Highly corrosion-resistant stainless electrode material and method for producing the same

Abstract

To provide a highly corrosion-resistant stainless electrode material composed of austenitic stainless steel having enhanced corrosion resistance, and a method for producing the same.SOLUTION: An electrode material is composed of an alloy having a metal structure in which a dispersed phase composed of Cu or a Cu alloy is dispersed with an average particle diameter of 50 μm or less in a matrix phase composed of austenitic stainless steel, where Cu is contained at 6.5 to 30 mass% relative to the entire material, while the Cu is contained at 80 mass% or more in the dispersed phase and 20 mass% or less in the matrix phase. This electrode material is produced by electromagnetic stirring and melting using an Fe-Cu alloy containing at most 20 mass% of Cu in Fe.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a highly corrosion-resistant stainless steel electrode material made of austenitic stainless steel and a method for producing the same. [Background technology]

[0002] The use of hydrogen energy has been proposed, and much research is being done on technologies to obtain hydrogen from the electrolysis of water, particularly from seawater, which is abundant on Earth. Here, the electrodes used in electrolysis are required to have high corrosion resistance against the electrolyte in order to ensure stable reaction.

[0003] For example, Patent Document 1 discloses a metal electrode material used in alkaline water electrolysis, which is one method of electrolysis that produces hydrogen gas and oxygen gas from water by electrolysis. It states that nickel-based electrodes should be used, but that electrodes made of stainless steel corrode severely on the anode surface, generating large amounts of sludge and easily causing clogging of the piping in the device, and that the device, including the electrode cell, needs to be periodically maintained to remove the sludge. On the other hand, it also states that stainless steel electrodes have a lower overvoltage than pure nickel electrodes, and therefore can provide higher electrolysis performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-122255 A Summary of the Invention [Problem to be solved by the invention]

[0005] Stainless steel electrodes are made of austenitic stainless steel, such as SUS304 or SUS316, which has been made more corrosion resistant by adding Mo. Austenitic stainless steel is generally considered to be corrosion resistant even in environments that contain chlorine, such as seawater, but depending on the application, this corrosion resistance is not sufficient and higher corrosion resistance is required.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a highly corrosion-resistant stainless steel electrode material made of austenitic stainless steel having higher corrosion resistance, and a method for manufacturing the same. [Means for solving the problem]

[0007] The electrode material according to the present invention is a highly corrosion-resistant stainless steel electrode material having a metal structure in which a dispersed phase made of Cu or a Cu alloy is dispersed in a matrix phase made of austenitic stainless steel, and is characterized in that the electrode material contains Cu in a range of 6.5 to 30 mass% based on the total, and the dispersed phase contains 80 mass% or more and the matrix phase contains 20 mass% or less of Cu, and the average particle size of the dispersed phase is 50 μm or less.

[0008] According to this feature, it is possible to obtain an electrode material having higher corrosion resistance than the austenitic stainless steel alone that constitutes the matrix phase.

[0009] In the above invention, the matrix phase may contain Fe together with 16-20 mass% Cr and 8-14 mass% Ni, and the Cr content of the dispersed phase may be 10 mass% or less. The matrix phase may have a component composition consisting of Fe, Cr, Ni, Cu, and unavoidable impurity elements. The matrix phase may further contain Mo in the range of 2-4 mass%. With these characteristics, an electrode material having higher corrosion resistance than electrode materials made of general austenitic stainless steels such as SUS304 and SUS316 can be obtained.

[0010] The method for producing an electrode material according to the present invention is a method for producing a highly corrosion-resistant stainless steel electrode material having a metal structure in which a dispersed phase made of Cu or a Cu alloy is dispersed in a matrix phase made of an austenitic stainless steel, and is characterized by comprising the steps of: preparing a master alloy having a composition containing 20 mass% or less of Cu with the remainder being Fe and unavoidable impurities, and in which Cu particles having an average particle size of 50 μm or less are dispersed in an Fe matrix; melting the master alloy in a high-frequency induction heating furnace by electromagnetic stirring and melting the master alloy and additive elements containing Ni and Cr in accordance with the amount of Fe in the master alloy so that the composition is the austenitic stainless steel except for Cu; and casting the master alloy into a cast ingot containing 6.5 to 30 mass% of Cu overall, 80 mass% or more of the dispersed phase, and 20 mass% or less of the matrix phase, and having an average particle size of the dispersed phase of 50 μm or less.

