U.S. patent application number 13/048576 was filed with the patent office on 2011-07-07 for coating material for metallic base material surface.
This patent application is currently assigned to BABCOCK-HITACHI KABUSHIKI KAISHA. Invention is credited to Yuji FUKUDA, Yoshitaka KOJIMA, Toshinari OKAGAITO.
Application Number | 20110165334 13/048576 |
Document ID | / |
Family ID | 42678546 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110165334 |
Kind Code |
A1 |
OKAGAITO; Toshinari ; et
al. |
July 7, 2011 |
COATING MATERIAL FOR METALLIC BASE MATERIAL SURFACE
Abstract
A spraying material for coating a metallic member, being
inexpensive and having superior corrosion and erosion resistance
even in high temperature environments, wherein the material is
composed of an Fe--Si based compound and comprises an alloy
composed of 10 to 35% by weight of Si and the remainder of Fe and
inevitable impurities, and further, up to 5% by weight of B may be
added to the material in terms of improvement in hardness and
adhesiveness of the coating is provided in order to protect
components such as heaters and water walls of coal fired boilers
and heat exchanger tubes of fluidized bed boilers, etc., from
corrosion and erosion. The spraying material is formed into a
coating by, for example, high velocity flame spraying or
atmospheric plasma spraying.
Inventors: |
OKAGAITO; Toshinari;
(Hiroshima, JP) ; FUKUDA; Yuji; (Hiroshima,
JP) ; KOJIMA; Yoshitaka; (Ibaraki, JP) |
Assignee: |
BABCOCK-HITACHI KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
42678546 |
Appl. No.: |
13/048576 |
Filed: |
March 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12398577 |
Mar 5, 2009 |
|
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13048576 |
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Current U.S.
Class: |
427/452 |
Current CPC
Class: |
B22F 2998/00 20130101;
C22C 38/02 20130101; C23C 4/04 20130101; Y10T 428/31678 20150401;
B22F 1/0011 20130101; C22C 38/002 20130101; C23C 30/00 20130101;
B22F 2998/00 20130101; C22C 33/0278 20130101; B22F 9/082 20130101;
B22F 9/082 20130101; B22F 9/04 20130101; B22F 9/04 20130101; B22F
2998/00 20130101 |
Class at
Publication: |
427/452 |
International
Class: |
C23C 4/04 20060101
C23C004/04; C23C 4/10 20060101 C23C004/10; C23C 4/12 20060101
C23C004/12 |
Claims
1. A method for preparing a coating for a metallic base material
surface, comprising an alloy composed of 19.82 to 35% by weight of
Si and the remainder of Fe and inevitable impurities the method
comprising, providing a coating composition comprising Si, and the
remainder of Fe and inevitable impurities; and spraying the coating
composition onto the metallic base material surface by high
velocity flame spraying or atmospheric plasma spraying.
2. A method for preparing a coating for a metallic base material
surface, comprising an alloy composed of 19.82 to 35% by weight of
Si and the remainder of Fe and inevitable impurities the method
comprising, providing a coating composition comprising Si, B and
the remainder of Fe and inevitable impurities; and spraying the
coating composition onto the metallic base material surface by high
velocity flame spraying or atmospheric plasma spraying.
3. A method of coating a metallic base material surface, the method
comprising: providing a coating composition, comprising a member
selected from the group consisting of Fe.sub.2Si, Fe.sub.5Si.sub.3
and FeSi; and spraying the coating composition onto the metallic
base material surface by high velocity flame spraying or
atmospheric plasma spraying, wherein the coating composition
comprises an alloy composed of 19.82 to 35% by weight of Si, 1.02
to 5% by weight of B, and the remainder of Fe.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Divisional of U.S. application
Ser. No. 12/398,577 filed Mar. 5, 2009, which is expressly
incorporated by reference herein in its entirety.
DESCRIPTION
[0002] 1. Technical Field
[0003] The present invention relates to a surface coating material
(thermal spraying material) for a metallic base material, having
superior corrosion and erosion resistance in environments, such as
heat exchanger tubes and water walls of coal fired boilers, heat
exchanger tubes and wall surfaces of fluidized bed boilers,
etc.
