WO2019021935A1 - Sintered member - Google Patents

Abstract

A sintered member comprising an iron-based alloy, wherein the Ni content in the iron-based alloy as a whole is more than 0.2% by mass and no more than 10% by mass, the C content is more than 0% by mass and no more than 2.0% by mass, and the total content of one or more elements selected from Mo, Mn, Cr, B, and Si is more than 0% by mass and no more than 5.0% by mass, with the remainder being Fe and unavoidable impurities. The Ni content in a localized region of the iron-based alloy is more than 0.2% by mass and less than 21% by mass. The relative density of the sintered member is at least 97%.

Description

焼結部材Sintered member

　本開示は、焼結部材に関する。本出願は２０１７年７月２６日出願の日本特許出願第２０１７－１４４８０１号に基づく優先権を主張し、前記日本特許出願に記載された全ての内容を援用するものである。 The present disclosure relates to a sintered member. This application claims priority based on Japanese Patent Application No. 2017-144801 filed on Jul. 26, 2017, and incorporates the entire contents of the Japanese Patent Application.

　特許文献１は、Ｎｉ，Ｍｏ，Ｍｎ，Ｃを特定の範囲で含み、残部がＦｅからなる組成を有し、焼戻しマルテンサイトからなる組織にＮｉリッチマルテンサイト部を点在させた鉄系の焼結体を開示する。 Patent Document 1 has a composition in which Ni, Mo, Mn, and C are contained in a specific range, and the remainder is composed of Fe, and an iron-based fired in which a Ni rich martensite portion is dispersed in a structure composed of tempered martensite. Disclose the body.

特開平１１－２４６９５１号公報Japanese Patent Application Laid-Open No. 11-246951

　本開示の焼結部材は、
　鉄基合金からなる焼結部材であって、
　　鉄基合金全体における、Ｎｉの含有量が０．２質量％を超え１０質量％以下であり、Ｃの含有量が０質量％を超え２．０質量％以下であり、Ｍｏ，Ｍｎ，Ｃｒ，Ｂ，及びＳｉから選択される１種以上の元素が合計で０質量％を超え５．０質量％以下であり、残部がＦｅ及び不可避不純物であり、
　　鉄基合金の局所的な領域におけるＮｉの含有量が０．２質量％を超え２１質量％未満であり、
　相対密度が９７％以上である。 The sintered member of the present disclosure is
A sintered member made of an iron-based alloy,
The content of Ni in the entire iron-based alloy is more than 0.2% by mass and 10% by mass or less, the content of C is more than 0% by mass and 2.0% by mass or less, Mo, Mn, Cr, One or more elements selected from B and Si are more than 0% by mass and 5.0% by mass or less in total, and the balance is Fe and an unavoidable impurity,
The content of Ni in the local region of the iron-based alloy is more than 0.2% by mass and less than 21% by mass,
The relative density is 97% or more.

図１は、試験例１において、焼結部材の相対密度と引張強さとの関係を示すグラフである。FIG. 1 is a graph showing the relationship between relative density and tensile strength of sintered members in Test Example 1. 図２は、試験例２において、焼結部材のＮｉ量と引張強さとの関係を示すグラフである。FIG. 2 is a graph showing the relationship between the amount of Ni and the tensile strength of the sintered member in Test Example 2. 図３は、試験例３において、焼結部材の酸素量と引張強さとの関係を示すグラフである。FIG. 3 is a graph showing the relationship between the oxygen content of the sintered member and the tensile strength in Test Example 3.

［本開示が解決しようとする課題］
　静的強度がより高く、疲労強度にも優れる焼結部材が望まれている。 [Problems to be solved by the present disclosure]
A sintered member having higher static strength and excellent fatigue strength is desired.

　特許文献１に記載される鉄系の焼結体では、引張強さが１４００ＭＰａ程度に過ぎず、静的強度の更なる向上が望まれる。特に、溶製材の引張強さと同等程度以上の強度を有する焼結部材が好ましい。 In the iron-based sintered body described in Patent Document 1, the tensile strength is only about 1400 MPa, and a further improvement in static strength is desired. In particular, a sintered member having a strength equal to or higher than the tensile strength of the molten material is preferable.

　引張強さだけでなく、繰り返しの曲げなどを受けても破断し難いこと、即ち疲労強度といった動的な強度にも優れることも望まれる。 In addition to tensile strength, it is also desired to be excellent in dynamic strength such as fatigue strength that is not easily broken even under repeated bending or the like.

　そこで、静的強度が高く、疲労強度にも優れる焼結部材を提供することを目的の一つとする。　 Therefore, it is an object to provide a sintered member having high static strength and excellent fatigue strength.

