JP6798297B2 - Stainless steel - Google Patents

Description

The present invention relates to stainless steel.

In recent years, the development of fuel cell vehicles that run on hydrogen as fuel and the practical research of hydrogen stations that supply hydrogen to fuel cell vehicles have been promoted. Stainless steel is one of the candidate materials used for applications such as in-vehicle piping, containers, valves or fittings of fuel cell vehicles. However, in a high-pressure hydrogen gas environment, even stainless steel may cause embrittlement due to hydrogen gas (hydrogen environment embrittlement). According to the standards for exemplifying compressed hydrogen containers for automobiles stipulated in the High Pressure Gas Safety Act, the use of austenitic SUS316L as a stainless steel that does not cause hydrogen embrittlement is permitted.

However, considering the weight reduction of fuel cell vehicles and the need for high-pressure operation of hydrogen stations, stainless steel used for containers or pipes has a high strength of SUS316L or higher, and hydrogen is used in a hydrogen gas environment. There is a demand for stainless steel that does not cause environmental embrittlement.

In response to such needs, for example, Patent Document 1 uses precipitation strengthening of the γ'phase (Ni ₃ Ti), which is an intermetallic compound, to have a tensile strength of 1150 MPa or more and in a hydrogen gas environment. Stainless steels that do not cause hydrogen embrittlement are disclosed. Further, Patent Document 2 proposes an Fe—Ni group alloy having excellent high temperature characteristics and hydrogen embrittlement characteristics, which does not contain the η phase in the metal structure and contains the γ'phase at a volume fraction of 15% or more. There is.

Japanese Unexamined Patent Publication No. 2014-047409 Japanese Unexamined Patent Publication No. 2014-129576

The strength of the alloy can be extremely increased by using the precipitation strengthening of the γ'phase, but there is still room for improvement because the hot workability of such an alloy may deteriorate.

An object of the present invention is to solve the above problems and to provide a stainless steel having excellent hot workability and excellent mechanical properties in a high-pressure hydrogen gas environment.

The present invention has been completed in order to solve the above problems, and the gist of the present invention is the following stainless steel.

(1) The chemical composition is mass%
C: 0.08% or less,
Si: 0.2-1.0%,
Mn: 0.2-2.0%,
P: 0.04% or less,
S: 0.0003 to 0.005%,
Ni: 20.0 to 32.0%,
Cr: 12.0 to 23.0%,
Ti: 2.0-5.0%,
Al: 0.5-3.0%,
N: 0.02% or less,
B: 0.0005 to 0.010%,
V: 0-1.0%,
Nb: 0-1.0%,
Ta: 0-1.0%,
Hf: 0-1.0%,
Mo: 0-3.0%,
W: 0-6.0%,
Cu: 0-5.0%,
Co: 0-3.0%,
Including,
Mg: 0.0001 to 0.010%,
Ca: 0.0001 to 0.010%, and
REM: 0.001 to 0.10%,
Including one or more selected from
The rest is Fe and impurities,
Satisfy the following equations (i) to (iii),
Stainless steel.
3.5 ≤ Ti + 48/27 Al ≤ 6.5 ... (i)
0.30 ≤ Ti / (Ti + 48/27 Al) ≤ 0.80 ... (ii)
0.0003 ≤ S + 2 x O-32 (Σ [REM / A (REM)] + Mg / 24 + Ca / 40) ≤ 0.0015 ... (iii)
However, each element symbol in the formula represents the content (mass%) of each element contained in the steel, and A (REM) represents the atomic weight of each rare earth element.

(2) The chemical composition is mass%.
V: 0.01-1.0%,
Nb: 0.01-1.0%,
Ta: 0.01-1.0%, and
Hf: 0.01-1.0%,
Contains one or more selected from
The stainless steel according to (1) above.