[0011] According to this feature, it is possible to easily obtain an electrode material having higher corrosion resistance than the austenitic stainless steel that constitutes the matrix phase.

[0012] In the above-mentioned invention, the matrix phase may contain Fe, Cr in the range of 16 to 20 mass %, and Ni in the range of 8 to 14 mass %, and the amount of each element dissolved in the dissolving step may be adjusted so that the Cr content of the dispersed phase is 10 mass % or less. Here, the dissolving step may include the addition of Cu. The matrix phase may have a component composition consisting of Cr, Ni, Cu, and unavoidable impurity elements in Fe. Furthermore, the dissolving step may include adding and dissolving Mo so that the matrix phase further contains Mo in the range of 2 to 4 mass %. According to this feature, an electrode material having higher corrosion resistance than that of general austenitic stainless steels such as SUS304 and SUS316 can be easily obtained. [Brief description of the drawings]

[0013] [Figure 1] 1 is an SEM image of a typical cross-sectional structure of a highly corrosion-resistant stainless steel electrode material according to the present invention. [Diagram 2] 1 is a table showing the range of component compositions of the highly corrosion-resistant stainless steel electrode material according to the present invention and the component compositions of the examples. [Diagram 3] FIG. 1 is a flowchart showing the manufacturing process of a highly corrosion-resistant stainless steel electrode material according to the present invention and a diagram showing the preparation of the component composition. [Figure 4] FIG. 2 is an X-ray diffraction profile diagram of the highly corrosion-resistant stainless steel electrode material according to the present invention. [Diagram 5] 1 is a graph showing the change over time of the current flowing through the electrodes, where (a) is a graph for a highly corrosion-resistant stainless steel electrode material according to the present invention, and (b) is a graph for an electrode material (SUS316) according to a comparative example. [Figure 6] 1 is a photograph showing the change in appearance of a test piece made of a highly corrosion-resistant stainless steel electrode material according to the present invention when immersed in an alkaline aqueous solution. [Figure 7] 1 is a photograph showing the change in appearance when a test piece (SUS316) according to a comparative example is immersed in an alkaline aqueous solution. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The highly corrosion-resistant stainless steel electrode material according to the present invention will be described with reference to FIGS.

[0015] 1, the highly corrosion-resistant stainless steel electrode material 10 in this embodiment is made of an alloy having a two-phase structure in which a matrix phase 1 made of austenitic stainless steel, such as SUS304 or SUS316, is used as a base, and a dispersed phase 2 made of Cu with an average particle size of 50 μm or less is finely dispersed in the matrix phase 1 made of this austenitic stainless steel. However, as described later, the matrix phase 1 is not the pure austenitic stainless steel on which it is based, but contains Cu, and similarly, the dispersed phase 2 can be a Cu alloy containing the component elements of the austenitic stainless steel, that is, Fe, Cr, Ni, Mo, etc.

[0016] 2, the stainless steel electrode material 10 contains, as a whole, 6.5 to 30.0 mass% Cu, at least 16 to 20 mass% Cr, 8 to 14 mass% Ni, and, as necessary, 2 to 4 mass% Mo. Furthermore, in addition to elements that stabilize the austenite phase together with Cu, elements such as Mn, Nb, Ti, and C may be contained for other purposes.

[0017] As described above, the matrix phase 1 has the composition of the base austenitic stainless steel, typically SUS304 or SUS316, and contains 16-20 mass% Cr, 8-14 mass% Ni, and, as necessary, 2-4 mass% Mo. When elements such as Mn, Nb, Ti, and C are added, they may be mainly contained in the matrix 1.

