JP3263426B2 - Ferritic stainless steel sheet excellent in weather resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel having excellent weather resistance and to be used as a roof, an exterior material and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Stainless steel is roughly classified into austenitic and ferritic. Austenitic stainless steel excellent in workability, weldability, and the like has been used for the roof and exterior materials. However, with the increase in the size of buildings, the use of long objects has increased, and in austenitic stainless steel having a large thermal expansion coefficient, problems such as breakage of welds and turning-up at corners have occurred.

[0003] Ferritic stainless steel has a small coefficient of thermal expansion, and poses little problem of danger such as breakage of a welded portion or curling at a corner portion. However, taking SUS430, which is a representative type of ferritic stainless steel, as an example, the corrosion resistance and weather resistance are not sufficient even in a rural area where the corrosive environment is mild, as seen in the generation of rust in a short period of time. Further, there is a disadvantage that intergranular corrosion is easily generated by heating and cooling during welding.

In order to improve the weather resistance, it is effective to increase the amount of Cr or to add Mo. The decrease in toughness accompanying the increase in Cr and Mo has been restored by reducing C and N. Reduction of C and N is also effective for improving intergranular corrosion resistance. However, the reduction of C and N has its own limit.
At an industrially achievable C and N content level, intergranular corrosion susceptibility cannot be completely eliminated. Therefore, the adverse effects of C and N on intergranular corrosion are eliminated by adding a stabilizing element such as Ti or Nb which can fix C and N alone or in combination.

[0005]

On the basis of these technical backgrounds, for example, low carbon / low nitrogen 30Cr-2.0
Like Mo-Nb steel, Mo-containing high Cr steel having excellent weather resistance has been developed. However, when exposed to a corrosive environment containing chlorine ions, such as in a coastal area or on the sea, rust may be generated in a short period of time, and the weather resistance is still insufficient.

[0006] The generation of rust is caused by the destruction of the passive film and the progress of the corrosion reaction by chlorine ions. That is, the surface of stainless steel is usually covered with a passive film that suppresses rust such as rust. However, the passivation film is destroyed in the coastal area or on the sea, and corrosion proceeds due to the arrival of sea salt particles containing chloride ions which have an effect of preventing its renewal.

An object of the present invention is to provide a ferritic stainless steel sheet having excellent weather resistance even in a corrosive environment containing chlorine ions by forming a passivation film having an Al-enriched layer.

[0008]

The ferritic stainless steel sheet of the present invention has a C: 0.0
25% by weight or less, Si: 0.6% by weight or less, Mn: 1.
0% by weight or less, P: 0.04% by weight or less, S: 0.01
Wt% or less, Ni: 1.0 wt% or less, Cr: 16 to 3
5% by weight, Mo: 0.3 to 6% by weight, N: 0.025% by weight or less, Al: 0.01 to 0.5% by weight, Nb: 0.
1 to 0.6% by weight, Ti: 0.05 to 0.3% by weight, the balance being Fe and unavoidable impurities, and C +
N ≦ 0.04% by weight and Nb + Ti ≧ 7 (C + N) +
Satisfy 0.15, B ₁ defined by B ₁ = Cr + 3Mo
Value is 23.5 or more, P ₁ = 5Ti + 20 (Al−0.0
The ferrite-based stainless steel having a P ₁ value of 1.0 or more defined in 1) as a base material, and the Al amount in a portion where Al is concentrated most is the amount of Al contained in the base material. 2
A passivation film having an Al concentration layer that is twice or more is formed on the surface of the base material.

The ferritic stainless steel used as the base material is
Further, Cu: 0.1 to 1.0% by weight can be contained.
In this case, instead of the B ₁ value, B ₂ = Cr + 3 (Mo + C
The B ₂ value defined in u) is used and the B ₂ value is 23.5
It is necessary to be above. Zr: 0.05-
It can also contain 0.3% by weight. In this case, instead of the P ₁ value, P ₂ = 5 (Ti + Zr) +20 (Al−0.01)
P ₂ value THAT defined is used, it is required that P ₂ value of 1.0 or more.

