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: 25.0% to 35.0%; Al: 0.030% to 0.50%; Ni: 0.01% to 0.50%; Cu: 0.10% to 1.50%; Nb: 0.010% to 0.70%; Ti: 0.01% to 0.40%; Mo: 0.01% to 2.50%; and N: 0.030% or less, with the balance being Fe and impurities, and satisfying formula (1). 0.5Cr-10Al-5Si≥5.00 (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, 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 electric heating catalysts are known. As a first method, there is a method of attaching an electric heater for catalyst heating to a honeycomb cylindrical carrier on which a 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. In addition, 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 coat 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 thinly conductive metal, the honeycomb body comprising a plurality of corrugated thin metal strips wound in a spiral shape that extends through electrically insulated connector plates in an electrically parallel connection.

[0007] Patent Document 4 below describes a thin strip of stainless steel 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: 25.0 to 35.0%, Al: 0.030 to 0.50%, Ni: 0.01 to 0.50%, Cu: 0.10 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.40%, Mo: 0.01 to 2.50%, N: 0.030% or less, REM: 0 to 0.20%, B: 0 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, 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. 0.5Cr - 10Al - 5Si ≥ 5.00 …(1) However, the element symbols in formula (1) represent the content (mass%) of each element. [2] The chemical composition of the steel is in mass%, REM: 0.003 - 0.20%, B: 0.0002 - 0.0050%, Zr: 0.01 - 0.50%, V: 0.01 - 0.50%, Sn: 0.01 - 0.50%, 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 ferritic stainless steel sheet according to [1] or [2], having an electrical resistivity of 1.30 μΩ·m or less by the four-terminal method at 1000°C. [5] The ferritic stainless steel sheet according to [1] or [2], having a thermal expansion coefficient of 1.30% or less when heated from 30°C to 1000°C. [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: 25.0 - 35.0%, Al: 0.030 - 0.50%, Ni: 0.01 to 0.50%, Cu: 0.10 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.40%, Mo: 0.01 to 2.50%, N: 0.030% or less, REM: 0 to 0.20%, B: 0 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, 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), 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. 0.5Cr - 10Al - 5Si ≧ 5.00 …(2) However, the element symbols in formula (2) mean the content (mass%) of each element. [7] The chemical composition of the steel is, in mass%, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0.01 to 0.50%, V: 0.01 to 0.50%, Sn: 0.01 to 0.50%, 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 these, the ferritic stainless steel sheet according to [6]. [8] The ferritic stainless steel sheet according to [6] or [7], having a coefficient of thermal expansion of 1.30% 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: 25.0 to 35.0%, Al: 0.030 to 0.50%, Ni: 0.01 to 0.50%, Cu: 0.10 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.40%, Mo: 0.01 to 2.50%, N: 0.030% or less, REM: 0 to 0.20%, B: 0 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, 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 a step of cold rolling a ferritic stainless steel sheet satisfying formula (3); After the cold rolling, a step of final annealing under 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 such that the residence time between at least 700 to 500°C is 60 to 120 seconds; A step of performing final cold rolling to adjust the thickness; A method for manufacturing a ferritic stainless steel sheet having these. 0.5Cr - 10Al - 5Si ≥ 5.00 …(3) However, the element symbols in formula (3) mean the content (% by mass) of each element. A method for manufacturing a member for an electric heating catalyst, which includes 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 studied 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, the ferritic stainless steel sheet, the member for an electric heating catalyst, the electric heating catalyst, the method for manufacturing a ferritic stainless steel sheet, and the method for manufacturing a member for an electric heating catalyst according to the embodiments of the present invention will be described.

[0015] The ferritic 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: 25.0 to 35.0%, Al: 0.030 to 0.50%, Ni: 0.01 to 0.50%, Cu: 0.10 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.40%, Mo: 0.01 to 2.50%, N: 0.030% or less, REM: 0 to 0.20%, B: 0 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, 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). It is a ferritic stainless steel sheet.

[0016] 0.5Cr - 10Al - 5Si ≥ 5.00 …(1) However, the element symbols in formula (1) represent the content (mass%) of each element.

