Ferritic stainless steel sheet, member for electric heating catalyst, electric heating catalyst, method for producing ferritic stainless steel sheet, and method for producing member for electric heating catalyst

Abstract

To provide a ferritic stainless steel sheet having low electrical resistivity at high temperatures, offering superior high-temperature oxidation resistance, and being capable of exhibiting a low thermal expansion coefficient.SOLUTION: A ferritic stainless steel sheet is employed, the sheet consisting of, in mass%: C: 0.001% to 0.030%; Si: 0.01% to 1.50%; Mn: 0.01% to 1.00%; P: 0.050% or less; S: 0.010% or less; Cr: 15.00% to 25.00%; Al: 2.50% to 5.50%; Ni: 0.01% to 0.50%; Cu: 0.15% to 1.50%; Nb: 0.010% to 0.70%; Ti: 0.01% to 0.30%; N: 0.030% or less; REM: 0.003% to 0.20%; B: 0.0002% to 0.0050%; with the balance being Fe and impurities, and satisfying formula (1). 10Al+5Si-15Cu-0.5Cr≤25.0 (1). Here, each elemental symbol in formula (1) represents the content (mass%) of the respective element.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a ferritic stainless steel sheet, a member for an electric heating catalyst, an electric heating catalyst, a method for manufacturing a ferritic stainless steel sheet, and a method for manufacturing a member for an electric heating catalyst.

Background Art

[0002] As a means for treating harmful substances in exhaust gas discharged from an automobile engine, a catalyst supported on a carrier is generally used. By the way, when the temperature of the catalyst is low and below the activation temperature, such as at the time of engine startup, the catalyst may not function sufficiently and the exhaust gas may not be sufficiently purified. As a countermeasure against this, development of an electric heating catalyst (EHC) that heats the catalyst supported on the carrier to the activation temperature before or at the time of engine startup by preheating the catalyst with an in-vehicle power source has been progressing.

[0003] Two heating methods of the electric heating catalyst are known. As a first method, there is a method of attaching an electric heater for heating the catalyst to a honeycomb cylindrical carrier on which the catalyst is supported. As a second method, there is a method of heating the catalyst by generating heat in the conductive carrier on which the catalyst is supported by energizing the carrier. In either method, there are problems such as high power consumption. Therefore, the members constituting the electric heating catalyst are required to have a low electrical resistivity at high temperatures. Further, since the electric heating catalyst comes into contact with high-temperature exhaust gas, it is required to have excellent high-temperature oxidation resistance. Furthermore, since the electric heating catalyst is heated up to about 1000°C, it is required to exhibit a low coefficient of thermal expansion.

[0004] Patent Document 1 below describes an electric heating type catalyst device including an electrically heatable carrier substrate, a catalyst coating layer formed in an exhaust gas passage of the carrier substrate and composed of an oxide carrier and at least a noble metal supported on the oxide carrier, and a heating means for heating the carrier substrate by energizing the carrier substrate.

[0005] Patent Document 2 below describes a core for an electrically heatable catalytic converter, which consists of a central structural member and a segmented outer shell, each of which is electrically insulated from any other segment except that it passes through a number of thin metal alloy heater strips exhibiting high temperature resistance.

[0006] Patent Document 3 below describes a honeycomb body made of a thin metal with low conductivity, the honeycomb body comprising a plurality of corrugated thin metal strips wound in a spiral shape that extends between electrically insulated connector plates in an electrically parallel connection.

[0007] Patent Document 4 below describes a stainless steel strip having a region coated with a nickel alloy coating material on at least one of its surfaces and an adjacent region coated with a refractory metal oxide.

[0008] However, Patent Documents 1 to 4 do not disclose a material for an electric heating catalyst that has a low electrical resistivity at high temperatures, excellent high temperature oxidation resistance, and a low coefficient of thermal expansion.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above circumstances, and provides a ferritic stainless steel sheet, a member for an electric heating catalyst, an electric heating catalyst, a method for manufacturing a ferritic stainless steel sheet, and a method for manufacturing a member for an electric heating catalyst, which have a low electrical resistivity at high temperatures, excellent high-temperature oxidation resistance, and can exhibit a low coefficient of thermal expansion.

Means for Solving the Problems

[0011] In order to solve the above problems, the present invention adopts the following configuration. [1] The chemical composition of the steel is, by mass%, C: 0.001 to 0.030%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 to 25.00%, Al: 2.50 to 5.50%, Ni: 0.01 to 0.50%, Cu: 0.15 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.30%, N: 0.030% or less, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, Mo: 0 to 2.5%, W: 0 to 2.0%, Hf: 0 to 0.50%, Mg: 0 to 0.015%, Ca: 0 to 0.015%, Ta: 0 to 1.00%, Sb: 0 to 0.50%, Co: 0 to 1.00%, The balance consists of Fe and impurities, satisfying formula (1), Ferritic stainless steel sheet. 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(1) However, the element symbols in formula (1) mean the content (mass%) of each element. [2] The chemical composition of the steel is in mass%, Zr: 0.01 - 0.50%, V: 0.01 - 0.50%, Sn: 0.01 - 0.50%, Mo: 0.01 - 2.5%, W: 0.01 - 2.0%, Hf: 0.01 - 0.50%, Mg: 0.0005 - 0.015%, Ca: 0.0005 - 0.015%, Ta: 0.01 - 1.00%, Sb: 0.01 - 0.50%, The ferritic stainless steel sheet according to [1], containing one or more of Co: 0.01 - 1.00%. [3] When heated at 600°C for 1 hour, in an observation field of 500 nm × 500 nm of the cross-section of the steel sheet, 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more can precipitate. The ferritic stainless steel sheet according to [1] or [2]. [4] The electrical resistivity by the four-terminal method at 1000°C is 1.40 μΩ·m or less. The ferritic stainless steel sheet according to [1] or [2]. [5] The thermal expansion coefficient when heated from 30°C to 1000°C is 1.50% or less. The ferritic stainless steel sheet according to [1] or [2]. [6] The chemical composition of the steel is in mass%, C: 0.001 - 0.030%, Si: 0.01 - 1.50%, Mn: 0.01 - 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 - 25.00%, Al: 2.50 - 5.50%, Ni: 0.01 - 0.50%, Cu: 0.15 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.30%, N: 0.030% or less, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, Mo: 0 to 2.5%, W: 0 to 2.0%, Hf: 0 to 0.50%, Mg: 0 to 0.015%, Ca: 0 to 0.015%, Ta: 0 to 1.00%, Sb: 0 to 0.50%, Co: 0 to 1.00%, The balance consists of Fe and impurities, satisfies formula (2), and in an observation field of 500 nm × 500 nm of the cross-section of the steel sheet, there are 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more, a ferritic stainless steel sheet. 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(2) However, the element symbols in formula (2) mean the content (% by mass) of each element. [7] The chemical composition of the steel is, in mass%, Zr: 0.01 to 0.50%, V: 0.01 to 0.50%, Sn: 0.01 to 0.50%, Mo: 0.01 to 2.5%, W: 0.01 to 2.0%, Hf: 0.01 to 0.50%, Mg: 0.0005 to 0.015%, Ca: 0.0005 to 0.015%, Ta: 0.01 to 1.00%, Sb: 0.01 to 0.50%, The ferritic stainless steel sheet according to [6], containing one or more of Co: 0.01 to 1.00%. [8] The ferritic stainless steel sheet according to [6] or [7], having a thermal expansion rate of 1.50% or less when heated from 30°C to 1000°C. [9] A member for an electric heating catalyst, made of the ferritic stainless steel sheet according to [6] or [7].