[0004] 2. Background Art
[0005] As capabilities a coating material for the aforementioned
heat exchanger tubes and wall surfaces of coal fired boilers, etc.,
should possess, (1) that coating has corrosion resistance in high
temperature operating environment, low oxygen partial pressure and
high sulfur partial pressure, and (2) that porosity of a sprayed
coating can be reduced, thereupon preventing corrosive gas from
penetrating into an interface between the coating and the base
material are cited. At the same time, (3) resisting erosion due to
coal ash is required in terms of erosion resistance for the
aforementioned coating material. Also, (4) that coating is not
cracked due to thermal cycles caused by operating/stopping of a
boiler and removal of the slag deposit from the surface of the
coating is required. In addition, since the boiler members have a
wide area and thus a large amount of thermal spraying material, (5)
being superior in cost efficiency is required.
[0006] As a corrosion- and erosion-resistant thermal spraying
material of industrial boilers, Ni base materials such as Ni--50Cr
and metallic carbide material such as Cr.sub.3C.sub.2/NiCr are
conventionally used and coated by a high velocity flame spraying or
atmospheric plasma spraying.
[0007] Although those materials have high corrosion and erosion
resistance, expensive nickel (Ni) and metallic carbide are
included.
[0008] Further, although a high corrosion-resistant coating can be
obtained when the high velocity flame spraying is used for those
materials, there is a problem that a chromic oxide lowers toughness
of the coating and thus cracks and spalling are caused by thermal
cycle.
[0009] Sulfidation corrosion environments of boiler furnace walls
feature a high temperature at approximately 500.degree. C., low
oxygen partial pressure and high sulfur partial pressure. As
elements capable of forming a stable oxide coating even in such
environments, chromium (Cr), aluminum (Al) and silicon (Si) are
known.
[0010] Oxide is produced due to heat of a spraying flame when a
coating is formed with those elements by a spraying method. A
thermal expansion coefficient of oxide is lower than that of a base
material metal. In a coating which contains a large amount of
oxide, operating/stopping of the boiler and removal of the slag
deposit from the surface of the coating cause cracks due to thermal
induced tensile stress, which results in spalling off the outer
surface of the coating. As described above, there is a disadvantage
that a crack due to thermal cycles tends to be caused when a
sprayed coating of a simple element having corrosion resistance is
used.
[0011] A high temperature- and corrosion-resistant thermal spraying
material as disclosed in Patent Literature 1 is such that Si
particles not more than 35% by weight are mixed into a powder
having a base material composition. It is disclosed that by making
into a powder with a composition similar to the base material, a
difference in thermal expansion coefficient with the base material
becomes small and thus a corrosion-resistant coating superior in
spalling resistance can be obtained.
[0012] Patent Literature 2 discloses that a material having a main
constituent of magnetite (Fe.sub.3O.sub.4 and/or FeFe.sub.3O.sub.4)
and added with carbide, nitride, silicide, boride and/or oxide is
sprayed on a metallic base material, and a corrosion- and
erosion-resistant layer is formed on the base material.
[0013] Patent Literature 3 discloses that a bond coat layer
composed of an Si compound and a top coat layer composed of
SiO.sub.2 are coated on an upper surface of a heat exchanger tube
or fire grate of an air heater, a steam generator and the like by a
spraying method and further the topcoat layer is provided with
porous sealing, thereby maintaining high temperature corrosion
resistance of the base material. [0014] [Patent Literature 1]
Japanese Published Unexamined Patent Application 2005-240106 [0015]
[Patent Literature 2] Japanese Translation of International
Application (Kohyo) No. 2003-522289 [0016] [Patent Literature 3]
Japanese Published Unexamined Patent Application 2005-272927
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0017] In the invention as described in the aforementioned Patent
Literature 1, a thermal spraying material obtained by mixing Si
powder and powder with a base material composition is used. In
thermal spraying of a mixed material, part of the powder is
combined in processing. However, the majority of the coating is
maintained at the original composition. When the present invention
is applied to a low-alloy steel base material, a thermal spraying
material composition becomes a mixture of Fe particles, Si
particles, and Fe--Si composition. Fe particles are inferior in
corrosion resistance. Thus, superior corrosion resistance cannot be
achieved by this coating.
[0018] In the invention as described in the aforementioned Patent
Literature 2, the thermal spraying material is composed of
magnetite with addition of carbide, nitride, silicide and boride.
