Note: Descriptions are shown in the official language in which they were submitted.
NSC-7842/PCT
~030538
DESCRIPTION
TITLE OF THE INVENTION
Process for Preparing Rollable Metal Sheet from
Quench Solidified Thin Cast Sheet as Starting
Material
TECHNICAL FIELD
The present invention relates to a process for
preparing a rollable metal sheet from a quench
solidified thin cast sheet as a starting material
capable of providing a good rolled shape when rollable
metal sheets including various alloy sheets, such as
soft iron, stainless steel, silicon steel, nickel-iron
(permalloy), cobalt-iron (permendur), nickel, aluminum
and copper sheets are prepared from a quench solidified
thin cast slab or cast thin strip (hereinafter generally
referred to as "thin cast sheet") as a starting
material.
BACKGROUND ART
Conventionally, various rollable metal sheets are
produced by, for example, (i) a continuous casting to
prepare a 200 mm-thick cast slab, (ii) heating the slab,
(iii) hot rolling, (iv) annealing the hot rolled
material, (v) cold rolling, and (vi) an optional heat
treatment for working. Recent demands for a reduction
in production costs have led to proposals of various
methods of eliminating the above-described steps (ii)
and (iii) including the single roll and twin roll
methods, which comprise continuously feeding a molten
metal onto a cooling material having one or two cooling
surfaces being transferred and renewed for quench
solidification, thereby preparing a thin cast sheet
having a thickness of several ten ~m to about l0 mm.
The above-described single and twin roll methods, etc.,
provide a rollable metal with a high productivity at a
low cost but are plagued by several fundamental
problems, and therefore, currently the technology in
2030538
-- 2
this field is incomplete, although some products have
been put to practical use.
Among the above-mentioned problems, one of the most
serious is a loss of the rolling property. In general,
contrary to the smooth surface of a hot rolled sheet
prepared by the conventional hot rolling process, the
surface of a thin cast sheet prepared by the single roll
method, twin roll method or the like often has an
unevenness of as much as several ten % or more of the
sheet thickness, due to rippling, and further, suffers
from large variations in the thickness of the sheet in
the width direction thereof.
This is a defect inherent to the quench solidifying
system and is attributable to a localized difference in
the shrinkage accompanying the solidification of the
molten metal and a thermal deformation of the roll
surface, etc., and can be avoided to some extent by
attention to the design and operation of the machinery.
This alleviation, however, is limited because, in a
rollable metal sheet prepared by a series of production
steps wherein a cold rolling or warm rolling step is
essential, a ripple or the like on the surface of the
metal is squeezed in the rolling direction during the
rolling and causes a dimple to be formed in the
direction of the sheet body; this is the cause of the
occurrence of scab . The above-described uneven
portion also is often a cause of a cracking of a fragile
material during cold rolling. In recent years, various
methods have been proposed, including a method which
comprises casting a soft iron sheet or a stainless steel
sheet to a thickness of several ten ~m to several mm
through a single or twin roll method, and annealing and
cold rolling the sheet to prepare a foil strip having a
thickness of several ten ~m to several hundred ~m.
Nevertheless, in this method also, the uneven portion
present in the thin cast sheet is a cause of contraction
or breaking during the cold rolling. As described
203053~
above, compared to the conventional hot rolling process,
the single or twin roll method is an excellent
production method having not only the merit of a
reduction of costs, such as an elimination of steps and
the need for less plant and equipment investment, but
also having an advantage in that a cold rolled material
having a thickness as small as about several ten ~m can
be directly prepared. These methods, however, have not
been put to practical use, due to problems with the
rolling process.
In particular, when the above-described thin cast
sheet is used as a starting material for stainless steel
sheets, technical problems having an influence on the
product quality, such as corrosion resistance,
appearance, gloss, polishing property and further, in BA
products, streaks and defects called ~gold dust", exist
on the surface of the steel sheet.
The problem of the surface of the stainless steel
sheet has hitherto been solved by conducting a
mechanical descaling and pickling after annealing the
hot rolled sheet, polishing the whole surface of the
coil to remove various defects, and cold-rolling the
coil with a large number of passes using a sendzimir
mill comprising a multiple roll having a small diameter.
