WO2024202153A1 - Nickel clad plate and method for manufacturing same - Google Patents

Abstract

The present invention provides a nickel clad plate and a method for manufacturing the same, the nickel clad plate comprising a metal base material layer and a nickel material layer laminated onto one or both surfaces of the metal base material layer, wherein a Vickers hardness measured from the surface of the nickel material layer with a test force of 0.2 N is greater than a Vickers hardness measured from the surface of the nickel material layer with a test force of 9.8 N by a difference of 30.0 or more.

Description

Nickel clad plate and its manufacturing method

This disclosure relates to nickel clad plates and their manufacturing methods.

Clad plates, which are made by joining different types of metals (hereafter referred to as "dissimilar metals") together using methods such as rolling and pressure welding, have a high level of balance between the excellent properties of the constituent dissimilar metals, and therefore have new properties that cannot be achieved with single metals or alloys.

Nickel has been used for a long time as a cathode material for salt electrolysis equipment used in caustic soda manufacturing plants, for example, because it has high corrosion resistance in environments immersed in strong alkaline solutions. In addition, in recent years, its use has been expanding as a constituent material for infrastructure equipment supporting a hydrogen society, such as electrodes for alkaline water electrolysis equipment and electrodes for secondary batteries. For nickel used as a component for such electrolysis equipment, plate materials made of a single nickel have been used.
However, nickel is expensive, and the price of nickel bullion tends to fluctuate dramatically due to changes in the global supply and demand balance of nickel ore. In particular, with demand increasing sharply toward the realization of a carbon-neutral society, supply shortages and a sharp rise in nickel bullion prices are expected in the near future.

As mentioned above, nickel is a metal that has extremely high corrosion resistance in strong alkaline environments, so there is almost no problem with thinning due to alkaline corrosion during use, and as long as its mechanical strength is maintained, it can withstand long-term practical use. In other words, the inner layer, excluding the outer layer, of the plate material used as an electrode does not utilize the characteristics of nickel, and since nickel is soft and easily deformed, it can also be considered a disadvantage in terms of maintaining mechanical strength.

From this perspective, it is conceivable to use an inexpensive general-purpose metal as the material constituting the inner layer of the plate material, and to use a composite material in which nickel is placed only in the outer layer portion as the electrode material. One example of this is nickel plating the surface of ordinary steel, an inexpensive general-purpose metal. Nickel plating can be achieved by electrolytic plating or electroless plating using a catalyst. However, it is difficult to achieve a thick, uniform nickel plating layer that can withstand bending, and there is also the problem of the high cost of plating thickly. In addition, in order to obtain a nickel plating layer with excellent adhesion, nickel alloy plating containing alloying elements such as Si is often applied. In this case, there is a risk that the original purpose of corrosion resistance in a strong alkaline environment will be lost, and there is also a risk of adverse effects on secondary workability such as bending.

An example of a composite material that does not undergo plating is a nickel clad plate, in which nickel is bonded to the surface of a base material made of an inexpensive general-purpose metal. In this case, it is advantageous to select a material with strength characteristics or deformation behavior similar to nickel as the base material layer, both in the manufacturing process and in the forming process during actual use, and typically ordinary steel or stainless steel can be selected. Since ordinary steel or stainless steel used as the base material and nickel used as the cladding material have a high affinity in the hot rolling temperature range, they can be easily mutually diffused at the interface during hot rolling bonding to produce nickel clad steel plate. In addition, for example, ordinary steel and austenitic stainless steel have the same fcc structure as nickel in the hot rolling temperature range and have the same hot strength, so their deformation behavior is similar and they are advantageous for manufacturing nickel clad steel plate. In addition, the thickness of clad plate manufactured by rolling method is determined by the mechanical gap of the rolling rolls, so the thickness can be controlled uniformly. Such nickel clad plate can be used as a composite material that has a thick and uniform thickness of the outer nickel layer and can withstand bending processing.

For example, Patent Document 1 discloses "a method for manufacturing a clad product, the method including: preparing a welded assembly including a clad material disposed on a substrate, both of the substrate and the clad material being individually selected from alloys, wherein at least a first edge of the clad material does not extend to a first edge of the substrate and provides a margin between the first edges, and wherein a material adjacent the first edge of the clad material within the margin is an alloy having a higher hot strength than the clad material; and hot rolling the welded assembly to provide a hot rolled strip, wherein the material within the margin is adapted to prevent the clad material from extending beyond the edge of the substrate during hot rolling."
Patent Document 1 discloses that "the substrate is stainless steel and the clad is nickel or a nickel alloy."

Patent Document 2 also discloses "a metal plate having nickel disposed on its surface, the concentration of nickel hydroxide among chemical species detected on the surface by X-ray photoelectron spectroscopy being greater than 0 atomic % and less than or equal to 14 atomic %."

Patent Document 3 also discloses a nickel-based alloy clad steel that is "combined with a nickel-based alloy consisting of, by mass%, C: 0.02% or less, Cr: 14-25%, Mo: 5-18%, W: 0-5% or less, Fe: 6% or less, with the remainder being essentially Ni and unavoidable impurities, and has a carbon steel base material, and is characterized in that the hardness (Vickers hardness under a load of 500 g) within 0.1 mm from the surface on the back side of the base material is 180 or less."

Patent Document 4 also discloses a method for manufacturing lead frame materials, which comprises assembling single-sided or double-sided clad plate materials in which the surface material is either Ni, Ni-Cu alloy, or Fe-Ni alloy, and the base material as the core material is either an Fe-based material, an Fe-Ni-based alloy, a Cr-based stainless steel, or a Cr-Ni-based stainless steel, creating a vacuum at the interface between the materials, hot rolling the assembly to form a clad bond between the surface material and the base material, and then cold rolling the assembly until the thickness of the surface layer is 5% or less of the total thickness if the surface layer is Ni or Ni-Cu-based.