(3) The chemical composition is mass%.
Mo: 0.01-3.0%,
W: 0.01-6.0%,
Cu: 0.01-5.0, and
Co: 0.01-3.0%,
Contains one or more selected from
The stainless steel according to (1) or (2) above.

According to the present invention, it is possible to obtain a stainless steel having good hot workability, not causing embrittlement of the hydrogen environment in a hydrogen gas environment, and having excellent mechanical properties.

As a result of detailed investigation of the hot workability and strength characteristics of γ'precipitation strengthening stainless steel, the present inventors have obtained the following findings.

(A) Hot workability is improved by reducing S, which is an impurity element, and also containing Mg, Ca, and a rare earth element (REM) that stably fix S in steel.

(B) On the other hand, it was found that when Mg, Ca and REM were excessively contained, the strength after the precipitation treatment of the γ'phase, that is, after the aging treatment was reduced. It is presumed that the cause of this is that the free S has the effect of increasing the precipitation sites when the γ'phase is precipitated, and that the precipitation sites are reduced as a result of the depletion of the free S.

(C) In order to achieve both hot workability and post-aging strength, in addition to Mg, Ca, REM and S, the content of O that easily binds to Mg, Ca and REM should be strictly adjusted. is necessary.

The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.

1. 1. Chemical composition The reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%".

C: 0.08% or less C is an austenite-stabilizing element, but at the same time, it is an element that also causes sensitization. Therefore, in the present invention, the C content should be low. If the C content exceeds 0.08%, carbides are likely to precipitate at the grain boundaries, which adversely affects toughness and the like. Therefore, the C content is set to 0.08% or less. The C content is preferably 0.07% or less, more preferably 0.06% or less.

Si: 0.2 to 1.0%
Si is an element that has a deoxidizing effect and is effective in improving corrosion resistance and oxidation resistance at high temperatures. In order to obtain such an effect, the Si content needs to be 0.2% or more. However, when the Si content exceeds 1.0%, the stability of austenite decreases, which promotes the formation of intermetallic compounds such as the σ phase. Therefore, the Si content is set to 0.2 to 1.0%. The Si content is preferably 0.8% or less, more preferably 0.6% or less.

Mn: 0.2 to 2.0%
Like Si, Mn is an element that has a deoxidizing effect and also contributes to the stabilization of austenite. In order to obtain such an effect, the Mn content needs to be 0.2% or more. However, if the Mn content exceeds 2.0%, the hot workability and toughness are deteriorated. Therefore, the Mn content is set to 0.2 to 2.0%. The Mn content is preferably 1.7% or less, more preferably 1.5% or less.

P: 0.04% or less P is contained in steel as an impurity, and when it is contained in a large amount, hot workability and weldability are significantly deteriorated. Therefore, the upper limit of the P content is set to 0.04% or less. The content of P is preferably 0.035% or less, and more preferably 0.03% or less. It is preferable to reduce the P content as much as possible, but the extreme reduction causes an increase in manufacturing cost. Therefore, the P content is preferably 0.0005% or more, and more preferably 0.0008% or more.

S: 0.0003 to 0.005%
S is contained in steel as an impurity and is an important element that promotes the precipitation of the γ'phase. In order to obtain this effect, the S content needs to be 0.0003% or more. On the other hand, since S lowers the hot workability, it is necessary to avoid an excessive content. Therefore, the S content is set to 0.0003 to 0.005%. The S content is preferably 0.004% or less, and more preferably 0.003% or less.

Ni: 20.0 to 32.0%
Ni is an austenite stabilizing element, which is an element that precipitates a fine γ'phase [cubic Ni ₃ (Ti, Al)] and acts to increase the strength of steel. If the Ni content is less than 20.0%, these effects cannot be sufficiently obtained. On the other hand, when the Ni content exceeds 32.0%, dislocation localization (planarization) is likely to occur, and the hydrogen environment embrittlement property is deteriorated. Therefore, the Ni content is set to 20.0 to 32.0%. The Ni content is preferably 22.0% or more, and more preferably 23.0% or more. Further, the Ni content is preferably 31.0% or less, and more preferably 30.0% or less.

