JP6653606B2 - Al-containing ferritic stainless steel and method for producing the same - Google Patents

Description

  The present invention relates to an Al-containing ferritic stainless steel and a method for producing the same, and more particularly to an Al-containing ferritic stainless steel having excellent resistance to sulfidation corrosion and a small linear expansion coefficient, and a method for producing the same.

  In recent years, photovoltaic power generation has been developing as one of the main energies replacing fossil fuels, and the technical development of solar cells is accelerating. Conventionally, ceramics or glass having a small linear expansion coefficient (the definition is the same as the thermal expansion coefficient) made of an insulator have been widely used for solar cell substrates.

  However, since glass is brittle and heavy, it is not easy to mass-produce a solar cell substrate having a light absorbing layer formed on the surface of glass. Therefore, application of stainless steel having excellent heat resistance as a substrate material has been studied.

  For example, Patent Documents 1 and 2 disclose an insulating material in which a smooth stainless steel plate is coated with an alumina, silicon oxide, or silicon nitride film on the surface. A general-purpose ferritic stainless steel SUS430 (17Cr steel) is used as a material of the steel plate.

  Patent Document 3 discloses a material that defines both surface roughness parameters Rz and Rsk as a stainless steel surface having good film formability. The material is a ferritic stainless steel containing Cr: 18.2%, Cu: 0.48% and Nb: 0.41%, and a general-purpose steel containing Cr: 18.4% and Ni: 8.2%. Austenitic stainless steel is used.

  Here, among solar cells, compound solar cells such as CIS-based thin films are expected to spread in the future as solar cells that achieve both low cost and high efficiency. Compound-based thin-film solar cells include, for example, forming an insulating layer on a substrate, forming a first electrode layer made of a Mo layer on the insulating layer, and coating a chalcopyrite-type compound layer thereon as a light absorbing layer. Then, a second electrode layer is formed. The chalcopyrite-type compound is a quinary alloy represented by a Cu-In-Ga-Se-S system (hereinafter, CIS system).

For example, in Patent Document 4, an insulating film is formed on the surface of a stainless steel foil having a thickness of 20 to 200 μm, and a back electrode made of a Mo layer is formed thereon. A method for manufacturing a solar cell substrate material for forming a light absorption layer made of Cu (In _1-x Ga _x ) Se ₂ is disclosed. SUS430, SUS444 (18Cr-2Mo), and SUS447J1 (30Cr-2Mo) are used as the material of the stainless steel foil.

Patent Documents 5 and 6 disclose an electrode for a CIS solar cell in which a Mo electrode and a Cu (In _1-x Ga _x ) Se _2- type compound layer are formed on a Cu coating layer in a Cu-coated steel sheet having a Cu coating layer. A substrate is disclosed. Here, as a material of the Cu-coated steel sheet, C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.001 to 1.2%, P: 0.001 to 0 0.04%, S: 0.0005-0.03%, Ni: 0-0.6%, Cr: 11.5-32.0%, Mo: 0-2.5%, Cu: 0-1. 0%, Nb: 0 to 1.0%, Ti: 0 to 1.0%, Al: 0 to 0.2%, N: 0 to 0.025%, B: 0 to 0.01%, V: 0 to 0.5%, W: 0 to 0.3%, total of Ca, Mg, Y, and REM (rare earth element): 0 to 0.1%, with the balance being Fe and stainless steel composed of unavoidable impurities. It is disclosed for use. However, the ferritic stainless steel used in the examples is limited to SUS430.

Further, Patent Document 7 discloses a stainless steel material on which an insulating film having good heat resistance is formed and a method for manufacturing the same. The stainless steel serving as the base material is C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.001 to 2.0%, P: 0.001 to 0.05. %, S: 0.0005 to 0.03%, Ni: 0 to 2.0%, Cu: 0 to 1.0%, Cr: 11.0 to 32.0%, Mo: 0 to 3.0% , Al: 1.0 to 6.0%, Nb: 0 to 1.0%, Ti: 0 to 1.0%, N: 0 to 0.025%, B: 0 to 0.01%, V: 0 to 0.5%, W: 0 to 0.3%, total of Ca, Mg, Y, and REM (rare earth element): 0 to 0.1%, the balance being Fe and unavoidable impurities, and an Al oxide layer , A mixed layer of NiO and NiFe ₂₂ O ₄ having a thickness of 1.0 μm or more is formed.

Here, the mixed layer of NiO or the like and the Al oxide layer are formed by forming a Ni plated layer by electroplating, forming an Al oxide layer at the interface between the Ni plated layer and the substrate by heat treatment in the air, And NiFe ₂₂ O ₄ to form a mixed layer.