Patent Document 1: JP-T-2008-502486 A Patent Document 2: JP-A-2017-179441 A Patent Document 3: JP-A-2002-194466 A Patent Document 4: JP-A-6-275770 A

Here, in the conventional manufacturing process for making nickel clad plate into a plate product, including Patent Documents 1 to 4, the hot-rolled clad plate that has been joined in the hot rolling process is deoxidized by pickling or surface cutting to remove scale, then cold-rolled to a predetermined plate thickness, and finished by a finish annealing process to make the product. The typical product plate thickness in this case is about 0.5 mm to 2.0 mm, and the thickness of the outer nickel material layer is extremely thin, about 50 to 200 μm.
Nickel is extremely soft and can be scratched by external forces. This is not a problem for a pure nickel metal plate, but if the surface of a nickel-clad plate with a thin outer nickel material layer is scratched, there is a risk that the inner base material layer will be exposed to the surface during subsequent bending, for example. Therefore, it is desirable for the surface of the nickel-clad plate to have excellent scratch resistance.
On the other hand, in order to improve the scratch resistance of the surface of, for example, ordinary steel or stainless steel, a method of hardening the surface by carrying out a treatment such as carburizing or nitrogen absorption is known.

However, nickel does not dissolve carbon or nitrogen even at high temperatures, so carburizing or surface hardening by nitrogen absorption cannot be applied. On the other hand, nickel can dissolve a certain amount of oxygen, unlike ordinary steel or stainless steel. However, when the nickel surface comes into contact with oxygen in the heat treatment atmosphere, a hydroxide or oxide is formed, forming a protective coating, which prevents oxygen from penetrating to the metal base layer.
For this reason, including those disclosed in Patent Documents 1 to 4, it has been conventionally difficult to harden the surface of the nickel material layer of the outer layer to improve scratch resistance.

The objective of this disclosure is to provide a nickel-clad plate with improved scratch resistance on the surface of the nickel material layer that forms the outer layer, and a method for manufacturing the same.

Means for solving the above problems include the following aspects.
<1> A metal base material layer,
A nickel material layer laminated on one or both sides of the metal base material layer;
Including,
A nickel clad plate having a Vickers hardness measured from the surface of the nickel material layer at a test force of 9.8 N and a Vickers hardness measured from the surface of the nickel material layer at a test force of 0.2 N that is greater by a difference of 30.0 or more.
<2> The nickel clad plate according to <1>, wherein the oxygen concentration in the surface layer of the nickel material layer is higher than the oxygen concentration in the central part of the thickness of the nickel material layer, and is 0.20% or more and 0.55% or less in mass%.
<3> A hot rolling process for obtaining a hot-rolled clad plate by hot rolling and bonding a laminate in which a nickel material to be a nickel material layer is superimposed on one or both sides of a steel material to be a metal base material layer, the hot rolling being started after heating the laminate to a temperature 150° C. or more higher than the _A3 transformation point of the steel material, and finishing the hot rolling at a temperature equal to or higher than the _A3 transformation point of the steel material;
a cold rolling step of cold rolling the hot-rolled clad plate while the oxide scale generated in the hot rolling step remains attached to the nickel material to obtain a cold-rolled clad plate;
A bright annealing process of annealing the cold-rolled clad sheet in a non-oxidizing atmosphere at 700°C or higher;
A method for producing a nickel clad plate comprising the steps of:
<4> The method for producing a nickel-clad plate according to <3>, wherein in the hot rolling step, four peripheries including the longitudinal ends and the widthwise ends of the laminate are joined and sealed before the hot rolling.

This disclosure makes it possible to provide a nickel-clad plate with improved scratch resistance on the surface of the nickel layer that forms the outer layer, and a method for manufacturing the same.

FIG. 1 is an explanatory diagram showing the overall configuration of an example of a nickel-clad plate according to the present disclosure. FIG. 2 is a graph showing an example of the relationship between the Vickers hardness HV and the tip penetration depth h of a Vickers indenter in the nickel-clad plate of the present disclosure.

An example of the present disclosure will be described below.
In the present disclosure, the "%" designation for the content of each element in a chemical composition means "mass %."
When the lower limit of the content of each element in the chemical composition is expressed as "0", it means that the element is an optional component and does not have to be contained.
In a numerical range expressed using "to", when the numerical values before and after "to" are not followed by "more than" or "less than", it means a range that includes these numerical values as the lower and upper limits. In addition, when the numerical values before and after "to" are followed by "more than" or "less than", it means a range that does not include these numerical values as the lower and upper limits.
In the numerical ranges described in stages, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range described in stages, or may be replaced by a value shown in an example. Also, the lower limit of a certain numerical range may be replaced by the lower limit of another numerical range described in stages, or may be replaced by a value shown in an example.
The term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

The nickel clad plate of the present disclosure (hereinafter also referred to simply as "clad plate") includes a metal base layer and a nickel material layer laminated on one or both sides of the metal base layer, and the difference in Vickers hardness measured from the surface of the nickel material layer with a test force of 0.2 N is greater than the Vickers hardness measured from the surface of the nickel material layer with a test force of 9.8 N by 30.0 or more. In the nickel clad plate of the present disclosure, the metal base layer and the nickel material layer are laminated, which means that the metal base layer and the nickel material layer are laminated by metallic bonding. On the other hand, in the present disclosure, "laminate" means the overlapping materials before becoming a clad.

The nickel clad plate disclosed herein has the above-mentioned configuration, where the surface of the nickel material layer (i.e., the surface of the nickel material layer opposite the side bonded to the metal base material layer) is harder than the inside, resulting in a nickel clad plate with improved scratch resistance of the surface of the nickel material layer that forms the outer layer.

