JPH05320866A - Ferritic stainless steel and its production - Google Patents

Abstract

PURPOSE:To develop the ferritic stainless steel having excellent oxidation resistance at a high temp. by subjecting an Al-contg. ferritic stainless steel to an ion bombardment treatment, then to a heat treatment under specific conditions. CONSTITUTION:The ferritic stainless steel contg., by weight %, 10 to 25% Cr or 16 to 25% Cr, 3 to 6% Al and 0.01 to 5.0% Si is heated to from a room temp. to 450 deg.C range and then, 0 to -500V bias voltage is held impressed thereto, the steel is subjected to the ion bombardment treatment to form oxide layers mainly composed of Cr or Al on the surfaces of the ferritic stainless steel; thereafter, the steel sheet is heated to 450 to 1200 deg.C in a furnace kept at a nonoxidative atmosphere of -15 to -60 deg.C dew point temp. and is held at the temp. for about >=1 seconds. The dense oxide layers are formed on the surfaces of the stainless steel, by which the ferritic stainless steel products having the greatly improved oxidation resistance are produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is useful in high temperature environments, such as 400
TECHNICAL FIELD The present invention relates to a ferritic stainless steel which is used in a high temperature environment of ℃ or higher and has excellent oxidation resistance, and a manufacturing method thereof.

[0002]

2. Description of the Related Art For parts materials used at high temperatures, such as automobile exhaust manifolds, automobile exhaust gas reforming catalyst carriers, heat exchanger members, heating furnace materials, heating member combustion members, etc., simply in the application environment. Not only the oxidation resistance of
(1) Long-term application life including scale peeling resistance in an application environment where high temperature heating and cooling are repeated, (2) heat resistant high temperature strength including creep strength and mechanical strength at room temperature, (3)
Cold workability to process complex shaped parts, (4)
Weldability, and in some cases, extremely wide range of properties such as (5) rust resistance against condensation and (6) brightness at high temperature are required. Further, these materials are required to be mass-produced as industrial products, and are also required to be inexpensive.

Conventionally, ferritic heat-resisting steel has been used as a relatively inexpensive material for such applications. For automotive exhaust manifolds, SUH409 and other 12% Cr-based ferritic stainless steels containing 17% Nb and Cu. It is well known that Cr-type ferritic stainless steel or the same type of 19% Cr-ferritic stainless steel is used. In addition, rare earth elements such as S in steel are used as a vehicle exhaust gas reforming catalyst carrier.
Stabilized 20% Cr-5% Al-based ferritic stainless steel foil is used as a combustion material for heating equipment.
It is a well-known fact that 18% Cr-based 18% Cr-based or 18% Cr ferritic stainless steel containing 2.5% Si has been developed and applied according to the application.

Generally, Fe--Cr alloys exhibit a ferrite single phase or a ferrite + austenite two phase at high temperatures in terms of metallography. Basically, compared to austenitic steel, which contains a large amount of Ni, which enhances high-temperature strength in steel, ferrite-based steel shows a marked decrease in high-temperature strength in the temperature range of over 900 ° C, and 12% Cr-based ferritic stainless steel mainly contains 800 It has been used only for applications that do not require high temperature strength of about 850 ℃. In addition, when applied in the temperature range from 850 ℃ to 950 ℃, 16 to 20
% Cr steel has been applied.

In general, in Fe-Cr ferritic stainless steel, in order to improve the oxidation resistance at high temperature, Cr, which is an oxidation resistance improving element, is added in an amount of more than 12%, preferably more than 16%. In addition, Si or Al, which is extremely effective for improving the oxidation resistance, has been added in an amount of more than 0.5%, preferably more than 1%. However, the composition for ensuring the necessary and sufficient performance is required. In that case, either of them has a problem that workability in hot or cold is significantly deteriorated. Especially 12% Cr
Since the ferritic stainless steel is excellent in cold workability, such deterioration of cold work becomes a problem.

Therefore, C and N in the steel, which deteriorates the toughness at around room temperature, are extremely lowered, an appropriate amount of a stabilizing element is added for the purpose of suppressing deterioration of corrosion resistance in the welded portion, or at high temperature. S in steel, which reduces the oxidation resistance of the steel, deteriorates the thermal fatigue properties, and significantly reduces the hot workability.
At present, manufacturing is performed by adding rare earth elements such as La and Ce or trace elements such as Y and Ca that form stable sulfide-based inclusions at high temperatures to improve manufacturability and secure yield. is there.