Patent Documents 8 and 9 disclose that in a film forming process of a compound-based thin film solar cell, Cu, In, and Ga, which are precursors of a light absorbing layer, are formed on a substrate by sputtering and then converted into a CIS-based compound thin film. A heat treatment step (sulfurization step) in which a gas atmosphere having a high corrosiveness of hydrogen (H ₂ S) is exposed is disclosed. In Patent Literature 8, for example, a method is used in which a corrosion-resistant layer is formed on a back surface of a metal substrate exposed to a highly corrosive gas atmosphere by, for example, forming a film of silica by a sputtering method.

  As a method that does not rely on surface treatment such as coating, Patent Documents 8 and 9 disclose a method of forming an alumina layer on the back surface of a metal substrate by applying a ferritic stainless steel substrate having a high Al content. It has been disclosed. Specifically, in Patent Document 9, application of a ferrite stainless steel substrate containing JFE18-3USR: 3.4% of Al is studied.

  Patent Document 10 discloses a ferritic stainless steel sheet for a solar cell member having excellent corrosion resistance and a method for producing the same. The stainless steel sheet as a member contains 14 to 18% of Cr, and the Cr concentration in the oxide film on the surface layer of the steel sheet and the Cr concentration immediately below the oxide film are (Cr concentration in the oxide film (mass%)) + 3 × ( (Cr concentration (mass%) immediately below the oxide film)> 62 (mass%). Here, the stainless steel sheet is heated to a temperature range of 580 ° C. to 720 ° C. in an inert gas atmosphere adjusted to a dew point of −70 ° C. to −40 ° C., and the residence time in the temperature range is set to 5 seconds or more. It is obtained by performing a heat treatment.

JP-A-6-299347 JP-A-6-306611 JP 2011-204723 A JP 2012-169479 A JP 2012-59854 A JP 2012-59855 A JP 2012-214886 A JP 2014-203936 A JP 2014-127712 A JP 2014-118620 A

  To expand the spread of CIS-based compound thin-film solar cells as the main photovoltaic power generation in the future, it is important to improve productivity. For this purpose, it is necessary to improve the film-forming properties by reducing the coefficient of linear expansion while increasing the sulfidation corrosion resistance of the stainless steel plate for the substrate so that complicated surface treatment such as coating can be omitted. .

  In this regard, the techniques disclosed in Patent Documents 1 to 8 have a problem that surface treatment such as coating or plating is required. Patent Literatures 8 and 9 disclose techniques that do not require coating, but have a high linear expansion coefficient due to the need to contain a high concentration of Al, and do not solve the problem.

  In the technique disclosed in Patent Literature 10, although corrosion resistance deterioration of the light absorbing layer (CIGS layer) that occurs during film formation of 14 to 18 Cr steel is suppressed, no consideration is given to sulfidation corrosion resistance. As described above, there is no conventional technology that satisfies both the two problems of the sulfidation corrosion resistance and the film forming property.

  The present invention has a resistance to sulfidation corrosion, does not depend on surface treatment such as coating or plating, and does not contain excessive amount of Al, has a small linear expansion coefficient, and has a low film forming property of an insulating film and a compound-based thin film. An object of the present invention is to provide a good Al-containing ferritic stainless steel and a method for producing the same.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive experiments and studies on the relationship between the surface film and the sulfidation corrosion resistance, and the relationship between the linear expansion coefficient and the Al content in an Al-containing ferritic stainless steel. As a result, the following findings were obtained.

(A) A high-purity ferritic stainless steel typified by SUS430LX and SUS430J1L is exposed to an atmosphere containing several percent of hydrogen sulfide gas at a high temperature of 400 to 700 ° C. for about 0.5 to 2 hours when exposed to a steel substrate. Sulfidation corrosion progresses until shedding. Such sulfidation corrosion progresses by Fe and Cr, which are constituent elements of stainless steel, reacting with S in the atmosphere gas to form FeS ₂ and FeCr ₂ S ₄ and erosion the steel.

(B) In the case of a ferritic stainless steel containing 3% or more of Al, a continuous film of Al ₂ O ₃ is formed in a high-temperature environment, so that the above-described sulfidation corrosion is improved. On the other hand, in the case of a ferritic stainless steel having an Al content of less than 3%, the sulfidation corrosion resistance is affected by the film composition on the surface. Usually, a passivation film of Fe and Cr as thin as about several nm is formed on the surface after pickling or polishing. Sulfidation corrosion is likely to occur when a passive film mainly composed of Fe and Cr is formed on the surface.

To reduce the Fe and Cr concentrations in the surface film, it is effective to increase the Si + Ti concentration in addition to Al, and it is possible to suppress sulfidation corrosion even with a low Al content. However, excessive addition of Si rather lowers the resistance to sulfidation corrosion. This is considered to be because SiO ₂ has an effect of impairing the protection of the continuous film of Al ₂ O ₃ .