[0017] Moreover, the ferritic stainless steel sheet of this embodiment preferably contains one or more of REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0.01 to 0.50%, V: 0.01 to 0.50%, Sn: 0.01 to 0.50%, 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] Furthermore, when the ferritic 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] In addition, the ferrite stainless steel sheet of this embodiment preferably has an electrical resistivity of 1.30 μΩ·m or less at 1000°C by the four-terminal method.

[0020] In addition, the ferrite stainless steel sheet of this embodiment preferably has a coefficient of thermal expansion of 1.30% or less when heated from 30°C to 1000°C.

[0021] In addition, the ferrite stainless steel sheet of this embodiment is a ferrite stainless steel sheet that has the above chemical composition and in which 20 or more metal Cu phases with an equivalent circle 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 this 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 also 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 oxidation resistance at high temperatures. 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 0.10% or more, 0.20% or more, and may also be 1.20% or less, 1.00% or less, 0.80% or less, or 0.50% or less.

[0025] Mn: 0.01 to 1.00% Mn is an element to be contained as a deoxidizer, but if 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, or 0.30% 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 sheet substrate becomes large, and the surface of the ferritic stainless steel sheet may become rough. Therefore, the lower limit of the Mn content is set to 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 sheet and also reduces the toughness of the welded part when the steel sheet is welded. Therefore, the upper limit of the P content is set to 0.050% or less. On the other hand, excessively reducing the P content of the stainless steel sheet leads to an increase in manufacturing cost, so 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 corrosion resistance and hot cracking of the welded part, so the upper limit of the S content is 0.010% or less, preferably 0.003% or less. Since the improvement in 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: 25.00 - 35.00% 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 an element necessary to ensure 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 25.00%, 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 25.00% 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 35.00% or less. Also, considering weldability, the Cr content is desirably 26.00% or more and 35.00% or less. The Cr content may be 28.00% or more and 34.50% or less, or may be 28.00% or more and 32.00% or less.

[0029] Al: 0.030~0.50% 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 0.030%, sufficient high-temperature oxidation resistance cannot be obtained. Therefore, the lower limit of the Al content is set to 0.030% 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 0.50% or less. The Al content may be 0.050% or more, 0.100% or more, or 0.150% or more, or may be 0.45% or less, 0.40% or less, or 0.30% or less.

[0030] Ni: 0.01~0.50% Ni is an element that improves high-temperature oxidation resistance. When the Ni content is less than 0.01%, no improvement effect on high-temperature oxidation resistance can 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: 0.10~1.50% Cu is an element that reduces the electrical resistivity of the steel sheet. When the Cu content is less than 0.10%, no reduction in electrical resistivity is expected, so the lower limit of the Cu content is set at 0.10% 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. Furthermore, considering manufacturability and oxidation resistance, the Cu content is preferably 0.10% or more and desirably 1.40% 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. Furthermore, 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 also be 0.50% or less or 0.40% or less.

[0033] Ti: 0.01 - 0.40% 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 0.40%, the workability of the steel sheet deteriorates significantly, so the upper limit of the Ti content is set at 0.40% or less. Furthermore, considering high-temperature oxidation resistance and manufacturability, the Ti content is preferably 0.05% or more and desirably 0.30% or less.

[0034] Mo: 0.01 - 2.50% Mo is an element that improves the corrosion resistance of the steel sheet. When the Mo content is less than 0.01%, no further improvement in corrosion resistance is expected, so the lower limit of the Mo content is set at 0.01% or more. On the other hand, excessive inclusion 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 2.50% or less. The Mo content is preferably 0.20% or more and preferably 2.10% or less. The Mo content may also be 1.00% or less.

[0035] N: 0.030% or less Similar to 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.

[0036] The ferritic stainless steel sheet of this embodiment may contain one or more of REM: 0.20% or less, B: 0.0050% or less, Zr: 0.50% or less, V: 0.50% or less, Sn: 0.50% 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 each of these elements may be 0%.