Cr: 12.0 to 23.0%
Cr is an essential element for ensuring oxidation resistance and corrosion resistance at high temperatures. In the range of the above Ni content, in order to obtain the above effect, the Cr content needs to be 12.0% or more. However, when the Cr content exceeds 23.0%, the stability of austenite at high temperatures deteriorates, which promotes the precipitation of the σ phase, which is an intermetallic compound, and causes a decrease in toughness. Therefore, the Cr content is set to 12.0 to 23.0%. The Cr content is preferably 13.0% or more, and more preferably 13.5% or more. Further, the Cr content is preferably 21.0% or less, and more preferably 20.0% or less.

Ti: 2.0-5.0%
Ti binds to Ni and precipitates in the grains as a fine intermetallic compound to strengthen precipitation. It also precipitates as carbides, making austenite crystal grains finer and contributing to the improvement of tensile strength. In order to obtain these effects, the Ti content needs to be 2.0% or more. However, when the Ti content becomes excessive, a large amount of the intermetallic compound phase is precipitated, which causes deterioration of hot workability and toughness. Therefore, the Ti content is set to 2.0 to 5.0%. The Ti content is preferably 2.3% or more, more preferably 2.5% or more. The Ti content is preferably 4.7% or less, more preferably 4.5% or less.

Al: 0.5-3.0%
Al has a deoxidizing action and, like Ti, binds to Ni and precipitates in the grain as a fine intermetallic compound, which contributes to improvement of creep strength and tensile strength at high temperature. In order to obtain these effects, the Al content needs to be 0.5% or more. However, when the Al content becomes excessive, β phase (NiAl) is precipitated instead of γ'phase, which causes a decrease in strength. Therefore, the Al content is set to 0.5 to 3.0%. The Al content is preferably 0.7% or more, and more preferably 0.8% or more. The Al content is preferably 2.7% or less, and more preferably 2.5% or less.

3.5 ≤ Ti + 48/27 Al ≤ 6.5 ... (i)
0.30 ≤ Ti / (Ti + 48/27 Al) ≤ 0.80 ... (ii)
However, each element symbol in the formula represents the content (mass%) of each element contained in the steel.

Both Ti and Al form a γ'phase, which is an intermetallic compound with Ni. Therefore, it is necessary to adjust the content not only in consideration of each content but also in consideration of both. If both the Ti and Al contents are low, sufficient precipitation of the γ'phase cannot be obtained and good creep characteristics cannot be obtained. On the other hand, if the contents of both Ti and Al are excessive, a large amount of precipitation of the γ'phase causes a decrease in toughness. Therefore, it is necessary to satisfy the above equation (i). The middle value of the above equation (i) is preferably 3.8% or more, and preferably 4.0% or more. The mid-edge value is preferably 6.2% or less, and more preferably 6.0% or less.

The ratio of Ti and Al also affects the amount and morphology of the intermetallic compound. When the ratio of Ti to Ti and Al decreases in terms of atomic weight ratio, the amount of γ'phase precipitated decreases. On the other hand, as the ratio of Ti to Ti and Al increases, the amount of finely precipitated γ'phase decreases, and the η phase (hexagonal Ni ₃ Ti), which is a needle-like coarse precipitate, increases and creeps. It causes a decrease in strength and a decrease in toughness. Therefore, it is necessary to satisfy the above equation (ii). The middle value of the above equation (ii) is preferably 0.35 or more, and more preferably 0.40 or more. The mid-edge value is preferably 0.75 or less, and more preferably 0.70 or less.