  (C) To reduce the Fe and Cr concentrations in the surface coating described above, it is effective not to increase the contents of Al and Si + Ti in stainless steel, but to add Mg as a trace element.

  Mg is a surface active element and is concentrated on the surface even when added in a small amount, and furthermore, Mg forms an oxide and suppresses the oxidation of Fe or Cr, effectively acting on the formation of a film mainly composed of Al. This effect makes it possible to reduce the Al content while maintaining the resistance to sulfidation corrosion, and to reduce the linear expansion coefficient of stainless steel.

  The present invention has been made based on the above findings, and has the following Al-containing ferritic stainless steel and a method for producing the same.

(1) The chemical composition of the base material is expressed in mass%
C: 0.03% or less,
Si: 0.02 to 1.5%,
Mn: 0.03-2.0%,
Cr: 13.0 to 22.0%,
P: 0.05% or less,
S: 0.01% or less,
Al: 0.20% or more and less than 1.4%,
Ti: 0.03 to 0.5%,
N: 0.03% or less,
Mg: 0.0005-0.05%,
The balance: Fe and inevitable impurities,
Having a film with a thickness of 30 nm or less on the surface,
An Al-containing ferritic stainless steel in which the content of each element contained in the coating satisfies the following formulas (i) to (iii).
Al> 5 (i)
15 <Si + Ti <33 (ii)
Fe <50 (iii)
However, each symbol in the above formula represents the content (atomic%) of each element in the components other than O, C and N contained in the film.

  (2) The chemical composition of the base material further contains, by mass%, Ga: 0.1% or less, and the total content of Mg and Ga is more than 0.001% and 0.15% or less. The Al-containing ferritic stainless steel according to (1).

(3) The Al-containing ferritic stainless steel according to (1) or (2), wherein the base material has a linear expansion coefficient at 20 to 700 ° C of less than 12.4 × 10 ⁻⁶ (1 / ° C).

(4) The Al-containing ferritic stainless steel according to any one of (1) to (3), wherein the content of S contained in the coating satisfies the following formula (iv).
S <3.0 (iv)
However, S in the above formula represents the content (atomic%) of S in the components other than O, C and N contained in the film.

(5) The chemical composition of the base material further includes,
Ni: 1.0% or less,
Cu: 1.0% or less,
Mo: 2.0% or less,
Nb: 0.5% or less,
V: 0.5% or less,
Sn: 0.2% or less,
Sb: 0.2% or less,
W: 1.0% or less,
Co: 0.5% or less,
B: 0.005% or less,
Ca: 0.005% or less,
Zr: 0.5% or less,
Hf: 0.1% or less,
REM: 0.1% or less, and Ta: 0.1% or less,
The Al-containing ferritic stainless steel according to any one of the above (1) to (4), containing at least one member selected from the group consisting of:

  (6) The Al-containing ferritic stainless steel according to any one of (1) to (5), which is used as a solar cell substrate.

(7) A method for producing the Al-containing ferritic stainless steel according to any one of the above (1) to (6),
An Al-containing ferritic stainless steel obtained by heat-treating a steel having the chemical composition according to the above (1), (2) or (5) in a temperature range of 700 to 1100 ° C. and then pickling in hydrofluoric acid or sulfuric acid. Steel production method.

  (8) The method for producing an Al-containing ferritic stainless steel according to (7), wherein after the pickling, electrolytic pickling is further performed in a nitric acid aqueous solution of 3 to 20% by mass.

  ADVANTAGE OF THE INVENTION According to this invention, it has sulfide corrosion resistance, does not depend on surface treatments, such as coating or plating, does not contain excess Al, has a small linear expansion coefficient, and forms an insulating film and a compound thin film. An Al-containing ferritic stainless steel having good properties is obtained.

  Hereinafter, each requirement of the present invention will be described in detail.

1. Chemical composition of base material The reasons for limiting each element are as follows. In the following description, “%” for the content means “% by mass”.

C: 0.03% or less C forms a solid solution in a ferrite phase or forms a Cr carbide to reduce oxidation resistance, and inhibits formation of a surface film according to the present invention. Therefore, the C content is preferably as low as possible, and is set to 0.03% or less. The C content is preferably 0.02% or less. However, since an excessive reduction leads to an increase in refining cost, the C content is preferably set to 0.001% or more, more preferably 0.002% or more.

