0001]
The present invention relates to a plated steel sheet and a method for
producing the same.
Background Art
[0002]
Stainless steel sheets have been widely used as heat-resistant uses. For
example, stainless steel is used in an exhaust system of an automobile, which is
15 required to have corrosion resistance performance in a high-temperature corrosive
environment. Since stainless steel is expensive, replacement with aluminum plating,
which is less expensive and is excellent in heat resistance, is pursued; however, since
aluminum plating has only insufficient corrosion resistance in an environment in
which it is exposed to NOx and SOx, such as around a muffler, most of the materials
20 are still stainless steel.
[0003]
Thus, the present inventors have worked toward the development of heatresistant
Ni-Cr alloy plating using Ni and Cr that does not dissolve in nitric acid or
sulfuric acid, with the purpose of providing a material that is inexpensive and is
25 excellent in high-temperature corrosion resistance and corrosion resistance in NOx
and SOx environments, and that can take the place of stainless steel.
[0004]
As methods for producing Ni-Cr alloy plating, various technologies of
performing thermal diffusion treatment on two-layer plating of Cr and Ni are
30 disclosed.
For example, Patent Literature 1 mentions that Cr plating is performed on a
PCT/JP2016/061955
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steel sheet in the first place and Ni plating is performed on the Cr plating, then the
steel sheet is heat-treated in a non-oxidizing atmosphere at 600°C to 9l0°C for 60
seconds to 20 hours, and thereby a component that is made to resemble 18-8 stainless
steel is obtained. Further, Patent Literature 2 mentions that Cr plating and Ni
5 plating are performed on a steel sheet, then the steel sheet is heat-treated in a molten
salt bath at 750 to 900°C for 1 to 4 hours, and thereby a component that is made to
resemble 18-8 stainless steel is obtained. Further, Patent Literature 3 mentions that
Cr plating is performed on a steel sheet in the first place and Ni plating is performed
on the Cr plating, then the steel sheet is heat-treated, and thereby plating including a
10 Ni-Cr alloy layer and a Cr-Fe-Ni alloy layer is obtained.
Patent Literature
[0005]
15 Patent Literature I:
Patent Literature 2:
Patent Literature 3:
Citation List
JPH7-310166A
JP S61-41760A
JPH4-72091A
Summary of Invention
20 Technical Problem
[0006]
However, the technologies described in Patent Literatures 1 and 2 above
have the problem that heat treatment for a long time is needed in order to obtain the
target composition, and hence productivity is low. Furthermore, Fe is diffused up to
25 the surface of the plating by performing thermal diffusion for a long time;
consequently, when the product is then exposed to a high-temperature oxidizing
atmosphere, oxidization occurs form the Fe diffused to the surface as a starting point.
[0007]
Patent Literature 2 mentions that, in the first place, a Cr covering is formed
30 with a plating thickness of 4 to 15 fill by the electroplating method. However, due
to the fact that Cr plating has low cathodic current efficiency, there is a disadvantage
5
PCT/JP2016/061955
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that a high treatment current density and a long electrolytic cell are needed in order
to provide such thick plating by the electroplating method, and hence equipment
costs are high and productivity is low.
[0008]
On the other hand, in the method described in Patent Literature 3, the
deposited amount of Cr plating is as small as 0.01 to 0.2 g/m2
, and there is no
problem with equipment costs or productivity. However, since the amount of Cr is
small and Cr is not uniformly electrodeposited on the steel sheet, there is a
disadvantage that not only Cr-Fe but also Fe-Ni is produced at the plating interface,
10 and the Fe-Ni plating portion peels off in a high-temperature oxidizing atmosphere or
Fe diffuses to the plating surface; consequently, oxidation proceeds from these
portions as starting points.
[0009]
As above, the technologies disclosed in the past have so far failed to obtain
15 sufficient heat resistance performance, or have the problem that productivity is very
low.
[001 0]
Thus, the present invention has been made in view of the problems
mentioned above, and an object of the present invention is to provide a plated steel
20 sheet excellent in heat resistance and productivity and a method for producing the
25
same.
Solution to Problem
[0011]
In order to solve the above problems, according to an aspect of the present
invention, there is provided a plated steel sheet including: a steel sheet; and an alloy
plating layer formed on a surface of the steel sheet, in which the alloy plating layer
consists of, in mass%, Cr: 5 to 91%, Fe: 0.5 to 10%, and the balance: Ni and
unavoidable impurities, the Ni concentration in the alloy plating layer gradually
30 decreases from an outermost surface of the alloy plating layer to a side of the steel
sheet, the ratio of the Ni concentration to the Cr concentration is Ni/Cr > 1 in an area
PCT/JP2016/061955
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extending 300 nm or more from the outermost surface of the alloy plating layer, the
Fe concentration in the alloy plating layer gradually decreases from the side of the
steel sheet to the outermost surface of the alloy plating layer, the Fe concentration in
the outermost surface of the alloy plating layer is 0.5% or less, the total thickness of
5 an alloy layer formed in the alloy plating layer and containing Cr and Fe is 500 to
2000 nm, and the total amount of the alloy plating layer deposited to the steel sheet is
4.5 to 55.5 g/m2
.
[0012]
Here, the deposited amount of Cr plating in the alloy plating layer may be
10 3.5 to 28.8 g/m2
, the deposited amount ofNi plating in the alloy plating layer may be
3.0 to 26.7 g/m2
, and the ratio of the deposited amount of Cr/Ni plating in the alloy
plating layer may be 0.9 to 5.0.
15
[0013]
Further, conditions (a) and (b) below may be satisfied,
(a) the deposited amount ofCr plating of a Cr plating layer is more than 3.5
g/m2 and 28.8 g/m2 or less, and
(b) at least one of a condition that the deposited amount ofNi plating on the
Ni plating layer be 5.0 to 10.0 g/m2 and a condition that the ratio of the deposited
amount ofCr/Ni plating be 1.2 to 3.0 is satisfied.
20 [0014]
25
The components in an area extending I 0 nm in depth from the outermost
surface of the alloy plating layer may be, in mass%, 0 to 35% of Cr, 65 to I 00% of
Ni, and 0.5% or less ofF e.
[0015]
The alloy plating layer may include a Ni-Cr alloy layer.
[0016]
The alloy plating layer may include aNi layer on a Ni-Cr alloy layer.
[0017]
The total thickness of the Cr-Fe-containing alloy layer may be 300 nm or
30 more.
[0018]
PCT/JP2016/061955
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According to another aspect of the present invention, there is provided a
method for producing a plated steel sheet that produces the plated steel sheet, the
method including: a step of performing Cr plating with a surface density of 1.5 to
28.8 g/m2 on one surface or both surfaces of a steel sheet and thereby forming a Cr
5 plating layer on the one surface or both surfaces of the steel sheet; a step of
performing Ni plating with a surface density of3 to 26.7 g/m2 on the Cr plating layer
and thereby forming aNi plating layer on the Cr plating layer; and a step of holding
the steel sheet on which the Cr plating layer and the Ni plating layer are formed at a
temperature of 600°C to 900°C for a time more than 0 seconds and 60 seconds or
10 less in a non-oxidizing atmosphere or a reducing atmosphere.
[0019]
Here, the deposited amount of Cr plating of the Cr plating layer may be 3.5
to 28.8 g/m2
, the deposited amount ofNi plating of the Ni plating layer may be 3.0 to
26.7 g/m2
, and the ratio of the deposited amount ofCr/Ni plating may be 0.9 to 5.0.
