Stainless steel sheet with Al coating

Abstract

In a stainless steel sheet with an Al coating on a base steel sheet and on the surface of the base steel sheet, the base steel sheet is a stainless steel with a specified composition and a thickness of 100 μm or less, and the total content of Fe and Cr at the first depth of the Al coating is set to 20 to 70 mass%.

Description

Technical Field

[0001] The present invention relates to an Al-coated stainless steel sheet suitable as a base material for manufacturing a resistance heating element or the like. Background Art

[0002] The method of heating an object by using the Joule heat generated when an electric current flows through a resistance heating element is called resistance heating. This method has a good conversion efficiency from electrical energy to thermal energy, and the control device is also simple. Therefore, this method is used in a wide range of fields such as industrial electric furnaces and electric rice cookers.

[0003] The resistance heating element used in the resistance heating can be classified into metal heating elements represented by Ni-Cr alloy and Fe-Cr alloy and non-metal heating elements represented by SiC. Among them, metal heating elements have excellent processability compared with non-metal heating elements, so they can be processed into foil and wire. Therefore, metal heating elements can also be used for thin parts such as window glass and floor, and parts that bear bending loads such as gloves.

[0004] As such metal heating elements, for example, JIS C 2520 specifies three types of Ni-Cr alloys (types 1 to 3 of nickel-chromium wires and strips for electric heating) and two types of Fe-Cr alloys (types 1 to 2 of iron-chromium wires and strips for electric heating) as alloy wires and alloy strips for electric heating. Here, the Ni-Cr alloy is a Ni-based alloy with Cr: 15 to 21% and Si: 0.75 to 3% as main additive elements (it should be noted that the "%" of each element is mass %, and the same applies hereinafter). The Fe-Cr alloy is a Fe-based alloy with Cr: 17 to 26%, Al: 2 to 6%, and Si: 1.5% or less as main additive elements.

[0005] Among them, Fe-Cr alloys, especially stainless steel sheets containing a large amount of Al (hereinafter referred to as Al-containing stainless steel sheets) have excellent oxidation resistance at high temperatures and are cheaper than Ni-Cr alloys. Therefore, Al-containing stainless steel sheets are widely used as resistance heating elements.

[0006] As such a technology involving Al-containing stainless steel sheets, for example, Patent Document 1 discloses "a method for manufacturing a stainless steel sheet with a high Al content, comprising the following steps: overlapping an Al plate on at least one side of a stainless steel sheet containing one or more of C≤0.03%, Cr≤30%, 0.01-0.8% Ti, Nb, V or Mo so as to be in a ratio equivalent to the amount of Al contained, making the sheet pass between rollers to form a laminated press-bonded sheet, and subjecting the obtained laminated press-bonded sheet to a diffusion treatment at a temperature in the range of 600-1300°C under the condition that the Al layer is not melted but alloyed."

[0007] In addition, Patent Document 2 discloses "a Fe-Cr-Al series stainless steel sheet, characterized in that it contains, by mass%, Cr: 10% to 30%, Al: more than 6.5% and 15% or less, Ti: 0.02% to 0.1%, Nb: one or both of 0.02% to 0.3%, La: 0.01% to 0.1%, Ce: 0.01% to 0.1%, P: 0.01% to 0.05%."

[0008] Prior art documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Laid-Open No. 2-133563

[0011] Patent Document 2: Japanese Patent Laid-Open No. 2004-169110 Summary of the invention

[0012] Here, in the technology of Patent Document 1, a laminated and press-bonded plate in which an Al plate is overlapped on at least one surface of a stainless steel plate that is to be a base material plate is prepared, and a prescribed heat treatment (hereinafter, also referred to as diffusion heat treatment) is performed on the laminated and press-bonded plate. Thereby, Al diffuses into the base material plate, and the Al content of the Al-containing stainless steel plate that becomes the final product is increased.

[0013] In addition, in the technology of Patent Document 2, a multilayer plate in which Al or an Al alloy is adhered to the surface of a stainless steel plate that is to be a base material plate is prepared, and a prescribed diffusion heat treatment is performed on the multilayer plate. Thereby, Al diffuses into the base material plate, and the Al content of the Al-containing stainless steel plate as the final product is increased.

[0014] Hereinafter, a steel plate having a base material plate made of a stainless steel plate and an Al coating on the surface of the base material plate (including the Al plate described in Patent Document 1 and Al or an Al alloy described in the technology of Patent Document 2) is collectively referred to as an Al-coated stainless steel plate.

[0015] However, Al is an element with high solid solution strengthening ability. That is, Al is an element that significantly increases the strength of steel by solid solution in the steel. Therefore, Al-containing stainless steel plates generally have low workability.

[0016] For example, for the Al-containing stainless steel plates disclosed in Patent Documents 1 and 2, when performing corrugation processing, which is a processing method generally performed when used as a resistance heating element, there are cases where it cannot be processed into a desired shape and cases where cracks are generated due to bending loads.

[0017] To avoid such problems, for example, it is considered to perform corrugation processing on the Al-coated stainless steel plate to form a desired shape before performing the diffusion heat treatment, and then perform the diffusion heat treatment to allow Al to diffuse.

[0018] However, in the case of corrugating a stainless steel plate with an Al coating, there is a problem that the Al coating on the surface peels off due to friction with processing tools such as dies.

[0019] That is, it cannot be said that the strength of the Al coating itself and the adhesion between the Al coating and the base steel plate of the stainless steel plate with the Al coating are sufficient. Therefore, if the stainless steel plate with the Al coating is corrugated, there is a problem that the Al coating peels off.

[0020] If the Al coating peels off, it will lead to a decrease in the Al content diffused into the base steel plate during the diffusion heat treatment, an increase in the maintenance cost for removing the Al attached to the die, and the like.

[0021] The present invention has been developed in view of the above situation, and an object thereof is to provide a stainless steel plate with an Al coating that is suitable as a material for manufacturing a resistance heating element or the like, and that can significantly improve the adhesion of the Al coating while ensuring sufficient workability. Detailed Embodiments

[0022] In addition, the inventors have repeatedly conducted various studies to solve the above problems.

[0023] As a result, it has been found that the inventors can improve the adhesion between the Al coating and the base steel plate while avoiding a decrease in workability by performing heat treatment (hereinafter, also referred to as pre-heat treatment) under specific conditions on the stainless steel plate with the Al coating as a pre-treatment for the diffusion heat treatment.

[0024] The inventors consider the reason as follows.

[0025] That is, in order to completely diffuse the Al contained in the Al coating into the base steel plate, it is usually necessary to perform heat treatment at a temperature above 1000°C for 30 minutes or more. However, if such heat treatment is performed to completely diffuse the Al contained in the Al coating into the base steel plate, the strength of the base steel plate increases and the workability of the base steel plate decreases.

