JP6089186B2 - Ultra-fine powder, high-strength steel sintered body, and production method thereof - Google Patents
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本発明は、室温強度と高温クリープ強度に優れた鋼製の超微細粉末、この粉末を焼結して製造した高強度鋼焼結体、及びそれらの製造方法に関するものである。 The present invention relates to an ultrafine powder made of steel excellent in room temperature strength and high-temperature creep strength, a high-strength steel sintered body produced by sintering this powder, and a production method thereof.
近年環境負荷の低減、リサイクル性の向上のため、金属材料においては合金元素の低減が重要視されており、高強度化に当たっても化学組成を従来のものと大きく変えることなく特性を向上させることが求められている。結晶粒を微細化させることで機械的性質が改善されることはよく知られているが、微細化により室温強度は向上するものの、高温では粒界すべりによりクリープ強度が低下してしまう。 In recent years, in order to reduce environmental impact and improve recyclability, reduction of alloying elements has been regarded as important in metal materials, and even if the strength is increased, the characteristics can be improved without changing the chemical composition from the conventional one. It has been demanded. Although it is well known that the mechanical properties are improved by refining crystal grains, although the room temperature strength is improved by the refining, the creep strength is lowered at high temperatures due to grain boundary sliding.
室温における強度と粒径の間には、以下のホールペッチの関係があり、粒径が小さいほど室温強度は高くなる。
［式（１）］
ここで、ｄは粒径、σYは降伏応力、ｋは定数、σ０は単結晶の場合の降伏応力である。
There is the following Hall Petch relationship between the strength at room temperature and the particle size. The smaller the particle size, the higher the room temperature strength.
[Formula (1)]
Here, d is the grain size, σ Y is the yield stress, k is a constant, and σ 0 is the yield stress in the case of a single crystal.
また、高温におけるクリープ強度に関してはDornのひずみ速度式（２）が得られており、粒径が小さいほどひずみ速度が大きくなる、すなわちクリープ強度が低くなる。これは結晶粒の微細化により粒界すべりが起きやすくなるためである。
［式（２）］
ここで、A,Dは定数、頻度因子、b,Gは、バーガースベクトルの大きさ、剛性率であり、p,nは、粒径指数、応力指数である。
As for the creep strength at high temperature, Dorn's strain rate equation (2) is obtained. The smaller the particle size, the larger the strain rate, that is, the lower the creep strength. This is because grain boundary slipping easily occurs due to the refinement of crystal grains.
[Formula (2)]
Here, A and D are constants and frequency factors, b and G are Burgers vector magnitude and rigidity, and p and n are particle size index and stress index.
室温強度、高温クリープ強度の粒径依存性を図１に示すが、粒径を小さくすれば室温強度が上がるが高温クリープ強度は低下する。このように結晶粒の微細化のみでは室温強度と高温クリープ強度を共に高めることははなはだ困難なことであった。 The particle size dependence of room temperature strength and high temperature creep strength is shown in FIG. 1. If the particle size is reduced, the room temperature strength increases but the high temperature creep strength decreases. Thus, it is very difficult to increase both the room temperature strength and the high temperature creep strength only by refining the crystal grains.
従来の鋼焼結体として、特許文献１−３に開示されたものがある。特許文献１のものは、フェライト相を主体とする粉末とオーステナイト相を主体とする粉末とを所定比率で混合した混合粉末を成形、焼結して製造したステンレス鋼焼結体であるが、粉末を水噴霧法により製造しているために粒径が大きく、このため焼結体の硬さはHRCで約２０（ビッカース硬さHv約２３０）程度という低強度のものである。 As a conventional steel sintered body, there is one disclosed in Patent Documents 1-3. The thing of patent document 1 is the stainless steel sintered compact manufactured by shape | molding and sintering the mixed powder which mixed the powder which mainly has a ferrite phase, and the powder which mainly has an austenite phase by a predetermined ratio, Is produced by the water spraying method, and the particle size is large. For this reason, the hardness of the sintered body is as low as about 20 (Vickers hardness Hv about 230) in HRC.
また、マトリックスに微細な粒子を分散させた粒子分散強化は、微細な粒子が転位の移動の障害となるために、室温強度と高温クリープ強度が共に高くなることが知られている。この場合において、粒子間隔が狭いほど強度は高くなる。 In addition, it is known that particle dispersion strengthening in which fine particles are dispersed in a matrix increases both room temperature strength and high temperature creep strength because fine particles obstruct dislocation movement. In this case, the strength increases as the particle interval decreases.