15 [0020]
Further, conditions (a) and (b) below may be satisfied,
(a) the deposited amount of Cr plating of the Cr plating layer is more than
3.5 g/m2 and 28.8 g/m2 or less, and
(b) at least one of a condition that the deposited amount ofNi plating of the
20 Ni plating layer be 5.0 to I 0.0 g/m2 and a condition that the ratio of the deposited
amount ofCr/Ni plating be 1.2 to 3.0 is satisfied.
25
Advantageous Effects oflnvention
[0021]
A plated steel sheet according to the present invention is excellent in heat
resistance and productivity.
Brief Description of Drawings
[0022]
30 [FIG. I] FIG. I is an example of a schematic cross-sectional view of a covering film
of a Ni-Cr-plated steel sheet according to the present embodiment.
PCT/JP2016/061955
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[FIG. 2] FIG. 2 is an example of an analysis by glow discharge optical emission
spectrometry of a plated steel sheet according to the present embodiment.
Description of Embodiments
5 [0023]

A plated steel sheet according to the present embodiment includes a steel
sheet and an alloy plating layer formed on the steel sheet. The steel sheet usable in
the present embodiment is not particularly limited, and a commonly known steel
10 sheet such as a hot rolled steel sheet or a cold rolled steel sheet may be used. For
the steel type, Al-killed steel, ultralow carbon steel to which Ti, Nb, or the like is
added, and high-tensile steel in which an element such as P, Si, or Mn is added to
these may be used. The steel sheet is preferably a cold rolled steel sheet. The
alloy plating layer has the characteristic configuration described below. Thus, the
15 plated steel sheet according to the present embodiment has high heat resistance and
productivity.
[0024]
<2. Configuration of alloy plating layer>
Next, the configuration of the alloy plating layer according to the present
20 embodiment is described in detail. The alloy plating layer consists of, in mass%,
Cr: 5 to 91%, Fe: 10% or less, and the balance: Ni and unavoidable impurities. In
the following description, unless otherwise stated, the concentration of each
component represents the concentration in mass%. Furthet~ unless otherwise stated,
the concentration of each component represents the concentration of the component
25 existing in the entire area in the thickness direction of the alloy plating layer. The
concentration of each component can be measured by glow discharge spectroscopy
(GDS). Since the alloy plating layer contains such components, a Ni-Cr alloy layer
excellent in heat resistance and a Cr-Fe alloy layer excellent in adhesiveness to the
steel sheet are formed in the alloy plating layer. The alloy plating layer includes
30 these alloy layers, and satisfies the conditions described later. Thereby, the plated
steel sheet according to the present embodiment exhibits excellent heat resistance
5
PCT/JP2016/061955
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and corrosion resistance. Furthennore, the plated steel sheet needs only short time
for heat treatment, that is, only short holding time, and is therefore excellent also in
productivity. The heat treatment is described later.
[0025]
In the case where the Cr concentration in the alloy plating layer is less than
5%, a Ni-Cr alloy layer is not sufficiently formed in the alloy plating layer.
Consequently, the target heat resistance cannot be obtained. In the case where the
Cr concentration is more than 91%, it is difficult to ensure 300 nm or more of an area
where Ni/Cr > I, and consequently the fault described later may occur. In the case
10 where the Fe concentration in the alloy plating layer is more than I 0%, the oxidation
15
20
of the alloy plating layer proceeds from Fe in the alloy plating layer as a starting
point, and consequently the heat resistance and the corrosion resistance of the plated
steel sheet are reduced.
[0026]
The Ni concentration in the alloy plating layer gradually decreases from the
outermost surface (exposed surface) of the alloy plating layer to the steel sheet side.
The ratio of the Ni concentration to the Cr concentration is Ni/Cr > 1 in an area
extending 300 nm or more from the outermost surface of the alloy plating layer.
[0027]
The oxidation of the plated steel sheet under high temperature is suppressed
by the alloy plating layer having the configuration mentioned above. That is, heat
resistance is improved. In the case where the thickness of the area where Ni/Cr > I
is less than 300 nm, Cr is likely to be exposed on the outennost surface of the alloy
plating layer. The Cr exposed on the outermost surface may absorb oxygen and
25 nitrogen in the air under high temperature, and may embrittle. That is, the Cr
exposed on the outermost surface may impair the heat resistance of the plated steel
sheet. The thickness of the area where Ni/Cr > I is preferably I 000 nm or more,
and more preferably 2000 nm or more. In the case where the thickness of the area
where Ni/Cr > 1 is more than 5000 nm, electrodeposition of a large amount of Ni
30 plating is needed, or long-time heating is needed in the production process; hence,
this is not economical. Thus, the thickness of the area is preferably 5000 nm or less.
PCT/JP2016/061955
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[0028]
The Fe concentration (mass%) in the alloy plating layer gradually decreases
from the steel sheet side to the outermost surface of the alloy plating layer. The Fe
concentration in the outermost surface of the alloy plating layer is 0.5% or less.
5 Specifically, the Fe concentration in an area in a range of I 0 nm in depth from the
outetmost surface of the alloy plating layer is 0.5% or less. If Fe is present at more
than 0.5% in the outermost surface of the alloy plating layer, the oxidation of the
alloy plating layer proceeds from Fe of the outermost surface as a starting point, and
consequently the corrosion resistance and the heat resistance of the plated steel sheet
10 may be reduced. The Fe concentration in the plating outermost surface is more
preferably 0.1% or less.
[0029]
In the alloy plating layer, an alloy layer containing Cr and Fe (hereinafter,
occasionally referred to as "Cr-Fe-containing alloy layer") is formed. The Cr-Fe-
15 containing alloy layer is formed near the interface between the alloy plating layer and
the steel sheet. Examples of the Cr-Fe-containing alloy layer include a Cr-Fe alloy
layer and a Ni-Cr-Fe alloy layer. Of these, either one may be formed in the alloy
plating layer, or both may be formed in the alloy plating layer. The total thickness
of the Cr-Fe-containing alloy layer (in the case where a plurality of kinds of Cr-Fe-
20 containing alloy layers are formed, the total thickness of these) is 500 nm or more
and 2000 nm or less. The Cr-Fe-containing alloy layer can enhance the
adhesiveness between the steel sheet and the alloy plating layer. In the case where
the thickness of the Cr-Fe-containing alloy layer is less than 500 nm, the
adhesiveness between the alloy plating layer and the steel sheet is not sufficient.
25 [0030]
In the case where the Cr-Fe-containing alloy layer is too thick, Fe in the
alloy plating layer is, in a heat-resistant environment, likely to diffuse to the
outermost surface of the alloy plating layer. The diffusion of Fe is lessened by
increasing the Cr concentration in the alloy plating layer. However, increasing the
30 Cr concentration is not desirable in terms of economy and environment. Thus, the
total thickness of the Cr-Fe-containing alloy layer needs to be set to 2000 nm or less
PCT/JP2016/061955
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from the viewpoints of the ensuring of stable heat resistance performance, economy,
and environment.
[0031]
The total amount of the alloy plating layer deposited to the steel sheet
5 (hereinafter, occasionally referred to as "the deposited amount of alloy plating") is
4.5 to 55.5 g/m 2 . In the case where the deposited amount of alloy plating is less
than 4.5 g/m2
, it is difficult to ensure sufficient heat resistance. The deposited
amount of alloy plating is preferably 10 g/m2 or more from the viewpoint of
enhancing the heat resistance of the plated steel sheet. If the deposited amount of
10 alloy plating is more than 55.5 g/m2
, only a reduction in productivity and an increase
in cost are brought about, and no improvement in performance is exhibited. It is
preferable that Cr be contained at a concentration of 0 to 35%, Ni at 65 to 100%, and
Fe at 0.5% or less in an area extending I 0 nm in depth from the outermost surface of
the alloy plating layer.