Although this material possesses high temperature and oxidation
resistance, iron oxide is reduced into iron sulfide in environments
of high temperature, low oxygen partial pressure and high sulfur
partial pressure, and accordingly corrosion resistance cannot be
achieved by this coating. Further, the sprayed coating composed of
a mixed material of oxide-intermetallic compound becomes porous,
and thus a corrosive gas passes through pores in the coating,
corrosion advances on the interface between the coating and the
base material.
[0019] In the invention as described in the aforementioned Patent
Literature 3, this material has the same problem regarding the
porosity in the coating as the above-described Patent Literature 2.
As a result, a sealing treatment with an inorganic glass material
is required in order to fill the pores within the top coat. The
sealing treatment is such that slurry of inorganic glass such as
aluminosilicate glass is applied on a surface of the sprayed
coating, heated at approximately 1000.degree. C. Since thermal
deformation and strength reduction in the member occur due to the
sealing treatment, the invention cannot be applied to a low-alloy
steel base material. The same applies to the bond coat layer.
Although an Si compound layer composed of Cr.sub.3Ni.sub.5Si,
Fe.sub.3Si and Cr.sub.3Si, etc., is formed by a thermal diffusion
method, this treatment also requires heating at high temperature.
When the invention is applied to a low alloy steel, thermal
deformation and strength reduction occur.
[0020] Accordingly, it is an object of the present invention to
provide a coating material for a metallic base material capable of
forming a fine coating with superior corrosion and thermal shock
and thermal cycle resistance even in high temperature environments
in order to protect members such as heaters and water walls of coal
fired boilers, heat exchanger tubes of fluidized bed boilers, etc.,
from corrosion and erosion.
Means for Solving the Problems
[0021] The aforementioned object of the present invention can be
solved by the following means.
[0022] The invention according to claim 1 is a coating material for
a metallic base material surface, comprising an alloy composed of
10 to 35% by weight of Si and the remainder of Fe and inevitable
impurities.
[0023] The invention according to claim 2 is a coating material for
a metallic base material surface, comprising an alloy composed of
10 to 35% by weight of Si, 0 to 5% by weight of B and the remainder
of Fe and inevitable impurities.
[0024] The invention according to claim 3 is a high temperature-
and corrosion-resistant member wherein a surface of a metallic base
material is coated by at least one or more kinds of compounds among
a group of iron-silicon compounds composed of Fe.sub.3Si,
Fe.sub.2Si, Fe.sub.5Si.sub.3 and FeSi.
[0025] The present inventors have conducted research and then
acquired from findings that a practicable, fine, corrosion- and
erosion-resistant thermal spray coating can be obtained by using a
spraying material whose main constituent is an iron-silicon based
compound that is a compound stable and difficult to be decomposed
by heat in coating process and which is classified into an
appropriate particle size.
[0026] The present invention is a surface coating material of an
Fe-based alloy containing 10 to 35% by weight of Si. In terms of
improvement in erosion resistance, up to 5% by weight of boron, an
element lowering a melting point and strengthening the bonding
between particles in the coating, may be added to the above
material. The spraying material is formed into a coating by a
thermal spraying method as represented by a high velocity flame
spraying, atmospheric plasma spraying, etc.
[0027] The coating of the metallic base material surface in the
present invention exerts high corrosion resistance by being formed
by an Fe--Si based compound having high corrosion resistance such
as Fe.sub.3Si, Fe.sub.2Si, Fe.sub.5Si.sub.3, FeSi, etc.
[0028] A mixed material of powder with the base material
composition and Si powder is used as the spraying material of the
Patent Literature 1 as described in paragraph [0029], "In the
embodiment, the base material 34 is a Japan Industrial Standard
(JIS) SUS310S material, and accordingly mixed powder of mixing
SUS310S powder and Si powder is used as the spraying material."
[0029] When the Patent Literature 1 is applied to an iron-based
base material, the powder becomes a mixture of Fe and Si. Heat
quantity is insufficient to completely melt and alloy the mixed
powder in the aforementioned spraying method, and a ferrite phase
which is poor in corrosion resistance remains. Consequently,
corrosion resistance under low oxygen partial pressure condition
cannot be obtained as already described. Additionally, simple Si is
high in reactivity, and mainly inclusion of oxide such as SiO.sub.2
is caused and pores are produced in coating, whereupon adhesiveness
of the coating is lowered.