N: 0.02% or less N is contained in the alloy as an impurity, and when the content is excessive, it is precipitated as coarse TiN, which reduces the amount of solid solution Ti. As a result, the amount of γ'phase precipitated decreases, leading to a decrease in strength. In addition, coarse TiN precipitates result in deterioration of toughness and hot workability. Therefore, the upper limit of the N content is set to 0.02% or less. The N content is preferably 0.017% or less, more preferably 0.15% or less. It is preferable to reduce the N content as much as possible, but an extreme reduction causes an increase in manufacturing cost. Therefore, the N content is preferably 0.002% or more, and more preferably 0.004% or more.

B: 0.0005 to 0.010%
B is an element that segregates at the grain boundaries to strengthen the grain boundaries and improve hot workability. In order to obtain this effect, the B content needs to be 0.0005% or more. However, if the B content is excessive, the weldability is deteriorated and the hot workability is deteriorated. Therefore, the B content is set to 0.0005 to 0.010%. The B content is preferably 0.008% or less, and more preferably 0.006% or less.

V: 0-1.0%
V combines with C to form fine carbides, which contributes to the refinement of crystal grains and the improvement of tensile strength. Therefore, V may be contained if necessary. However, if the V content is excessive, a large amount of carbide or carbonitride is precipitated, resulting in a decrease in ductility. Therefore, the V content is set to 1.0% or less. The V content is preferably 0.8% or less, more preferably 0.5% or less. On the other hand, when the above effect is desired, the V content is preferably 0.01% or more.

Nb: 0-1.0%
Like V, Nb binds to C and precipitates in the grains as fine carbides, which contributes to the refinement of crystal grains and the improvement of tensile strength. Therefore, Nb may be contained if necessary. However, if the Nb content is excessive, a large amount of carbide or carbonitride is precipitated, resulting in a decrease in ductility and toughness. Therefore, the Nb content is set to 1.0% or less. The Nb content is preferably 0.8% or less. On the other hand, when the above effect is desired, the Nb content is preferably 0.01% or more.

Ta: 0-1.0%
Like V and Nb, Ta binds to C and precipitates in the grains as fine carbides, which contributes to the refinement of crystal grains and the improvement of tensile strength. Therefore, Ta may be contained if necessary. However, if the Ta content is excessive, a large amount of carbide or carbonitride is precipitated, resulting in a decrease in ductility and toughness. Therefore, the Ta content is 1.0% or less. The Ta content is preferably 0.8% or less. On the other hand, when the above effect is desired, the Ta content is preferably 0.01% or more.

Hf: 0 to 1.0%
Like V, Nb and Ta, Hf binds to C and precipitates in the grains as fine carbides, which contributes to the refinement of crystal grains and the improvement of tensile strength. Therefore, Hf may be contained if necessary. However, if the Hf content is excessive, a large amount of carbide or carbonitride is precipitated, resulting in a decrease in creep ductility and toughness. Therefore, the Hf content is set to 1.0% or less. The Hf content is preferably 0.8% or less. On the other hand, when the above effect is desired, the Hf content is preferably 0.01% or more.

When two or more elements selected from V, Nb, Ta and Hf are compounded and contained, the total amount is preferably 2.0% or less, and preferably 1.8% or less. More preferred.

Mo: 0-3.0%
Mo dissolves in the matrix and contributes to the improvement of tensile strength as a solid solution strengthening. Therefore, Mo may be contained if necessary. However, when the Mo content becomes excessive, the stability of austenite is lost and the toughness is deteriorated. Therefore, the Mo content is set to 3.0% or less. On the other hand, when the above effect is desired, the Mo content is preferably 0.01% or more.

W: 0-6.0%
Like Mo, W dissolves in the matrix and contributes to the improvement of tensile strength as a solid solution strengthening. Therefore, W may be contained if necessary. However, when the W content becomes excessive, the stability of austenite is lost and the toughness is deteriorated. Therefore, the W content is set to 6.0% or less. On the other hand, when the above effect is desired, the W content is preferably 0.01% or more.

When Mo and W are contained in combination, the value of Mo + 1 / 2W is preferably 4.0% or less, and more preferably 3.5% or less.