A process comprising the steps of annealing, picking,
surface polishing, and cold rolling by a small diameter
roll is an established technique for preparing a thin
strip of stainless steel having a fine surface, and 2D,
2B, and BA products specified in JIS have been produced
thereby. The manufacturing techniques for these
products are disclosed in detail in Sawatani et al,
"Seitetsu Kenkyu (Study in Iron Manufacturing)", N292
(1977), p. lO0. Further, to satisfy the need for an
elimination of steps, studies have been made into the
elimination of the steps of annealing the hot rolled
sheet and of surface polishing (see Japanese Examined
Patent Publication Nos. 57-38654, 59-46287 and
2030~38
-- 4
58-56013). In these studies, however, it was found that
the elimination of these steps often has an adverse
affect on the surface appearance.
In addition to the above-described prior art, when
a product is prepared through the use of the above-
described thin cast sheet as a starting material, by the
conventional process, compared to the conventional
process wherein use is made of a hot rolled sheet as a
starting material, the crystal grain of the product
becomes large, which leads to serious defects, and thus
this step reducing process cannot be put to practical
use.
As described above, all of the prior art processes
aim at a mirror polish effect on the steep sheet,
obtained from the roll, or a change in the dispersed
state of a carbide of a steel sheet, and do not always
provide a satisfactory solution to the problem.
Further, when a thin cast slab, in which recent
remarkable developments have been made, is used as a
starting material, a problem arises in that a grain
pattern is formed in the product if only the prior art
method is applied. Therefore, a novel and useful method
of solving the above problem is required.
When a unidirectional silicon steel is used as the
starting material for the above-described thin cast
sheet, a proposal has been made for a technique that
will solve a problem of the conventional process for
preparing a unidirectional silicon steel sheet, i.e., a
problem of a limitation of the silicon content to 4% or
less, for example, as disclosed in Japanese Unexamined
Patent Publication Nos. 55-69223 and 60-38462, a process
for preparing a cold-rollable high silicon steel sheet
through the use of a starting material comprising a cast
slab having a thickness of not more than several
hundred ~m prepared by continuously feeding a molten
metal containing 4 to 10% by weight of silicon, etc.,
onto a cooling material having a cooling surface being
5 2030538
transferred and renewed to quench the molten metal. A
similar method is disclosed in Japanese Unexamined
Patent Publication No. 63-11619. This method is applied
to a cast slab having a thickness of 0.7 to 2.0 mm.
All of the silicon steel sheets prepared by the
above-described improved method exhibit a good
mechanical property when the silicon content is high,
but are unsatisfactory from the viewpoint of obtaining a
high magnetic property, and stably reproducing these
properties.
Specifically, the process for preparing an
unidirectional silicon steel sheet wherein use is made
of a step of preparing a thin cast sheet by quench
solidification is advantageous in that it is possible to
eliminate the hot rolling step and increase the silicon
content, but is unsatisfactory in the attaining of
excellent properties and in the reproducibility of the
conventional material subjected to the hot rolling.
Further, a satisfactory cold rolling property is not
attained in a high silicon content material.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a
method which solves the problem of the loss of the cold
rolling property, which is a serious problem common to
the production of a rollable metal sheet from a starting
material comprising a quench solidified thin cast sheet
prepared by the above-described single or twin roll
method, i.e., to remarkably alleviate the fundamental
difficulties encountered by the single or twin roll
method when putting these methods to practical use.
An object of the present invention is to provide a
novel method of improving the surface appearance of a
thin cast sheet for general stainless steels, wherein
the surface appearance is considered important in a cold
rolled sheet or in the stage of final annealing, without
a limitation to an austenitic stainless steel typically
comprising 18% Cr-8% Ni or a ferritic stainless steel
- 6 - 2030538
typically comprising 16.5% Cr. Further, another object
of the present invention is to provide a process for
stably preparing a unidirectional silicon steel having a
low core loss, through a suitable regulation of the
integrity and grain size of a {110} <001> secondary
recrystallized grain of a unidirectional silicon steel
in a thin cast sheet form.
The present inventors made various studies with a
view to solving the above-described problems of the
prior art, and as a result, found that a particular
working followed by a recrystallization of a fine grain
in the worked region by annealing will suitably solve
the above-described problems of the loss of the rolling
property, etc., and thus completed the present
invention.
Accordingly, the object of the present invention is
to provide a process for preparing a metal sheet having
an excellent rolling property, etc., i.e., a rollable
metal sheet, which process comprises the basic steps of:
continuously feeding a molten metal onto a cooling
material having one or two cooling surfaces being
transferred and renewed for quench solidification, to
thereby prepare a thin cast sheet preferably having a
thickness of 10 ~m to about 6 mm; impinging a small
rigid body particle onto the surface of the resultant
thin cast sheet, to work the cast sheet; heat-annealing
the worked sheet in such a manner that the worked region
becomes a fine recrystallized grain layer; and
subjecting the sheet to a cold or warm rolling,
optionally after a removal of oxides present on the
surface; and an optional step of heat-treating the
rolled sheet for working.