[0007]

Since the oxidation resistance improving element in steel is consumed by oxidation over time, unless the generated surface oxide scale is extremely excellent in protective property and stable, the application environment The more severe the condition, the faster the consumption of the oxidation resistance improving element in the base material and the shorter the applicable life.

[0008] In some cases, if Si or Al is vapor-deposited on the surface layer and then subjected to a diffusion treatment, it is difficult in a normal manufacturing process due to a decrease in workability during hot working. , Al has also been attempted to enrich the base material. As an example, an attempt to apply it to the production of 6.5% silicon steel sheet, an attempt to produce 20% Cr-5% Al for Al-rich automobile exhaust gas reforming catalyst carrier using 20% Cr-3% Al as a vapor deposition base material, etc. Is mentioned.

However, when Si or Al is enriched by vapor deposition, the efficiency of thermal diffusion treatment at high temperature due to the oxide layer existing at the interface between the vapor deposition film and the base material decreases, more than the problem of adhesion. Alternatively, technical problems of diffusion condition control are expected. Now, in the above ferritic stainless steel, if the high temperature resistance can be further improved without impairing its basic characteristics, it is expected to have an extremely large effect in practical use and social benefit. .. Therefore, an object of the present invention is to provide a ferritic stainless steel which has the basic characteristics and advantages of the ferritic stainless steel as they are, and which is remarkably excellent in oxidation resistance at high temperatures, and a manufacturing method thereof.

[0010]

Here, the present inventors
The following findings were obtained and the present invention was completed. A base material having a proper component for improving the oxidation resistance at high temperature is subjected to an ion bombardment treatment in a plasmaized atmosphere to mainly contain Cr, which is extremely preferable for improving the oxidation resistance in the outermost layer, and , An oxide layer containing Si, or an oxide layer mainly containing Al and containing Si and Cr can significantly improve the oxidation resistance of the ferritic stainless steel.

Conventionally, ion bombardment treatment in plasma has been carried out as a pretreatment for vapor deposition, but in the conventional ion bombardment treatment, the passivation film of stainless steel existing on the surface layer is removed from the viewpoint of improving adhesion. It is carried out for the purpose of, the oxide layer mainly composed of Cr is extremely preferable for the improvement of the oxidation resistance in the outermost layer, and Cr is mainly composed,
Al, oxide layer containing Si, or Al as the main component, S
Ion bombardment treatment was not performed for the purpose of forming an oxide layer containing i and Cr.

In order to form an oxide layer mainly containing Cr or Al mainly effective for improving the oxidation resistance on the surface, the substrate preheating temperature before the ion bombardment treatment is
From room temperature to 450 ° C., high temperature oxidation is extremely difficult to proceed as it is, or is set to a temperature at which it does not proceed at all, whereby high temperature oxidation accompanied by ordinary thermal diffusion is effectively suppressed.

In the oxide layer thus formed on the surface layer, only the elements that are easily oxidized, such as Cr, Al, and Si, which are exposed on the outermost surface layer, and in some cases, a part of the elements are knocked out by the plasma. However, it is presumed that it is related to the situation in which it is bonded to oxygen regardless of thermal diffusion from the inside of the base material. In this regard, according to the conventional knowledge, when thermal diffusion is involved,
As a result of the formation of a Cr-deficient layer just below the oxide layer due to oxidation,
It is said that the corrosion resistance or the oxidation resistance deteriorates.

An oxide layer mainly composed of Cr, an oxide layer mainly composed of Cr and containing Al and Si, or an oxide layer mainly composed of Al and containing Si and Cr, having such excellent characteristics. The present inventors speculate that the formation of erythrocyte is due to a special phenomenon in plasma, but its exact mechanism has not yet been clarified.

Cr is the main component, which is extremely effective for improving the high temperature oxidation resistance generated by the ion bombardment treatment, and
l, an oxide layer containing Si, or Al as the main component, and C
For oxide layers containing r and Si, dew point temperature -1
A surface generated in plasma by performing a treatment for holding at a temperature of 450 ° C. or higher and 1200 ° C. or lower for 1 second or longer in a furnace in a non-oxidizing atmosphere of 5 to −60 ° C., where normal high temperature oxidation proceeds Oxidation resistance can be further improved by generating a denser oxide layer of 200 A or more on the surface of the steel sheet by high-temperature oxidation accompanied by thermal diffusion while being affected by the oxide layer.

