JP4696263B2 - High strength and high ductility carbon steel and its manufacturing method - Google Patents
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Description
本発明は、航空機、自動車等の一般構造用途をはじめ、マイクロマシン等の微小構造用部材への適用においても有用な、ナノオーダーの結晶粒で形成された、高強度と高延性とのバランスを有する炭素鋼材とその製造方法に関するものである。 The present invention has a balance between high strength and high ductility, which is formed of nano-order crystal grains, and is useful for application to microstructural members such as micromachines as well as general structural uses such as aircraft and automobiles. The present invention relates to a carbon steel material and a manufacturing method thereof.
従来より、炭素鋼の高強度化とその延性の向上について様々な観点から検討が進められている。鉄鋼材料の高強度化の方策としては、結晶粒組織の微細化が有効な手段として考えられており、そのための工夫も提案されている。 Conventionally, investigations have been made from various viewpoints on increasing the strength of carbon steel and improving its ductility. As a measure for increasing the strength of steel materials, refinement of the grain structure is considered as an effective means, and a device for that purpose has also been proposed.
たとえば、中・低炭素鋼に関して、均質な組織によって高強度化、高延性化、高靱性化を達成した鋼線、線材および棒鋼についての提案がされている。（特許文献１）
これら、フェライトを主相とし、平均フェライト粒径が２μｍ未満、フェライト粒のアスペクト比が１．５未満であることを特徴とする超微細粒を有する材料であって、炭素濃度範囲は０．０５〜０．３５ｗｔ％としている。また、この材料では、伸線加工などを熱間で行うことにより、動的再結晶を利用して、バルク材を出発材とした結晶粒組織の微細化を行っている。For example, regarding medium and low carbon steels, proposals have been made for steel wires, wire rods and steel bars that have achieved high strength, high ductility, and high toughness with a homogeneous structure. (Patent Document 1)
These are materials having ultrafine grains characterized in that ferrite is the main phase, the average ferrite grain size is less than 2 μm, and the ferrite grain aspect ratio is less than 1.5, and the carbon concentration range is 0.05 ˜0.35 wt%. In addition, in this material, the grain structure is refined using a bulk material as a starting material by using dynamic recrystallization by performing wire drawing or the like hot.
高強度−高延性が得られた材料の例として、炭素濃度０．２５質量％の材料について平均粒径１．２６μｍを得ており、結果として、降伏強度１２９０ＭＰａ、引張伸び値８．６％を得ている。
As an example of a material having high strength and high ductility, an average particle size of 1.26 μm was obtained for a material having a carbon concentration of 0.25% by mass . As a result, a yield strength of 1290 MPa and a tensile elongation value of 8.6% were obtained. It has gained.
しかし、この材料では、強度特性、延性のレベルとそのバランスは必ずしも十分ではない。 However, this material does not necessarily have sufficient strength characteristics, ductility level and balance.
そこで、炭素含有料０．２質量％以下の普通低炭素鋼または０．１％以下でマルテンサイト変態促進に有効な量のＢを添加した普通低炭素鋼のオーステナイト結晶粒を粗大化させた後に水冷することにより得られたマルテンサイト相が９０％以上の鋼材を低ひずみ加工することで、引張強度が８００ＭＰａ以上であり、均一伸びが５％以上、破断伸びが２０％以上の高強度・高延性炭素鋼とすることが提案されている。（特許文献２）
ここでは、平均結晶粒径として、１．０μｍ以下の超微細結晶粒フェライト組織を特徴としている。
Therefore, after coarsening the austenite crystal grains of a normal low carbon steel having a carbon content of 0.2% by mass or less or a normal low carbon steel to which 0.1% or less of an effective amount of B is added to promote martensitic transformation. High-strength and high tensile strength is 800 MPa or more, uniform elongation is 5% or more, and breaking elongation is 20% or more by low-strain processing of a steel material having a martensite phase of 90% or more obtained by water cooling. It has been proposed to use ductile carbon steel. (Patent Document 2)
Here, the average crystal grain size is characterized by an ultrafine grain ferrite structure of 1.0 μm or less.