Cu: 0-5.0%
Cu stabilizes austenite and precipitates as a Cu phase in the matrix during aging, contributing to the improvement of strength. Therefore, Cu may be contained if necessary. However, if the Cu content is excessive, the hot workability deteriorates. Therefore, the Cu content is 5.0% or less. On the other hand, when the above effect is desired, the Cu content is preferably 0.01% or more if only the stability of austenite is to be obtained. Further, when it is desired to obtain reinforcement by precipitation of the Cu phase, the Cu content is preferably 2.0% or more.

Co: 0-3.0%
Co stabilizes austenite. Therefore, Co may be contained if necessary. However, if the Co content is excessive, the manufacturing cost will increase. Therefore, the Co content is set to 3.0% or less. On the other hand, when the above effect is desired, the Co content is preferably 0.01% or more.

Mg: 0.0001 to 0.010%,
Ca: 0.0001 to 0.010%, and
REM: 0.001 to 0.10%,
One or more of Mg, Ca and REM selected from the above form a compound with S to reduce the amount of S in the matrix and improve hot workability. The above effects can be obtained by containing one or more selected from Mg, Ca and REM.

When only Mg is selected and contained, it is necessary to contain 0.0001% or more in order to obtain the above-mentioned effect. However, when the Mg content becomes excessive, it combines with O and significantly lowers the cleanliness, and rather deteriorates the hot workability. Therefore, the Mg content is 0.010% or less. The Mg content is preferably 0.008% or less, more preferably 0.005% or less. The Mg content is preferably 0.0002% or more, more preferably 0.0003% or more.

When only Ca is selected and contained, it is necessary to contain 0.0001% or more in order to obtain the above-mentioned effect. However, when the Ca content becomes excessive, it binds to O and significantly lowers the cleanliness, and rather deteriorates the hot workability. Therefore, the Ca content is 0.010% or less. The Ca content is preferably 0.008% or less, more preferably 0.005% or less. The Ca content is preferably 0.0002% or more, and more preferably 0.0003% or more.

The total amount of Mg and Ca compounded is preferably 0.010% or less, and more preferably 0.008% or less.

When only REM is selected and contained, it is necessary to contain 0.001% or more in order to obtain the above-mentioned effect. However, an excessive REM content results in deterioration of hot workability and weldability. Therefore, the REM content is set to 0.10% or less. The REM content is preferably 0.09% or less, more preferably 0.08% or less. The REM content is preferably 0.002% or more, more preferably 0.003% or more, and even more preferably 0.005% or more.

In addition, REM is a general term for a total of 17 elements of Sc, Y and lanthanoid, and REM content refers to the total content of one or more of these elements. Further, REM is generally contained in misch metal. Therefore, for example, it may be added in the form of mischmetal to adjust the amount of REM within the above range.

0.0003 ≤ S + 2 x O-32 (Σ [REM / A (REM)] + Mg / 24 + Ca / 40) ≤ 0.0015 ... (iii)
However, each element symbol in the formula represents the content (mass%) of each element contained in the steel, and A (REM) represents the atomic weight of each rare earth element.

As described above, Mg, Ca and REM reduce the S of the matrix and improve the hot workability by fixing S as a compound, but if S is fixed too much, the strength after aging is lowered. .. In addition, since these elements are easily combined with O, it is necessary to consider the O content in the steel as well. Based on these facts, adjustments are made to satisfy the above equation (iii).

In the chemical composition of the stainless steel of the present invention, the balance is Fe and impurities. Here, the "impurity" is a component mixed with raw materials such as ore and scrap, and various factors in the manufacturing process when steel is industrially manufactured, and is allowed as long as it does not adversely affect the present invention. Means something.