Accordingly, the gist of the present invention is that it has an oxide layer formed on the surface by an ion bombardment treatment mainly containing Cr, and contains 10 to 25% by weight of Cr. It is a ferritic stainless steel with excellent oxidation resistance.

From another point of view, the gist of the present invention is that the surface has an oxide layer mainly composed of Al and produced by an ion bombardment treatment containing Si and Cr,
By weight, Cr: 16-25%, Al: 3-6%, and Si: 0.
It is a ferritic stainless steel with excellent oxidation resistance characterized by containing 01 to 5.0%.

In yet another aspect, the invention is based on weight percent.
Ferritic stainless steel containing 10 to 25% Cr is stored at room temperature or above 0 ℃ to 450 ℃ below 0 to -50
This is a method for producing a ferritic stainless steel having excellent oxidation resistance, which is characterized in that an ion bombardment treatment is applied by applying a bias voltage of 0 V to generate an oxide mainly containing Cr on the surface.

Further, the gist of the present invention is that, in weight%, Cr: 16 to 25%, Al: 3 to 6%, and Si:
Ferrite stainless steel containing 0.01 to 5.0% at room temperature or above room temperature and preheated to 450 ° C or less
A method for producing a ferritic stainless steel having excellent oxidation resistance, which comprises subjecting an ion bombardment treatment to a bias voltage of 500 V to generate an oxide mainly containing Al on the surface.

After the above ion bombardment treatment, further 450 in a furnace in a non-oxidizing atmosphere having a dew point temperature of -15 to -60 ° C.
By holding for 1 second or more while being heated to a temperature of up to 1200 ° C, a denser oxide layer is formed, and the oxidation resistance can be further improved.

Here, the ion bombardment treatment means 10 ^-3.
This is a treatment in which an object to be treated is placed in an excited non-oxidizing gas plasma of about 10 ⁻⁴ Torr and is not particularly limited in the present invention, but the excited state is preferably high. Generally, the ion bombardment treatment is a method of hitting the surface of the object to be treated with gas plasma to remove the deposits or the passive film of stainless steel, but compared with this, the ion bombardment treatment in this method is The difference is that an oxide layer preferable for improving the oxidation resistance is positively generated in plasma. The ion bombardment process is usually performed under reduced pressure, but may be performed in plasma under normal pressure by a special method such as controlling the oxidation potential.

[0022]

Next, the reason why the present invention is limited to the above range will be described. When generating an oxide mainly composed of Cr,
10 to 25%, while limiting the Al content to 3.0 to 6.0% when forming an oxide mainly composed of Al, Cr: 16
-25% and Si: 0.01-5.0%, but the reason is as follows.

Cr: Cr in steel is a basic alloying element that is extremely demanded for ensuring oxidation resistance at high temperatures. In the present invention, the lower limit is 16.00% and the upper limit is 25.00%. This is because a Cr content of 16% or more is required to secure sufficient oxidation resistance above 400 ° C, while the Cr content in steel is
If added over 25%, the effect of improving the oxidation resistance by this method becomes unclear, so the upper limit was made 25%. When the oxide layer mainly composed of Cr is provided, the lower limit is 10.00%
And

Al: Al in steel is one of the important basic additive elements along with Cr in the steel of the present invention, which is important for ensuring the oxidation resistance. If it is less than 3.0%, sufficient oxidation resistance cannot be ensured, and if it is added over 6.0%, the toughness decrease at room temperature becomes extremely remarkable, making industrial production difficult. , The upper limit is 6.0%. However, when an oxide layer mainly composed of Cr is provided, Al is preferably 0.001
Limited to ~ 1.0%.

Si: Si is a basic deoxidizing element for adding Al in a good yield, and on the other hand, has an effect of improving oxidation resistance. The lower limit is 0.01% and the upper limit is 5.0%. Cr
When an oxide layer mainly containing is provided, the upper limit thereof is preferably 4.0%.