15 [0032]
If the Cr concentration in the area mentioned above is more than 35%, a
large amount of Cr may be exposed on the outermost surface of the alloy plating
layer. The Cr may absorb oxygen and nitrogen in the air under high temperature,
and may embrittle. Consequently, the heat resistance of the plated steel sheet may
20 be impaired. If the Fe concentration in the area mentioned above is more than 0.5%,
a large amount of Fe may be exposed on the outermost surface of the alloy plating
layer. The Fe is oxidized by oxygen in the air. Consequently, the corrosion
resistance and the heat resistance of the plated steel sheet may be reduced. From
the viewpoints of corrosion resistance and heat resistance, for the concentration of
25 each plating component in the area mentioned above, it is preferable that the
concentration of Cr be 0 to 15%, Ni 85 to 100%, and Fe 0.1%, and it is more
preferable that the concentration of Cr be 0 to 4%, Ni 96 to 100%, and Fe 0%.
[0033]
Ni or Ni-Cr alloy is excellent in stability in a high-temperature atmosphere;
30 however, in the case where plating of only Ni or Ni-Cr alloy is performed on a steel
sheet, the plating layer peels off together with scales produced at the interface
PCT/JP2016/061955
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between the plating layer and the steel sheet in a high-temperature oxidizing
atmosphere. Thus, in the present embodiment, a large amount of Cr is incorporated
near the interface between the alloy plating layer and the steel sheet. Thereby, the
adhesiveness between the alloy plating layer and the steel sheet in a high-temperature
5 environment is enhanced. From this point of view, it is preferable that a Cr-Fe alloy
layer be formed with a thickness of 300 nm or more near the interface between the
alloy plating layer and the steel sheet.
[0034]
The following is combinations of plating configuration, in descending order
10 of preferability in heat resistance performance:
I. a Ni layer, a Ni-Cr alloy layer, a Cr layer, and a Cr-Fe alloy layer in this order
from the outermost surface of the alloy plating layer (see FIG. I);
2. a Ni layer, a Ni-Cr alloy layer, and a Cr-Fe alloy layer in this order from the
outermost surface of the alloy plating layer;
15 3. aNi layer, a Ni-Cr alloy layer, a Ni-Cr-Fe alloy layer, and a Cr-Fe alloy layer in
this order from the outermost surface of the alloy plating layer;
4. aNi layer, a Ni-Cr alloy layer, and a Ni-Cr-Fe alloy layer in this order from the
outermost surface of the alloy plating layer;
5. a Ni-Cr alloy layer, a Cr layer, and a Cr-Fe alloy layer in this order from the
20 outermost surface of the alloy plating layer;
6. a Ni-Cr alloy layer, a Ni-Cr-Fe alloy layer, and a Cr-Fe alloy layer in this order
from the outermost surface of the alloy plating layer;
7. a Ni-Cr alloy layer and a Cr-Fe alloy layer in this order from the outermost surface
of the alloy plating layer; and
25 8. a Ni-Cr alloy layer and a Ni-Cr-Fe alloy layer in this order from the outermost
surface of the alloy plating layer.
[0035]
A Ni-Cr alloy layer is included in all of the configurations. That is, in the
present embodiment, the presence of a Ni-Cr alloy layer is important, and desired
30 heat resistance and the like are achieved by the Ni-Cr alloy layer.
[0036]
PCT/JP2016/061955
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The concentration of each component in the alloy plating layer can be
measured by glow discharge spectroscopy (GDS). The concentration distribution in
the sheet thickness direction of each component can be identified by the glow
discharge spectroscopy. An example of the measurement data is shown in FIG. 2.
5 The horizontal axis represents the distance (depth) (J.lm) from the outermost surface
of the alloy plating layer, and the vertical axis represents the concentration of each
component (mass%). The plated steel sheet showing the result of FIG. 2 was
produced by the following process. That is, Cr plating was performed with an
deposited amount of7.2 g/m2 on a cold rolled steel sheet. Subsequently, Ni plating
10 was performed with an deposited amount of I 0 g/m2 on the Cr plating layer.
Subsequently, the cold rolled steel sheet on which the Cr plating layer and the Ni
plating layer were formed was introduced into an annealing furnace. Subsequently,
the internal temperature of the annealing furnace was increased up to 820°C in 82
seconds, and the cold rolled steel sheet was held for 20 seconds. By this process, a
15 plated steel sheet was obtained. The measurement conditions are as shown in Table
I. Also in Examples described later, the concentration of each component was
measured using similar measurement conditions. The concentration in the entire
area in the thickness direction can be calculated on the basis of the integrated value
obtained by integrating the measured data in the depth direction.
20 [0037]
[Table I]
c--------------- ----- - ------ ---- ..
(Table I)
Discharge condition 35 W (constant power mode)
Ar-pressure 600 Pa
Discharge mode Nonnal sputtering
Discharge range Diameter of 4 mm
Measurement elements B, C, Cr, Cu, Fe, Mn, N, NL 0, and Sn, total of lO elements
Measurement time 100 sec
Reading interval time 0.02 sec/point
Qualitative/quantitative measurement Quantitative measurement
[0038]
Further, the present inventors conducted extensive studies on the
25 composition of the alloy plating layer necessary to enhance the long-term heat
resistance of the plated steel sheet. As described above, in order to enhance the heat
PCT/JP2016/061955
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resistance of the alloy plating layer, it is necessary to form a Ni-Cr layer in the alloy
plating layer. To what degree the Cr-Ni layer is formed in the alloy plating layer
depends on the deposited amount of Cr plating (g/m2
), the deposited amount of Ni
plating (glm\ and the ratio of the deposited amount of Cr/Ni plating in the alloy
5 plating layer. Thus, the present inventors have found that the deposited amount of
Cr plating (g/m2
), the deposited amount of Ni plating (g/m2
), and the ratio of the
deposited amount of Cr/Ni plating in the alloy plating layer are important. Here,
the deposited amount of Cr plating represents the mass of Cr contained in a unit area
and the entire area in the thickness direction of the alloy plating layer, and the
10 deposited amount of Ni plating represents the mass of Ni contained in the unit area
and the entire area in the thickness direction of the alloy plating layer. The ratio of
the deposited amount of Cr/Ni plating is the value obtained by dividing the deposited
amount of Cr plating by the deposited amount ofNi plating. The deposited amount
ofCr plating and the deposited amount ofNi plating can be calculated on the basis of
15 the Cr concentration and the Ni concentration in the alloy plating layer.
[0039]
Specifically, it is preferable that the deposited amount of Cr plating in the
alloy plating layer be 3.5 to 28.8 g/m2
, the deposited amount of Ni plating in the
alloy plating layer be 3.0 to 26.7 g/m2
, and the ratio of the deposited amount ofCr/Ni
20 plating in the alloy plating layer be 0.9 to 5.0. In this case, long-term heat
resistance is further improved.