2. 2. Production Method The method for producing precipitation-strengthened stainless steel of the present invention is not particularly limited, and for example, it can be produced by hot-working a steel ingot or slab having the above-mentioned chemical composition. Further, after the hot working, if necessary, hot working by a different method such as hot extrusion or cold working such as cold rolling may be performed.

Further, after the above steps, in order to suppress variations in the metallographic structure and mechanical properties of each part and to temporarily dissolve the non-uniform precipitation caused by hot working, the mixture is heated to a temperature range of 850 to 1000 ° C. It is preferable to perform a solution heat treatment for holding for 3 minutes or more. After the heating and holding, it is preferable to quench the alloy member by water cooling or the like.

Next, the γ'phase is precipitated by aging heat treatment. High strength can be achieved by performing the above treatment and strengthening precipitation. In order to properly precipitate the γ'phase, the aging heat treatment temperature is preferably 630 to 770 ° C., and the heat treatment time is preferably 8 hours or more.

By setting the aging heat treatment temperature to 630 ° C. or higher, the γ'phase can be sufficiently precipitated and the target strength can be obtained. However, when the aging heat treatment temperature exceeds 770 ° C., overaging occurs, the γ'phase becomes coarse, and the strength decreases. Further, if the aging heat treatment time is less than 8 hours, the precipitation of the γ'phase is insufficient and the desired strength cannot be obtained. There is no particular upper limit to the aging heat treatment time, but if the heat treatment time is excessively long, aging occurs, the strength decreases, and the manufacturing cost increases. Therefore, it is preferably 24 hours or less.

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

Stainless steel having the chemical composition shown in Table 1 was melted by high-frequency vacuum melting to obtain a 50 kg ingot. Then, hot forging and hot rolling were performed to obtain a plate material having a thickness of 15 mm.

A round bar tensile test piece having an outer diameter of 10 mm was cut out from the plate material after hot rolling, and a tensile test was performed at 1000 ° C. at 1000 ° C. with a strain rate of 10 (s ^-1 ) to obtain a drawing value. In the evaluation of hot workability, a case where the drawing value in the hot-rolled state was 70% or more was evaluated as acceptable (◯), and a case where the drawing value was less than 70% was evaluated as rejected (x).

Then, the plate material after hot rolling was further subjected to cold rolling to obtain a cold-rolled steel sheet having a thickness of 10.5 mm. Then, the obtained cold-rolled steel sheet was first subjected to a solution heat treatment of holding it at 900 ° C. for 30 minutes and then cooling it with water. Subsequently, a test material was obtained by subjecting it to aging treatment in which it was held at 750 ° C. for 24 hours and then allowed to cool.

A round bar tensile test piece having a parallel portion diameter of 2.5 mm was collected from the longitudinal direction of the test material, and the strain rate was 3 × 10 ^-6 (s) in the normal temperature atmosphere and in the high pressure hydrogen gas at room temperature of 85 MPa. ^A tensile test was carried out in ^-1 ), and the tensile strength and relative breaking elongation were measured. In the evaluation of the tensile strength, the case where the tensile strength in the high-pressure hydrogen gas was 1150 MPa or more was evaluated as acceptable (◯), and the case where the tensile strength was less than 1150 MPa was evaluated as rejected (x).

Since the effect of hydrogen appears remarkably on the decrease in ductility, the ratio of the elongation at break in hydrogen to the elongation at break in the atmosphere was defined as the relative elongation at break, as expressed by the following equation. If the relative elongation at break is 80% or more, the decrease in ductility due to hydrogen is slight, and it can be judged that the hydrogen-resistant environment embrittlement property is excellent. Therefore, in the evaluation of the hydrogen embrittlement resistance property, the case where the relative elongation at break is 80% or more is regarded as a pass (◯), and the case where the relative elongation at break is less than 80% is regarded as a fail (x).
Relative breaking elongation (%) = (breaking elongation in hydrogen) / (atmospheric breaking elongation) x 100

These results are summarized in Table 2.