[0037] REM: 0 to 0.20% REM is an element that can improve hot workability and steel cleanliness and is effective in improving the corrosion resistance of steel plates. It may be contained as needed. When REM is contained, it is preferably 0.003% or more for its effect to be manifested. However, excessive content 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, or 0.10% or less. REM may also be 0.03% or more, or 0.10% or less. REM is an element belonging to atomic numbers 57 to 71, and one or more of these elements can be contained in the steel. The REM content means the total content of these elements. Examples of REM include La, Ce, Nd, etc.

[0038] B: 0 to 0.0050% B is an element that can improve secondary workability during part forming and can be contained as needed. 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, it is desirable that the B content is 0.0002% or more, or 0.0005% or more. Also, it is desirable that it is 0.0040% or less or 0.0025% or less.

[0039] Zr: 0 to 0.50% Zr can be contained as needed 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 0.30% or less.

[0040] V: 0 to 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 to 0.50% or less. Furthermore, considering manufacturability, 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 0.30% or less.

[0041] Sn: 0 to 0.50% Since Sn is an element that further improves corrosion resistance and high-temperature strength, it can be contained as necessary. When the Sn content is 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 0.01% or more. On the other hand, when the Sn content exceeds 0.50%, manufacturability deteriorates significantly, so the upper limit of the Sn content is set to 0.50% or less. Furthermore, considering workability, high-temperature oxidation resistance, and alloy cost, the Sn content is desirably 0.10% or more and 0.30% or less.

[0042] W: 0 to 2.0% W can be contained as necessary to improve corrosion resistance. It is advisable to contain W at 0.01% or more. Although W is an important element for suppressing the corrosion rate, excessive content deteriorates manufacturability 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 contain 0.01% or more as necessary. However, excessive content may cause a decrease in workability and manufacturability, so 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% Mg forms Mg oxides together with Al in the molten steel and acts as a deoxidizer. In addition, it acts as a crystallization nucleus for TiN. TiN becomes a solidification nucleus of the ferrite phase during the solidification process. By promoting the crystallization of TiN, the ferrite phase can be finely formed during solidification. By refining the solidification structure, it is possible to prevent surface defects caused by coarse solidification structures such as ridging and roping, which are likely to occur when the steel plate is processed into the product shape, and to improve workability. Therefore, Mg is contained as needed. When containing Mg, in order to exhibit these effects, it is advisable to contain 0.0005% or more. However, when the Mg content exceeds 0.015%, the manufacturability deteriorates. Therefore, the upper limit of the Mg content is set at 0.015% or less. The Mg content is preferably 0.0010% or more, or 0.010% or less in consideration of manufacturability.

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

[0046] Ta: 0 - 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, when the Ta content exceeds 1.00%, it may cause a decrease in ductility and toughness at room temperature. For this reason, the Ta content is preferably 1.00% or less. More preferably, it is 0.10% or more, and 0.50% or less or 0.30% or less.

[0047] Sb: 0 - 0.50%, Sb can be contained as needed 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. Therefore, the upper limit of the content is set at 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 in an amount of 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 set to 1.00% or less. A more desirable range is 0.10% or more and 0.50% 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 herein are 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] Also, the ferritic stainless steel sheet of this embodiment needs to satisfy the following formula (1). By satisfying formula (1), it is possible to improve high-temperature oxidation resistance, suppress an increase in the thermal expansion coefficient, and reduce the electrical resistivity.

[0051] 0.5Cr - 10Al - 5Si ≧ 5.00 …(1) However, the element symbols in formula (1) mean the content (% by mass) of each element.

[0052] The ferritic stainless steel sheet of this embodiment has an electrical resistivity of 1.30 μΩ·m or less at 1000°C by the four-terminal method. As the resistivity measuring device, an electrical resistance 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 ferrite stainless steel sheet of the present embodiment has a coefficient of thermal expansion of 1.30% or less when heated from 30°C to 1000°C. As the measuring device for the coefficient of thermal expansion, a thermomechanical analyzer TD5000SA manufactured by NETZSCH can be used. The measuring method is a horizontal differential detection rod type with a reference temperature of 30°C, and the 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 ferrite stainless steel sheet of the present embodiment has excellent high-temperature oxidation resistance. In the present 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-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 less for 5 minutes is repeated until the cumulative heating time at 1000°C reaches 600 hours (1440 cycles) in a heating-cooling test, and the increase in weight of the test piece before and after the heating-cooling test is 2 2.0 mg / m or less.