The nickel-clad plate of the present disclosure will be described in detail below.
FIG. 1 is an explanatory diagram showing the overall configuration of an example of a nickel-clad plate according to the present disclosure.
1, for example, a nickel material layer 2, a metal base material layer 3, and a nickel material layer 4 are laminated in this order. That is, the nickel clad plate 1 includes the metal base material layer 3 and the nickel material layers 2 and 4 laminated on both sides of the metal base material layer 3.
However, the nickel material layer 4 is a layer that is optionally provided as necessary. That is, the nickel clad plate 1 may include the metal base material layer 3 and the nickel material layer 2 laminated on one side of the metal base material layer 3.
Further, the nickel clad plate 1 may have a metal base material layer laminated on the nickel material layer 4 in addition to the nickel material layer 2, the metal base material layer 3, and the nickel material layer 4. That is, the nickel clad plate 1 may have a nickel material layer and a metal base material layer laminated repeatedly.
It is preferable that both sides of the nickel clad plate 1 are made of nickel layers.

Below, each element and characteristic of the nickel clad plate disclosed herein will be explained in detail. However, reference numerals will be omitted in the explanation.

(Metal base layer)
Examples of the metal base material layer include a metal base material layer made of ordinary steel and a metal base material layer made of stainless steel.
In particular, a metal base material layer made of ordinary steel is suitable as the metal base material layer. A nickel clad plate using a metal base material layer made of ordinary steel has an outer surface covered with a nickel material layer, and exhibits excellent corrosion resistance in a high-concentration alkaline environment, which is a characteristic of nickel. In addition, if the metal base material layer is made of ordinary steel, which is an inexpensive general-purpose metal, the cost of the metal as a whole for the nickel clad plate can be kept low. In addition, when comparing the deformation behavior of ordinary steel and nickel used in the metal base material layer, the strength at which plastic deformation begins due to an external force, that is, the yield strength of ordinary steel, is greater than the proof strength of nickel. Therefore, a nickel clad plate using a metal base material layer made of ordinary steel has the characteristic of excellent structural strength.

As for ordinary steel, ordinary steel suitable for cold rolling during the manufacturing process is suitable. Representative examples include SPCC, SPCD, SPCE, SPCF, SPCG, etc., as specified in JIS G 3141:2017.

Stainless steel types include, for example, ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, austenitic-ferritic duplex stainless steel, and precipitation hardened stainless steel. Specific steel types include SUS304 (austenitic stainless steel), SUS316 (austenitic stainless steel), SUS301 (austenitic stainless steel), SUS302 (austenitic stainless steel), SUS403 (martensitic stainless steel), SUS430 (ferritic stainless steel), SUS329J1 (austenitic-ferritic duplex stainless steel), and SUS821L1 (austenitic-ferritic duplex stainless steel), which are specified in JIS G 4304:2015 or JIS G 4305:2015.

The metal base layer may be made of pure aluminum or an aluminum alloy.

(Nickel material layer)
The nickel material layer includes a nickel material layer made of pure nickel material containing, by mass%, 98% or more (preferably 99% or more) of nickel, with the remainder being impurities. The impurities mainly include elements or impurities necessary for deoxidization in the refining process, and specific examples include carbon, oxygen, silicon, aluminum, magnesium, phosphorus, sulfur, manganese, chromium, cobalt, copper, iron, etc. Representative examples of pure nickel materials include NW2200 and NW2201, which are standardized in JIS G 4902:2019.
The nickel material layer may be a nickel material layer made of a nickel alloy material. The nickel alloy material may be an alloy containing Fe, Cr, Cu, etc. in addition to nickel. Examples of the nickel alloy material include NCF600, NW4400, etc., which are standardized in JIS G 4902:2019, and PC, etc., which are standardized in JIS C 2531:1999.

(Vickers hardness)
Both values are measured from the surface of the nickel material layer (i.e., the surface of the nickel material layer opposite the side joined to the metal base material layer), but the Vickers hardness measured with a test force of 0.2 N (hereinafter also referred to as "surface Vickers hardness HV0.02") is greater by a difference of 30.0 or more than the Vickers hardness measured with a test force of 9.8 N (hereinafter also referred to as "internal Vickers hardness HV1").

Here, the fact that the hardness of the surface layer is harder than that of the inside of the nickel material layer that is the outer layer can be confirmed by investigating how the hardness obtained by a Vickers hardness test standardized in JIS Z 2244:2009 changes depending on the penetration depth of the tip of a Vickers indenter.
That is, if the test force in the Vickers hardness test is F (N), the Vickers hardness is HV, and the penetration depth of the tip of the Vickers indenter is h (μm), h is calculated from the relational equation: h = 62.1√(F/HV) [μm], and the hardness of the inside and surface layers of the nickel material layer is compared.

FIG. 2 shows a graph illustrating an example of the relationship between the Vickers hardness HV and the tip penetration depth h of the Vickers indenter in the nickel-clad plate of the present disclosure.
As shown in Fig. 2, the Vickers hardness shows almost the same hardness at a position where h is deeper than 10 μm, so the Vickers hardness in this range may be considered to be equivalent to the hardness of the inside of the nickel material layer in an annealed state. More preferably, the hardness of the inside of the nickel material layer can be evaluated under the condition where h is deeper than 15 μm. Considering that the hardness of the inside of the nickel material layer of the outer layer in an annealed state is 80 to 100 HV, the hardness of the inside of the nickel material layer can be evaluated by evaluating the internal Vickers hardness HV1 at a test force of 9.8 N.