Next, the preheating temperature during the ion bombardment treatment is extremely important in the present invention in addition to the components in the steel. When preheating above 450 ° C, so-called high temperature oxidation accompanied by thermal diffusion before ion bombardment becomes remarkable and the effect of ion bombardment treatment is reduced by half or no effect can be expected, so the upper limit of preheating temperature should be 450 ° C. To do. The lower limit is room temperature.

The bias voltage during the ion bombardment process is 0 to -500V. When the bias voltage is increased,
A decrease in the ion bombardment treatment effect, which is presumed to be due to the effect that the gas atoms turned into plasma hit the surface too strongly, is observed. The upper limit is -500V.

The ion bombardment process itself is already well known and may be carried out in accordance with a commonly used means except the above-mentioned conditions, and a further description will be omitted. The high temperature heat treatment involving thermal diffusion after the ion bombardment treatment is as follows.

The annealing temperature is set to 450 to 1200 ° C., which is considered to be accompanied by thermal diffusion. The upper limit temperature is set to 1200 ° C., which is considered to be annealed in view of high temperature strength of ferritic stainless steel, which is a component range of the steel of the present invention.
The holding time is not always limited because the densification of the oxide scale or the growth rate greatly changes depending on the temperature condition to be held. The lower limit was 1 second, which was industrially determined.

The atmosphere in the furnace for carrying out such an annealing treatment is extremely important. It is extremely important that the dew point is maintained at −15 to −60 ° C. in a non-oxidizing atmosphere mainly containing Ar, N ₂ , H ₂ or the like, or in a reduced pressure atmosphere. This is because the composition and structure of the surface oxide layer formed depending on the dew point change, and this has an extremely large effect on the oxidation resistance in the application environment. In an environment with a dew point above −15 ° C., the oxidation of Fe is likely to proceed preferentially, and even if a film with good oxidation resistance is formed by the ion bombardment treatment, a dense oxide scale layer This is because it is difficult for the growth to proceed and adversely affects the progress of oxidation at a high temperature, which is an application environment later. On the other hand, when the dew point is less than -60 ° C, not only it becomes extremely difficult to industrially control the atmosphere, but also the growth of the oxide is slow and it is not preferable, so the lower limit was made -60 ° C.

The composition of the ferritic stainless steel to which the present invention is applied is not particularly limited as long as it has the above-mentioned composition, but more practically, in consideration of the specifications and the like, more specifically, The ferritic stainless steel according to the present invention is, by weight%, C: 0.0001 to 0.0050%, N: 0.0001 to 0.0100%, S: 0.
00001 to 0.0020%, Cr: 16.00 to 25.00%, Al: 3.00 to
6.00%, Si: 0.01 to 1.00%, Mn: 0.01 to 1.00%, P: 0.
030% or less, one or two kinds of Ti and Nb in total of 4 times or more of the amount of C + N, 1.0% or less, rare earth elements such as Ce and La, or one or two or more kinds of Y and Ca of 0.20. % Or less If necessary, Mo: 0.01 to 5.0% In addition, Cu and Ni are contained in the steel at 0.8% or less as impurities, and the steel composition has the balance Fe and unavoidable impurities.

Further, from another aspect, the ferritic stainless steel according to the present invention is, by weight%, C: 0.0001 to 0.030%, N: 0.0001 to 0.030%, S: 0.
00001 to 0.0020%, Cr: 10.00 to 25.00%, Al: 0.001
~ 1.0%, Si: 0.01 ~ 5.0%, Mn: 0.01 ~ 1.00%,
P: 0.030% or less, one or two of Ti and Nb in total C
+ 4 times more than N amount, 1.0% or less, and if necessary, C
0.20% or less of rare earth elements such as e and La, or one or more of Y and Ca, and / or Mo: 0.01 to 5.0.
%, In addition, 0.8% or less of Cu and Ni are contained in the steel as impurities, and the steel composition has the balance Fe and unavoidable impurities.

Although the present invention is not limited by such a steel composition, the reason why the steel composition is limited as described above will be described as a preferred example.

C: C is an element that significantly reduces the toughness at room temperature, and forms Cr ₂₃ C ₆ type carbides when applied at high temperature or in the weld heat affected zone, and the oxidation resistance by Cr is increased. It has the effect of significantly reducing the improvement effect of.
In addition, it has an adverse effect of causing scale peeling. The lower the better. On the other hand, the upper limit is made 0.030% for the purpose of improving the toughness at around room temperature.