[0010] The passivation film having an Al-enriched layer is obtained by subjecting the ferritic stainless steel after annealing to an acid treatment including an electrolytic treatment in nitric acid and a dipping treatment in a mixed acid solution of nitric acid and hydrofluoric acid. It is formed.

[0011]

The present inventors have conducted detailed studies on the effects of the composition of the passive film and the alloying elements on the weather resistance of ferritic stainless steel. As a result, when the concentrated layer of Al is present in the passivation film, improvement in weather resistance is recognized, and the amount of Al in the portion where Al is most concentrated in the passive film is included in the steel. It was found that the effect was increased when the amount of Al was twice or more.

The enrichment of Al in the passivation film is based on Ti and A
After annealing the steel to which l is added in combination, the pickling is promoted by performing an electrolytic treatment in nitric acid and a pickling treatment including a dipping treatment in a mixed acid of nitric acid and hydrofluoric acid. However, for steel to which Al has not been added, or steel to which Al has been added but Ti has not been added, after annealing, electrolytic treatment in nitric acid and immersion treatment in a mixed acid of nitric acid and hydrofluoric acid are performed. Even when pickling was carried out, no or little Al concentration was observed in the passive film.

[0013] Further, although the combined addition of Ti and Al is effective for improving the weather resistance, the addition of more than a certain amount of Ti enhances local corrosion. This is presumed to be due to the fact that, when the amount of Ti added increases, the passivation film becomes stronger, and when the film becomes defective due to a flaw or the like, corrosion concentrates on the defective portion. Furthermore, since excessive addition of Ti tends to cause surface scratches during rolling, working, etc., Ti
It is necessary to minimize the content. For these reasons, when the upper limit of the amount of Ti added is regulated, it is difficult to prevent intergranular corrosion by adding Ti alone. Therefore,
Further, Nb is added in combination. Further, by adding an appropriate amount of Cu and / or Zr, the weather resistance can be further improved.

Hereinafter, the alloy components and the contents of the ferritic stainless steel used as the base material will be described. C, N: elements inevitably contained in stainless steel. When the contents of C and N are reduced, the material becomes soft, the workability is improved, and the generation of carbides and nitrides is reduced. Further, as the C and N contents are reduced, the weldability and the corrosion resistance of the welded portion are also improved. Therefore, the upper limit of the C content is set to 0.02.
The upper limit of the content of N was set to 0.025% by weight, respectively.

Si: An element harmful to hot cracking of the weld and toughness of the weld. Further, since the stainless steel is hardened, the lower the Si content, the better. Therefore, the upper limit of the Si content is set to 0.6% by weight.

Mn: S present in a trace amount in stainless steel
By forming soluble sulfide MnS
It is a harmful element that reduces weather resistance. Therefore, the upper limit of the Mn content is set to 1.0% by weight.

P: Since the toughness of the base material and the weld is impaired, P
The lower the content, the better. However, it is difficult to remove P from Cr-containing steel such as stainless steel, and extremely lowering the P content causes an increase in manufacturing cost. Therefore, the upper limit of the P content is set to 0.04% by weight.

S: Since it is a harmful element that adversely affects weather resistance and hot cracking of a welded portion, it is preferable that the S content is low. Therefore, the upper limit of the S content is set to 0.01% by weight.

Ni: an alloy element effective for improving the toughness of ferritic stainless steel. However, a large amount of Ni causes high cost. In the present invention, the upper limit of the Ni content is set to 1.0% by weight which is mixed as an unavoidable impurity in ordinary ferritic stainless steel.

