DESCRIPTION
HEARTH ROLL AND MANUFAC'fURlNG METHOD THEREFOR
Technical Field
[0001] The present invention relates to a hearth roll and a method of prodocing the same.
Background Art
[0002] In metal sheet production facilities, especially in steelmaking process lines,
phenomeaa, such as slipping or meandering of a steel sheet and fouling or build-up on
surfaces of conveyor rolls, occur when a steel sheet is couveyed by high speed rotation of
conveyor rolls. Especially, since hearth lulls for continuous annealing furnaces convey a
steel sheet in a high temperature state, the build-up tends to occur on surfaces ofhearth rolls.
The build-up is a phenomenon in which matters, such as iron or manganese oxide, on a
surface of a steel sheet attach to surfaces of health rolls and grow. As the build-up proceeds,
contaminating objects adhering to the surfaces of hearth rolls gradually grow, and fonn, for
example, projections having diameters of about 100 pm. As a result, protruding shapes of
the matters attaching to the surfaces of hearth rolls are transferred to the surface of the steel
sheet, to generate recess-shaped defects (referred to as "transferred defects" or "picked-up
defects"), as a result of which the quality of the steel sheet deteriorates, and, in addition,
removal of matters attaching to roll surfaces is necessary at periodic maintenance, which is a
factor that decreases the productivity.
[0003] In view of these, various proposals have been made with respect to means for
suppressing attachment of contaminating objects to hearth roll surfaces, and, in particulal;
many of them relate to itnprovement of the material of a thermally sprayed coating on the
surfaces of hearth rolls.
[0004] For example, Japanese Patent (JP-B) No. 3234209 discloses a method for producing
a sliding member, the method enabling formation a sliding surface having superior
anti-sticking properties. This method includes: irradiating a thermally sprayed coating
provided on a base with a laser beam in a pattern such as in dots or in lines, thereby partly
modifying the coating by heating artd strtictoral changes in parts of the coating; and causing
laser-irradiated areas or laser-non-irradiated areas to be depressed to fonn oil pools, b):
mainly, selective abrasion during finishing processing or sliding.
[0005] Fo~thel;J apanese Patent Application Laid-Open (JP-A)N o. 2013-95974 discloses a
method for forming a densified layer in a thermally sprayed coating, the method including
irradiating the surface of a thermally sprayed coating with a high energy beam, thereby
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causing remelting and resolidification of a coating coltlposition in a surface layer of the
thermally sprayed coating and thereby detlsifying the surface layer.
[0006] Howevel; even by utilizing the techniques disclosed in JP-B No. 3234209 and JP-A
No. 2013-95974, it is difiicult to sufficiently suppress the occurrences of the build-up on the
surfaces of health rolls, and fitrther impmvetnerlts in build-up resistance have been desired.
SUMMARY OF INVENTION
[0007] Embodiments in the present specification mainly aim to provide a hearth roll capable
of suppressing attachment of contaminating objects to its roll surface during conveyance of a
sheet, and a method of producing the hearth roll.
[0008] According to an aspect in the present specification, a hearth roll is provided which
includes a base roll, a thermally sprayed coating fonned on the base roll, and a modified
coating formed on the thennally sprayed coating, the modified coating being formed by
modifying a part or the whole of a surface ofthe thermally sprayed coating by melting and
solidification of the thermally sprayed coating, by irradiating a part or the whole of the
surface ofthe thermally sprayed coating with an energy beam,
the thickness of the modified coating being from 2 to 20 pm, and
the Vickers hardness HV of the modified coating being from 1.2 to 1.4 times larger
than the Vickers hardness HV of the thermally sprayed coating.
[0009] According to atlother aspect of the present specification, a method of producing a
hearth roll is provided, the method including a step of irradiating a pact or the whole of a
surface of a thermally sprayed coating formed on a base roll with at1 energy beam, thereby
modifying a part or the whole of the thermally sprayed coating by melting and solidification
of the thermally sprayed coating, to fonn a modified coating having a thickness of from 2 to
20 pin and a Vickers hardness HV that is from 1.2 to 1.4 times larger than the Vickers
hardness HV of the thermally sprayed coating.
BRIEF DESCRIPTION OF DRAWINGS
[OOIO] Figare 1 is a schematic diagram illustrating an example of a continoous atlnealing
furnace according to a first embodiment of the present specification.
Figore 2A is a perspective vie\\? and an enlarged partial cross-sectional view
illustrating a hearth roll for a colltilluous annealing furnace according to the first embodiment.
Figure 2B is a perspective view and an enlarged partial cross-sectional view
illustrating a hearth roll for a continuous annealing furnace according to the first embodiment.
Figore 3A is an enlarged partial cross-sectional view illustrating a health roll for a
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continuoils annealing fnrnace according to the first embodiment.
Figure 38 is an enlarged partial cross-sectional view illustrating a health tnll for a
continnous annealing fi~rnacea ccording to the first embodiment.
Figure 4 is an exatnple of a scanning electron microscope (SEM) ~nicrograph of a
thermally sprayed coating and a modified coating of a hearth l u l l for a continuous annealing
furnace according to the first embodiment.
Figure 5 is a flowchart illustrating an exa~npleo fa process flow ofa method of
producing a hearth roll for a continuous annealing furnace according to the first embodiment.
Figure 6 is a sche~naticd iagram illustrating a method of producing a hearth roll for a
continnous annealing fi~rnacea ccording to the first embodiment.
DESCRIPTION OF EMBODIMENTS
1001 I ] According to an aspect ofthe invention:
( I ) A hearth mll is provided which includes:
a base roll;
a thermally sprayed coating formed on the base roll; and
a modified coating fornied on the thermally sprayed coating, the modified coating
being formed by modifying a part or the whole of a surface of the thermally sprayed coating
by melting and solidification of the thermally sprayed coating, by irradiating a part or the
whole of the surface of the thermally sprayed coating with an energy beam,
the thickness of the modified coating being ftom 2 to 20 pm, and
the Vickers hardness W of the modified coating being from 1.2 to 114 times larger
than the Vickers hardness HV of the thermally sprayed coating.
[0012] (2) In the hearth roll according to ( I ) , preferably, cracks are present on a surface of
the modified coating, and the average spacingbehveen adjacent cracks in a cross-section of
the hearth roll cut in the thickness direction is fi.om 10 to 100 pn, and the opening widths of
the cracks are less than 5 pm
[0013] (3) In the hearth roll according to ( I ) or (2), preferably, the modified coating includes
from 0.5 to 2% by mass of oxygen.
[0014] (4) In the health roll according to any one of (1) to (3), preferably;AlzO, is present in
a dispersed state in a surface of the modified coating, and the proportion of the area ofA120,
in the surface of the modified coating is fiom 5 to 40%.
1001 51 (5) The health roll according to any one of ( I ) to (4) preferably fin-ther includes a
chromium oxide layer formed on the modified coating, or on the modified coating and the
thermally sprayed coating.