N: N, like C, is an element that significantly reduces toughness at room temperature. Further, by forming a nitride by combining with Cr and Al in the steel, there is an adverse effect that Cr and Al reduce the oxidation resistance at high temperature. The upper limit is 0.030%.
For the purpose of fixing C and N in steel and reducing the adverse effects of C and N, Ti and Nb, which have a stronger affinity for C and N than Cr or Al.
Stabilizing element is added. There is no problem if Nb contains Ta as an impurity. In order to improve the toughness at room temperature and reduce the deterioration of oxidation resistance at high temperature, the addition amount has an appropriate value. In order to fix C and N in steel, Ti or Nb which is 4 times or more that of C + N (%) in steel is required. Further, excessive addition of Ti and Nb causes a decrease in toughness, so the upper limit is set to 1.00% for Ti + Nb (%).

S: S in steel regulates the upper limit to 0.0020% and forms more stable sulfide at a temperature higher than Mn.
It is immobilized by adding rare earth metals such as La and Ce, and Y and Ca. The rare earth element may be added at the steelmaking stage by using industrially inexpensive misch metal or the like. For the purpose of enhancing the effect of adding rare earth metals such as La and Ce, Y, and Ca that are added as S-fixing elements, it is preferable that the O concentration in steel is low. This is because these additional elements tend to form oxides, are consumed as oxides before they function as S-fixing elements in steel, and the effective amount decreases. It is preferable that the O + S (%) value in steel is low, but S + O (%) ≤ 0.008%, and more desirably O + S (%) ≤ 0.005% is a necessary condition.

Mn: Mn may be added to secure strength at high temperature. It is desirable that the content is about 0.01 to 1.00%. Mo: Mo may be added to secure strength at high temperature or to secure corrosion resistance. The addition amount is 0.01% or more and 5.0% or less. If it is added in an amount of more than 5.0%, the toughness is significantly reduced due to the formation of intermetallic compounds.

P: P is not positively added. In principle, it is an impurity. Contains 0.030% or less. La, Ce: La, Ce and other rare earth elements, Y and Ca are S-fixing elements in steel as described above. Since it has a strong affinity with O in steel and is also consumed as an oxide, the total amount is 0.
Add within 20% or less. Cu, Ni: Cu and Ni in steel may improve the corrosion resistance of the base material. May be contained as 0.8% or less as an impurity.

The oxide layer formed on the surface is mainly composed of Al oxide and an oxide in which Cr and Si oxide coexist, or an oxide mainly composed of Cr oxide. Fe oxide is also included, but from the gist of the present invention, it has a strong impurity-like meaning, and it is speculated that the improvement effect in terms of performance is reduced, but at the present time, generation cannot be prevented, It has not been possible to separate and clarify the impact on performance. The above situation is limited to “an oxide layer mainly containing Al and containing Cr and Si” and “an oxide layer mainly containing Cr”. Next, the present invention will be further described with reference to specific examples.

[0040]

【Example】

(Example 1) Steel Nos. 1 to 14 having the composition shown in Table 1 are melted in a vacuum melting furnace and subjected to forging, hot rolling and cold rolling to obtain a cold rolled sheet with a thickness of 1 mm. .. Using various steel plates produced in this way as vapor deposition substrates, degreasing and cleaning with an organic solvent, preheating the substrates to 300 ° C, and then H ₂ O partial pressure of 1.3 × 10 ^-5 Torr, Ar
Ion bombardment was performed by applying a bias voltage of 0 to -500 V in the atmosphere.

From the steel plate thus obtained, a thickness of 1 mm
× Width 20 mm × Length 25 mm test piece is cut out and 1000 ℃ in air
An oxidation test was conducted by heating for 100 hours. Oxide weight change with composition of oxide layer by ion bombardment treatment (mg / c
The results of m ² ) and the treatment conditions are summarized in Table 2. In the oxidation test, the oxidation resistance was evaluated based on the amount of increase in oxidation after the test.

Steel No. 1 according to the present invention shown in Table 2
Steel Nos. 7, 8 and 10 and Comparative Steel Nos. 13 and 950 ° C
FIG. 1 shows the time-dependent change in the oxidation at the temperature. 2 (a)-(d)
Cr, Fe, A in the vicinity of the steel plate surface of Steel No. 1 of the present invention example
It is a graph which shows the result obtained by secondary ion mass spectrometry (SIMS) about l, Si, and O concentration. 3 (a)-(d)
Cr, Fe, A in the vicinity of the steel plate surface of Steel No. 7 of the present invention example
It is a graph which shows the result obtained by secondary ion mass spectrometry (SIMS) about l, Si, and O concentration.

