JP5125600B2 - Ferritic stainless steel with excellent high-temperature strength, steam oxidation resistance and workability - Google Patents

Description

  The present invention relates to ferritic stainless steel, and in particular, high temperature strength, steam oxidation resistance used for members used in high temperature environments such as automobile and motorcycle exhaust pipes, catalyst outer cylinders, and exhaust ducts of thermal power plants. The present invention relates to ferritic stainless steel having excellent properties and workability.

  Materials used for exhaust system members typified by automobile exhaust manifolds, exhaust pipes, converter cases, and mufflers are required to be excellent in moldability and heat resistance. Therefore, for such applications, type 429 (14Cr-0.9Si-0.4Nb) steel added with Nb and Si, which has excellent moldability at room temperature and relatively high proof stress at high temperature, has been conventionally used. Many Cr-containing steels are used. However, as the engine performance improves, the exhaust gas temperature tends to rise, and when the temperature rises to near 900 ° C., Type 429 steel has become insufficient in high-temperature proof stress.

  In order to solve this problem, Cr-containing steel in which Nb and Mo are added to improve high-temperature yield strength, SUS444 (19Cr-0.2Nb-1.8Mo) steel defined in JIS G4305, and the like have been developed. Yes. However, in response to improvements in automobile fuel efficiency and stricter exhaust gas regulations, the temperature of exhaust gas from engines tends to rise further, and materials used for automobile exhaust system members have better heat resistance. Is becoming required. In addition, increasing the high-temperature strength of the materials used for exhaust system members enables thinning of the members and contributes to the weight reduction of the automobile body, so that the demand for improvement of the high-temperature strength is increasing.

Under such circumstances, various materials for exhaust system members have been developed. For example, Patent Documents 1 to 5 disclose Cr-containing steel and ferritic stainless steel in which high temperature strength and oxidation resistance are improved by adding W in addition to addition of Nb and Mo. Patent Documents 6 to 8 disclose Cr-containing steels and ferritic stainless steels that have improved high-temperature strength by adding Cu in addition to the addition of Nb, Mo, and W.
Japanese Patent Laid-Open No. 2002-212585 JP 2003-213377 A JP 2004-018921 A JP 2004-018914 A JP 2004-076154 A JP 2005-206944 A JP 2001-303202 A JP 2002-004011 A

  However, the Cr-containing steel and ferritic stainless steel disclosed in Patent Documents 1 to 5 are insufficient in heat resistance for use in exhaust system members. In addition, Cr-containing steels and ferritic stainless steels disclosed in Patent Documents 6 to 8 need to add a large amount of alloy elements such as Nb, Mo, W, and Cu, so that the workability of the steel sheet is lowered. There is a problem that the processing of parts must be performed warmly. In particular, when Cu is added in excess of 1%, there is a problem that ε-Cu is precipitated at the time of final annealing cooling in the steel sheet manufacturing process, and the room temperature workability is lowered. Further, when Cu is added in excess of 1%, a new problem that has not been known so far has been revealed that oxidation resistance is reduced in an environment containing water vapor of 900 ° C. or higher.

Accordingly, an object of the present invention is to advantageously solve the above-mentioned problems of the prior art, and has a high strength and excellent steam oxidation resistance even at a high temperature of 900 ° C., and a ferritic stainless steel having excellent workability at room temperature. Is to propose. Here, “high strength” in the present invention means that the 0.2% yield strength at 900 ° C. is 27 MPa or more and the 0.2% yield strength at 650 ° C. is 280 MPa or more. “Excellent steam oxidation resistance” means that the increase in oxidation when held in air having a dew point of + 55 ° C. for 1000 hours × 200 hours is 5 mg / cm ² or less. Further, “excellent processability at room temperature” means that the hole expansion rate at room temperature (20 ° C.) is 120% or more.