この鋼材においては、強度−延性バランスの改善の方策として、セメンタイト粒子の均一分散を指摘している。 In this steel material, the uniform dispersion of cementite particles is pointed out as a measure for improving the strength-ductility balance.
ただ、この提案された鋼材の場合には、炭素濃度が比較的低いこととあいまって、６００℃での結晶粒成長が容易に生起し、結果的に強度−延性バランスは必ずしも満足できるものとはなってないのが実情である。 However, in the case of this proposed steel material, combined with a relatively low carbon concentration, crystal grain growth at 600 ° C. occurs easily, and as a result, the strength-ductility balance is not necessarily satisfactory. The situation is not.
また、従来より結晶粒微細化の手段として、強いひずみ加工が知られており、例として、ＥＣＡＥまたはＥＣＡＰ（Equal-Channel-Angular-Extrusion／Equal-Channel-Angular-Pressing）法がある（たとえば非特許文献１−２）。せん断押出加工、または、メカニカル・ミリング法により素材に大ひずみを導入し、再結晶による結晶粒組織の微細化が図られてきた。しかしながら、ＥＣＡＰを施された合金は、引張ひずみにして０．２〜０．３程度の延性を示すものの、降伏強度は７００〜８００ＭＰａ程度しか無かった。また、メカニカル・ミリング法により創製された鉄鋼材料では、粉末をバルク体に固化する手法として、これまではホットプレスが用いられてきた。（たとえば非特許文献３−４）。 Conventionally, strong strain processing is known as a means for grain refinement, and examples include ECAE or ECAP (Equal-Channel-Angular-Extrusion / Equal-Channel-Angular-Pressing) methods (for example, non- Patent Document 1-2). A large strain has been introduced into a material by shear extrusion or mechanical milling, and the crystal grain structure has been refined by recrystallization. However, although the alloy subjected to ECAP exhibits ductility of about 0.2 to 0.3 in terms of tensile strain, the yield strength is only about 700 to 800 MPa. Moreover, in the steel material created by the mechanical milling method, the hot press has been used until now as a method of solidifying the powder into a bulk body. (For example, nonpatent literature 3-4).
このホットプレスを用いた固化では、２５００ＭＰａ程度の極めて高い降伏応力が得られているが、その半面、延性は６％以下と極めて低い延性しか得られていない。
本発明は、以上のとおりの背景から、従来技術の問題点を解消して、従来に比べてより強度と大きな延性とをバランスさせた新しい鉄鋼材料とその製造方法を提供することを課題としている。 From the background as described above, the present invention has an object to provide a new steel material and a method for manufacturing the same, which solves the problems of the prior art and balances the strength and the large ductility as compared with the prior art. .
本発明は、上記の課題を解決するものとして以下のことを特徴とする炭素鋼材とその製造方法を提供する。 In order to solve the above problems, the present invention provides a carbon steel material characterized by the following and a method for producing the same.
第１：０．１〜２．１質量％の範囲の炭素を含有する鉄及び不可避的不純物とよりなる炭素鋼材の製造方法であって、純鉄と炭素の各々の粉末、もしくは炭素鋼の粉末を出発材料としてメカニカル・ミリングを行い、得られた粉末を放電プラズマ焼結して固化させて、母相の平均結晶粒径が１μｍ未満で、１００ｎｍ以下のサイズのセメンタイト粒子が分散した組織を有する炭素鋼材とする高強度・高延性炭素鋼材の製造方法。
1: A method for producing a carbon steel material comprising iron containing carbon in the range of 0.1 to 2.1% by mass and unavoidable impurities, each powder of pure iron and carbon, or powder of carbon steel The starting powder is subjected to mechanical milling, and the resulting powder is solidified by spark plasma sintering to have a structure in which cementite particles having a mean crystal grain size of the parent phase of less than 1 μm and a size of 100 nm or less are dispersed. A method for producing a carbon steel material having high strength and high ductility.
