U.S. patent application number 16/077169 was filed with the patent office on 2019-01-31 for cermet powder, protective-coating-coated member and method of producing same, and electroplating-bath-immersed roll and method of producing same.
This patent application is currently assigned to JFE STEEL CORPORATION. The applicant listed for this patent is JFE STEEL CORPORATION, TOCALO CO., LTD.. Invention is credited to Yuya BABA, Yoshifumi KOBAYASHI, Junichi TAKEUCHI.
Application Number | 20190032239 16/077169 |
Document ID | / |
Family ID | 59625070 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190032239 |
Kind Code |
A1 |
BABA; Yuya ; et al. |
January 31, 2019 |
CERMET POWDER, PROTECTIVE-COATING-COATED MEMBER AND METHOD OF
PRODUCING SAME, AND ELECTROPLATING-BATH-IMMERSED ROLL AND METHOD OF
PRODUCING SAME
Abstract
Disclosed is a cermet powder that enables preparation of a
cermet coating having both high wear resistance and high corrosion
resistance against a strong acid having a pH of less than 1. The
disclosed cermet powder contains tungsten carbide particles in an
amount of 40 mass % or more; molybdenum carbide particles in an
amount of 10 mass % to 40 mass %; and Ni or a Ni alloy as a matrix
metal, wherein the cermet powder further contains chromium, either
as a carbide or a metal or alloy element contained in the matrix
metal, in an amount of 8 mass % or more.
Inventors: |
BABA; Yuya; (Chiyoda-ku,
Tokyo, JP) ; TAKEUCHI; Junichi; (Kobe-shi, Hyogo,
JP) ; KOBAYASHI; Yoshifumi; (Kobe-shi, Hyogo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION
TOCALO CO., LTD. |
Chiyoda-ku Tokyo
Kobe-shi, Hyogo |
|
JP
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
Chiyoda-ku Tokyo
JP
TOCALO CO., LTD.
Kobe-shi, Hyogo
JP
|
Family ID: |
59625070 |
Appl. No.: |
16/077169 |
Filed: |
February 14, 2017 |
PCT Filed: |
February 14, 2017 |
PCT NO: |
PCT/JP2017/005385 |
371 Date: |
August 10, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 5/04 20130101; C23C
4/10 20130101; C23C 4/123 20160101; C23C 4/129 20160101; Y10T
428/12028 20150115; C23C 4/073 20160101; C22C 29/067 20130101; Y10T
428/12146 20150115; C25D 7/0657 20130101; C23C 4/067 20160101; C25D
7/06 20130101; C25D 17/10 20130101; C23C 4/134 20160101; C22C 29/08
20130101; B22F 7/08 20130101; C23C 4/06 20130101; Y10T 428/12014
20150115 |
International
Class: |
C25D 17/10 20060101
C25D017/10; C22C 29/08 20060101 C22C029/08; C23C 4/10 20060101
C23C004/10; C25D 5/04 20060101 C25D005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2016 |
JP |
2016-030368 |
Claims
1. A cermet powder containing: tungsten carbide particles in an
amount of 40 mass % or more; molybdenum carbide particles in an
amount of 10 mass % to 40 mass %; and Ni or a Ni alloy as a matrix
metal, wherein the cermet powder further contains chromium, either
as a carbide or a metal or alloy element contained in the matrix
metal, in an amount of 8 mass % or more.
2. The cermet powder according to claim 1, wherein the tungsten
carbide particles have a content of 70 mass % or less.
3. The cermet powder according to claim 1, wherein the tungsten
carbide particles have a particle size distribution within a range
of 0.1 .mu.m to 6 .mu.m.
4. The cermet powder according to claim 1, wherein the molybdenum
carbide particles have a particle size distribution within a range
of 0.1 .mu.m to 6 .mu.m.
5. A protective-coating-coated member comprising: a stainless steel
base member; and a cermet coating formed on the stainless steel
base member, wherein the cermet coating comprises a matrix made of
Ni or a Ni alloy, in which tungsten carbide particles and
molybdenum carbide particles are dispersed, and the cermet coating
contains the tungsten carbide particles in an amount of 40 mass %
or more, the molybdenum carbide particles in an amount of 10 mass %
to 40 mass %, and chromium, either as a carbide or a metal or alloy
element contained in the matrix, in an amount of 8 mass % or
more.
6. The protective-coating-coated member according to claim 5,
wherein the tungsten carbide particles have a content of 70 mass %
or less.
7. The protective-coating-coated member according to claim 5,
wherein the tungsten carbide particles in the cermet coating have a
particle size distribution within a range of 0.1 .mu.m to 6
.mu.m.
8. The protective-coating-coated member according to claim 5,
wherein the molybdenum carbide particles in the cermet coating have
a particle size distribution within a range of 0.1 .mu.m to 6
.mu.m.
9. The protective-coating-coated member according to claim 5,
wherein the cermet coating has a surface roughness Ra of 0.5 .mu.m
to 10 .mu.m.
10. A method of producing a protective-coating-coated member,
comprising thermal spraying the cermet powder as recited in claim 1
onto a stainless steel base member.
11. The method of producing a protective-coating-coated member
according to claim 10, wherein the thermal spraying is HVOF thermal
spraying.
12. An electroplating-bath-immersed roll comprising the
protective-coating-coated member as recited in claim 5.
13. An electroplating-bath-immersed roll comprising a roll shaft
portion and a roll body portion, both made of stainless steel,
wherein only the roll body portion comprises the
protective-coating-coated member as recited in claim 5.