As shown in Table 2, Test Nos. Satisfying the provisions of the present invention. In 1 to 6, the drawing value at 1000 ° C. is 70% or more, which is excellent in hot workability, the tensile strength in high-pressure hydrogen gas is 1150 MPa or more, and the relative elongation is 80% or more, which is good. The results showed excellent hydrogen-resistant environmental embrittlement characteristics.

On the other hand, Test No. which is a comparative example. In 7 to 12, at least one of hot workability, tensile strength and hydrogen embrittlement property was inferior. Specifically, the test No. In No. 7, since the middle value of Eq. (iii) exceeds the upper limit, grain boundary embrittlement occurs due to grain boundary segregation of S, the aperture value of the greeble test is less than 70%, and the hot workability is inferior. It became. In addition, the test No. In No. 8, the middle value of Eq. (iii) was less than the lower limit and the solid solution S was eliminated, so that the hot workability was good, but the precipitation density of the γ'phase was lowered and the tensile strength was inferior. It became.

Test No. In No. 9, since the middle value of Eq. (I) was less than the lower limit value, the amount of γ'phase precipitated was small and the tensile strength was inferior. Test No. In No. 10, since the middle value of the formula (i) exceeds the upper limit, the precipitation of the γ'phase is sufficient and the strength is satisfied, but the hot workability is deteriorated.

Test No. In No. 11, since the middle value of Eq. (Ii) exceeded the upper limit, the precipitation of the η phase became remarkable, the tensile strength was inferior, and the hydrogen embrittlement property also deteriorated. Test No. In No. 12, since the middle value of Eq. (Ii) was less than the lower limit, the amount of γ'phase precipitated was small, resulting in inferior tensile strength.

According to the present invention, it is possible to obtain a stainless steel having good hot workability, not causing embrittlement of the hydrogen environment in a hydrogen gas environment, and having excellent mechanical properties. Therefore, the stainless steel of the present invention is suitable for use as a tank, pipe, etc. for high-pressure hydrogen gas.

Claims (3)

The chemical composition is mass%,
C: 0.08% or less,
Si: 0.2-1.0%,
Mn: 0.2-2.0%,
P: 0.04% or less,
S: 0.0003 to 0.005%,
Ni: 20.0 to 32.0%,
Cr: 12.0 to 23.0%,
Ti: 2.0-5.0%,
Al: 0.5-3.0%,
N: 0.02% or less,
B: 0.0005 to 0.010%,
V: 0-1.0%,
Nb: 0-1.0%,
Ta: 0-1.0%,
Hf: 0-1.0%,
Mo: 0-3.0%,
W: 0-6.0%,
Cu: 0-5.0%,
Co: 0-3.0%,
Including,
Mg: 0.0001 to 0.010%,
Ca: 0.0001 to 0.010%, and
REM: 0.001 to 0.10%,
Including one or more selected from
The rest is Fe and impurities,
Satisfy the following equations (i) to (iii),
Stainless steel.
3.5 ≤ Ti + 48/27 Al ≤ 6.5 ... (i)
0.30 ≤ Ti / (Ti + 48/27 Al) ≤ 0.80 ... (ii)
0.0003 ≤ S + 2 x O-32 (Σ [REM / A (REM)] + Mg / 24 + Ca / 40) ≤ 0.0015 ... (iii)
However, each element symbol in the formula represents the content (mass%) of each element contained in the steel, and A (REM) represents the atomic weight of each rare earth element. When the chemical composition is mass%,
V: 0.01-1.0%,
Nb: 0.01-1.0%,
Ta: 0.01-1.0%, and
Hf: 0.01-1.0%,
Contains one or more selected from
The stainless steel according to claim 1. When the chemical composition is mass%,
Mo: 0.01-3.0%,
W: 0.01-6.0%,
Cu: 0.01-5.0, and
Co: 0.01-3.0%,
Contains one or more selected from
The stainless steel according to claim 1 or 2.