When a rollable metal sheet is prepared from a
starting material comprising a quench solidified thin
cast sheet formed by the single or twin roll method, the
cold rolling property with regard to the surface
smoothness, sheet thickness controllability, and
;, 203~38
frequency of occurrence of problems such as a breaking
of the metal sheet prepared by the prior art method is
for inferior to a sheet subjected to hot rolling. In
contrast, according to the present invention, the cold
rolling property and surface appearance can be
remarkably improved through the introduction of the
above-described step of working and the step of
recrystallizing a fine grain in the worked region.
Further, even in the case of a unidirectional
silicon steel having a high silicon content and a small
thickness, the secondary recrystallization can be
remarkably stabilized, and the grain size made small,
which makes it possible to prepare a unidirectional
silicon steel sheet having a core loss of about 5% or
more, which is superior to that of the conventional
product. Further, the fine recrystallization at the
surface portion of the cold rolling material steel sheet
according to the present invention has the effect of not
only improving the secondarily recrystallized grain but
also remarkably improving the cold rolling property, so
that according to the present invention, even a cast
slab having a high silicon content and a thickness of up
to 2.5 mm can be advantageously cold-rolled, compared to
the known quench solidification method, for example, a
method disclosed in Japanese Unexamined Patent
Publication No. 63-11619, wherein the upper limit of the
thickness of the cast slab is 2.0 mm.
The reasons why the production conditions in the
present invention are limited as described above will
now be described in detail.
There is no particular limitation on the metal used
in the present invention, and a thin cast sheet prepared
by the single or twin roll method, i.e. by continuously
feeding a molten metal onto a cooling material having
one or two cooling surfaces being transferred and
renewed for quench solidification, is used as a starting
material. The present invention can be advantageously
203û538
applied to the production of various known rollable
metal or alloy sheets, such as soft steel, stainless
steel, silicon steel, nickel-iron, cobalt-iron, nickel,
aluminum and copper sheets because, in these materials,
the worked region can be finely crystallized through the
steps of working and annealing, which are essential in
the present invention, and the fine crystallization
enables a remarkable improvement of the cold rolling
property.
The reason why the thickness of the thin cast sheet
is preferably limited to lO ~m to 6.0 mm is as follows.
When the thickness exceeds 6.0 mm, the advantage of the
elimination of the step is reduced and a relatively good
rolling property can be obtained without the use of the
present invention because, even when uneven portions
exist, the proportion thereof in the whole sheet
thickness is small. The thickness must be lO ~m or more
because there is substantially no need to use a starting
material having a thickness of less than lO ~m, as
rolling is conducted in the present invention as an
indispensable step and it is almost impossible to
prepare a thin cast sheet having a thickness of less
than lO ~m.
In the case of a grain oriented silicon steel, the
thickness is preferably 0.5 to 2.5 mm.
The thin cast sheet prepared by the quench
solidification method is then worked by impinging a
small rigid body particle against the surface of the
cast sheet. Specifically, a numerous number of
particles of iron, sand or other material are impinged
at a high speed against the surface of the thin cast
sheet, for working; i.e., the thin cast sheet is
subjected to blasting. "Grit" having an irregular shape
and very sharp, or a shot having a relatively spherical
shape, are used as the particles for the working. To
impinge the above-described particles at a high speed,
in general, use is made of a centrifugal projecting
2030~38
apparatus wherein the particles are accelerated by the
rotation of a blade of a disk wheel, or a pneumatic
blasting apparatus wherein compressed air ejected from a
nozzle is utilized.
preferably, the above-described working is applied
to both surfaces, these surfaces including a side edge
face or one surface depending upon the surface
appearance, because a working of one surface causes
warping.
Regarding the size of the grit, shot, etc., the use
of a large size shot not only increases the depth of the
worked region but also increases the size of the
impressions, and consequently, increases the surface
roughness. In general, the size is preferably two times
to a fraction of the thickness of the thin cast sheet.
The blasting time varies depending upon the type of
metal, the unevenness of the thin cast sheet, and the
purpose thereof, etc., but the working must be conducted
in such a manner that substantially no unworked region
exists and at least the surface of the sheet is covered
with a fine recrystallized grain in the subsequent
annealing.
The thin cast sheet thus worked is then heat-
annealed. The optimum temperature varies, depending
upon the type of metal; for example, heating is
preferably conducted at 650 to 1300C for silicon-iron
steel, stainless steel and nickel-iron, at 350 to 900C
for copper, and at 300 to 600C for aluminum, for zero
second to several hours.