Si: 0.02 to 1.5%
Si is an important element for ensuring the sulfurization corrosion resistance aimed at by the present invention. Si forms a solid solution in the oxide film and also concentrates at the oxide film / steel interface, thereby suppressing hydrogen sulfide (H ₂ S) from penetrating into the steel and improving the resistance to sulfidation corrosion. Therefore, the Si content is set to 0.02% or more. However, when Si is contained excessively, SiO ₂ impairs the protection of the continuous film of Al ₂ O ₃ and significantly reduces the resistance to sulfidation corrosion. Further, the toughness and workability of the steel are reduced. Therefore, the Si content is set to 1.5% or less. In order to increase the Si concentration in the film during pickling, the Si content is preferably 0.1% or more, more preferably 0.5% or more. Further, from the viewpoint of resistance to sulfidation corrosion and basic characteristics, the Si content is preferably 1.2% or less.

Mn: 0.03-2.0%
Mn has the effect of suppressing the surface oxidation of Fe and promoting the formation of a surface film in which the composition of Al, Si and Ti falls within the range specified in the present invention. Therefore, the Mn content is set to 0.03% or more. However, if Mn is excessively contained, the oxidation resistance is reduced, leading to the deterioration of the sulfidation corrosion resistance. Therefore, the Mn content is set to 2.0% or less. The Mn content is preferably at least 0.1%, more preferably at least 0.2%. From the viewpoints of oxidation resistance and sulfidation corrosion resistance, the Mn content is preferably 1.0% or less.

Cr: 13.0 to 22.0%
Cr is a basic constituent element in forming the surface film according to the present invention and ensuring resistance to sulfidation corrosion in addition to corrosion resistance. If the Cr content is less than 13.0%, the target sulfidation corrosion resistance is not sufficiently ensured, and the linear expansion coefficient is further increased. Therefore, the Cr content is set to 13.0% or more. However, when Cr is excessively contained, the Cr concentration in the surface film is increased, and when exposed to a high-temperature hydrogen sulfide atmosphere, the sulfur corrosion resistance is deteriorated, and the alloy cost is increased. For this reason, the Cr content is set to 22.0% or less from the viewpoint of resistance to sulfidation corrosion and alloy cost. The Cr content is preferably at least 15.0%, more preferably at least 16.0%. Further, the Cr content is preferably 20.0% or less, more preferably 19.0% or less.

P: 0.05% or less P is an element that deteriorates the manufacturability and weldability, and the lower the content, the better. Therefore, the P content is set to 0.05% or less. The P content is preferably at most 0.04%, more preferably at most 0.03%. However, since excessive reduction leads to an increase in refining costs, the P content is preferably set to 0.003% or more, more preferably 0.005% or more, and more preferably 0.01% or more. More preferred.

S: 0.01% or less S is an unavoidable impurity element contained in steel and deteriorates sulfidation corrosion resistance. In particular, S present in the surface film, or Mn-based inclusions or solid solution S present in the steel, act as a starting point for breaking the surface film when exposed to a high-temperature hydrogen sulfide atmosphere. Therefore, the lower the S content, the better, and the S content is set to 0.01% or less. The S content is preferably 0.002% or less, and more preferably 0.001% or less. However, excessive reduction leads to an increase in the cost of raw materials and refining, so that the content is preferably 0.0001% or more, and more preferably 0.0002% or more.

Al: 0.20% or more and less than 1.4% Al is an element that has a deoxidizing effect and is essential for achieving the target sulfidation corrosion resistance of the present invention by modifying the surface film. Element. Heretofore, it has been considered that if the Al content is less than 3%, sufficient sulfurization corrosion resistance cannot be obtained. However, in the present invention, since a surface film having a predetermined composition is formed, the target sulfuration corrosion resistance is sufficiently exhibited if the Al content is 0.20% or more. Therefore, the Al content is 0.20% or more. On the other hand, when the Al content is 1.4% or more, the linear expansion coefficient increases, and not only the film forming property of the insulating film is deteriorated, but also the manufacturability is deteriorated and the alloy cost is increased. Therefore, the Al content is set to less than 1.4%. The Al content is preferably 0.80% or more, and more preferably 1.3% or less.

Ti: 0.03 to 0.5%
Ti has the effect of improving oxidation resistance through the purification of steel by the action of stabilizing elements that fix C and N, as well as the effect of improving sulfidation corrosion resistance by coating modification. Therefore, the Ti content is set to 0.03% or more. However, excessive addition of Ti leads to an increase in alloy cost and a reduction in productivity due to an increase in recrystallization temperature. Therefore, the Ti content is set to 0.5% or less. The Ti content is preferably 0.05% or more, more preferably 0.1% or more. Further, the Ti content is preferably 0.35% or less, more preferably 0.25% or less.

N: 0.03% or less N is an element that deteriorates the sulfidation corrosion resistance like C. Therefore, the lower the N content, the better, and it is set to 0.03% or less. The N content is preferably 0.02% or less. However, since an excessive reduction leads to an increase in refining costs, the N content is preferably set to 0.002% or more, more preferably 0.005% or more.