14. A method of producing an electroplating-bath-immersed roll, the
method comprising: preparing a roll member comprising a roll shaft
portion and a roll body portion, both made of stainless steel; and
forming a cermet coating only onto the roll body portion by thermal
spraying the cermet powder as recited in claim 1.
15. The method of producing an electroplating-bath-immersed roll
according to claim 14, wherein the thermal spraying is HVOF thermal
spraying.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a cermet powder, a
protective-coating-coated member and a method of producing the
same, and an electroplating-bath-immersed roll and a method of
producing the same.
BACKGROUND
[0002] Conventionally, as a method of producing a conductor roll
used in an electroplating bath, the following have been proposed.
JPH1198460A (PTL 1) describes a method in which plasma arc spraying
is performed on a surface of a carbon steel roll using as a thermal
spraying material an alloy containing Co or Ni as a main component
and an additive of Cr, C, Fe, Mo, or the like under a low-pressure
oxygen-free atmosphere, and the coating is then subjected to a hot
melt treatment by plasma arc heating under the same atmosphere to
form a nonporous thermal sprayed coating.
[0003] JPH5295592A (PTL 2) describes a method in which a
thermal-spray coated layer is formed by thermal spraying a mixed
powder composed of a carbide cermet powder and a C-containing
nickel chromium alloy powder on the surface of a carbon-steel roll
body portion, then causing redeposition of carbide by heating the
thermal spray coating layer to form a redeposited-carbide-dispersed
thermal sprayed coating, and subsequently shrink-fitting the roll
body portion to the outside of the roll base member.
[0004] JP200288461A (PTL 3) describes a method of producing a
conductor roll having enhanced corrosion resistance, in which a
mixed powder composed of WC--Ni cermet and the balance consisting
of a Ni-base self-fluxing alloy is thermal sprayed on the surface
of a SS-400 roll, and thereafter a remelting treatment is carried
out to form a coating layer.
[0005] JP2006183107A (PTL 4) describes a method of producing a
conductor roll, in which a self-fluxing alloy thermal sprayed layer
containing WC cermet is formed on the surface of a SS-400 roll and
a WC cermet coating is further formed thereon.
CITATION LIST
Patent Literature
[0006] PTL 1: JPH1198460A [0007] PTL 2: JPH5295592A [0008] PTL 3:
JP200288461A [0009] PTL 4: JP2006183107A
SUMMARY
Technical Problem
[0010] In PTL 1, a plating solution of a strong acid having a pH of
less than 1 has the problem that the plating solution infiltrates
from the surface of the coating after continuous use, causing the
adhesion between the roll substrate and the thermal sprayed coating
to decrease and the coating to peel off from the surface of the
substrate. In fact, the technique of PTL 1 is not implemented under
severe circumstances such as a pH below 1, in which the
implementation conditions are only demonstrated in the current
density range as low as 5 A/dm.sup.2 to 20 A/dm.sup.2, and the
operation period is as short as 1,000 hours. This means that the
technique of PTL 1 fails to address a long-term operation, such as
one month continuous operation. In addition, since the thermal
melting treatment of the coating is performed after thermal
spraying, there is a problem of increased manufacturing cost.
[0011] Again, in PTL 2, a plating solution of a strong acid having
a pH of less than 1 has the problem that the plating solution
infiltrates from the surface of the coating after continuous use,
causing the adhesion between the roll substrate and the thermal
sprayed coating to decrease and the coating to peel off from the
surface of the substrate. In addition, the edge of the roll is acid
corroded by the plating solution, leading to the problem of
fragments lowering the product yield. It is also necessary to carry
out remelting treatment on the roll after thermal spraying, causing
a problem that the time and cost associated with roll regeneration
including shrink-fitting are increased.
[0012] Also in PTL 3, a plating solution of a strong acid having a
pH of less than 1 has the problem that the plating solution
infiltrates from the surface of the coating after continuous use,
causing the adhesion between the roll substrate and the thermal
sprayed coating to decrease and the coating to peel off from the
surface of the substrate. It is also necessary to carry out
remelting treatment on the roll after thermal spraying, causing a
problem that the time and cost associated with roll regeneration
are increased. In addition, when applying this coating to a
stainless steel roll, the remelting treatment causes cracking at
the crystal grain boundary due to heating of the stainless steel,
and the roll is damaged. For this reason, carbon steel having low
corrosion resistance has to be used, leading to the problem of
fragments of acid-corroded carbon steel lowering the product
yield.
[0013] Also in PTL 4, a plating solution of a strong acid having a
pH of less than 1 has the problem that the plating solution
infiltrates from the surface of the coating after continuous use,
causing the adhesion between the roll substrate and the thermal
sprayed coating to decrease and the coating to peel off from the
surface of the substrate. Actually, in the test of acid
corrosiveness by immersion in a plating solution in PTL 4, the pH
is 3.0, and no test was conducted under severe environments such as
a pH below 1. It is also necessary to carry out remelting treatment
on the roll after thermal spraying, causing a problem that the time
and cost associated with roll regeneration are increased. In
addition, when applying this coating to a stainless steel roll, the
remelting treatment causes cracking at the crystal grain boundary
due to heating of the stainless steel, and the roll is damaged. For
this reason, carbon steel having low corrosion resistance has to be
used, leading to the problem of fragments of acid-corroded carbon
steel lowering the product yield.
[0014] As described above, the conventional conductor rolls are
primarily characterized in that carbon steel is used as the roll
material, and for the purpose of preventing reaction of the carbon
steel with the plating solution, a coated layer of a NiCr-based
alloy is formed on the roll surface. This coated layer is
characterized by containing a carbide (or cermet) mainly composed
of WC for the purpose of preventing wear due to rubbing against a
steel sheet. This may greatly reduce reaction and wear in an acidic
plating bath of pH.gtoreq.1, secure the roll life, and reduce the
defective rate.