[10] An electric heating catalyst provided with the member for an electric heating catalyst according to [9].

[11] The chemical composition of the steel, in mass%, is C: 0.001 to 0.030%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 to 25.00%, Al: 2.50 to 5.50%, Ni: 0.01 to 0.50%, Cu: 0.15 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.30%, N: 0.030% or less, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, Mo: 0 to 2.5%, W: 0 to 2.0%, Hf: 0 to 0.50%, Mg: 0 to 0.015%, Ca: 0 to 0.015%, Ta: 0 to 1.00%, Sb: 0 to 0.50%, Co: 0 to 1.00%, the balance being Fe and impurities, and satisfying the formula (3), and a step of cold rolling the ferritic stainless steel sheet; After the cold rolling, a step of final annealing under the conditions of a soaking temperature of 950 to 1050°C and a soaking time of 60 to 120 seconds; After the final annealing, a step of cooling so that the residence time between at least 700 to 500°C is 60 to 120 seconds; A step of performing final cold rolling for adjusting the thickness; A method for manufacturing a ferritic stainless steel sheet having the above steps. 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(3) However, the element symbols in the formula (3) mean the content (% by mass) of each element. A method for manufacturing a member for an electric heating catalyst, which has a step of heating a ferritic stainless steel sheet obtained by the method for manufacturing a ferritic stainless steel sheet described in

[11] at 600°C or higher for 1 hour or more.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a ferritic stainless steel sheet, a member for an electric heating catalyst, an electric heating catalyst, a method for manufacturing a ferritic stainless steel sheet, and a method for manufacturing a member for an electric heating catalyst, which have a low electrical resistivity at high temperatures, excellent high-temperature oxidation resistance, and can exhibit a low coefficient of thermal expansion.

Embodiments for Carrying Out the Invention

[0013] The inventors of the present invention examined a ferritic stainless steel sheet that can have a low electrical resistivity at high temperatures, excellent high-temperature oxidation resistance, and a low coefficient of thermal expansion as a material for an electric heating catalyst. As a result, it was found that a ferritic stainless steel sheet having specific chemical components can exhibit excellent high-temperature oxidation resistance and a low coefficient of thermal expansion, and can also reduce the electrical resistivity at high temperatures. Further, it was found that by precipitating a metallic Cu phase in the structure of the steel sheet, the electrical resistivity at high temperatures can be further reduced.

[0014] Hereinafter, a ferritic stainless steel sheet, a member for an electric heating catalyst, an electric heating catalyst, a method for manufacturing a ferritic stainless steel sheet, and a method for manufacturing a member for an electric heating catalyst according to embodiments of the present invention will be described.

[0015] The ferrite stainless steel sheet of this embodiment consists of, by mass%, C: 0.001 to 0.030%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 to 25.00%, Al: 2.50 to 5.50%, Ni: 0.01 to 0.50%, Cu: 0.15 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.30%, N: 0.030% or less, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, Mo: 0 to 2.5%, W: 0 to 2.0%, Hf: 0 to 0.50%, Mg: 0 to 0.015%, Ca: 0 to 0.015%, Ta: 0 to 1.00%, Sb: 0 to 0.50%, Co: 0 to 1.00%, with the balance being Fe and impurities, and satisfies the formula (1), and is a ferrite stainless steel sheet.

[0016] 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(1) However, the element symbols in formula (1) mean the content (mass%) of each element.

[0017] Moreover, the ferrite stainless steel sheet of this embodiment preferably contains one or more of Zr: 0.01 to 0.50%, V: 0.01 to 0.50%, Sn: 0.01 to 0.50%, Mo: 0.01 to 2.5%, W: 0.01 to 2.0%, Hf: 0.01 to 0.50%, Mg: 0.0005 to 0.015%, Ca: 0.0005 to 0.015%, Ta: 0.01 to 1.00%, Sb: 0.01 to 0.50%, Co: 0.01 to 1.00% by mass%.

[0018] Moreover, when the ferrite stainless steel sheet of this embodiment is heated at 600 °C for 1 hour, it is preferable that 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more can precipitate in an observation field of 500 nm × 500 nm of the cross-section of the steel sheet.

[0019] Moreover, the ferrite stainless steel sheet of this embodiment preferably has an electrical resistivity of 1.40 μΩ·m or less at 1000 °C by the four-terminal method.