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[0016] (6) In the health roll according to any one of (1) to (5), preferabl): the ther~nally
sprayed coating is a cermet coating consisting of a heat-resistant alloy and a cera~nic,
wherein the ceramic including, in tenns of% by volume, Cr3C2 at fro111 50 to 90%,
AI2O3 at from 1 to 40%, Yz03 at frotn 0 to 3%, and ZrB2 at ftom 0 to 40%, and the balance
being cotnposed of impurities and pores,
the heat-resistant alloy including, in tenns of % by rnass, Cr at froin 5 to 20%, Al at
from 5 to 20%, and at least one of Y o? Si at from 0.1 to 6%, and the balance being co~nposed
of at least one of Co or Ni and itnpurities, and
from 50 to 90% by volume of the cermet coating being the ceramic, and the balance
being the heat-resistant alloy.
[0017] (7) In the hearth roll according to (6), preferably, the heat-resistant alloy further
includes, in terms of % by tnass, at least one of Nb at from 0.1 to 10% or Ti at ftom 0.1 to
10%.
[0018] According to another aspect of the invention:
(8) A niethod of producing a hearth roll is provided which includes a step of
irradiating a pait or the whole of a surface of a therlnally sprayed coating fonned on a base
roll with an energy beam, thereby modifying a part or the whole of the surface of the
thermally splayed coating by melting and solidification of the thermally sprayed coating, to
form a modified coating having a thickness of fiotn 2 to 20 pm and a Vickers hardness HV
that is from 1.2 to 1.4 times larger than the Vickers hardness HV of the thennally sprayed
coating.
[0019] (9) In the method of producing a health roll according (8), preferably, irradiation with
the energy beam is performed in the attnosphere.
[0020] (10) In the lnetllod of producing a hearth roll according to (8) or (9), preferably, a
chromate treatment is performed after the modified coating is fonned.
[0021] Favorable embodiments it1 the present specification will be described in detail below;
with refereuce to the attached drawings. In the present specification and the drawings,
elen~entsh aving substantially the same function and structure are denoted by the same
reference character, and repeated explanation thereof is omitted.
[0022] (Configuration of Continuous Annealing Furnace)
First, a continuous annealing filmace to which the health roll for a continuous
annealing furnace according to a first embodiment of the present specification is applied is
described with reference to Figure 1.
[0023] As illushated in Figure 1, a continuous annealing furnace 1 is niachinery configured
to continuously anneal a strip-shaped steel sheet 2 in order to adjust the mechanical properties
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(such as hardness) of the steel sheet 2 produced in a cold rolling process. The continuous
annealing furnace I applies a heat cycle including heating, soaking, cooling, and the like to
the steel sheet 2 as the steel sheet 2 passes through sections beheen plural rolls placed in the
fi~rnace, thereby continuously subjecting the steel sheet 2 to continuous annealing. Here, the
steel sheet 2 is an example ofa metal strip that is to be annealed, and is, for example, a thin
sheet that has been cold rolled by couti~n~oucos ld-rolling machinery not shown in the figure
(for example, a cold-rolled strip-shaped steel sheet having a sheet thickness of from 0.14 tnm
to 3.2 mm). The metal strip is not limited with respect to its material, insofar as the metal
strip is a strip-shaped metal material (metal strip) that is to be annealed.
[0024] As illustrated in Figure I , the continuous annealing furnace 1 includes, for example,
a heating zone 3, a soaking zone 4, a primary cooling zone 5, an overaging zone 6, and a
secondary cooling zone 7 disposed in this order from the entty-side. The continuous
annealing furnace 1 continuously anneals the steel sheet 2 while conveying the steel sheet 2
using plural hearth rolls 10 for a continuous annealing fiirnace provided in each zone.
Although not illustrated in the figure, the upstreatn of the heating zone 3 is provided with, for
example, a pay-off reel, a sheaf; an entry-side cleaniug apparatus, an entry-side looper and the
like, and the downstream of the secondary cooling zone 7 is provided with, for example, a
water cooling tank, a skin pass roll, an exit-side loopel; a triminel; a coiler and the like.
[0025] The heating zone 3 heats the steel sheet 2 to a high temperature of, for example, from
700 to 900°C by using a heatiug method such as direct-fired oxidation-free heating or
radiation tube heating. The soaking zone 4 conducts heat treatment to maintain the steel
sheet.2 at a prescribed temperature, using a heating method such as radiation tube heating or
indirect electric heating. The primary cooling zone 5 rapidly cools the steel sheet 2, using a
cooling method such as roll contact cooling, gas jet cooling or mist cooling. The overaging
zone 6conducts overagiug treatment in \vhich the steel sheet 2 is maintained at a prescribed
temperature for a prescribed time period (for example, at from 300 to 400°C for 3 min) by
using, for example, an electric heater. Fu~tI~etlh;e seconda~yc ooling zone 7 cools the steel
sheet 2 after the overaging treatment, using any of the various cooling systems described
.above.
[0026] As described above, the continuous annealing fi~rntice I adjusts the mechanical
properties of the steel sheet 2 by applying a prescribed heat cycle to the steel sheet 2 by
causing the steel sheet 2 to continuously pass through the plural furnaces. In this process,
the heat cycle is set so as to satisfy the annealing conditions that are in accordance with the
quality ofthe steel sheet to be produced (such as a high-tensile steel sheet, a general
cold-rolled steel sheet, a tin-plated steel sheet, or a steel sheet for drawing).
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LO0271 (Configuration of I-lea~thR oll)
. ~ Next, thehearth roll for a continuous annealing furnace according to the present
embodiment will be described with reference to Figure 2A to Figure 4.
[0028] As illustrated in Figure 2A, the hearlh roll 10 for a continuous annealing fi~rnace
(hereinafter also referred to simply as "health roll 10") includes a roll shaft 12 and a roll barrel
14 mounted on the l u l l shaft 12. The health roll 10 has a roll width that is greater than the
width ofthe steel sheet 2 supplied into the continuous an~~ealitflugr nace 1, and the roll width
ofthe roll barrel 14 is, for example, from about 1,000 mm to about 2,500 mm, and the roll
diameter 4 ofthe roll barrel 14 is, for example, from about 600 mtn to about 1,000 mm. The
hearth roll 10 is a drive roll, and functions as a steel sheet conveyor roll configured to convey
the steel sheet 2 in the continuons antlealing furnace 1. More specifically, when the
circumferential surface of the roll barrel 14 (hereinafter sometimes also referred to as "roll
circumferential surface") contacts the steel sheet 2 while the health roll 10 rotates around the
roll shaft 12, the hearth roll 10 conveys the steel sheet 2 while changing the travelling
directiot~o f the steel sheet 2 wound around the roll barrel 14 at a prescribed winding angle.
[0029] Furthel; as illustrated in Figure 2A, the roll barrel 14 of the hearth roll 10 includes a
base roll 20, a thermally sprayed coating 21 fonned on the surface of the base roll 20, and a
modified coating 22, which is the outermost coating formed on the surface of the thermally
splayed coating 21. Further, as illustrated in Figure 2B, an undercoat layer 24 may be
formed between the base loll 20 and the thermally sprayed coating 21, if necessary, by
undercoat thermal spraying of only a heat-resistant alloy, in order to prevent separation due to
a difference in thermal expansion coefficients.