[0015] However, in such a conventional conductor roll, in the
strong acid plating bath with pH<1, the acid corrosion amount of
the carbon steel itself greatly increases, and in addition, the
corrosion resistance of the coated layer itself containing carbide
becomes insufficient, raising the problem of the effect obtained
being small for the cost involved in the production of the roll.
That is, it is difficult to achieve both high wear resistance and
high corrosion resistance against a strong acid having a pH of less
than 1 in those rolls obtained by the conventional technique and
conventional surface treatment.
[0016] Further, it was found that in a conventional product having
a thermal sprayed coating on the carbon steel roll base member, the
thermal sprayed coating and the carbon steel roll base member are
damaged due to acid corrosion, and some fragments jump into the
plating product, resulting in defects such as pressing flaw and
thus lower product yield. In addition, in a general tin
electroplating process, it is known that tin ions in the plating
solution change to metallic tin, which may cause an
electrodeposition on the roll surface. This electrodeposited
metallic tin also causes defective products such as pressing flaw,
and such tendency becomes remarkable when the above-described
conventional roll is used.
[0017] It would thus be helpful to provide a cermet powder that
enables preparation of a cermet coating having both high wear
resistance and high corrosion resistance against a strong acid
having a pH of less than 1. It would also be helpful to provide a
protective-coating-coated member and an
electroplating-bath-immersed roll that are compatible with high
wear resistance and high corrosion resistance against a strong acid
having a pH of less than 1, as well as their production
methods.
Solution to Problem
[0018] We thus provide:
[0019] (1) A cermet powder containing: tungsten carbide particles
in an amount of 40 mass % or more; molybdenum carbide particles in
an amount of 10 mass % to 40 mass %; and Ni or a Ni alloy as a
matrix metal, wherein the cermet powder further contains chromium,
either as a carbide or a metal or alloy element contained in the
matrix metal, in an amount of 8 mass % or more.
[0020] (2) The cermet powder according to (1) above, wherein the
tungsten carbide particles have a content of 70 mass % or less.
[0021] (3) The cermet powder according to (1) or (2) above, wherein
the tungsten carbide particles have a particle size distribution
within a range of 0.1 .mu.m to 6 .mu.m.
[0022] (4) The cermet powder according to any one of (1) to (3)
above, wherein the molybdenum carbide particles have a particle
size distribution within a range of 0.1 .mu.m to 6 .mu.m.
[0023] (5) A protective-coating-coated member comprising: a
stainless steel base member; and a cermet coating formed on the
stainless steel base member, wherein the cermet coating comprises a
matrix made of Ni or a Ni alloy, in which tungsten carbide
particles and molybdenum carbide particles are dispersed, and, the
cermet coating contains the tungsten carbide particles in an amount
of 40 mass % or more, the molybdenum carbide particles in an amount
of 10 mass % to 40 mass %, and chromium, either as a carbide or a
metal or alloy element contained in the matrix, in an amount of 8
mass % or more.
[0024] (6) The protective-coating-coated member according to (5)
above, wherein the tungsten carbide particles have a content of 70
mass % or less.
[0025] (7) The protective-coating-coated member according to (5) or
(6) above, wherein the tungsten carbide particles in the cermet
coating have a particle size distribution within a range of 0.1
.mu.m to 6 .mu.m.
[0026] (8) The protective-coating-coated member according to any
one of (5) to (7) above, wherein the molybdenum carbide particles
in the cermet coating have a particle size distribution within a
range of 0.1 .mu.m to 6 .mu.m.
[0027] (9) The protective-coating-coated member according to any
one of (5) to (8) above, wherein the cermet coating has a surface
roughness Ra of 0.5 .mu.m to 10 .mu.m.
[0028] (10) A method of producing a protective-coating-coated
member, comprising thermal spraying the cermet powder as recited in
any one of (1) to (4) above onto a stainless steel base member.
[0029] (11) The method of producing a protective-coating-coated
member according to (10) above, wherein the thermal spraying is
HVOF thermal spraying.
[0030] (12) An electroplating-bath-immersed roll comprising the
protective-coating-coated member as recited in any one of (5) to
(9) above.
[0031] (13) An electroplating-bath-immersed roll comprising a roll
shaft portion and a roll body portion, both made of stainless
steel, wherein only the roll body portion comprises the
protective-coating-coated member as recited in any one of (5) to
(9) above.
[0032] (14) A method of producing an electroplating-bath-immersed
roll, the method comprising: preparing a roll member comprising a
roll shaft portion and a roll body portion, both made of stainless
steel; and forming a cermet coating only onto the roll body portion
by thermal spraying the cermet powder as recited in any one of (1)
to (4) above.
[0033] (15) The method of producing an electroplating-bath-immersed
roll according to (14) above, wherein the thermal spraying is HVOF
thermal spraying.
Advantageous Effect
[0034] With the cermet powder of the present disclosure, it is
possible to prepare a cermet coating that offers both high wear
resistance and high corrosion resistance against a strong acid
having a pH of less than 1.
[0035] Further, the protective-coating-coated member and the
electroplating-bath-immersed roll of the present disclosure can
achieve both high wear resistance and high corrosion resistance
against a strong acid having a pH of less than 1.