In order to solve the above-mentioned problems, the inventors paid attention to the component system possessed by the ferritic stainless steel and conducted extensive studies. As a result, by adding 0.3 to 1.0 mass% of Nb, 3.0 to 5.8 mass% of (Mo + W), and further adding 1.0 to 2.5 mass% of Cu to ferritic stainless steel. It has been found that high high-temperature strength can be obtained in a wide temperature range. Moreover, with respect to the decrease in hole expansibility associated with the addition of Cu, an appropriate amount of Al is added, and the content of Cr, Mo, W, Al, and Cu is expressed by the following formula (1);
0.2 × Cr + 10 × Si + 0.3 × Mo + 0.2 × W + 2 × (Nb−0.4) + 5 × (Cu−1) ≦ 11 (1)
In addition, the content of Cr, Mo, W, Nb and Cu is further reduced after reducing the Si content with respect to the decrease in steam oxidation resistance due to the addition of Cu. Is the following formula (2):
Cr + 2 × Mo + 0.5 × W + 12 × Al-4 × Cu ≧ 13.5 (2)
The present inventors have found that it is effective to control within an appropriate range so as to satisfy the above condition, and completed the present invention.

That is, the present invention includes C: 0.015 mass% or less, Si: 0.10 mass% or less, Mn: 2.0 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Cr: 14. 0 to 20.0 mass%, Ni: 1.0 mass% or less, N: 0.015 mass% or less, Nb: 0.3 to 1.0 mass%, Cu: 1.0 to 2.5 mass%, Al: 0.01 -0.30mass%, Mo: 0.8-3.0mass%, W: 1.0-5.0mass% and (Mo + W): 3.0-5.8mass% are satisfy | filled, Furthermore, the said component Are the following formulas (1) and (2);
0.2 × Cr + 10 × Si + 0.3 × Mo + 0.2 × W + 2 × (Nb−0.4) + 5 × (Cu−1) ≦ 11 (1)
Cr + 2 × Mo + 0.5 × W + 12 × Al-4 × Cu ≧ 13.5 (2)
Is a ferritic stainless steel having a component composition consisting of Fe and inevitable impurities.

Ferritic stainless steels of the present invention, in addition to the above chemical composition, B: 0.003 mass% or less, Ti: 0.25 mass% or less, REM: 0.08 mass% or less, Zr: 0.5 mass% hereinafter Contact And Co: one or more selected from 0.5 mass% or less.

  According to the present invention, it is possible to obtain a ferritic stainless steel not only having excellent heat resistance even at a high temperature of 900 ° C., but also having high proof stress and excellent steam oxidation resistance, and also excellent workability at room temperature. Can do. Therefore, the ferritic stainless steel of the present invention can be suitably used as a material for automobile exhaust system members, exhaust path members of thermal power generation systems, and solid oxide fuel cell members. Furthermore, since the ferritic stainless steel of the present invention contains Mo and W effective for improving the corrosion resistance, it can be used in applications where corrosion resistance is required.

The basic experiment that triggered the development of the present invention will be described.
C: 0.005-0.007 mass%, N: 0.004-0.006 mass%, Mn: 0.4 mass%, Cr: 15-17 mass%, Nb: 0.4-0.6 mass%, Mo: 1 .5 mass%, W: 2.7 mass%, Cu: 1.6 mass% and Al: 0.03 mass% as base compositions, and variously changing the Si content in the laboratory, It was cold-rolled, cold-rolled, and annealed to obtain a cold-rolled steel sheet having a thickness of 2 mm, which was subjected to the following hole expansion test.

In the hole expansion test, a hole having an initial hole diameter d ₀ (= 10 mmφ) is punched in the center of the test piece, a conical punch is pushed into the hole, and a crack generated in the periphery of the hole penetrates the plate thickness. The value λ obtained by the following formula is defined as the hole expansion rate.
Hole expansion rate λ (%) = {(d−d ₀ ) / d ₀ } × 100

FIG. 1 shows the result, and the component composition of the steel sheet is the following formula (1);
0.2 × Cr + 10 × Si + 0.3 × Mo + 0.2 × W + 2 × (Nb−0.4) + 5 × (Cu−1) ≦ 11 (1)
It can be seen that a hole expansion ratio of 120% or more is obtained when the above condition is satisfied.

  Next, C: 0.006 mass%, N: 0.007 mass% N, Si: 0.06 mass%, Mn: 0.4 mass%, Cr: 16 mass%, Nb: 0.49 mass%, Mo: 1.7 mass% , W: 2.3 mass% and Cu: 1.39 mass%, and various steels with various contents of Al were melted in the laboratory, hot-rolled, cold-rolled, and finished. A cold rolled steel sheet having a thickness of 2 mm was obtained by annealing. Next, a test piece was collected from the cold-rolled steel sheet, and subjected to a steam oxidation test that was held in an atmospheric furnace heated to 1000 ° C. at a dew point of + 55 ° C. for 200 hours, and an increase in oxidation was measured from a change in weight before and after the test.