Mg: 0.0005 to 0.05%
As described above, Mg is an element having a function of concentrating on the surface to suppress oxidation of Fe and Cr and promoting the formation of a film mainly containing Al and having a high content of Si and Ti. Therefore, the Mg content is set to 0.0005% or more. However, when Mg is excessively contained, not only does the cost of refining the steel rise and the manufacturability is deteriorated, but also the deterioration of the sulfidation corrosion resistance is caused. Therefore, the Mg content is set to 0.05% or less. The Mg content is preferably at least 0.001%, more preferably at most 0.03%.

  The Al-containing ferritic stainless steel of the present invention contains the above-mentioned elements from C to Mg, and has a chemical composition consisting of Fe and inevitable impurities.

  Here, the “unavoidable impurities” are components which are mixed due to various factors in the raw materials such as ores and scraps and the manufacturing process when steel is industrially manufactured, and are allowable as long as they do not adversely affect the present invention. Means what is done.

  The Al-containing ferritic stainless steel according to the present invention has the following amounts of Ga, Ni, Cu, Mo, Nb, V, Sn, Sb, W, Co, B, and One or more selected from Ca, Zr, Hf, REM and Ta may be contained.

Ga: 0.1% or less Ga is an element having a function of concentrating on the surface to suppress the oxidation of Fe and Cr and promoting the formation of a film having a high Si and Ti content mainly of Al, like Mg. . Therefore, Ga may be contained as necessary. However, when Ga is excessively contained, not only the refining cost of steel is increased and the manufacturability is deteriorated, but also the resistance to sulfide corrosion is deteriorated. Therefore, the Ga content is set to 0.1% or less. The Ga content is preferably 0.02% or less. In order to obtain the above effects, the Ga content is preferably set to 0.0005% or more, more preferably 0.001% or more. When Ga is contained, the total content of Mg and Ga is preferably more than 0.001% and 0.15% or less. It is more preferable that the total content of Mg and Ga is more than 0.002%.

Ni: 1.0% or less Cu: 1.0% or less Mo: 2.0% or less Nb: 0.5% or less V: 0.5% or less Sn: 0.2% or less Sb: 0.2% or less W : 1.0% or less Co: 0.5% or less The above-mentioned elements are effective elements for improving the high-temperature strength and corrosion resistance of stainless steel. Therefore, you may make it contain as needed. However, if it is contained excessively, it leads to an increase in alloy cost and deterioration in manufacturability. Therefore, the contents of Ni, Cu and W are set to 1.0% or less. Further, Mo is an element effective in suppressing high-temperature deformation due to a decrease in linear expansion coefficient, and therefore, the Mo content is 2.0% or less. Further, the contents of Nb, V and Co are set to 0.5% or less. The contents of Sn and Sb are set to 0.2% or less from the viewpoint of manufacturability. In order to obtain the above effects, it is preferable that at least one of the above elements is contained at 0.05% or more.

B: 0.005% or less Ca: 0.005% or less B and Ca are elements that improve hot workability and secondary workability, and may be contained as necessary. However, if it is contained excessively, the productivity is deteriorated, so that the contents of B and Ca are each set to 0.005% or less. In order to obtain the above effects, it is preferable to contain at least one of the above elements in an amount of 0.0001% or more.

Zr: 0.5% or less Hf: 0.1% or less REM: 0.1% or less Ta: 0.1% or less The above-mentioned elements improve hot workability and cleanliness of steel, and also have oxidation resistance. It is an effective element for improvement. Therefore, you may make it contain as needed. However, the target sulfurization corrosion resistance of the present invention does not depend on the effect of adding these elements. Therefore, the upper limit of each element is defined as described above. In order to obtain the above effects, at least one of Zr: 0.01% or more, Hf: 0.001% or more, REM: 0.001% or more, and Ta: 0.001% or more is satisfied. Is preferred.

  Here, REM indicates a total of 17 elements of Sc, Y and lanthanoid, and the content of REM indicates the total content of these elements.

  In addition to the above-described elements, the incorporation of impurity elements within a range that does not impair the effects of the present invention is allowed. It is preferable to reduce P, S, Zn, Bi, Pb, Se, Hf, and the like, which are general impurity elements, as much as possible. On the other hand, the content ratio of these elements is controlled to the extent that the object of the present invention is solved. If necessary, Zn: 500 ppm or less, Bi: 100 ppm or less, Pb: 100 ppm or less, Se: 100 ppm or less, Hf : One or more of 100 ppm or less may be contained.