[0055] Also, the ferrite 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. In the cross-section in the thickness direction of the steel sheet when the metal Cu phase precipitates, in a cross-sectional area of 500 nm × 500 nm, 20 or more metal Cu phases with an equivalent circle diameter of 5 nm or more are in a precipitated state. When the metal Cu phase precipitates, the electrical resistivity of the ferrite stainless steel sheet is further significantly reduced.

[0056] The precipitation state of the metallic Cu phase is confirmed by observing a thin film sample using a scanning transmission electron microscope (STEM) HD-2700 from Hitachi High-Technologies Corporation under the condition of an acceleration voltage of 200 kV. The analysis of Cu is identified using an energy dispersive X-ray spectroscopy (EDS) analyzer attached to the STEM. The observation field of view is set as a region of 500 nm × 500 nm and is carried out at three observation fields of view. In the observation field of view, metallic Cu phases with an equivalent circle diameter of 5 nm or more are specified, and it is confirmed that 20 or more metallic 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 one processed by the focused ion beam (FIB) method to have a thickness of 80 - 100 nm is used.

[0058] Moreover, 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 has 20 or more metallic Cu phases with an equivalent circle diameter of 5 nm or more in a 500 nm × 500 nm observation field of view of the cross-section of the steel sheet can be used as a member for an electric heating catalyst.

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

[0060] Also, as another means for heating the catalyst in the electric heating catalyst, there is a method of heating the catalyst by energizing 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, the manufacturing method of the ferritic stainless steel sheet of the present embodiment will be described. The manufacturing method of the ferritic stainless steel sheet of the present embodiment includes a step of cold rolling a ferritic stainless steel sheet having the above chemical composition and satisfying 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 to adjust the thickness.

[0062] 0.5Cr - 10Al - 5Si ≥ 5.00 …(3) However, the element symbols in formula (3) mean the content (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 may have the above chemical composition and satisfy 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] Before cold rolling, the ferritic stainless steel sheet may be subjected to hot-rolled sheet annealing or pickling. The hot-rolled sheet annealing preferably has conditions such as 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 air. 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 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 air.

[0066] Among the annealing operations 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 a soaking temperature of 950 to 1050°C and a soaking time of 60 to 120 seconds. By this final annealing, a 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 set the residence time between at least 700 and 500°C to 60 to 120 seconds. By satisfying this condition, when the steel sheet is heated at a heating temperature of 600°C for 1 hour later, the steel sheet is tempered so that a metal Cu phase can be precipitated in the cross-sectional structure of the steel sheet. It is presumed that extremely fine nuclei of metal Cu are generated by the tempering, and the metal Cu phase precipitates in the subsequent heating process starting from these nuclei.

[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, by performing final cold rolling to adjust the thickness, a steel sheet with a thickness of 0.03 to 0.10 mm is obtained. Note that the ferritic stainless steel sheet of this embodiment may also be in a form generally 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 1.30 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] By performing a step of heating the obtained ferritic stainless steel sheet under the conditions of 600 °C or higher for 1 hour or more, a member for an electric heating catalyst can be manufactured. By heating under the conditions of 600 °C or higher for 1 hour or more, a metallic Cu phase is precipitated, and a member for an electric heating catalyst with a further significantly reduced electrical resistivity is obtained. For example, the electrical resistivity by the four-terminal method at 1000 °C can be made 1.25 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] In addition, the heating process may be carried out taking advantage of the fact that the electric heating catalyst is heated when in use. That is, the electric heating catalyst is preheated before the engine of the vehicle is started and heated until it reaches a temperature equal to or higher than the activation temperature. Subsequently, when high-temperature exhaust gas is introduced by starting the engine, the electric heating catalyst is heated to about 600 to 800°C. Thus, 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 with a circle 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. Note 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 with 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 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, first-stage cold rolling was performed until the thickness reached 1.5 mm. After cold rolling, annealing was carried out under conditions of soaking temperature of 950 to 1050°C and soaking time of 60 to 120 seconds, and pickling was carried out under the same conditions as above to remove the oxide scale.