FIG. 2 shows the result, and the component composition of steel is the following formula (2);
Cr + 2 × Mo + 0.5 × W + 12 × Al-4 × Cu ≧ 13.5 (2)
When satisfying the above, it was found that the oxidation increase was 5 mg / cm ² or less, and excellent steam oxidation resistance was obtained.
The present invention has been developed based on the above findings and further studies.

Next, the component composition that the ferritic stainless steel according to the present invention should have will be described.
C: 0.015 mass% or less C is an element effective for increasing the strength of steel, and is preferably contained in an amount of 0.001 mass% or more in order to ensure a desired strength. On the other hand, when C is contained exceeding 0.015 mass%, deterioration of toughness and formability becomes remarkable. Therefore, in the present invention, C: 0.015 mass% or less. In addition, from the viewpoint of ensuring moldability, the lower the C content, the better, and 0.008 mass% or less is preferable. More preferably, C is 0.002 to 0.008 mass%.

Si: 0.10 mass% or less Si, as in the ferritic stainless steel of the present invention, contains Nb, Mo, W and further contains 1 mass% or more of Cu, as can be seen from the basic experiment described above. In order to improve hole expansibility, the lower the value on the left side of equation (1), the better. Therefore, the lower the Si content, the greater the influence coefficient, the better. Therefore, in the present invention, from the viewpoint of improving hole expandability and toughness at room temperature, the Si content is set to 0.10 mass% or less. More preferably, it is Si: 0.07 mass% or less

Mn: 2.0 mass% or less Mn is added as a deoxidizer and to increase the strength of the steel sheet, but the addition of excess Mn promotes the formation of a γ phase at high temperatures and reduces heat resistance. Let Therefore, in this invention, Mn content shall be 2.0 mass% or less. Preferably it is 1.5 mass% or less.

P: 0.040 mass% or less P is an impurity that is inevitably mixed in steel, and is a harmful element that lowers toughness. Therefore, it is desirable to reduce it as much as possible. Therefore, in this invention, it is 0.040 mass% or less. Preferably it is 0.030 mass% or less.

S: 0.010 mass% or less S is an impurity inevitably mixed in the steel, and lowers the elongation and r-value of the steel sheet, promotes precipitation of the Laves phase, hardens the steel, and lowers formability. It is a harmful element. Moreover, since it is also an element which reduces the corrosion resistance which is the basic characteristic of stainless steel, it is desirable to reduce it as much as possible. Therefore, in this invention, S is made into 0.010 mass% or less.

Cr: 14.0 to 20.0 mass%
Cr is a component necessary for ensuring the corrosion resistance of ferritic stainless steel, and is an important element for improving the steam oxidation resistance particularly in the steel of the present invention. In order to acquire the said effect, it is necessary to add Cr 14.0 mass% or more. On the other hand, Cr strengthens the solid solution and raises the hardness at room temperature to lower the ductility. In particular, when Cr is contained in excess of 20.0 mass%, this effect becomes significant, so the Cr content is 20.0 mass% or less. Therefore, in this invention, Cr is taken as the range of 14.0-20.0 mass%.

Ni: 1.0 mass% or less Ni is an element that improves the toughness of steel. However, Ni is not only expensive, but is a strong γ-phase-forming element, promotes the formation of γ-phase at high temperatures, and reduces oxidation resistance. Therefore, Ni is set to 1.0 mass% or less. Preferably, it is the range of 0.05-0.6 mass%.

N: 0.015 mass% or less N is an element that lowers the toughness and formability of steel, and when it exceeds 0.015 mass%, this effect becomes significant. For this reason, it is preferable to reduce N as much as possible. In the present invention, N is set to 0.015 mass% or less. Preferably it is 0.010 mass% or less.

Nb: 0.3-1.0 mass%
Nb is an element that fixes C and N and improves high temperature strength, formability, corrosion resistance, and intergranular corrosion resistance of welds. Such an effect is recognized by containing Nb: 0.3 mass% or more. On the other hand, when it contains exceeding 1.0 mass%, steel will embrittle. Therefore, Nb is set to a range of 0.3 to 1.0 mass%. Preferably it is the range of 0.4-0.6 mass%.

