JP4192249B2 - Method for producing ferritic oxide dispersion strengthened steel with coarse grain structure and excellent high temperature creep strength - Google Patents
Method for producing ferritic oxide dispersion strengthened steel with coarse grain structure and excellent high temperature creep strength Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 53
- 239000010959 steel Substances 0.000 title claims description 53
- 229910001175 oxide dispersion-strengthened alloy Inorganic materials 0.000 title claims description 22
- 238000004519 manufacturing process Methods 0.000 title claims description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 39
- 238000010438 heat treatment Methods 0.000 claims description 39
- 229910052760 oxygen Inorganic materials 0.000 claims description 39
- 239000001301 oxygen Substances 0.000 claims description 39
- 239000000843 powder Substances 0.000 claims description 27
- 230000009466 transformation Effects 0.000 claims description 24
- 229910000859 α-Fe Inorganic materials 0.000 claims description 13
- 230000015572 biosynthetic process Effects 0.000 claims description 12
- 238000005551 mechanical alloying Methods 0.000 claims description 8
- 238000010583 slow cooling Methods 0.000 claims description 8
- 229910045601 alloy Inorganic materials 0.000 claims description 7
- 239000000956 alloy Substances 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 239000002245 particle Substances 0.000 claims description 6
- 239000002994 raw material Substances 0.000 claims description 6
- 238000001192 hot extrusion Methods 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052721 tungsten Inorganic materials 0.000 claims description 2
- 239000013078 crystal Substances 0.000 description 24
- 239000000463 material Substances 0.000 description 24
- 239000011159 matrix material Substances 0.000 description 17
- 238000001816 cooling Methods 0.000 description 10
- 239000000203 mixture Substances 0.000 description 10
- 230000007423 decrease Effects 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 238000005728 strengthening Methods 0.000 description 6
- 150000001247 metal acetylides Chemical class 0.000 description 5
- 229910010413 TiO 2 Inorganic materials 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 3
- 239000010931 gold Substances 0.000 description 3
- 229910052737 gold Inorganic materials 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000000137 annealing Methods 0.000 description 2
- 239000002775 capsule Substances 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 238000001125 extrusion Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002579 anti-swelling effect Effects 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000000280 densification Methods 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000003758 nuclear fuel Substances 0.000 description 1
- 238000000879 optical micrograph Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 230000008961 swelling Effects 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/10—Nuclear fusion reactors
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- Powder Metallurgy (AREA)
Description
本発明は、高温クリープ強度に優れたフェライト系酸化物分散強化型鋼の製造方法に関し、さらに詳しくは、鋼中の過剰酸素量を調整して粗大結晶粒組織をもたらすことにより、優れた高温クリープ強度を付与することができるフェライト系酸化物分散強化型鋼の製造方法に関するものである。 The present invention relates to a method for producing a ferritic oxide dispersion-strengthened steel having excellent high-temperature creep strength, and more specifically, by adjusting the amount of excess oxygen in the steel to produce a coarse grain structure, excellent high-temperature creep strength. The present invention relates to a method for producing a ferritic oxide dispersion strengthened steel.
本発明のフェライト系酸化物分散強化型鋼は、特に高温での強度が求められる高速増殖炉燃料被覆管用材料、核融合炉第一壁材料、火力発電用材料等に好ましく利用できる。 The ferritic oxide dispersion-strengthened steel of the present invention can be preferably used for a fast breeder reactor fuel cladding tube material, a fusion reactor first wall material, a thermal power generation material, and the like that are particularly required to have strength at high temperatures.
優れた高温強度と耐中性子照射特性が要求される原子炉、特に高速炉の構成部材には、従来よりオーステナイト系ステンレス鋼が用いられてきたが、耐スエリング特性などの耐照射特性に限界がある。一方、フェライト系ステンレス鋼は耐照射特性に優れるものの、高温強度が低い欠点がある。 Austenitic stainless steel has been used for reactors that require excellent high-temperature strength and neutron resistance, especially fast reactors, but there are limits to anti-swelling properties such as swelling resistance. . On the other hand, although ferritic stainless steel is excellent in irradiation resistance, it has a defect of low high-temperature strength.
そこで、耐照射特性と高温強度特性に優れた材料として、フェライト系鋼中に微細な酸化物粒子を分散させたフェライト系酸化物分散強化型鋼が提案されている。またこのフェライト系酸化物分散強化型鋼の強度を向上させるためには、鋼中にＴｉを添加して酸化物分散粒子をさらに微細分散化させることが有効であることも知られている。 Therefore, as a material excellent in irradiation resistance and high-temperature strength characteristics, ferritic oxide dispersion strengthened steel in which fine oxide particles are dispersed in ferritic steel has been proposed. In order to improve the strength of this ferritic oxide dispersion strengthened steel, it is also known that it is effective to further finely disperse oxide dispersed particles by adding Ti to the steel.