The thin cast sheet wherein at least the surface
thereof is covered with a fine recrystallized grain
through the heat annealing is subjected to a step of
removing an oxide, etc., present on the surface thereof
according to need, and then to a series of steps
including cold or warm rolling as a basic step depending
upon the purpose, and then optionally, a heat treatment
for working, to thereby prepare a final product.
1~ 203~38
It is believed that the cold rolling property of
the quench solidified thin cast sheet is improved by the
present invention through the following mechanism. The
grit or shot blasting has the effect of smoothing uneven
portions, particularly the boundary regions thereof
present on the surface of the thin cast sheet, and the
smoothing effect reduces rippling , etc., during
rolling.
The most important feature of the present invention
is that the cold rolling is conducted in a state such
that the surface of the thin cast sheet is covered with
a fine recrystallized grain.
When a rolling roll is partially in contact with a
surface of a thin cast sheet having an uneven portion,
the "drape" between the surface of the thin cast sheet
having an uneven portion and the surface of rolling roll
is poor, due to a relationship thereof with the
deformation mode if surface particles are coarse. On
the other hand, when the surface grain comprises a fine
recrystallized grain, the "drape" between both surfaces
is good, and the whole surface can be leveled with a
very small rolling reduction. This difference in the
drape' between the coarse grain and the fine grain is
believed to exist because, when the surface grain is
coarse, the deformation due to a particular simple slip
system occurs over a relatively wide region and the
constraint on adjacent grains is large, and thus the
external shape of each grain is not always adhered to
the roll surface, but when the surface grain is fine,
the deformation of each grain occurs over a narrow
region, which enables the external shape of each grain
to be always adhered to the roll surface.
As described above, the present invention enables a
metal sheet useful to the industry to be prepared from a
quench solidified thin cast sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure l is a schematic explanatory view showing
11 203~3~
the process of the present invention;
Fig. 2 is a schematic diagram of a photomicrograph
showing a state of formation of a fine recrystallized
grain layer on the surface of a thin cast sheet having a
sagging portion, according to the present invention, and
Fig. 3 is a diagram showing the relationship
between the fine crystal grain size and the depth of the
grain layer from the surface thereof, in the process of
the present invention (stainless steel), in relation to
a surfzce defect.
BEST MODE OF CARRYING OUT THE INVENTION
The present invention will now be described in more
detail with regard to the case wherein the molten metal
is a stainless steel and a unidirectional electrical
sheet.
First a description will be given with reference to
a stainless steel thin case sheet.
The stainless steel used in the present invention
is formed of a stainless steel comprising known
ingredients, and as described above, must be subjected
to shot blasting and heat annealing (annealing for
softening) before cold rolling.
Figure 1 is a schematic explanatory view showing
the process of the present invention. A molten metal 2
in a tundish 1 is poured between cooling rolls 3 and is
quench-solidified in a gap between the rolls 3 to form a
thin cast sheet 4. The surface of the thin cast sheet 4
is subjected to blasting by a shot blasting apparatus 5.
The worked sheet is annealed for softening by a heat
annealing apparatus 6, scale is removed, and the sheet
is cold rolled by a cold rolling mill 7.
Figure 2 (a), (b), and (c) are each a schematic
view of a microphotograph wherein the sagging portion A
of the thin cast sheet 4 shown in Fig. 1 is subjected to
surface working and annealing. When the sagging portion
A is subject to blasting, a worked layer 8 is formed on
the surface as shown in Fig. 2 (b) and the acute angle
- 12 - 2030538
portion disappears. Further, when the sagging portion A
is annealed for softening, a fine recrystallized grain
layer 9 is formed as shown in Fig. 2 (c).
In the present embodiment, as shown in Fig. 3, the
above-described fine recrystallized grain 9 having an
average diameter of 100 ~m or less must be formed as a
surface layer having a depth of 30 ~m or more on the
thin cast sheet.
Figure 3 shows the results of an observation of the
surface appearance of metal sheets prepared by
subjecting a 3 mm-thick thin cast slab of SUS 304
comprising a coarse crystal grain to shot blasting under
various conditions, annealing the worked slab at 1100C
for various times, to vary the size of a fine crystal-
lized grain and the depth of a surface layer, removing
scale with aqua regia, and cold-rolling the slab at a
draft of 70%. It is apparent that, when outside the
scope of the present invention, the cold rolling causes
a rough surface, e.g., orange peel , to be formed due
to the coarse crystal grain of the thin cast slab.
