[Document Type] Specification
[Title of the Invention] COMPOSITE ROLLING MILL ROLL AND ROLLING
METHOD
[Technical Field of the Invention]
[OOOl]
The present invention relates to a composite rolling mill roll used in a rolling
among manufacturing of a metal product such as steel; and a rolling method. In
particular, the present invention relates to a composite rolling mill roll used in hot
rolling; and a rolling method.
Priority is claimed on Japanese Patent Application No. 2012-153880, filed on
July 9,2012, the amount of which is incorporated herein by reference.
[Related Art]
[0002]
For a rolling mill roll used in a rolling, a high-hardness material in which
ceramic components such as a carbide are dispersed in a metal matrix is used.
Typically, such a rolling mill roll is manufactured with a casting method. By
adjusting components or optimizing heat treatment conditions or the like, a material
having the strength and hardness required to be used as a rolling mill roll can be
manufactured.
[0003]
Meanwhile, as a rolling mill roll manufactured with a method other than a
casting method, rolling mill rolls formed of fiber reinforced metals (FRM) are known,
the FRM being reinforced by being manufactured using a combination of powder
particles used to fortn a metal matrix with a ceramic fiber and a sintering method
(Patent Documents 1,2, and 4). In addition, a rolling mill roll obtained with such a
method for manufacturing is also known to have higher wear resistance, seizing
resistance, and resistance of deterioration for roll surface than those of a rolling mill
roll manufactured with a casting method. In addition, a rolling mill roll which is
reinforced by adding ceramic powder particles to powder particles used to form a
metal matrix is known (Patent Document 3). However, these techniques disclosed in
these documents have problems described below.
[0004]
Patent Document 1 relates to a composite rolling mill roll in which an outer
layer formed of a wear-resistant material is provided around a steel shaft. This outer
layer formed of a wear-resistant material is manufactured by adding small pieces of a
ceramic fiber to a powder of an iron alloy and sintering the obtained mixture.
However, the present inventors found that, by adding a large amount of ceramic fiber
to a roll outer layer, the surface roughness of a roll may be increased, and the strength
of the roll outer layer may be decreased to cause cracking in the roll outer layer. The
present inventors found that, when 45 volume% of small pieces of a ceramic fiber is
added to a powder of an iron alloy to form a roll outer layer, material defects such as
cracking occur in the roll outer layer. Such findings are not disclosed in Patent
Document 1.
[0005]
Patent Document 2 relates to a metal which is reinforced by adding a ceramic
fiber thereto. This metal in which the ceramic fiber is added is manufactured by
sintering a mixture of a metal powder and the ceramic fibe~ Patent Document 2
discloses that, during the sintering, the internal pressure of a sintering furnace is
necessarily 0.1 to 7.0 MPa which is a relatively low pressure. However, the ceramicfiber-
added metal sintered under such a pressure is not suitable for an outer layer of a
rolling mill roll to which a large load is applied during use. This is because a sintered
material to which a sufficient pressure is not applied during sintering contains a large
number of voids, and these voids cause cracking when a large load is applied to the
sintered body. In order to be used for an outer layer of a rolling mill roll, it is
necessary that the ceramic-fiber-added metal be sintered by hot isostatic pressing (HIP)
under a high pressure.
[0006]
Patent Document 3 relates to an outer layer of a rolling mill roll which is
manufactured by mixing a powder of an iron alloy with Sic particles or B4C particles
and sintering the obtained mixed powder. However, Sic and B4C are not preferable
as a component of the ceramic powder which is mixed with the powder of the iron
alloy. This is because Sic and B4C react with iron to form an alloy during sintering.
The formed alloy inhibits the strength of a sintered metal from being improved by the
addition of a ceramic. The present inventors verified that, when powders of Sic and
B4C are mixed with a powder of an iron alloy, a sintered body obtained from the mixed
powder does not have sufficient strength for an outer layer of a rolling mill roll.
[0007]
Patent Document 4 relates to a rolling mill roll as a composite member
structure including an outer layer that is formed by mixing a powder of an iron-base
metal, in which a carbide having 10 pm or less of a diameter crystallizes, with small
pieces of an oxide ceramic fiber and sintering the obtained mixture. In the rolling
mill roll, a theoretical density of the outer layer is increased to be higher than or equal
to 99% with a sintering method. However, when the theoretical density is higher than
or equal to 99%, microdefects initiated by aggregation of a ceramic fiber cannot be
completely removed from the outer layer. In addition, when a rolling mill roll
including the outer layer is used for rolling, propagation of microcracks caused by the
microdefects is unavoidable. Due to the propagation of the microcracks, there is a
problem in that material lacking occures on a surface of the rolling mill roll, and the
surface of the rolling mill roll is deteriorated.
[Prior Art Document]
[Patent Document]
[0008]
[Patent Document 11 Japanese Unexamined Patent Application, First
PublicationNo. H11-28508
[Patent Document 21 Japanese Unexamined Patent Application, First
Publication No. 2003-119554
[Patent Document 31 Japanese Unexamined Patent Application, First
Publication No. H11-061349
[Patent Document 41 Japanese Unexamined Patent Application, First
Publication No. 2001-59147
[Disclosure of the Invention]
[Problenls to be Solved by the Invention]
[0009]
Along with improvement of rolling such as an increase in the rolling amount
of a high-strength steel and increase in rolling speed, conditions of the usage
environment of a rolling mill roll have became more severe, and further improvement
of wear resistance and resistance of deterioration for roll surface is required in the
rolling mill roll. In order to inlprove these properties, it is considered that the amount
of ceramic components in an outer layer of a composite rolling mill roll be increased.