Cr: a main element for increasing the corrosion resistance of stainless steel, it significantly improves weather resistance, pitting resistance, crevice corrosion resistance and general corrosion resistance. Cr to improve corrosion resistance
Is less than 16% by weight. But,
If the Cr content exceeds 35% by weight, remarkable embrittlement occurs, which causes difficulties in thin plate production, product processing, and the like. Therefore, the Cr content is set in the range of 16 to 35% by weight.

Mo: It is an effective alloying element that enhances weather resistance together with Cr, and its effect increases as the Cr content increases. At the Cr content level specified in the present invention, the Cr content is set to 0.1.
If the Mo content is less than 3% by weight, the effect of improving the weather resistance is small. Conversely, if Mo is added in excess of 6%, the ductility is reduced and the processing becomes difficult. Therefore, the Mo content is set to 0.3 to
It was set in the range of 6% by weight.

Al: An important alloying element for forming a passive film effective for corrosion inhibition. By adding Ti in combination, an Al-enriched layer is easily formed in the passive film by annealing and pickling, and the weather resistance is improved. Al content is 0.0
If it is less than 1% by weight, an Al-enriched layer is hardly formed. Conversely, if Al is added in excess of 0.5% by weight, the surface quality of the material is deteriorated and the weldability is deteriorated. Therefore, the Al content was set in the range of 0.01 to 0.5% by weight.

In cooperation with Nb: Ti, intergranular corrosion is prevented in ferritic stainless steel having a Cr content level specified in the present invention. To obtain this effect, an Nb content of 0.1% by weight or more is required. However, since the addition of excessive Nb impairs the weld toughness, the upper limit of the Nb content is set to 0.6% by weight.

Ti: an important alloying element for forming a passive film effective for inhibiting corrosion. By the addition of a composite with Al, an Al-enriched layer is easily formed in the passive film by annealing and pickling, and the weather resistance is improved. In order to form an Al-enriched layer and suppress intergranular corrosion, it is necessary to contain Ti at 0.05% by weight or more. Further, Ti
It also has the effect of fixing C and N. However, 0.3% by weight
If Ti is contained in excess of the above range, the surface quality of the material tends to deteriorate and local corrosion tends to be enhanced. So T
The i content was set in the range of 0.05 to 0.3% by weight.

Fixed elements such as Nb and Ti are consumed in combination with C and N. Therefore, it is necessary to control the Nb content and the Ti content by the sum of C + N. In this regard, the Nb content and the Ti content are set to Nb + Ti ≧ to fix C and N to improve intergranular corrosion resistance.
It is necessary to satisfy the relationship of 7 (C + N) +0.15. When a large amount of (C + N) is contained, the amounts of Ti and Nb are correspondingly increased, and as a result, the cleanliness of stainless steel is deteriorated. Therefore, the upper limit of the (C + N) amount is set to 0.
It was specified as 04% by weight. The lower the amount of (C + N), the better, and the lower limit is not particularly defined.

Cu, Zr: C added as an optional component
u and Zr are both alloying elements effective for improving the weather resistance. To obtain such an effect, Cu content of less than 0.1% by weight or Zr content of less than 0.05% by weight is not suitable. It is enough. However, if the content is too large, the weld toughness is impaired. Therefore, the upper limit of the Cu content is 1.0% by weight and the content of Zr is 0.3% by weight.

In addition to the provisions regarding the content of each component, B = Cr + 3 (Mo + Cu) ≧ 23.5 and P = 5 (T) among the components Cr, Mo, Al, Ti, Cu, and Zr.
It is necessary that the relationship of (i + Zr) +20 (Al−0.01) ≧ 1.0 is established. These equations are obtained as a result of an experiment by the present inventors. B
The value is an effective index for maintaining good weather resistance, and the P value is effective for forming an Al-enriched layer in the passive film.