特に、フェライト系酸化物分散強化型鋼の高温クリープ強度の改善には、粒界すべりを抑制するため結晶粒の大粒径化および等軸晶化を図ることが有効である。かような粗大結晶粒組織を得る方法として、Ａｃ3変態点以上に加熱保持する熱処理により十分なα→γ変態量を確保してα相からγ相へ相変態させることによりオーステナイト化し、その後に、γ相からα相へ相変態させてフェライト組織が得られるように十分遅い速度、すなわちフェライト形成臨界速度以下で徐冷する方法が提案されている（例えば特許文献１参照）。 In particular, in order to improve the high-temperature creep strength of ferritic oxide dispersion strengthened steel, it is effective to increase the grain size and equiaxed crystals in order to suppress intergranular slip. As a method for obtaining such a coarse crystal grain structure, a sufficient amount of α → γ transformation is ensured by heat treatment that is heated and held above the Ac 3 transformation point, and austenite is obtained by phase transformation from the α phase to the γ phase. There has been proposed a method of slow cooling at a sufficiently low speed, that is, a ferrite formation critical speed or less so that a ferrite structure is obtained by phase transformation from the γ phase to the α phase (see, for example, Patent Document 1).
しかしながら、フェライト系酸化物分散強化型鋼にＴｉを添加した場合には、Ｔｉがマトリックス中のＣと結合して炭化物を形成する結果、マトリックス中のＣ濃度が低下し、焼ならし熱処理時に十分なα→γ変態量が確保できないという問題がある。 However, when Ti is added to ferritic oxide dispersion strengthened steel, Ti combines with C in the matrix to form carbides, resulting in a decrease in the C concentration in the matrix, which is sufficient during normalizing heat treatment. There is a problem that the amount of α → γ transformation cannot be secured.
すなわち、上述したように、粗大結晶粒組織を得るためのフェライト系酸化物分散強化型鋼の熱処理は、Ａｃ3変態点以上に加熱保持する熱処理を施すことによってγ相とした後、フェライト形成臨界速度以下で徐冷するものであるが、Ｔｉはマトリックス中のγ相生成元素であるＣと親和力が強いため、ＴｉとＣとが結合して炭化物を形成し、その結果マトリックス中のＣ濃度が低下すると、Ａｃ3変態点以上で熱処理してもγ相の単相とならず、未変態のα相が残留する。そのため、γ相からフェライト形成臨界速度以下、例えば１００℃／時間以下で徐冷しても残留α相の存在によりγ相から変態したα相は細粒組織となってしまう。かような細粒組織は、高温強度の改善には寄与しない。 That is, as described above, the heat treatment of the ferritic oxide dispersion strengthened steel to obtain a coarse grain structure is made into a γ phase by performing a heat treatment that is held above the Ac 3 transformation point, and then the ferrite formation critical rate Although it is gradually cooled below, Ti has a strong affinity with C, which is a γ-phase-forming element in the matrix, so Ti and C combine to form a carbide, resulting in a decrease in the C concentration in the matrix. Then, even if heat treatment is performed at the Ac 3 transformation point or higher, a single phase of γ phase is not formed, and an untransformed α phase remains. For this reason, the α phase transformed from the γ phase becomes a fine-grained structure due to the presence of the residual α phase even if it is slowly cooled from the γ phase at a ferrite formation critical speed or less, for example, 100 ° C./hour or less. Such a fine grain structure does not contribute to the improvement of the high temperature strength.
そこで本発明は、フェライト系酸化物分散強化型鋼にＴｉを添加した場合でも、ＴｉとＣとの結合を抑制してマトリックス中のＣ濃度を維持し熱処理時に十分なα→γ変態を確保することにより、高温クリープ強度の改善に有効な粗大化した結晶粒組織を有するフェライト系酸化物分散強化型鋼を製造できる方法を提供することを目的とする。 Therefore, even when Ti is added to ferritic oxide dispersion strengthened steel, the present invention suppresses the bond between Ti and C, maintains the C concentration in the matrix, and ensures sufficient α → γ transformation during heat treatment. Thus, an object of the present invention is to provide a method capable of producing a ferritic oxide dispersion strengthened steel having a coarsened grain structure effective for improving high-temperature creep strength.
すなわち本発明は、元素粉末または合金粉末とＹ2Ｏ3粉末を混合して機械的合金化処理を行ない、熱間押出しにより固化した後、最終熱処理としてＡｃ3変態点以上への加熱保持とそれに続くフェライト形成臨界速度以下での徐冷熱処理を施すことにより、Ｃが０．０５〜０．２５％、Ｃｒが８．０〜１２．０％、Ｗが０．１〜４．０％、Ｔｉが０．１〜１．０％、Ｙ2Ｏ3が０．１〜０．５％、残部がＦｅおよび不可避不純物からなるＹ2Ｏ3粒子を分散させたフェライト系酸化物分散強化型鋼を製造する方法であって、鋼中の過剰酸素量（鋼中の酸素量からＹ2Ｏ3中の酸素量を差し引いた値）が
０．６７Ｔｉ−２．７Ｃ＋０．４５＞Ex.O＞０．６７Ｔｉ−２．７Ｃ＋０．３５
（式中、Ex.O：鋼中の過剰酸素量、質量％
Ｔｉ：鋼中のＴｉ含有量、質量％
Ｃ：鋼中のＣ含有量、質量％）
となるように機械的合金化処理に際して混合する原料粉末としてＦｅ2Ｏ3粉末を追加的に添加することを特徴とする粗大結晶粒組織を有する高温クリープ強度に優れたフェライト系酸化物分散強化型鋼の製造方法である。（なお、以下の本明細書中の記載において「％」はいずれも「重量％」を表すものとする。）
That is, in the present invention, elemental powder or alloy powder and Y 2 O 3 powder are mixed and mechanically alloyed, solidified by hot extrusion, and then heated to the Ac 3 transformation point or higher as the final heat treatment. Subsequent annealing heat treatment at a critical speed of ferrite formation or less causes C to be 0.05 to 0.25%, Cr is 8.0 to 12.0%, W is 0.1 to 4.0%, Ti Of ferrite-based oxide dispersion strengthened steel in which Y 2 O 3 particles consisting of 0.1 to 1.0% of Y 2 O 3 , 0.1 to 0.5% of Y 2 O 3 and the balance of Fe and inevitable impurities are dispersed The amount of excess oxygen in the steel (the value obtained by subtracting the amount of oxygen in Y 2 O 3 from the amount of oxygen in steel) is 0.67Ti-2.7C + 0.45>Ex.O> 0.67Ti -2.7C + 0.35
(In the formula, Ex.O: excess oxygen in steel, mass%
Ti: Ti content in steel, mass%
C: C content in steel, mass%)
Ferritic oxide dispersion strengthened steel having a coarse grain structure and excellent in high-temperature creep strength, characterized in that Fe 2 O 3 powder is additionally added as a raw material powder to be mixed during mechanical alloying treatment It is a manufacturing method. (In the following description of the present specification, “%” means “% by weight”.)