[0026] From this point of view, if pre-heat treatment is performed at a temperature lower than the diffusion heat treatment temperature for a short period of time, Fe and Cr diffuse from the base steel plate into the Al coating, and an appropriate amount of Fe and Cr are dissolved in the Al coating. As a result, the strength of the Al coating itself increases, and it is not easily peeled off even under loads such as friction and bending. At the same time, interdiffusion occurs near the interface between the Al coating and the base steel plate. Thereby, the interface between the Al coating and the base steel plate is strengthened. As a result, the adhesion between the Al coating and the base steel plate is improved. On the other hand, since the above-mentioned phenomena caused by the pre-heat treatment occur in the Al coating and near the interface between the base steel plate and the Al coating, the diffusion of Al from the Al coating to the base steel plate does not progress significantly.

[0027] Therefore, the inventors et al. believe that by performing pre-heat treatment on the stainless steel plate with an Al coating, it is possible to improve the adhesion between the Al coating and the base steel plate while avoiding a decrease in workability.

[0028] And, based on the above understanding, the inventors et al. repeatedly studied the diffusion state of Fe and Cr in the Al coating after pre-heat treatment, and as a result, obtained the following understanding.

[0029] (A) Figure 1 The total content of Fe and Cr at the first depth of the Al coating shown, specifically, the depth from the surface of the Al coating: (depth a + depth b) / 2 is not only an effective index for inferring the diffusion state of Fe and Cr from the base steel plate into the Al coating, but also an effective index for inferring the diffusion state of Al from the Al coating to the base steel plate.

[0030] Here, depth a and depth b are defined as follows respectively.

[0031] Depth a: When the depth at which the Al intensity takes the maximum value in the Al concentration distribution in the depth (plate thickness) direction from the surface of the Al coating is set as point A, in the depth region from the surface of the Al coating to point A, the depth at which the Al intensity is [the maximum value of the Al intensity] / 2

[0032] Depth b: In the depth region from point A to the interface between the base steel plate and the Al coating, the depth at which the Al intensity is ([the maximum value of the Al intensity] + [the Al intensity equivalent to the Al content of the base steel plate (hereinafter, also referred to as the Al intensity of the base steel plate)]) / 2

[0033] (B) And, in particular, by controlling the total content of Fe and Cr at the first depth of the Al coating within the range of 20 to 70% by mass, it is possible to significantly improve the adhesion between the Al coating and the base steel plate while ensuring sufficient workability.

[0034] The present invention was further studied and completed based on the above understanding.

[0035] That is, the gist of the present invention is constituted as follows.

[0036] 1. A stainless steel sheet with an Al coating, having a base substrate steel sheet and an Al coating on the surface of the base substrate steel sheet,

[0037] The above-mentioned base substrate steel sheet is a stainless steel sheet with a thickness of 100 μm or less, and has the following composition by mass%: C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.040% or less, S: 0.010% or less, Cr: 11.0 - 30.0%, Al: 0.01 - 6.50%, Ni: 0.01 - 0.50%, and N: 0.020% or less, and the balance is composed of Fe and inevitable impurities.

[0038] And, the thickness of the above-mentioned Al coating is 0.5 - 10.0 μm.

[0039] And, the total content of Fe and Cr at the first depth of the above-mentioned Al coating is 20 - 70% by mass.

[0040] Among them, the first depth of the Al coating is the depth from the surface of the Al coating: (depth a + depth b) / 2.

[0041] In addition, depth a and depth b are defined as follows respectively.

[0042] Depth a: When the depth at which the Al intensity takes the maximum value in the Al concentration distribution from the surface of the Al coating in the depth (sheet thickness) direction is set as point A, in the depth region from the surface of the Al coating to point A, the depth at which the Al intensity is [the maximum value of the Al intensity] / 2

[0043] Depth b: In the depth region from point A to the interface between the base substrate steel sheet and the Al coating, the depth at which the Al intensity is ([the maximum value of the Al intensity] + [the Al intensity corresponding to the Al content of the base substrate steel sheet]) / 2

[0044] 2. The stainless steel sheet with an Al coating according to the above 1, wherein the composition of the above-mentioned base substrate steel sheet further contains, by mass%, one or more selected from Cu: 0.10% or less, Ti: 0.50% or less, Nb: 0.50% or less, V: 0.50% or less, Zr: 0.20% or less, Hf: 0.20% or less, Mo: 6.00% or less, W: 6.00% or less, B: 0.0050% or less, REM: 0.20% or less, Ca: 0.0100% or less, and Mg: 0.0100% or less.

[0045] According to the present invention, a stainless steel sheet with an Al coating can be obtained, which is suitable as a material for manufacturing a resistance heating element or the like, and while ensuring sufficient workability, the adhesion of the Al coating is greatly improved.

[0046] In addition, by using the stainless steel sheet with an Al coating of the present invention, various shaped components having a high Al content can be more advantageously manufactured, such as heating elements of exhaust heating devices disposed directly in front of exhaust gas purification devices of automobiles or the like, heating elements of electric furnaces and rice cookers, and catalyst carriers.

[0047] Symbol Explanation

[0048] Figure 1 is a schematic diagram for explaining the definition of the first depth of the Al coating.

[0049] Figure 2 is a schematic diagram showing the measurement positions of line analysis of the Al concentration distribution.

[0050] Figure 3 is a schematic diagram showing an example of the concentration distribution of the stainless steel sheet with an Al coating.

[0051] Figure 4 is a schematic diagram showing the construction essentials of corrugation processing.

[0052] The present invention will be described based on the following embodiments.

[0053] First, the composition of the base steel sheet (hereinafter, also simply referred to as the base steel sheet) of the stainless steel sheet with an Al coating according to an embodiment of the present invention will be described. It should be noted that the units in the composition are all "mass%", and hereinafter, unless otherwise specified, only "% " is represented.

[0054] C: 0.030% or less

[0055] If the C content exceeds 0.030%, the toughness of the steel decreases, and the manufacture of the base steel sheet becomes difficult. Therefore, the C content is 0.030% or less. The C content is preferably 0.020% or less, more preferably 0.010% or less. There is no particular limitation on the lower limit of the C content, and the C content is preferably 0.001% or more.

[0056] Si: 1.00% or less

[0057] Si has the effect of increasing the resistivity. The effect of increasing the resistivity per unit mass % of Si is approximately the same as that of Al. From the viewpoint of obtaining such an effect, the Si content is preferably 0.01% or more. The Si content is more preferably 0.10% or more. However, if the Si content exceeds 1.00%, the steel solidifies excessively and it becomes difficult to manufacture the base substrate steel plate. Therefore, the Si content is 1.00% or less. The Si content is preferably 0.50% or less, and more preferably 0.20% or less.