Cr and Mo are basic components for improving the weather resistance, and Mo has a larger contribution to the improvement of the weather resistance than Cr. Therefore, the coefficient at the B value is set to three times that of Cr. Since Cu has the same effect as Mo, the coefficient is made the same as Mo. When the B value is less than 23.5%,
Sufficient weather resistance cannot be obtained. Therefore, the lower limit of the B value is 2
It was regulated to 3.5%.

The Al-enriched layer in the passive film is made of Ti and A
1 is easily formed when annealing and pickling stainless steel to which composite addition is added, and the weather resistance is remarkably improved. Also, Z
When r is added in a composite manner, the behavior is almost the same as that of Ti. Therefore, it is considered that Ti has the same effect in forming the Al-enriched layer. However, in order to obtain these effects between Ti, Zr and Al, P
It was determined experimentally that a value was needed.

The amount of Al in the portion where Al is concentrated most in the passivation film is the amount of A contained in the base stainless steel.
When the amount is less than twice the amount of l, the effect of the passive film on the improvement of weather resistance is small. Therefore, the amount of Al in the Al-enriched layer is set to be at least twice the amount of Al contained in the base material.

The Al-enriched layer in the passivation film is formed by annealing and pickling. At this time, the concentration of Al in the passivation film is promoted by pickling including the electrolytic treatment in nitric acid and the immersion treatment in a mixed acid of nitric acid and hydrofluoric acid. The reason why the Al-enriched layer is formed in two steps of the electrolytic treatment and the immersion treatment is presumed as follows.

On the stainless steel surface after annealing, a thicker porous oxide scale is formed as compared with the passive film. This oxide scale contains Al diffused from the substrate,
Ti is enriched. Elements such as Cr and Fe are also included in the oxide scale. When the annealed stainless steel is subjected to nitric acid electrolysis, oxides and sulfides such as Fe and Mn, which are easily eluted, contained in the oxide scale are preferentially removed from the oxide scale, and the concentration of Al is promoted. When the stainless steel after the nitric acid electrolysis is immersed in a mixed acid solution of nitric acid and hydrofluoric acid, the porous oxide scale is removed and a dense passive film is formed. This passivated film is a film having an Al-enriched layer derived from Al concentrated on the oxide scale. Further, the coexistence of Ti promotes densification of the passive film.

[0033] In this respect, if the stainless steel after annealing is subjected to nitric acid electrolysis only, porous oxide scale remains on the surface and does not exhibit sufficient corrosion resistance. In addition, if the nitric acid electrolysis is omitted and only immersion treatment in a mixed acid solution of nitric acid and hydrofluoric acid is performed, the formed passive film does not have Al concentration, and the weather resistance is insufficient.

[0034]

EXAMPLES Various stainless steels having the chemical components shown in Table 1 were melted and hot-rolled to produce hot-rolled sheets having a thickness of 3.5 mm. Then, cold-rolled to a thickness of 1.0 mm,
After annealing at 1000 to 1050 ° C., it was used as a test material.

In Table 1, samples Nos. 1 to 10 are stainless steels satisfying the components and compositions regulated by the present invention.
In each case, Nb and Ti are compounded and added as fixed elements, and Al is contained as a trace element. No.8 is C
No. 9 is Zr-containing steel, No. 10 is Cu, Zr
Contains steel. On the other hand, no Ti was added to the stainless steels of Samples Nos. 11 to 13 and Nos. 11 and 12
Is a stainless steel that does not satisfy the P value specified in the present invention. The stainless steel of sample No. 14 is a stainless steel that does not satisfy the B value.

[0036]

[Table 1]

Each test material was pickled under the conditions shown in Table 2. The electrolytic treatment was performed by immersing the test material in a 5% nitric acid solution maintained at 60 ° C. and performing anodic electrolysis on the test material at a current density of 2.5 A / dm ² . In the immersion treatment using the mixed acid solution, the test material was immersed in a mixed acid solution of 6% nitric acid and 0.5% hydrofluoric acid maintained at 55 ° C. Prior to the electrolytic treatment, a preliminary pickling was performed by immersing some of the test materials in a 5% sulfuric acid solution maintained at 55 ° C. Further, some of the test materials were kept at 55 ° C. after the immersion treatment with the mixed acid solution.
After immersion in an aqueous solution of hydrochloric acid, acid washing was performed.