2. Surface Coating The Al-containing ferritic stainless steel according to the present invention includes a coating having a thickness of 30 nm or less on the surface and a predetermined composition. In order to make the thickness of the film more than 30 nm, it is necessary to perform a special annealing and / or pickling treatment, so that productivity is deteriorated. The thickness of the film is preferably 20 nm or less, more preferably 15 nm or less. On the other hand, the lower limit of the film thickness is not particularly limited, but is preferably 3 nm or more in order to exert an effect on resistance to sulfurization corrosion in hydrogen sulfide.

Further, in order to improve the resistance to sulfidation corrosion in H ₂ S, it is necessary to increase the contents of Al and Si + Ti contained in the coating. Specifically, the content of each element contained in the film satisfies the following equations (i) to (iii).
Al> 5 (i)
15 <Si + Ti <33 (ii)
Fe <50 (iii)
However, each symbol in the above formula represents the content (atomic%) of each element in the components other than O, C and N contained in the film.

  Al is concentrated from the inner layer of the surface film to the interface with the iron base, and significantly suppresses the corrosive gas S from entering the steel. These effects are remarkably exhibited by setting the Al content in the surface coating to an amount exceeding 5 atomic%. The Al content is preferably at least 8 at%, more preferably at least 10 at%. The upper limit of the Al content is not particularly limited, but is preferably 30 atomic% or less in consideration of the efficiency of annealing and pickling.

  Further, Si and Ti are concentrated in the surface coating and at the interface with the iron base, and have the effect of increasing the resistance to sulfidation corrosion. To obtain these effects, the total content of Si and Ti in the surface film is set to an amount exceeding 15 atomic%. The total content of Si and Ti is preferably at least 20 atomic%. On the other hand, if Si and Ti become excessive, formation of a film mainly composed of Al is inhibited, so that the total content of Si and Ti is set to less than 33 atomic%. The total content of Si and Ti is preferably less than 30 atomic%. It is preferable that both elements of Si and Ti are contained in a complex form.

  In order to increase the content of Al and Si + Ti contained in the coating, it is necessary to relatively reduce the Fe content. Therefore, the Fe content in the surface film is set to less than 50 atomic%.

Further, the content of S contained in the film preferably satisfies the following formula (iv).
S <3.0 (iv)
However, S in the above formula represents the content (atomic%) of S in the components other than O, C and N contained in the film.

  In order to suppress the starting point of corrosion due to hydrogen sulfide at a high temperature, the S content in the coating is preferably less than 3.0 atomic%. The S content is more preferably less than 2.0 atomic%, and further preferably less than 1.0 atomic%. The lower limit of the S content is not particularly limited, but the lower the lower, the more preferable it is, and the non-detection is preferably zero.

  The method of analyzing the film composition is not particularly limited as long as quantitative analysis is possible. For example, the contents of Al, Si, Ti, Cr, Fe, and S in the film can be measured by Auger electron spectroscopy (AES), and the content of S is measured by X-ray photoelectron spectroscopy (XPS). be able to.

3. Linear Expansion Coefficient As described above, stainless steel used as a substrate for a CIS-based compound-based thin film solar cell is required to have high film-forming properties. In order to improve the film forming property, it is preferable to lower the linear expansion coefficient of steel. Specifically, the coefficient of linear expansion at 20 to 700 ° C. assuming a film forming process for a CIS solar cell is preferably less than 12.4 × 10 ⁻⁶ (1 / ° C.).

4. Production method The method for producing the Al-containing ferritic stainless steel according to the present invention is not particularly limited. For example, the production is performed by subjecting a steel material having the above chemical composition to the following treatment. Can be. When a steel plate is used as the steel material, for example, a thin plate, a foil, and a medium-thick plate can be used. Here, the thin plate has a thickness of 0.2 mm or more, the foil has a thickness of 0.02 to 0.2 mm, and the medium thickness plate has a thickness of 6 mm or more. It is not necessary to particularly define the surface roughness of the steel, and for example, it is specified in JIS G0203 (2009). 2B, no. 2D, No. It is only necessary to use one having a finish of 4 or the like.

  In addition, although there is no particular limitation on the type of steel sheet to be a steel material, annealing is performed on the hot-rolled steel strip as necessary, and after descaling, a cold-rolled cold-rolled sheet can be used. . In order to form a film defined by the present invention on the surface of the cold-rolled sheet, after cold rolling, a heat treatment of finish annealing in a temperature range of 700 to 1100 ° C. is performed, and then pickling is performed in nitric hydrofluoric acid or sulfuric acid. If necessary, it is preferable to further perform electrolytic pickling in an aqueous nitric acid solution.