上述したごとき本発明によれば、原料粉末として不安定酸化物であるＦｅ2Ｏ3粉末を追加的に添加して鋼中の過剰酸素量を所定の範囲とすることにより、ＴｉはＣと結合して炭化物を形成せずに、過剰酸素と結合して酸化物を形成するため、マトリックス中のＣ濃度を低下させることがない。この結果、Ａｃ3変態点以上での熱処理時に十分なα→γ変態が生じてγ単相とすることができ、さらにそれに続くフェライト形成臨界速度以下で徐冷する熱処理を行うことにより粗大化結晶粒組織を有するα相を形成することができ、高温クリープ強度の向上をもたらすことができる。 According to the present invention as described above, Ti is bonded to C by adding Fe 2 O 3 powder, which is an unstable oxide, as a raw material powder so that the amount of excess oxygen in the steel is within a predetermined range. In this way, the oxide is formed by combining with excess oxygen without forming carbides, so that the C concentration in the matrix is not lowered. As a result, a sufficient α → γ transformation occurs during the heat treatment at the Ac 3 transformation point or higher, so that a γ single phase can be obtained. An α phase having a grain structure can be formed, and high temperature creep strength can be improved.
以下に本発明のフェライト系酸化物分散強化型鋼の化学成分およびその限定理由について説明する。 The chemical components of the ferritic oxide dispersion strengthened steel of the present invention and the reasons for limitation will be described below.
Ｃｒは、耐食性の確保に重要な元素であり、８．０％未満となると耐食性の悪化が著しくなる。また１２．０％を超えると、靱性および延性の低下が懸念される。この理由から、Ｃｒ含有量は８．０〜１２．０％とする。 Cr is an important element for ensuring corrosion resistance. When the content is less than 8.0%, the corrosion resistance is remarkably deteriorated. Moreover, when it exceeds 12.0%, there exists a concern about a fall of toughness and ductility. For this reason, the Cr content is set to 8.0 to 12.0%.
Ｃの含有量は以下の理由から決定される。本発明は、一旦Ａｃ3変態点以上の熱処理を施すことによるα→γ変態とそれに続く徐冷熱処理により、等軸かつ粗大な結晶粒組織を得るものである。すなわち、等方的かつ粗大な結晶粒組織を得るためには、熱処理によりα→γ変態を生じさせることが不可欠である。
Ｃｒ含有量が８．０〜１２．０％の場合に、α→γ変態を生じさせるためには、Ｃを０．０５％以上含有させる必要がある。このα→γ変態は１０００〜１１５０℃×０．５〜１時間の熱処理により生じる。Ｃ含有量が高くなるほど炭化物（Ｍ23Ｃ6、Ｍ6Ｃ等）の析出量が多くなり高温強度が高くなるが、０．２５％より多量に含有すると加工性が悪くなる。この理由から、Ｃ含有量は０．０５〜０．２５％とする。
The C content is determined for the following reason. In the present invention, an equiaxed and coarse crystal grain structure is obtained by the α → γ transformation once subjected to the heat treatment at the Ac 3 transformation point or higher and the subsequent annealing treatment. That is, in order to obtain an isotropic and coarse crystal grain structure, it is essential to cause the α → γ transformation by heat treatment.
In order to cause the α → γ transformation when the Cr content is 8.0 to 12.0%, it is necessary to contain 0.05% or more of C. This α → γ transformation is caused by heat treatment at 1000 to 1150 ° C. for 0.5 to 1 hour. The higher the C content, the greater the amount of carbides (M 23 C 6 , M 6 C, etc.) precipitated and the higher the high-temperature strength. However, when the content is higher than 0.25%, the workability deteriorates. For this reason, the C content is set to 0.05 to 0.25%.