Cu: 1.0-2.5 mass%
Cu precipitates as ε-Cu in the temperature range of 500 to 750 ° C., thereby effectively contributing to improvement of strength in a wide temperature range from room temperature to the precipitation temperature. In particular, in order to achieve 0.2% proof stress at 650 ° C., which is the object of the present invention: 280 MPa or more, 1.0 mass% or more of Cu must be added. On the other hand, if the Cu content exceeds 2.5 mass%, a large amount of ε-Cu precipitates during cooling in the final annealing of steel sheet production, and the hole expandability and the toughness decrease significantly. Therefore, in order to achieve both high strength, workability, and toughness, Cu is set in the range of 1.0 to 2.5 mass%.

Al: 0.01-0.30 mass%
Al is an element necessary for improving the steam oxidation resistance. As can be seen from the coefficient on the left side of the formula (2) described later, a large effect can be obtained even with a relatively small amount of addition. However, when the Al content is 0.01 mass% or less, the steam oxidation resistance aimed by the present invention cannot be obtained. On the other hand, when it exceeds 0.3 mass%, it will have a bad influence on hole expansibility. Therefore, in the present invention, the Al content is in the range of 0.01 to 0.30 mass%. More preferably, it is the range of 0.02-0.10 mass%.

Mo: 0.8-3.0 mass%
Mo is an important component in the present invention that has the effect of increasing the yield strength at high temperatures and improving the corrosion resistance and oxidation resistance by being present in a solid solution state in steel. Such an effect is recognized by addition of 0.8 mass% or more. On the other hand, when the content exceeds 3.0 mass%, precipitation of the Laves phase becomes remarkable, the amount of Mo existing in the solid solution state decreases, and the contribution to the improvement of high-temperature proof stress and corrosion resistance becomes small, and the strength at normal temperature is reduced. Increases the workability. Therefore, Mo is set to a range of 0.8 to 3.0 mass%. Preferably, it is the range of 1.0-3.0 mass%.

W: 1.0-5.0 mass%
W, like Mo, is an important component in the present invention because it has the effect of increasing high-temperature proof stress and improving corrosion resistance and oxidation resistance by being present in a solid solution state in steel. Such an effect is recognized by containing 1.0 mass% or more. On the other hand, if it exceeds 5.0 mass%, the Laves phase precipitates significantly, the amount of W existing in a solid solution state is saturated, and the toughness and workability are reduced. Therefore, W is set to a range of 1.0 to 5.0 mass%. Preferably it is the range of 2.0-4.0 mass%.

(Mo + W): 3.0 to 5.8 mass%
Mo and W are components having the same effect as described above. However, in order to achieve the high temperature strength targeted by the present invention, that is, 0.2% proof stress at 900 ° C .: 27 MPa or more and 0.2% proof stress at 650 ° C .: 280 MPa or more, the total amount of Mo and W ( Mo + W) needs to be 3.0 mass% or more. On the other hand, when (Mo + W) exceeds 5.8 mass%, the above-described effects are saturated, and toughness and workability are lowered. Therefore, (Mo + W) is in the range of 3.0 to 5.8 mass%. Preferably it is the range of 3.5-5.0 mass%.

0.2 × Cr + 10 × Si + 0.3 × Mo + 0.2 × W + 2 × (Nb−0.4) + 5 × (Cu−1) ≦ 11 (1)
The hole expandability of the steel sheet is affected by various metallurgical factors. In particular, in order to obtain high-temperature strength characteristics as in the steel sheet of the present invention, in a component system containing a large amount of Nb, Mo, W, and Cu, Laves phase precipitation due to addition of Nb, Mo, and W, Cu Precipitation of the ε-Cu phase is caused by the addition. In such a steel sheet, at the time of processing, the interface between these precipitation phases and the parent phase becomes a starting point of crack generation, and the hole expandability decreases. In particular, as shown in FIG. 1, when the value of the left side of equation (1) exceeds 11, the hole expansibility is drastically lowered. Therefore, in the present invention, each component composition is controlled within an appropriate range so as to satisfy 0.2 × Cr + 10 × Si + 0.3 × Mo + 0.2 × W + 2 × (Nb−0.4) + 5 × (Cu−1) ≦ 11. There is a need.

  Here, the left side of the expression (1) is an expression representing the contribution of each component that affects the hole expandability. From this equation, it can be seen that controlling Si and Cu having a large coefficient within an appropriate range is extremely important for improving hole expansibility.