BRIEF DESCRIPTION OF THE DRAWING
[0036] In the accompanying drawings:
[0037] FIG. 1 is a schematic cross-sectional view of a
protective-coating-coated member 100 according to one of the
embodiments of the present disclosure; and
[0038] FIG. 2A is a schematic cross-sectional view of a
conventional electroplating-bath-immersed roll 200, while FIG. 2B
is a schematic cross-sectional view of an
electroplating-bath-immersed roll 300 according to one of the
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0039] (Cermet Powder)
[0040] A cermet powder according to one of the embodiments of the
present disclosure contains: tungsten carbide particles in an
amount of 40 mass % or more; molybdenum carbide particles in an
amount of 10 mass % to 40 mass %; Ni or a Ni alloy as a matrix
metal; and chromium either as a carbide or a metal or alloy element
in the matrix, in an amount of 8 mass % or more. With this cermet
powder, it is possible to produce a cermet coating that offers both
high wear resistance and high corrosion resistance against a strong
acid having a pH of less than 1. Each component of the cermet
powder of the present disclosure will be described below.
[0041] The tungsten carbide particles serve to impart high wear
resistance and relatively high corrosion resistance to the cermet
coating. The tungsten carbide particles include for example WC
particles. The content of the tungsten carbide particles needs to
be 40 mass % or more. The reason is that if it is less than 40 mass
%, the cermet coating cannot provide sufficient wear resistance.
Also, the content of the tungsten carbide particles is preferably
70 mass % or less. The reason is that if it exceeds 70 mass %, the
content of the other components becomes so small that the cermet
coating cannot provide high corrosion resistance against a strong
acid having a pH of less than 1. From the viewpoint of reliably
achieving the effect of the present disclosure, the tungsten
carbide particles preferably have a particle size distribution
within a range of 0.1 .mu.m to 6 .mu.m.
[0042] The molybdenum carbide particles are important components in
the present disclosure, which plays a role of imparting to the
cermet coating not only high wear resistance but also high
corrosion resistance to a strong acid having a pH of less than 1.
The molybdenum carbide particles include for example Mo.sub.2C
particles. The content of the molybdenum carbide particles needs to
be 10 mass % to 40 mass %. The reason is that if the content is
less than 10 mass %, the cermet coating cannot provide high
corrosion resistance against a strong acid having a pH of less than
1, and if it exceeds 40 mass %, the content of the other
components, in particular, tungsten carbide particles, must be
reduced, resulting in insufficient wear resistance of the cermet
coating. From the viewpoint of reliably achieving the effect of the
present disclosure, the molybdenum carbide particles preferably
have a particle size distribution within a range of 0.1 .mu.m to 6
.mu.m.
[0043] The cermet powder of the present disclosure contains Ni or a
Ni alloy as a matrix metal. Examples of the Ni alloy include a
NiCr-based alloy, a NiCrMo-based alloy, and a NiCoCrAlY-based
alloy, containing Ni as a main component. Ni as a matrix metal
plays a role of imparting to the cermet coating high corrosion
resistance to a strong acid having a pH of less than 1. From this
viewpoint, the Ni content in the cermet powder is preferably 5 mass
% or more. Further, in view of the preferable content of the other
components, the Ni content in the cermet powder is preferably 20
mass % or less.
[0044] The cermet powder of the present disclosure contains
chromium, either as a carbide or a metal or alloy element contained
in the matrix metal, in an amount of 8 mass % or more. This
chromium plays a role of imparting to the cermet coating high
corrosion resistance to a strong acid having a pH of less than 1,
and from that viewpoint its content needs to be 8 mass % or more.
In view of the preferable content of the other components, the
content of chromium in the cermet powder is preferably 20 mass % or
less. In the case where the cermet powder of the present disclosure
contains chromium carbide particles (Cr.sub.3C.sub.2 particles),
from the viewpoint of ensuring the effect of the present
disclosure, the particle size distribution thereof is preferably
within a range of 0.1 .mu.m to 6 .mu.m.
[0045] The cermet powder of the present disclosure preferably
consists of the above components and inevitable impurities.
[0046] In the cermet powder of the present disclosure, the
molybdenum content is preferably not less than the chromium content
from the viewpoint of imparting to the cermet coating high
corrosion resistance to a strong acid having a pH of less than
1.
[0047] Regarding the cermet powder of the present disclosure, its
production method is not particularly limited, and it can be
produced by a known or arbitrary method such as a melt
pulverization method, a sintering pulverization method, or a
granulation sintering method.
[0048] (Protective-Coating-Coated Member and Method of Producing
the Same, and Electroplating-Bath-Immersed Roll and Method of
Producing the Same)
[0049] Referring to FIG. 1, a protective-coating-coated member 100
according to one of the embodiments of the present disclosure
comprises: a stainless steel base member 10; and a cermet coating
20 formed on the stainless steel base member. The cermet coating 20
is formed by thermal spraying the cermet powder of the present
disclosure as the thermal spray material onto the stainless steel
base member 10. Consequently, in the cermet coating 20, carbide
particles 24 containing tungsten carbide particles and molybdenum
carbide particles, and optionally chromium carbide, are dispersed
in a matrix 22 made of Ni or a Ni alloy. The content and particle
size distribution of the tungsten carbide particles, the content
and particle size distribution of the molybdenum carbide particles,
the Ni content, the chromium content, and the particle size
distribution of the chromium carbide particles in the cermet
coating 20 are the same as those described above in conjunction
with the cermet powder 20. In addition, an
electroplating-bath-immersed roll according to an embodiment of the
present disclosure comprises the protective-coating-coated member
100. The protective-coating-coated member and the
electroplating-bath-immersed roll thus formed according to the
present disclosure can achieve both high wear resistance and high
corrosion resistance against a strong acid having a pH of less than
1.