[0030] The base roll 20 is made of a metal such as steel and configures the basic shape of
the hearth roll 10. For the base roll 20, for example, stainless-steel-based heat-resistant cast
. steel is used, and, pa~ticularly, SCH22 is most suitable. The base roll 20 is subjected to
coating treatment such as thermal spraying. In the present embodiment, a thennally sprayed
coating 21 is formed on the surface of the base roll 20, and a modified coating 22 is fi~rther
. . formed on the surface of the thennally sprayed coating 21.
. ' [0031] The thermally sprayed coating 21 is formed'by thennal spraying of a thermal spray
. ~ '. material onto the surface of the base roll 20, the ther~iials pray material being a material in
which a heat-resistant alloy and a ceratnic are combined (cermet material). The material of
the thermally sprayed coating 21 will be described in detail below. Although the thickness
ofthe thennally sprayed coating 21 (thiclu~essd l in Figure 3A) is not particularly limited, the
thickness of the thermally sprayed coating 21 is, forexample, from 20 to 200 ptn.
[0032] The hardness of the thermally sprayed coating 21 is preferably from 600 to 1,000 in
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terms of Vickers hardness 11V as defined in IS0 6507-1. AVickers hardness HV of the
thermally sprayed coating 21 of less than 600 is not favorable because contaminating objects
such as imn that are the source of build-up tcnd to bite into the tl~ennallys prayed coating 21
and build-up tends to occur. 111 contrast, wlien the Vickers hardness HV of the thennally
sprayed coating 21 is fiom 600 to 1,000, the biting of contaminating objects such as iron into
the hard thermally sprayed coating 21 can be suppressed, and, therefore, the occurreuce of
build-up can be suppressed. A Vickers hardness HV of tlle thermally sprayed coating 21 of
more than 1,000 is not favorable since the them~allys prayed coating 21 becomes to have a
tendency to crack and detach. The Vickers hardness HV is tneasured according to the test
method as defined in IS0 6507-1.
[0033] On the thermally sprayed coating 21, a modified coating 22 is provided; the modified
coating 22 is formed by remelting the thermal spray material that forms the thennally sprayed
coating 21, and then solidifying the thermal spray material. The tnodified coating 22 has a
stnall surface roughness and is a dense coating, and the modified coating 22 bas a porosity of
almost 0%.
[0034] The thickness of the modified coating 22 (thickness d2 in Figure 3A) is preferably
from 2 to 20 ptn A thickness of the modified coating 22 of less than 2 pm is not favorable
because the possibility that the modified coating 22 is worn by abrasion during conveyance of
the steel sheet 2 becomes high. A thickness ofthe modified coating 22 of tnore than 20 pm
is not favorable because the modified coating 22 becomes to have a tendency to detach.
[0035] The thicknesses of the thermally sprayed coating 21 and the riiodified coating 22 can
be measured by observing a cross-section of the produced hearth roll 10 using a microscope
such as a scanning electron tnicroscope (SEM).
[0036] The Vickers hardness HV of the modified coating 22 according to the present
embodiment is preferably frorn 1.2 to 1.4 times larger than the Vickets hardness HV of the
thermally sprayed coating 21. Since the Vickers hardness HV of the thermally sprayed
coating 21 is, for example, from about 600 to about 1,000, the Vickers hardness HV of the
tnodified coating 22 according to the present etnbodiment would be from about 720 to about
1,400. Since the modified coating 22 has a liardness that is higher than the hardness ofthe
tliennally sprayed coating 21, biting of contaminating objects such as iron into the tnodified
coating 22 can more effectively be prevented, and, therefore, the occurrence of build-up call
be suppressed. When the hardness ratio in terms ofvickers hardness Hv is lower than 1.2,
biting ofcontaminating objects such as iron into the modified coating 22 tends to occur, and
build-up tends to occur. When the hardness ratio in tertns of Vickers hardness Hv is higher
than 1.4, the modified coating 22 tends to detach.
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[0037] As schematically illustrated in Figure 3A, cracks 23 are present in the surface of the
modificd coating 22 at a prescribed spacing. When cracks 23 are present in the ll~odificd
coating 22, the cracks 23 fi~nctiona s a stress relaxation mechanism to prevent fracture 01.
detachment ofthe modified coating 22 caused by a thern~als tress. The spacing LI between
adjacent cracks 23 in a cross-section of the hearth roll cut in the thickness direction. such as
that illustrated in Figure 3A, is preferably fiotn 10 to 100 [un. The opening width of the
crack 23 (distance L2 indicated in Figure 3B) is preferably less than 5 pm. A spacing LI of
less than 10 pm is not favorable because the modified coating 22 becomes to have tendency to
detach. When the spacing LI is more than 100 lun, the possibility that the opening width L2
of the crack 23 is 5 pnl or more becotncs high. When the opening width L2 ofthe crack 23
is 5 ptn or more, contaminating objects, such as iron, serving as the source of build-up tend to
bite in the opening, and, therefore, it becomes difficult to suppress the occurrence of build-up.
The opening width Lz of the crack 23 is preferably as stllall as possible, and the lower limit
thereof is not particularly determined. Howevel; from the viewpoint of the production of the
modified coating 22, an opening width L2 of 0.1 pm would be the tnitlitnuo~v alue possible.
[0038] The method employed for measuring the spacing LI between adjacent cracks 23 or
the opening width L2 of the crack is not patticularly limited, and can be measured using
known methods. For example, a cross-section of theproduced hearth roll 10 tnay be
enlarged to a magnification suitable for observation by using a microscope such as a SEM,
and the spacing between adjacent cracks 23 and the opening widths of the cracks 23 tnay be
measured at a freely selected position.
[0039] In the modified coating 22 according to the present embodiment, the oxygen content
in the modified coating 22 is preferably from 0.5 to 2% by mass. When the oxygen content
is less than 0.5% by mass, the hardness of the modified coating tends to be small. When the
oxygen content is more than 2% by mass, the coating tends to fracture and the modified
coating tends to detach. The oxygen is contained in the modified coating 22 in the state of
an oxide of an element contained in the modified coating 22.
[0040] In the modified coating 22 according to the present embodiment, AI203 is present in a ..
state of being dispersed on the surface of the tnodified coating 22. Since AI203 has a lower
tendency to react with the build-up source than that ofthe modified coating 22, superior . ~
build-up resistance is obtained. The proportion of the area ofA1203 011 the surface of the
modified coating 22 to the entire surface of the modified coating 22 is preferably from 5 to
40%. A proportion of the area ofAl203 of lower than 5% is not favorable because the
modified coating 22 becomes to have a tendency to react with the build-up source. Further,
a proportion of the area ofAl20, of higher than 40% is not favorable because ,4120, present
8
on the surface of the modified coating 22 becotnes to have a tendency to detach.