Ｗは、合金中に固溶し高温強度を向上させる重要な元素であり、０．１％以上添加する。Ｗ含有量を多くすれば、固溶強化作用、炭化物（Ｍ23Ｃ6、Ｍ6Ｃ等）析出強化作用、金属間化合物析出強化作用により、クリープ破断強度が向上するが、４．０％を超えるとδフェライト量が多くなり、かえって強度も低下する。この理由から、Ｗ含有量は０．１〜４．０％とする。 W is an important element that improves the high-temperature strength by dissolving in the alloy, and is added in an amount of 0.1% or more. Increasing the W content improves the creep rupture strength by solid solution strengthening action, carbide (M 23 C 6 , M 6 C, etc.) precipitation strengthening action, and intermetallic compound precipitation strengthening action, but 4.0% If it exceeds, the amount of δ ferrite increases, and the strength also decreases. For this reason, the W content is 0.1 to 4.0%.
Ｔｉは、Ｙ2Ｏ3の分散強化に重要な役割を果たし、Ｙ2Ｏ3と反応してＹ2Ｔｉ2Ｏ7またはＹ2ＴｉＯ5 という複合酸化物を形成して、酸化物粒子を微細化させる働きがある。この作用はＴｉ含有量が１．０％を超えると飽和する傾向があり、０．１％未満では微細化作用が小さい。この理由から、Ｔｉ含有量は０．１〜１．０％とする。 Ti is, Y 2 O play an important role in the dispersion strengthening of the 3, it reacts with Y 2 O 3 to form a Y 2 Ti 2 O 7 or the composite oxide of Y 2 TiO 5, the oxide particles fine There is a function to make it. This effect tends to saturate when the Ti content exceeds 1.0%, and if it is less than 0.1%, the refining effect is small. For this reason, the Ti content is set to 0.1 to 1.0%.
Ｙ2Ｏ3は、分散強化により高温強度を向上させる重要な添加物である。この含有量が０．１％未満の場合には、分散強化の効果が小さく強度が低い。一方、０．５％を超えて含有すると、硬化が著しく加工性に問題が生じる。この理由から、Ｙ2Ｏ3の含有量は０．１〜０．５％とする。 Y 2 O 3 is an important additive that improves high temperature strength by dispersion strengthening. When this content is less than 0.1%, the dispersion strengthening effect is small and the strength is low. On the other hand, if the content exceeds 0.5%, the curing is remarkably caused and a problem occurs in workability. For this reason, the content of Y 2 O 3 is set to 0.1 to 0.5%.
本発明によるフェライト系酸化物分散強化型鋼の製造方法は、金属元素粉末または合金粉末さらには酸化物粉末といった原料粉末を目標組成となるように調合し、いわゆる機械的合金化処理（メカニカルアロイング）によって合金化する。この合金化粉末を押出用カプセルに充填した後、脱気、密封して熱間押出しを行って固化し、例えば押出棒材とする。 The method for producing ferritic oxide dispersion strengthened steel according to the present invention comprises preparing a raw material powder such as a metal element powder or an alloy powder and further an oxide powder so as to have a target composition, and so-called mechanical alloying treatment (mechanical alloying). Alloy by. After this alloyed powder is filled into an extrusion capsule, it is degassed and sealed, and hot extruded to solidify, for example, to obtain an extruded bar.
得られた熱間押出棒材は、最終熱処理として、Ａｃ3変態点以上での加熱保持とそれに続くフェライト形成臨界速度以下での徐冷熱処理を施す。徐冷熱処理は通常は炉内で徐々に冷却する炉冷熱処理とすることができ、フェライト形成臨界速度以下の冷却速度は、一般的には１００℃／時間以下、好ましくは５０℃／時間以下とすることができる。
本発明のフェライト系酸化物分散強化型鋼の場合、Ａｃ3変態点は約９００〜１２００℃程度であり、Ｃ量が０．１３％の場合にはＡｃ3変態点は約９５０℃である。
As a final heat treatment, the obtained hot-extrusion rod is subjected to heating and holding at the Ac 3 transformation point or higher and subsequent slow cooling heat treatment at a ferrite forming critical speed or lower. The slow cooling heat treatment can be a furnace cooling heat treatment that usually cools gradually in the furnace, and the cooling rate below the ferrite formation critical rate is generally 100 ° C./hour or less, preferably 50 ° C./hour or less. can do.
In the case of the ferritic oxide dispersion strengthened steel of the present invention, the Ac 3 transformation point is about 900 to 1200 ° C., and when the C content is 0.13%, the Ac 3 transformation point is about 950 ° C.
本発明においては、鋼中のＴｉがＣと結合して炭化物を形成し、マトリックス中のＣ濃度が低下しないようにする手段として、機械的合金化処理に際して混合する原料粉末として、不安定酸化物であるＦｅ2Ｏ3粉末を追加的に混合して鋼中の過剰酸素量を増加させる方法も採用することができる。この場合、ＴｉはＦｅ2Ｏ3由来の鋼中の過剰酸素と結合して酸化物を形成し、Ｃと結合して炭化物を形成することがないから、マトリックス中のＣ濃度の低下を抑制することができる。 In the present invention, as a means to prevent Ti in the steel from combining with C to form carbides and lowering the C concentration in the matrix, the unstable oxide is used as the raw material powder to be mixed in the mechanical alloying process. A method of increasing the amount of excess oxygen in the steel by additionally mixing the Fe 2 O 3 powder can be employed. In this case, Ti combines with excess oxygen in steel derived from Fe 2 O 3 to form an oxide, and does not combine with C to form a carbide, thereby suppressing a decrease in C concentration in the matrix. be able to.
