JP2003321752A - High strength ferritic heat resistant steel and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide high strength heat resistant steel which has reduced reduction of strength even in use at a high temperature for a long time, and to provide a production method thereof. <P>SOLUTION: The high strength ferritic heat resistant steel has a composition containing, by mass, 0.02 to 0.1% C, ≤0.6% Si, 0.5 to 2.0% Mn, 0.5 to 15% Cr, 0.1 to 1% Mo, 0 to 2% W, 0.01 to 0.1% Ti, 0 to 0.2% Nb and 0 to 0.1% V, and the balance substantially Fe. The steel has a metallic structure substantially consisting of a ferrite single phase, and in which carbides with a particle diameter of <10 nm containing Mo and Ti as bases are dispersedly precipitated, and the number of the carbides is ≥80% of the number of all precipitates other than TiN. In the production method, steel is reheated to ≥950°C, is thereafter cooled from a temperature equal to or higher than an Ar<SB>3</SB>point to 550 to 700°C at a cooling rate of ≥2°C/s, within 600 s, is held at 550 to 700°C for ≥30 s, and is subsequently air-cooled. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has high high temperature strength,
The present invention relates to a high-strength ferritic heat-resistant steel that is excellent in high-temperature oxidation resistance and high-temperature corrosion resistance, is used as a member for high-temperature equipment, and is particularly suitable as a material for a heat-resistant pressure-resistant member, and a method for producing the same.

[0002]

2. Description of the Prior Art Cr-containing heat-resistant steels used in the fields of boilers, chemical industry, etc., have their strength secured by a transformation strengthening structure such as martensite as the matrix structure at the time of manufacture. The following methods (1) to (4) are basically used in order to maintain high strength as long as possible under use conditions and avoid softening during use.

(1) A large amount of solid solution strengthening elements such as Mo and W are added.

(2) Utilizing precipitation dispersion strengthening by precipitation of carbides such as M ₂₃ C ₆ and M ₆ C during use.

(3) As precipitates, special carbides such as Nb and V which are relatively finely dispersed and largely contribute to strength are utilized.

(4) Utilization of precipitation dispersion strengthening of an intermetallic compound containing Mo as a precipitate.

Regarding (1), Japanese Patent Laid-Open No. 10-287960
The publication discloses a technique for optimizing the amounts of Mo and W to secure high temperature strength. Also regarding (2),
Japanese Unexamined Patent Publication No. 10-287960 discloses a technique for suppressing the coarsening of M ₂₃ C ₆ by optimizing the amounts of Mo and W. Regarding (3), by optimizing the heat treatment during manufacturing in Japanese Patent Publication No. 4-59369, Nb, V
The technology for finely and uniformly dispersing the precipitates of (4)
With regard to the above, Japanese Patent Application Laid-Open No. 3-274223 discloses a technique in which an intermetallic compound is dispersed and precipitated by optimizing a heat treatment during manufacturing.

[0008]

However, the amount of Mo and W is optimized so as to secure high temperature strength.
The technique described in Japanese Patent Publication No. 87960 is Mo which is an expensive element.
In spite of adding a large amount of and W, its effect is smaller than that of precipitation dispersion strengthening, and cost performance is low.
On the other hand, JP-A-10-28796 utilizing precipitation dispersion strengthening
No. 0, Japanese Patent Publication No. 4-59369, Japanese Patent Laid-Open No. 3-2
The technique described in Japanese Patent No. 74223 is more effective than solid solution strengthening up to a certain temperature and time, but coarsening of precipitates occurs over time, and the effect is limited when used for a long time. There is.

As described above, in the conventional technique, even if a plurality of reinforcing mechanisms are combined in a complex manner, they are still not sufficient.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a high-strength heat-resisting steel and a manufacturing method thereof, in which the strength is less likely to decrease even when used at a high temperature for a long time. is there.

[0011]

The features of the present invention for solving the above problems are as follows.