[0077] Furthermore, second-stage cold rolling was performed until the thickness reached 0.4 mm. After cold rolling, final annealing was carried out 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-stage 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 22 were manufactured.

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

[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, a heating-cooling cycle consisting of a heating stage of maintaining at 1000 °C for 25 minutes in an air atmosphere 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 2.0 mg / m 2 or less per unit surface area of the test piece, it is regarded as qualified (G), and when it exceeds 2.0 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, an electrical resistance measuring device TER-2000RH (DC four-terminal method) manufactured by ULVAC-RIKO, Inc. was used. The electrical resistivity of a steel sheet 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 1.30 μΩ·m or less, it was judged as qualified (G), and when it exceeded 1.30 μΩ·m, it was judged as unqualified (B). In addition, the measurement of the electrical resistivity was also carried out on the steel sheet after the precipitation of the metallic Cu phase.

[0084] The evaluation of the coefficient of thermal expansion was carried out as follows. As the measuring device, a 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. In addition, the heating and cooling rate was 5 °C / min in an Ar atmosphere. In this way, the coefficient of thermal expansion of a steel sheet with a thickness of 0.4 mm was measured. Since the coefficient of thermal expansion of a steel sheet with a thickness of 0.4 mm was almost the same as that of a steel sheet with a thickness of 50 μm, a steel sheet 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 sheet was exposed, the steel sheet 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 a 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 an 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 12, the chemical components were 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 12, the high-temperature oxidation resistance, electrical resistivity, and thermal expansion coefficient were in the preferable ranges. Also, when a heating process at 600°C for 1 hour was carried out, a large number of metal Cu phases precipitated with a high density, and the electrical resistivity was further reduced.

[0087] On the other hand, for No.13 to 22, the chemical components were outside the scope of the present invention. Also, for No.13, 19, and 21, the manufacturing conditions were outside the scope of the present invention. Therefore, for No.13 to 22, one or more of the high-temperature oxidation resistance, electrical resistivity, and thermal expansion coefficient failed. Also, 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: 25.0 to 35.0%, Al: 0.030 to 0.50%, Ni: 0.01 to 0.50%, Cu: 0.10 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.40%, Mo: 0.01 to 2.50%, N: 0.030% or less, REM: 0 to 0.20%, B: 0 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, 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. 0.5Cr - 10Al - 5Si ≥ 5.00 …(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%, REM: 0.003 to 0.20%, B: 0.0002 to 0.0050%, Zr: 0.01 to 0.50%, V: 0.01 to 0.50%, Sn: 0.01 to 0.50%, 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 measured by the four-terminal method at 1000°C is 1.30 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 1.30% 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: 25.0 - 35.0%, Al: 0.030 - 0.50%, Ni: 0.01 - 0.50%, Cu: 0.10 - 1.50%, Nb: 0.010 - 0.70%, Ti: 0.01 - 0.40%, Mo: 0.01 - 2.50%, N: 0.030% or less, REM: 0 - 0.20%, B: 0 - 0.0050%, Zr: 0 - 0.50%, V: 0 - 0.50%, Sn: 0 - 0.50%, 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 20 or more metal Cu phases with an equivalent circle 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. 0.5Cr - 10Al - 5Si ≥ 5.00 …(2) However, the element symbols in formula (2) mean the content (mass%) of each element.

7. The chemical composition of the steel is, in mass%, REM: 0.003 - 0.20%, B: 0.0002 - 0.0050%, Zr: 0.01 - 0.50%, V: 0.01 - 0.50%, Sn: 0.01 - 0.50%, 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 the above, 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 1.30% 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: 25.0 to 35.0%, Al: 0.030 to 0.50%, Ni: 0.01 to 0.50%, Cu: 0.10 to 1.50%, Nb: 0.010 to 0.70%, Ti: 0.01 to 0.40%, Mo: 0.01 to 2.50%, N: 0.030% or less, REM: 0 to 0.20%, B: 0 to 0.0050%, Zr: 0 to 0.50%, V: 0 to 0.50%, Sn: 0 to 0.50%, 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 the 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 such 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. 0.5Cr - 10Al - 5Si ≥ 5.00 …(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 a 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 more.

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