［本開示の実施形態の説明］
　最初に本開示の実施態様を列記して説明する。
（１）本開示の一態様に係る焼結部材は、
　鉄基合金からなる焼結部材であって、
　　鉄基合金全体における、Ｎｉの含有量が０．２質量％を超え１０質量％以下であり、Ｃの含有量が０質量％を超え２．０質量％以下であり、Ｍｏ，Ｍｎ，Ｃｒ，Ｂ，及びＳｉから選択される１種以上の元素が合計で０質量％を超え５．０質量％以下であり、残部がＦｅ及び不可避不純物であり、
　　鉄基合金の局所的な領域におけるＮｉの含有量が０．２質量％を超え２１質量％未満であり、
　相対密度が９７％以上である。
　本開示において、「鉄基合金の局所的な領域におけるＮｉの含有量が０．２質量％を超え２１質量％未満」とは、以下を意味する。
　焼結部材の断面をとり、この断面から所定の大きさの測定視野をとる。この測定視野内におけるＮｉの含有量をＳＥＭ－ＥＤＸ装置によって測定する。測定視野におけるＮｉの最大含有量が２１質量％未満であり、かつＮｉの最小含有量が０．２質量％を超える。測定方法については後に詳しく述べる。 [Description of the embodiment of the present disclosure]
First, embodiments of the present disclosure will be listed and described.
(1) A sintered member according to an aspect of the present disclosure is
A sintered member made of an iron-based alloy,
The content of Ni in the entire iron-based alloy is more than 0.2% by mass and 10% by mass or less, the content of C is more than 0% by mass and 2.0% by mass or less, Mo, Mn, Cr, One or more elements selected from B and Si are more than 0% by mass and 5.0% by mass or less in total, and the balance is Fe and an unavoidable impurity,
The content of Ni in the local region of the iron-based alloy is more than 0.2% by mass and less than 21% by mass,
The relative density is 97% or more.
In the present disclosure, “the content of Ni in the local region of the iron-based alloy is more than 0.2% by mass and less than 21% by mass” means the following.
The cross section of the sintered member is taken, and a measurement field of a predetermined size is taken from this cross section. The content of Ni in this measurement field of view is measured by the SEM-EDX apparatus. The maximum content of Ni in the measurement field of view is less than 21% by mass, and the minimum content of Ni is more than 0.2% by mass. The measurement method will be described in detail later.

　上記の焼結部材は、相対密度が９７％以上と高く緻密であるため、相対密度が９７％未満である焼結部材と比較して、引張強さが高く、静的強度に優れる。かつ、上記の焼結部材は、Ｎｉの濃度分布が上述の特定の範囲を満たしており、上述のＮｉリッチマルテンサイト部が存在するというＮｉが不均一に分布する焼結部材と比較して、Ｎｉが均一的に分布しているといえる。このような上記の焼結部材は、引っ張った場合に割れ難いだけでなく、繰り返しの曲げを受けた場合でも破断し難く、疲労強度にも優れる。この理由の一つは、以下のように考えられる。 The above-mentioned sintered member has high relative density of 97% or more and is dense, and therefore has higher tensile strength and excellent static strength than a sintered member having a relative density of less than 97%. And, in the above-mentioned sintered member, the concentration distribution of Ni satisfies the above-mentioned specific range, and compared to the sintered member in which the above-mentioned Ni-rich martensite portion exists and Ni is unevenly distributed, It can be said that Ni is uniformly distributed. Such a sintered member as described above is not only difficult to break when pulled, but also difficult to break even when subjected to repeated bending, and is excellent in fatigue strength. One of the reasons for this can be considered as follows.

　従来、焼結部材の引張強さを高めるには、相対密度をより高くして緻密にすることが好ましいと考えられている。気孔が割れや破断の起点になり易いからである。気孔の周囲に上述のＮｉリッチマルテンサイト部を備えていれば、Ｎｉによって気孔の周囲材料の機械的特性を局所的に高められて、気孔が割れや破断の起点となることを低減できると考えられる。しかし、本発明者らが検討した結果、相対密度が９７％以上である緻密な焼結部材では、上記Ｎｉリッチマルテンサイト部を備えるといった、焼結部材全体に対してＮｉが不均一に存在する組成では、引張強さが低下するとの知見を得た。上述のＮｉが不均一な組成では、Ｎｉの含有量が局所的に多い箇所を含む反面、局所的に少ない箇所も含み、このＮｉの低濃度箇所が強度の低下を招くと考えられる。 Heretofore, in order to increase the tensile strength of the sintered member, it is considered preferable to make the relative density higher to make it denser. This is because the pores are likely to be the starting point of cracking and breakage. If the above-mentioned Ni rich martensite part is provided around the pores, it is thought that the mechanical properties of the material around the pores can be locally enhanced by Ni, and the pores can be reduced to be the origin of cracking or breakage. Be However, as a result of investigations by the present inventors, in a dense sintered member having a relative density of 97% or more, Ni is present nonuniformly with respect to the entire sintered member, such as including the Ni rich martensite portion. In the composition, it was found that the tensile strength decreased. In the case where the composition of the above-mentioned Ni is nonuniform, although the region containing the locally high content of Ni is included, the region containing the locally low content is also included, and it is considered that the low concentration location of Ni causes a reduction in strength.