第２：メカニカル・ミリング後の粉末の内部結晶平均粒径が５００ｎｍ以下であり、構成相がフェライト単相またはフェライトとセメンタイトの二相とする上記の高強度・高延性炭素鋼材の製造方法。 Second: The method for producing a high strength / high ductility carbon steel material according to the above, wherein the internal crystal average particle size of the powder after mechanical milling is 500 nm or less and the constituent phase is a ferrite single phase or a ferrite and cementite two phase.
第３：不活性ガス雰囲気もしくは真空雰囲気下でメカニカル・ミリングを行う高強度・高延性炭素鋼材の製造方法。 Third: A method for producing a high-strength, high-ductility carbon steel material in which mechanical milling is performed in an inert gas atmosphere or a vacuum atmosphere.
第４：放電プラズマ焼結後の相対密度を９５％以上とする高強度・高延性炭素鋼材の製造方法。 Fourth: A method for producing a high-strength, high-ductility carbon steel material in which the relative density after spark plasma sintering is 95% or more.
第５：５２０〜７００℃の温度範囲で１分以上放電プラズマ焼結を行う高強度・高延性炭素鋼材の製造方法。 5th: The manufacturing method of the high strength and highly ductile carbon steel material which performs discharge plasma sintering for 1 minute or more in the temperature range of 520-700 degreeC.
第６：降伏強度が１５００ＭＰａ以上で、真ひずみ０．２以上の延性を有する炭素鋼材とする上記いずれかの製造方法。 6th: Any one of the above production methods for producing a carbon steel material having a yield strength of 1500 MPa or more and a ductility of true strain of 0.2 or more.
第７：０．１〜２．１質量％の範囲の炭素を含有する鉄及び不可避的不純物とよりなる炭素鋼材であって、母相の平均結晶粒径が１μｍ未満で、１００ｎｍ以下のサイズのセメンタイト粒子が分散した組織を有し、降伏強度が１５００ＭＰａ以上で、真ひずみ０．２以上の延性を有する高強度・高延性炭素鋼材。
Seventh: a carbon steel material composed of iron containing carbon in the range of 0.1 to 2.1% by mass and unavoidable impurities, and having an average crystal grain size of a parent phase of less than 1 μm and a size of 100 nm or less A high-strength, high-ductility carbon steel material having a structure in which cementite particles are dispersed, having a yield strength of 1500 MPa or more and a ductility of 0.2 or more in true strain.
第８：母相の平均結晶粒径が５０〜５００ｎｍの範囲で、５０ｎｍ以下のサイズのセメンタイト粒子が分散した組織を有している高強度・高延性炭素鋼材。 Eighth: A high-strength and high-ductility carbon steel material having a structure in which cementite particles having a size of 50 nm or less are dispersed in a range where the average crystal grain size of the parent phase is 50 to 500 nm.
第９：硬度が６ＧＰａ以上である高強度・高延性炭素鋼材。 Ninth: A high strength and high ductility carbon steel material having a hardness of 6 GPa or more.
上記のとおりの本発明の鋼材の製造方法によれば、（１）メカニカル・ミリング法による結晶粒組織のナノオーダー化を行い、（２）得られた粉末を放電プラズマにより、比較的低温で焼結を行うことにより、セメンタイト相の均一分散とナノオーダーの超微細結晶粒組織を維持させている。 According to the method for manufacturing a steel material of the present invention as described above, (1) the nano-order of the grain structure is performed by mechanical milling, and (2) the obtained powder is sintered at a relatively low temperature by discharge plasma. As a result of the sintering, a uniform dispersion of the cementite phase and a nano-order ultrafine grain structure are maintained.
このため、本発明によれば、極めて高い降伏強度の大きな延性を有する高強度−高延性炭素鋼が提供される。 For this reason, according to the present invention, a high strength-high ductility carbon steel having a large ductility with an extremely high yield strength is provided.