[0018] The dispersed phase 2 contains 80% by mass or more of Cu, that is, it is allowed to contain up to 20% by mass of elements other than Cu. Although the detailed mechanism of corrosion resistance is not clear, from the viewpoint of maintaining the properties including the corrosion resistance of the matrix phase 1, it is preferable that the amount of elements of the matrix 1 other than Cu that diffuse into the dispersed phase 2 is small, and should be 10% by mass or less, and more preferably 5% by mass or less. In other words, the dispersed phase 2 preferably contains 90% by mass or more of Cu, and more preferably contains 95% by mass or more of Cu.

[0019] The dispersed phase 2 is finely dispersed with an average particle size of 50 μm or less, preferably 30 μm or less, and more preferably 20 μm or less, thereby exhibiting high corrosion resistance as described below while maintaining electrical conductivity as an electrode comparable to that of austenitic stainless steel not containing Cu, which is the master alloy.

[0020] [Manufacturing method] Next, a method for producing a highly corrosion-resistant stainless steel electrode material according to the present invention will be described with reference to FIG.

[0021] However, the solubility limit of Cu in Fe is not high, and even if an attempt is made to add Cu in an amount exceeding the solubility limit, for example, 6.5 mass% or more in the entire alloy, it cannot be dissolved in the Fe matrix. In addition, the two components have different solidification temperatures and specific gravities, which tend to cause gravitational segregation. Therefore, electromagnetic stirring and melting in a high-frequency induction melting furnace is used to manufacture the stainless steel electrode material 10. Although a master alloy with the target composition may be directly melted, in order to obtain a two-phase structure with good controllability, a master alloy in which pure Cu is dispersed in pure Fe is used.

[0022] First, a master alloy made of an Fe-Cu alloy is preliminarily melted (FIG. 3, S1: master alloy preparation step). In other words, pure Fe and pure Cu are placed in a high-frequency induction melting furnace in a mass ratio of 90:10 to 80:20 and melted with electromagnetic stirring. When this is cast into an ingot, a master alloy made of an Fe-Cu alloy is obtained in which Cu is dispersed in an Fe matrix with an average particle size of 50 μm or less. From the viewpoint of uniformly dispersing Cu, it is preferable that the amount of Cu is about 10% relative to Fe.

[0023] Next, the additive material is placed in a high-frequency induction melting furnace together with a predetermined amount of the above-mentioned mother alloy and melted with electromagnetic stirring to obtain the desired alloy composition (FIG. 3, S2: melting step).

[0024] As shown in FIG. 3(b), the amount of the mother alloy is determined according to the amount of Fe in the desired composition of the entire electrode material, and the amount of Cu that is insufficient and the amount of additive elements such as Cr, Ni, and Mo, if necessary, that should be added are also determined. Then, a part of the mother alloy, typically 30-50%, is first put into a high-frequency induction melting furnace together with Cu and additive elements, and the temperature is raised to 1550-1600°C to form a molten metal. After sufficient electromagnetic stirring and melting, the remaining mother alloy is added and further electromagnetic stirring and melting is performed. In other words, additive elements including Ni and Cr are added together with the mother alloy in accordance with the amount of Fe in the mother alloy, and then electromagnetic stirring and melting are performed so that the composition of the austenitic stainless steel of the matrix phase 1 is obtained except for Cu.

[0025] In the casting process, the material is poured into a casting flask at a temperature of 1550 to 1600°C to obtain a bulk material (Fig. 3, S3: casting process). If necessary, a heat treatment may be performed for homogenization.

[0026] According to the above, it is possible to easily obtain an electrode material having the same corrosion resistance as that of a precious metal such as platinum or palladium, and it is possible to use the electrode material in an environment such as seawater without the need for pretreatment. It has also been found that the electrode material has excellent antifouling properties.

[0027] [Evaluation test] Next, a test material was prepared in which a dispersed phase 2 made of Cu was dispersed in a matrix phase 1 equivalent to SUS316 (17Cr-12Ni-2.5Mo), and an evaluation test was performed. The composition of the test piece used in the evaluation test is shown in the lower part of Figure 2. A test piece made of SUS316 was also prepared as a comparative example.

[0028] Figure 4 shows the X-ray diffraction profile of the cross section of the test piece, in which peaks of fcc-Fe and Cu were detected.