(1) C: 0.02 to 0.1% by mass%, Si:
0.6% or less, Mn: 0.5-2%, Cr: 0.5-15%, Mo: 0.1-1
%, W: 0 to 2%, Ti: 0.01 to 0.1%, Nb: 0 to 0.2%, V: 0 to
Containing 0.1%, the balance substantially consisting of Fe, the metal structure is substantially ferrite single phase, the carbide having a particle size of less than 10 nm containing Mo and Ti as a base is dispersed and precipitated, and the carbide High-strength ferritic heat-resistant steel, characterized in that the number is 80% or more of the total number of precipitates excluding TiN.

(2) Heating temperature of the formed steel material: 950
Reheating to ℃ or above, cooling after reheating, cooling start temperature:
Ar ₃ points or more, cooling end temperature: 550 to 700 ℃, cooling rate 2 ℃ / s
Cool the above, within 550 seconds after the end of the cooling, 550 ~ 700
The method for producing a high-strength ferritic heat-resistant steel as set forth in (1), which is characterized by holding at 30 ° C. for 30 s or more and then air cooling.

(3) Steel is hot-rolled at a heating temperature of 950 ° C. or higher and a rolling finishing temperature: Ar ₃ points or higher, and cooling after hot rolling is performed by cooling start temperature: Ar ₃ points or higher, cooling end temperature: 550-70
Accelerated cooling at 0 ° C. and a cooling rate of 2 ° C./s or more, holding at 550 to 700 ° C. for 30 s or more within 600 s after completion of the accelerated cooling, and then performing air cooling, high temperature according to (1) Method for producing high-strength ferritic heat-resistant steel.

(4) Steel is hot-rolled at a heating temperature of 950 ° C. or higher and a rolling finishing temperature: Ar ₃ points or more, and cooling after hot rolling is performed by cooling start temperature: Ar ₃ points or more, cooling end temperature: 600-70
The method for producing a high-strength ferritic heat-resistant steel as described in (1), characterized in that accelerated cooling is performed at 0 ° C. and a cooling rate of 2 ° C./s or more, and then air cooling is performed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As a method for ensuring high temperature strength, the inventors of the present invention have noticed that unprecedented thermally extremely stable precipitates are used, and the thermal stability of various precipitates is improved. If the temperature is 700 ° C or less, the composite carbide of Mo and Ti is suitable as a precipitate that hardly changes in size when precipitated during production and therefore hardly causes strength reduction. Found. Furthermore, the inventors have found a method of stably and uniformly dispersing and precipitating the present precipitate during production.

The high strength heat resistant steel of the present invention will be described in detail below.

The precipitate used in the present invention is a carbide containing Mo and Ti as a base and having a particle size of less than 10 nm. High strength is achieved by the effect of dispersion strengthening by this extremely fine precipitate. Further, this precipitate is very stable thermally, and high temperature strength is secured by hardly coarsening in the temperature range of 700 ° C or lower. Mo and Ti are elements that form carbides in the steel, and it has been conventionally performed to strengthen the steel by precipitation of the carbides.However, in the present invention, Mo and Ti are added in combination to obtain Mo and Ti. Characteristically, by finely precipitating a composite carbide containing as a base material in steel, a greater strength improving effect and thermal stability are obtained compared with the case of precipitation strengthening Mo and / or Ti alone. .

When the composite carbide containing Mo and Ti as a base is composed of only Mo, Ti, and C, the total amount of Mo and Ti and the amount of C are approximately 1: 1 in atomic ratio, and NaCl. These are compounded as a mold, and are extremely effective in strengthening, but as the content of Ti in the steel material increases, undissolved carbides of Ti will be generated during heating, and strengthening will reach the ceiling. There is a problem that becomes. In the present invention, in the composite carbide composed only of Mo, Ti, C, if a certain amount of Ti is contained in the carbide, other elements also have the same function as Ti, and in the formation of fine precipitates. It was found to contribute. That is, by adding Nb and / or V, Mo, Ti, Nb and / or
It was also found that a composite carbide containing V or V was precipitated.