[0058] Mn: 1.00% or less

[0059] If the Mn content exceeds 1.00%, the oxidation resistance of the steel decreases. Therefore, the Mn content is 1.00% or less. The Mn content is preferably 0.50% or less, and more preferably 0.15% or less. Among them, if the Mn content is less than 0.01%, refining becomes difficult, so the Mn content is preferably 0.01% or more.

[0060] P: 0.040% or less

[0061] If the P content exceeds 0.040%, the toughness and ductility of the steel decrease and it becomes difficult to manufacture the base substrate steel plate. Therefore, the P content is 0.040% or less. The P content is preferably 0.030% or less. There is no particular limitation on the lower limit of the P content, but excessive P removal will increase the cost. Therefore, the P content is preferably 0.005% or more.

[0062] S: 0.010% or less

[0063] If the S content exceeds 0.010%, the hot workability decreases and it becomes difficult to manufacture the base substrate steel plate. Therefore, the S content is 0.010% or less. The S content is preferably 0.004% or less, and more preferably 0.002% or less. There is no particular limitation on the lower limit of the S content, but excessive S removal will increase the cost. Therefore, the S content is preferably 0.0005% or more.

[0064] Cr: 11.0 - 30.0%

[0065] Cr is an element required to ensure oxidation resistance at high temperatures. Here, if the Cr content is less than 11.0%, the oxidation resistance at high temperatures cannot be sufficiently ensured. On the other hand, if the Cr content exceeds 30.0%, the toughness of the slab and hot-rolled steel plate in the manufacturing process decreases and it becomes difficult to manufacture the base substrate steel plate. Therefore, the Cr content is 11.0 - 30.0%. The Cr content is preferably 15.0% or more, and more preferably 18.0% or more. In addition, the Cr content is preferably 26.0% or less, and more preferably 22.0% or less.

[0066] Al: 0.01 - 6.50%

[0067] Al has the effect of increasing resistivity. In addition, Al also has the effect of generating Al at high temperatures when used as a resistance heating element. 2 O 3 The oxide film with Al as the main component has the effect of improving the oxidation resistance. However, in the final product such as the resistance heating element, the Al content is increased by diffusing the Al of the Al coating into the base steel plate through diffusion heat treatment. Therefore, the Al content in the component composition of the base steel plate does not have to be so much. Therefore, the Al content is more than 0.01%. In addition, as the amount of Al diffusion into the base steel plate through diffusion heat treatment increases, deformation is more likely to occur. Therefore, it is preferred to increase the Al content in the base steel plate to reduce the amount of Al diffusion from the Al coating. Therefore, the Al content is preferably more than 4.00%, more preferably more than 5.00%. On the other hand, if the Al content exceeds 6.50%, the toughness of the steel decreases and the manufacture of the base steel plate becomes difficult. Therefore, the Al content is less than 6.50%.

[0068] Ni: 0.01~0.50%

[0069] Ni has the effect of improving the brazing property when manufacturing resistance heating elements. From the viewpoint of obtaining such an effect, the Ni content is preferably 0.01% or more. On the other hand, Ni is an element that promotes the formation of austenite structure. Therefore, if the Ni content exceeds 0.50%, austenite structure is easily generated when used as a resistance heating element. That is, if used as a resistance heating element, when oxidation at high temperature proceeds and Al in the steel is depleted, austenite structure is easily generated. If austenite structure is generated, the thermal expansion coefficient of the component sometimes changes, resulting in undesirable phenomena such as breakage of the component. Therefore, the Ni content is less than 0.50%. The Ni content is preferably less than 0.20%.

[0070] N: 0.020% or less

[0071] If the N content exceeds 0.020%, the toughness of the steel decreases and the manufacturing of the base steel sheet becomes difficult. Therefore, the N content is 0.020% or less. The N content is preferably 0.010% or less. There is no particular limit on the lower limit of the N content, but excessive denitrification leads to increased costs. Therefore, the N content is preferably 0.001% or more.

[0072] As described above, the basic components of the base steel plate have been explained. In addition to the above basic components, it may further appropriately contain Cu: 0.10% or less, Ti: 0.50% or less, Nb: 0.50% or less, V: 0.50% or less, Zr: 0.20% or less, Hf: 0.20% or less, Mo: 6.00% or less, W: 6.00% or less, B: 0.0050% or less, REM: 0.20% or less, Ca: 0.0100% or less, and Mg: 0.0100% or less.

[0073] Cu: 0.10% or less

[0074] Cu has the effect of precipitating in the steel to improve the high-temperature strength, so it can be arbitrarily contained at 0.01% or more. However, if the Cu content exceeds 0.10%, the toughness of the steel decreases. Therefore, when Cu is contained, the content is 0.10% or less. The Cu content is more preferably 0.05% or less, and further preferably 0.03% or less.

[0075] Ti: 0.50% or less

[0076] Ti has the effects of combining with C and N in the steel to improve toughness and improving oxidation resistance. Therefore, Ti can be arbitrarily contained at 0.01% or more. The Ti content is more preferably 0.05% or more. However, if the Ti content exceeds 0.50%, when used as a resistance heating element, a large amount of Ti oxide is mixed into the Al 2 O 3 coating film. As a result, the oxidation resistance at high temperatures decreases. Therefore, when Ti is contained, the content is 0.50% or less. The Ti content is more preferably 0.20% or less.

[0077] Nb: 0.50% or less

[0078] Nb has the effect of combining with C and N in the steel to improve toughness. Therefore, Nb can be arbitrarily contained at 0.01% or more. The Nb content is more preferably 0.05% or more. However, if the Nb content exceeds 0.50%, when used as a resistance heating element, a large amount of Nb oxide is mixed into the Al 2 O 3 coating film. As a result, the oxidation resistance at high temperatures decreases. Therefore, when Nb is contained, the content is 0.50% or less. The Nb content is more preferably 0.20% or less.

[0079] V: 0.50% or less

[0080] V has the effect of combining with C and N in steel to improve toughness. Therefore, V can be contained in an amount of 0.01% or more arbitrarily. The V content is more preferably 0.05% or more. However, if the V content exceeds 0.50%, a large amount of V oxide is mixed into the Al 2 O 3 film formed at high temperature when used as a resistance heating element. As a result, the oxidation resistance at high temperature decreases. Therefore, when V is contained, the content is 0.50% or less. The V content is more preferably 0.20% or less, and further preferably 0.10% or less.

[0081] Zr: 0.20% or less

[0082] Zr improves the adhesion of Al 2 O 3 formed at high temperature when used as a resistance heating element. In particular, Zr has the effect of improving the peel resistance of the Al 2 O 3 film in an environment where oxidation occurs repeatedly, thereby improving the oxidation resistance. In addition, Zr also has the effect of extending the life when used as a resistance heating element by reducing the growth rate of Al 2 O 3 . From the viewpoint of obtaining such effects, the Zr content is preferably 0.01% or more. The Zr content is more preferably 0.02% or more. However, if the Zr content exceeds 0.20%, intermetallic compounds such as Zr and Fe are formed, and the toughness decreases. Therefore, when Zr is contained, the content is 0.20% or less. The Zr content is more preferably 0.15% or less, and further preferably 0.05% or less.