[0041] The tnethod e~nployedfo r measuring the oxygen content in the modified coating 22
and the method employed for ~neasuringth e proportion of the area ofA1203 on the surface of
the modifiedcoating 22 are not particularly limited, and can be measured by known methods.
For example, a wavelength-dispersive electron probe micro analyzer (wavelengt11-dispersive
EPMA) or the like may be used.
[0042] As described below, tlie modified coating 22 as described above is preferably formed
by modifying a portion of a prescribed thickness fro111 the surface of the thermally sprayed
coating 21 by irradiating the surface ofthe thermally sprayed coating 21 with a laser beam
having an energy density of from 1x 10' to 1x10~w / c ~ I ~W. het1 the energy density is 1x loS
W/cm2 or less, it becomes difficult to melt the thermally sprayed coating 21, and the
processing time elongates more than necessary. When the energy density is 1 x 1 o7 W/cm2 or
more, the density of the energy with which the thermally sprayed coating 21 is melted
becomes excessively high, and a modified coating 22 having a suitable thick~lesso r cracks is
not obtained even by adjustment of the prescribed conditions. In this regard, various
properties, such as the thickness of the tnodified coating 22 to be formed, the spacing between
adjacent cracks 23, the opening width of the crack 23, and the proportion of the area ofAlzO3,
can be regulated by adjusting the energy density ofthe laser employed for irradiation.
[0043] After the modified coating 22 is formed, the modified coating 22 is preferably
subjected to chromate treatment. By irradiating a part or the whole of the surface ofthe
modified coating 22 with a laser beam, tlie modified coating 22 can be formed at necessary
portions of the thermally sprayed coating 21, which may be a part of the surface or the whole
of the surface. When the modified coating 22 is formed in portions on the thermally sprayed
coating 21, fine pores in regions of the thermally sprayed coating 21 that are not the modified
coating 22 are preferably subjected to chromate treatment, thereby enhancing the build-up.
resistance by filling of the fine pores with chromiotn oxide. Further, cracks 23 occurring in
the film surface of the modified coating 22 are preferably subjected to chromate treatment,
thereby enhancing the build-up resistance thereof by filling of the cracks 23 with cliromiom~
oxide. The chromate treatment can be performed by applying or spraying a chronlic . ..
acid-containing aqueous solution~ontoth e surface of the hearth roll, and then performing -.
heating at frotn 350 to 550°C. When such treatment is repeated, the coating thickness of the
chromate treatment can be changed. For the purpose of filling the fine pores in the tl~ern~ally
sprayed coating 21 or the cracks 23 in the modified coating 21, chromate treatment conducted
. . three times or fewer times would suffice.
[0044] (Material for Thermally Sprayed Coating)
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Next, the material of the thermally sprayed coating 21 covering the hearth mll 10 will
be described in detail. The inventors ofthe present application prepared various thermally
sprayed coatings for testing, and examined the characteristics, the occurrence of build-up, and
the like ofthe thermally sprayed coatings for testing. As the result, the inventors has found
that the below-described cermet coating composed of a heat-resistant alloy and a ceramic has
a large effect in terms of silppression of build-up, and a low tendency to degrade even in a
long time use in a continaous annealing furnace.
[0045] The thermally sprayed coating 21 according to the present etnboditnent is preferably
a cermet coating cornposed of a heat-resistant alloy and a ceramic. I-Iere, the ceramic
includes Cr3C2 at fiom 50 to 90% by volume, A1203 at fsom I to 40% by volume, Y203 at
from 0 to 3% by volutne, and ZrB2 at fiorn 0 to 40% by volume, the balance being composed
of impurities and pores. Y203 and ZrBz are optional components (selective components),
which may be incorporated as tlecessaly.
[0046] The heat-resistant alloy itlcludes Cr at from 5 to 20% by mass, Al at from 5 to 20%
by mass, and at least one of Y or Si at from 0.1 to 6% by mass, the balance being composed of
at least one of Co or Ni and impurities.
[0047] With respect to the volume ratio of the cermet coating, it is preferable that 50 to 90%
by volume of the cermet coating is a ceramic, and the balance is a heat-resistant alloy.
[0048] Specific examples of the cermet coating fonning the thermally sprayed coating 21 of
the hearth roll according to the present embodiment will be described in detail below.
In the cermet coating, 50 to 90% by volu~neo f the cermet coating is a ceramic, and
the balance is a heat-resistant alloy, such as CoNiCrAIY, CoCrAIY, NiCrAIY, or
CoNiCrAISiY. When the proportion of ceramic is less that1 50% by volume, the anlount of
heat-resistant alloy, which easily reacts with iron, becomes too large, and build-up tends to
occur. When the proportion of ceramic exceeds 90% by volume, the coating becomes
porous during thermal spraying due to the high melting point of the ceramic, and build-up
sources bite in the pores and build-up tends to occur. Further, from the viewpoint of
enhancing the build-up resistance, the proportion of ceratnic is more preferably fiom.60 to
80% by volume.
[0049] Next, the material of the ceramic will be described.
The main component ofthe ceramic is C&, and the ceramic includes CljCz at a
content of fi011150 to 90% by volume. Cr3c2 has little tendency to be oxidized even in high
temperature environments such as in an annealing furnace, and Cr3C2 has little tendency to
react with iron or manganese or oxides thereof. Therefore, Cr3C2 can prevent the occurrence
of build-up. When the propostion of Cr3C2 is lower than 50% by volume, the effect in terms
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of suppression of build-up is not obtained, and when the proporti011 of Cr3C2 is higher than
90% by volutne, the content of ceramic component, which suppresses diffi~siono f carbon, in
Cr3C2 becomes relatively low, as a result ofwhich the coating becotnes fragile due to carbon
diffusion. Furthe!; from the viewpoint of enhatlcing the build-op resistance, the proportion
of Ct'3C2 is niore preferably set to be from 60 to 80% by volume.
[0050] It is preferable that the particle size of CuC2 is, for example, fiom I to 10 pm.
When the particle size of Cr3C2 is less than 1 pin, the surface area contacting with the
heat-resistant alloy becomes large, and carbon diffi~siort~en ds to occur. When the particle
size is more than 10 pm, the roughness ofthe coating snrface becomes large, and iron or
nianganese, or an oxide thereof, tends to build up. Further, &om the viewpoint of enhancing
the build-up resistance, the particle size of Cr3C2 is Inore preferably set to be from 5 to 8 pm.
[005 11 The diffusion coefficient of carbon in A1203 and Y2O3 is low. Therefore, A1203 and
Y203 can suppress carbon contained in Cr3C2 from diffusing into the heat-resistant alloy.