Further, in the composite carbide containing Mo, Ti, Nb and / or V of the present invention, a part of Mo can be replaced with W. W is an element that can be replaced with Mo in a mass ratio of 2 to 1, and is a fine composite carbide containing Mo, W, and Ti, or Mo, W, Ti, Nb, and It forms a fine composite carbide containing V and / or V, and greatly contributes to the increase in strength.

Next, in order to uniformly disperse and precipitate the fine precipitates in the steel material, it is preferable that the structure of the parent phase is substantially a ferrite single phase.

Since the fine precipitates of the present invention are so-called phase interface precipitation type precipitates which are precipitated at the same time that austenite is transformed into ferrite, the higher the ferrite fraction of the matrix phase structure, the higher the precipitation strengthening ability. It will be demonstrated efficiently. On the other hand, when rapidly cooled to a temperature range where it transforms directly from austenite to bainite or martensite, instead of depositing the fine precipitates of the present invention, coarse cementite as carbides preferentially precipitates, High strength cannot be achieved. Further, when the matrix is partially bainite and the ratio of the portion where cementite is precipitated is large, a phenomenon in which coarsening occurs even if fine precipitates are present at the same time is observed. Therefore, in order to uniformly precipitate fine precipitates in the steel material and suppress coarsening, it is necessary that the matrix phase is substantially a ferrite single phase. However, if the volume fraction of the structure other than ferrite is low, the effect can be ignored, so other metal structures with a total volume fraction of 10% or less, namely bainite, martensite, cementite, pearlite, etc.,
You may contain 1 type (s) or 2 or more types.

In the steel of the present invention, the matrix phase is substantially a ferrite single phase, and the compound carbide containing Mo and Ti in the matrix basically (composite carbide containing Mo and Ti, Mo, Ti and
A composite carbide containing Nb and / or V, Mo, W, and
A composite carbide containing Ti, Mo, W, Ti, and a composite carbide containing Nb and / or V) are dispersed and precipitated, but as a precipitate, other than the above composite carbide, Ti
It also contains precipitates such as N and NbTiCN. Other precipitates may be contained as long as they do not impair the effect of increasing the strength of the present invention. However, in order to obtain the above-described effect of precipitation strengthening that is not conventional, 80% or more of the number of precipitates is a composite carbide containing carbides that basically contain Mo and Ti having a particle size of less than 10 nm. is necessary. It is preferably 95% or more. Since TiN is more stable than the composite carbide containing Mo and Ti as a base and is always precipitated, it is excluded from the number of the above-mentioned precipitates. Since TiN has a cubic shape, it can be easily distinguished from other precipitates.

In order to make the most of the precipitation strengthening, it is desirable to limit the content ratio of the elements forming the carbide as follows. That is, C content and M in atomic%
C / (M, which is the ratio of the total amount of o, Ti, W, Nb, and V
o + Ti + W + Nb + V) is preferably 0.5 to 3.0.
In order to effectively utilize the precipitation strengthening by the composite precipitate of the present invention, the C content and the carbide forming elements Mo, Ti, W,
The relationship between the amounts of Nb and V is important, and by adding these elements in a proper balance, a thermally stable and extremely fine composite precipitate can be obtained.

Next, the chemical composition of the high strength heat resistant steel of the present invention will be described.

C: 0.02 to 0.1% C is an element that contributes to precipitation strengthening as a carbide, but if it is less than 0.02%, a composite carbide required for precipitation strengthening cannot be obtained and sufficient strength cannot be secured. If it exceeds 0.1%, a low-temperature transformation phase other than ferrite easily forms, so the C content is specified to be 0.02 to 0.1%.

Si: 0.6% or less. Si is added for deoxidation and solid solution strengthening, but if it exceeds 0.6%, it raises the Ar ₃ point to promote high temperature precipitation and causes coarsening of the precipitate.
The content is specified to be 0.6% or less.