[0040]
In the case where the ratio of the deposited amount of Cr/Ni plating is more
than 5.0, when the plated steel sheet is exposed under high temperature for a long
25 time, Cr absorbs nitrogen and oxygen, and embrittles. In the case where the ratio of
the deposited amount of Cr/Ni plating is less than 0.9, a large amount ofNi forms an
alloy with Fe. The Ni-Fe alloy is, upon being oxidized, likely to peel off from the
steel sheet. Consequently, the heat resistance of the alloy plating layer is reduced.
[0041]
30 Here, the deposited amount of Cr plating is preferably more than 3.5 g/m2
.
The deposited amount of Ni plating is more preferably 3.0 to 15.0 g/m2
, and still
5
PCT/JP2016/061955
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more preferably 5.0 to 10.0 g/m2
• The ratio of the deposited amount of Cr/Ni
plating is more preferably 1.2 to 3.0. In this case, long-term heat resistance is
further improved.
[0042]
It is more preferable that the deposited amount of Cr plating (gtm\ the
deposited amount ofNi plating (g/m2
), and the ratio of the deposited amount ofCr/Ni
plating satisfY conditions (a) and (b) below. In this case, long-term heat resistance
is further improved.
(a) The deposited amount ofCr plating is more than 3.5 g/m2 and 28.8 g/m2 or less.
10 (b) At least one of the condition that the deposited amount of Ni plating be 5.0 to
10.0 g/m2 and the condition that the ratio of the deposited amount ofCr/Ni plating be
1.2 to 3.0 is satisfied.
[0043]
Here, in regard to condition (b), it is more preferable that both of the
15 condition that the deposited amount of Ni plating be 5.0 to 10.0 g/m2 and the
condition that the ratio of the deposited amount of Cr/Ni plating be 1.2 to 3.0 be
satisfied.
20
[0044]

Next, a method for producing a plated steel sheet according to the present
embodiment is described. The method for producing a plated steel sheet is roughly
as follows. First, Cr plating is performed with an deposited amount of 1.5 to 28.8
g/m2 on one surface or both surfaces of a steel sheet, and thereby a Cr plating layer is
formed on the one surface or both surfaces of the steel sheet. Subsequently, Ni
25 plating is performed with an deposited amount of 3 to 26.7 g/m2 on the Cr plating
layer, and thereby aNi plating layer is formed on the Cr plating layer. Subsequently,
the steel sheet on which the Cr plating layer and the Ni plating layer are fmmed is
held at a temperature of 600°C to 900°C for a time more than 0 seconds and 60
seconds or less in a non-oxidizing atmosphere or a reducing atmosphere. By this
30 process, a plated steel sheet according to the present embodiment is produced.
Details ofthe production method are as follows.
PCT/JP2016/061955
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[0045]
First, a steel sheet is subjected to degreasing and pickling treatment.
Subsequently, Cr plating is performed with an deposited amount of 1.5 to 28.8 g/m2
on one surface or both surfaces of the steel sheet. Thereby, a Cr plating layer is
5 formed on the steel sheet. The method of Cr plating is not particularly limited, and
may be the electrolysis method, for example. In the case where Cr plating is
performed by the electrolysis method, production conditions such as plating bath
conditions are not particularly limited.
10
[0046]
In the case where the deposited amount of Cr plating is less than 1.5 g/m2
, a
Cr-Fe-containing alloy layer effective in the adhesiveness of the alloy plating layer in
a high-temperature environment cannot be sufficiently formed. Thus, it is difficult
to form a Cr-Fe-containing alloy layer with a total thickness of 300 nm or more. In
the case where the deposited amount of Cr plating is more than 28.8 g/m2
, the cost
15 needed for Cr plating treatment is increased due to the increase in the time of plating
treatment and the like. Thus, this is not economical. In addition, processability
such as bendability is reduced. The deposited amount of Cr plating is preferably
2.0 to 15.0 g/m2
, and more preferably 3.5 to 6 g/m2
• The deposited amount of Cr
plating is preferably more than 3.5 g/m2 from the viewpoint of improving the long-
20 term heat resistance of the plated steel sheet.
[0047]
Subsequently, Ni plating is performed on the Cr plating layer, and thereby a
Ni plating layer is formed on the Cr plating layer. The method ofNi plating is not
particularly questioned; in the case where a Ni plating layer is formed on the Cr
25 plating layer, a Ni strike bath with a low pH or the like may be used. The
conditions of the Ni strike bath are not particularly limited.
[0048]
In the case where the deposited amount ofNi plating is less than 3.0 g/m2
,
the underlying Cr cannot be sufficiently covered with a Ni plating layer.
30 Accordingly, the Ni-Cr alloy layer after heat treatment is thin and non-uniform. In
addition, it is difficult to form an area where Ni/Cr > 1 with a thickness of 300 nm or
PCT/JP2016/061955
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more. Consequently, an alloy plating layer having heat resistance is not obtained.
Furthermore, in this case, even if firing is performed, the purity of the Cr plating
layer remains high. Furthermore, the Cr plating layer is insufficiently covered with
aNi plating layer. Consequently, the high-purity Cr plating layer is not only likely
5 to embrittle under room temperature, but also absorbs oxygen and nitrogen under
high temperature and is likely to embrittle even more. Also from this point, heat
resistance is reduced.
[0049]
On the other hand, in the case where the deposited amount of Ni plating is
10 more than 26.7 g/m2, the cost needed for Ni plating treatment is increased due to the
increase in the expense of Ni plating treatment, the increase in the time of plating
treatment, and the like. Thus, this is not economical. In addition, the adhesiveness
between the Ni plating layer and the Cr plating layer is reduced. Hence, it is likely
that part of the alloy plating layer will peel off at the interface between these layers
15 (specifically, the interface between the layer in which Ni > Cr and the layer in which
Ni < Cr) during bending or the like. From the above points of view, the deposited
amount ofNi plating is preferably 3.0 to 15.0 g/m2, and more preferably 5.0 to 10.0
g/m2.
20
25
[0050]
The deposited amount of Cr plating and the deposited amount of Ni are
adjusted so that the Cr concentration in the alloy plating layer is 5 to 91%. After
that, the heat treatment described below is performed; thereby, an alloy plating layer
satisfying the requirements described above is formed on the steel sheet.
[0051]
Subsequently, the steel sheet on which the Cr plating layer and the Ni
plating layer are formed is heat-treated. Specifically, the steel sheet is held at a
temperature of 600°C to 900°C for a time more than 0 seconds and 60 seconds or
less in a non-oxidizing atmosphere or a reducing atmosphere. In order to prevent
the oxidation of the end surface of the Cr plating layer or the Cr plating layer
30 exposed from a pinhole in the Ni plating layer, the heat treatment of the steel sheet
on which the Cr plating layer and the Ni plating layer are fanned is thus performed
PCT/JP2016/061955
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in a non-oxidizing atmosphere or a reducing atmosphere. Here, examples of the
non-oxidizing atmosphere or the reducing atmosphere include an atmosphere of N2
gas, Ar gas, H2 gas, or a mixed gas of these. The heating method is not particularly
limited, and any of furnace heating, energization heating, induction heating, and the
5 like may be used. Components in the steel sheet, the Ni plating layer, and the Cr
plating layer are diffused by the heat treatment. For example, Cr in the Cr plating
layer diffuses into the Ni plating layer, and Ni in the Ni plating layer diffuses into the
Cr plating layer. Further, Fe in the steel sheet diffuses into the Cr plating layer and
the Ni plating layer. In the case where heat treatment is not performed, not only is it
10 impossible to obtain the alloy plating layer described above, but also the
adhesiveness between the Ni plating layer and the Cr plating layer is insufficient.