本発明の製造方法は、メカニカル・ミリングによる強いひずみ加工を所定の時間行うことにより、炭素粉末と鉄粉末の均一混合が可能である。この場合、あらかじめ所定の濃度を有する炭素鋼を出発材料とすることも可能である。上記の両出発材料ともに、メカニカル・ミリング中に新生界面が導入されることにより、結晶粒組織の超微細化を可能としている。また、メカニカル・ミリングにより製造された粉末の超微細結晶粒組織を維持するために、従来のホットプレス法と比較して、約２／３程度の温度で焼結を可能とする放電プラズマ焼結の併用が不可欠である。 In the production method of the present invention, carbon powder and iron powder can be uniformly mixed by performing strong strain processing by mechanical milling for a predetermined time. In this case, carbon steel having a predetermined concentration in advance can be used as a starting material. In both of the above starting materials, a new interface is introduced during mechanical milling, thereby enabling ultrafine grain structure. In addition, in order to maintain the ultrafine grain structure of the powder produced by mechanical milling, compared with the conventional hot press method, the discharge plasma sintering enables sintering at a temperature of about 2/3. The combined use is essential.
超微細結晶粒組織の形成と維持に不可欠なセメンタイト粒子を形成させるために、炭素濃度は、０．１〜２．１質量％の範囲になるようにする。より好適には０．３〜１．５質量％の範囲である。 In order to form cementite particles that are indispensable for the formation and maintenance of an ultrafine crystal grain structure, the carbon concentration is set in the range of 0.1 to 2.1% by mass. More preferably, it is in the range of 0.3 to 1.5% by mass.
メカニカル・ミリングを施すことにより、時間経過と共に粉末内部の結晶粒組織は微細化される。ある所定の結晶粒径に到達するためには、回転数やプロセス中の温度管理が不可欠であるが、ここではプロセス終了後の到達粒径が最終バルク材の強度−延性バランス向上に重要な因子であるため、プロセスの回転数や時間の選定は、メカニカル・ミリングプロセス後の到達結晶粒径を１μｍ以下となるようにする。より好ましくは粉末母相の平均結晶粒径は１００ｎｍ以下となるようにする。 By applying mechanical milling, the crystal grain structure inside the powder is refined over time. In order to reach a certain crystal grain size, the rotational speed and temperature control during the process are indispensable, but here the final grain size after the end of the process is an important factor for improving the strength-ductility balance of the final bulk material. Therefore, the selection of the rotation speed and time of the process is performed so that the ultimate crystal grain size after the mechanical milling process is 1 μm or less. More preferably, the average crystal grain size of the powder matrix is set to 100 nm or less.
メカニカル・ミリング中に酸素が混入すると脆弱な酸化物相が形成されるため、延性が著しく低下する。そのため、メカニカル・ミリング開始時から酸素が極力排除された雰囲気とすることが重要である。 When oxygen is mixed during mechanical milling, a brittle oxide phase is formed, and ductility is significantly reduced. Therefore, it is important to create an atmosphere in which oxygen is excluded as much as possible from the start of mechanical milling.
放電プラズマ焼結時の温度として、結晶粒が粗大化しないための上限温度を７００℃、固化後に高密度のバルク体を得るための下限温度として、５２０℃を設定する。なお、焼結に必要な時間を１分以上とし、保持後の結晶粒径が１μｍを越えない範囲で保持時間を設定する。 As a temperature at the time of spark plasma sintering, an upper limit temperature for preventing crystal grains from becoming coarse is set to 700 ° C., and a lower limit temperature for obtaining a high-density bulk body after solidification is set to 520 ° C. The time required for sintering is set to 1 minute or longer, and the holding time is set in a range where the crystal grain size after holding does not exceed 1 μm.