Mn: 0.5 to 2% Mn is added for solid solution strengthening and Ar ₃ point reduction, but if it is less than 0.5%, its effect is not sufficient, and if it exceeds 2%, a low temperature transformation phase is likely to be generated,
Since the phases other than ferrite easily form, change the Mn content.
Specify 0.5 to 2%.

Cr: 0.5 to 15% Cr is added to prevent oxidation and corrosion at high temperatures, but if it is less than 0.5%, its effect cannot be sufficiently obtained. The addition amount can be appropriately adjusted depending on the use temperature and environment, but if it exceeds 15%, properties other than weldability, toughness, etc., and properties other than corrosion resistance are impaired, so the Cr content is specified to be 0.5-15%.

Mo: 0.1 to 1%. Mo is an important element in the present invention, and forms a fine composite carbide containing Mo and Ti as a base, and greatly contributes to the increase in strength. 0.
If it is less than 1%, the composite carbide required for precipitation strengthening cannot be obtained, and sufficient strength cannot be secured. If it exceeds 1%, a low temperature transformation phase other than ferrite easily forms, so the Mo content should be
Specify from 0.02 to 0.4%.

Ti: 0.01 to 0.1%. Ti, like Mo, is an important element in the present invention, forms a complex carbide with Mo, and greatly contributes to the increase in strength. If it is less than 0.01%, the composite carbide required for precipitation strengthening cannot be obtained, and sufficient strength cannot be secured. Even if added in excess of 0.1%, undissolved carbides will remain during heating and the strength increasing effect will be saturated, so the Ti content is specified to be 0.01 to 0.1%.

Nb: 0 to 0.2% Nb improves toughness by making the structure finer, but forms a composite carbide with Ti, Mo, and W, and contributes to strength increase. However, if it exceeds 0.2%, a low-temperature transformation phase other than ferrite easily forms, so when Nb is contained, the content is specified to be 0 to 0.2%.

V: 0 to 0.1% V is Ti and M as well as Nb
It forms a complex precipitate with o and W and contributes to the strength increase.
However, if it exceeds 0.1%, a low-temperature transformation phase other than ferrite easily forms, so when V is contained, the content is 0 to 0.
Specify 1%.

W: 0 to 2% W is an element that can be replaced with Mo in a mass ratio of 2: 1, and Mo, W, and T
to form a fine composite carbide containing i and
It greatly contributes to the strength increase. If it exceeds 2%, a low temperature transformation phase other than ferrite is easily formed, so when W is contained, the content is specified to be 0 to 2%.

The balance other than the above is substantially Fe.
The fact that the balance consists essentially of Fe means that those containing other trace elements including unavoidable impurities can be included in the scope of the present invention unless the effects of the present invention are lost.

Next, a method for producing the high strength heat resistant steel of the present invention will be described.

The high-strength heat-resistant steel of the present invention uses a steel having the above-described composition and is manufactured by a conventional forming method, and then the formed steel material is reheated at a reheating temperature of 950 ° C. or higher. Subsequent cooling is performed at a cooling start temperature of Ar ₃ points or more, a cooling end temperature of 550 to 700 ° C., and a cooling rate of 2 ° C./s or more. Within 600 s after completion of the cooling, hold at 550 to 700 ° C. for 30 s or more. Then, by cooling with air, fine composite carbide containing Mo and Ti as a base can be dispersed and precipitated to be manufactured (first manufacturing method). Further, using a steel having the above-mentioned composition, heating temperature: 950 ° C. or higher, rolling finishing (end) temperature: hot rolling with Ar ₃ points or more, accelerated cooling after hot rolling, cooling start temperature: Ar ₃ points or more, cooling rate: 2 ° C / s or more, cooling end temperature: 550 to 700 ° C, and by holding at 550 to 700 ° C for 30s or more within 600s from the end of accelerated cooling, Mo and Ti are combined. It can be manufactured by dispersing and precipitating the fine composite carbide contained as a base (second manufacturing method). Further, using a steel having the above-mentioned composition, heating temperature: 950 ° C. or higher, rolling finishing (end) temperature: hot rolling with Ar ₃ points or more, accelerated cooling after hot rolling, cooling start temperature: Ar ₃ points or more, cooling rate: 2 ℃ / s
As described above, by performing cooling at a cooling end temperature of 600 to 700 ° C. and air-cooling after completion of accelerated cooling, it is possible to disperse and precipitate fine composite carbide containing Mo and Ti as a base (third manufacturing method).