[0083] Hf: 0.20% or less

[0084] Hf improves the adhesion of Al 2 O 3 formed at high temperature when used as a resistance heating element. In particular, Hf has the effect of improving the peel resistance of the Al 2 O 3 film in an environment where oxidation occurs repeatedly, thereby improving the oxidation resistance. In addition, Hf also has the effect of extending the life when used as a resistance heating element by reducing the growth rate of Al 2 O 3 . From the viewpoint of obtaining these effects, the Hf content is preferably 0.01% or more. The Hf content is more preferably 0.02% or more. However, if the Hf content exceeds 0.20%, intermetallic compounds such as Hf and Fe are formed, and the toughness decreases. Therefore, when Hf is contained, the content is 0.20% or less. The Hf content is more preferably 0.15% or less.

[0085] Mo: Below 6.00%

[0086] Mo has the effect of suppressing warping and deformation such as substrate steel plate warping and deformation during diffusion heat treatment by increasing strength at high temperatures. In addition, Mo also contributes to the extension of the life of the resistance heating element by increasing strength at high temperatures. These effects are obtained when the Mo content is 0.01% or more. The Mo content is more preferably 1.00% or more. On the other hand, if the Mo content exceeds 6.00%, the workability decreases. Therefore, when Mo is contained, the content is 6.00% or less. The Mo content is more preferably 4.00% or less.

[0087] W: Below 6.00%

[0088] W has the effect of suppressing warping and deformation such as substrate steel plate warping and deformation during diffusion heat treatment by increasing strength at high temperatures. In addition, W also contributes to the extension of the life of the resistance heating element by increasing strength at high temperatures. These effects are obtained when the W content is 0.01% or more. The W content is more preferably 1.00% or more. On the other hand, if the W content exceeds 6.00%, the workability decreases. Therefore, when W is contained, the content is 6.00% or less. The W content is more preferably 5.00% or less, and further preferably 3.50% or less.

[0089] It should be noted that when both Mo and W are contained, from the viewpoint of preventing a decrease in workability, it is preferable that the total content of Mo and W is 6.00% or less.

[0090] B: Below 0.0050%

[0091] B has the effect of strengthening the grain boundaries of the steel and preventing cracks during hot rolling in the manufacturing process of the substrate steel plate. This effect is obtained when the B content is 0.0002% or more. The B content is more preferably 0.0010% or more. On the other hand, if the B content exceeds 0.0050%, the oxidation resistance decreases. Therefore, when B is contained, the content is 0.0050% or less. The B content is more preferably 0.0040% or less.

[0092] REM: Below 0.20%

[0093] REM refers to Sc, Y, and lanthanide elements (elements with atomic serial numbers 57 - 71 such as La, Ce, Pr, Nd, Sm, etc.). REM improves the adhesion of the Al 2 O 3 film formed when used as a resistance heating element at high temperatures. In particular, REM has the effect of improving the adhesion of this Al 2 O 3The effect of the peeling resistance of the film in an environment where oxidation occurs repeatedly. This effect is obtained when the REM content (the total content of Sc, Y and lanthanide elements mentioned above) is 0.01% or more. The REM content is more preferably 0.03% or more. On the other hand, if the REM content exceeds 0.20%, the hot workability decreases and the manufacture of the base steel sheet becomes difficult. Therefore, when REM is contained, the content is 0.20% or less. The REM content is more preferably 0.10% or less.

[0094] In addition, as REM, one element among the above-mentioned Sc, Y and lanthanoid elements may be contained, or two or more elements may be contained simultaneously.

[0095] Ca: 0.0100% or less

[0096] Appropriate amount of Ca can improve Al 2 O 3 The film has the effect of improving the adhesion of the steel and reducing the growth rate to improve the oxidation resistance. 2 O 3 The film is formed when used as a resistive heating element. This effect is obtained when the Ca content is 0.0002% or more. A more preferred Ca content is 0.0005% or more. A further preferred Ca content is 0.0010% or more. However, if Ca is contained in excess, toughness and oxidation resistance are reduced. Therefore, when Ca is contained, the content is 0.0100% or less. The Ca content is more preferably 0.0050% or less.

[0097] Mg: 0.0100% or less

[0098] An appropriate amount of Mg has the effect of increasing the Al content when used as a resistance heating element. 2 O 3 The film has the effect of improving the adhesion of the steel and reducing the growth rate to improve the oxidation resistance. This effect is obtained when the Mg content is 0.0002% or more. The Mg content is more preferably 0.0010% or more. However, if Mg is contained excessively, the toughness and oxidation resistance are reduced. Therefore, when Mg is contained, the content is 0.0100% or less. The Mg content is more preferably 0.0050% or less, and further preferably 0.0015% or less.

[0099] In addition, components other than the above are Fe and inevitable impurities.

[0100] In addition, the thickness of the base steel plate is 100 μm or less. When using a stainless steel steel plate with an Al coating as a material for manufacturing a resistive heating element such as an exhaust heating device mounted directly in front of an exhaust gas purification device, in order to reduce the back pressure and increase the contact area between the resistive heating element and the exhaust gas, a thinner plate thickness is preferred. In addition, when used as a heating element such as in a rice cooker, the smaller the cross-sectional area and the larger the surface area, in other words, the thinner the plate thickness, the higher the heating efficiency. The thickness of the base steel plate is preferably 80 μm or less.

[0101] In addition, there is no particular limitation on the lower limit of the thickness of the base steel plate. In order to ensure strength, it is preferably 20 μm or more.

[0102] Next, the Al coating formed on the surface of the base steel plate of the stainless steel with an Al coating will be described. It should be noted that the Al coating of the stainless steel steel plate with an Al coating can be provided only on one side of the base steel plate, or can also be provided on both sides.

[0103] Thickness of the Al coating: 0.5 to 10.0 μm

[0104] If the thickness of the Al coating is less than 0.5 μm, the Al diffused into the base steel plate is insufficient. Therefore, in a resistive heating element or the like that becomes the final product, the desired Al content cannot be obtained. On the other hand, if the thickness of the Al coating exceeds 10.0 μm, too much Al diffuses into the base steel plate, and the base steel plate may be deformed during the diffusion heat treatment.

[0105] Therefore, the thickness of the Al coating is 0.5 to 10.0 μm. The thickness of the Al coating is preferably 1.0 μm or more. In addition, the thickness of the Al coating is preferably 5.0 μm or less.