In particular, in the case where a Ni plating layer is formed thick using a Watts bath
or the like, the adhesiveness is particularly insufficient.
[0052]
15 The rate of temperature increase is not particularly limited, and may be
substantially equal to that of heating treatment performed in the production line of a
conventional plated steel sheet. However, if a time longer than 120 seconds elapses
until the target peak temperature is reached, the time ofthennal diffusion is long and
this is not economical, and furthermore Fe may diffuse up to the surface. Thus, the
20 time required until the target peak temperature is reached is preferably 120 seconds
or less.
[0053]
The rate of diffusion of each component is proportional to the square root of
the diffusion coefficient. For Fe, the diffusion coefficient of y-Fe, the temperature
25 of which is highe1~ is smaller than the diffusion coefficient of a.-Fe, the temperature
of which is lower. When y-Fe is diffused, a deformation of the steel sheet is likely
to occur due to a phase transformation of Fe caused by cooling. In particular, in the
case where the steel sheet is thin, a deformation of the steel sheet appears
significantly. On the other hand, a-Fe has a tendency to diffuse rapidly at the grain
30 boundary. Hence, it is preferable that the heat treatment temperature be 900°C or
less, that is, Fe be diffused in the state of a-Fe. On the other hand, in the case where
PCT/JP2016/061955
17/34
the heat treatment temperature is less than 600°C, even a-Fe has a low rate of
diffusion. Hence, a long time is needed for diffusion, and productivity is poor.
Thus, the heat treatment temperature, that is, the holding temperature is 600 to 900°C.
[0054]
5 The holding time after temperature increase is set to more than 0 seconds
and 60 seconds or less. It is preferably set to 1 to 30 seconds. In the case where
the holding time is longer than 60 seconds, there is a possibility that the
concentration ratio ofNi to Cr of the outermost surface of the alloy plating layer will
be Ni/Cr < I. In particular, this possibility increases as the deposited amount ofNi
10 plating decreases. Furthermore, the thickness of the Cr-Fe layer is made larger than
2000 nm, and Fe diffuses up to the outermost surface of the alloy plating layer;
consequently, heat resistance is reduced.
[0055]
The holding temperature and the holding time are adjusted in the ranges
15 mentioned above in accordance with the deposited amount of Cr plating and the
deposited amount of Ni plating. That is, the holding temperature and the holding
time are adjusted so that an alloy plating layer satisfying the requirements described
above is formed on the steel sheet.
(0056]
20 After the heat treatment, the plated steel sheet is cooled. Here, the cooling
rate is not particularly limited, and may be substantially equal to that of cooling
treatment perfmmed in the production line of a conventional plated steel sheet.
[0057]
Further, the present inventors conducted extensive studies on the heat
25 treatment conditions needed to enhance the heat resistance of the plated steel sheet
(in particular, long-term heat resistance). IfNi is excessively thermally diffused in
the alloy plating layer during heat treatment, a Ni-Fe layer peels off from the steel
sheet in a high-temperature oxidizing atmosphere. To what degree Ni diffuses in
the alloy plating layer depends not only on the holding temperature and the holding
30 time but also on the deposited amount of Cr plating. Thus, the present inventors
have found that there is a strong correlation between the deposited amount of Cr
5
PCT/JP2016/061955
18/34
plating, and the holding temperature and the holding time. Specific heat treatment
conditions are as follows. In the case where the heat treatment conditions satisfy
the following conditions, also the bendability of the plated steel sheet is improved.
[0058]
In the case where the deposited amount ofCr plating is 1.5 to 3.5 g/m2
, it is
preferable that the holding temperature be 600°C, and the holding time be as short as
possible (for example, less than I second).
[0059]
In the case where the deposited amount of Cr plating is more than 3.5 g/m2
10 and 6.0 g/m2 or less, it is preferable that the holding temperature be 600 to 800°C,
and the upper limit value of the holding time be 5 or less times as large as the
reference time found by Mathematical Formulae (I) and (2) below. The lower limit
value of the holding time is preferably I 0 seconds or more.
15
T=kTo (I)
T0 =-0.15*(H-600)+50 (2)
Here, in Mathematical Formulae (1) and (2), T represents a reference
temperature, and T0 represents a reference time when the deposited amount of Cr
plating is 6 g/m2
• k represents a correction factor, and is a value obtained by
dividing the deposited amount of Cr plating (g/m2
) of the Cr plating layer of the
20 object to be fired by 6 g/m2 (that is, the maximum deposited amount). H represents
the holding temperature.
[0060]
In the case where the deposited amount of Cr plating is more than 6.0 g/m2
and 15.0 g/m2 or less, it is preferable that the holding temperature be 650 to 800°C,
25 and the upper limit value of the holding time be 5 or less times as large as the
reference time found by Mathematical Formulae (3) and ( 4) below. The lower limit
value of the holding time is preferably 10 seconds or more.
T=kTo (3)
T0 = -0.13*(H- 600) +50 (4)
30 Here, in Mathematical Formulae (3) and (4), T represents a reference
temperature, and T0 represents a reference time when the deposited amount of Cr
PCT/JP2016/061955
19/34
plating is 15.0 g/m2
• k represents a correction factor, and is a value obtained by
dividing the deposited amount of Cr plating (g/m2
) of the Cr plating layer of the
object to be fired by 15.0 g/m2 (that is, the maximum deposited amount). H
represents the holding temperature.
5 [0061]
In the case where the deposited amount ofCr plating is more than 15.0 g/m2
and 28.8 g/m2 or less, it is preferable that the holding temperature be 700 to 900°C,
and the upper limit value of the holding time be 5 or less times as large as the
reference time found by Mathematical Formulae (5) and (6) below. The lower limit
10 value of the holding time is preferably 10 seconds or more.
T=kTo (5)
To= -0.12*(H- 600) + 60 (6)
Here, in Mathematical Formulae (5) and (6), T represents a reference
temperature, and To represents a reference time when the deposited amount of Cr
15 plating is 28.8 g/m2
• k represents a correction factor, and is a value obtained by
dividing the deposited amount of Cr plating (g/m2
) of the Cr plating layer of the
object to be fired by 28.8 g/m2 (that is, the maximum deposited amount). H
represents the holding temperature.
20
[0062]
In the case where the heat treatment conditions satisfy the requirements
described above, at least short-term heat resistance is improved. In the case where
these heat treatment conditions are satisfied and at the same time the deposited
amount of Cr plating, the deposited amount of Ni plating, and the ratio of the
deposited amount of Cr/Ni plating satisfy the requirements described above, not only
25 shmi-term heat resistance but also long-term heat resistance is improved.
[0063]
Thus, the plated steel sheet according to the present embodiment is excellent
not only in heat resistance but also in corrosion resistance and adhesiveness.
Furthermore, in the method for producing a plated steel sheet, since the holding time
30 is short, the plated steel sheet according to the present embodiment can be produced
with high productivity.