Accordingly, the above-described fine recrystal-
lized grain must be used in the present embodiment.
To produce the above-described fine recrystallized
grain after annealing for softening, a rigid body
particle, such as shot or grit, is projected onto the
steel sheet before the annealing for softening, to
thereby form a worked layer on the surface layer of the
steel sheet. Specifically, a large number of particles
of iron, sand or other material are impinged at a high
speed onto the surface or the thin cast sheet, for
working. The blasting may be conducted under the same
conditions as described above.
The thus blasted thin cast sheet is then annealing
for softening. in the present embodiment, heat
annealing at a temperature of 700 to 1300C for one sec
to 10 min may be conducted, to recrystallize the grain
to the above-described state. When the annealing
- 1-3 - 2030~38
temperature and time are lower than 700C and shorter
than 1 sec, respectively, no recrystallization occurs.
On the other hand, when the annealing temperature and
time are more than 1300C and 10 min, respectively, this
is not only cost-inefficient but also it becomes
difficult to prepare a fine grain due to the growth of
the crystal grain.
In the present embodiment, the surface defect of
the cold-rolled sheet is alleviated through the
following mechanism. Specifically, in the present
embodiment, when the cold rolling is conducted in a
state such that the surface of a thin cast sheet is
covered with a fine recrystallized grain, the "drape"
between the surface of the thin cast sheet and the
surface of the rolling rolls becomes good, which causes
the surface of the thin cast sheet to be actively
polished, whereby a mirror surface is obtained. If the
surface grains of the thin cast sheet are coarse, each
crystal grain tends to have an external shape different
from the surface of the rolls, due to the relationship
with a slip system of the crystal grain. That is, it is
believed that the formation of patterns different from
particle to particle can be avoided because the "drape"
with the surface of the rolling rolls becomes poor.
As described above, according to the present
embodiment, it becomes possible to prepare a thin
stainless steel sheet having an excellent surface
appeararlce .
A description will now be made of a gain oriented
silicon steel.
In the present embodiment, the steel composition is
limited to 2.5 to 6.5% by weight of silicon, an
inhibitor ingredient necessary for a gain oriented steel
sheet, with the balance being iron and unavoidable
impurities. When the silicon content is less than 2.5%,
a 7 phase is formed at a high temperature, which makes
it unable to use a final annealing temperature of 1000C
2030~38
- 14 -
or higher due to the growth of a secondary recrystal-
lization, so that substantially no magnetic property can
be secured. For this reason, the silicon content is
limited to 2.5% or more. On the other hand, the upper
limit of the silicon content is set to 6.5% for the
reason that, when the silicon content exceeds 6.5%, the
cold rolling property becomes remarkably poor because
the steel sheet becomes remarkably embrittled.
The effect of the present embodiment can be
obtained in a gain oriented silicon steel sheet
containing any known inhibitor ingredient. There is no
particular limitation on the ingredients of the intended
steel sheet, and the steel sheet may comprise 0.0005 to
0.10% of C, 0.02 to 0.35% of Mn, 0.0005 to 0.040% of
sol. Al, 0.0005 to 0.04% of S, 0.0005 to 0.012% of N,
0.04% or less of Se, and 0.4% or less of at least one of
Sn, Sb, As, Bi, Cu, Cr and Ni.
According to the present embodiment, a molten metal
having the above-described composition is then continu-
ously fed onto a cooling material having one or twocooling surfaces being transferred and renewed for
quench solidification, thereby preparing a thin cast
sheet having a thickness of 0.5 to 2.5 mm. In this
case, when the thickness exceeds 2.5 mm, the cooling
rate becomes too low. On the other hand, when the
thickness is less than 0.5 mm, it becomes difficult to
conduct cold rolling with a final cold rolling draft of
80 to 98%. For these reasons, the thickness is
preferably 0.5 to 2.5 mm. After solidification, the
thin cast sheet having a thickness of 0.5 to 2.5 mm
prepared by the above-described casting method is cooled
to 1000C at a cooling rate of 102 to 104C/sec.
Thereafter, the thin cast sheet usually peels from the
cooling material. In this case, it is preferred to
spray water or warm water for cooling.
The thin cast sheet thus prepared is then subjected
to an essential step of the present embodiment.
203Q~3~
- 15 -
Specifically, a small rigid body particle is impinged
against the thin cast sheet, for working the surface
portion. A suitable size of the small rigid body
particle varies depending upon the shape of the
particle, impact speed, and incident angle, etc., but
the particle size is preferably 0.2 to 2 times the
thickness of the thin cast sheet. The shape of the
particle is preferably angular rather than spherical.