To improve scratch resistance, it is effective for the nickel layer to have a high hardness in the range of several μm deep from the surface. The prototype material shown as a comparative example in Figure 2 is an example in which no clear effect on scratch resistance was observed, while the prototype material shown as an example of the present invention is a prototype material in which improved scratch resistance was observed. In other words, improved scratch resistance is observed when the Vickers hardness from the surface of the nickel layer to a depth of at least 2 μm is 30.0 or more greater than that of the interior of the nickel layer. In this case, the hardness of the surface layer of the nickel layer can be evaluated by evaluating the surface layer Vickers hardness HV0.02 at a test force of 0.2 N.

In this way, since the surface layer Vickers hardness HV0.02 is greater than the internal Vickers hardness HV1, the surface layer of the nickel material layer is harder than the internal portion, and the scratch resistance of the surface of the nickel material layer, which becomes the outer layer, is improved.
Here, since the internal metal structure of the nickel material layer is required to be in an annealed state with ordered crystal grains, it is necessary to avoid increasing the Vickers hardness to the inside of the nickel material layer. If the Vickers hardness is increased to the inside, there is a concern that the ductility of the entire sheet material will be impaired and formability will be hindered. Therefore, it is necessary to increase the scratch resistance by hardening only the surface layer of the nickel material layer from the surface layer to a depth of at least 2 μm.

Compared with the internal Vickers hardness HV1, the surface layer Vickers hardness HV0.02 measured from the surface of the nickel material layer with a test force of 0.2 N is preferably 30.0 or more larger, and more preferably 40.0 or more larger.
However, from the viewpoint of preventing surface roughness or surface cracks during bending, the difference between the internal Vickers hardness HV1 and the surface layer Vickers hardness HV0.02 is preferably 100 or less.

From the viewpoint of improving the scratch resistance of the surface of the nickel material layer that forms the outer layer, the lower limit of the surface layer Vickers hardness HV0.02 is preferably 110, and more preferably 115. The upper limit of the surface layer Vickers hardness HV0.02 is preferably 210, and more preferably 195. The surface layer Vickers hardness HV0.02 may be 110 to 210, or 115 to 195.

Here, the Vickers hardness is the arithmetic average value measured at any five points on the surface of the nickel layer of the nickel clad plate to be measured, in the central part in the clad plate width direction, based on JIS Z 2244:2009, using each of the above test forces. However, the arbitrary measurement points are those that are 500 μm or more apart in terms of the distance between the centers of the indentations when measuring HV1, and 80 μm or more apart when measuring HV0.02.

(Oxygen Concentration)
It is preferable that the oxygen concentration in the surface layer of the nickel material layer (i.e., the surface layer of the nickel material layer on the side opposite to the side joined to the metal base material layer) is higher than the oxygen concentration in the center of the thickness of the nickel material layer.
The oxygen concentration in the surface layer of the nickel material layer is higher than that in the central portion of the nickel material layer, so that the surface layer is harder than the inside of the nickel material layer. This makes it easier for the Vickers hardness measured from the surface of the nickel material layer with a test force of 9.8 N and the Vickers hardness measured from the surface of the nickel material layer with a test force of 0.2 N to satisfy the above relationship. As a result, the scratch resistance of the nickel material layer surface, which is the outer layer, is easily improved.
From the viewpoint of improving the scratch resistance of the surface of the nickel material layer which becomes the outer layer, the difference in oxygen concentration between the surface layer of the nickel material layer and the central part of the layer thickness of the nickel material layer is preferably 0.15 to 0.50% by mass, and more preferably 0.18 to 0.40%.
From the same viewpoint, the oxygen concentration in the surface layer of the nickel material layer is preferably 0.20 to 0.55% by mass, and more preferably 0.23 to 0.45%.

The surface layer of the nickel material layer refers to the region from the surface of the nickel material layer to a depth of 1 μm to 4 μm. On the other hand, the region where the surface hardness of the nickel material layer becomes hard is limited to a depth of up to 20 μm from the outer surface. In other words, the position 20 μm or deeper from the outer surface is nickel with uniform characteristics whose metal structure has been adjusted by annealing. Therefore, the center of the nickel material layer refers to a position deeper than 20 μm from the outer surface of the nickel material layer. Also, considering that the HV hardness and oxygen concentration are measured from the outer surface layer, the characteristics of the center of the nickel material layer can be measured using the average value in the region from a depth of 20 μm to a depth of 40 μm from the surface of the nickel material layer.

Here, the oxygen concentration is measured as follows.
After ultrasonically cleaning the nickel clad plate to be measured with acetone, the surface side of the nickel material layer is sputtered in the depth direction by glow discharge optical emission spectrometry (quantitative GDS) to measure the depth direction distribution of the intensity of the elements contained in the nickel material layer (O, Ni, Fe, Cr, Mn, Si, Cu, N, C).The oxygen concentration in the surface layer and the central part of the thickness of the nickel material layer is calculated from the arithmetic average of the intensity ratio of O (oxygen) to all the elements contained in the nickel material layer in the surface layer and the central part of the thickness of the nickel material layer.
The measurement conditions are as follows:
・Measuring equipment: Horiba, model number: GD-Profiler2
Measurement conditions: RF output 35 W, discharge area φ4 mm, argon pressure 600 Pa, measurement depth 50 μm
Measurement location: center of clad plate width Sputtering rate: 0.09 μm/sec
Measurement timing: every 0.008 (μm) of cutting depth due to sputtering

(Thickness)
The total thickness of the clad plate of the present disclosure is preferably 0.3 to 6.0 mm, and more preferably 0.5 to 5.0 mm.
The ratio of the thickness of the nickel material layer to the total thickness of the clad plate (thickness of nickel material layer/total thickness of the clad plate) is preferably 5/100 to 25/100, and more preferably 8/100 to 20/100.
The thickness of the nickel material layer is preferably 0.05 to 1.0 mm, and more preferably 0.08 to 0.5 mm.
By setting the total thickness of the clad plate and the thickness of each layer within the above ranges, the plate is suitable for use as a cathode material in a sodium chloride electrolysis device, an electrode in an alkaline water electrolysis device, and an electrode for a secondary battery.