Ｆｅ2Ｏ3粉末の混合量は、鋼中の過剰酸素量が
０．６７Ｔｉ−２．７Ｃ＋０．４５＞Ex.O＞０．６７Ｔｉ−２．７Ｃ＋０．３５
（式中、Ex.O：鋼中の過剰酸素量（％）
Ｔｉ：鋼中のＴｉ含有量（％）
Ｃ：鋼中のＣ含有量（％）
となるようにする。かような過剰酸素量の上限および下限の設定理由を以下に説明する。
The mixing amount of the Fe 2 O 3 powder is such that the excess oxygen amount in the steel is 0.67Ti-2.7C + 0.45>Ex.O> 0.67Ti-2.7C + 0.35.
(In the formula, Ex.O: Excess oxygen in steel (%)
Ti: Ti content in steel (%)
C: C content in steel (%)
To be. The reason for setting the upper limit and the lower limit of such excess oxygen amount will be described below.
表１は、フェライト系酸化物分散強化型鋼試作材の目標組成と成分の特徴をまとめて示している。 Table 1 summarizes the target composition and component characteristics of the ferritic oxide dispersion strengthened steel prototype.
各試作材とも、元素粉末あるいは合金粉末と酸化物粉末を目標組成に調合し、高エネルギーアトライター中に装入後、９９．９９％のＡｒ雰囲気中で撹拌して機械的合金化処理を行った。アトライターの回転数は約２２０ｒｐｍ、撹拌時間は約４８ｈｒとした。得られた合金化粉末を軟鋼製カプセルに充填後、高温真空脱気して約１１５０〜１２００℃、７〜８：１の押出比で熱間押出しを行い、熱間押出棒材を得た。 For each prototype, elemental powder or alloy powder and oxide powder are prepared to the target composition, and after charging into a high-energy attritor, stirring is performed in a 99.99% Ar atmosphere for mechanical alloying. It was. The rotation speed of the attritor was about 220 rpm, and the stirring time was about 48 hours. The obtained alloyed powder was filled into a mild steel capsule and then subjected to high temperature vacuum degassing and hot extrusion at an extrusion ratio of about 1150 to 1200 ° C. and 7 to 8: 1 to obtain a hot extruded bar.
表１中、試作材ＭＭ１３とＴ１４が基本組成であり、Ｔ３はＴ１４の組成にＦｅ2Ｏ3を添加することにより過剰酸素量を増加させた試料、Ｔ４はＴｉ添加量を増加させた試料、Ｔ５はＴｉ添加量を増加させるとともにＦｅ2Ｏ3を添加して過剰酸素量を増加させた試料である。 In Table 1, prototype materials MM13 and T14 are basic compositions, T3 is a sample in which the amount of excess oxygen is increased by adding Fe 2 O 3 to the composition of T14, T4 is a sample in which the amount of Ti addition is increased, T5 is a sample in which the amount of excess oxygen is increased by increasing the amount of Ti added and adding Fe 2 O 3 .
上記で得られた各試作材（熱間押出棒材）の成分分析結果を表２にまとめて示す。
ここで、過剰酸素量とは、化学成分の分析結果における試作材中の酸素量から分散酸化物（Ｙ2Ｏ3）中の酸素量を差し引いた値である。
Table 2 summarizes the component analysis results of each prototype material (hot extruded rod) obtained above.
Here, the excess oxygen amount is a value obtained by subtracting the oxygen amount in the dispersed oxide (Y 2 O 3 ) from the oxygen amount in the prototype material in the analysis result of the chemical component.
これらの試作材について、最終熱処理として、熱処理（Ａｃ3変態点以上での加熱保持：１０５０℃×１ｈｒ）とそれに続く炉冷熱処理（フェライト形成臨界速度以下での徐冷熱処理：３７℃／ｈｒの速度で１０５０℃から６００℃まで徐冷）を施した。 For these prototype materials, as the final heat treatment, heat treatment (heat retention above the Ac 3 transformation point: 1050 ° C. × 1 hr) and subsequent furnace cooling heat treatment (slow cooling heat treatment below the critical rate of ferrite formation: 37 ° C./hr) (Slow cooling from 1050 ° C. to 600 ° C.).
熱処理後の各試作材の金相組織の光学顕微鏡写真を図１（Ｔ１４、ＭＭ１３、Ｔ３、Ｔ４）と図２（Ｔ５）に示す。これらを観察してわかるように、炉冷熱処理により結晶粒が十分成長している試料と成長していない試料がある。結晶粒成長が生じているＴ３は、基本組成にＦｅ2Ｏ3を添加した試料である。Ｔ３においては、鋼中のＴｉと化学結合する過剰酸素量が十分に存在するため、炭化物ＴｉＣの形成によるマトリックス中のＣ濃度の減少を抑えられる結果、熱処理時におけるα→γ変態、その後の炉冷熱処理での結晶粒成長が効果的に生じると考えられる。 An optical micrograph of the gold phase structure of each prototype after heat treatment is shown in FIG. 1 (T14, MM13, T3, T4) and FIG. 2 (T5). As can be seen from these observations, there are samples in which crystal grains are sufficiently grown by furnace cooling heat treatment and samples in which crystals are not grown. T3 where crystal grain growth occurs is a sample in which Fe 2 O 3 is added to the basic composition. In T3, since there is a sufficient amount of excess oxygen chemically bonded to Ti in the steel, the decrease in the C concentration in the matrix due to the formation of carbide TiC can be suppressed. As a result, the α → γ transformation during heat treatment, the subsequent furnace It is considered that crystal grain growth is effectively caused by the cold heat treatment.