　一方、焼結後に焼入れ及び焼戻しを行うと、焼入れ焼戻しの双方を行わない場合や焼入れのみを行う場合に比較して、特に強度を高められ、高い引張強さと高い疲労強度とをバランスよく有し易い。上述のＮｉの低濃度箇所は、焼入れ性に劣るため、焼入れを行った場合にマルテンサイトに変態せず、強度に劣る残留オーステナイトとなり易く、割れや破断の起点になり得ると考えられる。 On the other hand, if quenching and tempering are performed after sintering, the strength can be particularly enhanced compared to the case where neither quenching nor tempering is performed or only quenching, and high tensile strength and high fatigue strength are balanced. easy. Since the low concentration portion of Ni described above is inferior in hardenability, it is considered that it does not transform to martensite when it is quenched, tends to become retained austenite inferior in strength, and can be a starting point of cracking or breaking.

　これに対し、相対密度が９７％以上であり、かつＮｉの濃度分布が上述の特定の範囲を満たせば、Ｎｉの不均一な存在に起因する強度の低下を招き難く、静的強度や疲労強度に優れると考えられる。焼入れ焼戻しを行った場合には、Ｎｉが均一的に存在することで、実質的にその全体が（焼戻し）マルテンサイトに変態でき、残留オーステナイトが少なく、好ましくは実質的に存在せず、静的強度や疲労強度により一層優れると考えられる。 On the other hand, if the relative density is 97% or more and the concentration distribution of Ni satisfies the above-mentioned specific range, it is difficult to cause a decrease in strength due to the uneven presence of Ni, and static strength and fatigue strength It is considered excellent. When quenching and tempering is carried out, substantially the whole can be transformed to (tempered) martensite due to the uniform presence of Ni, and the retained austenite is small, preferably substantially absent. It is considered that the strength and fatigue strength are more excellent.

（２）上記の焼結部材の一形態として、
　鉄基合金全体における、Ｎｉの含有量が２質量％を超え８質量％未満である形態が挙げられる。 (2) As one form of the above-mentioned sintered member,
There is a form in which the content of Ni in the entire iron-based alloy is more than 2% by mass and less than 8% by mass.

　上記形態は、Ｎｉの含有量が上記の特定の範囲を満たすことで、引張強さがより高く、静的強度により優れる上に、疲労強度にもより優れる。 The above-mentioned form is higher in tensile strength, more excellent in static strength, and more excellent in fatigue strength as the content of Ni satisfies the above specific range.

（３）上記の焼結部材の一形態として、
　酸素の含有量が３０００質量ｐｐｍ未満である形態が挙げられる。 (3) As one form of the above-mentioned sintered member,
A form in which the content of oxygen is less than 3000 mass ppm is mentioned.

　本発明者らは、相対密度が９７％以上である緻密な焼結部材について、引張試験を行って破断面を調べたところ、破断面に酸化物が存在し、この酸化物が破断の起点となり得るとの知見を得た。上記形態は、酸素の含有量が上述の特定の範囲を満たしており酸素が少ないため、割れや破断の起点となり得る酸化物を低減し易い。従って、上記形態は、引張強さがより高く、静的強度により優れる上に、疲労強度にもより優れる。 The inventors of the present invention conducted a tensile test on a dense sintered member having a relative density of 97% or more and examined the fracture surface. As a result, an oxide is present on the fracture surface, and this oxide becomes the origin of fracture. I got the knowledge that I could get it. In the above-described embodiment, since the content of oxygen satisfies the above-described specific range and the amount of oxygen is small, it is easy to reduce an oxide that can be a starting point of cracking or breakage. Therefore, the above-mentioned form has higher tensile strength, is more excellent in static strength, and is more excellent in fatigue strength.

（４）上記の焼結部材の一形態として、
　マルテンサイトからなる組織を有する形態が挙げられる。 (4) As one form of the above-mentioned sintered member,
The form which has a structure | tissue which consists of martensite is mentioned.

　上記形態は、代表的には焼結後に焼入れ焼戻しを施されてなるものである。このような上記形態は、焼入れ焼戻しが施されていない場合に比較して、引張強さがより高く、静的強度により優れる上に、疲労強度にもより優れる。 The above-mentioned form is typically subjected to quenching and tempering after sintering. Such a form as described above is higher in tensile strength, more excellent in static strength, and more excellent in fatigue strength as compared with the case where quenching and tempering are not performed.

［本開示の実施形態の詳細］
　以下、本開示の実施の形態を詳細に説明する。以下の説明において元素の含有量は、質量割合（質量％又は質量ｐｐｍ）を示す。 Details of Embodiments of the Present Disclosure
Hereinafter, embodiments of the present disclosure will be described in detail. In the following description, the content of the element indicates a mass ratio (mass% or mass ppm).