<Method of manufacturing nickel clad plate>
Next, an example of a method for manufacturing a nickel-clad plate according to the present disclosure will be described. Note that the example of the method for manufacturing a nickel-clad plate according to the present disclosure is an example in which a steel material is used as a metal material to be a metal base material layer (i.e., a metal base material layer made of steel is used as a metal base material layer).

The method for producing a nickel clad plate according to the present disclosure includes the steps of:
a hot rolling step of hot rolling a laminate in which a nickel material to be a nickel material layer is superimposed on one or both sides of a steel material to be a metal base material layer, and bonding the laminate by hot rolling to obtain a hot rolled clad plate, the hot rolling step being performed after heating the laminate to a temperature 150°C or higher than the _A3 transformation point of the steel material, and then the hot rolling is started and the hot rolling is completed at a temperature equal to or higher than the _A3 transformation point of the steel material;
a cold rolling process in which the hot-rolled clad plate is cold-rolled while the oxide scale formed in the hot rolling process remains attached to the nickel material to obtain a cold-rolled clad plate;
A bright annealing process of annealing the cold-rolled clad sheet in a non-oxidizing atmosphere at a temperature of 700°C or higher;
Includes.

In the conventional method for manufacturing nickel clad plate, the hot-rolled clad plate is annealed in air after hot rolling, and then the oxide scale on the surface is removed by pickling or surface cutting before cold rolling. This is because if the oxide scale is crushed by the processing during cold rolling, it will cause scratches or roughness on the surface of the clad plate.
On the other hand, when a hot-rolled clad plate that has been hot-rolled and not annealed in air is cold-rolled with the oxide scale remaining, the oxide scale on the surface of the nickel material that will become the nickel material layer has ductility in the cold rolling and is maintained without being fractured. The oxide scale after hot rolling (hot-rolled scale) and the oxide scale after annealing (annealed scale) have different properties, and while the annealed scale is prone to fracture during cold rolling, the hot-rolled scale is ductile and easy to stretch.

In addition, compared with a nickel clad plate that is cold rolled after removing the oxide scale after hot rolling as in the conventional manufacturing method, a nickel clad plate that is cold rolled and bright annealed with the oxide scale after hot rolling still attached has an increased hardness of the surface layer of the nickel material layer. This is because nickel oxide is dispersed in the surface layer of the nickel material layer by cold rolling while leaving the oxide scale after hot rolling, and part of the oxygen liberated by the reduction of nickel oxide during the final step of bright annealing dissolves in metallic nickel, forming an oxygen-enriched layer in the surface layer of the nickel material layer and hardening it.
In addition, the nickel material layer that constitutes the surface of the nickel clad steel plate is difficult to harden by conventional surface hardening treatments such as nitriding or carburizing. Also, when oxygen is introduced into the surface of the nickel material layer by ion implantation or the like, a nickel hydroxide film is formed on the surface, making it difficult to introduce oxygen.

From the above, the nickel clad plate method disclosed herein can obtain a nickel clad plate that satisfies the relationship between the Vickers hardness at the surface of the nickel material layer at each of the above test forces, and the oxygen concentration at the surface layer and the center of the plate thickness of the nickel material layer.

In addition, in the conventional manufacturing method of nickel clad plate, when removing the oxide scale on the surface, the thickness of the metal part of the nickel material is also reduced to a certain extent, and the thickness ratio of the nickel material layer to the metal base material layer changes from the state immediately after hot rolling.
On the other hand, if cold rolling is performed without carrying out deoxidation scale treatment, a part of the nickel material that will become the nickel material layer will not be removed by pickling or cutting. Therefore, the thickness ratio of the nickel material layer to the metal base material layer can be maintained in the state immediately after bonding by hot rolling while cold rolling is performed. As a result, it is possible to produce the nickel clad plate, which is the product, while keeping the nickel material layer uniform at a constant thickness.

In addition, in cold rolling, when soft nickel material comes into contact with rolling rolls under high pressure, the nickel material adheres to the rolling rolls, causing damage to the surface properties and rolling defects. However, by carrying out cold rolling with oxide scale attached to the surface of the nickel material, it is possible to prevent deterioration of surface properties and rolling defects caused by adhesion of the nickel material.

Below, each step of an example of a manufacturing method for the nickel clad plate disclosed herein is explained.

(Hot rolling process)
In the hot rolling process, a laminate in which a nickel material to be a nickel material layer is laminated on one or both sides of a steel material to be a metal base material layer is hot rolled to bond and roll the laminate, thereby obtaining a hot rolled clad plate. Specifically, for example, the process is as follows.

In the hot rolling process, first, for example, slabs or thick plates are prepared as steel and nickel materials. It is preferable that the slabs or thick plates are of uniform thickness and free of irregularities, scratches, and dirt.

Next, for example, a steel material is laminated with a nickel material as a cladding material on one or both sides of the steel material. Before hot rolling, the laminated body is sealed and sealed around all four sides, including the longitudinal and widthwise ends. This prevents oxide scale from forming between the steel material and the nickel material when hot rolling, and ensures good bonding.

Next, the laminated body is hot-rolled to be bonded and rolled. The hot rolling is started after heating the laminated body to a temperature 150° C. or more higher than the _A3 transformation point of the steel material (i.e., the temperature before hot rolling) and is finished at a temperature equal to or higher than the _A3 transformation point of the steel material (i.e., the hot rolling end temperature). The temperature indicates the surface temperature of the laminated body.