[0106] It should be noted that the thickness of the Al coating is the thickness per single side. In addition, when there are Al coatings on both sides of the base steel plate, the thickness of the Al coating on each surface (hereinafter, also referred to as the first surface and the second surface) is within the above range.

[0107] Here, the thickness of the Al coating is measured by the following method.

[0108] That is, a test piece with a width of 10 mm and a length of 15 mm is cut out from a stainless steel plate with an Al coating, and is embedded in resin in such a way that the cross-section in the length direction (rolling direction) is exposed, and the cross-section is mirror-polished. Next, the cross-section is observed at a magnification of 5000 times using a scanning electron microscope (SEM). At each surface (the first surface and the second surface), the thickness of the Al coating (the distance from the interface between the Al coating and the base steel plate to the surface of the Al coating) is measured at 5 positions at intervals of 1 mm along the length direction (rolling direction) from the center position in the length direction (rolling direction) of the test piece. The average value of these measured values is taken as the thickness of the Al coating of the stainless steel plate with the Al coating. It should be noted that the thickness of the Al coating on each surface (the first surface and the second surface) is the average value of the above-mentioned measured values on each surface.

[0109] Total content of Fe and Cr at the first depth of the Al coating: 20 to 70 mass%

[0110] As described above, the total content of Fe and Cr at the first depth of the Al coating is an effective index for the diffusion state of Fe and Cr from the base steel plate to the Al coating due to pre-heat treatment. In addition, the total content of Fe and Cr at the first depth of the Al coating also becomes an effective index for inferring the diffusion state of Al from the Al coating to the base steel plate.

[0111] That is, if the total content of Fe and Cr at the first depth of the Al coating is less than 20 mass%, the diffusion of Fe and Cr from the base steel plate to the Al coating is insufficient, and the desired adhesion between the Al coating and the base steel plate cannot be obtained. On the other hand, if the total content of Fe and Cr at the first depth of the Al coating exceeds 70 mass%, the diffusion of Al from the Al coating to the base steel plate proceeds excessively, and the workability of the base steel plate is reduced. Therefore, the total content of Fe and Cr at the first depth of the Al coating is 20 to 70 mass%. The total content of Fe and Cr at the first depth of the Al coating is preferably 30 mass% or more, and more preferably 40 mass% or more.

[0112] Here, the first depth of the Al coating is as Figure 1 shown, the depth from the surface of the Al coating: (depth a + depth b) / 2.

[0113] In addition, depth a and depth b are defined as follows, respectively.

[0114] Depth a: When the depth at which the Al intensity is the maximum value in the Al concentration distribution in the depth (plate thickness) direction from the surface of the Al coating is set as point A, in the depth region from the surface of the Al coating to point A, the depth (the distance from the surface of the Al coating) at which the Al intensity is [the maximum value of the Al intensity] / 2

[0115] Depth b: In the depth region from point A to the interface between the base steel plate and the Al coating, the depth (distance from the surface of the Al coating) at which the Al intensity is ([maximum value of Al intensity] + [Al intensity corresponding to the Al content of the base steel plate (hereinafter also referred to as the Al intensity of the base steel plate)]) / 2

[0116] It should be noted that when Al coatings exist on both sides of the base steel plate, the first depth, depth a, depth b, and point A are determined for the Al coatings on the first side and the second side respectively, and the total content of Fe and Cr at the first depth of the Al coating is obtained. In this case, for each of the first side and the second side, the total content of Fe and Cr at the first depth of the Al coating must satisfy the above range (20 to 70% by mass).

[0117] In addition, the Al concentration distribution in the depth (plate thickness) direction from the surface of the Al coating is obtained as follows.

[0118] That is, a test piece with a width of 10 mm and a length of 15 mm is cut out from the stainless steel plate with an Al coating, and is embedded in resin with the cross-section in the length direction (rolling direction) exposed, and the cross-section is mirror-polished. Next, at the center position in the length direction (rolling direction) of this cross-section, an electron probe microanalyzer (EPMA) or an energy dispersive X-ray spectrometer (EDX) is used, as Figure 2 shown, to perform line analysis on the cross-section of the Al coating from the surface of the Al coating toward the depth (plate thickness) direction, thereby obtaining the Al concentration distribution.

[0119] In addition, the total content of Fe and Cr at the first depth of the Al coating is obtained as follows.

[0120] That is, using the above test piece, the Fe and Cr concentration distributions in the depth (plate thickness) direction from the surface of the Al coating are obtained in the same manner as the Al concentration distribution. Since the Al coating is basically composed of Al, Fe, and Cr, the intensities of the Al, Fe, and Cr concentration distributions at the first depth of the Al coating determined by the Al concentration distribution are used to obtain the total content of Fe and Cr at this position. This measurement is performed at 5 positions (5 positions spaced 1 mm apart in the length direction (rolling direction) from the center position in the length direction (rolling direction) of the cross-section in the length direction (rolling direction)), and the average of these values is taken as the total content of Fe and Cr at the first depth of the Al coating. It should be noted that when Al coatings exist on both sides of the base steel plate, the above measurement is performed separately on both sides (5 positions per single side), and the average value of the total content of Fe and Cr is obtained for each side. And these values are taken as the total content of Fe and Cr at the first depth of the Al coating for each side.

[0121] Figure 3Examples of the concentration distribution of the Al-coated stainless steel sheet measured in the above method are shown. It should be noted that Figure 3 The vertical axis is in arbitrary units and the scales are not uniform.

[0122] Figure 3 (a) of is an example of the concentration distribution of the Al-coated stainless steel sheet before pre-heat treatment. From this concentration distribution, it can be seen that Fe and Cr hardly diffuse into the Al coating before pre-heat treatment.

[0123] Figure 3 (b) of is an example of the concentration distribution of the Al-coated stainless steel sheet in which the total content of Fe and Cr at the first depth of the Al coating is controlled within the range of 20 to 70 mass% by performing pre-heat treatment under appropriate conditions. In this Al-coated stainless steel sheet, the diffusion of Fe and Cr into the Al coating proceeds moderately. Therefore, the strength of the Al coating itself increases. In addition, interdiffusion occurs near the interface between the Al coating and the base steel sheet, and the interface between the Al coating and the base steel sheet is strengthened. As a result, the adhesion between the Al coating and the base steel sheet is improved. On the other hand, the diffusion of Al from the Al coating into the base steel sheet hardly occurs, so workability is also ensured.

[0124] Figure 3 (c) of is an example of the concentration distribution of the Al-coated stainless steel sheet in which the total content of Fe and Cr at the first depth of the Al coating exceeds 70 mass% by pre-heat treatment. In this Al-coated stainless steel sheet, the diffusion of Fe and Cr into the Al coating proceeds excessively, and the diffusion of Al from the Al coating into the base steel sheet proceeds excessively. Therefore, workability is reduced.