特許文献２のものは、原料粉末と酸化物粉末を混合して機械的合金化処理を行い、熱間押出しにより固化して製造された粗大結晶粒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であるが、母相が粗大結晶粒であるので、室温強度は低いという欠点がある。
特許文献３のものは、フェライト系合金粉末に、平均粒径１０μｍ以下のＮｉ粉末を添加した原料粉末とバインダーからなる組成物を射出成形して、脱バインダー後の成形体を焼結して製造したオーステナイト系ステンレス鋼焼結体であるが、原料粉末の粒径が１μｍ超と大きいため室温強度が低い。また、酸化物等の粒子が分散されていないため高温クリープ強度も低いという問題がある。
The thing of
以上のような従来技術の問題に鑑み、本発明は、高い室温強度と高い高温クリープ強度を併せ持つ高強度鋼焼結体に用いる超微細粉末、この超微細粉末から製造した高強度鋼焼結体及びそれらの製造方法を提供することを目的とする。 In view of the problems of the prior art as described above, the present invention provides an ultrafine powder used for a high strength steel sintered body having both high room temperature strength and high temperature creep strength, and a high strength steel sintered body produced from the ultrafine powder. And it aims at providing those manufacturing methods.
本発明の高強度鋼焼結体は、粒径が１０〜３００ｎｍで鋼からなる球状粒子であって表面に酸化物層が形成された超微細粉末を焼結して製造された高強度鋼焼結体であって、焼結後の結晶粒径が５００ｎｍ超〜１０００ｎｍ未満であって、この結晶粒内に１０〜１００ｎｍの微細酸化物粒子が粒子間距離１００ｎｍ未満で分散されており、焼結まま材の 室温におけるビッカース硬さが８００以上であることを特徴とする高強度鋼焼結体。The high-strength steel sintered body of the present invention is a high-strength steel sintered body manufactured by sintering ultrafine powder having a particle size of 10 to 300 nm and made of steel and having an oxide layer formed on the surface. The sintered body has a crystal grain size after sintering of more than 500 nm to less than 1000 nm, and fine oxide particles of 10 to 100 nm are dispersed in the crystal grains with an inter-particle distance of less than 100 nm. A high-strength steel sintered body characterized in that the Vickers hardness of the raw material at room temperature is 800 or more.
本発明の高強度焼結体の製造方法は、水素ガス含有雰囲気中で鋼にアーク放電するアークプラズマ強制蒸発法によって１０〜 ３００ｎｍの鋼の超微細粉末を製造する第１工程と、前記超微細粉末を酸素ガス雰囲気中に導入し加熱して、表面が酸化された超微細粉末を 製造する第２工程と、超微細粉末を加圧しつつ放電プラズマにより７００℃超〜１０００℃未満に加熱して、焼結後の結晶粒径が５００ｎｍ超〜１０００ｎｍ未満である結晶粒内に、１０〜１００ｎｍの微細酸化物粒子を粒子間距離１００ｎｍ未満で分散させた焼結体を製造する第３工程と、からなることを特徴とするものである。The method for producing a high-strength sintered body according to the present invention includes a first step of producing an ultrafine powder of steel having a thickness of 10 to 300 nm by an arc plasma forced evaporation method in which a steel is arc-discharged in an atmosphere containing hydrogen gas, and the ultrafine powder Introducing the powder into an oxygen gas atmosphere and heating to produce a superfine powder with an oxidized surface, and heating the superfine powder to over 700 ° C. to less than 1000 ° C. by discharge plasma while applying pressure. A third step of producing a sintered body in which fine oxide particles of 10 to 100 nm are dispersed with a distance between particles of less than 100 nm in crystal grains having a crystal grain size after sintering of more than 500 nm and less than 1000 nm; It is characterized by comprising.
本発明の高強度鋼焼結体用の超微細粉末は、粒径が１０〜３００ｎｍと超微細であるので、焼結後の結晶粒径を微細にして室温強度を従来のものより高くすることができる。 Since the ultrafine powder for high strength steel sintered body of the present invention has an ultrafine particle size of 10 to 300 nm, the crystal grain size after sintering should be made fine to increase the room temperature strength compared to the conventional one. Can do.