[0029] Figure 5 shows the time course of the current I flowing through the test electrode in an alkaline aqueous solution consisting of alkaline simulated seawater (1M KOH + 0.5M NaCl). The vertical axis shows the initial current I 0 The figure shows the percentage ratio of current I to

[0030] As shown in FIG. 5(a) and FIG. 6, in an electrode according to one embodiment of the present invention, an initial current I 0 The percentage ratio of current I to the electrode hardly changes over time, and there is almost no change when observing the electrode surface.

[0031] On the other hand, as shown in FIG. 5(b) and FIG. 7, in the comparative electrode, the initial current I 0The percentage ratio of current I to current I became smaller, and the current almost stopped flowing. Brown deposits were observed covering the surface of the electrode, and it is assumed that the current stopped flowing due to these deposits. Such deposits easily fall off, and are thought to be the cause of the unstable current.

[0032] Although the embodiments of the present invention and modifications based thereon have been described above, the present invention is not necessarily limited to these examples. In addition, a person skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0033] 1 Matrix phase 2 Dispersed phase 10 Electrode material

Claims

1. A highly corrosion-resistant stainless steel electrode material having a metal structure in which a dispersed phase made of Cu or a Cu alloy is dispersed in a matrix phase made of austenitic stainless steel, A highly corrosion-resistant stainless steel electrode material, characterized in that it contains Cu in a range of 6.5 to 30 mass% based on the total, and in that the dispersed phase contains 80 mass% or more and the matrix phase contains 20 mass% or less, and the average particle size of the dispersed phase is 50 μm or less.

2. The highly corrosion-resistant stainless steel electrode material according to claim 1, characterized in that the matrix phase contains 16 to 20 mass% of Cr and 8 to 14 mass% of Ni together with Fe, and the Cr content of the dispersed phase is 5 mass% or less.

3. 3. A highly corrosion-resistant stainless steel electrode material according to claim 2, wherein the matrix phase has a composition consisting of Cr, Ni, Cu and unavoidable impurity elements in Fe.

4. 4. The highly corrosion-resistant stainless steel electrode material according to claim 3, wherein the matrix phase further contains Mo in the range of 2 to 4 mass %.

5. A method for producing a highly corrosion-resistant stainless steel electrode material having a metal structure in which a dispersed phase made of Cu or a Cu alloy is dispersed in a matrix phase made of austenitic stainless steel, comprising: A master alloy preparation step of preparing a master alloy having a composition containing 20 mass% or less of Cu with the remainder being Fe and unavoidable impurities, and in which Cu particles having an average particle size of 50 μm or less are dispersed in an Fe matrix; a melting step of adding additive elements including Ni and Cr together with the mother alloy in a manner corresponding to the amount of Fe in the mother alloy so as to obtain a composition of the austenitic stainless steel except for Cu in a high-frequency induction heating furnace, and then magnetically stirring and melting the mother alloy; and a casting step of casting the alloy into a cast ingot containing Cu in the ranges of 6.5 to 30 mass % based on the total mass, 80 mass % or more in the dispersed phase, and 20 mass % or less in the matrix phase, and the average particle size of the dispersed phase being 50 μm or less.

6. 6. The method for producing a highly corrosion-resistant stainless steel electrode material according to claim 5, wherein the dissolving step includes the addition of Cu.

7. The method for producing a highly corrosion-resistant stainless steel electrode material according to claim 5 or 6, characterized in that the matrix phase contains 16 to 20 mass% Cr and 8 to 14 mass% Ni together with Fe, and the amount of each element dissolved in the dissolution step is adjusted so that the Cr content of the dispersed phase is 10 mass% or less.

8. 7. The method for producing a highly corrosion-resistant stainless steel electrode material according to claim 6, wherein the matrix phase has a composition consisting of Cr, Ni, Cu and unavoidable impurity elements in Fe.

9. The method for producing a highly corrosion-resistant stainless steel electrode material according to claim 8, characterized in that in the dissolving step, Mo is added and dissolved so that the matrix phase further contains Mo in a range of 2 to 4 mass %.

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