However, according to the findings by the present inventors, in a composite rolling
mill roll (FRM rolling mill roll) in which FRM is used as an outer layer, when a
blending amount of a ceramic fiber is increased to increase the amount of ceramic
components, ceramic fibers are intertwined with each other, and defects are likely to
occur by fiber aggregation during the manufacturing of the FRM rolling mill roll. As
a result, it is difficult to manufacture a robust roll. However, when a composite
rolling mill roll having the same blending amount of a ceramic as that of the FRM
rolling mill roll is manufactured using only a powder of an iron alloy and a ceramic
powder, the ceramic powder functions as a propagation path of cracks, and thus cracks
are likely to be propagated. The present inventors found that, when a sintered body is
manufactured by blending a ceramic powder into a powder of an iron alloy, the
performance of a composite rolling mill roll can be improved by further blending a
ceramic fiber into the powder of the iron alloy to suppress the propagation of cracks
caused by the ceramic powder. In addition, as a result of further study, the present
inventors found that, by blending both a ceramic fiber and a ceramic powder into a
powder of an iron alloy, the amount of ceramic components in a sintered body of an
outer layer of a composite rolling mill roll can be increased without the propagation of
cracks caused by the aggregation of the ceramic fiber and the ceramic powder,
[OO lo]
An object of the present invention is to provide a composite rolling mill roll
having higher properties than those of a FRM rolling mill roll of the related art, in
which both of tribological properties such as wear resistance and resistance of
deterioration for roll surface and mechanical properties such as cracking resistance and
strength, which are required in a composite rolling mill roll, are satisfied.
[Means for Solving the Problem]
[OOII]
In order to solve the above-described problen~st,h e following invention is
provided.
(1) According to a first aspect of the present invention, there is provided a
composite rolling mill roll including: a steel roll shaft, and an outer layer provided
around the roll shaft, in which the outer layer includes a sintered body including a base
metal which is an r, a fibrous inclusion which consists of a ceramic and has an average
diameter of 1 to 30 pm and an average aspect ratio of 10 to 500, and a particulate
inclusion which consists of a ceramic and has an average diameter of powder of 1 to
100 pm, an amount of the fibrous inclusion is 5 to 40 volume% relative to a volume of
the sintered body, and an amount of the particulate inclusion is 5 to 30 volume%
relative to the volume of the sintered body.
(2) In the composite rolling mill roll according to (I), a chemical
composition of the base metal of the sintered body may include: 0.8 to 3.5 wt% of C; 1
to 13 wt% of Cr; 0 to 18 wt% ofMo; 0 to 28 wt% ofW, 0 to 15 wt% ofNi; 0 to 18
wt% of Co; 2 to 20 wt% of one or more of elements in total, the elements being
selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and a remainder
including Fe and an impurity.
(3) In the composite rolling mill roll according to (1) or (2), the particulate
inclusion and the fibrous inclusion may be one or more of an oxide, a nitride, and a
carbide.
(4) In the composite rolling mill roll according to (3), the particulate
inclusion may be one or more of an alumina, a zirconia, a titania, a boron nitride, a
silicon nitride, and a zirconium nitride.
(5) In the composite rolling mill roll according to (3) or (4), the fibrous
inclusion may be one or more of the alumina, a mullite, the boron nitride, and the
silicon nitride.
(6) In tlie composite rolling mill roll according to one of (I) to (5), a total
amount of the particulate inclusion and the fibrous inclusion may be 35 to 70 volume%
relative to the volume of the sintered body.
(7) According to a second aspect of the present invention, there is provided a
composite rolling mill roll including: a steel roll shaft; and an outer layer provided
around the roll shaft, in which the outer layer includes a sintered body obtained by
sintering a mixture of (a) a powder of an iron alloy, (b) a ceramic fiber which has an
average diameter of 1 to 30 pm and an average aspect ratio of 10 to 500, and (c) a
ceramic powder which has an average diameter of powder of 1 to 100 pm, a blending
amount of (b) the ceramic fiber before the sintering is 5 to 40 volume% relative to a
total amount of (a) the powder of the iron alloy, (b) the ceramic fiber, and (c) the
ceramic powder before the sintering, a blending amount of (c) the ceramic powder
before the sintering is 5 to 30 volume% relative to the total amount of (a) the powder
of the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before the sintering,
and (b) the ceramic fiber and (c) the ceramic powder exist independently after the
sintering.
(8) In the composite rolling mill roll according to (7), a chemical
composition of (a) the powder of the iron alloy before the sintering may include: 0.8 to
3.5 wt% of C; 1 to 13 wt% of Cr; 0 to 18 wt% of Mo; 0 to 28 wt% of W, 0 to 15 wt%
of Ni; 0 to 18 wt% of Co; 2 to 20 wt% of one or more of elements in total, the elements
being selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and a remainder
including Fe and an impurity.
(9) In the composite rolling mill roll according to (7) or (8), (c) the ceramic
powder may be one or molt of an oxide, a nitside, and a carbide.
(10) In the composite rolling mill roll according to (9), (c) the ceramic
powder may be one or more of an alumina, a zirconia, a titania, a boron nitride, a
silicon nitride, and a zirconium nitride.
(11) In the composite rolling mill roll according to one of (7) to (lo), (b) the
ceramic fiber may be one or more of an oxide-type fiber, a carbide-type fibel; and a
nitride-type fiber.
(12) In the conlposite rolling mill roll according to one of (7) to (Il), a total
blending amount of (b) the ceramic fiber and (c) the ceramic powder before the
sintering may be 35 to 70 volume% relative to the total amount of (a) the powder of
the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before the sintering.
(13) According to a third aspect of the present invention, there is provided a
method for rolling including: rolling a metallic material with the composite rolling mill
roll according to one of (1) to (12).
(14) According to a fourth aspect of the present invention, there is provided
a method for manufacturing a composite rolling mill roll including an outer layer and a
roll shaft, the method including: mixing a powder of an iron alloy, a ceramic powder
having 1 to 100 pm of an average diameter of powder, and a ceramic fiber having 1 to
30 pm of an average diameter and 10 to 500 of an average aspect ratio to obtain a raw
mixture; and filling the raw mixture into a tubular capsule installed around the roll
shaft, then degassing inside of the capsule, and then sintering the raw mixture by hot
isostatic pressing under 70 to 120 MPa of a pressure to obtain the composite rolling
Inill roll in which the outer layer is joined around the roll shaft, in which a blending
amount of the ceramic fiber before the sintering is 5 to 40 volume% relative to the total
amount of the raw mixture before the sintering, and a blending amount of the ceralnic
powder before the sintering is 5 to 30 volume% relative to the total amount of the raw
mixtuse before the sintering.
[Effects of the Invention]
[0012]
According to the composite rolling mill roll of the present invention, as
compared to a FRM rolling mill roll of the related art (which is formed of a composite
of a powder of an iron alloy and a ceramic fiber, or a composite of a powder of an iron
alloy and a ceramic powder), the wear resistance and the resistance of deterioration for
roll surface are improved, and the cracking resistance can be maintained at the same
level as that of the FRM rolling mill roll of the related art. As a result, when the
composite rolling mill roll is used in a rolling, the life of the composite rolling mill roll
can be increased, the replacement cycle of the colnposite rolling mill roll can be
significantly increased, and not only improvement in unit consumption of a roll but
improvement in productivity and yield can be expected.