また、本発明の高強度鋼焼結体は、焼結後の結晶粒径が１０００ｎｍ（１μｍ）未満と微細で、かつ、マトリックスに１０〜１００ｎｍの微細酸化物粒子が粒子間距離１００ｎｍ未満で分散されているので、従来よりも高い室温強度と高温クリープ強度を有する。 Moreover, the high strength steel sintered body of the present invention has a fine crystal grain size after sintering of less than 1000 nm (1 μm), and fine oxide particles of 10 to 100 nm dispersed in a matrix with an interparticle distance of less than 100 nm. Therefore, it has higher room temperature strength and higher temperature creep strength than conventional.
本発明の高強度鋼焼結体用の超微細粉末の製造方法は、水素ガス含有雰囲気中で鋼にアーク放電するアークプラズマ強制蒸発法によって粉末を製造するので、１０〜３００ｎｍの超微細粉末を製造することができる。また、酸素ガス雰囲気中で加熱することによって、超微細粒子の表面に酸化物層を形成することができる。 The method for producing an ultrafine powder for a high-strength steel sintered body of the present invention is produced by an arc plasma forced evaporation method in which an arc discharge is performed on steel in a hydrogen gas-containing atmosphere. Can be manufactured. Moreover, an oxide layer can be formed on the surface of the ultrafine particles by heating in an oxygen gas atmosphere.
また、本発明の高強度鋼焼結体の製造方法は、表面に酸化物層を有する超微細粉末を加圧しつつ７００℃超〜１０００℃未満で放電プラズマにより焼結するので、焼結による結晶粒の成長を１０００ｎｍ未満に抑えることができるとともに、結晶粒内に１０〜１００ｎｍの微細酸化物粒子を粒子間距離１００ｎｍ未満で微細に分散させることができるので、室温強度と高温クリープ強度とが共に高い高強度鋼焼結体を製造することができる。 In addition, the method for producing a high-strength steel sintered body according to the present invention sinters with ultra-fine powder having an oxide layer on the surface while being sintered by discharge plasma at a temperature exceeding 700 ° C. to less than 1000 ° C. Grain growth can be suppressed to less than 1000 nm, and fine oxide particles of 10 to 100 nm can be finely dispersed in the crystal grains with an inter-particle distance of less than 100 nm, so that both room temperature strength and high temperature creep strength can be achieved. A high strength steel sintered body can be produced.
以下に、本発明の高強度鋼焼結体の製造方法を詳細に説明する。 Below, the manufacturing method of the high strength steel sintered compact of this invention is demonstrated in detail.
本発明の高強度鋼焼結体用に超微細粉末の製造方法は、水素ガス含有雰囲気中で鋼にアーク放電するアークプラズマ強制蒸発法によって１０〜３００ｎｍの鋼の超微細粉末を製造する第１工程と、前記超微細粉末を酸素ガス含有雰囲気中に導入して、表面が酸化された鋼酸化微粉末を製造する第２工程と、からなる。 The method for producing an ultrafine powder for a high-strength steel sintered body according to the present invention is a first method for producing an ultrafine powder of steel having a thickness of 10 to 300 nm by an arc plasma forced evaporation method in which an arc discharge is performed on the steel in an atmosphere containing hydrogen gas. And a second step of producing a steel oxide fine powder having a surface oxidized by introducing the ultrafine powder into an oxygen gas-containing atmosphere.
図１は、アークプラズマ強制蒸発法を説明する概念図である。また、図２はアークプラズマ強制蒸発法を実施するための超微細粉末製造装置の概略構成図である。図において、チャンバー１内には、陽極である水冷銅ハース２と陰極であるタングステン電極３が配設されており、両者は電源４と接続されている。チャンバー１には排気用の真空ポンプ５とAｒボンベ６、水素ボンベ７が接続されている。また、チャンバー１には超微細粉末回収通路８が設けられており、この途中にフィルター９とポンプ１０が配設されている。
FIG. 1 is a conceptual diagram illustrating the arc plasma forced evaporation method. FIG. 2 is a schematic configuration diagram of an ultrafine powder manufacturing apparatus for performing the arc plasma forced evaporation method. In the figure, a water-cooled
金属即ち鋼を水冷銅ハース２の上に載置して水素ガス含有雰囲気中でアーク放電を行うと、鋼は１０４K程度の高温に加熱されて、水素イオンが鋼中に溶解し、再結合して放出されるので、蒸気イオンが放出されてナノ粒子が発生する。放電電流として、例えば１５０Aを用いることができる。ポンプ１０により超微細粉末回収通路８に吸引されたナノ粒子である超微細粉末はフィルター９に補足されて回収される。なお、鋼として、合金鋼、耐熱鋼、ステンレス鋼を用いることができる。また、水素ガス含有雰囲気として、例えばアルゴンガス５０％、水素ガス５０％の混合ガスを用いることができる。
When a metal or steel is placed on the water-cooled
アークプラズマ強制蒸発法によって粒径が１０〜３００ｎｍの超微細粉末を製造する。粒径が１０ｎｍ未満とする必要はなく１０ｎｍ以上で焼結後においても微細な結晶を得ることができるからである、また、３００ｎｍ以下とするのは、これを超えると焼結後において微細な結晶粒を得ることが困難となって、室温強度の低下をもたらすからである。 An ultrafine powder having a particle size of 10 to 300 nm is produced by an arc plasma forced evaporation method. This is because it is not necessary that the particle size be less than 10 nm, and fine crystals can be obtained even after sintering at 10 nm or more. If it exceeds 300 nm, fine crystals are obtained after sintering. This is because it becomes difficult to obtain grains, resulting in a decrease in room temperature strength.