［実施形態］
＜焼結部材＞
　実施形態の焼結部材は、Ｆｅを主体とする鉄基合金からなる複数の金属粒子が結合されてなり、気孔が非常に少なく、緻密なものである。詳しくは、実施形態の焼結部材は、鉄基合金からなる焼結部材であって、鉄基合金全体における、Ｎｉの含有量が０．２質量％を超え１０質量％以下であり、Ｃの含有量が０質量％を超え２．０質量％以下であり、Ｍｏ，Ｍｎ，Ｃｒ，Ｂ，及びＳｉから選択される１種以上の元素が合計で０質量％を超え５．０質量％以下であり、残部がＦｅ及び不可避不純物であり、相対密度が９７％以上である。 [Embodiment]
<Sintered member>
The sintered member of the embodiment is a compact one in which a plurality of metal particles composed of an iron-based alloy mainly composed of Fe are combined, and the number of pores is very small. Specifically, the sintered member according to the embodiment is a sintered member made of an iron-based alloy, and the content of Ni in the entire iron-based alloy is more than 0.2% by mass and 10% by mass or less, and C The content is more than 0% by mass and 2.0% by mass or less, and at least one element selected from Mo, Mn, Cr, B, and Si is more than 0% by mass and 5.0% by mass or less in total The balance is Fe and unavoidable impurities, and the relative density is 97% or more.

　特に、実施形態の焼結部材ではＮｉが均一的に存在する。詳しくは、実施形態の焼結部材は、鉄基合金の局所的な領域におけるＮｉの含有量が０．２質量％を超え２１質量％未満である。以下、より詳細に説明する。 In particular, Ni is uniformly present in the sintered member of the embodiment. Specifically, in the sintered member of the embodiment, the content of Ni in the local region of the iron-based alloy is more than 0.2% by mass and less than 21% by mass. A more detailed description will be given below.

《全体組成》
　実施形態の焼結部材は、Ｆｅに加えて、強度向上効果を有するＮｉ，Ｃ，及び上述のＭｏ等の元素を含むため、強度に優れる。 << Whole composition >>
The sintered member of the embodiment is excellent in strength because it contains elements such as Ni, C having the strength improvement effect, and the above-described Mo in addition to Fe.

　鉄基合金全体においてＮｉを１０％以下の範囲で含有することで焼入れ性にも優れ、焼入れ焼戻しを施した場合に残留オーステナイトを低減し、マルテンサイト組織を有し易い。そのため、焼結部材の機械的特性を向上し易い。Ｎｉの含有量が１％以上であると、引張強さをより高められ、２％以上であることがより好ましい。更なる高強度化を望む場合には、Ｎｉの含有量は２％を超え８％未満であることが好ましく、２．５％以上７．５％以下、更に３％以上７％以下、４％以上６％以下であると、より高強度な焼結部材とし易い。 By containing Ni in the range of 10% or less in the entire iron-based alloy, the hardenability is also excellent, and when quenching and tempering is performed, retained austenite is reduced and it is easy to have a martensitic structure. Therefore, the mechanical properties of the sintered member can be easily improved. If the content of Ni is 1% or more, the tensile strength can be further enhanced, and more preferably 2% or more. When further strengthening is desired, the content of Ni is preferably more than 2% and less than 8%, 2.5% or more and 7.5% or less, and further 3% or more and 7% or less, 4% When the content is 6% or less, a sintered member having high strength can be easily obtained.

　Ｃを２．０％以下の範囲で含有することで強度に優れる。特に、Ｃの含有量が０．１％以上１．５％以下、更に０．２％以上１．０％以下、０．２％以上０．８％以下であると、より高強度な焼結部材とし易い。 It is excellent in intensity | strength by containing C in 2.0% or less of range. In particular, when the content of C is 0.1% or more and 1.5% or less, and further 0.2% or more and 1.0% or less, and 0.2% or more and 0.8% or less, higher-strength sintering is performed. Easy to use as a member.

　Ｍｏ等の元素を合計で５．０％以下の範囲で含有することで強度に優れる。特に、これらの元素の含有量が合計で０．１％以上３．０％以下、更に０．２％以上２．０％以下であると、より高強度な焼結部材とし易い。また、特に、Ｍｏ及びＭｎの少なくとも一方、好ましくは双方を含むと、更に高強度な焼結部材とし易い。Ｍｏの含有量及びＭｎの含有量はそれぞれ、０．１％以上１．０％以下、更に０．１５％以上０．８％以下が挙げられる。 It is excellent in intensity | strength by containing elements, such as Mo, in 5.0% or less in total. In particular, when the total content of these elements is 0.1% or more and 3.0% or less, and further 0.2% or more and 2.0% or less, a sintered member having higher strength can be easily obtained. In addition, when at least one, preferably both, of Mo and Mn is included, it is easy to obtain a sintered member having higher strength. The content of Mo and the content of Mn are respectively 0.1% or more and 1.0% or less, and further 0.15% or more and 0.8% or less.