Here, when cold rolling is performed on the hot-rolled joint body after hot rolling, the thickness ratio of the steel material to be the metal base material layer and the nickel material to be the nickel material layer (i.e., the combined material) is substantially unchanged before and after cold rolling. Therefore, it is preferable to adjust the thickness ratio of the steel material to be the metal base material layer and the nickel material to be the nickel material layer (i.e., the combined material) to a desired ratio immediately after hot rolling.
However, if the hot rolling conditions are not appropriate, the deformation amounts of the respective materials due to the hot rolling are not uniform, making it difficult to achieve the target thickness ratio. Such non-uniform deformation amounts mainly occur when the high-temperature deformation resistances of the steel material to be the metal base material layer and the nickel material to be the nickel material layer do not match in the heating temperature range of the hot rolling.

If the high-temperature deformation resistance of the steel material that will become the metal base layer and the nickel material that will become the nickel material layer differs, the amount of thinning in the thickness direction due to hot rolling will differ between the two materials, resulting in a difference in the amount of elongation in the longitudinal direction or width direction. If the difference in deformation resistance between the two materials is small within a certain range, the difference in the amount of thinning is absorbed as a deviation in the amount of elongation in the width direction, and hot rolling is unlikely to be hindered.
However, if the difference in deformation resistance between the two materials exceeds a certain range, the difference in the amount of thinning appears not only in the width direction but also as a deviation in the amount of elongation in the longitudinal direction. This causes the weld seal to become misaligned in the longitudinal direction, and if the length of the nickel material used as the joining material is excessive, out-of-plane deformation occurs and the thickness ratio changes. If the length of the nickel material is insufficient, excessive thinning may occur, causing breakage and chipping. If the weld is destroyed, it may cause problems with joining by hot rolling.

To prevent this from happening, hot rolling is performed under the above temperature conditions.

In addition, in order to ensure that oxide scale is sufficiently formed on the surface of the nickel material layer of the hot-rolled joint after hot rolling, it is advisable to preheat the laminate before hot rolling using a burner-type heat source that uses combustion gas such as natural gas, and then perform hot rolling.

(Cold rolling process)
In the cold rolling process, the hot-rolled clad plate is cold-rolled while the oxide scale formed in the hot rolling process is still attached to the nickel material, to obtain a cold-rolled clad plate. Specifically, the hot-rolled clad plate after the hot rolling process is cold-rolled without air annealing and while the oxide scale is still attached to the nickel material. By not performing air annealing, it is possible to prevent new oxide scale from being formed with voids, and since the oxide scale, which is a continuous body compressed and integrated in the hot rolling process, has ductility, cold rolling can be performed without crushing. Nickel oxide is then dispersed in the surface layer of the nickel material layer.

If deoxidation scale treatment such as pickling and surface grinding is carried out to remove the oxide scale, not only will the oxide scale be removed but a significant amount of the nickel material will also be removed. As a result, the thickness ratio of the nickel material layer in the nickel clad plate will change from the state immediately after hot rolling. In this respect, there is an advantage to not carrying out deoxidation scale treatment.

The cold rolling conditions are not particularly limited, and the cold rolling can be carried out under well-known conditions.
Between the hot rolling and the cold rolling, annealing may be performed in a non-oxidizing atmosphere or an atmosphere with a reduced oxygen concentration.
In addition, if a sufficient amount of oxide scale has adhered to the nickel material, a descaling treatment may be carried out to remove a portion of the oxide scale.

(Bright annealing process)
In the bright annealing step, the cold-rolled clad sheet is bright annealed.
Bright annealing is performed under conditions that prevent the formation of new oxide scale and the thinning of the nickel material layer due to deoxidation scale treatment, and therefore, bright annealing is performed in a non-oxidizing atmosphere.
Examples of the non-oxidizing atmosphere include a mixed gas of nitrogen and hydrogen, an atmosphere of nitrogen gas, hydrogen gas, argon gas, and the like, and a vacuum atmosphere.

The bright annealing is carried out under conditions that reduce at least a part of the nickel oxide present on the surface of the nickel material layer of the cold-rolled clad sheet after cold rolling, and that allow the liberated oxygen to form a solid solution in nickel.
Therefore, the bright annealing temperature is set to 700° C. or higher. The bright annealing temperature is more preferably 800° C. or higher. However, from the viewpoint of preventing excessive grain growth, the bright annealing temperature is preferably 1000° C. or lower.
The dew point of the bright annealing atmosphere is preferably -75°C or higher and lower than -30°C, and more preferably -75°C or higher and lower than -40°C.

(Temper rolling)
When it is desired to increase the structural strength of a member manufactured using the nickel clad plate of the present disclosure, temper rolling can be performed following bright annealing in order to increase the material strength of the nickel clad plate in advance. The reduction ratio of temper rolling may be appropriately set according to the target material strength, but if an excessively large reduction ratio is applied, the ductility of the material is impaired, so the reduction ratio of temper rolling is preferably in the range of 0.5% to 10.0%, more preferably in the range of 1.0% to 5.0%. For this rolling, a general temper rolling mill can be used, and both the presence and absence of rolling lubricant oil are applicable. However, in order to accurately realize a small reduction ratio and to perform temper rolling while maintaining good flatness of the plate, it is desirable to perform temper rolling using large diameter rolls with a work roll diameter of 250 mm to 1000 mm, more preferably 400 mm to 1000 mm.

Through the above steps, the nickel clad plate disclosed herein is obtained.

The effects of this disclosure will be explained below using examples, but this disclosure is not limited to the conditions used in the following examples.