Cr + 2 × Mo + 0.5 × W + 12 × Al-4 × Cu ≧ 13.5 (2)
Cu is a component that reduces steam oxidation resistance. Therefore, in order to eliminate the adverse effects caused by Cu, it is necessary to make the balance with Cr, Mo, W and Al, which are components improving the steam oxidation resistance, within an appropriate range. In particular, in the component system in which Si, which is an element for improving oxidation resistance, is reduced as in the present invention, it is extremely important to maintain this balance. As shown in FIG. 2, in the component system of the present invention, in order to improve the steam oxidation resistance, the left side of the above-described formula (2) needs to be 13.5 or more, and this condition is satisfied. Therefore, the increase in oxidation due to steam oxidation is set to 5 mg / cm ² or less when the steam oxidation test is performed by continuously heating the target value of the present invention, that is, dew point + 55 ° C. in air at 1000 ° C. for 200 hours. can do. Therefore, in this invention, each component composition is controlled to an appropriate range so that Cr + 2 × Mo + 0.5 × W + 12 × Al-4 × Cu ≧ 13.5 may be satisfied.

In addition to the above components, the ferritic stainless steel of the present invention may further contain one or more selected from B, Ti, REM, Zr, V and Co in the following range.
B: 0.003 mass% or less B is an element effective for improving workability, particularly secondary workability. This effect is manifested at B: 0.0005 mass% or more. On the other hand, if the content exceeds 0.003 mass%, a large amount of BN is generated, resulting in a decrease in workability. Therefore, when adding B, it is preferable to set it as 0.003 mass% or less.

Ti: 0.25 mass% or less Ti is an effective component for improving elongation and r value. However, when it exceeds 0.25 mass%, the reduction in steam oxidation resistance becomes significant. Therefore, when adding Ti, it shall be 0.25 mass% or less.

REM: 0.08 mass% or less, Zr: 0.5 mass%
REM (rare earth element) and Zr are both elements that improve oxidation resistance, and can be contained as necessary. However, the content exceeding REM: 0.08 mass% embrittles the steel. Further, if the Zr content exceeds 0.5 mass%, a Zr intermetallic compound precipitates, and the steel is also embrittled. For this reason, when adding REM, it is preferable to set it as 0.08 mass% or less, and when adding Zr, it is preferable to set it as 0.5 mass% or less.

V: 0.5 mass% or less V is an element effective for improving moldability. However, excessive content exceeding 0.5 mass% causes coarse V (C, N) to precipitate and deteriorates the surface properties. For this reason, when adding V, it is preferable to set it as 0.5 mass% or less.

Co: 0.5 mass% or less Co is an element effective for improving toughness, but the effect is saturated even when added in excess of 0.5 mass%. Moreover, since Co is also an expensive component, when adding it, 0.5 mass% or less is preferable.
In the steel sheet of the present invention, the balance other than the above components is Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.

  The manufacturing method of the ferritic stainless steel of this invention is not specifically limited, A well-known method is applicable. For example, steel having a component composition suitable for the present invention is melted by a known method such as a converter or an electric furnace, and further subjected to secondary refining such as ladle refining or vacuum refining, and then continuous casting. Steel strip (slab) is formed by the method or ingot-bundling rolling method. Then, it is preferable to make it a cold-rolled annealing board through each process of hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and pickling sequentially. The cold rolling may be performed once or twice or more with intermediate annealing. Further, in addition to cold rolling, finish annealing and pickling steps may be repeated. Moreover, you may abbreviate | omit hot-rolled sheet annealing. Furthermore, when glossiness is required on the steel sheet surface, a skin pass or the like may be applied.

  No. having the component composition shown in Table 1. Steels 1 to 20 were melted in a vacuum melting furnace to form 50 kg steel ingots. These steel ingots were heated to 1170 ° C. and then hot-rolled to form hot rolled sheets having a thickness of 5 mm. Subsequently, these hot-rolled sheets are subjected to hot-rolled sheet annealing (annealing temperature: 1040 ° C.), pickling, cold rolling (cold rolling reduction ratio: 60%), and finish annealing (annealing temperature: 1050 ° C., average). (Cooling rate: 20 ° C./sec) and pickled to obtain a cold-rolled annealed plate having a thickness of 2 mm. As reference examples, cold-rolled annealed plates were prepared in the same manner for the steel sheets described as Examples in Patent Documents 6 to 8, and No. 1 is shown in Table 1. Shown as 21-24.