  If the heating temperature in the finish annealing is lower than 700 ° C., the softening and recrystallization of the steel become insufficient, and the desired material properties may not be obtained. Therefore, the heating temperature is preferably set to 700 ° C. or higher. In order to lower the dew point of the atmospheric gas, the heating temperature is more preferably set to 800 ° C. or higher, further preferably 850 ° C. or higher. On the other hand, when the heating temperature exceeds 1100 ° C., the crystal grains become coarse, and the toughness and ductility of the steel may be deteriorated. Therefore, the heating temperature is preferably set to 1100 ° C or lower, more preferably 1000 ° C or lower.

  Further, in the pickling after the heat treatment, it is preferable to use either hydrofluoric or nitric acid composed of 0.1 to 5% hydrofluoric acid and 5 to 15% nitric acid or 5 to 15% sulfuric acid. It is preferable to perform pickling. By pickling, the Fe content in the coating can be reduced and the Al and Si + Ti content can be increased.

  Further, in order to reduce the S content in the film, it is preferable to perform electrolytic pickling in an aqueous nitric acid solution. The nitric acid concentration is preferably in the range of 3 to 20% by weight in order to remove S and Fe adhering to the surface by electrolysis. When the nitric acid concentration is less than 3%, the effect of electrolytic pickling is hardly obtained. On the other hand, if the nitric acid concentration exceeds 20%, the concentration of Cr in the surface film proceeds, which leads to deterioration of the sulfidation corrosion resistance due to a decrease in the content of Al and Si + Ti. The nitric acid electrolysis is preferably performed in an industrial electrolytic pickling apparatus, for example, after performing a cleaning step such as water washing and dilute sulfuric acid electrolytic pickling in a facility equipped with a pretreatment tank and a plurality of electrolytic pickling tanks. Alternatively, nitric acid electrolysis may be performed. The current density and temperature of the nitric acid electrolysis are not particularly limited as long as the composition of the film is not impaired.

  Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.

A ferritic stainless steel (steel A to U) having the chemical composition shown in Table 1 is melted, hot-rolled and annealed, cold-rolled, and a foil or thin plate having a thickness of 0.1 to 0.5 mm. After that, each steel was subjected to the following treatment (Test Nos. 1 to 23). The foil or thin plate was annealed at 950 ° C. at which recrystallization was completed, and then pickled at 55 ° C. with 2.5% HF-5% HNO ₃ . Test No. The 2, 3, 9 and 10 steel sheets were further subjected to nitric acid electrolytic pickling in an 8% aqueous nitric acid solution. In order to investigate the effect of pickling, Test No. The steel sheets 3 and 12 were descaled by polishing after pickling.

About the obtained steel plate, the composition of the surface film was measured by AES analysis. For the AES analysis, a scanning FE Auger electron spectrometer (manufactured by ULVAC-PHI) was used. The acceleration voltage of the electron gun was 10 kV, the acceleration voltage of the ion gun (Ar) was 3 kV, and the sputtering rate was 10 nm / min (SiO ₂ measured values) and converted to the film thickness in the plate thickness direction.

From the obtained Auger electron spectra, the Auger peak heights of Fe, Cr, Al, Si, Ti, and S (the heights between peaks in the differential spectrum) were read, and the relative concentrations were calculated. The film thickness was determined by measuring the profile of O and obtaining the half-value width at which the intensity of O becomes half the value. Table 2 shows the film thickness and composition.

  Moreover, the linear expansion coefficient was measured using the above-mentioned steel sheet. A test piece having a thickness of 2.0 mm, a width of 3.0 mm, and a length of 18 mm was cut out from each steel sheet, and the average coefficient of linear expansion was determined by a thermomechanical analysis (TMA) method. The device used was TMA8140 (differential expansion type) manufactured by Rigaku Corporation. The measurement atmosphere was He, the load was 5 gf, and the standard sample was alumina. Assuming a film forming process of a CIS solar cell, the temperature was measured at a temperature of 20 ° C. to 700 ° C. at a rate of 5 ° C./min.

In the present invention, when the coefficient of linear expansion is less than 12.4 × 10 ⁻⁶ (1 / ° C.), it is determined that the film-forming property is good, and is evaluated as “○”, and 12.4 × When it was 10 ⁻⁶ (1 / ° C.) or more, it was judged that the film-forming property was inferior, and was evaluated as “×”.

Subsequently, the above steel sheets were evaluated for resistance to sulfidation corrosion. Specifically, 700 ° C., 2% H ₂ S-bal. It was carried out heat treatment for 1h held in an atmosphere of N _2. And, by visual judgment, “◎” indicates that no peeling occurred, and “○” indicates that the amount of corrosion increased was 2 mg / cm ² or less although slight peeling occurred. Those exceeding / cm ² were evaluated as “x”. In the present invention, when the above result corresponds to “◎” or “○”, it is determined that the sulfidation corrosion resistance is excellent.