[0030] For the above reasons, it is preferable to use a compound
(alloy) powder obtained for example by an atomizing or crushing an
ingot having the aforementioned composition, as the thermal
spraying material of the present invention.
[0031] An addition amount of Si is more preferably in a range from
12 wt % where ferrite is not produced by heat in terms of corrosion
resistance to 25 wt % in terms of controlling hardness of particles
for lowering porosity of coating. An addition amount of B is more
preferably in a range of 3 wt % or less in terms of controlling
hardness of particles.
[0032] A size range of powder for high velocity flame spraying is
from 10 .mu.m to 40 .mu.m, more preferably 10 .mu.m to 30 .mu.m. On
the other hand, a size range of powder for atmospheric plasma
spraying is from 10 .mu.m to 150 .mu.m, more preferably 30 .mu.m to
60 .mu.m.
[0033] The spraying material of the present invention is not
limited to a case of being composed of only alloy powder having the
aforementioned composition. As long as the outer surface of the
coating is a compound with the aforementioned composition in the
end, a composition of the original spraying particles, coating
process, presence of a bond coat layer and presence of thermal
treatment are not limited.
[0034] In addition, the sprayed coating with the aforementioned
composition is composed of at least one or more kinds of Fe--Si
based compounds among Fe.sub.3Si, Fe.sub.2Si, Fe.sub.5Si.sub.3 and
FeSi. Since a ferrite phase that triggers deterioration of
corrosion resistance and an oxide phase that triggers deterioration
of thermal shock resistance are hard to produce, superior corrosion
resistance and thermal shock resistance can be achieved.
[0035] A chemical composition of the spraying material according to
the present invention and its limiting reasons are described.
[0036] An Fe--Si based alloy generates an iron-silicon compound
such as Fe.sub.3Si, Fe.sub.2Si, Fe.sub.5Si.sub.3, FeSi, etc., and
does not generate a ferrite phase by rendering the addition amount
of Si at 10% by weight or more. Those iron-silicon compounds are
stable and able to form a fine SiO.sub.2 coating even under low
oxygen partial pressure. Accordingly, the compounds can not only
make the coating superior in corrosion resistance but also have a
feature of having superior erosion resistance due to their
hardness.
[0037] When the addition amount of Si is less than 10% by weight, a
ferrite phase low in corrosion resistance appears on the spraying
particles, and corrosion resistance is reduced. When the addition
amount of Si exceeds 35% by weight, on the other hand, FeSi.sub.2
which is easily decomposed by heat is formed. If a material
containing FeSi.sub.2 is used for coating by thermal spraying,
FeSi.sub.2 is decomposed to FeSi and Si phase. Si is easily
oxidized to SiO.sub.2. SiO.sub.2 is poor in bonding strength and is
subjected to cracks by thermal cycles or thermal shocks. In terms
of thermal shock resistance, the threshold amount of Si is 35% by
weight.
[0038] Addition of boron (B) to the aforementioned Fe--Si based
material allows for lowering of a melting point of the spraying
particles and improvement in adhesiveness of the coating. However,
the hardness of the spraying particles is increased with the
increase in the amount of boron, and coating formation becomes
difficult. Thus, the additional amount of boron is 5% by weight at
the maximum.
[0039] The high velocity flame spraying and atmospheric plasma
spraying are available for coating methods of the spraying material
of the present invention. In generally, the atmospheric plasma
spraying is an unsuitable for hard facing for erosion protection.
However, the spraying material of the present invention provides
high corrosion- and erosion-resistance coating.
[0040] For coating formation of the material of the present
invention, a particle size range needs to be 10 .mu.m or more in
terms of prevention of stoppage of a spraying gun nozzle by the
powder. Further, a maximum particle size capable of forming a
coating is different between both spraying methods. When a thermal
spray coating is formed by the high velocity flame spraying, an
optimum particle size range is preferably 10 .mu.m to 30 .mu.m for
the purpose of preventing erosion by other spraying particles in
processing. When a coating is formed by the atmospheric plasma
spraying method, on the other hand, the particle size is preferably
in a range of 30 .mu.m to 60 .mu.m in terms of controlling thermal
decomposition of the particles.