Each manufacturing method will be described in detail below. First, the first manufacturing method will be described.

Forming step: A steel material is formed by using a normal method for producing heat-resistant steel. Ordinary heat-resisting steel is subjected to normalizing and tempering treatments after forming, but in the present invention, the steel material is strengthened by performing the following heat treatment.

Reheating temperature: 950 ° C. or higher. If the reheating temperature of the formed steel material is lower than 950 ° C, the solid solution of carbide is insufficient and the required strength cannot be obtained.

As for cooling after reheating, if cooling is carried out by cooling or gradual cooling, precipitates are precipitated from a high temperature range, so the precipitates are easily coarsened and the strength is lowered. Therefore, rapid cooling (accelerated cooling) is performed to an optimum temperature for precipitation strengthening to prevent precipitation from a high temperature range. As for the cooling method, any cooling equipment such as water cooling equipment can be used. After accelerated cooling, 550
The composite carbide containing Mo and Ti as a base is precipitated by holding at a temperature of 700 ° C. for a certain period of time or more.

Specifically, the cooling is started at a cooling start temperature: Ar ₃
Point or more, cooling rate: 2 ℃ / s or more, cooling end temperature: 550 to 70
Performed at 0 ℃, within 600s after the completion of accelerated cooling, 550-700 ℃
Hold for 30s or more. If the cooling rate in the temperature range from Ar ₃ point to 700 ° C. is less than 2 ° C./s, carbide precipitates and coarsens. Therefore, it is necessary to cool this range at 2 ° C./s or more.
However, when cooled to below 550 ° C, bainite or martensite transformation proceeds, so the cooling end temperature is 550
~ 700 ℃ After accelerated cooling, hold at 550-700 ° C for 30s or longer. Means such as heating and cooling can be appropriately used to maintain the temperature range. By holding for 30 s or more, it is possible to obtain a ferrite single structure in which precipitates containing Mo and Ti as a base are dispersed and precipitated. If the temperature is lower than 550 ° C, bainite is formed, and if it exceeds 700 ° C, the precipitates become coarse and sufficient strength cannot be obtained.
0 to 700 ° C. If it can be maintained at 550 to 700 ° C, the temperature can be raised or lowered within this temperature range, and it is not always necessary to maintain it at a constant temperature. Also, the retention time
If it is less than 30 s, the ferrite transformation is not completed, and bainite or pearlite is generated in the subsequent cooling, so the holding time is set to 30 s or more. If the ferrite transformation is completed by holding at 550 to 700 ° C, the subsequent cooling rate may be any rate. However, after the cooling is finished, if the temperature drops due to air cooling and the state of less than 550 ° C continues for more than 600s, bainite transformation proceeds. There is a need. To maintain the high temperature, any equipment such as atmosphere heating and induction heating may be used.

Next, the second manufacturing method will be described. In the second manufacturing method, hot rolling is performed under the following conditions as a steel material forming step, and the cooling step and the subsequent steps are performed in the same manner as the first manufacturing method.

Heating temperature: 950 ° C. or higher. The heating temperature is 9
If the temperature is less than 50 ° C, the solid solution of carbide is insufficient and the required strength cannot be obtained.

Rolling finishing (end) temperature: Ar ₃ points or more. A
If it is less than r ₃ points, the cooling start temperature will also be less than Ar ₃ points,
Since carbides precipitate and coarsen, the rolling finish temperature is set to Ar ₃
It is more than a point.