  The above results are also shown in Table 2.

  Test No. Nos. 1 to 11 are steels according to the present invention satisfying the requirements of the present invention. As can be seen from Table 2, it can be seen that the steel of the present invention has excellent film-forming properties and resistance to sulfidation corrosion. In addition, the test No. In No. 3, since the descaling was performed by polishing, the Fe concentration in the film was expected to be high, and the amounts of Al, Cr, and Si + Ti were expected to decrease relatively. The content decreased, and the amounts of Al, Cr, and Si + Ti relatively increased, and the evaluation was “○”.

  On the other hand, Test Nos. Using steels whose chemical composition deviated from the requirements of the present invention were used. In Nos. 12 to 23, one of the film forming property and the sulfidation corrosion resistance was inferior. Specifically, in Test No. 12, since the Al content exceeded the upper limit of the specified range, the coefficient of linear expansion increased, resulting in poor film formability. Test No. In No. 20, since the Cr content was less than the lower limit of the specified range, the sulfide corrosion resistance was poor, the linear expansion coefficient was high, and the film-forming properties were poor.

  Further, the test No. Regarding 13 to 19 and 21 to 23, since various chemical compositions are out of the specified range, even if the preferred annealing and pickling specified in the present invention are performed, the film composition does not satisfy the specification of the present invention, The result was inferior sulfide corrosion resistance.

  ADVANTAGE OF THE INVENTION According to this invention, it has sulfide corrosion resistance, does not depend on surface treatments, such as coating or plating, does not contain excess Al, has a small linear expansion coefficient, and forms an insulating film and a compound thin film. An Al-containing ferritic stainless steel having good properties is obtained. Therefore, the Al-containing ferritic stainless steel according to the present invention is used for a substrate of a compound thin film solar cell manufactured through a film forming process including a heat treatment exposed to a sulfide atmosphere such as hydrogen sulfide gas in an oil cooking or combustion environment. It can be suitably used.

Claims (8)

The chemical composition of the base material is
C: 0.03% or less,
Si: 0.02 to 1.5%,
Mn: 0.03-2.0%,
Cr: 13.0 to 22.0%,
P: 0.05% or less,
S: 0.002 % or less,
Al: 0.20% or more and less than 1.4%,
Ti: 0.03 to 0.5%,
N: 0.03% or less,
Mg: 0.0005-0.05%,
The balance: Fe and inevitable impurities,
Having a film with a thickness of 30 nm or less on the surface,
An Al-containing ferritic stainless steel in which the content of each element contained in the coating satisfies the following formulas (i) to (iii).
Al> 5 (i)
15 <Si + Ti <33 (ii)
Fe <50 (iii)
However, each symbol in the above formula represents the content (atomic%) of each element in the components other than O, C and N contained in the film.   The chemical composition of the base material further contains, by mass%, Ga: 0.1% or less, and the total content of Mg and Ga is more than 0.001% and 0.15% or less. 2. The Al-containing ferritic stainless steel according to 1. The Al-containing ferritic stainless steel according to claim 1 or 2, wherein a linear expansion coefficient of the base material at 20 to 700 ° C is less than 12.4 × 10 ⁻⁶ (1 / ° C). The Al-containing ferritic stainless steel according to any one of claims 1 to 3, wherein the content of S contained in the coating satisfies the following formula (iv).
S <3.0 (iv)
However, S in the above formula represents the content (atomic%) of S in the components other than O, C and N contained in the film. The chemical composition of the base material further includes,
Ni: 1.0% or less,
Cu: 1.0% or less,
Mo: 2.0% or less,
Nb: 0.5% or less,
V: 0.5% or less,
Sn: 0.2% or less,
Sb: 0.2% or less,
W: 1.0% or less,
Co: 0.5% or less,
B: 0.005% or less,
Ca: 0.005% or less,
Zr: 0.5% or less,
Hf: 0.1% or less,
REM: 0.1% or less, and Ta: 0.1% or less,
The Al-containing ferritic stainless steel according to any one of claims 1 to 4, comprising at least one selected from the group consisting of:   The Al-containing ferritic stainless steel according to any one of claims 1 to 5, which is used as a solar cell substrate. A method for producing an Al-containing ferritic stainless steel according to any one of claims 1 to 6, wherein
An Al-containing ferritic stainless steel obtained by heat-treating a steel having the chemical composition according to claim 1, 2 or 5 in a temperature range of 700 to 1100 ° C., and then pickling in hydrofluoric acid or sulfuric acid. Manufacturing method.   The method for producing an Al-containing ferritic stainless steel according to claim 7, wherein electrolytic pickling is further performed in an aqueous solution of 3 to 20% by mass of nitric acid after the pickling.