[0050] In particular, in the present embodiment, referring to FIG.
2B, it is preferable that a roll member comprising a roll shaft
portion 30 and a roll body portion 32, both made of stainless
steel, is prepared, and a cermet coating 34 is formed only onto the
roll body portion by thermal spraying the cermet powder disclosed
herein to thereby produce a electroplating-bath-immersed roll
300.
[0051] According to the present disclosure, the
protective-coating-coated member of the present disclosure and the
method of producing the same, and the electroplating-bath-immersed
roll and the method of producing the same were completed based on
our discoveries as described below.
[0052] As mentioned above, using conventional rolls, the life of
the rolls and the product yield are greatly reduced in a
strong-acid plating bath such as a methanesulfonic acid solution
with pH<1. In order to elucidate this phenomenon and examine
countermeasures, our attention was focused on the electrochemical
reaction occurring in a roll in the plating solution. First, it was
considered that in a conductor roll in a plating bath, unlike
ordinary corrosion reaction, a substitution reaction is in progress
that is composed of two main reactions, one being a corrosion
reaction (anode reaction) in which Fe (or, for example, Ni in the
coated layer) becomes ions in the surface and dissolves in the
solution, and the other in which Sn ions in the solution undergo
electrodeposition (cathode reaction). For example, when the roll
component is Fe and the plating component is Sn, these reactions
can be expressed as:
cathode reaction: Sn.sup.2++2e.sup.-.fwdarw.Sn (1)
anode reaction: Fe.fwdarw.Fe.sup.2++2e.sup.- (2).
[0053] The reactions of formulas (1) and (2) are electrochemically
equivalent, and the total amount of electrons (e.sup.-) generated
in the anode reaction is equal to the total amount of electrons
consumed in the cathode reaction. On the surface of the conductor
roll under such an electrochemical reaction environment, the
dissolution reaction proceeds at a portion where the potential
increases locally (i.e., anode), while the electrodeposition
reaction proceeds at a portion where the potential lowers locally
(i.e., cathode).
[0054] In the case where the corrosion potential when the roll is
immersed in the solution is relatively high, the sites where these
reactions take place can be regarded as being uniformly distributed
in microscopic scales, and the corrosion uniformly proceeds over
the entire surface. Consequently, the surface morphology can
maintain an initial good state. However, under such conditions that
the plating solution is a strong acid with pH<1 or the current
density of plating is set excessively high, the reaction may
proceed as a result of a cathode or anode reaction taking place in
a locally fixed site. In such a case, the surface morphology
changes greatly as described below, which may damage the plated
product.
[0055] First, with respect to the deposition of plating components
such as Sn resulting from the cathode reaction, the reaction tends
to concentrate at the site where deposition is initially generated,
causing a metal to grow. Then, the grown metal deposit grows to a
certain size, then falls off due to a load of, for example, rubbing
against the steel sheet, and the site where the cathode reaction
concentrates shifts to another place. By repeating such a reaction,
deposition of a plating metal such as Sn progresses non-uniformly
on the surface, and at the same time fragments of the plating metal
that fall off may damage the surface of the steel sheet as a
product.
[0056] Further, when the reaction concentrates as a result of the
anode reaction being fixed at a certain site, a particular element
(such as Fe in the roll) constituting the site is selectively
dissolved at the grain boundary or the like, which may cause the
roll surface or the coated layer to partially fall off as
fragments. These fragments that have fallen off from the surface
may damage the surface of the steel sheet as a product.
[0057] In other words, in a conventional roll as described above,
the corrosion potential relatively decreases in a strong acid
plating bath with pH<1 or when the current density is
excessively high, and the microscopic uniformity of the
distribution of the anode and the cathode is reduced,
adhesion/detachment of the plating metal and partial damage in the
roll surface become conspicuous as a result of localized
immobilization, and this may be the cause of decrease in the
product yield.
[0058] Therefore, in order to secure the roll life and to maintain
a high product yield even in a strong acid plating bath with
pH<1 or even when the current density is set high for the
purpose of increasing the line speed, it is necessary to find out a
material that can prevent as much as possible the phenomenon in
which the reaction would concentrate as a result of a cathode or
anode reaction taking place in a locally-fixed site as described
above, rather than focusing simply on the amount of reaction.
Conversely, providing such a material can prevent the progress of
local corrosion as described above, guaranteeing the life of the
roll and the product yield.
[0059] In view of the above, static immersion tests were conducted
on roll materials in a tin plating solution using methanesulfonic
acid with pH<1, where the change of corrosion potential with
time was measured and the degree of substitution reaction was
evaluated. The test results revealed that when carbon steel was
used as the roll material, the amount of reaction was extremely
high, metallic Sn was deposited at every part of the surface, and
the deposited lump of metallic Sn repeatedly grew and dropped. On
the other hand, when stainless steel such as SUS 316L was used as
the roll material, the amount of reaction was considerably low and
metal Sn deposition was not found clearly, although a thin reaction
layer was observed on the surface. In addition, the reaction layer
on the surface could be easily removed by washing with water and
chemical washing, and deposition of metallic Sn on the removed
surface was not observed. The corrosion potentials at the time when
20 days passed after immersion were compared. As a result, it was
found that stainless steel had a potential higher than that of
carbon steel by 0.1 V or more, and maintained a potentially noble
state.