本発明では純鉄ならびに炭素の粉末を出発材としてメカニカル・ミリングを施すことにより、ナノオーダーまで結晶粒を超微細し、高強度鉄鋼粉末材料を作製している。その後に放電プラズマ焼結による温間プレス固化を従来ホットプレス法の約２／３程度の比較的低温度で実施することにより、セメンタイト相の粗大化を抑制しながら、その均一分散を図ることにより、超微細結晶粒組織の粗大化を効果的に抑制し、例えば、実施例で示したように、平均結晶粒径１５０ｎｍを得ている。この例示の材料では１．９ＧＰａの極めて高い降伏強度を示しながら、圧縮ひずみにして０．３５の延性を示している。 In the present invention, by performing mechanical milling using pure iron and carbon powder as starting materials, the crystal grains are made ultrafine to the nano order, and a high-strength steel powder material is produced. After that, by carrying out warm press solidification by spark plasma sintering at a relatively low temperature of about 2/3 of the conventional hot press method, while suppressing the coarsening of the cementite phase, the uniform dispersion is achieved. The coarsening of the ultrafine crystal grain structure is effectively suppressed, and for example, as shown in the examples, an average crystal grain size of 150 nm is obtained. This exemplary material exhibits a very high yield strength of 1.9 GPa while exhibiting a compressive strain of 0.35 ductility.
本発明の炭素鋼材においては、その組成は、上記のとおりの０．１〜２．１質量％、より好ましくは０．３〜１．５質量％の範囲の炭素を含有する鉄と炭素並びに不可避的不純物とよりなるものである。そして母相の平均結晶粒径が１μｍ未満、よりこのましくは５０〜５００ｎｍの範囲で、１００ｎｍ以下のサイズの、より好ましくは５０ｎｍ以下のサイズのセメンタイト粒子が均一に分散されて組織を有している。 In the carbon steel material of the present invention, the composition is 0.1 to 2.1% by mass as described above, more preferably iron and carbon containing carbon in the range of 0.3 to 1.5% by mass, and unavoidable. It is made up of mechanical impurities. The average crystal grain size of the parent phase is less than 1 μm, more preferably in the range of 50 to 500 nm, and cementite particles having a size of 100 nm or less, more preferably 50 nm or less, are uniformly dispersed and have a structure. ing.
本発明の鋼材は、降伏強度１５００ＭＰａ以上、真ひずみ０．２以上の延性を示すものである。さらに好適なものとして、硬度が６ＧＰａ以上、相対密度が９５％以上のものが提供される。 The steel material of the present invention exhibits ductility with a yield strength of 1500 MPa or more and a true strain of 0.2 or more. More preferably, a material having a hardness of 6 GPa or more and a relative density of 95% or more is provided.
そこで以下に、実施例と参考例を示す。もちろん、以下の例によって本発明が限定されることはない。 Then, an Example and a reference example are shown below. Of course, the present invention is not limited by the following examples.
以下の実施例と参考例は、Ｆｅ−０．８質量％Ｃの炭素鋼である。
＜参考例１＞
純度９９．９９％の鉄粉および純度９９．９９９％の炭素粉末を出発材として、メカニカル・ミリングを実施した。メカニカル・ミリングには市販の遊星ボールミルを使用し、ミリングのポットならびにボールはステンレス鋼とした。ステンレスボールと混合粉末の重量比を１０：１となるように混合粉末を秤量し、アルゴン雰囲気中で容器を密閉後、ミリングを開始した。ミリングの条件として、毎分２５０回転に設定し、合計１００時間実施した。なお、２０時間毎に２時間の運転停止を行い、温度上昇を防止した。
The following examples and reference examples are carbon steel of Fe-0.8 mass % C.
<Reference Example 1>
Mechanical milling was performed using iron powder with a purity of 99.99% and carbon powder with a purity of 99.999% as starting materials. A mechanical planetary ball mill was used for mechanical milling, and the milling pot and balls were made of stainless steel. Milling was started after the mixed powder was weighed so that the weight ratio of the stainless ball to the mixed powder was 10: 1 and the container was sealed in an argon atmosphere. Milling conditions were set at 250 revolutions per minute for a total of 100 hours. The operation was stopped for 2 hours every 20 hours to prevent the temperature from rising.