　焼結部材の全体組成の測定には、例えば、高周波誘導結合プラズマ発光分光分析法（ＩＣＰ－ＯＥＳ）などを利用できる。 For example, high frequency inductively coupled plasma emission spectroscopy (ICP-OES) can be used to measure the overall composition of the sintered member.

《局所的な領域におけるＮｉの濃度分布（含有量）》
　実施形態の焼結部材では、鉄基合金の局所的な領域におけるＮｉの含有量（以降、単にＮｉの濃度分布と記載する場合がある）が０．２質量％を超え２１質量％未満である。つまり、Ｎｉの含有量が０．２％以下である箇所（以下、低Ｎｉ領域と呼ぶ）、及び２１％以上である箇所（以下、高Ｎｉ領域と呼ぶ）の双方が実質的に存在しない。低Ｎｉ領域では、Ｎｉの含有量が少な過ぎるため、特に焼入れ性に劣り、焼入れ焼戻しを施した場合に残留オーステナイトとなって存在し易い。高Ｎｉ領域は、Ｎｉの含有量が多過ぎるため、オーステナイトが安定化し易く、焼入れ焼戻しを施した場合にマルテンサイトに変態し難く、上述の低Ｎｉ領域と同様に残留オーステナイトとして存在し易い。即ち、低Ｎｉ領域及び高Ｎｉ領域を有する焼結部材では、焼入れ焼戻しを行っても、（残留）オーステナイトが局所的に存在して、引張強さや疲労強度に劣る。 << Distribution of Ni Concentration in Local Region (Content) >>
In the sintered member of the embodiment, the content of Ni in the local region of the iron-based alloy (hereinafter sometimes referred to simply as the concentration distribution of Ni) is more than 0.2% by mass and less than 21% by mass . That is, both the location where the content of Ni is 0.2% or less (hereinafter referred to as a low Ni region) and the location where 21% or more (hereinafter referred to as a high Ni region) do not substantially exist. In the low Ni region, since the content of Ni is too small, the hardenability is particularly poor, and when subjected to quenching and tempering, retained austenite is easily present. Since the content of Ni is too high, the austenite tends to be stabilized, and when subjected to quenching and tempering, the high Ni region is difficult to transform to martensite, and tends to exist as retained austenite as in the low Ni region described above. That is, in a sintered member having a low Ni region and a high Ni region, (residual) austenite is locally present even if quenching and tempering are performed, and the tensile strength and the fatigue strength are inferior.

　Ｎｉの濃度分布の幅が小さいほど、即ちＮｉの含有量のうち、最大値と最小値との差が小さいほど、Ｎｉがより均一的に存在して、割れや破断の起点となり得る低Ｎｉ領域などを低減し易い。Ｎｉの濃度分布は、０．３％以上２０％以下、更に０．４％以上１８％以下、０．５％以上１６％以下、１％以上１２％以下が好ましい。Ｎｉの濃度分布の幅（上記の差）が実質的にゼロであることがより好ましい。この場合、焼結部材の全体組成におけるＮｉの含有量と、Ｎｉの濃度分布における上述の最大値及び最小値とが実質的に等しい。 The smaller the width of the concentration distribution of Ni, that is, the smaller the difference between the maximum value and the minimum value of the content of Ni, the more uniformly Ni exists and a low Ni region which can be a starting point of cracking or breakage. Etc. are easy to reduce. The concentration distribution of Ni is preferably 0.3% to 20%, further preferably 0.4% to 18%, and 0.5% to 16%, and 1% to 12%. More preferably, the width of the concentration distribution of Ni (the above difference) is substantially zero. In this case, the content of Ni in the overall composition of the sintered member and the above-described maximum value and minimum value in the concentration distribution of Ni are substantially equal.

《酸素量》
　実施形態の焼結部材は、更に酸素の含有量が少ないと、割れや破断の起点となり得る酸化物を低減でき、引張強さや疲労強度により優れて好ましい。定量的には、酸素の含有量は３０００ｐｐｍ未満であることが好ましく、２５００ｐｐｍ以下、更に２０００ｐｐｍ以下がより好ましい。 << amount of oxygen >>
In the sintered member of the embodiment, when the content of oxygen is further small, an oxide which can be a starting point of a crack or a break can be reduced, and it is preferable because of excellent tensile strength and fatigue strength. Quantitatively, the content of oxygen is preferably less than 3000 ppm, more preferably 2500 ppm or less, and even more preferably 2000 ppm or less.