製造された超微細粉末は、例えば１％酸素−Ar雰囲気ガス中、室温で１２時間酸化させて表面が酸化された酸化微粉末を得る。酸素ガスの含有率、及び酸化時間、温度は特に限定されるものではなく、超微細粒子の表面に酸化膜を形成させることができればよい。 The produced ultrafine powder is oxidized in, for example, 1% oxygen-Ar atmosphere gas at room temperature for 12 hours to obtain an oxidized fine powder whose surface is oxidized. The oxygen gas content, the oxidation time, and the temperature are not particularly limited as long as an oxide film can be formed on the surface of the ultrafine particles.
本発明の高強度鋼焼結体の製造方法は、前記鋼酸化微粉末を加圧しつつ放電プラズマにより７００℃超〜１０００℃未満に加熱して、焼結後の結晶粒径が５００ｎｍ超〜１０００ｎｍ未満である結晶粒内に、１０〜１００ｎｍの微細酸化物粒子を粒子間距離１００ｎｍ未満で分散させた焼結体を製造する第３工程と、からなることを特徴とする。 The method for producing a high-strength steel sintered body according to the present invention is such that the steel oxide fine powder is heated to over 700 ° C. to less than 1000 ° C. by discharge plasma while pressurizing, and the sintered crystal grain size is over 500 nm to 1000 nm. And a third step of manufacturing a sintered body in which fine oxide particles of 10 to 100 nm are dispersed in a crystal grain having a distance of less than 100 nm.
すなわち、上記したような酸化微粉末を、図４に示す放電プラズマ焼結装置を用いて焼結する。当該装置は、真空チャンバー内に円筒状のグラファイトダイを備えている。ダイの内部に前記酸化微粉末を装入して上下からグラファイトパンチにて加圧しつつDCパルス電流を流して加熱して酸化微粉末を焼結する。放電プラズマ焼結装置においては、酸化微粉末の粒子表面のみの自己発熱による急速昇温が可能なため、酸化微粉末の粒成長を抑制して焼結を行うことができるという利点がある。 That is, the oxidized fine powder as described above is sintered using the discharge plasma sintering apparatus shown in FIG. The apparatus includes a cylindrical graphite die in a vacuum chamber. The oxidized fine powder is charged into the die and heated by applying a DC pulse current while pressing with a graphite punch from above and below to sinter the oxidized fine powder. In the discharge plasma sintering apparatus, rapid temperature rise by self-heating of only the particle surface of the oxidized fine powder is possible, so that there is an advantage that sintering can be performed while suppressing the grain growth of the oxidized fine powder.
焼結温度は、７００℃超〜１０００℃未満とする。７００℃以下では、焼結強度が弱く高い硬さを得ることが困難となるからであり、一方１０００℃を超えると結晶粒が粗大化して硬さの低下を招くからである。 Sintering temperature shall be more than 700 degreeC-less than 1000 degreeC. This is because if it is 700 ° C. or lower, the sintered strength is weak and it is difficult to obtain a high hardness, while if it exceeds 1000 ° C., the crystal grains become coarse and the hardness decreases.