一方、結晶粒成長の少ないＴ４とＴ５は、基本組成よりＴｉ添加量を増量させた試料（Ｔ４）、およびＦｅ2Ｏ3を添加しているがＴｉ添加量も増量させた試料（Ｔ５）である。これらの試料においては、多量のＴｉがＣと化学結合して炭化物を形成するためマトリックス中のＣ濃度が極度に減少してしまうか（Ｔ４）、あるいはＦｅ2Ｏ3を添加しても多量のＴｉとＣとの化学結合を阻止するほどに十分の過剰酸素量が存在していない（Ｔ５）と考えられる。 On the other hand, T4 and T5 with little crystal grain growth are the sample (T4) in which the Ti addition amount is increased from the basic composition and the sample (T5) in which Fe 2 O 3 is added but the Ti addition amount is also increased. is there. In these samples, a large amount of Ti chemically bonds with C to form carbides, so the C concentration in the matrix is extremely reduced (T4), or even if Fe 2 O 3 is added, a large amount It is considered that there is not a sufficient amount of excess oxygen to prevent chemical bonding between Ti and C (T5).
なお、ＭＭ１３とＴ１４はいずれも基本組成であり組成的には同等のものであるが、ＭＭ１３（過剰酸素量：０．１３７％）は結晶粒が成長しており、Ｔ１４（過剰酸素量：０．１１０％）は結晶粒成長が少なくなっている。この理由は、組成が同じであっても機械的合金化処理やその後の熱処理等の過程で、鋼中に混入する酸素量が微妙に相違し、ＭＭ１３は鋼中のＴｉと化学結合するに十分な過剰酸素量が存在したたためと考えられる。 Note that MM13 and T14 are both basic compositions and equivalent in composition, but MM13 (excess oxygen amount: 0.137%) has crystal grains grown and T14 (excess oxygen amount: 0). .110%) has less crystal grain growth. The reason for this is that even if the composition is the same, the amount of oxygen mixed in the steel is slightly different in the process of mechanical alloying and subsequent heat treatment, and MM13 is sufficient to chemically bond with Ti in the steel. This is probably because there was a large excess of oxygen.
図３のグラフは、各試作材のＴｉ含有量と過剰酸素量との関係を示している。このグラフから、Ｅｘ．Ｏ＞０．６１Ｔｉ［Ｅｘ．Ｏ：過剰酸素量（％）、Ｔｉ：鋼中のＴｉ含有量（％）］の関係を満たしている試作材ＭＭ１３、Ｔ３については、炉冷熱処理により結晶粒の粗大化が生じていることがわかる。 The graph of FIG. 3 shows the relationship between the Ti content and the excess oxygen amount of each prototype material. From this graph, Ex. O> 0.61Ti [Ex. In the prototype materials MM13 and T3 satisfying the relationship of O: excess oxygen amount (%), Ti: Ti content in steel (%)], the crystal grains are coarsened by the furnace cooling heat treatment. Recognize.
以上の結果はすべて鋼中の炭素量が約０．１３％の場合の結果である。上記のＥｘ．Ｏ＞０．６１Ｔｉをモル量に単位換算すると
Ｅｘ．Ｏ′(mol/g)＞１．８６Ｔｉ′≒２Ｔｉ′(mol/g)
となり、鋼中のすべてのＴｉがＴｉＯ2を形成できるだけの過剰酸素量が存在した場合（マトリックス中の残存Ｃ量が０．１３％以上の場合）には、結晶粒の粗大化が生じると考えられる。
The above results are all the results when the carbon content in the steel is about 0.13%. Ex. When O> 0.61Ti is converted into a molar amount, Ex. O ′ (mol / g)> 1.86 Ti′≈2 Ti ′ (mol / g)
Thus, when there is an excess amount of oxygen that allows all Ti in the steel to form TiO 2 (when the amount of residual C in the matrix is 0.13% or more), it is considered that crystal grains become coarse. It is done.
上述の結果から、本発明のフェライト系酸化物分散強化型鋼では、ＴｉＯ2およびＴｉＣの形成を考慮したマトリックス中の残存Ｃ量が０．１３％（１．０８×１０-4mol/g）以上であれば、熱処理時に十分なα→γ変態が生じて炉冷熱処理により結晶粒の粗大化が生じると考えられる。ＴｉＯ2およびＴｉＣの形成を考慮したマトリックス中の残存Ｃ量（Ｃ′ｒ mol/g）は次式のように表わされる。 From the above results, in the ferritic oxide dispersion strengthened steel of the present invention, the residual C content in the matrix considering the formation of TiO 2 and TiC is 0.13% (1.08 × 10 −4 mol / g) or more. If this is the case, it is considered that a sufficient α → γ transformation occurs during the heat treatment, and the crystal grains become coarse due to the furnace cooling heat treatment. The amount of residual C (C′r mol / g) in the matrix considering the formation of TiO 2 and TiC is expressed by the following equation.