[0038]

[Table 2]

In Table 2, the pickling conditions A and B are in accordance with the present invention, and the pickling condition B is obtained by adding a dipping treatment in sulfuric acid as pre-pickling. Pickling condition D
In E and E, the immersion treatment in the mixed acid solution of nitric acid and hydrofluoric acid was omitted, and in the pickling condition F, the electrolytic treatment was omitted.

The surface of each of the specimens subjected to the pickling treatment was analyzed by a glow discharge optical emission spectrometer, and the distribution of the alloy elements in the depth direction was measured. FIG. 1 shows several examples of the measurement results. FIG. 1 (a) shows the surface state when the test material of sample No. 2 was treated under the pickling condition A, and FIG.
Shows the surface condition when the test material of sample No. 12 was treated under the pickling condition A. As described above, the concentration distribution of the elements contained in the passivation film formed on the surface of the base material greatly changed depending on the type of the stainless steel used and the pickling conditions.

For each test material after the pickling treatment, the value obtained by dividing the amount of Al in the portion where Al was most concentrated in the passive film by the amount of Al in the base stainless steel (hereinafter referred to as the Al concentration ratio) ) With the P value [= 5 (Ti + Zr) +20 (Al−
0.01)], the result shown in FIG. 2 was obtained. In addition, in FIG.
The sample No. of the stainless steel shown in Table 2 is shown, and the alphabet shows the pickling conditions shown in Table 2.

P = 5 (Ti + Zr) + defined in the present invention
Even if the stainless steel satisfying the requirement of 20 (Al-0.01) and being combined with Ti and Al was subjected to pickling under pickling conditions C to F, the Al concentration ratio was less than 2. Also, P = 5
Sample No. 13 stainless steel satisfying (Ti + Zr) +20 (Al-0.01) but not adding Ti, P = 5 (Ti + Zr) +20 (Al-0.01)
N that does not satisfy the conditions and does not contain Ti and / or Al
o For stainless steels 11 and 12, pickling conditions A or B
, The Al concentration ratio was less than 2. From this, P = 5 (Ti + Zr) +20 (Al−0.0
It can be seen that an Al concentration ratio of 2 or more can be obtained only when A or B is pickled using stainless steel that satisfies 1) and that combines Ti and Al.

Pickling conditions A were applied to the stainless steels shown in Table 1.
And C were pickled (hereinafter referred to as pickling material), and the pitting potential was measured. The measurement was performed using a 20% NaCl solution deaerated with Ar while maintaining the liquid temperature at 80 ° C., and the sweep rate was 20 mV /
Min electrokinetic method. The measured pitting potential is calculated as B value [=
[Cr + 3 (Mo + Cu)] is shown in FIG.

A sample No. satisfying the composition specified in the present invention.
Regarding the stainless steels 1 to 10, the pitting potential of the pickling material A was significantly higher than that of the pickling material C. However, Sample Nos. 11 to 11 out of the composition range regulated by the present invention were used.
No. 14 stainless steel showed no significant difference in pitting potential between pickling materials A and C, and both had lower pitting potential than pickling material A of samples No. 1 to No. 10. I understand. Also, Al
The pickling material A of sample No. 14 having a concentration ratio of 2 or more also had a low pitting potential, which was due to Cr + 3 (Mo + Cu).
Is smaller than the lower limit of 23.5.

A sample No. satisfying the composition specified in the present invention.
FIG. 4 shows the results obtained by subjecting the stainless steel No. 2 to pickling under pickling conditions A to F and measuring the pitting potential. Also, for comparison,
The stainless steel of sample No. 12, which does not satisfy the composition specified in the present invention, was similarly pickled and the pitting potential was measured. The measurement of the pitting potential was based on the same electrokinetic method as in FIG.