焼結後の結晶粒径は、５００ｎｍ超〜１０００ｎｍ未満とする。５００ｎｍ以下では、粒界すべりが起きやすくなって高い高温クリープ強度を得ることができないからであり、１０００nm以上では、室温強度の低下が大きくなるからである。 The crystal grain size after sintering is more than 500 nm to less than 1000 nm. This is because grain boundary sliding tends to occur when the thickness is 500 nm or less, and a high-temperature creep strength cannot be obtained. When the thickness is 1000 nm or more, the decrease in room temperature strength becomes large.
結晶粒内に分散させる酸化物粒子の粒径は、１０〜１００ｎｍとする。酸化物粒子の粒径は１０ｎｍ未満とする必要はなく、一方１００ｎｍ超では、高い強度を得ることができないからである。 The particle size of the oxide particles dispersed in the crystal grains is 10 to 100 nm. This is because the oxide particles need not have a particle size of less than 10 nm, whereas if it exceeds 100 nm, high strength cannot be obtained.
分散させた酸化物粒子の粒子間距離は、転位の移動の障害となり強度を高めるために、１００ｎｍ未満とする。１００ｎｍ以上では、十分な高強度化を図ることができないからである。粒子間距離は、１０ｎｍ以上が望ましい。 The inter-particle distance of the dispersed oxide particles is less than 100 nm in order to hinder dislocation movement and increase the strength. This is because sufficient strength cannot be achieved at 100 nm or more. The interparticle distance is preferably 10 nm or more.
以下に本発明方法の実施例について説明する。 Examples of the method of the present invention will be described below.
アークプラズマ強制蒸発法によって製造した超微細粉末を、室温で１２時間酸化させて得た酸化微粉末の走査電子顕微鏡写真（SEM写真）を図５に示す。SEM写真から５００個の粒子について粒径を測定した。その測定結果を図６に示すが、粒径は２０〜２５０ｎｍの間に分布しており、平均粒径は５９ｎｍと超微細なものであった。出発材であるステンレス鋼と酸化微粉末の化学分析値を表１に示すが、出発材の酸素は０％であったが、酸化微粉末においては１０．２７％（質量％）に増加していた。 FIG. 5 shows a scanning electron micrograph (SEM photograph) of the oxidized fine powder obtained by oxidizing the ultrafine powder produced by the arc plasma forced evaporation method at room temperature for 12 hours. The particle size was measured for 500 particles from the SEM photograph. The measurement results are shown in FIG. 6, and the particle size was distributed between 20 to 250 nm, and the average particle size was 59 nm and very fine. The chemical analysis values of the starting material stainless steel and oxidized fine powder are shown in Table 1. Although the oxygen content of the starting material was 0%, the oxidized fine powder increased to 10.27% (mass%). It was.
図１６に、素材板と、製造した酸化微粉末のＸ線回折結果を示す。素材板はｂＢＣＣ相とＦＣＣ相の混合であるが、酸化微粉末はＢＣＣ単相からなることを確認した。 FIG. 16 shows the X-ray diffraction results of the material plate and the manufactured fine oxide powder. The material plate was a mixture of bBCC phase and FCC phase, but the oxidized fine powder was confirmed to consist of BCC single phase.
この酸化微粉末を、図４に示した放電プラズマ焼結装置を用いて焼結した。図７には、圧縮荷重４５MPaにおける被焼結体の圧縮量、即ち変位量△Zの焼結温度依存性を示すが、４７０〜５２０℃付近で急激に変異が増加しており、最低５２０℃から固化成形可能であることが分かった。そこで、焼結条件を、圧縮荷重４５MPa、焼結温度５２０〜９８０℃として焼結を行い、焼結体の特性を調査した。 The oxidized fine powder was sintered using the discharge plasma sintering apparatus shown in FIG. FIG. 7 shows the sintering temperature dependence of the amount of compression of the sintered body under a compression load of 45 MPa, that is, the displacement amount ΔZ, and the mutation increases rapidly in the vicinity of 470 to 520 ° C., with a minimum of 520 ° C. From this, it was found that solidification molding was possible. Therefore, the sintering was performed under the conditions of a compressive load of 45 MPa and a sintering temperature of 520 to 980 ° C., and the characteristics of the sintered body were investigated.
図８には、結晶粒径の温度依存性、図９には焼結体の密度の温度依存性を示すが、低温度域では百数十ｎｍ程度であった結晶粒が、７８０〜８８０℃の間で急激に粗大化して７００ｎｍ超まで成長しているが、最大でも８００ｎｍ未満に留まっている。これに伴い６．６ｇ/ｃｍ３程度であった密度が７．３ｇ/ｃｍ３程度まで増加している。 FIG. 8 shows the temperature dependence of the crystal grain size, and FIG. 9 shows the temperature dependence of the density of the sintered body. The crystal grains that were about a few hundreds of nanometers in the low temperature range were 780 to 880 ° C. It grows rapidly to over 700 nm, but stays below 800 nm at the maximum. Accordingly, the density, which was about 6.6 g / cm 3 , has increased to about 7.3 g / cm 3 .