[0060] From these results, we judged that the amount of reaction is
small and immobilization of the anode and the cathode on the
surface is not likely to occur even in a strong acid solution with
pH<1 as long as the stainless steel has a corrosion potential of
about 0.1 V higher than that of carbon steel. However, since the
hardness of stainless steel is at most about HV 200, there is
concern that the wear resistance to rubbing against the steel sheet
is low. Accordingly, we made further investigations on the material
of the coated layer for protecting stainless steel. It is necessary
for the material for protecting stainless steel to have high
hardness, excellent wear resistance, and good corrosion resistance
in a strong acid plating bath. Although carbide cermets are
promising as such a material, it is known that good properties
cannot be obtained with the ones described in PTLs 1 to 4. However,
we determined that these carbide cermets may be able to improve the
electrochemical characteristics in a strong acid plating bath by
adjusting the components, and engaged in further studies.
[0061] Specifically, samples were prepared by coating the surface
of stainless steel as a base member with more than ten kinds of
carbide cermet powders for thermal spraying including commercially
available ones by HVOF thermal spraying, and immersion experiments
were conducted using a strong acid plating solution with pH<1.0.
The experimental results revealed that Ni or a NiCr-based alloy is
superior for the matrix of the cermet, and when the carbide
contains Mo carbide rather than WC particles alone, good corrosion
resistance can be obtained. Therefore, as a result of our further
investigations, we discovered that in order to obtain high
corrosion resistance in a strong acid solution, it is desirable
that Cr be contained as carbide or an alloy element in the matrix
in an amount of 8 mass % or more and the content of Mo contained as
carbide be at least equal to or more than the content of Cr. It was
also found that Mo.sub.2C is preferable as the Mo carbide, and that
if the content of Mo contained in the cermet is larger than the
content of Cr, corrosion resistance will not be impaired, but
conversely if the content of Mo is not more than half of the
content of Cr, it is difficult to obtain a desired corrosion
resistance.
[0062] That is, in a carbide cermet coating for protecting
stainless steel from the substitution reaction as described above
in a strong acid solution with pH <1 and for ensuring sufficient
wear resistance against sliding operation with a steel sheet, it is
desirable that carbide particles containing tungsten carbide
particles and molybdenum carbide particles are dispersed in a
matrix made of Ni or a Ni alloy, wherein the cermet coating
contains the tungsten carbide particles in an amount of 40 mass %
or more, the molybdenum carbide particles in an amount of 10 mass %
to 40 mass %, and chromium either as a carbide or a metal or alloy
element contained in the matrix, in an amount of 8 mass % or more.
As a matrix containing Ni as a main component, good results were
obtained with a NiCr-based alloy, a NiCrMo-based alloy, and a
NiCoCrAlY-based alloy.
[0063] Specimens were prepared with a carbide cermet coating
satisfying the above conditions being formed on stainless steel by
HVOF thermal spraying to form a protective coating, and were
subjected to constant-current anode/cathode polarization
dissolution experiments. The experimental results demonstrated that
the formation of a reaction layer was not significant and the
surface morphology was still better than the stainless steel. In
addition, as a result of measuring the corrosion potential, a
potential higher by about 0.1 V than that of the stainless steel
was obtained. The above results indicate that the uniformity of the
distribution of the anode and the cathode formed on the surface of
the above-described carbide cermet coating formed by HVOF thermal
spraying is achieved at a finer level than that of stainless steel.
It was thus found that there is almost no possibility of the steel
sheet being damaged by the reaction product. In this way, we
discovered that a protective layer having good corrosion resistance
can be formed even in a strong acid plating bath, while having
excellent wear resistance.
[0064] Here, it was determined that it is important to adjust the
particle size of the tungsten carbide particles and the molybdenum
carbide particles, which are the main components of the cermet, for
achieving both wear resistance and corrosion resistance in a
trade-off relationship. Specifically, it was found that when
carbides, which are the main component of the cermet, having
particle sizes of less than 0.1 .mu.m are used, the wear resistance
is remarkably deteriorated, and when particles having a particle
size of 6 .mu.m or more are used, the uniformity of the
distribution of the anode and the cathode in the solution cannot be
maintained sufficiently in microscopic scales. It was determined
that when the particle size of the tungsten carbide particles and
the molybdenum carbide particles is in the range of 0.1 .mu.m to 6
.mu.m, both wear resistance and corrosion resistance can be
compatible.
[0065] As a method of forming a protective layer, a high-velocity
flame spraying method such as HVOF or HVAF was found to be
desirable. For example, when comparing the cermet coating obtained
by a high-velocity flame spraying method such as HVOF or HVAF with
the cermet coating by plasma spraying or other thermal spraying
method, the porosity greatly differs, and in the case of a layer
obtained by a thermal spraying method other than the high-velocity
flame spraying method such as HVOF or HVAF, it was difficult to
maintain a satisfactory surface condition; for example, the
solution infiltrated into the layer. Also, when heat treatment is
performed on the resulting layer at a high temperature for the
purpose of lowering the porosity, the carbide is decarburized into
lower carbide or a reaction phase forms with the matrix components,
causing a remarkable degradation in wear resistance and corrosion
resistance. Such a tendency was also seen in the layers formed by
weld overlaying and cladding method. That is, a high-velocity flame
spraying method such as HVOF or HVAF is preferable as the method of
forming a carbide cermet coating.
[0066] It was found that even with a protective layer formed by a
high-velocity flame spraying method such as HVOF or HVAF, the
probability of scratching the steel sheet with protrusions of
carbide increases when the surface roughness Ra exceeds 10 .mu.m,
and when Ra is less than 0.5 .mu.m, the frictional force is not
sufficient and the roll idly rotates on the steel sheet, resulting
in impairment of the surface condition of the steel sheet.
Therefore, the surface roughness Ra of the carbide cermet coating
is preferably 0.5 .mu.m to 10 .mu.m.