[0052] In the material of the ceramic, the propottion ofA1203 is set to be froin 1 to 40% by
volume, and the proportion of Y203 is set to be 3% by volurne or less. Since Y203 is an
optional component (selective cotnponent), which may be incorporated, if necessary,
especially for purpose of obtaining an effect in terms of suppression of carbon diffusion, the
amount of Y203 is h l n 0 to 3% by volume. When the proportion of A1203 is less than 1%
by volume, an effect in terms of suppression of carbon diffusion is not obtained, and, when
the proportion ofAl203 exceeds 40% by volume, the coating becomes fragile and cracks tend
to occur during use, as a result of which the build-up resistance deteriorates. Since Y203 has
a tendency to react with manganese oxide, a Y203 proportion of higher than 3% by volume
deteriorates the build-up resistance. When Y203 is incorporated in order to obtain an effect
in tenns of suppression of carbon diffusion, it is effective to incorporate Y2O3 at 0.5% by
volume or more. Wit11 respect to A1203, the content ofA1203 is more preferably set to be
frotn 10 to 30% by volutne from the viewpoint of further enhancing the build-up resistance.
[0053] A1203 or Y203 may be incorporated, in the form of an oxide, into a powder of raw
materials. I-Iowever, for tlle purpose of suppressing carbon diffusion from Cr3C2, it is
preferable to oxidize Y or A1 that has been incorporated in the heat-resistant alloy by
oxidation treatment in the stage of raw materials, during coating or after coating, thereby
allowing A1203 or Y203 to fonn in the surface of the heat-resistant alloy.
[0054] In a case in which the hardness of the them~allys prayed coating at high temperatares
is to be enhanced for the porpose of using at high temperatores, it is preferable to incorporate
ZrB2, wl1ic11 is stable and has high hardness at high temperatures, at 40% by volume or less.
When ZrB2 is incorporated at more that1 40% by volulne, build-ap tends to occur due to the
11
build-up resistance of ZrB2 being inferior to that of Cr&. Since ZrB2 is an optional
cornpotlent (selective component), which may be incorporated, if necessa~ye, specially for the
purpose of use at high temperatures, the amount of ZrB2 in the coating is preferably kom 0 to
40% by volume. In a case ill which ZrB2 is incorporated for use at high temperatures, the
effect in terms of enhancing the hardness at high temperatures is small with an amount of
incorporated ZrBz of less than 5% by volu~ne. Therefore, it is preferable to incorporate ZrBz
at 5% by volume or more. Further, fro111 the viewpoint of enhancing the build-up resistance,
ZrB2 is more preferably incorporated at from 15 to 30% by volume.
The remaining part of the above-described ceramic corresponds to impurities and
pores.
[OOSS] Next, the material of the heat-resistant alloy will be described.
In the heat-resistant alloy, Cr is included at from 5 to 20% by mass. When Cr is
included at less than 5% by mass, the oxidation resistance at high temperatures is inferior, and
the coating is continuously oxidized and becomes to have a tendency to detach. At a Cr
content of more than 20% by mass, the heat-resistant alloy becomes fragile aud becomes to
have a tendency to detach whet1 carbonization occurs, whereas the heat-resistant alloy reacts
with manganese oxide and build-up tends to occur when oxidization occurs.
[0056] The heat-resistant alloy also it~cludesA l at from S to 20% by mass. When A1 is
included at less than 5% by mass, A1203 cannot be obtained in a desired aniount even by
conducting various oxidation tteatments. When A1 is included at more than 20% by mass,
the hardness of the coating at high temperatures decreases and therefore there is a tendency
for iron to stick into the coating and cause build-up.
[OOS7] Y and Si both have an effect in terms of stably forming an oxide coating and
preventing detachment ofthe oxide coating. Either one of Y or Si, or both of Y and Si, is/are
preferably incorporated at from 0.1 to 6% by mass. When Y or Si is.included at more thatl
6% by mass, the hardness of the coating at high temperatures decreases, as a result of which
there is a tendency for iron to stick into the coating and cause build-up. Y and Si is each
preferably-incorporated at 0.1% by tnass or more, and is each more effectively incorporated at
0.5% by tnass or more.
[0058] In [he heat-resistant alloy, at least one ofNb at from 0. I to1 0% by tnass or Ti at from
0.1 to 10% by tnass is preferably incorporated. When Nb orTi is included in the
heat-resistant alloy, the Ni or Ti forms a stable carbide preferentially to the formation of
carbide from Cr contained in the heat-resistant alloy, as a result ofwhich reactions between Cr
and carbon are suppressed aud the coatiug is thereby suppressed fiom becoming fragile for a
long time. When the content of NbITi is less than 0.1% by mass, the eftkt in terms of
12
suppressing reactions between Cr and carbon is not obtained. With a Nb/fi content of more
than 10% by mass, when oxidation occurs, the Nb or Ti tends to react with manganese oxide
and build-up tends to occur.
The remaining part of the heat-resistant alloy described above corresponds to at least
one of Co or Ni, and impurities.
[0059] One example of a scanning electron microscope (SEM) micrograph of a cross-section
of the thennally sprayed coating 21 and the modified coating 22 having the configurations as
described above is illustrated in Figure 4. In the SEM tnicrograph illustrated in Figure 4, a
dense modified coating 22 having a small roughness is formed on the surface of the thermally
sprayed coating 21, in which spaces are present. In the example illustrated in Figure 4, the
thickness of the modified coating 22 is about 5 pin. It is also seen that plural cracks are
formed extending from the surface ofthe modified coating 22 toward the thermally sprayed
coating 21.
[0060] Fonning the modified coating 22 on the thermally sprayed coating 21 enables
suppression ofthe occurrence of build-up on the hearth roll I0 in the present embodiment.
[0061] (Method of Producing Hearth Roll)
Next, a method of producing a health roll for a continuous annealing furnace
according to the present embodiment will be described with reference to Figure 5 and Figure
6.
[0062] In the method of producing a hearth roll according to the present embodiment, first,
the thermally sprayed coating 21 is formed by thermally spraying a thermal spray material
onto the.circumferential surface ofthe base roll 20 for the health roll 10 (step SlOl), as
illustrated in Figure 5. In order to enhance the adhesive power ofthe thermally sprayed
coating 21, known pre-thermal-spraying blasting treatments or forming of the undercoat layer
24 cornposed solely of a heat-resistant alloy (see Figure 2B) may be performed, if necessary,
prior to the thermal spray treatment.
[0063] The forming of the thennally sprayed coating 21 by thermal spray treatment (step
S10.l) will be described in detail. In the thermal spray treatment, a raw material powder
including a powder ofthe ceramic at from 50 to 90% by volume and a powder of the
heat:resistatlt alloy as the balance, is thermally sprayed onto the'surface of a base roll 20,
thereby forming a cermet coating on the surface of the base roll 20. As the raw material
powder to be thermally sprayed, a raw material powder in which a ceramic powder of Cr3cZ,
A1203 and the like and a heat-resistant alloy powder containing Cr and A1 are mixed can be
used. The thernlally spraying tnay be performed preferably using a raw material powder in
which a ceramic powder and a heat-resistant alloy powder have been combined and together
13
granulated in advance, whereby a thermally sprayed coating 21 having higher mlifortnity can
be formed.