[0020] In addition, the ferrite stainless steel sheet of the present embodiment preferably has a thermal expansion coefficient of 1.50% or less when heated from 30°C to 1000°C.

[0021] Moreover, the ferrite stainless steel sheet of the present embodiment is a ferrite stainless steel sheet that has the above chemical composition and in which 20 or more metal Cu phases with a circle equivalent diameter of 5 nm or more are present in an observation field of 500 nm × 500 nm of the cross section of the steel sheet.

[0022] Hereinafter, the chemical composition of the ferrite stainless steel sheet of the present embodiment will be described. In the description of the chemical composition, “%” means mass%.

[0023] C: 0.001 to 0.030% Since C deteriorates the corrosion resistance of the steel sheet, its content needs to be kept low, and the C content is 0.030% or less. However, since excessive reduction of the C content increases the refining cost, considering the oxidation resistance as well, the C content may be 0.001% or more or 0.004% or more, and may be 0.010% or less, 0.015% or less, or 0.025% or less.

[0024] Si: 0.01 to 1.50% Si is useful as a deoxidizer and is an element effective for corrosion resistance, high-temperature strength, and high-temperature oxidation resistance. On the other hand, Si increases the electrical resistivity and deteriorates the workability. Therefore, the Si content is 1.50% or less. On the other hand, since excessive reduction of the Si content increases the refining cost, the lower limit of the Si content is 0.01% or more. The Si content may be 0.02% or more, 0.03% or more, and may be 1.00% or less, 0.50% or less, 0.40% or less, or 0.30% or less.

[0025] Mn: 0.01 to 1.00% Mn is an element to be contained as a deoxidizer, but if it is contained in excess, the corrosion resistance and high-temperature oxidation resistance will deteriorate. Therefore, the Mn content should be 1.00% or less. The Mn content may be 0.90% or less, 0.50% or less, 0.30% or less, or 0.20% or less. On the other hand, when the Mn content is less than 0.01%, the unevenness at the interface between the hot-rolled scale formed during hot rolling and the steel plate substrate becomes large, and the surface of the ferritic stainless steel plate may become rough. Therefore, the lower limit of the Mn content should be 0.01% or more. The Mn content may be 0.05% or more or 0.10% or more.

[0026] P: 0.050% or less P reduces the toughness of the steel plate and also reduces the toughness of the welded part when the steel plate is welded. Therefore, the upper limit of the P content should be 0.050% or less. On the other hand, excessively reducing the P content of the stainless steel plate will lead to an increase in manufacturing cost. Therefore, the lower limit of the P content is preferably 0.005% or more or 0.010% or more. The P content may be 0.040% or less or 0.030% or less.

[0027] S: 0.010% or less S is a harmful element that has an adverse effect on the corrosion resistance and hot cracking of the welded part. Therefore, the upper limit of the S content should be 0.010% or less, preferably 0.003% or less. Since the improvement of corrosion resistance due to the reduction of the S content saturates at 0.0005%, the lower limit of the S content may be 0.0005% or more.

[0028] Cr: 15.00 - 25.00% Cr is an essential element for improving corrosion resistance and high-temperature oxidation resistance in the steel sheet of this embodiment. In particular, Cr is a necessary element for ensuring good oxidation resistance in a high-temperature environment of about 1000°C. Also, Cr reduces the coefficient of thermal expansion and the electrical resistivity. When the Cr content is less than 15.00%, the high-temperature oxidation resistance becomes insufficient, the coefficient of thermal expansion increases, and the electrical resistivity rises. Therefore, the lower limit of the Cr content is set to 15.00% or more. On the other hand, excessive Cr content deteriorates the workability of the steel sheet, so the upper limit of the Cr content is set to 25.00% or less. Also, considering weldability, the Cr content is desirably 16.00% or more and 25.00% or less. The Cr content may be 17.00% or more and 23.00% or less, or 18.00% or more and 20.00% or less.

[0029] Al: 2.50 to 5.50% Al is contained as a deoxidizing element. Also, Al is an element that improves high-temperature oxidation resistance. When the Al content is less than 2.50%, sufficient high-temperature oxidation resistance cannot be obtained. Therefore, the lower limit of the Al content is set to 2.50% or more. On the other hand, excessive Al content deteriorates the workability of the steel sheet and extremely increases the coefficient of thermal expansion and the electrical resistivity. Therefore, the upper limit of the Al content is set to 5.50% or less. The Al content may be 2.80% or more, 3.00% or more, or 3.20% or more, and may also be 5.00% or less, 4.50% or less, 4.00% or less, or 3.70% or less.

[0030] Ni: 0.01 to 0.50% Ni is an element that improves high-temperature oxidation resistance. When the Ni content is less than 0.01%, the effect of improving high-temperature oxidation resistance cannot be expected, so the lower limit of the Ni content is set to 0.01% or more. On the other hand, when the Ni content exceeds 0.50%, not only does the high-temperature oxidation resistance of the steel sheet deteriorate, but the workability may also deteriorate. Therefore, the upper limit of the Ni content is set to 0.50% or less. Furthermore, considering manufacturability, oxidation resistance, and alloy cost, the Ni content is desirably 0.05% or more and desirably 0.30% or less.

[0031] Cu: 0.15 to 1.50% Cu is an element that reduces the electrical resistivity of the steel sheet. When the Cu content is less than 0.15%, no reduction in electrical resistivity is expected, so the lower limit of the Cu content is set at 0.15% or more. On the other hand, when the Cu content exceeds 1.50%, the ductility of the steel sheet deteriorates significantly, so the upper limit of the Cu content is set at 1.50% or less. Further, considering manufacturability and oxidation resistance, the Cu content is desirably 0.20% or more, and desirably 1.40% or less or 1.00% or less.