[Brief Description of the Drawing]
[0013]
FIG. 1 is a diagram illustrating a simultaneous sintering method which uses a
hot isostatic pressiug.
FIG. 2 is a flow chart illustrating a method for manufacturing a composite roll.
[Embodiments of the Invention]
[0014]
A composite rolling mill roll according to an embodiment of the present
invention is a coniposit roll in which an outer layer is provided outside (around) the
steel roll shaft (core). The outer layer is concentrically provided around the roll shaft,
and the thickness thereof is typically about 10 rnm to 100 nlm. An intermediate layer
may be formed between the roll shaft and the outer layer. The outer layer contains a
sintered body which is obtained by sintering a mixture of (a) a powder of an iron alloy,
(b) a ceramic fiber, and (c) a ceramic powder.
[0015]
It is preferable that the powder of the iron alloy according to the present
embodiment includes: 0.8 to 3.5 wt% of C; 1 to 13 wt% of Cr; 0 to 18 wt% of Mo; 0 to
28 wt% of W, 0 to 15 wt% of Ni; 0 to 18 wt% of Co; 2 to 20 wtYo of oue or more of
elements selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and a ~emainder
including Fe and an impurity. It is more preferable that the powder of the iron alloy
according to the present embodiment contain: 1.0 to 2.8 wt% of C; 2 to 10 wtYo of Cr;
Oto 15wt%ofMo;Oto20wt%ofW,Oto10wtY0ofNi;Oto 15wt%ofCo;3to 15
wt% of one or more of elements selected fiom a group consisting of V, Nb, Ti, Ta, Zr,
and Hf; and a remainder including Fe and an impurity. Hereinafter, the reason for
providing the chemical composition of the powder of the iron alloy will be described.
[0016]
(C: 0.8 to 3.5 wt%)
C is contained to form a carbide. The preferable upper limit of the C content
is 3.5 wtYo, and the preferable lower limit thereof is 0.8 wt%. When the C content is
less than the lower limit, the amount of precipitated carbide may be small, and the
wear resistance of the sintered body may not be sufficiently secured. When the C
content is greater than the upper limit, the carbide may not be uniformly dispersed in
the sintered body, which may cause a problem in the toughness and the resistance of
deterioration for roll surface of the sintered body. The C content is more preferably
1.0 to 2.8 wt%.
[0017]
(Cr: 1 to 13 wtYo)
Cr forms a Cr-based carbide and contributes improvement in the wear
resistance of the sintered body. In order to obtain the effect, the Cr content is
preferably 1 to 13 wt%. When the Cr content is greater than the upper limit, the
crystallization amount of a Cr-based carbide may be excessively increased, and the
toughness and the cracking resistance may be decreased. When the Cr content is less
than the lower limit, the hardenability may be decreased. The Cr content is more
preferably 2 to 10 wt%.
[0018]
(Mo: 0 to 18 wt%)
(W: 0 to 28 wt%)
In order to improve the hardenability and the high-temperature hardness of the
sintered body, it is preferable that Mo and W be contained in the sintered body.
Further, W may be contained as an element used to form a carbide. In order to obtain
the effect, the Mo content is preferably 0 to 18 wt%, and the W content is preferably 0
to 28 wt%. When the Mo content and the W content are greater than the upper limits,
the toughness and the resistance of deterioration for roll surface of the sintered body
may deteriorate. The Mo content is more preferably 0 to 15 wt%. The W content is
more preferably 0 to 20 wt%.
[0019]
(Ni: 0 to 15 wt%)
(Co: 0 to 18 wt%)
Ni is an element used to in~proveh ardenability. In order to obtain the effect,
the Ni content is preferably 0 to 15 wt%. When the Ni content is greater than the
upper limit, tlie amount of residual austenite in the sintered body may be increased, and
cracking and deterioration for roll surface during rolling may be likely to occur. By
Co being contained, advantageous effects are obtained in resistance to temper
softening and secondary hardening. In order to obtain the effects, the Co content is
preferably 0 to 18 wt%. Wlien the Co content is greater than the upper limit, the
hardenability may deteriorate. The Ni content is more preferably 0 to 10 wt%. The
Co content is more preferably 0 to 15 wt%.
[0025]
(one or more of elements selected from a group consisting of V, Nb, Ti, Ta, Zr, and HE
2 to 20 wt%)
V, Nb, Ti, Ta, Zr, and Hf form a MC carbide and contribute to improvement in
wettability between the melted iron alloy and the ceramic fiber. Further, V, Nb, Ti, Ta,
Zr, and Hf form a pro-precipitated carbide (carbide crystallized in c~ystagl rains) and
consume C. As a result, the crystallization amount of a secondary precipitated
carbide (carbide crystallized in grain boundaries) which is formed by binding between
C and Mo, Cr, or W is decreased. A carbide crystallized in grain boundaries may be
distributed in the sintered body in a network shape and may form a crack propagation
path, which may decrease the toughness and the resistance of deterioration for roll
surface of the sintered body. In order to obtain the effects, the total amount of one or
two or more elements selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf is
preferably 2 to 20 wt%. When the total amount of one or two or more elements
selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf is less than 2 wt%, the
crystallization amount of a MC carbide may be small, and the improvement of the
wear resistance may be insufficient. Moreover, a secondary precipitated carbide may
be likely to be crystallized in a network shape, which may adversely affect the
toughness and the resistance of deterioration for roll surface. In addition, when tlie
total amount of the elements is greater than the upper limit, a large pro-precipitated
carbide may be crystallized, which may cause deterioration for roll surface. The total
amount of one or two or more elements selected from a group consisting of V, Nb, Ti,
Ta, Zr, and Hf is more preferably 3 to 15 wt0/0.
[0021]
The powder of the iron alloy according to an aspect of the present
embodiment contains the above-described components and a remainder including Fe
and an impurity. For example, the impurity is impurities contained in raw materials
such as ore or scrap and impurities contained during manufacturing.