[Examples]
[0064]

PCT/JP2016/061955
20/34
In Experimental Example I, the following experiment was conducted in
5 order to verify that the plated steel sheet according to the present embodiment has
high heat resistance. First, a cold rolled steel sheet (thickness: 0.8 mm) was
prepared as a steel sheet. Subsequently, the cold rolled steel sheet was subjected to
alkaline degreasing and sulfuric acid pickling, and thereby the water wettability of
the cold rolled steel sheet was sufficiently ensured. Subsequently, Cr plating was
10 performed on the cold rolled steel sheet, and thereby a Cr plating layer was fmmed
on the cold rolled steel sheet. The Cr plating was performed by the electrolysis
method. The plating conditions are shown in (A) below. Further, the deposited
amount of Cr plating is shown in Table 2. Subsequently, Ni plating was performed
on the Cr plating layer, and thereby aNi plating layer was formed on the Cr plating
15 layer. Also the Ni plating was performed by the electrolysis method, and a strike
bath was used as the plating bath. The plating conditions are shown in (B) below.
Further, the deposited amount ofNi plating is shown in Table 2.
[0065]
(A) Electrolytic Cr plating
20 (I) Plating bath components: Sargent bath
Chromic acid: 250 gil
Sulfuric acid: 3 g/1
(2) Electrolysis conditions
Temperature: 50°C
25 Current density: 30 A/dm2
[0066]
(B) Electrolytic Ni plating
- Strike bath
(I) Plating bath components
30 Nickel chloride: 240 g/1
Hydrochloric acid: 125 ml/1
(2) Electrolysis conditions
pH: 1.0 to 1.5
Temperature: room temperature (25°C)
Current density: 4 A/dm2
5 - Watts bath
(I) Plating bath components
Nickel sulfate: 240 gil
Nickel chloride: 45 gil
Boric acid: 30 g/1
10 (2) Electrolysis conditions
pH: 3.5 to 4.5
Temperature: 50°C
Current density: 5 A/dm2
(0067]
PCT/JP2016/061955
21/34
15 Subsequently, the cold rolled steel sheet on which the Cr plating layer and
the Ni plating layer were formed was introduced into an annealing furnace. The
interior of the annealing furnace was set to a 2 volume% H2-98 volume% N2
atmosphere. Next, the internal temperature of the annealing furnace was increased
at I 0°C/sec up to the holding temperature shown in Table 2. Subsequently, the
20 holding temperature was kept during the holding time shown in Table 2.
Subsequently, the plated steel sheet was rapidly cooled up to 200°C using N2 gas.
The cooling rate at this time was set to 70°C/sec. After that, the plated steel sheet
was allowed to cool. By this process, a sample of a plated steel sheet was produced.
In this Experimental Example 1, the deposited amount of Cr plating, the deposited
25 amount ofNi plating, and the heat treatment conditions were variously changed, and
thereby a plurality of kinds of samples (levels) were produced. The compositions
of the samples are collectively shown in Table 2. The concentration of each
component in the alloy plating layer was measured by glow discharge spectroscopy
(GDS). The measurement conditions are shown in Table 1. In Table 2, a preferred
30 range of each component is written as well. Numerical values that are out of the
preferred ranges are underlined. "Plating layer structure" shown in Table 2 shows
5
PCT/JP2016/061955
22/34
the class of the layer structure of the alloy plating layer. The corresponding
relationship between each class and the layer structure is shown in Table 3.
[0068]

To evaluate the heat resistance of the produced sample (plated steel sheet),
the sample was exposed in the air atmosphere at 600°C for 120 hours. After that,
the sample was allowed to cool in the air, and the oxidation state of the surface was
investigated.
[0069]
10 After the test, in the case where red rust derived from Fe had occurred on
the sample or the plating had peeled off during the allowing to cool in the air, the
heat resistance was evaluated as bad (B); in the case where the surface of the sample
had been oxidized and had much coarseness, the heat resistance was evaluated as
good (G); and in the case where there was little coarseness, the heat resistance was
15 evaluated as very good (VG). For the sample of VG, a heat resistance test was
further performed. At the stage of a total of250 hours, in the case where there was
little coarseness, the heat resistance was evaluated as excellent (E); and in the case
where there was much coarseness, the evaluation was kept VG as it was. The
coarseness was evaluated by the following method. That is, the surfaces of the
20 alloy plating layer before and after the test were compared by visual observation, and
thereby whether concavities and convexities (that is, coarseness) were formed on the
surface of the alloy plating layer after the test was assessed. In the case where the
size of the area where coarseness was formed was less than 50% relative to the entire
surface of the alloy plating layer, it was assessed that there was little coarseness; and
25 in the case where the size of the area where coarseness was formed was 50% or more
relative to the entire surface of the alloy plating layer, it was assessed that there was
much coarseness. Even in the case where there is much coarseness, there is no
practical problem. The results are shown in Table 2.
[0070]
30
To evaluate the processability of the produced sample, 0) the bending test
PCT/JP2016/061955
23/34
method out of the plating adhesiveness test method of JIS H 8504 was performed.
However, the bending-back described in JIS was not performed; and after that, in the
bent state as it was, further (I) the tape test method out of (g) the peeling test method
was performed using a JIS Z 1522 adhesive tape; thus, the plating adhesiveness of
5 the sample was evaluated.
[0071]
In the case where the plating was peeled off at the stage when the sample
was bent, the adhesiveness was evaluated as bad (B); in the case where the procedure
of sticking a tape to and then stripping it from the bent portion of the sample causes
10 part of the plating to be deposited to the tape, the adhesiveness was evaluated as
good (G); and in the case where the plating was not peeled off by the tape, the
adhesiveness was evaluated as VG. The results are shown in Table 2.
[0072]
[Table 2]
Table 21
... '
Heat treatment conditions
Components of alloy plating
Deposited Deposited Deposited
layer in area where Cr/Fe > I
amount of amount of amount of
alloy plating Cr plating Ni plating Holding
Holding time Cc Fo i + impuritie
No. temperature
wm' lim' om' 'C '" mass% mass% mass%
4.5-55.5 1.5-28.8 3.0-26.7 600-900 0 <,$. 60 5-91 ~ 10 Balance
I 6.6 3.6 3 600 20 54 2 44
2 18.6 3.6 15 600 20 18 3 79
3 10 5 5 700 10 49 3 48
4 8 5 3 700 10 62 2 36
5 13.5 5 8,5 800 20 36 3 61
6 15 5 10 800 20 33 3 64
7 10.5 7.5 3 700 10 70 3 27
8 12.5 7.5 5 800 20 57 4 39
9 16 7.5 8,5 800 20 46 3 51
10 17.5 7.5 10 800 20 37 5 58
II 22.5 7.5 15 800 60 29 7 64
12 34.2 7.5 26.7 800 60 19 6 75
13 13 10 3 800 10 75 3 22
14 25 10 15 800 60 39 8 53
15 36.7 10 26.7 800 60 23 8 69
16 55.5 28.8 26.7 900 30 50 10 41
17 17.5 7.5 10 800 15 42 3 55
IS 12.5 7.5 5 600 <1 60 0.5 39
19 28 1.5 26.5 600 20 5 2 93
20 32 28.5 3.5 800 <1 91 2 7
21 4.5 1.5 3 600 20 30 5 65
22 4.5 1.5 3 800 10 29 7 64
23 20 2.16 17.8 800 600 7 13 80
24 20 2.16 17.8 800 250 26 3 71
25 5 3.6 I 800 30 78 2 20
26 38 2 35.6 800 600 22 16 62
27 " ~ ~ 800 30 2 2 96
l
Fo Components in area of 10 nm from
Thickness concentr plating layer surface
of surface ation of
Ni>Cr outetmo Ni+
"~ ,, Cc Fo
impurities
surface
om mass% mass% mass% mass%
'-300 ~0.5 0-35 :s 0.5 65-100
390 <0.1 32 <0.1 68
1700 <0.1 0 <0.1 100
570 $0.1 22 $0.1 78
370 :s 0.1 35 <0.1 65
960 < 0.1 8 <0.1 92
1150 <0,1 0 <0.1 100
480 $0.1 36 $0.1 64
580 < 0.1 15 <0.1 75
960 <0.1 14 <0.1 86
1170 <0.1 0 <0.1 100
1700 :;:0.1 0 :::0.1 100
2850 ~0.1 0 <0.1 100
490 $0.1 37 :;:0.1 63
1650 :::0.1 0 <0.1 100
2650 <0.1 0 <0.1 100
2730 <0.1 0 <0.1 100
1140 :::0.1 0 :;:0.1 100
570 <0.1 0 <0.1 100
2850 :::0.1 0 :::0.1 100
520 :::0.1 11 <0.1 89
500 $0.1 22 :::0.1 78
530 OJ 21 0.3 79
3150 <0.1 14 <0.1 86
1430 $0.1 0 <0.1 100
200 0.5 46 0.5 54
4500 I 2 1 97
0.3 0 0.3 100
Total thickness
Plating ofCr-Fe"
layer ~ontainingalloy
structure layer
om
500-2000
No.7 600
No.2 800
No.6 780
No.7 620
No.5 1200
No.1 1270
No.7 700
No.6 1220
No.5 1130
No.1 1260
No.1 1740
No.1 1780
No.8 890
No.4 1820
No.4 1850
No.3 1930
No.3 900
No.3 100
No.1 800
No.7 680
No.5 650
No.5 680
No.5 5600
No.1 2100
No.5 700
No.9 5200
No. 10 350
Perfonnance evaluation
600°C, 250
h
Bending test
H~t
resistance Tape peeling
·~· VG VG
E VG
VG VG
VG VG
VG VG
E VG
VG VG
VG VG
VG VG
E VG
E VG
E G
VG VG
E VG
E G
VG G
E VG
E G
E G
VG G
VG VG
G VG
B VG
B VG
B B
B VG
B B
. .