EXAMPLES
Example 1
[0067] Samples were prepared in conformity with conventional roll
specifications and roll specifications according to the present
disclosure, and subjected to immersion tests for 20 days in a
strong-acid plating solution (methanesulfonic acid 50 g/L, tin ion
concentration 25 g/L) adjusted to pH<1. Five samples listed in
Table 1 were prepared. Specifically, in Sample No. 1, the base
member was a conventional carbon steel and the protective layer was
also a conventional sample. On the other hand, in Sample Nos. 2 to
5, the base member was made of stainless steel. Regarding the
protective layers, Sample No. 2 adopted a conventional layer as in
Sample No. 1, and Sample Nos. 3 to 5 used HVOF layers of various
carbide cermets using Ni or a Ni base alloy as the matrix; among
these, Sample No. 5 corresponds to the cermet specification of our
example of the present disclosure. In the layer of Sample No. 5,
the Mo content was 9.4 mass %, the Cr content was 8.7 mass %, the
WC particle size was 0.1 .mu.m minimum and 6 .mu.m maximum, the
particle size of Mo.sub.2C particles was 0.1 .mu.m minimum and 6
.mu.m maximum, and the surface roughness Ra was 3.0 .mu.m. Each
sample was prepared such that the exposed portion of the base
member and the protective layer portion had substantially the same
surface area and devised such that the properties of the boundary
portion between the layer and the base member could be
evaluated.
[0068] To evaluate the corrosion resistance of the protective
layer, the change in mass (weight loss due to corrosion) before and
after immersion was measured for each sample, and the results are
presented in Table 1. In addition to the change in mass, Table 1
lists the results of observation of the surface conditions of the
protective layer with the electron microscope after immersion for
20 days, as well as the measurements of the corrosion potential.
Table 1 also lists the results of Suga wear tests (#120-SiC paper,
load 3.25 kgf, 400 reciprocations) separately performed on the
protective layers. The layer observation results were evaluated
according to the following criteria: [0069] Excellent: almost no
change [0070] Good: slightly changed [0071] Fair: changed [0072]
Poor: significantly changed
TABLE-US-00001 [0072] TABLE 1 Coating Corrosion Change Amount
Sample Base observation potential in mass of wear No. Member
Coating components results (V vs. Ag/AgCl) (g) (mg) Category No. 1
SS400 46Ni--11Cr--2.5B--2.5Si--2.5Fe--35WC Poor -0.7 >0.46 2
Comparative Example No. 2 SUS316L
46Ni--11Cr--2.5B--2.5Si--2.5Fe--35WC Poor -0.6 0.35 2 Comparative
Example No. 3 SUS316L WC-20Cr.sub.3C.sub.2--7Ni Fair -0.6 0.33 0.5
Comparative Example No. 4 SUS316L Cr.sub.3C.sub.2--60CoNiCrAlY Fair
-0.5 0.34 1.5 Comparative Example No. 5 SUS316L
WC-10Mo.sub.2C--10Cr.sub.3C.sub.2--10Ni Excellent -0.4 0.26 0.5
Example
[0073] As is clear from the results in Table 1, in the plating
solution with pH <1, the change in mass was significant in
Sample Nos. 1 to 4 in accordance with the conventional
specifications, particularly in Sample No. 1 using carbon steel as
the base member, leading to deterioration in the surface
morphology. Furthermore, in the specimens in accordance with the
conventional specification using carbon steel as the base member,
the boundary between the layer and the base member was markedly
broken by corrosion. In contrast, it can be seen that not only the
change in mass was small but also the surface morphology was
difficult to deteriorate in those samples in which stainless steel
was protected with a cermet coating. In particular, in Sample No. 5
which is an example of the present disclosure, the surface
morphology was much better than the other samples. This also
corresponds to the measurement result of the corrosion potential
(the highest in the measurement sample), demonstrating that the
uniformity of the distribution of the anode and the cathode on the
surface of the coating was excellent. In addition, it can be seen
that our examples were excellent also from the viewpoint of wear
resistance.
Example 2
[0074] Focusing on the mix proportion of the protective layer of
Sample No. 5 in Example 1, various cermet powders containing Ni or
a Ni-20Cr alloy as a matrix, as well as WC particles,
Cr.sub.3C.sub.2 particles, and Mo.sub.2C particles with the
adjusted particle size distribution within a range of 0.1 .mu.m to
6 .mu.m, were prepared. Each obtained cermet powder was HVOF
thermal sprayed onto a stainless steel to form a protective layer.
The composition of the layer in each sample is presented in Table
2. Immersion tests were conducted in the same way as in Example 1,
and Suga wear tests were carried out. The evaluation results are
presented in Table 2.