As is clear from FIG. 4, in the sample No. 2, it is found that the pickling conditions greatly affect the pitting potential. That is, even if the components and compositions are the same stainless steel, the pitting potential of the pickling materials A and B is significantly higher than that of the pickling materials C to F. On the other hand, the sample No.
In stainless steel No. 12, no significant difference was detected in the pitting potential between the pickling materials A to F due to the difference in the pickling conditions. From this, it can be said that the pickling under the pickling conditions A and B is effective for stainless steel to which Ti and Al are added in combination.

For the stainless steel pickling materials A and C of Sample Nos. 1, 2, 5, 6, 11 to 13, a combined salt-dry and wet cycle test was conducted. In this test, 5% NaCl aqueous solution was sprayed for 15 minutes → 60 ° C, RH: dried at 20 to 30% for 1 hour → wet at 50 ° C, RH 90 to 95% for 3 hours, and repeated after 400 cycles. The rust state is determined by the rate of red rust occurrence. The rate of red rust generation is based on JIS D
0201. As is clear from FIG. 5 showing the test results, Sample N satisfying the composition specified in the present invention.
The pickling material A of o, 1, 2, 5, and 6 has a small rust generation rate of 5% or less as compared with other pickling agents, and it is understood that it is excellent in weather resistance.

[0048]

As described above, in the present invention, the Al enrichment of the passive film formed on the surface of the base material of the ferritic stainless steel whose component and content are specified is determined by the Al content of the base material. More than twice. The combination of the Al concentration and the component system of the base material provides excellent weather resistance. The stainless steel on which the passivation film is formed is used in a wide range of fields as a structural material for roofing materials, exterior materials, outdoor tanks such as hot water storage tanks, etc., utilizing the property of excellent weather resistance.

[Brief description of the drawings]

FIG. 1 is a graph showing the change in element concentration in the depth direction by subjecting a test material after pickling to surface analysis using a glow discharge optical emission spectrometer.

FIG. 2 is a graph showing a relationship between an Al concentration ratio and a P value.

FIG. 3 is a graph showing the relationship between the pitting potential of pickling materials A and C and the B value.

FIG. 4 is a graph showing the effect of differences in pickling conditions on pitting potential.

FIG. 5 is a graph showing rust generation rates of pickling materials A and C.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazu Shirayama 4976 Nomura Minami-cho, Shinnanyo-shi, Yamaguchi Prefecture Inside Nisshin Steel Co., Ltd. Steel Research Laboratory (56) References JP-A-5-70899 (JP, A) JP-A Sho JP-A-49-31523 (JP, A) JP-A-49-59021 (JP, A) JP-A-63-118011 (JP, A) JP-A-2-115346 (JP, A) JP-A-4-80347 (JP, A A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 9/46-9/48

Claims (5)