[0022]
The powder of the iron alloy contains a carbide ceramic component. When
the powder of the iron alloy is converted into the sintered body, this carbide ceramic
component improves the strength, the toughness, and the hardness of the sintered body
of the iron alloy to a sufficient level as a composite rolling mill roll. However, a
sintered body which is obtained using only the powder of the iron alloy does not have
sufficient performance as a composite rolling mill roll. In order to impart sufficient
performance to a sintered body, it is necessary that the ceramic fiber atid the ceramic
powder are mixed with the powder of the iron alloy to increase the ceramic content in
the sintered body.
[0023]
(Average Diameter of Powder of Iron alloy: 1 to 100 pm)
The average diameter of the powder of the iron alloy is 1 to 100 pm. When
the average diameter of the powder of the iron alloy is less than 1 pm, powders of the
iron alloy may aggregate with each other, and it may be difficult to sufficiently
suppress void defects during sinter molding. On the otlier hand, when the average
diameter of the powder of the iron alloy is greater than 100 pm, there is a concern that
gaps between ceramic portions derived from the ceramic powder and the ceramic fiber,
which are arranged around the powder of the iron alloy by being mixed with the
powder of the iron alloy, may be excessively widened. In this case, the properties of
the sintered body such as wear resistance, seizing resistance, and resistance of
deterioration for roll surface may deteriorate. The preferable average diameter of the
powder of the iron alloy is 5 to 50 pm
In the present embodiment, the term "the average diameter of the powder of
the iron alloy" refers to the diameter (median size) of an intermediate value
(cumulative value: 50%) in a cumulaiive diameter distribution curve which is
measured with a laser diffraction scattering method. As a measuring device, for
example, SALD-3 100 manufactured by Shimadzu Corporation is used.
[0024]
In the composite rolling mill roll according to the present embodiment, the
blending amount of (b) the ceramic fiber before sintering is 5 to 40 volume% relative
to the total amount of (a) the powder of the iron alloy, (b) the ceramic fibel; and (c) the
ceramic powder before sintering, and the blending amount of (c) the ceramic powder
before sintering is 5 to 30 volume% relative to the total amount of (a) the powder of
the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before sintering.
[0025]
(Blending Amount of Ceramic Fiber Before Sintering: 5 to 40 volume%)
When the blending amount of the ceramic fiber before sintering is less than 5
volume%, the wear resistance, the resistance of deterioration for roll surface, and the
cracking resistance required for the composite rolling mill roll are not sufficiently
obtained. On the other hand, when the blending amount of the ceramic fiber before
sintering is greater than 40 volume%, ceramic fibers are intertwined with each other
and fiber aggregation occurs. This fiber aggregation causes voids during sinter
fornling. Due to these voids, it is difficult to sufficiently suppress material defects.
Further, when the blending amount of the ceramic fiber before sintering is greater than
40 volume%, the resistance of deterioration for roll surface of the roll deteriorates.
This is because microvoid-like defects occur by aggregation of fiber. The blending
amount of the ceramic fiber before sintering is preferably 10 to 30 volume%.
[0026]
(Blending Amount of Ceramic Powder Before Sintering: 5 to 30 volume%)
When the blending amount of the ceramic powder before sintering is less than
5 volume%, the effects of improving the properties such as wear resistance, seizing
resistance, and resistance of deterioration for roll surface are not obtained as compared
to a composite rolling mill roll of the related art obtained by compositing only (b) the
ceramic fiber and (a) the powder of the iron alloy. On the other hand, when the
blending amount of the ceramic powder before sintering is greater than 30 volume%,
the mechanical properties such as toughness and cracking resistance, which are
required when the sintered body is used as an outer layer of a composite rolling mill
roll cannot be sufficiently ensured.
[0027]
(Total Blending Amount of Ceramic Fiber and Ceramic Powder Before Sintering: 35 to
70 volumeo/~)
The total blending amount of (b) the ceramic fiber and (c) the ceramic powder
before sintering is preferably 35 to 70 volume%. As a result, in the sintered body,
more preferably than the techniques of the related art, the mechanical properties such
as toughness and cracking resistance which are required for a composite rolling mill
roll can be ensured, and the tribological properties such as wear resistance and
resistance of deterioration for roll surface can be improved. When the total blending
amount is less than 35 volume%, it may be difficult to improve the tribological
properties such as wear resistance and resistance of deterioration for roll surface as
compared to the techniques of the related art. When the total blending amount is
greater than 70 volume%, the mechanical properties such as toughness and cracking
resistance which are required for a composite rolling mill roll may not be ensured.
Further, in order to sufficiently exhibit the effects of the present embodiment, it is
preferable that the total blending amount of (b) the ceramic fiber and (c) the ceramic
powder before sintering is 40 to 60 volume%.
[0028]
(Component of Ceramic Powder: One or More of Oxide, Nitride, and Carbide)
It is preferable that the ceramic powder be one or more elements selected
from an oxide, a nitride, and a carbide. As the oxide, for example, an alumina, a
zirconia, or a titania is preferably used. As the nitride, for example, a boron nitride, a
silicon nitride, a zirconium nitride, or a titanium nitride, is preferably used. As the
carbide, for example, a vanadium carbide, a chromium carbide, or a titanium carbide is
preferably used.
However, among carbides, a silicon carbide (Sic) and a boron carbide (B4C)
are not appropriate as the ceramic powder according to the present embodiment. This
is because Sic and B4C react with Fe in the powder of the iron alloy to form an alloy
during sintering. When the alloy is formed, the addition effects of these ceramic
powders deteriorate, and the wear resistance of the roll deteriorates. The present
inventors verified that, when powders of Sic and B4C are mixed with a ceramic fiber
and a powder of an iron alloy, a sintered body obtained from a mixed powder does not
have sufficient wearing resistance as a material of an outer layer of a composite rolling
mill roll even though the strength is slightly improved as compared to a case where the
powders are not added. However, when another metal is coated on the surfaces of the
powders of SiC and B4C by means of PVD, plating, or the like, this coating inhibits the
reaction of SiC and B4C with Fe, and thus, SiC and B4C can exhibit a capability of
improving the strength and the wear resistance of the sintered body. Accordingly, it is
necessary that the ceramic powder according to the present embodiment exists
independently after sintering. The expression "exist independently" implies that there
is substantially no case where the ceramic powder reacts with a surrounding base metal
to form a compound.