Notes
Example
Comparative
Example
N
:..,).
>tJ
~
"0 '
>-'
0>
0
">-''
<:>
""''
Tablel)
Plating laver structure No.
I Ni layer, Ni-Cr alloy layer, Ni-Cr-Fe alloy layer, and Cr-Fe alloy layer in th~ orderfrom outermost surface of alloy plating layer
2 Ni layer, Ni-Cr alloy layer, and Ni-Cr-Fe alloy layer in th~ order from outermost surface of alloy plating layer
3 Ni layer, Ni-Cr alloy layer, Cr layer, and Cr-Fe alloy layer in this order from outermost surface of alloy plating layer
4 Ni layer; Ni-Cr alloy layer, and Cr-Fe alloy layer in~ order from outermost surface of alloy plating layer
5 Ni-Cr alloy layer, Ni-Cr-Fe alloy layer, and Cr-Fe layer in this order from outermost surface of alloy plating layer
6 Ni-Cr alloy layer and Ni-Cr-Fe alloy layer in~ order from outermost surface of alloy plating layer
7 Ni-Cr alloy layer and Cr-Fe layer in this order from outermost surface of alloy plating layer
8 Ni-Cr alloy layer, Cr layer, and Cr-Fe layer in th~ order from outermost surface of alloy plating layer
9 Nilayer, Ni-Cr-Fe alloy layer, and Ni-Fe alloy layer in~ order from outermost surface of alloy plating layer
10 Ni-Cr-Fe alloy layer and Ni-Fe alloy layer in this order from outermost surface of alloy plating layer
Notes
Example
Comparative Example
~ 8 cr __,
"- w w ~
~
N
V> ;_:,;.,
"d
~
,0"_ '.
~
,O_'.l
"en'
en
PCT/JP2016/061955
26/34
[0074]

In Experimental Example 2, the influence on heat resistance, in particular
long-term heat resistance, by the deposited amount of Cr plating, the deposited
5 amount ofNi plating, the ratio of the deposited amount ofCr/Ni plating, and the heat
treatment conditions was investigated further in detail. First, a plurality of kinds of
samples (plated steel sheets) between which the deposited amount of Cr plating, the
deposited amount of Ni plating, the ratio of the deposited amount of Cr/Ni plating,
and the heat treatment conditions were different were produced by a similar method
10 to Example I. The deposited amount of plating and the heat treatment conditions of
each sample are shown in Table 4. In Table 4, preferred ranges of the deposited
amount of plating and the like are written as well. In the sample corresponding to
Example, it has been verified that the parameters shown in Table 2 satisfY the
requirements of the present embodiment.
15 [0075]

To evaluate the heat resistance of the produced sample, the sample was
exposed in the air atmosphere at 600°C for 120 hours. Subsequently, the sample
was allowed to cool in the air, and the oxidation state of the surface was investigated
20 (the heat resistance test: short). The sample evaluated as good (G) or better by the
following evaluation criterion was further exposed for 280 hours (that is, a total of
400 hours) (the heat resistance test: long). Subsequently, the sample was allowed to
cool in the air, and the oxidation state of the surface was investigated.
25
[0076]
The oxidation state of the surface in each heat resistance test was evaluated
by the following criterion. In the case where the area where red rust derived from
Fe had occurred was 80% or more relative to the entire surface of the alloy plating
layer or the plating had peeled off during the allowing to cool in the air, the heat
resistance was evaluated as bad (B). In the case where the area where red rust had
30 occurred was 30% or more and less than 80% relative to the entire surface of the
alloy plating layer (in the case where the occurrence of red rust was at a level with no
PCT/JP2016/061955
27/34
practical problem), the heat resistance was evaluated as good (G). In the case
where the area where red rust had occurred was less than 30% relative to the entire
surface of the alloy plating layer or there was much coarseness, the heat resistance
was evaluated as very good (G). In the case where the area where red rust had
5 occurred was substantially equal to that of VG and the surface had little coarseness
(or no coarseness), the heat resistance was evaluated as excellent (E). The
coarseness was evaluated in a similar manner to Experimental Example I. The
evaluation results are shown in Table 4.
(0077]
10 [Table 4]
T~bl~41 '
Deposited Deposited Deposited
amount of alloy CrtNi amount ofCr amount of
plating plating Ni plating
No, glrri g/m' glm'
0.9-5.0 3.5-28.8
3.0-26.7
4.5-55.5 3.0-15.0
1.2-3.0 3.5 <; ~ 28.8
5.0-10.0
1 4.7 3 3.5 1.2'
2 6.4 1.2 3.5 2.9
3 4.2 5 3.5 0.7
4 7.4 0.9 3.5 3.9
5 8 3 6 2
6 9 2 6 3
7 11 1.2 6 5
8 7.2 5 6 L2
9 12.7 0.9 6 6.7
10 20 3 15 5
II 27,5 1.2 15 12.5
12 18 5 15 3
13 3L7 0.9 15 16.7
14 2.7 3 • 0.7
15 3.7 L2 2 1.7
16 2.4 5 2 0.4
17 4.2 0.9 • 2.2
18 20 1.5 12 8
19 7.4 0.9 3.5 3.9
20 9 2 6 3
21 9 2 6 3
22 7.4 0.9 3.5 3.9
23 12.5 1.5 7.5 5
24 17.5 0.75 7.5 10
25 34.2 0.3 7.5 26.7
26 10 1 5 5
27 10 I 5 5
,,,,,,,,,
Heat treatment conditions
Holding temperature Holding time T, T
oc sec sec sec
600 <1 0 0
600 <1 0 0
600 <1 0 0
600 <1 0 0
600 <1 0 0
800 20 20 20
800 20 20 20
800 20 20 20
800 20 20 20
800 20 24 24
800 20 24 24
800 20 24 24
800 20 24 24
800 <1 0 0
800 <1 0 0
800 < 1 0 0
800 < 1 0 0
800 20 24 19.2
600 <1 0 0
800 2000 20 20
1000 60 -10 -10
600 65 0 0
800 20 24 12
800 20 24 12
800 60 24 12
700 10 35 29.2
800 2000 20 16.7
Heat resistance test: short Heat resistance test: long
B
B
B
E G
B B
E E
E E
B
E E
E E
E E
E VG
E G
B
B
B
B
E E
E G
G B
G B
G B
E E
E B
E B
E E
VG B
Notes
Comparative Example
Examole
Comparative Example
Example
Comparative Example
Example
Comparative Example
Example
'
N
00 w....