[0032] Nb: 0.010 - 0.70% Nb is an element that improves high-temperature strength. If Nb is 0.010% or more, the high-temperature strength can be improved, so the lower limit of Nb is set at 0.010% or more. On the other hand, when the Nb content exceeds 0.70%, the workability of the steel sheet deteriorates significantly, so the upper limit of the Nb content is set at 0.70% or less. Further, considering manufacturability, high-temperature oxidation resistance, and alloy cost, the Nb content may be 0.050% or more or 0.10% or more, and may be 0.50% or less, 0.40% or less, or 0.30% or less.

[0033] Ti: 0.01 - 0.30% Ti is an element that combines with C, N, and S to improve the corrosion resistance of the steel sheet. When the Ti content is less than 0.01%, no improvement in corrosion resistance is expected, so the lower limit of the Ti content is set at 0.01% or more. On the other hand, when the Ti content exceeds 0.30%, the workability of the steel sheet deteriorates significantly, so the upper limit of the Ti content is set at 0.30% or less. Further, considering high-temperature oxidation resistance and manufacturability, the Ti content is desirably 0.02% or more, and desirably 0.20% or less or 0.15% or less.

[0034] N: 0.030% or less Like C, N deteriorates the formability and corrosion resistance of the steel sheet, so it is set at 0.030% or less. On the other hand, excessive reduction of the N content increases the refining cost, so the N content may be 0.001% or more, preferably 0.002% or more. Also, the N content may be 0.020% or less, or 0.015% or less.

[0035] REM: 0.003 - 0.20% REM is an element that improves hot workability and steel cleanliness and is effective in improving the corrosion resistance of steel plates. The REM content should be 0.003% or more for its effect to be manifested. However, excessive inclusion of REM leads to an increase in alloy cost and a decrease in productivity, so the upper limit is set at 0.20% or less. Preferably, considering the effect, economy, and productivity, the REM content is 0.005% or more and 0.10% or less. REM may also be 0.03% or more. REM belongs to elements with atomic numbers 57 - 71, and one or more of these elements can be included in the steel. The REM content means the total content of these elements. Examples of REM include La, Ce, Nd, etc.

[0036] B: 0.0002 - 0.0050% B is an element that improves secondary workability during component forming. When the B content exceeds 0.0050%, productivity deteriorates significantly, so the upper limit of the B content is set at 0.0050% or less. Furthermore, considering workability, high-temperature oxidation resistance, and alloy cost, the B content is 0.0002% or more. The B content may be 0.0005% or more. Also, the B content may be 0.0040% or less or 0.0025% or less.

[0037] The ferritic stainless steel plate of this embodiment may contain one or more of Zr: 0.50% or less, V: 0.50% or less, Sn: 0.50% or less, Mo: 2.5% or less, W: 2.0% or less, Hf: 0.50% or less, Mg: 0.015% or less, Ca: 0.015% or less, Ta: 1.00% or less, Sb: 0.50% or less, Co: 1.00% or less. The lower limit of these elements may each be 0%.

[0038] Zr: 0 - 0.50% Zr can be contained as necessary to improve corrosion resistance. It is advisable to contain Zr at 0.01% or more. Zr is an important element for suppressing the corrosion rate, but excessive content deteriorates productivity and cost, so the upper limit of the content is set at 0.50% or less. A more desirable range of Zr is 0.10% or more. Also, Zr may be 0.40% or less, or 0.35% or less.

[0039] V: 0 - 0.50% V is an element that improves corrosion resistance. When the V content exceeds 0.50%, the corrosion resistance and workability of the steel sheet deteriorate, so the upper limit of the V content is set at 0.50% or less. Further, considering productivity, high-temperature oxidation resistance, and alloy cost, the V content is preferably 0.01% or more. The V content may be 0.03% or more, or 0.10% or more, and may also be 0.40% or less.

[0040] Sn: 0 - 0.50% Since Sn is an element that further improves corrosion resistance and high-temperature strength, it can be contained as necessary. By setting the Sn content at 0.01% or more, further improvement in corrosion resistance and high-temperature strength is expected, so the lower limit of the Sn content may be set at 0.01% or more. On the other hand, when the Sn content exceeds 0.50%, productivity deteriorates significantly, so the upper limit of the Sn content is set at 0.50% or less. Further, considering workability, high-temperature oxidation resistance, and alloy cost, it is desirable that the Sn content be 0.10% or more and 0.30% or less.

[0041] Mo: 0 - 2.5% Since Mo is an element that improves the corrosion resistance of the steel sheet, it can be contained as necessary. By setting the Mo content at 0.01% or more, further improvement in corrosion resistance is expected, so the lower limit of the Mo content may be set at 0.01% or more. On the other hand, excessive content of Mo deteriorates the workability and high-temperature oxidation resistance of the steel sheet and leads to an increase in alloy cost, so the upper limit of the Mo content is set at 2.5% or less. The Mo content is preferably 0.20% or more, and is also preferably 2.0% or less. The Mo content may be 1.50% or less.

[0042] W: 0 to 2.0% W can be contained as necessary to improve corrosion resistance. It is preferable to contain W at 0.01% or more. Although W is an element important for suppressing the corrosion rate, excessive content deteriorates productivity and cost, so the upper limit of the content is set to 2.0% or less. A more desirable range of W is 0.10% or more, or 1.5% or less.

[0043] Hf: 0 to 0.50% Hf is an element that improves corrosion resistance, high-temperature strength, and high-temperature oxidation resistance. Hf may be contained at 0.01% or more as necessary. However, since excessive content may lead to a decrease in workability and manufacturability, the upper limit of the content is preferably 0.50% or less. The Hf content is preferably 0.10% or more, or 0.30% or less.

[0044] Mg: 0 to 0.015% In molten steel, Mg forms Mg oxide together with Al and acts as a deoxidizer. In addition, Mg acts as a crystallization nucleus for TiN. TiN becomes a solidification nucleus of the ferrite phase during the solidification process, and by promoting the crystallization of TiN, the ferrite phase can be finely formed during solidification. By refining the solidification structure, surface defects caused by coarse solidification structures such as ridging and roping, which are likely to occur when the steel sheet is processed into a product shape, can be prevented, and workability can be improved. Therefore, Mg is contained as necessary. When containing Mg, in order to exhibit these effects, it is preferable to contain 0.0005% or more. However, since the manufacturability deteriorates when the Mg content exceeds 0.015%, the upper limit of the Mg content is set to 0.015% or less. The Mg content is preferably 0.0010% or more, or 0.010% or less, considering manufacturability.