[0029]
(Average Diameter of Ceramic Powder: 1 to 100 pmn)
The average diameter of the ceramic powder is 1 to 100 pm. When the
average diameter of the ceramic powder is less than 1 pm, ceramic powders aggregate
with each other, and it may be difficult to sufficiently suppress void defects during
sinter molding. In order to reliably prevent the aggregation of the ceramic powder
portions, the lower limit of the average diameter of the ceramic powder may be 2 pm,
greater than 2 pm, 5 ptn, 15 pm, or 20 pm. On the other hand, when the average
diameter of the ceramic powder is greater than 100 pm, and when the obtained sintered
body is used as a composite rolling mill roll a particulate inclusion in the sintered body
caused by the ceramic powder may function as a propagation path, and the mechanical
properties of the composite rolling mill roll may deteriorate. In the present
embodiment, it is preferable that a ceramic powder having an average diameter of 3 to
50 pm be used.
The limitation of a powder shape by an aspect ratio is less common in this
technical field and the powder technology field. Typically, the term "powder" refers
to a particle having an aspect ratio of about 1 to 2 (when the shape of a powder is ovalspherical,
the ratio expressed by a quotient of long diameterlsho~dt iameter).
However, in the present embodiment, the specific numerical value of the aspect ratio of
the ceramic powder is not limited.
In the present embodiment, the term "the average diameter of the ceramic
powder" refers to the diameter (median size) of an intermediate value (cumulative
value: 50%) in a cu~nulatived iameter distribution curve which is measured with a laser
diffraction scattering method. As a measuring device, for example, SALD-3100
manufactured by Shimadzu Corporation is used.
[0030]
(Component of Ceramic Fiber: One or More of Oxide, Nitride, and Carbide)
It is preferable that the ceramic fiber be one or more of an oxide-type fiber, a
carbide-type fibel; and a nitride-type fiber. As the oxide-type fiber, the carbide-type
fiber, or the nitride-type fiber, for example an alumna fiber, a mullite fibel; a boron
nitride fiber, a silicon nitride fiber, or a SiBN3C fiber is preferably used.
ISowever, a silicon carbide (Sic) and a boron carbide (B4C) cannot be used as
a component of the ceramic fiber according to the present embodiment. The reason is
the same as the reason why these compounds cannot be used as a component of the
ceramic powder according to the present embodiment. Howevel; when another metal
is coated on the surfaces of the fibers of Sic and B4C by means of PVD, plating, or the
like, Sic and B4C can exhibit a capability of improving the strength and tlie wear
resistance of the sintered body. Accordingly, it is necessary that the ceramic fiber
according to the present embodiment exist independently afier sintering.
[003 11
(Shape of Ceramic Fiber: 1 to 30 pm ofAverage Diameter, 10 to 500 of Average
Aspect Ratio)
The average diameter of the ceramic fiber is 1 to 30 pm and preferably 3 to 15
pm. When the average diameter of the ceramic fiber is less than 1 pm, fibers are
intertwined with each other during manufacturing, and void-like defects unavoidably
occur. On the other hand, when the average diameter of the ceramic fiber is greater
than 30 pm, the surface rougliness of the composite rolling mill roll is increased with
the use of the composite rolling mill roll as a rolling mill roll, and deterioration for roll
surface is likely to occur due to the generation of excessive frictional heat.
The average aspect ratio of the ceramic fiber is 10 to 500 and more preferably
about 30 to 300. When the average aspect ratio of the ceramic fiber is less than 10,
the ceramic fiber cannot exhibit a function of fiber reinforcement. That is, only
substantially the same effects as those of a method for lnanufacturing in which only
ceramic particles are mixed with a powder of an iron alloy are obtained, and the effects
obtained by mixing the ceramic fiber and the ceramic powder cannot be obtained. In
this case, as in the case where a FRM rolling mill roll is manufactured using only a
powder of an iron alloy and a ceramic powder, there is a concern that the ceramic fiber
functions as a propagation path of cracks and cracks are likely to be propagated. On
the other hand, when the average aspect ratio of the ceramic fiber is greater 500, fibers
are likely to be intertwined with each other, and void-like defects unavoidably occur.
In the present embodiment, the average diameter and the average aspect ratio
of the ceramic fiber are obtained by the following means. First, 50 or more fiber
portions are randomly selected. Next, the fiber portions are observed with a
microscope to measure the diameters and lengths thereof. Then, the arithmetic mean
values of these measured values are obtained. The arith~neticm ean value of the
diameters of the ceramic fiber is the average diameter of the ceramic fiber, and a value
obtained by dividing the arithmetic mean value of the lengths of the ceramic fiber by
the arithmetic mean value of the diameters of the ceramic fiber is the average aspect
ratio of the ceramic fiber.
[0032]
As described above, the composite rolling mill roll according to the present
embodiment contains (a) the powder of the iron alloy, (b) the ceramic fiber, and (c) the
ceramic powder. The ceramic in the sintered body manufactured by the sinter
forming of the mixed powder includes a ceramic derived from the ceramic powder and
the ceramic fiber which are mixed as raw materials; and further includes a carbide
which is derived from the components of the powder of the iron alloy and is
precipitated or crystallized in portions derived from the powder of the iron alloy in the
sintered body. The carbide which is precipitated or c~ystallizedin portions derived
from the powder of the iron alloy is necessary to secure the strength, the toughness,
and the hardness of the sintered body which is obtained by the sinter forming of the
powder of the iron alloy. In the present embodiment, the sintered body includes the
carbide which is precipitated or crystallized in portions derived from the powder of the
iron alloy and further includes the ceramic derived from the ceramic fiber and the
ceramic powder. As a result, a composite rolling mill roll having higher tribological
properties such as wear resistance and resistance of deterioration for roll surface and
higher mechanical properties, such as cracking resistance and strength, than those of
the related art can be realized.
[0033]
The composite rolling mill roll according to the present embodiment can be
manufactured with the following method illustrated in FIG. 2. That is, a composite
rolling mill roll in which an outer layer is provided around a roll shaft can be obtained
by:
(1) mixing (a) a powder of an iron alloy, (b) a ceramic powder having 1 to 100
pm of an average diameter, and (c) a ceramic fiber having an average diameter of 1 to
30 pm and an average aspect ratio of 10 to 500 to obtain a raw mixture in mixing; and
(2) filling the raw mixture into a tubular capsule installed around the roll shaft,
then degassing the inside of tlie capsule, and then sintering the raw mixture by hot
isostatic pressing under 70 to 120 MPa of pressure in hot isostatic pressing.