>tl
~
"0 "
"""' 0
"""" "01'
01
PCT/JP2016/061955
29/34
[0078]
From Experimental Examples I and 2, it has been revealed that the plated
steel sheet according to the present embodiment has high heat resistance. It has also
been revealed that, in the case where the deposited amount of Cr plating, the
5 deposited amount of Ni plating, the ratio of the deposited amount of Cr/Ni plating,
and the heat treatment conditions satisfy the prescribed conditions, also long-term
heat resistance is improved.
[0079]
In some Examples (for example, No. 18 of Experimental Example 1 and the
10 like), the result of the bending test was slightly worsened. As described above, the
heat treatment conditions include the conditions for satisfYing long-term heat
resistance. In the case where the heat treatment conditions satisfy these conditions,
also bendability is improved. Therefore, it is presumed that, in No. 18 of
Experimental Example 1 and the like, bendability was slightly reduced because the
15 heat treatment conditions did not satisfY these conditions. For example, in No. 18
of Experimental Example 1, since the deposited amount of Cr plating is 7.5 g/m2
, a
preferred holding temperature is 650 to 800°C. Further, the reference time of the
holding time is 50 seconds. Hence, both the holding temperature and the holding
time of No. 18 are a value lower than the preferred range. Further, from Nos. 20, 21,
20 and 27 of Experimental Example 2, it has also been revealed that long-term heat
resistance is reduced in the case where at least one of the holding temperature and the
holding time is larger than the preferred range.
[0080]
The preferred embodiment(s) of the present invention has/have been
25 described above with reference to the accompanying drawings, whilst the present
invention is not limited to the above examples. A person skilled in the ati may find
various alterations and modifications within the scope of the appended claims, and it
should be understood that they will naturally come under the technical scope of the
present invention.
30
Industrial Applicability
5
PCT/JP2016/061955
30/34
[0081]
As described above, the plated steel sheet according to the present invention
is excellent in heat resistance and adhesiveness after a high temperature test, and can
be widely used as members in high-temperature environments.
5

Claim l
31/34
CLAIMS
A plated steel sheet comprising:
a steel sheet; and
PCT/JP2016/061955
an alloy plating layer formed on a surface of the steel sheet,
wherein the alloy plating layer consists of, in mass%, Cr: 5 to 91%, Fe: 0.5
to I 0%, and the balance: Ni and unavoidable impurities,
the Ni concentration in the alloy plating layer gradually decreases from an
outermost surface of the alloy plating layer to a side of the steel sheet,
the ratio of the Ni concentration to the Cr concentration is Ni/Cr > I in an
area extending 300 nm or more from the outermost surface of the alloy plating layer,
the Fe concentration in the alloy plating layer gradually decreases from the
side of the steel sheet to the outermost surface of the alloy plating layer,
the Fe concentration in the outermost surface of the alloy plating layer is
15 0.5% or less,
20
25
the total thickness of a Cr-Fe-containing alloy layer formed in the alloy
plating layer and containing Cr and Fe is 500 to 2000 nm, and
the total amount of the alloy plating layer deposited to the steel sheet is 4.5
to 55.5 g/m2
•
Claim 2
The plated steel sheet according to claim I,
wherein the deposited amount of Cr plating in the alloy plating layer is 3.5
to 28.8 g/m2
,
the deposited amount of Ni plating in the alloy plating layer is 3.0 to 26.7
g/m2
, and
the ratio of the deposited amount of Cr/Ni plating in the alloy plating layer
is 0.9 to 5.0.
30 Claim 3
The plated steel sheet according to claim 2,
PCT/JP20 16/061955
32/34
wherein conditions (a) and (b) below are satisfied,
(a) the deposited amount of Cr plating of a Cr plating layer is more than 3.5
g/m2 and 28.8 g/m2 or less, and
(b) at least one of a condition that the deposited amount ofNi plating in the
5 alloy plating layer be 5.0 to 10.0 g/m2 and a condition that the ratio of the deposited
amount ofCr/Ni plating in the alloy plating layer be 1.2 to 3.0 is satisfied.
10
Claim 4
The plated steel sheet according to any one of claims I to 3,
wherein Cr is contained at a concentration of, in mass%, 0 to 35%, Ni at 65
to I 00%, and Fe at 0.5% or less in an area extending I 0 nm in depth from the
outermost surface of the alloy plating layer.
ClaimS
15 The plated steel sheet according to any one of claims I to 4, wherein the
alloy plating layer includes a Ni-Cr alloy layer.
Claim 6
The plated steel sheet according to any one of claims I to 5, wherein the
20 alloy plating layer includes aNi layer on a Ni-Cr alloy layer.
25
Claim 7
The plated steel sheet according to any one of claims I to 6, wherein the
total thickness of the Cr-Fe-containing alloy layer is 300 nm or more.
Claim 8
A method for producing a plated steel sheet that produces the plated steel
sheet according to any one of claims I to 7, the method comprising:
a step of performing Cr plating with an deposited amount of 1.5 to 28.8
30 g/m2 on one surface or both surfaces of a steel sheet and thereby forming a Cr plating
layer on the one surface or both surfaces of the steel sheet;
PCT/JP2016/061955
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a step of performing Ni plating with an deposited amount of 3 to 26.7 g/m2
on the Cr plating layer and thereby forming aNi plating layer on the Cr plating layer;
and
a step of holding the steel sheet on which the Cr plating layer and the Ni
5 plating layer are formed at a temperature of 600°C to 900°C for a time more than 0
seconds and 60 seconds or less in a non-oxidizing atmosphere or a reducing
atmosphere.
10
15
Claim 9
The method for producing a plated steel sheet according to claim 8,
wherein the deposited amount ofCr plating of the Cr plating layer is 3.5 to
28.8 g/m2
,
the deposited amount ofNi plating of the Ni plating layer is 3.0 to 26.7 g/m2
,
and
the ratio of the deposited amount ofCr/Ni plating is 0.9 to 5.0.
Claim 10
The method for producing a plated steel sheet according to claim 9,
wherein conditions (a) and (b) below are satisfied,
20 (a) the deposited amount of Cr plating of the Cr plating layer is more than
25
3.5 g/m2 and 28.8 g/m2 or less, and
.,
(b) at least one of a condition that the deposited amount ofNi plating of the
Ni plating layer be 5.0 to I 0.0 g/m2 and a condition that the ratio of the deposited
amount ofCr/Ni plating be 1.2 to 3.0 is satisfied.