図１０には、７８０℃、８８０℃における焼結体の透過電子顕微鏡写真（TEM写真）を、図１１には８８０℃焼結体の拡大TEM写真を示すが、７８０℃では、酸化微粉末と同程度の小さい粒子の界面に酸化物が存在しているのに対し、８８０℃では、結晶粒が成長するとともに、界面の酸化物が消失し粒内に３０〜１００ｎｍの微細な酸化物粒子が約５０ｎｍの間隔で分散している。上記したＴＥＭ写真の模式図を、図１８に示す。マトリックス中に微細な酸化物粒子が分散している。 FIG. 10 shows a transmission electron micrograph (TEM photograph) of the sintered body at 780 ° C. and 880 ° C., and FIG. 11 shows an enlarged TEM photograph of the 880 ° C. sintered body. While oxides are present at the interface of the same small particles, at 880 ° C., the crystal grains grow and the interface oxide disappears, and fine oxide particles of 30 to 100 nm are formed in the grains. Dispersed at intervals of about 50 nm. A schematic diagram of the above TEM photograph is shown in FIG. Fine oxide particles are dispersed in the matrix.
焼結体のＸ線回折結果を、図１７に示す．酸化微粉末(ナノパウダー)はＢＣＣ単相であるのに対し、８８０℃焼結体は主としてＦＣＣ相からなる。 The X-ray diffraction result of the sintered body is shown in FIG. The oxidized fine powder (nano powder) is a BCC single phase, whereas the 880 ° C. sintered body is mainly composed of an FCC phase.
焼結体の室温におけるビッカース硬さに及ぼす焼結温度の影響を図１２に示す。焼結温度８８０℃でビッカース硬さHv900以上の高硬度を得ている。図１３には、結晶粒径と硬さの関係を示すが、８８０℃焼結体は粒径が７００ｎｍ程度と大きいにも関わらず硬さが高い。結晶粒の粗大化により一般に硬さは低下するが、この硬さ上昇は微細な酸化物粒子の分散によってもたらされたものである。 FIG. 12 shows the influence of the sintering temperature on the Vickers hardness of the sintered body at room temperature. A high hardness of Vickers hardness Hv900 or higher is obtained at a sintering temperature of 880 ° C. FIG. 13 shows the relationship between the crystal grain size and the hardness, but the 880 ° C. sintered body has a high hardness although the grain size is as large as about 700 nm. Although the hardness generally decreases due to the coarsening of crystal grains, this increase in hardness is caused by the dispersion of fine oxide particles.
５７０℃焼結体、８８０℃焼結体について、温度１０２３Ｋ、圧縮荷重５５ＭＰａにて圧縮して真ひずみの時間依存性を調べた。その結果を図１４に示すが、５７０℃においては、時間とともに真ひずみが大きくなったが、８８０℃焼結体では０．０４程度で真ひずみは飽和した。この値は出発材である通常ステンレス鋼の約半分と小さく、優れた高温クリープ特性を有することが分かる。 The 570 ° C. sintered body and the 880 ° C. sintered body were compressed at a temperature of 1023 K and a compression load of 55 MPa, and the time dependence of the true strain was examined. The result is shown in FIG. 14. Although the true strain increased with time at 570 ° C., the true strain was saturated at about 0.04 in the 880 ° C. sintered body. It can be seen that this value is as small as about half of the usual stainless steel starting material and has excellent high temperature creep characteristics.
図１５には各材料の真ひずみ速度の時間依存性を、表２には、各材料の最小ひずみ速度を示す。 FIG. 15 shows the time dependence of the true strain rate of each material, and Table 2 shows the minimum strain rate of each material.
880℃焼結材の最小ひずみ速度は５．９５×１０−７ｓ−１と通常ステンレス鋼(出発材)の約６０％であり、高い高温クリープ強度を有することが分かった。 The minimum strain rate of the 880 ° C. sintered material was 5.95 × 10 −7 s −1, which was about 60% of that of normal stainless steel (starting material), and was found to have high high temperature creep strength.
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