Ｃ′ｒ＝Ｃ′−（Ｔｉ′−０．５Ｅｘ．Ｏ′）
ここで、Ｃ′ｒ(mol/g)：ＴｉＯ2およびＴｉＣの形成を考慮したマトリックス中の残存Ｃ量
Ｃ′(mol/g)：鋼中のＣ含有量
Ｔｉ′(mol/g)：鋼中のＴｉ含有量
Ｅｘ．Ｏ′(mol/g)：鋼中の過剰酸素量
である。
C'r = C '-(Ti'-0.5Ex.O')
Here, C′r (mol / g): the amount of residual C in the matrix considering the formation of TiO 2 and TiC
C ′ (mol / g): C content in steel
Ti ′ (mol / g): Ti content in steel
Ex. O ′ (mol / g): The amount of excess oxygen in the steel.
よって、結晶粒粗大化の条件式は下式となる。
Ｃ′ｒ＝Ｃ′−（Ｔｉ′−０．５Ｅｘ．Ｏ′）≧１．０８×１０-4
単位を mol/g から％に変換して整理すると上式は
Ｅｘ．Ｏ＞０．６７Ｔｉ−２．７Ｃ＋０．３５
となる。
Therefore, the conditional expression for crystal grain coarsening is as follows.
C′r = C ′ − (Ti′−0.5Ex.O ′) ≧ 1.08 × 10 −4
When the unit is converted from mol / g to% and rearranged, the above equation becomes Ex. O> 0.67Ti-2.7C + 0.35
It becomes.
過剰酸素は金属Ｔｉ、Ｙ2Ｏ3と結合して微細な複合酸化物を形成するとともに、マトリックス中のＣとＴｉの結合を抑制して、マトリックス中に十分なＣ量を確保する重要な元素である。しかし、０．６７Ｔｉ−２．７Ｃ＋０．４５以上の過剰酸素は、分散粒子の微細高密度化を著しく阻害する。また、過剰な酸素の混入は靱性の著しい低下を引き起こすとともに、少量のＳｉ、Ｍｎ等と介在物を形成しやすくなるため、過剰酸素量の上限値を０．６７Ｔｉ−２．７Ｃ＋０．４５とする。 Excess oxygen combines with metals Ti and Y 2 O 3 to form fine composite oxides, and suppresses the binding of C and Ti in the matrix to ensure a sufficient amount of C in the matrix It is. However, excess oxygen of 0.67Ti-2.7C + 0.45 or more remarkably hinders the fine densification of the dispersed particles. In addition, excessive oxygen contamination causes a significant decrease in toughness and easily forms inclusions with a small amount of Si, Mn, etc., so the upper limit of the excess oxygen amount is 0.67Ti-2.7C + 0.45. .
図４のグラフは、上述した結晶粒粗大化の条件式の上限と下限の範囲を斜線部分で表し、各試作材の実測値をプロットしたものである。条件式はＣ量を０．１３％として計算しているが、結晶粒が成長した試作材ＭＭ１３、Ｔ３はすべて斜線範囲内に位置し、結晶粒が成長しなかった試作材Ｔ１４、Ｔ５、Ｔ４はすべて斜線範囲外に位置しており、この条件式が妥当であることを示している。なお、図４のグラフ中で試作材番号が記されていないプロットについても、斜線範囲内に位置する試作材では結晶粒の粗大化が生じており、斜線範囲外に位置するものでは結晶粒の粗大化が生じていないことが確認されている。 The graph of FIG. 4 represents the range of the upper limit and the lower limit of the conditional expression for the grain coarsening described above with hatched portions, and plots the actual measurement values of each prototype material. Although the conditional expression is calculated with the C content being 0.13%, the prototype materials MM13 and T3 with crystal grains grown are all located within the hatched area, and the prototype materials T14, T5 and T4 with no crystal grains grown are used. Are all located outside the shaded area, indicating that this conditional expression is valid. In addition, in the plot in which the prototype material number is not described in the graph of FIG. 4, the crystal grains are coarsened in the prototype material located within the hatched range, and the crystal grains of the plot located outside the shaded range are generated. It has been confirmed that no coarsening has occurred.
以上詳述した理由により、本発明において、機械的合金化処理に際して混合する原料粉末としてＦｅ2Ｏ3粉末を追加的に混合して鋼中の過剰酸素量を増加させ場合には、鋼中の過剰酸素量が結晶粗大化の条件式
０．６７Ｔｉ−２．７Ｃ＋０．４５＞Ex.O＞０．６７Ｔｉ−２．７Ｃ＋０．３５
となるようにＦｅ2Ｏ3粉末を添加する。
For the reason detailed above, in the present invention, when the excess oxygen amount in the steel is increased by additionally mixing Fe 2 O 3 powder as a raw material powder to be mixed in the mechanical alloying treatment, Conditional expression for excessive oxygen content is crystal coarsening 0.67Ti-2.7C + 0.45>Ex.O> 0.67Ti-2.7C + 0.35
Fe 2 O 3 powder is added so that
〈高温クリープ破断試験〉
試作材Ｔ３に対して、本発明による熱処理、すなわち、熱処理（Ａｃ3変態点以上での加熱保持：１０５０℃×１ｈｒ）とそれに続く炉冷熱処理（フェライト形成臨界速度以下での徐冷熱処理：３７℃／ｈｒの速度で１０５０℃から６００℃まで徐冷）を施して、結晶粒を粗大化させた試料（Ｔ３（ＦＣ材））を準備した。
<High temperature creep rupture test>
For the prototype T3, heat treatment according to the present invention, that is, heat treatment (heat retention above the Ac 3 transformation point: 1050 ° C. × 1 hr) and subsequent furnace cooling heat treatment (slow cooling heat treatment below the ferrite formation critical speed: 37) A sample (T3 (FC material)) in which the crystal grains were coarsened by slow cooling from 1050 ° C. to 600 ° C. at a rate of ° C./hr was prepared.
