplements the
disadvantage, and in particular, local corrosion resistance such as
pitting or crevice corrosion can be improved.
[0038] N: 0.01 wt % to 0.1 wt %
[0039] Nitrogen (N) is an element which is added to increase
hardness through a reinforcing heat treatment and improve
resistance against pitting and crevice corrosion. It is preferable
that 0.01 wt % of nitrogen be added to obtain the effect, but
because nitrogen bubbles are generated to form pores or pin holes
during the casting process when the content of nitrogen exceeds 0.1
wt %, it is preferable that the content of N range from 0.01 wt %
to 0.1 wt %.
[0040] P: 0.03 wt % or less
[0041] Phosphorus (P) is an element existing as impurities of
steel, and because inter-granular crystals are present and a hot
processing property is lowered if the content of phosphorus (P) is
excessive, the upper limit is defined to 0.03 wt % or less.
[0042] S: 0.03 wt % or less
[0043] Sulfur (S) is an element existing as impurities of steel
like phosphorus, and because hot processing efficiency is lowered
as sulfur exists in inter-granular crystals or sulfides if the
content of sulfur is excessive, the upper limit is defined to 0.03
wt %.
[0044] In accordance with the method of manufacturing a THIN
MARTENSITIC STAINLESS STEEL SHEET according to the present
disclosure provided as described above, the difference between the
reduction ratios of the central part and the edge of the thin cast
strip during hot rolling is 0.8 or less so that a very uniform
reduction ratio can be give, and accordingly, edge cracks of 30 mm
or less may be generated or no edge cracks may be generated, making
it possible to secure a considerably excellent edge quality. In
general, when martensitic stainless steel is manufactured, edge
cracks of 60 mm or less may be generated, and accordingly, when it
is considered that the edge of the thin steel sheet is trimmed by
about 60 mm, it can be seen that the method of the present
disclosure secures a very excellent edge quality.
[0045] Hereinafter, exemplary embodiments of the present disclosure
will be described in detail. Meanwhile, the following embodiments
of the present disclosure are merely examples for describing the
present disclosure in detail, and do not limit the scope of the
present disclosure.
First Embodiment
[0046] A thin cast strip is obtained from 0.65 wt % of C, 13.5 wt %
of Cr, 0.3 wt % of Si, 0.65 wt % of Mn, 0.2 wt % of Ni, 0.03 wt %
of N, 0.02 wt % of P, and 0.001 wt % of S, Fe and other inevitable
impurities by using a twin roll type strip casting method. The
width of the thin cast strip is 1300 mm and the thickness of the
thin cast strip is 3.0 mm, and the thin cast strip is hot rolled
and wound and is manufactured into a thin steel sheet having a
thickness of 2 mm. Meanwhile, the bending force of the rolling roll
is controlled as illustrated in Table 1 during hot rolling, and the
crown size of the rolling roll is 30 .mu.m. In this way, for the
manufactured thin steel sheet, edge cracks exceeding 30 mm, an edge
wave, a distortion, and a difference between reductions of the
central part and the edge of the thin steel sheet were observed and
the result is illustrated in Table.
TABLE-US-00001 TABLE 1 Generation of Difference Class- Bending
Generation of Generation distortion between ifica- force edge crack
(30 of edge (serpentine reduction tion (kN) mm or more) wave mark)
ratios Compar- 10 x 0.1 ative exam- ple 1 Compar- 20 x 0.1 ative
exam- ple 2 Inven- 30 x x x 0.2 tion exam- ple 1 Inven- 50 x x x
0.3 tion exam- ple 2 Inven- 100 x x x 0.4 tion exam- ple 3 Inven-
300 x x x 0.6 tion exam- ple 4 Inven- 500 x x x 0.8 tion exam- ple
5 Compar- 600 x x 1.0 ative exam- ple 3 Compar- 800 -- -- 1.1 ative
exam- ple 4
[0047] As can be seen from Table 1, in Invention Examples 1 to 5
satisfying the bending force condition suggested by the present
disclosure, a uniform reduction ratio was given such that edge
cracks exceeding 30 mm were not generated and surface quality was
excellent, and neither an edge wave nor a distortion was generated
such that an excellent shape quality was secured.
[0048] However, in Comparative Examples 1 and 2 which do not reach
the condition of bending force suggested by the present disclosure,
a high reduction ratio was given to the edge such that edge cracks
were not generated but an edge wave and a distortion were generated
by an excessive reduction ratio.
[0049] Meanwhile, in Comparative Examples 3 and 4 which exceed the
bending force suggested by the present disclosure, it can be seen
that edge cracks were generated as a low reduction ratio was given
to the edge as compared with the central part, and in particular,
in Comparative Example 4, edge cracks were severely generated so
that a strip breakage was generated.
[0050] FIGS. 3 and 4 illustrate pictures obtained by observing the
thin steel sheets of Invention Example 3 and Comparative Example 3.
As can be seen from FIGS. 3 and 4, it can be seen that in Invention
Example 3 satisfying the condition of the present disclosure, edge
cracks were not generated so that quality of the edge was
excellent, but it can be seen that in Comparative Example 3, edge
cracks were generated as an excessive bending force is given.
Second Embodiment
[0051] A thin steel sheet was manufactured in the same condition as
the first embodiment except that the bending force was set to 600
kN and the crown of the rolling roll is controlled as illustrated
in Table 2, and for the manufactured thin steel sheet, edge cracks
exceeding 30 mm, an edge wave, and a distortion were observed, and
the result is illustrated in Table 2.
TABLE-US-00002 TABLE 2 Generation of Generation of distortion
Classif- Crown size edge crack (30 Generation of (serpentine
ication (.mu.m) mm or more) edge wave mark) Compar- 0 x x ative
example 5 Compar- 30 x x ative example 6 Inven- 50 x x x tion
example 6 Inven- 80 x x x tion example 7 Inven- 100 x x x tion
example 8 Inven- 150 x x x tion example 9 Inven- 200 x x x tion
example 10 Inven- 250 x x x tion example 11 Compar- 300 x ative
example 8
[0052] As can be seen from Table 2, in Invention Examples 6 to 11
satisfying the crown size condition of the rolling roll suggested
by the present disclosure, a uniform reduction ratio is given such
that edge cracks exceeding 30 mm were not generated and surface
quality is excellent, and neither an edge wave nor a distortion is
generated such that an excellent shape quality is secured.
[0053] However, it can be seen that in Comparative Examples 5 and 6
which do not reach the crown size condition of the rolling roll
suggested by the present disclosure generate edge cracks as a low
reduction ratio is given to the edge as compared with the central
part, and it can be seen that in Comparative Example 8 which
exceeds the crown size of the rolling roll suggested by the present
disclosure, edge cracks were not generated as a high reduction
ratio is given to the edge, but an edge wave and a distortion are
generated by an excessive reduction ratio.
[0054] According to the present disclosure, a THIN MARTENSITIC
STAINLESS STEEL SHEET having an excellent edge quality can be
manufactured by effectively reducing edge cracks which may be
easily generated during hot rolling in manufacturing a THIN
MARTENSITIC STAINLESS STEEL SHEET using a strip caster.
* * * * *