上記メカニカル・ミリングの後に粉末を内径１０ｍｍの炭素型に入れ、市販の放電プラズマ焼結装置（住友石炭鉱業・製）を用いて固化を実施した。固化は、１０-3Ｐａ以下の真空中で、付加荷重を５．５ｋＮ（固化応力として７０ＭＰａに相当）とし、保持時間１０分、温度４００℃にて実施した。After the mechanical milling, the powder was put into a carbon mold having an inner diameter of 10 mm and solidified using a commercially available spark plasma sintering apparatus (Sumitomo Coal Mining Co., Ltd.). Solidification was performed in a vacuum of 10 −3 Pa or less, with an applied load of 5.5 kN (corresponding to 70 MPa as a solidification stress), a holding time of 10 minutes, and a temperature of 400 ° C.
固化後に得られたバルク材について、Ｘ線回折による観察を行ったところ、メカニカル・ミリング直後の粉末には見られなかったセメンタイトのピークが確認された（図１参照）。固化の後に得られたバルク材の平均結晶粒径、格子ひずみ、硬度、相対密度を測定したところ、表１に示すように４０ｎｍ以下の超微細結晶粒組織が形成されているが、相対密度は７８％を示しており、硬度も２．１ＧＰａ程度であった。バルク試験片について圧縮試験を行ったところ、弾性変形途中で破断に至り、高強度−高延性は得られなかった。＜参考例２＞
上記のプロセス条件として放電プラズマ焼結の温度のみを５００℃に変更して、素材プロセスを実施した。When the bulk material obtained after solidification was observed by X-ray diffraction, a cementite peak that was not found in the powder immediately after mechanical milling was confirmed (see FIG. 1). When the average crystal grain size, lattice strain, hardness, and relative density of the bulk material obtained after solidification were measured, an ultrafine grain structure of 40 nm or less was formed as shown in Table 1, but the relative density was The hardness was 78% and the hardness was about 2.1 GPa. When a compression test was performed on the bulk test piece, it was broken during elastic deformation, and high strength-high ductility was not obtained. <Reference Example 2>
The material process was carried out by changing only the discharge plasma sintering temperature to 500 ° C. as the above process conditions.
固化後に得られたバルク材について、Ｘ線回折による観察を行ったところ、上記４００℃の場合と同様にメカニカル・ミリング直後の粉末には見られなかったセメンタイトのピークが確認された（図１参照）。固化の後に得られたバルク材の平均結晶粒径、格子ひずみ、硬度、相対密度を測定したところ、表１に示すように６０ｎｍ以下の超微細結晶粒組織が形成されているが、相対密度は８９％を示していた。また、硬度は６ＧＰａ程度まで増加した。バルク試験片について圧縮試験を行ったところ、２ＧＰａ程度の極めて高い降伏強度が得られたが、塑性ひずみは０．０５程度であり、高延性は得られなかった。
＜実施例１＞
上記のプロセス条件として放電プラズマ焼結の温度のみを６００℃に変更して、素材プロセスを実施した。When the bulk material obtained after solidification was observed by X-ray diffraction, a cementite peak that was not found in the powder immediately after mechanical milling was confirmed as in the case of 400 ° C. (see FIG. 1). ). When the average crystal grain size, lattice strain, hardness, and relative density of the bulk material obtained after solidification were measured, an ultrafine grain structure of 60 nm or less was formed as shown in Table 1, but the relative density was 89%. Moreover, the hardness increased to about 6 GPa. When a compression test was performed on the bulk specimen, an extremely high yield strength of about 2 GPa was obtained, but the plastic strain was about 0.05, and high ductility was not obtained.
<Example 1>
The material process was carried out by changing only the discharge plasma sintering temperature to 600 ° C. as the above process conditions.