The mixing order of the powders and the fiber which are the raw materials is
not limited as long as a sufficient mixing time is secured. For example, (b) the
ceramic fiber may be mixed with a mixture of (a) tlie powder of the iron alloy and (c)
the ceramic powder. Alternatively, (c) the ceramic powder may be mixed with a
mixture of (a) the powder of the iron alloy and (b) the ceramic fiber.
[0034]
Hereinafter, the above-described method for manufacturing will be described
in detail.
For example, the outer layer of the composite rolling mill roll according to the
present embodiment is manufactured by filling the raw mixture into a tubular soft steel
capsule, mounting and welding a soft steel lid (to which a degassing pipe is connected)
on the capsule to seal the capsule, degassing through the degassing pipe to vacuum seal,
and then, sintering the raw mixture by hot isostatic pressing (HIP). The material of
the capsule is a soft steel plate having about 2 to 10 mm of a thickness. The capsule
is formed around the roll shaft such that the shape of the sintered body after hot
isostatic pressing is a shape having a sufficient finishing allowance to be worked into a
desired shape of the outer layer of the roll. In addition, the capsule shape is
determined in consideration of the defonnation of the sintered body during hot isostatic
pressing. When the capsule is provided around the roll shaft to manufacture the
composite rolling mill roll (that is, a simultaneous sintering method with the roll shaft),
the roll shaft and the capsule are joined by welding or the like such that the powders
and the fiber as the raw materials do not leak.
[0035]
FIG. 1 is a diagram illustrating a simultaneous sintering method which uses
hot isostatic pressing. A tubular iron capsule 2 is welded on an outer circumference
of a roll shaft 1. A raw mixture 4 which is a mixture of the powder of the iron alloy,
the ceramic fiber, and the ceramic powder is filled into a filling space formed by the
roll shaft 1 and the capsule 2. A lid 3 is installed to the capsule 2. The periphery of
the lid 3 is welded (welding portion 6). Degassing is perfomed (reference numeral 5
represents a degassing port). Vacuum sealing is performed, followed by hot isostatic
pressing. The raw mixture 4 in the capsule 2 is sintered by hot isostatic pressing and
is metallurgically joined with the roll shaft at the same time.
[0036]
In order to obtain a composite rolling mill roll having a sufficient strength, it
is necessary that the sinter forming of the outer layer be performed by hot isostatic
pressing under 70 MPa or higher of a pressure. If a sufficient pressure is not applied,
voids are initiated in the sintered body, and the strength of the outer layer (sintered
body) is decreased. The lower limit of the pressure during hot isostatic pressing is
preferably 85 MPa.
The upper limit of the pressure during hot isostatic pressing does not need to
be limited. However, in consideration of facility capacity, the upper limit of the
pressure during hot isostatic pressing is typically 120 MPa.
[0037]
The sintered body formed with a sintering method may be treated with
selecting heat treatment condition and polishinglgrinding condition depending on the
components of the powder of the iron alloy and the usage conditions of the roll such
that the required hardness and the surface roughness are obtained.
[0038]
The outer layer of the composite rolling mill roll according to the present
embodiment, which is obtained using the above-described materials and the abovedescribed
method for manufacturing, includes a sintered body including a base metal
which is an iron alloy, a fibrous inclusion which consists of a ceramic and has an
average diameter of 1 to 30 pm and an average aspect ratio of 10 to 500, and a
particulate inclusion which consists of a ceramic and has an average diameter of 1 to
100 pm. The amount of the fibrous inclusion is 5 to 40 volume% relative to a volume
of tlie sintered body, and the amount of the particulate inclusion is 5 to 30 volume%
relative to the volume of the sintered body.
The base metal which is the iron alloy is derived fio~nth e powder of the iron
alloy, the fibrous inclusion is derived ffom the ceramic fiber, and the particulate
inclusion is derived from the ceramic powder. The ceramic powder and the ceramic
fiber exist independently in tlie sintered body as the particulate inclusion and the
fibrous inclusion. Accordingly, the ceramic powder and the ceramic fiber do not
form a compound with the powder of the iron alloy. Depending on the setting
temperature during sintering, a conipound may be formed, but the amount thereof is
very sniall. Accordingly, the chemical compositions of the base metal, the fibrous
inclusion, and the particulate inclusion are substantially the same as those of the
powder of the iron alloy, the ceramic fiber, and the ceramic powder, respectively.
Further, the shapes of the fibrous inclusion and the particulate inclusion are
substantially the same as those of tlie ceermic fiber and the ceramic powder,
respectively. Accordingly, the preferable shapes of the fibrous inclusion and the
particulate inclusion are substantially the same as those of tlie ceramic fiber and the
ceramic powder, respectively.
The chemical composition of the base metal of the sintered body of the
composite rolling mill roll according to the present embodiment may include: 0.8 to
3.5 wt% of C; 1 to 13 wt% of Cr; 0 to 18 wt% of Mo; 0 to 28 wt% of W, 0 to 15 wt%
of Ni; 0 to 18 wt% of Co; 2 to 20 wt% of one or more of elements in total, the elements
being selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf, and a remainder
including Fe and an impurity. More preferably, the chemical composition of the base
metal of the sintered body of the composite rolling mill roll according to the present
embodiment may include: 1.0 to 2.8 wt% of C; 2 to 10 wt% of Cr; 0 to 15 wt% of Mo;
0 to 20 wt% of W, 0 to 10 wt% of Ni; 0 to 15 wt% of Co; 3 to 15 wt% of one or more
of elements selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf, and a
remainder including Fe and an impurity. The particulate inclusion and the fibrous
inclusion may be one or more of an oxide, a nitride, and a carbide. The particulate
inclusion may be one or more of an alumina, a zirconia, a titania, a boron nitride, a
silicon nitride, and a zirconium nitride. The fibrous inclusion may be one or more of
the alumina, a mullite, the boron nitride, and the silicon nitride. Further, the shapes
and the amounts of the ceramic fiber and the ceramic powder are substantially the
same as those of the fibrous inclusion and the particulate inclusion, respectively. The
total amount of the particulate inclusion and the fibrous inclusion according to the
present embodiment may be 35 to 70 volume% relative to the volume of the sintered
body. Tile effects of the present embodiment obtained by the above-described
configurations are the same as the effects obtained by selecting the raw materials to
obtain the above-described configurations.