Cooling start temperature of accelerated cooling after hot rolling: Ar
₃ points or more, cooling rate: 2 ° C / s or more, cooling end temperature: 550 to 7
Set to 00 ° C. The cooling rate in the temperature range from Ar ₃ point to 700 ° C is 2
If it is less than ° C / s, carbides precipitate and coarsen,
It is necessary to cool this range at 2 ° C / s or more. But 550
Bainite or martensitic transformation proceeds when cooled to below ℃, so the cooling end temperature is set to 550 to 700 ℃.

Within 600 seconds after the completion of accelerated cooling, 550 to 700
Hold at ℃ for 30s or more. By holding for 30s or more,
It is possible to obtain a ferrite single structure in which precipitates containing Mo and Ti as a base are dispersed and precipitated. If the temperature is lower than 550 ° C, bainite is generated, and if it exceeds 700 ° C, the precipitates become coarse and sufficient strength cannot be obtained.
℃.

Next, the third manufacturing method will be described. Since the third manufacturing method is common to the second manufacturing method up to the molding step, only the cooling method will be described.

For the accelerated cooling after hot rolling, the cooling start temperature:
Ar ₃ points or more, cooling rate: 2 ° C / s or more, cooling end temperature: 600
Perform at ~ 700 ° C, then air cool. If the cooling rate in the temperature range from Ar ₃ point to 700 ° C. is less than 2 ° C./s, carbide precipitates and coarsens. Therefore, it is necessary to cool this range at 2 ° C./s or more. Therefore, the cooling end temperature should be 700 ° C or less.
As described above, after the accelerated cooling is completed, it is necessary to finely precipitate the carbides by maintaining the temperature at 550 to 700 ° C. for a certain time or longer, and in the third manufacturing method, the carbides are precipitated by air cooling. If air cooling from 600 ° C or higher, 550 ~
Since the holding time at 700 ℃ can be sufficiently secured, the cooling end temperature should be 600 ℃ or higher. Therefore, the cooling end temperature should be 600-70
By setting the temperature to 0 ° C. and then air-cooling, fine composite carbide containing Mo and Ti as a base is precipitated, and the high-strength heat-resistant steel of the present invention can be obtained.

In the steel of the present invention produced by the above-mentioned production method using the steel having the above component composition, fine composite carbides containing Mo and Ti as basic elements are dispersed and precipitated in the ferrite structure. Therefore, it has high strength in the temperature range of 700 ° C or less.

[0051]

[Examples] Table 1 shows the test steels used in this example (reference A to A).
J)) (the balance not shown in Table 1 is substantially Fe)
And unavoidable impurities). Reference signs A, C, E, G,
I has a chemical component within the scope of the present invention, and has the symbols B, D, F,
H and J are conventional steels as comparative examples. Symbols A and B are 1%
Cr-based steel, symbols C and D are 2.25% Cr-based steel, symbols E and F are 5% Cr
System steels, reference symbols G and H are 9% Cr system steels, and reference symbols I and J are 12% Cr system steels. A slab containing these chemical components was heated, rolled, and cooled to produce a steel plate having a plate thickness of 12 mm.

[0052]

[Table 1]

The steel sheet with the code A which is an example of the present invention is manufactured by the first manufacturing method described in the embodiment of the invention,
The steel plates designated by the reference signs C, G, and I are manufactured by the second manufacturing method, and the steel plate designated by the reference sign E is manufactured by the third manufacturing method. The steel plates with reference numerals B, D, F, H, and J, which are comparative examples, were manufactured by a normalizing and tempering process, which is a conventional heat-resistant steel manufacturing method. In addition, the steel plates with the reference numerals A, B, D, F, H, and J are heating temperatures of 1250 ° C., rolling finishing temperature of about 900 ° C., and cooling after the rolling finishing is performed by air cooling to room temperature. ,
It is manufactured by reheating. The production conditions of each steel sheet are shown in Tables 2, 3 and 4.