[0125] It should be noted that the Al coating is mainly composed of Al, Fe, and Cr. In addition, the Al coating may contain Si of 15 mass% or less in addition to Al, Fe, and Cr. It should be noted that when Si is contained, the total content of Fe and Cr at the first depth of the Al coating is obtained from the Al, Fe, and Cr concentration distributions as described above. The same applies when the following unavoidable impurities are contained.

[0126] Moreover, the Al coating may have unavoidable impurities. It should be noted that examples of the unavoidable impurities include B, Be, Mg, Ca, Sr, Ti, Mn, Co, Ni, Cu, Zn, Sn, Pb, As, Sb, Bi, La, Ce, etc., and the total amount is usually 1 mass% or less.

[0127] Next, a preferred manufacturing method of the Al-coated stainless steel sheet according to an embodiment of the present invention will be described.

[0128] First, a base steel sheet having the above composition is prepared.

[0129] For example, molten steel with a composition is melted by known methods such as a converter, an electric furnace, a vacuum melting furnace, etc., and a slab is obtained by a continuous casting method or an ingot - blooming method.

[0130] Next, rolling processing is performed on the slab to obtain a stainless steel sheet that becomes a base material sheet.

[0131] The rolling processing method is not particularly limited and can be based on common methods. For example, it can be cited that hot rolling is performed on the slab to obtain a hot - rolled sheet, and a method of performing cold rolling and cold - rolled sheet annealing on the hot - rolled sheet, a method of performing hot rolling on the slab to make a hot - rolled sheet, and then performing cold rolling after performing hot - rolled sheet annealing on the hot - rolled sheet, etc. It should be noted that hot - rolled sheet annealing and cold - rolled sheet annealing are optional processes, and both of them can be carried out, or only one of them can be carried out, or neither of them can be carried out. In addition, the conditions for hot rolling, hot - rolled sheet annealing, cold rolling, and cold - rolled sheet annealing are not particularly limited and can be carried out by conventional methods.

[0132] For example, after heating the slab at 1100 - 1250 °C for 1 - 24 hours, hot rolling is performed to make a hot - rolled sheet with a sheet thickness of about 2.0 - 6.0 mm. Then, optionally, descaling is carried out by pickling or mechanical polishing, and cold rolling and cold - rolled sheet annealing are carried out to obtain a stainless steel sheet with a specified sheet thickness that becomes a base material sheet.

[0133] Next, an Al coating is applied to the base material sheet to obtain a stainless steel sheet with an Al coating that becomes a pre - heat - treated material (hereinafter, also referred to as a pre - heat - treated material or a stainless steel sheet with an Al coating (pre - heat - treated material)). The Al coating method is not particularly limited, and methods such as evaporation coating, hot - dip coating, and laminated rolling can be applied.

[0134] In the case of using the evaporation coating method, for example, physical vapor deposition (PVD) such as vacuum evaporation coating and ion plating, chemical vapor deposition (CVD) such as thermal CVD and metal - organic chemical vapor deposition can be used. For the processing conditions, there is no particular limitation and they can be carried out by conventional methods.

[0135] It should be noted that the thickness of the Al coating in the case of using the evaporation coating method can be controlled as follows, for example.

[0136] That is, a mask tape with a size of 10 mm square is pasted on a part of the area of the base steel plate on which Al evaporation coating is performed. After the Al evaporation coating treatment, the mask tape is peeled off from the base steel plate. Then, using a contact surface roughness meter, the difference in height between the coated part (the area where the mask tape is not attached) and the uncoated part (the area where the mask tape is attached) is obtained, and this difference in height is taken as the thickness of the Al coating (Al evaporation coating). While changing the treatment time of Al evaporation coating, the same operation is carried out multiple times, and thereby the relationship between the treatment time and the thickness of the Al coating to be evaporated is obtained. Based on the relationship thus obtained, the treatment time for obtaining the desired thickness of the Al coating is calculated, and thereby the thickness of the Al coating can be controlled.

[0137] In the case of using the hot-dip coating method, for example, a method of manufacturing in a general continuous hot-dip coating apparatus can be adopted. There are no particular limitations on the treatment conditions, but the temperature of the coating bath (hereinafter, also referred to as the bath temperature) is preferably in the range of (solidification start temperature + 20°C) to 750°C. Here, the lower limit of the preferred bath temperature is set to (solidification start temperature + 20°C) to suppress the local solidification of the coating components due to the local decrease in the bath temperature of the coating bath. In addition, if the bath temperature exceeds 750°C, it is difficult for the coating metal attached to the surface of the base steel plate to cool rapidly, which may cause an appearance defect called sagging. Therefore, the appropriate upper limit of the bath temperature is 750°C. In addition, considering the viewpoint of forming a sufficient amount of coating layer on the surface of the base steel plate, the immersion time in the coating bath is preferably 0.5 seconds or more. For treatment conditions other than the above, conventional methods can be used.

[0138] It should be noted that the solidification start temperature can be obtained by calculation using the thermodynamic calculation software Thermo-Calc.

[0139] In addition, as the coating bath, a hot-dip Al bath and a hot-dip Al-Si alloy bath can be cited. Here, the composition of the hot-dip Al bath is Al and inevitable impurities, and the composition of the hot-dip Al-Si alloy bath is Al, Si of 15.0 mass% or less, and inevitable impurities.

[0140] It should be noted that Si contained in the hot-dip Al-Si alloy bath suppresses the formation of the Fe-Al intermetallic compound phase at the interface between the Al coating and the base steel plate during the coating treatment, and has the effect of improving the peel resistance and workability of the Al coating. However, if the Si content of the Al coating exceeds 15.0 mass%, columnar Si precipitates in the Al coating, and the peel resistance and workability may be reduced instead. Therefore, the Si content of the hot-dip Al-Si alloy bath is preferably 15.0 mass% or less. It should be noted that the lower limit of the Si content of the hot-dip Al-Si alloy bath is not particularly limited, but is preferably 1.0 mass%.

[0141] In addition, as inevitable impurities in the hot-dip Al bath and hot-dip Al-Si alloy bath, for example, B, Be, Mg, Ca, Sr, Ti, Mn, Co, Ni, Cu, Zn, Sn, Pb, As, Sb, Bi, La, Ce, etc. can be cited, and the total amount thereof is usually 1% by mass or less.

[0142] In addition, the thickness of the Al coating in the case of using the hot-dip coating method can be adjusted, for example, by N 2 gas wiping. And the conditions of pretreatment such as degreasing are not particularly limited, and can be carried out by conventional methods. On the contrary, the temperature of the base steel plate (plate temperature) when immersed in the plating bath is not particularly limited. In the case of using a continuous hot-dip coating apparatus, from the viewpoints of ensuring the plating characteristics of the operation and preventing the change of the bath temperature, it is preferably controlled within ±20°C of the temperature of the plating bath.