[0064] With respect to a method etnployed for forming the them~allysp rayed coating 21 on
the circumferential surface of the roll, the forming is preferably carried out by performing a
high velocity oxygen-file1 thermal spraying process (also referred to as "HVOF") after
performing grid blasting for enhancing the adllesivelless and imparting roughness. In the
HVOF, it is ordinaty to use any of kerosene, C3H8, C2N2, or C3H6 as a file1 gas, and to set the
pressure of the fuel gas to be from 0.1 to 1 MPa, the flow rate of the fitel gas to be from 10 to
500 Llmin, the pressure of oxygen gas to be from 0.1 to I MPa, and the flow rate of oxygeu
gas to be from 100 to 1,200 Llmin.
[0065] During the thenual spraying, the base roll 20 is preferably heated to be from 300'C to
600°C. The heating may be carried out by bringing a flame of a thennal spraying gun close
to the base roll 20, or by separately providing a gas burner. As a result ofheating the base
roll 20 to 300°C or highel; Al andlor Y in the heat-resistant alloy is oxidized, and a desired
amount ofA1203 and/or Y 2 0 3 can be obtained. When the heating temperature is set to be
higher than 600'C, oxidation of the coating proceeds excessively and the coating becomes
porous, as a result of which build-up tends to occur. Further, from the viewpoint of
enhancing the build-up resistance, the range for the heatiug temperature is more preferably
from 400 to 500°C.
[0066] In the HVOF thermal spraying, the flow rate of oxygen gas as the NVOF combustion
gas component is preferably set to be from 1,000 to 1,200 Lhnin. When the flow rate of
oxygen gas is set to be 1,000 Llmin or more, A1 andlor Y in,the heat-resistant alloy is oxidized,
whereby a desired amount ofAl203 andlor Y z 0 3 can be obtained. When the flow rate of
oxygen gas is set to be more than 1,200 Llmin, oxidatiotl of the raw material powder proceeds
excessively during the tllertnal spraying and the coating.becomes porous, as a result of wl~ich
build-up tends to occur.
[0067] After the thermal spraying, the thermally sprayed coating 21 is preferably subjected
. . to oxidation treatment at from 300 to 600°C for from 1 to 5 hours. The oxidation treatment
. may be performed by heating the surface of the thermally sprayed coating 21 using a gas
'. burnel; or by placing the hearth roll in a furnace filled with the atmosphere or an inert gas
(such as nitrogen or argon) containing a small amount oxygen and conducting heat treatment.
By performing heating at 300'C or higher for 1 hour or more, A1 andlor Y in the heat-resistant
alloy is oxidized, and a desired amount ofA120, and/or YzO3 can be obtained. When the
heating is performed at a temperature higher than 600°C or is performed longer than 5 hours,
oxidation of the coating proceeds excessively and the coating becomes porous, as a result of
14
which build-up tends to occur. Further, fiom the viewpoint of enhancing the build-up
resistance, the range of the heating tclnpcrature is more preferably fiom 400 to 500'C.
[0068] In a case in which the raw material powder is subjected to thcrmal spraying after the
raw material powder is subjected to oxidation treatment, heat treatnlent is carried ont at from
300 to 600°C for fro111 1 to 5 honrs in the atmosphere or in an inert gas (such as nitrogen or
argon) containing a small amount oxygen. With a heating at a temperatare of lower than
300°C or for less than 1 houl; Y or A1 is not oxidized. When the heating is performed at a
temperature higher than 600°C or performed for more than 5 hours, the amount of oxidized
ceramics increases, as a result of which the melting point of the raw material powder
increases and the coating beconles porous. Furthei; f?om the viewpoint of enhancing the
build-up resistance, the heating temperature is more preferably set to be in the range of from
400 to 500°C.
[0069] After the thermally sprayed coating 21 is fonned on the base roll 20 by the thermal
spraying treatment as described above, then the surface layer of the thermally sprayed coating
21 is irradiated with a laser beam so as to cause remelting and resolidification of a portion of
the thermally sprayed coating that extends fiom the surface layer to a prescribed depth,
whereby a modified coating 22 is formed (step S103). The thickness of the modified coating
22 formed is preferably from 2 to 20 pm. The irradiation with a laser beam is preferably
carried out in the atmosphere. This is because the irradiation in the atmosphere promotes
oxidation reactions of metal cotnponents contained in the thermally sprayed coating 2 1 during
irradiation with a laser beam.
. - [0070] Various properties concerning the thickness or cracks of the modified coating 22 to
be formed can be regulated by the energy density of the laser beam used for the irradiation of
the surface of the thermally sprayed coating 21. In the method of producing a health roll
. . . according to the present embodiment, as scl~e~naticallilylu strated in Figare 6, the surface of ,
the ther~nallys prayed coating 21 is irradiated in a scanning manner at a prescribed speed
using a laser beam 30 emitted from a known laser emitter while the hearth roll 10 having the
thermally sprayed coating 21 formed thereon is being rotated. Here, in order to regulate the
- laser energy density on the surface of the thermally sprayed coating 21, the degree of
, L condensing of the laser beam 30 at the surface of the thermally sprayed coating 21 and the
scanning speed are regnlated using known optical systems.
[0071] Although it is preferable to set the energy density of the laser beam used for
irradiation of the surface of the thermally sprayed coating 2 1 to be fro111 1 x 10' to 1 x lo7
~ ~ l cth~e dneg~re,e of light condensing or the scanning speed is not particular restricted. For
example, irradiation with a laser beam may be performed under the following conditions.
15
Specifically, the surface ofthe thermally sprayed coating 21 is irradiated by one time or plural
times scanning with a laser beam having an output power of 1,000 W altd condensed to a
diameter of 300 lcm at the surface ofthe them~allys prayed coating 21 (energy density: about
1 . 41~ o 6 WICLII~a)t ,a scanning speed of 10 mls and a pitch of 50 ~ I IuIs ing a NdIYAG laser
device (laser wavelength: 1,064 nm). Performing remelting and resolidification of the
thermally sprayed coating 21 under the conditions as described above enables the modified
coating 22 as described to be formed. The process conditions described above are tnerely
one example, and the process conditions, soch as the degree of light condensing, the scanning
speed, the pitch, and the number of times of scanning, may be selected, as appropriate, in
accordance with the wavelength or output power of the laser to be used, such that the
thickness of the modified coating 22 becomes to be preferably ftom 2 to 20 pm.
Althougll a NdIYAG laser (laser wavelength: 1064 nm) is used in the above,
near-infrared lasers having a laser wavelength within the range of 6om 900 to 1,100 nm are
preferably used, such as a Yb-based fiber laser (laser wavelength: 1,070 nnl) and a disk laser
(laser wavelength: 1,030 nm). Beside laser beams, it is also possible to use, for example, an
electron beam. Laser beams and electron beams are exatnples of energy beams.
[0072] By the above-described processes, the health roll for a continuous annealing furnace
according to the present emboditnent can be produced.
[0073] In the above, the hearth roll for a continuous antlealing fi~rnacea ccording to the
present e~nboditnenat nd a method of producing the health roll have been described.