[0039]
The sintered body of the composite rolling mill roll includes the ceramic
derived from the ceramic fiber and the ceramic powder and further includes the carbide
derived from the powder of the iron alloy. The carbide exists in the sintered body as a
mixture of carbides of the respective elements contained in the powder of the iron alloy.
Accordingly, the ceramic derived from the ceramic fiber and the ceramic powder and
the carbide derived from the powder of the iron alloy can be identified by analyzing
the components thereof. Specifically, in a case where a target is analyzed with a
device, such as EPMA, capable of local analysis, when the target is a ceramic which is
a composite carbide including Fe, Cr, Mo, and W, the target can be identified as the
carbide derived from the powder of the iron alloy. Typically, the average diameter of
the carbide derived from the powder of the iron alloy is about 0.1 to 2 pm, but varies
depending on the temperature and the time of hot isostatic pressing and the conditions
of the subsequent heat treatment which is optionally performed.
[0040]
(Rolling Method)
Using the composite rolling mill roll obtained in the present embodiment, a
metal material can be rolled. That is, the composite rolling mill roll according to the
present embodiment can be desirably used not only as a hot rolling mill roll for thin
steel strip, but also as a tool for hot working such as seamless processing, wire rolling,
hot pressing, or forging, a cold rolling mill roll for thin steel strip, and a tool for cold
working. In addition, the composite rolling mill roll according to the present
embodiment as a material having high wear resistance can be applied to rollers and
guides surrounding a rolling mill.
Examples
[0041]
Using raw materials and methods described below, various composite rolling
mill rolls according to Examples and Comparative Examples were prepared, and
properties thereof were evaluated.
[0042]
(Used Raw Materials)
As the powder of the iron alloy, a powder including 2.1 wt% of C, 4.8 wt% of
Cr,6.0wt'YoofV,5.1 wt%ofMo,4.5wt%ofW, 1.3wt%ofSi,O.9wt'YoofMn,anda
remainder substantially including Fe an impurity was used. As the average diameter
of the powder of the iron alloy, several diameter were selected and used in a range of
0.5 to 125 pm. As the ceramic powder, an alumina powder, a Sic powder, a B4C
powder, and a silicon nitride powder whose average diameter were selected in a range
of 0.7 to 125 pm were used. As the ceramic fiber, an alumina fiber (average
diameter: 0.8 to 3.6 pm, average aspect ratio: about 8 to 603), a silicon nitride fiber
(average diameter: 10 pm, average aspect ratio: 105), a Sic fiber (average diameter: 8
pm, average aspect ratio: 89), and a B4C fiber (average diameter: 7 pm, average aspect
ratio: 95 were used.
[0043]
(Preparation of Composite Roll)
Using the above-described powders and fibers, composite rolling mill rolls
(diameter: 11 0 mm, body length: 300 mm) were prepared according to the blending
amounts shown in Tables 1 and 2. An iron capsule as a molding die was provided
around a roll shaft (Cr-Mo steel). Araw mixture of the powder of the iron alloy, the
ceramic powder, and the ceramic fiber shown in Tables 1 and 2 was filled into the
capsule. The raw mixture of the powder of the iron alloy, the ceramic powder, and
the ceramic fiber was obtained by sufficiently mixing the powder of the iron alloy with
the ceramic powder and then further mixing the ceramic fiber therewith. The mixing
was performed with a rotary ball mill. Next, a lid of the capsule was welded, and the
inside of the capsule was degassed, followed by hot isostatic pressing at 1050°C under
60 MPa to 120 MPa of a predetermined pressure. After cooling, the capsule was
removed and a heat treatment of hardening and tempering under conditions close to
heat treatment conditions for a tool material on which a composition is similar to the
iron alloy component such that the Shore hardness was about 85 to 90.
[0044]
(Hot Coil Rolling Experiment)
When 4000 m of rolled coil of common steel was rolled using each of the
composite rolling mill rolls prepared as above in a hot coil rolling experiment, the
depth of wear, the crack depth, and the surface roughness of the composite rolling mill
roll were measured. The measurement methods are as follows.
Defects of sintered body: Whether or not defects occurred was checked by
ultrasonic inspection. A sample where defects were observed was evaluated as "Bad"
Depth of wear: The depth of wear was measured from a difference of a roll
profile before and after rolling. A sample where the depth of wear was greater than or
equal to 15 pm was evaluated as "Bad".
Crack depth: The roll after rolling was cut to observe the vicinity of a roll
surface, and the maximum depth of cracks was considered as the crack depth. A
sample where the crack depth was greater than or equal to 100 pm was evaluated as
"Bad".
Surface roughness: The arithmetic average roughness (center line average
roughless) Ra was measured. The measurement method was performed according to
JIS B0601. A sample where the surface roughness was greater than or equal to 0.8
pmRa was evaluated as "Bad".
With the above-described measurement methods, the composite rolling mill
rolls were evaluated. A sample which passed all the measurements was evaluated as
a passed product (Good).
Hot coil rolling experiment conditions were 800°C of a heating temperature,
100 dmin of a rolling speed, 1 kgf7mtn2 of a entry-side tension, 3 kgf/mm2 of an exitside
tension, 43% to 46% of a rolling reduction, and no lubricating oil.
The results are shown in Tables 1 and 2.
[Table 11
[Table 21
100451
Since Comparative Examples 1 to 17 were out of the limited ranges according
to the present invention, the depth of wear, the crack depth, and/or the surface
roughness was decreased.
Contrary to Comparative Examples, in Examples which were manufactured
within the limited ranges according to the present invention, the wear resistance was
high and defects such as voids caused by aggregation wliich was likely to occur during
sinter forming did not occur. Further, in Examples, the surface roughness of the roll
after rolling was small, the resistance of deterioration for roll surface was satisfactory,
and the crack propagation depth was small. That is, in Examples, as compared to the
techniques of the related art, the tribological properties such as wear resistance and
resistance of deterioration for roll surface can be improved while maintaining and
improving the mechanical properties. In addition, the following was found: when the
blending amount of the alumina fiber was greater than the limited blending amount
according to the present invention, defects occurred during manufacturing; and when
the blending amount of the ceramic fiber was less than the limited blending amount
according to the present invention, the effects of improving the wear resistance and the
resistance of deterioration for roll surface were not able to be obtained. It was found
that, when the blending amounts of the ceramic fiber and the ceramic powder were
increased within the ranges according to the present invention, the composite rolling
mill roll exhibited higher performance.