The sputter time (min) on the horizontal axis in FIGS. 2 and 3 corresponds to the depth from the plate surface, and zero sputter time represents the steel plate surface. From the oxidation test results shown in Table 2, it can be seen that the steel sheet containing Cr and Al as appropriate components has excellent oxidation resistance. On the other hand, steel sheets containing a small amount of Cr and Si, especially Al, have poor oxidation resistance.

From the results shown in FIG. 2, it can be seen that an oxide layer mainly composed of Cr is formed, and from FIG. 3 that an oxide layer mainly composed of Al is formed. On the other hand, it can be seen that if the bombard bias voltage is out of the proper range, it is difficult to form a dense oxide on the surface. Further, when the substrate heating temperature is higher than the proper range, an oxide layer mainly containing Fe is formed, and the effect of oxidation resistance is lost. Further, it is understood that the one to which Mo is added has excellent corrosion resistance. Since the adverse effect on the oxidation resistance due to the addition of Mo is rarely seen, the addition of Mo in the proper component is extremely effective.

(Example 2) Steel according to the present invention used in Example 1
The No. 1 and 7 ferritic stainless steel sheets were heat-treated under the conditions shown in Table 3. The results of SIMS analysis of the No. 7 steel plate thus obtained are shown in FIGS. 4 (a) and 4 (b). Regarding the high temperature heat treatment involving thermal diffusion after the ion bombardment treatment, the results of SIMS analysis in Fig. 4 indicate that within the proper range, densification occurs due to the growth of the oxide scale and the oxidation resistance is improved. On the other hand, it is understood that when the heating temperature is too high, Fe atoms diffuse to form an oxide.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

As described above, according to the present invention, the oxidation resistance of ferritic stainless steel, which is a relatively inexpensive material, can be significantly improved, and it can be used as a material for automobiles or a material for heat-resistant structural members. Demonstrate usefulness.

[Brief description of drawings]

FIG. 1 is a graph showing the oxidation resistance of the materials obtained in the examples.

2 (a) to 2 (d) are graphs showing the results of elemental analysis on the surface of the steel sheet after the ion bombardment treatment.

3 (a) to 3 (d) are also graphs showing the results of elemental analysis on the surface of the steel sheet after the ion bombardment treatment.

FIG. 4 is a graph showing the effect of heat treatment after ion bombardment treatment in Examples.

Claims (5)

[Claims] 1. An oxide layer is formed on the surface by an ion bombardment treatment containing Cr as a main component, and Cr is contained in a weight percentage.
Ferritic stainless steel with excellent oxidation resistance, characterized by containing 10 to 25%. 2. A surface is provided with an oxide layer containing Al as a main component and produced by an ion bombardment treatment containing Si and Cr, and in weight%, Cr: 16 to 25%, Al: 3 to 6%, And S
i: Ferritic stainless steel with excellent oxidation resistance, characterized by containing 0.01 to 5.0%. 3. A ferritic stainless steel containing 10 to 25% by weight of Cr is subjected to ion bombardment by applying a bias voltage of 0 to −500 V in a state of being preheated to room temperature or above room temperature and 450 ° C. or less, A method for producing a ferritic stainless steel having excellent oxidation resistance, characterized in that an oxide mainly composed of Cr is formed on the surface. 4. Cr: 16 to 25%, Al: 3 to 6% by weight,
And Si: 0.01-5.0% ferritic stainless steel containing 0.01 to 5.0% is subjected to ion bombardment by applying a bias voltage of 0 to -500V in a state of preheating at room temperature or above room temperature to 450 ° C or less, with Al as the main surface. A method for producing a ferritic stainless steel having excellent oxidation resistance, which comprises producing an oxide. 5. After the ion bombardment treatment, a further 45 in a non-oxidizing atmosphere furnace having a dew point temperature of -15 to -60 ° C.
The method for producing a ferritic stainless steel excellent in oxidation resistance according to claim 3 or 4, characterized in that it is held for 1 second or more in a state of being heated to a temperature of 0 to 1200 ° C.