According to the present ealboditnent, a dense and highly strong modified coating that
appropriately regulates the surface roughness of the roll circumfel.ential sut-face of the hearth
roll I0 cat1 be provided, whereby attachment of contaminating objects, such as iron or
manganese oxide, to the roll circomferential surface can be remarkably reduced. Therefore,
attachtnent aud growing ofcontanlinating objects that are carried with the steel sheet 2 being
conveyed, to the roll circumferential surface of the health roll 10 (i.e., occurrence of build-up)
can be suppressed during the operation of the continuous annealing furnace I . This enables
prevention or suppression of the generation of transferred defects on the steel sheet 2 caused ...
by the build-up, aud the quality ofthe steel sheet 2 can be improved. . ~
. . [0074] Furthet; since the health roll 10 can be used stably for a long time in a high
temperature environment in the continoous annealing furnace 1, the lifetinle of the hearth roll
10 call be greatly prolonged. Moreovet; in scheduled maintenance of the continuous
annealing furnace 1, the necessity ofthe operation to retnove objects attaching to the roll
surface of the health roll 10 disappears or is remarkably reduced, whereby the efficiency of
the production of the steel sheet 2 it1 the continuous annealing furnace 1 can be increased.
16
EXAMPLES
[0075] Next, exatnples will be described. The following exalnples indicate the results of
tests carried out for demonstrating the effect of the invention, but the invention is uot limited
to the follo\ving examples.
[0076] Plural kinds of hearth lulls 10 were produced according to the above-described
method of producing a hearth roll, and measurements were carried out in which each health
roll 10 was used in a continuous annealing fi~rnaceI and the lifetime of each hearth roll 10
was meast~red With respect to the lifetime oftlle roll, the roll circumferential surface ofthe
hearth roll 10 was tneasured using a portable fluorescence X-ray in a continuous annealing
furnace 1 that is online, and the point of time at which the amount of iron (Fe) attaching to the
roll circumferential surface exceeds 5% by Inass is taken as the expiry of the lifetime. The
roll diameter 4 in the present embodiment was set to 1,000 tnm.
[0077] In the remelting and resolidifying treatment of the thennally sprayed coating 21, the
cotnposition ofthe thermally sprayed coating or the surface roughness also exert an influence,
and, therefore, the remelting and resolidifying treatment is performed while appropriately
adjusting the degree of light condensing and the scanning speed. For example, in the case of
a thennally sprayed coating indicated in Table 1 having a Vickers hardness HV of 950 and
including ceramic at 80% by volume of the therlnally sprayed coating (Cr3C2 at 79% by
volume and A1203 at 1% by volume) and the remaining part cotnposed of a heat-resistant
alloy that includes, in terms of % by mass, Cr at lo%, Al at 5%, Y at 2%, Ti at 0.1%, and Co
as the balance, one time scanning treatment at a pitch of 50 pm and a scanning speed of 10 .
tnls performed using a laser beam from a NdNAG laser device having an output power of
1,000 W condensed to a diameter of 300 pm at the surface of the thermally sprayed coatillg
21 resulted in a thickness of the modified coating 22 of 11 pm as determined by measurement
of a simtlltaneous test specimen. When the scanning treatment was performed hvice under
the sattle conditions, a thickness of the tnodified coating 22 of 13 pm was obtained. With a
degree of light condettsation of 1,000-ptn diatneter under the same cortditions, one time - .
scanning resulted in a thickness of the lnodified coating 22 of 2 !urn. When one-titne -
scanning treatment was performed with an output power of 500 W, light condensation to <'
300-pnl diameter, a pitch of 60 pln, and a scanning speed of 8 mls, the thickness of the
tnodified coating 22 was 8 pm. Therefore, in the exatnples indicated in Table I , the degree
of light condensation, the scanttitlg speed, the pitch, and the number of times of scanning,
were designed, as appropriate, based on the above findings, thereby preparing tnodified
coatings 22 having the thicknesses indicated in Table 1
17
[0078] The co~ilpositiono f the thermally sprayed coating 21 forn~cdo n the mll
circumferential snrface, and the properties of the thermally sprayed coating 21 and the
modified coating 22 are collectively indicated in Table 1.
In Table 1, the thickless, crack spacing, and crack width of the modified coating 22
were measured by observing a cross-section of an obtained hearth roll simultaneous sa~nple
with a SEM. The crack spacings and the crack widths were measured in 10 visual fields in
the cross-section observed with the SEM at a measurement tnagtlification of 1,000 fold, and
the average value thereof was calculated. As for the proportion of the areas ofA1203 at the
surface of the modified coating 22, surface images of 10 visual fields were obtained using a
wavelength-dispersive EPMA at a measurement magnification of 500 fold, and backscattered
electron images were binarized such that areas detennined as A1203 bya qualitative analysis
were colored white and such that the other areas were colored black, thereby determining the
proportions of the A1203 area, and the average value of the area proportions was calculated.
As for the oxygen content of the modified coating 22, quantitative analysis was perfortlled on
the 10 visual fields observed rrsing a wavelength-dispersive EPMA at a measurement
magnification of 500 fold, thereby detennining the oxygen contents, and the average value of
the oxygen contents was calculated. Further, the Vickers hardnesses HV of the ther~nally
sprayed coating 21 and the modified coating 22 were measured according to the method
defined in IS0 6507-1, and the hardness change ratio obtained by pickers hardness HV of
modified coating 22 / Vickers hardness HV of thermally sprayed coating 21) is also indicated
in Table 1. Further, the roll lifetime, which was obtained as a test result, is also indicated in
Table 1.
[0079] Table 1
Ral Co-lnChSAl-7v.n 1Ti
Modified Coating
Thiclolcss
(pm)
2
3
4
5
6
. - - . ~ ~~ ~ ~ ~~~~~ - -. ~
ppp 6 0.5 / 950 79Cr3Cz-1AI20, Bal.Co-1OCr-5Al-2Y-O.1Ti Yes 1.37 4.9
--
12 1 5 1 1320 / 40 1 1.8 6 0.6 1 950 79Cr3C2-1AI2O3
Examples Bal.Co-1OCr-5Al-2Y-O.1Ti Yes 1.39 5.0
13 1 15 1 1160 1 120 1 5.2 6 0.5 1 950 79Cr,C,-1 A1.0, V 117 A 7
Thermally Spraycd Coating ' -
7
8
9
10
Chromate
Treatment
Hardncss
Hv
Hardncss
Hv
4
2
10
20
10
10
10
10
20
.
ardncss
Change
Ratio
Crack
Spacing
(pm)
Proportion of Ceramic in
Coating (% by volume)
"1330 '
1300
1300
I300
1140
- 21
22
23
24
Roll
Lifetime
(years)
Proportions of Components in
Heat-resistant Alloy
(%by mass)
I300
1330
1140
1150
Cnck
Width (p~)
- 40
40
40
40
40
18
16
18
15
40
40
100
150
Proportion
of Area of
AlzO, (%I
1.8
1.8
1.8
1.8
1.8
800
8 5 0
:850 '
800
Oxygcn
Contcnt
(%by
1.8
1.8
4.2
5.6
6
6
6
6
6
100
100
100
100
6
6
6
6
0.4
0.4
0.4
0.4
0.4
4.0
3.0
4.0
4.0
0.4
0.4
0.5
0.4
950
950
950
950
950
10
6
10
5
~~~
950
950
950
950
79Cr3C2-1AI2O1
79Cr3C2-1AI2Os
79Cr3CrlAIz03
79Cr3C2-1AIzO3
79Cr.C,-IAI-0,
4.5
4.0
3.5
4.1
- -~,-. -~ ~~
79Cr,CrlAI2O3
79Cr3C2-1AI2O3
79Cr3C2-1Ah03
79Cr,C,-1AI9O2
- -. . - . . . -. . . .. - . - . . . .