[0143] On the contrary, from the viewpoint of improving productivity, after plating Al on a base steel plate with a thickness exceeding 100 μm, additional cold rolling can be carried out to obtain a stainless steel steel plate with an Al coating (a pre-heat-treated material to be processed) as the final plate thickness.

[0144] For example, hot-dip Al can be carried out on a base steel plate with a thickness of about 300 μm, and after forming a hot-dip Al layer with a thickness of about 40 μm on each side of the base steel plate, additional cold rolling (hereinafter, also referred to as finish rolling) is carried out to obtain a stainless steel steel plate with an Al coating (a pre-heat-treated material to be processed) with a thickness of about 50 μm.

[0145] At this time, in the stainless steel steel plate with an Al coating (a pre-heat-treated material to be processed) obtained after finish rolling, the finish rolling conditions, the thickness of the base steel plate before finish rolling, and the thickness of the Al coating are adjusted so that the thickness of the base steel plate is 100 μm or less and the thickness of each side of the Al coating is in the range of 0.5 to 10.0 μm. For example, in the above case, the thickness of the base steel plate before finish rolling is 300 μm, and the thickness of each side of the Al coating is 40 μm, so the thickness of this steel plate (the overall thickness) is 380 μm. If this steel plate is rolled to 50 μm by finish rolling, the reduction ratio is about 87%. At this time, the Al coating is also rolled, and the thickness of the Al coating after finish rolling is also estimated to be reduced by about 87% to about 5.2 μm. Thus, in the stainless steel steel plate with an Al coating (a pre-heat-treated material to be processed) obtained after finish rolling, it is only necessary to adjust the finish rolling conditions, the thickness of the base steel plate before finish rolling, and the thickness of the Al coating so that the thickness of the base steel plate is 100 μm or less and the thickness of each side of the Al coating is in the range of 0.5 to 10.0 μm.

[0146] The pre-heat treated workpiece obtained as described above is further pre-heat treated to cause a certain amount of Fe and Cr to diffuse from the base steel plate into the Al coating. Specifically, the diffusion is carried out such that the total content of Fe and Cr at the first depth of the Al coating is 20 to 70% by mass. Thereby, while avoiding a reduction in workability, the adhesion between the Al coating and the base steel plate can be improved.

[0147] It should be noted that the amount of diffusion of Fe and Cr from the base steel plate into the Al coating needs to be controlled by adjusting the processing conditions of the pre-heat treatment, particularly the treatment temperature and treatment time.

[0148] That is, the diffusion rate of Fe and Cr from the base steel plate into the Al coating is affected by the composition of the base steel plate of the pre-heat treated workpiece, the formation method of the Al coating, the thickness of the Al coating, etc. Therefore, the appropriate processing conditions for the pre-heat treatment also change accordingly. Therefore, it is important to prepare in advance a preliminary test material identical to the pre-heat treated workpiece, use this preliminary test material, conduct preliminary tests with various changes in the treatment temperature and treatment time, and determine in advance the appropriate pre-heat treatment conditions.

[0149] As an example of the pre-heat treatment conditions, conditions of maintaining in a non-oxidizing atmosphere in a temperature range of 700°C to 1000°C for 10 to 60 seconds can be cited. In addition, generally, the higher the treatment temperature and the longer the treatment time, the greater the amount of diffusion of Fe and Cr from the base steel plate into the Al coating and the amount of diffusion of Al from the Al coating into the base steel plate.

[0150] In addition, for the atmosphere of the pre-heat treatment, in order to reduce the consumption of Al in the Al coating due to oxidation, it is preferably in a vacuum of 1×10 －1 Pa or less, an inert atmosphere such as Ar, an N 2 atmosphere, or a mixed atmosphere of H 2 and N 2 and other non-oxidizing atmospheres. In addition, the pre-heat treatment is carried out using a batch furnace that cuts the stainless steel plate with an Al coating (the pre-heat treated workpiece) into appropriate sizes. However, considering productivity, it is preferable to use a continuous heat treatment apparatus that can continuously process the steel strip.

[0151] As described above, a stainless steel plate with an Al coating according to an embodiment of the present invention can be manufactured.

[0152] Then, the stainless steel plate with an Al coating according to an embodiment of the present invention manufactured as described above is preferably processed into a desired shape such as a resistance heating element, and then a diffusion heat treatment is carried out to increase the Al content. From the viewpoint of obtaining high resistivity and excellent oxidation resistance, the Al content is preferably 6.5% or more.

[0153] From the viewpoint of homogenizing the diffused Al, the diffusion heat treatment is preferably carried out in a temperature range of 900°C to 1200°C for 10 minutes or more. The upper limit of the holding time is not particularly limited, and is preferably 120 minutes or less from the viewpoints of productivity and the like. It should be noted that in the case of performing brazing treatment at a high temperature during the manufacturing process of components such as resistance heating elements, or when the use temperature of the component exceeds 900°C, etc., these temperature increases can be used as an alternative to the diffusion heat treatment.

[0154] It should be noted that in the case where the processing conditions are not strict, etc., after performing diffusion heat treatment on the stainless steel sheet with an Al coating of one embodiment of the present invention to obtain a stainless steel sheet containing Al (preferably Al content: 6.5% or more), the stainless steel sheet containing Al can be processed into a desired shape.

[0155] Examples

[0156] The slab having the composition shown in Table 1 (the balance being Fe and inevitable impurities) melted by a 50 kg small vacuum melting furnace was heated to 1200°C and then hot-rolled in a temperature range of 900 to 1200°C to obtain a hot-rolled steel sheet with a thickness of 2.0 mm. It should be noted that in the steel symbol N in Table 1, since cracks occurred during hot rolling, subsequent evaluations were not performed. Next, the obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing in the atmosphere at 900°C for 1 minute, the surface scale was removed by pickling, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.3 mm.

[0157] This cold-rolled steel sheet was subjected to cold-rolled sheet annealing at 900°C for 20 seconds in a mixed atmosphere of H 2 and N 2 (by volume ratio, H 2 : N 2 = 75:25), and then further cold-rolled to obtain a base material steel sheet with the thickness shown in Table 2.

[0158] Next, test pieces with a length of 300 mm and a width of 100 mm were cut out from the obtained base material steel sheet, and Al coatings (Al vapor deposition layers) were formed on both sides of the test pieces by vacuum vapor deposition to obtain a pre-heat-treated material to be treated. The thickness of the Al coating is the same on the first side and the second side.

[0159] Next, the pre-heat-treated materials to be treated obtained as described above were respectively subjected to pre-heat treatment under the conditions shown in Table 2 to obtain stainless steel sheets with Al coatings shown in Table 2. The atmosphere for the pre-heat treatment was a mixed atmosphere of H 2 and N 2 (by volume ratio, H 2 : N 2= 75:25). It should be noted that, for comparison, a part is not subjected to pre-heat treatment.