(Example A: Invention Examples 1-2, Comparative Examples 3-6)
A small-scale prototype of a nickel clad plate was made as follows.
A cast slab equivalent to ordinary steel (SPCE as specified in JIS G 3141:2017) was prepared, and the cast slab was hot-rolled, and then the hot-rolled plate was cut to a predetermined width and length, and both sides of the hot-rolled plate were machined to obtain a SPCE thick plate having a thickness of 30 mm, a width of 500 mm, and a length of 1000 mm as a steel material for the metal base layer.
A hot coil of NW2201 standardized in JIS G 4902:2019 was prepared, and a nickel plate pulled out from the hot coil was flattened with a leveller, and then the surface of the nickel plate was belt-polished and washed, followed by fine cutting. As a result, a NW2201 plate having a thickness of 5 mm, a width of 480 mm, and a length of 980 mm was obtained as a nickel material (clad material) that would become the nickel material layer.
The joining surfaces of both the steel material and the nickel material were cut or polished until a metallic luster appeared and the metal surface was exposed.
A laminate was obtained by overlapping NW2201 plates on both sides of a SPCE thick plate, and the four periphery of the laminate, including the longitudinal ends and widthwise ends, was sealed by TIG welding using a welding rod.
The welded and sealed laminate was uniformly heated to the temperature (before hot rolling) shown in Table 1, and hot rolling was performed in a total of four passes using a reversible two-high hot rolling mill to produce a hot-rolled clad plate having a thickness of 5 mm. The hot rolling completion temperature was the temperature shown in Table 1. The _A3 transformation point of SPCE is 910°C.

The hot rolled clad sheets were then cold rolled without annealing and deoxidation scaling to the total thickness shown in Table 1. However, in some cases, the deoxidation scaling shown in Table 1 was performed.
Here, the thicknesses of the first layer (nickel material layer), second layer (steel base material layer), and third layer (nickel material layer) in the cold-rolled clad plate after cold rolling are shown in Table 1. The total thickness of the hot-rolled joint and the thicknesses of the first layer (nickel material layer), second layer (steel base material layer), and third layer (nickel material layer) correspond to the total thickness of the obtained nickel clad plate and the thicknesses of the first layer (nickel material layer), second layer (steel base material layer), and third layer (nickel material layer).

Next, the cold-rolled clad sheet was bright annealed in a non-oxidizing atmosphere using the atmospheric gas shown in Table 1 at an annealing temperature and a dew point of -60°C for a bright annealing time of 1.5 to 6.0 minutes.
Here, the bright annealing time was set according to the total thickness of the cold-rolled clad sheet as follows.
Cold-rolled clad plate total thickness 0.5 mm: Bright annealing time 1.5 minutes Cold-rolled clad plate total thickness 0.8 mm: Bright annealing time 2.4 minutes Cold-rolled clad plate total thickness 1.0 mm: Bright annealing time 3.0 minutes Cold-rolled clad plate total thickness 2.0 mm: Bright annealing time 6.0 minutes

Through the above steps, a nickel clad plate was obtained, the details of which are shown in Table 1.
The Vickers hardness and oxygen concentration of the nickel material layer shown in Table 1 indicate the values of the Vickers hardness and oxygen concentration of one of the nickel material layers (first layer).

The scratch resistance of the obtained nickel clad sheet was evaluated as follows.
The scratch resistance was evaluated by a pin-on-disk sliding test without lubrication. The evaluation sample was a disk of φ80 mm taken from the prototype plate sample. A round bar of φ5 mm made of tool steel SUJ2 was used as the processing pin, and the outer periphery of the flat tip surface was chamfered to use an effective area of φ4 mm. The pin tip was contacted at a position 30 mm from the center of the disk sample and pressed with a force of 300 gf in a direction perpendicular to the disk, while rotating the disk sample at a rotation speed of 60 rpm, and the disk surface state after 300 rotations (sliding distance 56 m) was evaluated according to the following evaluation criteria.
A: No defects were observed. B: Minor roughness that was not problematic was observed. C: Defects with a maximum depth of 2 μm or more were observed. D: Defects with a maximum depth of 5 μm or more were observed.

Examples No. 1 and 2 are examples that fall under the present disclosure. In these examples, joining by hot rolling and cold rolling could be performed without any problems. In addition, the difference between the surface Vickers hardness HV0.02 and the internal Vickers hardness HV1 was large, at 30.0 or more. In addition, the oxygen concentration in the surface layer of the nickel material layer (i.e., the surface layer of the nickel material layer on the side opposite to the side joined to the metal base material layer) was higher than the oxygen concentration in the center of the nickel material layer thickness. Therefore, the scratch resistance was evaluated as good.

Examples No. 3 and 4 are examples corresponding to comparative examples. In these examples, deoxidized scale treatment was performed by pickling or cutting after hot rolling, so the difference between the surface Vickers hardness HV0.02 and the internal Vickers hardness HV1 was small, less than 30.0. Therefore, the evaluation of scratch resistance was also poor.
Example No. 5 is an example corresponding to a comparative example. In this example, the bright annealing temperature was low at 680°C, and the difference between the surface Vickers hardness HV0.02 and the internal Vickers hardness HV1 was small at less than 30.0. This is considered to be because the oxide scale remaining on the surface of the cold-rolled clad sheet remained as it was, and an oxygen-enriched layer was not formed on the surface of the nickel material layer. Therefore, the evaluation of scratch resistance was also poor.
In Nos. 6 and 7, the temperature of hot roll bonding was low, and the deformation amounts of the SPEC material and the nickel material were inconsistent during hot rolling, which caused a deviation in the thickness of the nickel material, leading to fracture during cold rolling or hot rolling.

(Example B: Invention Examples 8 to 13)
Nickel clad steel sheets were manufactured using a production line as follows.
A cast slab equivalent to ordinary steel (SPCE as defined in JIS G 3141:2017) was prepared. The dimensions of the cast slab were 250 mm thick and 1600 mm wide. Both sides of the cast slab were machined to be smooth. As a result, a SPCE slab with a thickness of 245 mm and a width of 1600 mm was obtained as a steel material to be the metal base layer.
A thick plate of NW2201 standardized in JIS G 4902:2019 was prepared. Both sides of the thick plate were cut to a smooth finish, and then further cut. As a result, a NW2201 plate having a thickness of 40 mm and a width of 1550 mm was obtained as a nickel material (clad material) that would become the nickel material layer.
A laminate was obtained by overlapping NW2201 plates on both sides of the SPCE slab, and the four periphery including the longitudinal and widthwise ends was sealed by TIG welding using a welding rod.