It can be seen from the above-described results that, by using the composite
rolling mill roll according to the present invention, the wear resistance can be
significantly improved, the surface roughness can be maintained at a low level, the
resistance of deterioration for roll surface can be improved, and the crack depth can be
maintained at the same level as that of a FRM roll of the related art.
[Industrial Applicability]
[0046]
According to the composite rolling mill roll of the present invention, as
compared to a FRM roll of the related art, the wear resistance and the resistance of
deterioration for roll surface can be improved, and the accident resistance can be
maintained at the same level. As a result, the replacement cycle of the composite
rolling mill roll can be significantly increased, and not only improvement in unit
consumption of a roll but improvement in productivity and yield can be expected.
[Brief Description of the Reference Symbols]
[0047]
1: ROLL SHAFT
2: CAPSULE
3: LID
4: RAW MIXTURE
5: DEGASSING PORT
6: WELDING PORTION
S1: MIXING
S2: HOT ISOSTATIC PRESSING

[Document Type] CLAIMS
[Claim 1]
A composite rolling mill roll comprising:
a steel roll shaft; and
an outer layer provided around the roll shaft, wherein
the outer layer includes a sintered body including a base metal which is an
iron alloy, a fibrous inclusion which consists of a ceramic and has an average diameter
of 1 to 30 pm and an average aspect ratio of 10 to 500, and a particulate inclusion
which consists of a ceramic and has an average diameter of 1 to 100 pm,
an amount of the fibrous inclusion is 5 to 40 volume% relative to a volume of
the sintered body, and
an amount of the particulate inclusion is 5 to 30 volume% relative to the
volume of the sintered body.
[Claim 2]
The composite rolling mill roll according to claim 1, wherein
a chemical composition of the base metal of the sintered body comprises:
0.8 to 3.5 wt% of C;
1 to 13 wt% of Cr;
0 to 18 wt% of Mo;
0 to 28 wt% of W,
0 to 15wt%ofNi;
0 to 18 wt% of Co;
2 to 20 wt% of one or more of elements in total, the elements being selected
from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and
a remainder including Fe and an impurity.
[Claim 3]
The composite rolling mill roll according to claim 1 or 2, wherein
the particulate inclusion and the fibrous inclusion are one or more of an oxide,
a nitride, and a carbide.
[Claim 4]
The composite rolling mill roll according to claim 3, wherein
the particulate inclusion is one or more of an alumina, a zirconia, a titania, a
boron nitride, a silicon nitride, and a zirconium nitride.
[Claim 5]
The composite rolling mill roll according to claim 3 or 4, wherein
the fibrous inclusion is one or more of the alumina, a mullite, the boron nitride,
and the silicon nitride.
[Claim 6]
The composite rolling mill roll according to one of claims 1 to 5, wherein
a total amount of the particulate inclusion and the fibrous inclusion is 35 to 70
volume% relative to the volume of the sintered body.
[Claim 7]
A composite rolling mill roll comprising:
a steel roll shaft; and
an outer layer provided around the roll shaft, wherein
the outer layer includes a sintered body obtained by sintering a mixture of (a)
a powder of an iron alloy, (b) a ceramic fiber which has an average diameter of 1 to 30
pm and an average aspect ratio of 10 to 500, and (c) a ceramic powder which has an
average diameter of 1 to 100 pm;
a blending amount of (b) the ceramic fiber before tlie sintering is 5 to 40
volume% relative to a total amount of (a) the powder of the iron alloy, (b) the ceramic
fiber, and (c) the ceramic powder before the sintering;
a blending amount of (c) the ceramic powder before the sintering is 5 to 30
volume% relative to the total amount of (a) the powder of the iron alloy, (b) the
ceramic fiber, and (c) the ceramic powder before the sintering; and
(b) the ceramic fiber and (c) the ceramic powder exist independently after the
sintering.
[Claim 8]
The composite rolling mill roll according to claim 7, wherein
a chemical composition of (a) the powder of the iron alloy before the sintering
comprises:
0.8 to 3.5 wt% of C;
1 to 13 wt% of Cr;
Oto18wt%ofMo;
0 to 28 wt% of W,
0 to 15 wt% of Ni;
0 to 18 wt% of Co:
2 to 20 wt% of one or more of elements in total, the elements being selected
from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and
a remainder including Fe and an impurity.
[Claim 9]
The conlposite rolling mill roll according to claim 7 or 8, wherein
(c) the ceramic powder is one or more of an oxide, a nitride, and a carbide.
[Claim 10]
The composite rolling mill roll according to claim 9, wherein
(c) the ceramic powder.is one or more of an alumina, a zirconia, a titania, a
boron nitride, a silicon nitride, and a zirconium nitride.
[Claim 11]
The composite rolling mill roll according to one of claims 7 to 10, wherein
(b) the ceramic fiber is one or more of an oxide-type fiber, a carbide-type fiber,
and a nitride-type fiber.
[Claim 12]
The composite rolling mill roll according to one of claims 7 to 11, wherein
a total blending amount of (b) the ceramic fiber and (c) tlie ceramic powder
before the sintering is 35 to 70 volume% relative to the total amount of (a) the powder
of the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before the sintering.
[Claim 13]
A method for rolling comprising:
rolling a metallic material with the composite rolling mill roll according to
one of the claims 1 to 12.
[Claim 14]
A method for manufacturing a composite rolling mill roll including an outer
layer and a roll shaft, the method comprising:
mixing a powder of an iron alloy, a ceramic powder having an average
diameter of 1 to 100 pin, and a ceramic fiber having an average diameter of 1 to 30 pm
and an average aspect ratio of 10 to 500 to obtain a raw mixture; and
filling the raw mixture into a tubular capsule installed around the roll shaft,
then degassing inside of the capsule, and then sintering tlie raw mixture by hot isostatic
pressing under 70 to 120 MPa of a pressure to obtain the composite rolling mill roll in
which the outer layer is joined around tlie roll shaft; wherein
a blending amount of the ceramic fiber before the sintering is 5 to 40
volume% relative to the total amount of the raw mixture before the sintering; and
a blending amount of the ceramic powder before the sintering is 5 to 30
volume% relative to the total amount of the raw mixture before the sintering.