Bal.Co-lOCr-5AI-2Y-O.1Ti
Bal.Co-IOCr-5A1-2Y-0.1Ti
Bal.Co-lOCr-5A1-2Y-0.1Ti
Bal.Co-lOCr-5A1-2Y-0.1Ti
RnICn-IOCr-5A1.7V.O ITi
620
650
650
660
- -. . - - . . -. - . . . - . - . . . .
Bal.Co-lOCr-5A1-2Y-0.1Ti
Bal.Co-lOCr-5A1-2Y-O.ITi
Bal.Co-1OCr-5Al-2Y-O.1Ti
Bal.Co-1OCr-5Al-2Y-O.ITi
Yes
Yes
Yes
Yes
vrc
---
29.5Cr3C2-20ZrB-0.5Alza
28Cr3C2-20ZrBrlAlz03-1Y201
29Cr3Cz-10A1203-1Y203
40Z10~-10Y,03
. ?"
Yes
Yes
Yes
Yes
1.40
1.37
1.37
1.37
1 ?n
Bal.Co-20Cr-20Al-6Si-10Ti
Bal.Ni-IOCr-1OAI-6Y-O.1Nb
Bal.Co-15Cr-15Ai-IY-SNb
Bal.Co-15Cr-15Al-1Y
4.7
4.7
4.7
4.7
A 7
1.37
1.40
1.20
1.21
,.,
4.7
4.7
4.9
4 6
No
Yes
Yes
NO
1.29
1.31
1.31
1.21
--
3.8
3.9
4.4
? n
Table 1-continued
[0080] As is clear from Table I , it is clear that the health rolls according to Examplcs I to 24
include the modified coating 22 having a high Vickers hardness HV and have excelle~lrto ll
lifetime. In particular, it is seen that examples in which the values of tl~ecr ack spacing, the
crack width, and the proportion ofthe area ofAlzO3 are appropriate values have especially
superior roll lifetimes. 'l'hesc rcsults demonstrate that occuucnce of build-up is suitably
suppressed when a health roll is produced using the method of producing a hearth roll
according to the present specification.
[0081] In contrast, the hea~thro lls according to the co~nparativee xamples exhibited a roll
lifetime of less that1 2 years, demonstrating that the hearth rolls according to the comparative
exanlples did not succeed in suppressing the occurrence of build-up on tlie surface of the
hearth rolls.
[0082] The disclosure of Japanese Patent Application No. 2014-204108, filed October 2,
2014, is incorporated herein by reference in its entirety.
All publications, patent applications, and technical standards mentioned in this
specification are herein incorporated by reference to the same extent as if each individual
publication, patent application, or technical standard was specifically and individually
indicated to be incorporated by reference.
[0083] Although typical embodiments have been described above, tlie invention is not
limited to such embodiments. It is intended that the scope of the invention be defined by the
following claims.
CLAIMS
1 . A I~eatthr oll, comprising:
a base roll;
a thermally sprayed coating formed on the base roll; and
a modified coating formed on the thermally sprayed coating, the modified coating
being formed by modifying a part or the whole ofa surface of the thermally sprayed coating
by melting and solidification of the thermally sprayed coating, by irradiating a patt or the
whole of the surface of the thennally sprayed coating with an energy beam,
a thickness of the modified coating being from 2 to 20 pm, and
a Vickers hardness HV of the modified coating being from 1.2 to 1.4 times larger
than a Vickers hardness HV of the thennally sprayed coating.
2. The health roll according to claim 1, wherein cracks are present on a surface of
the modified coating, and an average spacing between adjacent cracks in a cross-section of the
heatth roll cut in a thickness direction is from 10 to 100 pm, and opening widths of the cracks
are less than 5 ptn.
3. The hearth roll according to claim 1 or claitn 2, wherein the modified coating
comprises from 0.5% to 2% by mass of oxygen.
4. The health roll according to any one of claims 1 to 3, wherein A1203 is present in
a dispersed state in a surface of the modified coating, and a propottion of an area ofAlz03 in
-the surface of the modified coating is from 5% to 40%.
5. The health roll according to any one of claims I to 4, fittther comprising a
chromiom oxide layer formed on the modified coating, or on the modified coating and the
thermally sprayed coating.
6. The heatth l u l l according to any one of claims 1 to 5, wherein the thern~ally
sprayed coating is a cennet coating consisting of a heat-resistant alloy and a ceramic,
the ceramic including, in terms of % by volume, Cr3C2 at fro111 50% to 90%, A1203 at
from 1% to 40%,Y203 at from 0% to 3%, and ZrB2 at fiom 0% to 40%, and the balance being
composed of impurities and pores,
22
tlie heat-resistant alloy includi~ig,i n terms of % by mass, Cr at from 5% to 20%, Al at
from 5% to 20%, aud at least one of Y or Si at fiom 0.1% to 6%, and the balance being
co~nposedo f at least one of Co 01 Ni and i~npuriticsa, cid
from 50 to 90% by volume of the ccrlccet coating bcijig tlie ceramic, a~idtl ie balance
being the heat-resistant alloy.
7. 7'lle Ileal th roll accortliug to claim 6, whereit~ tlie heat-resistant alloy furtlcer
includes, in ter~nso f % by mass, at least olie of Nb at from 0.1 to 10% or Ti at from 0.1 to
10%.
S. A method of producing a heart11 roll, comprising a step of irradiating a part or the
whole of a surface of a thermally sprayed coating formed on a base roll with all energy beam,
thereby modifyicig a part or tlie whole of the surface of tlce thermally sprayed coating by
melting aud solidificatio~oi f the thcrmall~rs prayed coating, to form a modified coating.l~aving
a thick~cesso f fio1112 to 20 p!n and a Vickers hardness HV that is from 1.2 to 1.4 times larger
than the Vickers haad~lessH V of the theniially sprayed coating.
9. The method of prod~rcinga hearth roll according to claim 8, wherein the
irradiating with the energy beam is pcrformctl in the atmosphcrc.
10. .The inetliod of producing a heal-tli roll according to clai~iiS or claim 9, wherein
a chromate treatment is performed after the ~iiodified coating is Sor~ned.