[0045] Ca: 0 to 0.015% Ca is an element that improves high-temperature oxidation resistance in trace amounts, and the Ca content is 0.015% or less. The Ca content may preferably be 0.0005% or more or 0.0010% or more, and may be 0.015% or less or 0.010% or less.

[0046] Ta: 0 to 1.00%, Ta is an element that improves corrosion resistance by modifying inclusions. The Ta content is preferably 0.01% or more. On the other hand, if the Ta content exceeds 1.00%, it may cause a decrease in ductility and toughness at room temperature. Therefore, the Ta content is preferably 1.00% or less. More preferably, it is 0.10% or more and 0.50% or less or 0.40% or less.

[0047] Sb: 0 to 0.50%, Sb can be contained as necessary to improve corrosion resistance. Sb can be contained at 0.01% or more. Sb is an important element for suppressing the corrosion rate, but excessive content deteriorates manufacturability and cost, so the upper limit of the content is 0.50% or less. A more desirable range is 0.10% or more and 0.30% or less.

[0048] Co: 0 to 1.00%, Co can be contained as necessary to improve corrosion resistance. Co can be contained at 0.01% or more. Co is an important element for suppressing the corrosion rate, but excessive content deteriorates manufacturability and cost, so the upper limit of the content is 1.00% or less. A more desirable range is 0.10% or more and 0.60% or less.

[0049] In the ferritic stainless steel sheet of this embodiment, the balance other than the above-described elements is Fe and impurities. However, other elements other than the above-described elements can also be contained within a range that does not impair the effects of this embodiment. Here, the impurities referred to mean components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when the ferritic stainless steel sheet of this embodiment is industrially manufactured, and are allowed within a range that does not adversely affect the present invention.

[0050] In addition, the ferritic stainless steel sheet of this embodiment needs to satisfy the following formula (1). By satisfying formula (1), it is possible to improve the high-temperature oxidation resistance, suppress the increase in the coefficient of thermal expansion, and reduce the electrical resistivity.

[0051] 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(1) However, the element symbols in formula (1) represent the content (mass%) of each element.

[0052] The ferritic stainless steel sheet of this embodiment has an electrical resistivity of 1.40 μΩ·m or less at 1000 °C by the four-terminal method. As the resistivity measuring device, the resistivity measuring device TER-2000RH (DC four-terminal method) manufactured by ULVAC-RIKO, Inc. can be used. Measurement is performed in a vacuum under the conditions of a measurement temperature of 1000 °C, a measurement current of 200 mA, and a voltage drop distance of 40 mm.

[0053] In addition, the ferritic stainless steel sheet of this embodiment has a coefficient of thermal expansion of 1.50% or less when heated from 30 °C to 1000 °C. As the coefficient of thermal expansion measuring device, the thermomechanical analyzer TD5000SA manufactured by NETZSCH can be used. The measurement method is the horizontal differential detection rod type with a reference temperature of 30 °C, and measurement is performed in the temperature range of 30 to 1000 °C. Also, the heating and cooling rate is 5 °C / min in an Ar atmosphere.

[0054] Furthermore, the ferritic stainless steel sheet of this embodiment has excellent high-temperature oxidation resistance. In this embodiment, excellent high-temperature oxidation resistance means that for a test piece with a width of 20 mm and a length of 25 mm, in an air atmosphere, a heating cycle consisting of a heating stage of maintaining at 1000 °C for 25 minutes and a cooling stage of cooling and maintaining at 100 °C or less for 5 minutes is repeated until the cumulative heating time at 1000 °C reaches 600 hours (1440 cycles) in a heating and cooling test, and the increase in weight of the test piece before and after the heating and cooling test is 1.0 mg / m 2 The following.

[0055] In addition, the ferritic stainless steel sheet of the present embodiment is heat-treated so that when heated at 600 °C for 1 hour, 20 or more metal Cu phases can precipitate in the cross-sectional structure of the steel sheet. When the metal Cu phase precipitates, in a cross-sectional area of 500 nm × 500 nm in the thickness direction of the steel sheet, 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more precipitate. When the metal Cu phase precipitates, the electrical resistivity of the ferritic stainless steel sheet is further significantly reduced.

[0056] The precipitation state of the metal Cu phase is confirmed by observing a thin film sample under the conditions of an acceleration voltage of 200 kV using a scanning transmission electron microscope STEM (Scanning Transmission Electron Microscope) HD-2700 of Hitachi High-Technologies Corporation. The analysis of Cu is identified using an EDS analyzer (Energy Dispersive X-ray Spectroscopy) attached to the STEM. The observation field is a region of 500 nm × 500 nm, and it is performed in three observation fields. Metal Cu phases with an equivalent circle diameter of 5 nm or more are specified in the observation field, and it is confirmed that 20 or more metal Cu phases exist on the image.

[0057] As the sample for observation, a sample with the cross-section of the steel sheet exposed is cut out and processed by the focused ion beam method (Focused Ion Beam, FIB) to have a thickness of 80 to 100 nm.

[0058] In addition, the ferritic stainless steel sheet of the present embodiment can be suitably used as a member for an electric heating catalyst. Specifically, a ferritic stainless steel sheet that satisfies the above chemical composition and formula (1) and in which 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more exist in a 500 nm × 500 nm observation field of the cross-section of the steel sheet can be used as a member for an electric heating catalyst.

[0059] In an electric heating catalyst, an electric heater may be built in as a means for heating the catalyst. The member for an electric heating catalyst of the present embodiment can be used as a wiring member for the electric heater.