The welded laminate was inserted into an atmospheric heating furnace at 1250°C (temperature before hot rolling) and uniformly heated, and a total of 19 passes of hot rolling were performed using a reversible four-high hot rolling mill to obtain a hot-rolled clad plate with a thickness of 150 mm. The heat source of the atmospheric heating furnace was a burner system using natural gas as fuel. However, the hot rolling completion temperature was 1000°C. The _A3 transformation point of the SPCE was 910°C.
The obtained hot-rolled clad plate having a thickness of 150 mm was again inserted into an atmospheric heating furnace at 1250° C. (temperature before hot rolling) to be uniformly heated, and was continuously rolled by a tandem hot rolling mill to obtain a hot-rolled clad plate having a thickness of 5 mm. The hot-rolled clad plate was then wound up into a hot-rolled bonded coil.
Here, the thicknesses of the first layer (nickel material layer), second layer (steel base material layer), and third layer (nickel material layer) in the cold-rolled clad plate after cold rolling are shown in Table 1. The total thickness of the hot-rolled joint and the thicknesses of the first layer (nickel material layer), second layer (steel base material layer), and third layer (nickel material layer) correspond to the total thickness of the obtained nickel clad plate and the thicknesses of the first layer (nickel material layer), second layer (steel base material layer), and third layer (nickel material layer).

A hot-rolled clad plate was pulled out from the obtained hot-rolled bonded coil, and without annealing or deoxidizing scale treatment, the hot-rolled clad plate was cold-rolled in a six-high cold rolling mill to obtain a cold-rolled clad plate having a total thickness shown in Table 1. The obtained cold-rolled clad plate was then wound into a plurality of cold-rolled bonded coils.

Next, the cold-rolled bonded coil was subjected to bright annealing in a non-oxidizing atmosphere using the atmospheric gas and the annealing temperature, dew point, and bright annealing time of 1.5 to 6.0 minutes shown in Table 1. Here, the bright annealing time was set to a time corresponding to the total thickness of the cold-rolled clad sheet, as in Example A.
In the example where the annealing temperature was 750° C. in an argon gas atmosphere, bright annealing was carried out in a batch annealing furnace.
In the example of a nitrogen gas atmosphere or a nitrogen gas and hydrogen gas atmosphere (nitrogen+hydrogen) and an annealing temperature of 850° C., bright annealing was performed by passing the cold-rolled clad sheet through a bright annealing line.
In addition, some of the coils were subjected to non-lubricated temper rolling using a two-high temper rolling mill with a work roll diameter of 610 mm after bright annealing. The rolling reduction was 2% in Example 12 and 4% in Example 13.

Through the above steps, a nickel clad plate was obtained, the details of which are shown in Table 1.
The obtained nickel clad plate was then subjected to the same evaluation of scratch resistance as above.
The Vickers hardness and oxygen concentration of the nickel material layer shown in Table 1 indicate the values of the Vickers hardness and oxygen concentration of one of the nickel material layers (first layer). The underlined values indicate values outside the scope of the present disclosure.

Nos. 8 to 13 are examples that fall under the scope of this disclosure. In these examples, joining by hot rolling and cold rolling could be performed without any problems. In addition, the difference between the surface Vickers hardness HV0.02 and the internal Vickers hardness HV1 was large, at 30.0 or more. In addition, the oxygen concentration in the surface layer of the nickel material layer (i.e., the surface layer of the nickel material layer on the side opposite to the side joined to the metal base material layer) was higher than the oxygen concentration in the center of the nickel material layer thickness. Therefore, the scratch resistance was evaluated as good.

 

The above results show that the clad plate disclosed herein has high scratch resistance on the surface of the nickel material layer that forms the outer layer.

The disclosure of Japanese Patent Application No. 2023-054363, filed on March 29, 2023, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated.

Reference Signs List 1 Nickel clad plate 2 Nickel material layer 3 Metal base material layer 4 Nickel material layer

Claims (4)

A metal base layer;
A nickel material layer laminated on one or both sides of the metal base material layer;
Including,
A nickel clad plate having a Vickers hardness measured from the surface of the nickel material layer at a test force of 9.8 N and a Vickers hardness measured from the surface of the nickel material layer at a test force of 0.2 N that is greater by a difference of 30.0 or more. The nickel clad plate according to claim 1, in which the oxygen concentration in the surface layer of the nickel material layer is higher than the oxygen concentration in the center of the thickness of the nickel material layer, and is 0.20% or more and 0.55% or less by mass. a hot rolling process for obtaining a hot rolled clad plate by hot rolling and bonding a laminate in which a nickel material to be a nickel material layer is superposed on one or both sides of a steel material to be a metal base material layer, the hot rolling being started after heating the laminate to a temperature 150° C. or more higher than the _A3 transformation point of the steel material, and the hot rolling being finished at a temperature equal to or higher than the _A3 transformation point of the steel material;
a cold rolling step of cold rolling the hot-rolled clad plate while the oxide scale generated in the hot rolling step remains attached to the nickel material to obtain a cold-rolled clad plate;
A bright annealing process of annealing the cold-rolled clad sheet in a non-oxidizing atmosphere at 700°C or higher;
A method for producing a nickel clad plate comprising the steps of: The method for manufacturing nickel clad plate according to claim 3, wherein in the hot rolling process, the four periphery including the longitudinal and lateral ends of the laminate are bonded and sealed before hot rolling.