《組織》
　実施形態の焼結部材は、焼結されたままのものとすることができるが、焼結後、焼入れ焼戻しが施されたものであると、引張強さがより高く、疲労強度にも優れて好ましい。この場合、実施形態の焼結部材は、（焼戻し）マルテンサイトからなる組織を有する。特に、実施形態の焼結部材は、上述のようにＮｉを均一的に含むため、焼結部材全体がマルテンサイトに変態し易く、残留オーステナイトが局所的に存在することを低減できる。好ましくは、焼結部材全体が実質的にマルテンサイトからなり、残留オーステナイトが実質的に含有しない組織とすることができる。 Organization
The sintered member of the embodiment can be one as it is sintered, but when it is sintered and subjected to quenching and tempering, the tensile strength is higher and the fatigue strength is also excellent. preferable. In this case, the sintered member of the embodiment has a structure of (tempering) martensite. In particular, since the sintered member according to the embodiment uniformly contains Ni as described above, the entire sintered member is easily transformed to martensite, and the local presence of retained austenite can be reduced. Preferably, the entire sintered member substantially consists of martensite, and the structure can be substantially free of retained austenite.

《密度》
　実施形態の焼結部材は、上述のようにＮｉを均一的に含有することに加えて、相対密度が９７％以上と緻密であり、気孔が非常に少ないため、気孔に起因する割れや破断も生じ難く、高強度である。上記相対密度を９７．５％以上、更に９８％以上、９８．５％以上とすることができる。 "density"
The sintered member of the embodiment, in addition to uniformly containing Ni as described above, has a relative density of 97% or more and a high density, and since the number of pores is very small, cracks and fractures caused by the pores are also generated. It is hard to occur and has high strength. The relative density can be 97.5% or more, further 98% or more, and 98.5% or more.

　焼結部材の相対密度（％）は、例えば、（焼結部材の見かけ密度／焼結部材の真密度）×１００によって求めることが挙げられる。焼結部材の見かけ密度は、例えば、アルキメデス法に準拠して求めることが挙げられる。詳細は後述する。 The relative density (%) of the sintered member may be determined, for example, by (apparent density of sintered member / true density of sintered member) × 100. The apparent density of the sintered member can be determined, for example, in accordance with the Archimedes method. Details will be described later.

　又は、焼結部材の相対密度（％）は、焼結部材の断面を市販の画像解析ソフトで画像解析することで求めることが挙げられる。詳しくは、焼結部材の断面において、複数の観察視野の画像を取得し、複数の視野を観察する（例えばｎ≧１０）。断面は任意の断面とする。１断面につき１視野として、複数の断面をとってもよいし、１断面につき複数の視野をとってもよい。各視野のサイズは、５００μｍ×６００μｍとする。各視野の画像を二値化処理して、各視野に占める金属部分の面積割合を求め、この面積割合を各視野の相対密度と見做す。そして、複数の視野の相対密度を平均し、この平均値を焼結部材の相対密度とする。 Alternatively, the relative density (%) of the sintered member can be obtained by image analysis of the cross section of the sintered member using commercially available image analysis software. Specifically, in the cross section of the sintered member, images of a plurality of observation views are acquired, and a plurality of views are observed (for example, n ≧ 10). The cross section is an arbitrary cross section. A plurality of cross sections may be taken as one field of view per cross section, and a plurality of fields of view may be taken per cross section. The size of each field of view is 500 μm × 600 μm. The image of each field of view is binarized to determine the area ratio of the metal part occupied in each field of view, and this area ratio is regarded as the relative density of each field of view. And the relative density of a several visual field is averaged, and let this average value be a relative density of a sintering member.

《機械的特性》
　実施形態の焼結部材は、上述のように緻密な上に、Ｎｉを均一的に含むため、引張強さが高く、静的強度に優れる。定量的には、引張強さが１４５５ＭＰａ超、更に１４６０ＭＰａ以上、１５００ＭＰａ以上、１５５０ＭＰａ以上、１５８０ＭＰａ以上、１６００ＭＰａ以上であることが挙げられる。上述の相対密度がより高いこと（後述の試験例１）、Ｎｉの濃度分布の幅がより小さいこと（同）、Ｎｉの含有量が５％に近いこと（後述の試験例２）、及び酸素の含有量がより少ないこと（後述の試験例３）の少なくとも一つを満たすと、引張強さがより高い傾向にある。 機械 Mechanical characteristics》
The sintered member according to the embodiment has high tensile strength and excellent static strength because it contains Ni uniformly in addition to being dense as described above. Quantitatively, the tensile strength is more than 1455 MPa, further 1460 MPa or more, 1500 MPa or more, 1550 MPa or more, 1580 MPa or more, 1600 MPa or more. The above-mentioned relative density is higher (Test Example 1 below), the width of the concentration distribution of Ni is smaller (same), the content of Ni is close to 5% (Test Example 2 below), and oxygen The tensile strength tends to be higher when at least one of the lower contents of (Example 3 below) is satisfied.