[0060] In addition, as another means of heating the catalyst in the electric heating catalyst, there is a method of heating the catalyst by passing an electric current through a conductive carrier on which the catalyst is supported to generate heat in the carrier. The member for the electric heating catalyst of the present embodiment can be used as a wiring member for supplying current to the carrier or the carrier itself.

[0061] Next, a method for manufacturing the ferritic stainless steel sheet of the present embodiment will be described. The method for manufacturing the ferritic stainless steel sheet of the present embodiment includes a step of cold rolling a ferritic stainless steel sheet having the above chemical components and satisfying the formula (3), a step of final annealing under the conditions of a soaking temperature of 950 to 1050 °C and a soaking time of 60 to 120 seconds after cold rolling, a step of cooling after final annealing so that the residence time between at least 700 and 500 °C is 60 to 120 seconds, and a step of performing final cold rolling for adjusting the thickness.

[0062] 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(3) However, the element symbols in the formula (3) mean the content (% by mass) of each element.

[0063] The ferritic stainless steel sheet used as the material may be a steel sheet manufactured by hot rolling. Also, the ferritic stainless steel sheet only needs to have the above chemical components and satisfy the formula (3). There are no particular restrictions on the steelmaking and casting processes before the hot rolling process. Also, there are no particular restrictions on the conditions of the hot rolling process.

[0064] The ferritic stainless steel sheet may be subjected to hot-rolled plate annealing or pickling before cold rolling. The hot-rolled plate annealing is preferably carried out under the conditions of, for example, a soaking temperature of 950 to 1050 °C and a soaking time of 60 to 120 seconds. The annealing atmosphere is not particularly limited and may be in the atmosphere. The thickness of the steel sheet may be, for example, in the range of 10 mm or less.

[0065] Next, the ferritic stainless steel sheet is cold-rolled to obtain a steel sheet with a thickness of 0.03 to 0.10 mm. The cold rolling may be performed in multiple stages. For example, a first stage of cold rolling until the thickness ranges from 1.2 to 2.0 mm, a second stage of cold rolling until the thickness ranges from 0.3 to 0.8 mm, and a third stage of cold rolling until the thickness ranges from 0.03 to 0.10 mm (cold rolling for final sheet thickness adjustment) may be sequentially performed. The cold rolling is not limited to three stages and may be four or more stages or two or fewer stages. Between each stage, annealing may be performed under the conditions of soaking temperature of 950 to 1050 °C and soaking time of 60 to 120 seconds. The annealing atmosphere is not particularly limited and may be in the atmosphere.

[0066] Among the annealings performed during multiple cold rollings, the annealing performed before the cold rolling for final sheet thickness adjustment is defined as the final annealing. The final annealing is performed under the conditions of soaking temperature of 950 to 1050 °C and soaking time of 60 to 120 seconds. By this final annealing, part or all of the Cu contained in the metal structure of the steel sheet is dissolved. If the soaking temperature is less than 950 °C, the solution does not proceed sufficiently, and if the soaking temperature exceeds 1050 °C, no further effect occurs, so the soaking temperature is 950 to 1050 °C. Similarly, if the soaking time is less than 60 seconds, the solution does not proceed sufficiently, and if the soaking time exceeds 120 seconds, no further effect occurs, so the soaking time is 60 to 120 seconds. The annealing atmosphere may be, for example, any of air, hydrogen, nitrogen, argon, or a mixed atmosphere thereof.

[0067] Cooling is performed after the final annealing. The cooling method is not particularly limited, but it is necessary to make the residence time between at least 700 and 500 °C be 60 to 120 seconds. By satisfying this condition, when heated at a heating temperature of 600 °C for 1 hour later, the steel sheet is tempered so that a metallic Cu phase can precipitate in the cross-sectional structure of the steel sheet. It is presumed that very fine nuclei of metallic Cu are generated by the tempering, and starting from these nuclei, the metallic Cu phase precipitates in a subsequent heating process.

[0068] In the cooling process, in order to adjust the residence time between 700 and 500 °C to 60 to 120 seconds, for example, the residence time can be adjusted by adjusting the flow rate of the cooling gas sprayed on the steel sheet to adjust the cooling rate between 700 and 500 °C.

[0069] After the cooling process, final cold rolling is performed to adjust the thickness to obtain a steel sheet with a thickness of 0.03 to 0.10 mm. Note that the ferritic stainless steel sheet of this embodiment is generally in a form called a steel foil because of its small thickness.

[0070] In the above manner, the ferritic stainless steel sheet of this embodiment is manufactured. By going through the above steps, the electrical resistivity of the steel sheet at 1000 °C can be adjusted to 1.40 μΩ·m or less. In addition, the structure can be tempered to a structure in which a metallic Cu phase can be precipitated by heating.

[0071] For the obtained ferritic stainless steel sheet, a step of heating under the conditions of 600 °C or higher and 1 hour or longer can be performed to manufacture a member for an electric heating catalyst. By heating under the conditions of 600 °C or higher and 1 hour or longer, a metallic Cu phase is precipitated, and a member for an electric heating catalyst with a further significantly reduced electrical resistivity can be obtained. For example, the electrical resistivity by the four-terminal method at 1000 °C can be made 1.35 μΩ·m or less. The heating step may be performed on the ferritic stainless steel sheet as it is, or may be performed in a state where the ferritic stainless steel sheet is incorporated into the electric heating catalyst as a member of the electric heating catalyst.

[0072] Alternatively, the heating process may be carried out taking advantage of the fact that the electric heating catalyst is heated when the electric heating catalyst is in use. That is, the electric heating catalyst is preheated before the engine of the automobile is started and heated until it reaches a temperature equal to or higher than the activation temperature. Then, when high-temperature exhaust gas is introduced by starting the engine, the electric heating catalyst is heated to about 600 to 800°C. In this way, the electric heating catalyst is heated to 600°C or higher in its operating state. At this time, precipitation of the metallic Cu phase proceeds in the metal structure of the member made of a ferritic stainless steel sheet, and 20 or more metallic Cu phases having a circular equivalent diameter of 5 nm or more are present, so that the electrical resistivity is further significantly reduced and the power consumption is significantly reduced.