TABLE-US-00002 TABLE 2 Evaluation results Immersion test Change in
Wear test Sample Chemical composition of coating (mass %) Coating
observation mass Amount of No. WC Cr.sub.3C.sub.2 Mo.sub.2C Ni
Ni--20Cr Mo content Cr content results (g) wear (mg) Category 1 73
20 0 7 0 0 17.3 Fair 0.33 0.5 Comparative Example 2 75 10 0 15 0 0
8.7 Fair 0.35 0.7 Comparative Example 3 75 10 0 0 15 0 11.7 Fair
0.34 0.7 Comparative Example 4 70 10 10 10 0 9.4 8.7 Good 0.26 0.5
Example 5 70 10 10 0 10 9.4 10.7 Good 0.26 0.5 Example 6 60 10 20
10 0 18.8 8.7 Good 0.25 0.7 Example 7 60 10 20 0 10 18.8 10.7 Good
0.25 0.7 Example 8 50 10 30 10 0 28.2 8.7 Excellent 0.24 0.9
Example 9 50 10 30 0 10 28.2 10.7 Excellent 0.24 0.9 Example 10 50
20 20 10 0 18.8 17.3 Excellent 0.25 1.0 Example 11 40 10 40 10 0
37.6 8.7 Excellent 0.24 1.0 Example 12 30 20 30 20 0 28.2 17.3
Excellent 0.24 1.2 Comparative Example 13 30 20 30 0 20 28.2 21.3
Excellent 0.24 1.2 Comparative Example 14 20 20 50 0 10 47.1 19.3
Excellent 0.23 1.3 Comparative Example 15 10 10 70 10 0 65.9 8.7
Excellent 0.23 1.3 Comparative Example
[0075] As is apparent from the results in Table 2, it is effective
to incorporate more Mo.sub.2C particles if it is intended to
improve the corrosion resistance to the plating solution, and it is
effective to incorporate more WC particles for improving the wear
resistance. It is found that Examples 4 to 11 of the present
disclosure provided both high wear resistance and high corrosion
resistance against a strong acid having a pH of less than 1.
[0076] In each sample in which the cermet powder described in
Example 2 was formed into a protective layer by atmospheric plasma
spraying method, the porosity was high and the adverse effect such
as the deterioration of the carbide was large, and as regards the
corrosion resistance and the wear resistance, it was not as good as
the layer produced by HVOF thermal spraying.
Example 3
[0077] A comparison is made between a conventional product and a
product according to the present disclosure when applied to a
conductor roll in an electroplating line. FIGS. 2A and 2B
illustrate a comparison between the structure of a conventional
roll and the structure of a roll according to the present
disclosure. In the conventional roll in FIG. 2A, a shaft portion
was formed by shrink-fitting a carbon steel tube to a copper shaft
core, and a body portion was formed by shrink-fitting a carbon
steel sleeve with a protective layer formed thereon by thermal
spraying to a roll body portion formed of a carbon steel tube, and
these were combined to form a whole roll body. In contrast, in the
present disclosure, as illustrated in FIG. 2B, it is only necessary
to form a thermal sprayed coating on the roll body made of
stainless steel, and it will be readily appreciated that the roll
body can be extremely easily fabricated. Sample No. 6 in Example 2
was adopted as the layer specification according to the present
disclosure.
[0078] Heat generation by energization of each roll was measured
with a thermoviewer, and both were determined to be within the
range of 0.14.degree. C./min to 0.16.degree. C./min, in which
operability is not impaired. The composition of the plating bath
was the same as in Example 1. The roll pressing pressure on the
steel sheet was 0.2 MPa and the sheet passing speed was in the
range of 150 m/min to 490 m/min. Each roll was used for 230 days.
After completion of use, each roll was pulled up from the bath, and
the surface roughness of the sheet passing portion and the amount
of Sn adhesion were investigated. The results are presented in
Table 3.
TABLE-US-00003 TABLE 3 Conventional product Our product Ra before
use 3.0 .mu.m 3.0 .mu.m Ra after use 0.81 .mu.m 1.08 .mu.m Tin
adhesion to roll surface 5.2 mass % 4.7 mass % Failure rate 2.37%
0.43%
[0079] The results in Table 3 demonstrated that the surface
roughness of the sheet passing portion of each conventional roll
decreased from Ra of 3.0 .mu.m before use to Ra of 0.81 .mu.m,
which is nearly 1/4, whereas in each roll to which the present
disclosure was applied Ra of 1.0 .mu.m or more was maintained after
use, and improvement of the layer life of 30% or more was achieved
compared to the conventional ones. It can also be seen that the
amount of Sn adhesion was reduced by about 10% in each roll of the
present disclosure as compared with the conventional ones. Both of
these results indicate that the corrosion resistance to the plating
solution and the wear resistance against the steel sheet can be
improved in accordance with the specifications of the present
disclosure. In fact, the failure rate of the product was
successfully lowered to 0.43%, which is 1/5 or less, in the case of
using rolls of the present disclosure, while it was as high as
2.37% in the case of using conventional rolls. The reason is
considered to be that due to the improvement of corrosion
resistance, the damage in the layer which would be the cause of
defect and the occurrence rate of coarsen fragments of the
electrodeposited Sn were greatly reduced.
[0080] From the results of the same actual operation, it is also
found that the use limit of rolls was up to Ra of 0.5 .mu.m in
surface roughness, and that the frequency at which the product
suffers scratches increased with a roll having an initial surface
roughness Ra exceeding 10 .mu.m. Therefore, the surface roughness
Ra of the cermet coating according to the present disclosure is
preferably from 0.5 .mu.m to 10 .mu.m.
INDUSTRIAL APPLICABILITY
[0081] The cermet powder of the present disclosure can be suitably
used as the material of a protective layer (cermet coating) in a
protective-coating-coated member such as an
electroplating-bath-immersed roll. The electroplating-bath-immersed
roll of the present disclosure can be suitably used, for example,
as a conductor roll or the like even in an electroplating bath of a
strong acid having a pH of less than 1.
REFERENCE SIGNS LIST
[0082] 100 protective-coating-coated member [0083] 10 base member
(stainless steel) [0084] 20 cermet coating [0085] 22 matrix [0086]
24 carbide particles (WC particles, Mo.sub.2C particles, and
optionally Cr.sub.3C.sub.2 particles) [0087] 300
electroplating-bath-immersed roll [0088] 30 roll shaft portion
[0089] 32 roll body portion [0090] 34 cermet coating (thermal
sprayed coating)
* * * * *