これとは別に、試作材Ｔ１４、Ｔ３に対して、焼ならし熱処理（１０５０℃×１ｈｒ・空冷(AC)）とそれに続く焼戻し熱処理（７８０℃×１ｈｒ・空冷(AC)）を施して、結晶粒が微細となっている試料（Ｔ１４（ＮＴ材）、Ｔ３（ＮＴ材））を準備した。 Separately, the samples T14 and T3 are subjected to normalizing heat treatment (1050 ° C. × 1 hr · air cooling (AC)) and subsequent tempering heat treatment (780 ° C. × 1 hr · air cooling (AC)) to produce crystals. Samples with fine grains (T14 (NT material), T3 (NT material)) were prepared.
これらの試料について、試験温度７００℃で単軸クリープ破断試験を行った結果を図５のグラフに示す。Ｆｅ2Ｏ3粉末を追加的に混合して過剰酸素量を増加さ せるとともに、炉冷熱処理で結晶粒を粗大化させたＴ３（ＦＣ材）が、その他の試作材に比べて高温クリープ強度が向上していることが図５のグラフからわかる。 The results of a uniaxial creep rupture test performed on these samples at a test temperature of 700 ° C. are shown in the graph of FIG. T3 (FC material), in which Fe 2 O 3 powder is additionally mixed to increase the amount of excess oxygen and the crystal grains are coarsened by furnace cooling heat treatment, has a higher temperature creep strength than other prototype materials. It can be seen from the graph of FIG.
以上説明したところからわかるように本発明によれば、フェライト系酸化物分散強化型鋼にＴｉを添加した場合でも、ＴｉとＣとの結合を抑制してマトリックス中のＣ濃度を維持し熱処理時に十分なα→γ変態を確保することができ、これにより粗大化した結晶粒を生成できる結果、優れた高温クリープ強度を有するフェライト系酸化物分散強化型鋼を得ることができる。 As can be seen from the above description, according to the present invention, even when Ti is added to the ferritic oxide dispersion strengthened steel, the bonding between Ti and C is suppressed and the C concentration in the matrix is maintained and sufficient during heat treatment. As a result, it is possible to obtain a ferrite-based oxide dispersion strengthened steel having excellent high-temperature creep strength.
Claims (1)
０．６７Ｔｉ−２．７Ｃ＋０．４５＞Ex.O＞０．６７Ｔｉ−２．７Ｃ＋０．３５
（式中、Ex.O：鋼中の過剰酸素量、質量％
Ｔｉ：鋼中のＴｉ含有量、質量％
Ｃ：鋼中のＣ含有量、質量％）
となるように機械的合金化処理に際して混合する原料粉末としてＦｅ2Ｏ3粉末を追加的に添加することを特徴とする粗大結晶粒組織を有する高温クリープ強度に優れたフェライト系酸化物分散強化型鋼の製造方法。 Elemental alloy or alloy powder and Y 2 O 3 powder are mixed and mechanically alloyed, solidified by hot extrusion, and then heated to the Ac 3 transformation point or higher as the final heat treatment, followed by the critical rate of ferrite formation By performing the slow cooling heat treatment below, by mass%, C is 0.05 to 0.25%, Cr is 8.0 to 12.0%, W is 0.1 to 4.0%, and Ti is A ferritic oxide dispersion strengthened steel in which Y 2 O 3 particles composed of 0.1 to 1.0%, Y 2 O 3 is 0.1 to 0.5%, and the balance is Fe and inevitable impurities is produced. The amount of excess oxygen in steel (the value obtained by subtracting the amount of oxygen in Y 2 O 3 from the amount of oxygen in steel) is 0.67Ti-2.7C + 0.45>Ex.O> 0.67Ti- 2.7C + 0.35
(In the formula, Ex.O: excess oxygen in steel, mass%
Ti: Ti content in steel, mass%
C: C content in steel, mass%)
Ferritic oxide dispersion strengthened steel having a coarse grain structure and excellent in high-temperature creep strength, characterized in that Fe 2 O 3 powder is additionally added as a raw material powder to be mixed during mechanical alloying treatment Manufacturing method.
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| CN106399807A (en) * | 2016-09-28 | 2017-02-15 | 天津大学 | Preparation method of oxide dispersion strengthened steel with micro-nano-scale double-crystal-grain structure |
| CN110885954B (en) * | 2018-09-07 | 2021-03-30 | 天津大学 | Application of ferrite-based ODS steel in supercritical water service condition |
| CN111349842B (en) * | 2020-02-27 | 2021-05-18 | 北京科技大学 | Method for preparing oxide dispersion strengthened steel through high-flux continuous smelting |
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