(57) [Claims] 1. C: 0.025% by weight or less, Si: 0.
6% by weight or less, Mn: 1.0% by weight or less, P: 0.04
% By weight, S: 0.01% by weight or less, Ni: 1.0% by weight or less, Cr: 16 to 35% by weight, Mo: 0.3 to 6%
% By weight, N: 0.025% by weight or less, Al: 0.01 to
0.5% by weight, Nb: 0.1 to 0.6% by weight, Ti:
Contains 0.05-0.3% by weight, with the balance being Fe and inevitable
And C + N ≦ 0.04% by weight and N
b + Ti ≧ 7 (C + N) +0.15, and B ₁ = C
B ₁ value defined by r + 3Mo is 23.5 or more, P ₁ = 5
Ti + 20 ferritic stainless steel P ₁ value defined by (Al-0.01) of 1.0 or more as a base material, Al amount of the portion most Al is concentrated is contained in said base material A ferritic stainless steel sheet having excellent weather resistance, characterized in that a passivation film having an Al-enriched layer that is twice or more the amount of Al is formed on the surface of the base material. 2. C: 0.025% by weight or less, Si: 0.
6% by weight or less, Mn: 1.0% by weight or less, P: 0.04
% By weight, S: 0.01% by weight or less, Ni: 1.0% by weight or less, Cr: 16 to 35% by weight, Mo: 0.3 to 6%
% By weight, N: 0.025% by weight or less, Al: 0.01 to
0.5% by weight, Nb: 0.1 to 0.6% by weight, Ti:
0.05 to 0.3% by weight, Cu: 0.1 to 1.0% by weight
With the balance being Fe and unavoidable impurities, and C + N ≦ 0.04% by weight and Nb + Ti ≧ 7 (C + N)
+0.15, the B ₂ value defined by B ₂ = Cr + 3 (Mo + Cu) is 23.5 or more, and P ₁ = 5Ti + 20
P ₁ value defined by (Al-0.01) is a ferritic stainless steel as a base material is 1.0 or more, most A
A passivation film having an Al-enriched layer in which the amount of Al in which l is concentrated is at least twice the amount of Al contained in the base material is formed on the surface of the base material. Ferritic stainless steel sheet with excellent weather resistance. 3. C: 0.025% by weight or less, Si: 0.
6% by weight or less, Mn: 1.0% by weight or less, P: 0.04
% By weight, S: 0.01% by weight or less, Ni: 1.0% by weight or less, Cr: 16 to 35% by weight, Mo: 0.3 to 6%
% By weight, N: 0.025% by weight or less, Al: 0.01 to
0.5% by weight, Nb: 0.1 to 0.6% by weight, Ti:
0.05 to 0.3% by weight, Zr: 0.05 to 0.3% by weight, the balance being Fe and unavoidable impurities, and C + N ≦ 0.04% by weight and Nb + Ti ≧ 7 (C +
N) +0.15, the B ₁ value defined by B ₁ = Cr + 3Mo is 23.5 or more, and P ₂ = 5 (Ti + Zr) +2
The base material is a ferritic stainless steel having a P ₂ value of 1.0 or more defined as 0 (Al-0.01), and the Al content of the most Al-enriched portion is contained in the base material. A ferritic stainless steel sheet having excellent weather resistance, characterized in that a passivation film having an Al-enriched layer that is twice or more the amount of Al is formed on the surface of the base material. 4. C: 0.025% by weight or less, Si: 0.
6% by weight or less, Mn: 1.0% by weight or less, P: 0.04
% By weight, S: 0.01% by weight or less, Ni: 1.0% by weight or less, Cr: 16 to 35% by weight, Mo: 0.3 to 6%
% By weight, N: 0.025% by weight or less, Al: 0.01 to
0.5% by weight, Nb: 0.1 to 0.6% by weight, Ti:
0.05 to 0.3% by weight, Cu: 0.1 to 1.0% by weight, Zr: 0.05 to 0.3% by weight, the balance being Fe
And B + Ti ≦ 7 (C + N) +0.15, and the B ₂ value defined by B ₂ = Cr + 3 (Mo + Cu) is 23.5 or more. ₂ = 5 (Ti + Zr) +20 (Al−
0.01) The base material is a ferritic stainless steel having a P ₂ value of 1.0 or more, and the Al content of the portion where Al is concentrated most is the Al content in the base material.
A ferritic stainless steel sheet excellent in weather resistance, wherein a passivation film having an Al-enriched layer whose amount is twice or more the amount thereof is formed on the surface of the base material. 5. After the ferritic stainless steel according to claim 1 is annealed, an acid treatment including an electrolytic treatment in nitric acid and a dipping treatment in a mixed acid solution of nitric acid and hydrofluoric acid is performed. A method for producing a ferritic stainless steel sheet having excellent weather resistance, wherein the method is performed.