Example

[0073] In order to confirm the effects of the present invention in detail, the following experiments were conducted. It should be noted that this example shows one example of the present invention, and the present invention is not limited to the following configuration.

[0074] Slabs of 30 kg were produced by vacuum melting steel having the compositions shown in Table 1A and Table 1B. The slabs were heated at 1230°C for 2 hours and then hot-rolled to produce hot-rolled steel sheets with a thickness of 3 mm. The hot-rolled steel sheets were annealed under the conditions of soaking temperature of 950 to 1050°C and soaking time of 60 to 120 seconds.

[0075] Next, the oxide scale was removed by immersing in a nitric-hydrofluoric acid solution (3% hydrofluoric acid, 10% nitric acid, balance water) at 60°C for 30 to 120 seconds.

[0076] Next, the first-stage cold rolling was performed until the sheet thickness reached 1.5 mm. After the cold rolling, annealing was performed under the conditions of soaking temperature of 950 to 1050°C and soaking time of 60 to 120 seconds, and pickling was performed under the same conditions as above to remove the oxide scale.

[0077] Furthermore, the second-stage cold rolling was performed until the sheet thickness reached 0.4 mm. After the cold rolling, final annealing was performed at the soaking temperatures and soaking times shown in Table 2.

[0078] Next, a cooling process was carried out. In the cooling process, the cooling rate was adjusted so that the residence time between 700 and 500 °C became the time shown in Table 2.

[0079] Finally, the third cold rolling for final thickness adjustment was carried out until the thickness became from 0.4 mm to 50 μm. In this way, ferritic stainless steel sheets numbered 1 to 26 were manufactured.

[0080] For the ferritic stainless steel sheet with a thickness of 50 μm, evaluation of high-temperature oxidation resistance and electrical resistivity was carried out. In addition, for the steel sheet with a thickness of 0.4 mm before the final cold rolling, evaluation of the thermal expansion coefficient was carried out.

[0081] Also, for the ferritic stainless steel sheet with a thickness of 50 μm, after performing a heating process under the conditions of a heating temperature of 600 °C and a heating time of 1 hour, the precipitation state of the metallic Cu phase precipitated in the metal structure of the steel sheet was confirmed.

[0082] The evaluation of high-temperature oxidation resistance was carried out as follows. The steel sheet with a thickness of 50 μm was cut into test pieces with a size of 20 mm in width and 25 mm in length. Three test pieces were prepared. For the test pieces, in an air atmosphere, a heating-cooling cycle consisting of a heating stage of maintaining at 1000 °C for 25 minutes and a cooling stage of cooling and maintaining at 100 °C or lower for 5 minutes was repeated until the cumulative heating time at 1000 °C reached 600 hours (1440 cycles). Then, the increased weight of the test pieces before and after the heating-cooling test was determined. When it is 1.0 mg / m per unit surface area of the test piece 2 or less, it is regarded as qualified (G), and when it exceeds 1.0 mg / m 2 it is regarded as unqualified (B).

[0083] The electrical resistivity was measured at 1000 °C by the four-terminal method. As the measuring device, the electrical resistance measuring device TER-2000RH (DC four-terminal method) manufactured by ULVAC-RIKO, Inc. was used. The electrical resistivity of a steel plate with a thickness of 50 μm was measured in a vacuum under the conditions of a measuring temperature of 1000 °C, a measuring current of 200 mA, and a voltage drop distance of 40 mm. When the electrical resistivity by the four-terminal method at 1000 °C was 1.40 μΩ·m or less, it was judged as qualified (G), and when it exceeded 1.40 μΩ·m, it was judged as unqualified (B). In addition, the measurement of the electrical resistivity was also carried out on the steel plate after the precipitation of the metallic Cu phase.

[0084] The evaluation of the thermal expansion coefficient was carried out as follows. As the measuring device, the thermomechanical analyzer TD5000SA manufactured by NETZSCH was used. The measuring method was a horizontal differential detection rod type, with a reference temperature of 30 °C, and the measurement was carried out in the temperature range of 30 to 1000 °C. Also, the heating and cooling rate was 5 °C / min in an Ar atmosphere. In this way, the thermal expansion coefficient of a steel plate with a thickness of 0.4 mm was measured. Since the thermal expansion coefficient of a steel plate with a thickness of 0.4 mm was almost the same as that of a steel plate with a thickness of 50 μm, a steel plate with a thickness of 0.4 mm was used as a sample for the sake of measurement simplicity.

[0085] The confirmation of the precipitation state of the metallic Cu phase after the heating process was carried out as follows. The cross-section in the thickness direction of the steel plate was exposed, the steel plate was cut out with a microtome, and a thin film sample with a thickness of 80 nm was prepared. For the obtained thin film sample, using the scanning transmission electron microscope STEM (Scanning Transmission Electron Microscope) HD-2700 of Hitachi High-Technologies Corporation, the thin film sample was observed under the condition of an acceleration voltage of 200 kV to confirm the precipitation state of metallic Cu. The analysis of Cu was identified using the EDS analyzer (Energy Dispersive X-ray Spectroscopy) attached to the STEM. The observation field was a region of 500 nm × 500 nm, and the precipitation state was confirmed for three observation fields. In the observation field, a metallic Cu phase with an equivalent circle diameter of 5 nm or more was specified, and it was confirmed that there were 20 or more metallic Cu phases on the image.

[0086] As shown in Table 1A to Table 2, for No.1 to 15, the chemical composition was within the scope of the present invention, and the manufacturing conditions were also within the scope of the present invention. Therefore, for No.1 to 15, the high-temperature oxidation resistance, electrical resistivity, and thermal expansion coefficient were within the preferable ranges. Further, when a heating process at 600 °C for 1 hour was carried out, a large number of metal Cu phases precipitated at a high density, and the electrical resistivity was further reduced.