[0041] The coating method of the spraying material of the present
invention is not limited to the high velocity flame spraying or
atmospheric plasma spraying. The coating can be formed by flame
spraying and electric arc spraying as well. Except for thermal
spraying, the coating can be formed by a plasma powder welding.
[0042] In addition, a cross-sectional microstructure of a high
velocity flame coating of Fe-20 wt % Si of the present invention is
shown by an optical microscopic image in FIG. 1.
Effects of the Invention
[0043] As described above, the Fe--Si based spraying material
exerts excellent corrosion and erosion resistance when used in
corrosive and erosive environments, which are conceivable in
coal-fired boiler component, such as water walls, heat exchanger
tubes, etc. Therefore, the material is suitable for a coating of
such a component as described above. In particular, the spraying
material of the present invention is an inexpensive Fe-based
material. Installation cost reduction effects can be obtained as
compared with a case where conventional Ni-based powder or metal
carbide powder is used.
BRIEF DESCRIPTION OF THE DRAWING
[0044] FIG. 1 is an optical microscopic image of a cross-sectional
microstructure of a high velocity flame spray coating of Fe-20 wt %
Si of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0045] Hereinafter, examples of materials of the present invention
are described as compared with materials having a composition
within and beyond the scope of the present invention. Spraying
materials having a composition of six kinds as shown in Table 1
were made into alloy powders by an atomizing, and the powder were
classified through a sieve respectively. Two kinds of powders in
particle size range of 10 to 30 .mu.m and 30 to 60 .mu.m were
obtained. Coatings were formed with those powders on a surface of a
0.5 Cr to 0.5 Mo low alloy steel used as a material for boiler
water walls, by the high velocity flame spraying and the
atmospheric plasma spraying.
[0046] A specific coating formation condition on the high velocity
flame spraying was 250 .mu.m in coating thickness with 15 built-up
layers at a propylene pressure of 700 kPa, an oxygen flow rate of
2.0.times.10.sup.-4 m.sup.3/s, a hydrogen flow rate of
2.7.times.10.sup.-4 m.sup.3/s, an air flow rate of
3.2.times.10.sup.-4 M.sup.3 and a powder feeding rate of 28 g/min.
DJ-2700 of Sulzer Metco Ltd. was used for a spraying device.
[0047] A specific coating formation condition on atmospheric plasma
spraying coating was 250 .mu.m in coating thickness with 20
built-up layers at 800A and 750V as a plasma condition, an argon
flow rate of 7.9.times.10.sup.-4 m.sup.3/s, a hydrogen flow rate of
0.6.times.10.sup.-4 m.sup.3/s and a powder feeding rate of 28
g/min. 9 MB of Sulzer Metco Ltd., was used for a spraying
device.
TABLE-US-00001 TABLE 1 Constituent (wt %) Material C Si Mn P S B Fe
O N Example 1 0.013 14.78 0.01 <0.001 0.001 <0.01 Bal. 90 ppm
16 ppm Example 2 0.018 19.82 0.01 0.001 0.001 <0.01 Bal. 110 ppm
13 ppm Example 3 0.032 20.03 0.02 0.002 0.001 1.03 Bal. 80 ppm 11
ppm Example 4 0.029 29.44 0.03 0.003 <0.001 1.02 Bal. 80 ppm 11
ppm Example 5 0.010 34.96 0.026 0.002 <0.001 <0.01 Bal. 80
ppm 11 ppm Comparative 0.010 4.97 0.01 0.001 <0.001 <0.01
Bal. 120 ppm 20 ppm Example 1 Comparative 0.033 40.50 0.02 0.003
0.001 <0.01 Bal. 130 ppm 15 ppm Example 2
[0048] Under the above-mentioned condition, a coating could be
formed in the high velocity flame spraying by using the powder size
range from 10 to 30 .mu.m. In addition, the coating was impossible
when the spraying particle size was 30 .mu.m or more. Further,
thermal shock test for the obtained coatings with heating at
600.degree. C. and water-cooling for 10 times is performed. The
atmospheric plasma spraying, a crack was observed in a coating with
a particle size range from 10 pro to 30 .mu.m. Since generation of
SiO.sub.2 and a difference in thermal expansion coefficient between
oxides and Fe--Si particles is the main cause of cracking.