The surface of the thin cast sheet should be covered
with impressions made by the impact of the small
particles.
The thin cast sheet is annealed for recrystal-
lization at 650 to 1300C for 30 min or less. When the
temperature is lower than 650C, it is difficult to
conduct recrystallization. On the other hand, when the
temperature is higher than 1300C, the inhibitor and
structure become poor. When the heating time is longer
than 30 min, the cost efficiency is lost. Therefore,
the annealing time is limited as described above. When
the heating temperature is low, the heating should be
conducted for a long time, for example, at 700C for
25 min, and when the heating temperature is high the
heating should be conducted for a short time, for
example, at 1250C for 10 sec.
The thin cast sheet thus prepared is subjected to
intermediate annealing, etc., according to need,
repeatedly cold-rolled, and subjected to cold rolling as
a final cold rolling at a draft of 80 to 98%. When the
draft is less than 80%, the integrity of the secondarily
recrystallized grain prepared after final annealing
often becomes poor in the {110} <001> orientation. On
the other hand, when the cold rolling draft is higher
than 98%, it becomes difficult to ensure the secondary
recrystallization.
The cold rolled sheet is then annealed at 600 to
1300C at least once. In the case of a relatively thin
cast sheet, a secondary recrystallization can be
2030538
attained even when the carbon content is e.g., 0.0030%
or less. In this case, annealing for the secondary
recrystallization may be conducted only once at 900 to
1300C. In general, however, since carbon is contained
in an amount of 0.0050% or more, it is preferred to
conduct the decarburizing annealing at 750 to 900C in a
wet hydrogen gas stream, followed by the second
annealing as a final annealing at 900 to 1300C.
In the present embodiment, it is believed that the
10integrity of grains having a {110} <001> orientation and
the size of the secondarily recrystallized grain are
improved by the formation of a fine recrystallized grain
on the surface of a cold rolled steel sheet, through the
following two mechanisms.
15One of the two mechanisms is the formation of a
Goss nucleus, and the other is the homogenization of the
primarily recrystallized matrix. In general, the
secondarily recrystallized grains having a {110} <001>
orientation of a gain oriented silicon steel sheet
product is formed through the growth of a grain having a
{110} <001> orientation among primarily recrystallized
grains while eating out primarily recrystallized grains
adjacent thereto. In this connection, a theory commonly
accepted in the art through studies in recent years is
that the origin of the "Goss nucleus" present in the
primarily recrystallized grain structure exists as a
Goss nucleus origin grain on the surface of the
hot-rolled material. When the thin cast sheet is used
as a cold rolling material as in the present invention,
however, compared to the hot rolled sheet, the number of
grains having an orientation suitable for the formation
of the Goss nucleus is small and the grain having a
{100} <ovw> orientation occupies the major portion of
the grains. It is believed that a grain having an
orientation corresponding to the Goss nucleus origin
grain is introduced by subjecting the above-described
thin cast sheet to working and recrystallization
2030538
- 1-7 -
according to the present embodiment. The other
mechanism for improving the property is that, as with
the present embodiment, the existence of a fine crystal
grain on a grain of the surface limits the growth of
grain in the central portion of the steel sheet, and
consequently, homogenizes the primarily recrystallized
matrix. The homogenization of the primarily
recrystallized matrix means a smooth growth of Goss
nucleus having a good orientation, i.e., a {110} <001>
orientation, and an improvement of the magnetic
properties.
As described above, according to the present
invention, it becomes possible to stably prepare a grain
oriented silicon steel sheet having a {110} <001>
orientation valuable in the industry at a low cost while
ensuring excellent properties thereof.
Example 1
Permalloy PC comprising 76% nickel, 4.5% copper,
and 4.5% molybdenum, with the balance being iron and
unavoidable impurities, was vacuum melted, and a 0.30 mm
thick thin cast sheet was prepared therefrom by a twin
roll having a roll diameter of 300 mm. The surface of
the thin cast sheets had a recessed portion in a streak
form and a sag. The thin cast sheet was divided into
two groups, i.e., groups A and B. The sheets of group B
were subjected to sand blasting by using sand having a
particle diameter of 0.4 mm. Thereafter, the sheets of
groups A and B were heat-annealed at 1100C for 300 sec,
descaled with aqua regia, and rolled to 0.10 mm by a
cold rolling mill.
The structure of the section of the material
immediately after heat annealing was observed, and as a
result, it was found that, in the materials of group B,
a layer of a fine grain having a diameter of about 30 to
50 ~m was formed in a 0.1 mm region on both surfaces.