《用途》
　実施形態の焼結部材は、各種の一般構造用部品、例えばスプロケット、ローター、ギア、リング、フランジ、プーリー、軸受けなどの機械部品などの焼結部品に好適に利用できる。 << Application >>
The sintered member of the embodiment can be suitably used for various general structural parts, for example, sintered parts such as mechanical parts such as sprockets, rotors, gears, rings, flanges, pulleys and bearings.

＜焼結部材の製造方法＞
　実施形態の焼結部材は、例えば、原料粉末を準備する工程と、原料粉末を加圧成形して圧粉成形体を作製する工程と、圧粉成形体を焼結して焼結材を作製する工程とを経て製造することが挙げられる。更に、焼結材に焼入れ焼戻しを施して熱処理材を作製する工程を行うことが挙げられる。以下、各工程を詳細に説明する。 <Method of Manufacturing Sintered Member>
The sintered member of the embodiment includes, for example, a step of preparing a raw material powder, a step of press-forming the raw material powder to produce a powder compact, and a step of sintering the powder compact to produce a sintered material. Manufacturing through the following steps. Furthermore, performing the process of quenching and tempering the sintered material to produce a heat-treated material can be mentioned. Each step will be described in detail below.

《原料準備工程》
　この工程では、鉄系粒子を複数有する鉄系粉末を含む原料粉末を準備する。鉄系とは、純鉄、又は鉄を主成分とする鉄合金をいう。原料粉末は、（１）Ｎｉを粉末として含む混合粉、（２）Ｎｉを添加元素として含む鉄合金粉、（３）混合粉と鉄合金粉との両方を含む複合粉のいずれか一つを有することが挙げられる。原料粉末に鉄合金粉を含むと、鉄系粉末自体がＮｉを均一的に含むため、上述のＮｉの濃度分布が特定の範囲を満たす実施形態の焼結部材を製造し易く、工業的な量産に適すると考えられる。 Raw material preparation process
In this step, a raw material powder containing an iron-based powder having a plurality of iron-based particles is prepared. The iron-based refers to pure iron or an iron alloy containing iron as a main component. The raw material powder is any one of (1) mixed powder containing Ni as powder, (2) iron alloy powder containing Ni as an additive element, and (3) composite powder containing both mixed powder and iron alloy powder. It is mentioned that it has. When the raw material powder contains iron alloy powder, the iron-based powder itself contains Ni uniformly, so it is easy to manufacture the sintered member of the embodiment in which the above-mentioned concentration distribution of Ni satisfies a specific range, industrial mass production It is considered suitable for

　（１）混合粉は、代表的には、純鉄粉と、Ｎｉ粉と、Ｃ粉と、Ｍｏ，Ｍｎ，Ｃｒ，Ｂ，及びＳｉから選択される１種以上の元素の粉末とを含むことが挙げられる。各粉末の配合割合は、所望の組成の焼結部材（但し、Ｎｉ，Ｃ，Ｍｏ等の元素の含有量は上述の範囲を満たす）が得られるように調整するとよい。この点は後述する（３）複合粉も同様である。 (1) The mixed powder typically contains pure iron powder, Ni powder, C powder, and powder of one or more elements selected from Mo, Mn, Cr, B, and Si. Can be mentioned. The blending ratio of each powder may be adjusted so as to obtain a sintered member of a desired composition (however, the content of elements such as Ni, C, Mo and the like satisfies the above-mentioned range). This point is the same as (3) composite powder described later.

　（２）鉄合金粉は、代表的には、Ｆｅを主成分とし、Ｎｉと上述のＭｏ等の元素とを含有するＦｅ－Ｎｉ系合金粉が挙げられる。Ｆｅ－Ｎｉ系合金におけるＮｉやＭｏ等の元素の含有量は、所望の組成の焼結部材（但し、Ｎｉ，Ｍｏ等の元素の含有量は上述の範囲を満たす）が得られるように調整するとよい。鉄合金粉を用いる場合、Ｃ（炭素）は、鉄合金の添加元素として含まず、独立した粉末（Ｃ粉）として原料粉末に含むことが挙げられる。 (2) The iron alloy powder typically includes an Fe-Ni alloy powder containing Fe as a main component and containing Ni and an element such as Mo described above. If the content of elements such as Ni and Mo in the Fe-Ni alloy is adjusted so as to obtain a sintered member of a desired composition (however, the content of elements such as Ni and Mo satisfies the above range) Good. When using an iron alloy powder, C (carbon) is not contained as an additive element of an iron alloy, but being contained in a raw material powder as an independent powder (C powder) is mentioned.