[0087] On the other hand, for No.16 to 26, the chemical composition was outside the scope of the present invention. Further, for No.19, 20, 23, 24, and 26, the manufacturing conditions were also outside the scope of the present invention. Therefore, for No.16 to 26, one or more of the high-temperature oxidation resistance, electrical resistivity, and thermal expansion coefficient failed. Further, when a heating process at 600 °C for 1 hour was carried out, a Cu precipitation state capable of reducing the electrical resistivity and thermal expansion could not be ensured.

[0088]

Table 1A

[0089]

Table 1B

[0090]

Table 2

Claims

1. The chemical composition of the steel is, by mass%, C: 0.001 to 0.030%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 to 25.00%, Al: 2.50 to 5.50%, Ni: 0.01 to 0.50%, Cu: 0.15 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.30%, N: 0.030% or less, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, Mo: 0 to 2.5%, W: 0 to 2.0%, Hf: 0 to 0.50%, Mg: 0 to 0.015%, Ca: 0 to 0.015%, Ta: 0 to 1.00%, Sb: 0 to 0.50%, Co: 0 to 1.00%, The balance consists of Fe and impurities, satisfying formula (1), A ferritic stainless steel sheet. 10Al + 5Si - 15Cu - 0.5Cr ≦ 25.0 …(1) However, the element symbols in formula (1) mean the content (mass%) of each element.

2. The chemical composition of the steel is, by mass%, Zr: 0.01 to 0.50%, V: 0.01 to 0.50%, Sn: 0.01 to 0.50%, Mo: 0.01 to 2.5%, W: 0.01 to 2.0%, Hf: 0.01 to 0.50%, Mg: 0.0005 to 0.015%, Ca: 0.0005 to 0.015%, Ta: 0.01 to 1.00%, Sb: 0.01 to 0.50%, Co: 0.01 to 1.00%, containing one or more of them, the ferritic stainless steel sheet according to Claim 1.

3. When heated at 600°C for 1 hour, in an observation field of 500 nm × 500 nm of the cross-section of the steel sheet, 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more can precipitate, the ferritic stainless steel sheet according to Claim 1 or Claim 2.

4. The electrical resistivity by the four-terminal method at 1000°C is 1.40 μΩ・m or less, the ferritic stainless steel sheet according to Claim 1 or Claim 2.

5. The thermal expansion rate when heated from 30°C to 1000°C is 1.50% or less, the ferritic stainless steel sheet according to Claim 1 or Claim 2.

6. The chemical composition of the steel is, by mass%, C: 0.001 to 0.030%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 - 25.00%, Al: 2.50 - 5.50%, Ni: 0.01 - 0.50%, Cu: 0.15 - 1.50%, Nb: 0.010 - 0.70%, Ti: 0.01 - 0.30%, N: 0.030% or less, REM: 0.003 - 0.20%, B: 0.0002 - 0.0050%, Zr: 0 - 0.50%, V: 0 - 0.50%, Sn: 0 - 0.50%, Mo: 0 - 2.5%, W: 0 - 2.0%, Hf: 0 - 0.50%, Mg: 0 - 0.015%, Ca: 0 - 0.015%, Ta: 0 - 1.00%, Sb: 0 - 0.50%, Co: 0 - 1.00%, The balance consists of Fe and impurities, satisfies formula (2), A ferritic stainless steel sheet in which in an observation field of 500 nm × 500 nm of the cross-section of the steel sheet, there are 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more. 10Al + 5Si - 15Cu - 0.5Cr ≤ 25.0 …(2) However, the elemental symbols in formula (2) mean the content (mass%) of each element.

7. The chemical composition of the steel is, in mass%, Zr: 0.01 - 0.50%, V: 0.01 - 0.50%, Sn: 0.01 - 0.50%, Mo: 0.01 - 2.5%, W: 0.01 - 2.0%, Hf: 0.01 - 0.50%, Mg: 0.0005 - 0.015%, Ca: 0.0005 - 0.015%, Ta: 0.01 - 1.00%, Sb: 0.01 - 0.50%, Co: 0.01 - 1.00%, containing one or more of these, the ferritic stainless steel sheet according to claim 6.

8. The ferritic stainless steel sheet according to claim 6 or claim 7, having a thermal expansion rate of 1.50% or less when heated from 30°C to 1000°C.

9. A member for an electric heating catalyst, made of the ferritic stainless steel sheet according to claim 6 or claim 7.

10. An electric heating catalyst provided with the member for an electric heating catalyst according to claim 9.

11. The chemical composition of the steel, in mass %, is C: 0.001 to 0.030%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.010% or less, Cr: 15.00 to 25.00%, Al: 2.50 to 5.50%, Ni: 0.01 to 0.50%, Cu: 0.15 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.30%, N: 0.030% or less, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, Mo: 0 to 2.5%, W: 0 to 2.0%, Hf: 0 to 0.50%, Mg: 0 to 0.015%, Ca: 0 to 0.015%, Ta: 0 to 1.00%, Sb: 0 to 0.50%, Co: 0 to 1.00%, and the balance consists of Fe and impurities, and a step of cold rolling a ferritic stainless steel sheet satisfying formula (3); a step of final annealing after the cold rolling under conditions of a soaking temperature of 950 to 1050°C and a soaking time of 60 to 120 seconds; a step of cooling after the final annealing so that the residence time between at least 700 and 500°C is 60 to 120 seconds; a step of performing final cold rolling for adjusting the thickness; A method for manufacturing a ferritic stainless steel sheet having the above steps. 10Al + 5Si - 15Cu - 0.5Cr ≦ 25.0 …(3) However, the element symbols in formula (3) mean the content (mass %) of each element.

12. A method for manufacturing a member for an electric heating catalyst, comprising a step of heating the ferritic stainless steel sheet obtained by the method for manufacturing a ferritic stainless steel sheet according to claim 11 at 600°C or higher for 1 hour or longer.

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