Some materials of group A brought about the
formation of a pore and broke, and all the materials of
2030538
- 18 -
group B were rollable. The above cold rolled materials
were cut to a width of 1 cm, coated with MgO as an
annealing releaser, wound in a toroidal form, maintained
in a dry hydrogen gas stream at 1100C for 3 hr, and
subjected to furnace cooling at a cooling rate of
100C/hr. The magnetic properties of the materials were
determined, and as a result, it was found that, as shown
in Table 1, the scattering in the magnetic properties
was large. It was found that the scattering was
attributed to the scattering in the thickness of the
cold sheet, and thus according to the present invention,
not only is the cold rolling property improved but also
variations in the magnetic properties can be prevented
through the prevention of variations in the thickness of
the cold rolled sheet.
Table 1
Group Cold rolling property Magnetic properties Classi-
A About 30Z caused for- ~o-Hc 0.007 x 10 to Co~par-
mation of pores and 0.010 x 10 (T) ative
breaking~ 12 104 t 19 104
.Variation in sheet ~ : 21 x 104 to 33 x 104
m
thickness was large: ~ (10 kHz): 1900 to 3200
0.07 - 0.13 mm
B All material was ~o-Hc 0.006 x 10 to Present
rollable to a thick- 0.007 x 10 (T) inven-
ness of 0.10 mm ~ : 18 x 10 to 22 x 10 tion
.Variation in sheet ~ 32 104 t 36 104
m
thickness was small: ~ (10 kHz): 2500 to 3800
0.09 to 0.11 mm
Example 2
2030538
-- 19 --
Austenitic stainless steel (SUS 304) comprising
0.053% carbon, 18% chromium, and 8% nickel, with the
balance being iron and unavoidable impurities, was
vacuum-melted and a thin cast sheet having a thickness
of 3.0 mm was prepared therefrom by a twin roll having a
roll diameter of 400 mm. The "sags" in a raindrop form
having a height of 1 to 2 mm and a ~'ripple" were
scatte~ed over the surface of the thin cast iron.
The above-melted thin cast sheet was divided into
two groups, i.e., groups A and B. In the sheets of
group B, a steel grit having a diameter of 0.8 mm was
blasted by a compressed air stream directed onto the
surface of the thin cast sheet for about 20 sec. This
caused the whole surface of the thin cast sheet to be
covered with a worked portion having an unevenness of
0.2 to 0.5 mm, and the average sheet thickness was
2.9 mm. The worked thin cast sheets were subjected to
heat annealing under various conditions of a heating
temperature of 600 to 1200C and a heating time of zero
sec to 3 hr. At this stage, the section of the sheet
was observed under a metallurgical microscope to confirm
whether or not the surface was covered with a fine
grain.
Thereafter, all samples of groups A and B were
cold-rolled to 1 mm by a four-stage rolling mill having
a roll diameter of 80 mm, and the surface appearance
thereof then observed. The results are shown in
Table 2.
As is apparent from Table 2, the materials of group
B subjected to fine recrystallization had a superior
surface appearance.
2030S~
- 2~ -
Table 2
Group Surface appearance Classi-
A .In about half of the materials, cold
(Neither rolling was interrupted due to cracking.
grit .Although the remaining materials were cold-
working rollable to a thickness of 1 mm, sagged Compar-
nor portions recessed and flawed. ative
annealing) .Uneven pattern occurred in orange peel
form.
.The sheet thickness was nonuniform:
0.75 to 1.05 mm.
B Incomplete .Although all the materials were
(Grit formation of cold-rollable to a thickness of
working) fine recrys- 1 mm, uneven pattern in orange
tallized peel form occurred in some.
grain layer
Formation of All the materials were cold-
fine recrys- rollable to a thickness of
tallized 1 mm.
grain layer .No trace of sagged portion Present
observed. inven-
.No uneven pattern in orange tion
peel form was observed.
.The sheet thickness was
uniform: 0.97 to 1.01 mm.