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

The microstructure of each manufactured steel sheet was observed and the creep rupture strength at a test temperature of 600 ° C. or 650 ° C. for 10 ⁴ hours was evaluated as a property. The results are shown in Table 5.

[0058]

[Table 5]

The microstructure was observed by an optical microscope and a transmission electron microscope (TEM) to measure the ferrite area fraction and the number of precipitates. The number of precipitates can be measured by using 0.
The measurement was performed on four areas of 5 × 0.5 μm. The composition of the precipitate was analyzed by energy dispersive X-ray spectroscopy (EDX).

1-5% Cr system steel (symbols A, B, C, D, E,
The creep rupture strength of 10 ⁴ hours at 600 ° C. in F), at 9 to 12% Cr steels (reference G, H, I, J) is
The high temperature strength of the steel of the present invention was compared with that of the conventional steel by evaluating the creep rupture strength at 650 ° C. for 10 ⁴ hours. At each Cr content level, the inventive examples had higher high-temperature strength than the comparative conventional steels. Since the steel according to the present invention is not coarsened after heat treatment fine precipitates for a long time, after a long study of 10 ⁴ hours decrease in strength is small, it can be maintained excellent high-temperature strength.

[0061]

As described above, according to the present invention, 70
In the temperature range of 0 ° C. or less, a ferritic heat-resistant steel having unprecedented high strength even during long-term use can be obtained. For this reason, it becomes possible to provide high-strength steel materials to the temperature and design stress sites where the conventional ferritic heat-resistant steel could not be applied.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Ishikawa             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Shigeru Endo             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Yoshimasa Funakawa             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Takeshi Shiozaki             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4K032 AA04 AA05 AA11 AA12 AA13                       AA16 AA17 AA19 AA20 AA22                       AA31 AA35 AA36 AA37 CA01                       CA02 CA03 CC03 CC04 CD02                       CD03 CE01

Claims (4)

[Claims] 1. In mass%, C: 0.02 to 0.1%, Si: 0.6% or less, Mn: 0.5 to 2%, Cr: 0.5 to 15%, Mo: 0.1 to 1%, W: 0 to
2%, Ti: 0.01 to 0.1%, Nb: 0 to 0.2%, V: 0 to 0.1%, the balance is substantially Fe, the metal structure is substantially a ferrite single phase, and Mo Carbides having a particle size of less than 10 nm containing Ti as a base are dispersed and precipitated, and the number of the carbides is
High-strength ferritic heat-resistant steel, characterized in that it is 80% or more of the total number of precipitates excluding TiN. 2. The formed steel material is reheated to a heating temperature of 950 ° C. or higher and cooled after the reheating, cooling start temperature: Ar ₃ points or higher, cooling end temperature: 550 to 700 ° C., cooling rate 2 ° C. Cool at above s / s, and within 3 seconds after the end of cooling, at 550-700 ℃, 3
The method for producing a high-strength ferritic heat-resistant steel according to claim 1, wherein the method is maintained for 0 s or more and then air-cooled. 3. Steel is hot-rolled at a heating temperature of 950 ° C. or higher and a rolling finishing temperature: Ar ₃ points or higher, and cooling after hot rolling is performed by cooling start temperature: Ar ₃ points or higher, cooling end temperature: 550. ~ 700 ℃,
Accelerated cooling at a cooling rate of 2 ° C / s or more, and after completion of the accelerated cooling 6
The method for producing a high-strength ferritic heat-resistant steel according to claim 1, characterized in that it is held within 00 s at 550 to 700 ° C for 30 s or more and then air-cooled. 4. Steel is hot-rolled at a heating temperature of 950 ° C. or higher and a rolling finishing temperature: Ar ₃ points or more, and cooling after hot rolling is performed by cooling start temperature: Ar ₃ points or more, cooling end temperature: 600. ~ 700 ℃,
The method for producing a high-strength ferritic heat-resistant steel according to claim 1, wherein accelerated cooling is performed at a cooling rate of 2 ° C / s or more, and then air cooling is performed.