[0049] Table 2 shows particle size range where a fine coating was
obtained and Table 3 shows a result of measuring a Vickers hardness
of a cross section of the coating. In addition, a measuring load of
the hardness was 3N, and an average of 5 times measuring was shown.
Compared with HV180 which is the hardness of the base material,
sprayed coatings of the examples 2 to 4 have a substantially
three-fold hardness, so that high erosion resistance can be
expected.
TABLE-US-00002 TABLE 2 High velocity Atmospheric flame spraying
plasma spraying Particle size range 10-30 .mu.m 30-60 .mu.m 10-30
.mu.m 30-60 .mu.m Example 1 .circleincircle. -- X .circleincircle.
Example 2 .circleincircle. -- X .circleincircle. Example 3
.circleincircle. -- X .circleincircle. Example 4 .circleincircle.
-- X .circleincircle. Example 5 .DELTA. -- .DELTA. .DELTA.
Comparative .circleincircle. .circleincircle. X X example 1
Comparative -- -- X -- example 2 .circleincircle. . . . fine
coating, X . . . crack produced due to thermal shock (coating
formation possible), .DELTA. . . . porous coating, -- . . . coating
formation impossible due to spraying particle erosion
TABLE-US-00003 TABLE 3 High velocity Atmospheric flame spraying
plasma spraying Particle size range 10-30 .mu.m 30-60 .mu.m Example
1 310 300 Example 2 530 400 Example 3 580 440 Example 4 600 580
Example 5 400 450 Comparative example 1 220 200
[0050] A corrosion test of coatings under conditions of simulating
an operational environment of a coal-fired boiler was carried out.
The test temperature was set to 500.degree. C., and the test time
was set to 100 hours. As a simulated corrosive gas composition, a
gas with a composition as shown in Table 4 was supplied at a flow
rate of 100 ml/min in order to bring into a low oxygen partial
pressure and a high sulfur partial pressure and the test was
carried out.
[0051] Table 4 shows a gas composition used in the corrosion test.
The gas composition was determined by a chemical-thermodynamic
calculation of the equilibrium composition of high sulfur coal
(sulfur content is approximately 3.3) combustion gas at
1200.degree. C.
TABLE-US-00004 TABLE 4 H.sub.2S SO.sub.2 CO CO.sub.2 H.sub.2
H.sub.2O N.sub.2 Composition 0.22% 0.14% 6.3% 13.0% 1.8% 10.0% Bal
(Volume fraction)
TABLE-US-00005 TABLE 5 High velocity Atmospheric flamespraying
plasmaspraying Particle size range 10-30 .mu.m 30-60 .mu.m Example
1 0.23 0.50 Example 2 0.04 0.21 Example 3 0.04 0.18 Example 4 0.28
0.30 Example 5 0.35 0.50 Comparative example 1 Decayed due Decayed
due to corrosion to corrosion 0.5Cr--0.5Mo steel 1.0
[0052] Table 5 shows a result of the corrosion test. These values
mean a ratio of weight loss per unit area between thermal spray
coatings and the base metal after removal of corrosion product
after descaling treatment (specimens were washed by boiling 18 wt %
sodium hydroxide +3 wt % potassium permanganate solution and
boiling 10 wt % ammonium citrate solution). As for the Fe--Si based
spraying materials of the examples, as shown in Table 5, the
examples 2 and 3 were one twenty-fifth of the base material in the
high velocity flame spray coating and approximately one-fifth in
the atmospheric plasma sprayed coating within the addition amount
of Si of the present invention. High thermal shock resistance,
coating hardness and corrosion resistance were obtained.
[0053] On the other hand, at a content of Si higher than the range
of the present invention, erosion by spraying particles occurs and
the coating becomes porous, thereupon being unable to obtain a
coating with high corrosion resistance. Further, at a content of Si
lower than the range of the present invention, a dense coating
could be obtained but was corroded and decayed by descaling
treatment.
INDUSTRIAL APPLICABILITY
[0054] The Fe--Si based material for thermal spraying of the
present invention exerts high corrosion resistance since a
SiO.sub.2 coating is formed on a surface of a sprayed coating.
Accordingly, the spraying material is applicable to environments of
high temperature and low oxygen partial pressure, for example, coal
fired boilers for power generation, fluidized bed boilers and
incinerators of refuse incinerating plants.
* * * * *