Example 3
A 2.1 mm-thick thin cast sheet of a stainless steel
comprising 0.06% carbon, 18.3% chromium, 8.4% nickel,
and 0.038% nitrogen, with the balance being iron and
unavoidable impurities, was prepared by a method wherein
a molten metal was poured into a gap between rotated
metallic rolls having a diameter of 300 mm. The thin
cast sheet was divided into two groups, i.e., groups A
and B. Both surfaces of the thin cast sheets of each
group were scanned a number of times by the "air grit
blasting machine" wherein a small sand particle together
with a high speed stream of compressed air was impinged
203~)53~
- 21 -
against the steel sheet. The sand particle had an
average particle diameter of 0.8 mm. The thin cast
sheets thus scanned were heat-annealed at 1150C for
2 min, subjected to a removal of scale formed during the
annealing, with aqua regia, and then cold-rolled to a
sheet thickness of 0.7 mm. After a rolling oil was
washed out, the cold rolled sheets were subjected to a
final annealing at 1100C for 60 sec, and the surface
appearance was observed. Blasting conditions (number of
times of scanning for varying the degree of working),
the degree of fine recrystallization on the surface of
the thin sheets in the heat annealing at 1150C after
blasting, and the results of observation of the surface
appearance of the resultant cold-rolled sheets are shown
in Table 3.
Table 3
Group Number Presence of Results of Classi-
of fine recrys- observation fication
times tallized of surface
of grain on appearance
blast- surface
ing after an-
nealing of
cast slab
(%)
A 0 0 Dim color, occurrence Compar-
of many orange peel ative
patterns
1 60 Dim color, occurrence
of orange peel pattern
B 3 100 Mirror surface, no Present
orange peel pattern Inven-
tion
100 Do.
100 Do.
- 22 - 2030~38
As apparent from Table 3, the surface appearance
was remarkably improved through the application of the
present invention.
Example 4
Thin cast sheets having a thickness of 2.5 mm
(group A), 1.3 mm (group B) and 0.9 mm (group C) and
comprising 0.06% carbon, 3.2% silicon, 0.71~ manganese,
0.025% oulfur, 0.019% sol. aluminum, 0.008% nitrogen,
and 0.15% tin, with the balance consisting essentially
of iron, were prepared by a method wherein a molten
metal was poured into a gap between rotated metallic
twin rolls having a diameter of 300 mm, while cooling
the resultant sheet with water at the outlet of the twin
roll. Both surfaces of these thin cast sheets were
scanned a number of times by the "air grit blasting
machine" wherein a small sand particle together with a
high speed stream of compressed air was impinged against
the steel sheet. The average particle diameter of the
sand was 1 mm for group A, 0.7 mm for group B and 0.5 mm
for group C. The thus scanned steel sheets were
annealed at 1100C for 2 min, and pickled and cold-
rolled to a final sheet thickness at a draft of 86%.
The steel sheets were subjected to decarburizing
annealing in a wet hydrogen gas stream, coated with MgO
as an annealing releaser, and subjected to secondary
recrystallization.purification annealing at 1180C for
15 hr in a dry hydrogen gas stream. The blasting
conditions (number of times of scanning for varying the
degree of working), the degree of fine recrystallization
on the surface of the steel sheets after the annealing
at 1100C after blasting, and the final magnetic
properties are shown in Table 4.
203053~
- 23 -
Table 4
Group Number Sheet thickness Presence of MagneticClassi-
ofof thin cast fine recrys- propertiesfication
times sheet tallized
of(thickness of grain on Magnetic
blast-product) surface density
ing after an- Blo (T)
nealing of
cast slab
(~)
2.5 mm 0 No 1.4 - 1.81Comparative
A 2 Yes 1.89 - 1.92Present
invention
(0.33mm) 3 Yes 1.90 - 1.93 Do.
Yes 1.90 - 1.93 Do.
1.3 mm 0 No 1.6 - 1.91Comparative
B 2 Yes 1.89 - 1.92Present
invention
(0.17mm) 3 Yes 1.85 - 1.93 Do.
Yes 1.90 - 1.93 Do.
0.9 mm 0 No 1.6 - 1.90Comparative
C 2 Yes 1.87 - 1.91Present
invention
(0.12mm) 3 Yes 1.89 - 1.93 Do.
Yes 1.89 - 1.93 Do.
INDUSTRIAL APPLICABILITY
As apparent from the foregoing description,
rollable metal sheets prepared from a quench solidified
thin cast sheet according to the present invention have
a far better cold rolling property than metal sheets
- 24 - 2030538
prepared from the conventional quench solidified thin
cast sheet. In particular, in the case of a stainless
steel, the products prepared according to the process of
the present invention have a superior surface appearance
compared to the products prepared by the conventional
process. Further, in the case of a grain oriented
silicon steel, the products according to the present
invention have superior magnetic properties. Further,
the present invention increases the practicability of
the process wherein a step of hot rolling has been
eliminated, which renders the present invention very
useful to industry from the viewpoints of energy saving,
and less plant and equipment investment.