固化後に得られたバルク材について、Ｘ線回折による観察を行ったところ、上記４００および５００℃の場合と同様にメカニカル・ミリング直後の粉末には見られなかったセメンタイトのピークが確認された（図１参照）。固化の後に得られたバルク材の平均結晶粒径、格子ひずみ、硬度、相対密度を測定したところ、表１に示すように１５０ｎｍ程度の超微細結晶粒と３０ｎｍ以下の微細なセメンタイト粒子の均一分散組織が形成されており（図２参照）、相対密度は９９％と極めて高い値が得られ、硬度は６．２ＧＰａ程度まで増加した。バルク試験片について圧縮試験を行ったところ、１．９ＧＰａ程度の極めて高い降伏強度が得られたが、塑性ひずみとしては０．３５程度の高延性が得られた。 When the bulk material obtained after solidification was observed by X-ray diffraction, a cementite peak that was not found in the powder immediately after mechanical milling was confirmed as in the case of 400 and 500 ° C. (FIG. 1). When the average crystal grain size, lattice strain, hardness, and relative density of the bulk material obtained after solidification were measured, as shown in Table 1, uniform dispersion of ultrafine crystal grains of about 150 nm and fine cementite particles of 30 nm or less A structure was formed (see FIG. 2), the relative density was as high as 99%, and the hardness increased to about 6.2 GPa. When a compression test was performed on the bulk specimen, an extremely high yield strength of about 1.9 GPa was obtained, but a high ductility of about 0.35 was obtained as the plastic strain.
［図１］開発合金（Ｆｅ−０．８質量％Ｃ）のＸ線回折結果を示した図であって
、メカニカル・ミリング直後の粉末（As-milled Fe-Ｃ）ではフェライトのピークのみで
あり、炭素がフェライト内部に固溶していることがわかり、放電プラズマ焼結（ＳＰ Ｓ）を行った後には、セメンタイト（Ｆｅ3Ｃ）に相当するピークの存在が確認される。
［図２］開発合金（Ｆｅ−０．８質量％Ｃ）の固化成型後の結晶粒組織と結晶粒径 分布を示した図であって、ここでは、実施例１の焼結温度６００℃にて得られた結果 を示しており、左図の左上隅に示した電子線回折パターンより、多結晶組織であるこ とと、また、中央図にセメンタイトの分布を白色で示しており、微細なセメンタイト 粒子が均一分散していることがわかり、右図の結晶粒度分布から、５０〜２００ｎｍ の範囲の結晶粒が大部分を占めており、平均結晶粒径が１５０ｎｍ程度であることが わかる。
[FIG. 1] A diagram showing the X-ray diffraction results of the developed alloy (Fe-0.8 mass % C), and the powder (As-milled Fe-C) immediately after mechanical milling has only a ferrite peak. It can be seen that carbon is dissolved in the ferrite, and after performing discharge plasma sintering (SPS), the presence of a peak corresponding to cementite (Fe3C) is confirmed.
FIG. 2 is a diagram showing the crystal grain structure and crystal grain size distribution after solidification molding of the developed alloy (Fe-0.8% by mass C). Here, the sintering temperature of Example 1 is set to 600 ° C. From the electron diffraction pattern shown in the upper left corner of the left figure, it shows a polycrystalline structure, and the center figure shows the distribution of cementite in white. It can be seen that the particles are uniformly dispersed, and from the crystal grain size distribution in the right figure, it can be seen that most of the crystal grains in the range of 50 to 200 nm occupy about 150 nm.
Claims (9)
A method for producing a carbon steel material comprising iron containing carbon in the range of 0.1 to 2.1% by mass and unavoidable impurities, each of pure iron and carbon powder, or carbon steel powder as a starting material A carbon steel material having a structure in which the obtained powder is solidified by spark plasma sintering, and an average crystal grain size of the parent phase is less than 1 μm and cementite particles having a size of 100 nm or less are dispersed. A method for producing a high-strength, high-ductility carbon steel material characterized by:
0.1 to 2.1 A method of manufacturing a weight percent range become more carbon steel and Tetsu及 beauty unavoidable impurities contains carbon, each of powders of pure iron and carbon, or a powder of carbon steel starting A carbon steel material having a structure in which cement milling is performed by performing mechanical milling as a material, and the obtained powder is sintered by discharge plasma sintering and has an average crystal grain size of a parent phase of less than 1 μm and cementite particles having a size of 100 nm or less are dispersed. A high-strength, high-ductility carbon steel material characterized by
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