The various cold-rolled annealed plates obtained as described above were subjected to the following evaluation tests.
(1) High-temperature strength Two tensile test pieces each having the rolling direction as the tensile direction were sampled from each cold-rolled annealed plate, and strains were measured at temperatures of 900 ° C. and 650 ° C. in accordance with JIS G0567. Speed: Perform high-temperature tensile test at 0.3% / min and measure 0.2% yield strength (σ _{0.2 at} 900 ° C.) at 900 ° C. and 0.2% yield strength (σ _{0.2 at} 650 ° C.) at 650 ° C. did. The evaluation of the high-temperature strength is as follows: σ _{0.2 at} 900 ° C. is good (◯) for 27 MPa or more, poor (×) if it is less than 27 MPa, and σ _{0.2 at} 650 ° C. is good (◯) for 280 MPa or more. Less than 280 MPa was determined to be defective (x).
(2) Hole expandability After punching an initial hole of d ₀ = 10 mmφ in each cold-rolled annealed plate, a conical punch is pushed into the hole and a hole expansion test is performed. Measure the hole diameter d when the penetrating crack occurs, and calculate the hole expansion rate λ by the following formula:
Hole expansion rate λ (%) = {(d−d ₀ ) / d ₀ } × 100
I asked for it. For the evaluation of the hole expandability, each cold-rolled annealed plate was subjected to five tests, and the average value of λ was determined to be good (◯) and less than 120% as poor (x).
(3) Steam oxidation resistance A 30 mm × 20 mm sample was cut out from each cold-rolled annealed plate, a 4 mmφ hole was made in the upper part of the sample, and the surface and end face were polished with emery paper (# 320), degreased, It was heated to 1000 ° C., suspended in a furnace in an air atmosphere humidified to a dew point of + 55 ° C., and held for 200 hours. After the test, the mass of the sample was measured, the difference from the mass before the test was calculated, and the oxidation increase was determined. This steam oxidation test was carried out twice. When the average value was 5 mg / cm ² or less, the steam oxidation resistance was good (◯), and when it exceeded 5 mg / cm ² , the steam oxidation resistance was poor (×). It was determined.

The results of the above test are shown in Table 2. From Table 2, all the steel sheets of the present invention have a 0.2% yield strength (σ _{0.2 at} 900 ° C.) at 900 ° C. of 27 MPa or more and a 0.2% yield strength (σ _{0.2 at} 650 ° C.) at 650 ° C. It can be seen that it has excellent high-temperature strength of 280 MPa or more, excellent workability with a hole expansion rate of 120% or more, and excellent oxidation resistance with an increase in oxidation of 5 mg / cm ² or less. On the other hand, it can be seen that none of the comparative examples or the prior art steel sheets outside the scope of the present invention satisfy one or more of the above characteristics.

  The ferritic stainless steel of the present invention can be suitably used as a material for automobile exhaust system members, exhaust path members of thermal power generation systems, solid oxide fuel cell members, and for applications that require further corrosion resistance. Can also be used.

It is a graph which shows the influence of (1) Formula left side which acts on a hole expansion rate. It is a graph which shows the influence of the (2) type | formula left side which acts on oxidation increase.

Claims (2)

C: 0.015 mass% or less, Si: 0.10 mass% or less, Mn: 2.0 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Cr: 14.0 to 20.0 mass% Ni: 1.0 mass% or less, N: 0.015 mass% or less, Nb: 0.3 to 1.0 mass%, Cu: 1.0 to 2.5 mass%, Al: 0.01 to 0.30 mass%, Mo: 0.8 to 3.0 mass%, W: 1.0 to 5.0 mass%, and (Mo + W): 3.0 to 5.8 mass% are satisfied. Further, the above components are represented by the following formula (1) And (2) formula;
0.2 × Cr + 10 × Si + 0.3 × Mo + 0.2 × W + 2 × (Nb−0.4) + 5 × (Cu−1) ≦ 11 (1)
Cr + 2 × Mo + 0.5 × W + 12 × Al-4 × Cu ≧ 13.5 (2)
And ferritic stainless steel having a component composition in which the balance is composed of Fe and inevitable impurities. In addition to the above chemical composition, B: 0.003 mass% or less, Ti: 0.25 mass% or less, REM: 0.08 mass% or less, Zr: 0.5 mass% hereinafter Contact and Co: less 0.5 mass% The ferritic stainless steel according to claim 1, comprising one or more selected from among them.

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