[0160] It should be noted that the component composition of the base steel plate of the obtained Al-coated stainless steel plate is measured by wet analysis of the cut powder taken from a part of the base steel plate from which the Al coating has been removed by grinding. The result is substantially the same as the component composition in Table 1, and any result is within the range of the component composition of the base steel plate of the Al-coated stainless steel plate in one embodiment of the present invention described above.

[0161] Next, on both sides of the obtained Al-coated stainless steel plate, the total content of Fe and Cr at the first depth of the Al coating is measured by the above method. The measurement results are shown in Table 2 together. It should be noted that the measurement is carried out using a scanning electron microscope (TM3000 manufactured by Hitachi High-Technologies) and the attached EDX (SwiftED3000 manufactured by Oxford Instruments, acceleration voltage 15 kV).

[0162] In addition, the obtained Al-coated stainless steel plate is used to evaluate (1) adhesion and (2) workability according to the following procedures. The evaluation results are shown in Table 4.

[0163] (1) Adhesion

[0164] As Figure 4 shown, the above Al-coated stainless steel plate (length: 80 mm, width: 50 mm) is passed between two gear-shaped rolls, thereby performing corrugation processing (minimum bending radius: 0.25 mm, wave pitch: 3.0 mm, wave height: 3.0 mm).

[0165] Next, visually confirm the surfaces of the corrugated Al-coated stainless steel plate and the gear-shaped rolls.

[0166] Moreover, the case where there is no peeling of the Al coating and no adhesion to the gear-shaped rolls is evaluated as ○ (good), and the case where there is peeling of the Al coating or adhesion to the gear-shaped rolls is evaluated as × (bad).

[0167] (2) Workability

[0168] Visually confirm the above corrugated Al-coated stainless steel plate to confirm whether fractures or cracks occur.

[0169] Then, the case where there are no fractures or cracks with a length of 1 mm or more is evaluated as ○ (very good), and the case where fractures or cracks with a length of 1 mm or more occur is evaluated as × (bad).

[0170] Next, a diffusion heat treatment is carried out on the Al-coated stainless steel sheet without corrugation processing by holding it at 1150 °C for 30 minutes in a vacuum, so that Al in the Al coating diffuses into the base steel sheet, and an Al-containing stainless steel sheet is obtained. It should be noted that for No. 2, 4 to 7, since the above-mentioned (1) adhesion or (2) workability evaluation is × (poor), subsequent evaluations are not carried out.

[0171] The component composition of the obtained Al-containing stainless steel sheet is measured by wet analysis of the cut powder taken from a part of the Al-containing stainless steel sheet. The measurement results are shown in Table 3. It should be noted that the remaining part is Fe and inevitable impurities.

[0172] In addition, using the obtained Al-containing stainless steel sheet, the following procedures are used to evaluate (3) oxidation resistance and (4) resistivity. The evaluation results are shown in Table 4.

[0173] (3) Oxidation resistance

[0174] Two test pieces with a width of 20 mm and a length of 30 mm are taken from the obtained Al-containing stainless steel sheet, and a treatment of oxidizing at 1100 °C for 400 hours is carried out in an atmospheric environment, and the oxidation increment (the value obtained by dividing the mass change of the test piece before and after the oxidation treatment by the surface area of the test piece before the oxidation treatment) is measured. Then, the average value of the oxidation increments of each test piece is used as the oxidation increment of the Al-containing stainless steel sheet, and the evaluation is carried out according to the following criteria.

[0175] ◎ (Qualified, particularly excellent): The oxidation increment is 8.0 g / m 2 The following

[0176] ○ (Qualified, excellent): The oxidation increment exceeds 8.0 g / m 2 And 12.0 g / m 2 The following

[0177] × (Unqualified, poor): The oxidation increment exceeds 12.0 g / m 2 Or film peeling occurs

[0178] (4) Resistivity

[0179] The resistivity is measured according to the four-probe method specified in JIS C 2525.

[0180] That is, five test pieces of 10 mm × 80 mm are cut out from the obtained Al-containing stainless steel sheet, and the volume resistivity is measured. And their average value is used as the volume resistivity of the Al-containing stainless steel sheet, and the evaluation is carried out according to the following criteria.

[0181] ◎ (Qualified, particularly excellent): The volume resistivity exceeds 140 μΩ·cm

[0182] ○ (Qualified, excellent): Volume resistivity exceeds 100 μΩ·cm and is below 140 μΩ·cm

[0183] × (Unqualified, defective): Volume resistivity is 100 μΩ·cm or below

[0184]

[0185]

[0186]

[0187] [Table 4]

[0188]

[0189] According to Table 4, in the inventive examples, the hermeticity and processability are all excellent. In addition, good antioxidant properties and resistivity can be obtained after diffusion heat treatment.

[0190] On the other hand, in the comparative examples, cracks occurred during hot rolling and test pieces could not be made, or it can be said that at least one of the hermeticity, processability, antioxidant properties, and resistivity is insufficient.

Claims

1. A stainless steel sheet with an Al coating, comprising a base substrate steel sheet and an Al coating on the surface of the base substrate steel sheet. The base substrate steel sheet is a stainless steel sheet with a thickness of 100 μm or less, having the following composition by mass percentage: C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.040% or less, S: 0.010% or less, Cr: 11.0 - 30.0%, Al: 0.01 - 6.50%, Ni: 0.01 - 0.50%, and N: 0.020% or less, with the balance being composed of Fe and inevitable impurities. Moreover, the thickness of the Al coating is 0.5 - 10.0 μm. Furthermore, the total content of Fe and Cr at the first depth of the Al coating is 20 - 70% by mass. Wherein, The first depth of the Al coating is the depth from the surface of the Al coating: (depth a + depth b) / 2. In addition, depth a and depth b are respectively defined as follows. Depth a: When the depth at which the Al intensity takes the maximum value in the Al concentration distribution from the surface of the Al coating in the depth direction (i.e., the plate thickness direction) is set as point A, in the depth region from the surface of the Al coating to point A, the depth at which the Al intensity is [the maximum value of the Al intensity] / 2. Depth b: In the depth region from point A to the interface between the base substrate steel sheet and the Al coating, the depth at which the Al intensity is ([the maximum value of the Al intensity] + [the Al intensity corresponding to the Al content of the base substrate steel sheet]) / 2.

2. The stainless steel sheet with an Al coating according to claim 1. Wherein, The composition of the base substrate steel sheet further contains, by mass, one or more selected from Cu: 0.10% or less, Ti: 0.50% or less, Nb: 0.50% or less, V: 0.50% or less, Zr: 0.20% or less, Hf: 0.20% or less, Mo: 6.00% or less, W: 6.00% or less, B: 0.0050% or less, REM: 0.20% or less, Ca: 0.0100% or less, and Mg: 0.0100%.

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