　（３）複合粉は、代表的には、純鉄粉と、Ｎｉ粉と、Ｎｉを含む鉄合金粉と、Ｃ粉とを含むことが挙げられる。複合粉を用いる場合、Ｎｉ粉と、Ｎｉを含む鉄合金粉とにおけるＮｉの合計含有量が上述の範囲（１０％以下）を満たすように配合割合を調整する。 (3) The composite powder typically includes pure iron powder, Ni powder, iron alloy powder containing Ni, and C powder. When the composite powder is used, the blending ratio is adjusted so that the total content of Ni in the Ni powder and the iron alloy powder containing Ni satisfies the above-described range (10% or less).

　鉄系粉末は、水アトマイズ粉、還元粉、ガスアトマイズ粉、カルボニル粉などが利用できる。鉄系粉末の平均粒径は、例えば２０μｍ以上２００μｍ以下が挙げられる。上記平均粒径が上記の範囲内であれば、鉄系粉末を取り扱い易く、加圧成形を行い易い。また、上記平均粒径が２０μｍ以上であれば、鉄系粉末の流動性を確保し易く、成形性に優れる。上記平均粒径が２００μｍ以下であれば、緻密な組織の焼結部材を得易い。上記平均粒径は更に５０μｍ以上１５０μｍ以下とすることができる。 As the iron-based powder, water atomized powder, reduced powder, gas atomized powder, carbonyl powder and the like can be used. The average particle diameter of the iron-based powder is, for example, 20 μm or more and 200 μm or less. If the above-mentioned average particle diameter is within the above-mentioned range, it is easy to handle the iron-based powder, and it is easy to carry out pressure forming. Moreover, if the said average particle diameter is 20 micrometers or more, it is easy to ensure the fluidity of iron-type powder, and it is excellent in moldability. If the said average particle diameter is 200 micrometers or less, it will be easy to obtain the sintered member of a precise | minute structure | tissue. The average particle size can be further set to 50 μm or more and 150 μm or less.

　Ｎｉ粉、Ｍｏ等の元素の粉末の平均粒径は、例えば１μｍ以上５０μｍ以下程度が挙げられる。Ｃ粉の平均粒径は、例えば１μｍ以上３０μｍ以下程度が挙げられ、鉄系粉末よりも小さいものを利用することが挙げられる。 The average particle diameter of powders of elements such as Ni powder and Mo is, for example, about 1 μm or more and 50 μm or less. The average particle diameter of the C powder is, for example, about 1 μm to 30 μm, and it is possible to use one smaller than the iron-based powder.

　上述の平均粒径とは、レーザ回折式粒度分布測定装置により測定した体積粒度分布における累積体積が５０％となる粒径（Ｄ５０）とする。 The above-mentioned average particle diameter is a particle diameter (D50) at which the cumulative volume in the volume particle size distribution measured by the laser diffraction type particle size distribution measuring device is 50%.

　原料粉末は、潤滑剤及び有機バインダーの少なくとも一方を含有することができる。この場合、潤滑剤及び有機バインダーの合計含有量が０．１％以下であると、緻密な圧粉成形体を得易く好ましい。潤滑剤及び有機バインダーを含有しなければ、緻密な圧粉成形体をより得易い上に、後工程で圧粉成形体を脱脂する必要もない。 The raw material powder can contain at least one of a lubricant and an organic binder. In this case, it is easy to obtain a compact green compact with the total content of the lubricant and the organic binder being 0.1% or less, which is preferable. If a lubricant and an organic binder are not contained, a compact green compact can be obtained more easily, and there is no need to degrease the green compact in a later step.

《成形工程》
　この工程では、原料粉末を加圧成形して、相対密度が９６％以上、更に９７％以上の圧粉成形体を作製することが好ましい。相対密度が９７％以上である焼結部材をより確実に得られるからである。圧粉成形体の相対密度が高いほど、相対密度が高く緻密な焼結部材を得易いことから、圧粉成形体の相対密度を９８％以上、更に９９％以上とすることが挙げられる。 << molding process >>
In this step, it is preferable to press-mold the raw material powder to produce a green compact having a relative density of 96% or more, and further 97% or more. This is because sintered members having a relative density of 97% or more can be obtained more reliably. As the relative density of the green compact is high, the relative density is high and it is easy to obtain a dense sintered member, so that the relative density of the green compact may be 98% or more, further 99% or more.

　圧粉成形体の形状は、焼結部材の最終形状に沿った形状や、後工程の切削加工に適した形状（例、円柱状や円筒状など）が挙げられる。圧粉成形体の作製には、上記形状を成形可能な適宜な成形装置を用いることが挙げられる。特に、円柱や円筒の軸方向に沿って一軸加圧が可能なプレス成形装置を用いると、上述のような緻密な圧粉成形体を得易く好ましい。一軸加圧には、上下に開口部を有するダイと、その上下の開口部に嵌め込まれる上パンチ及び下パンチとを備える金型を用いることが挙げられる。上記金型におけるダイのキャビティ内に原料粉末を充填し、キャビティ内の原料粉末を上パンチと下パンチとで圧縮することで圧粉成形体を作製する。 The shape of the green compact may be a shape along the final shape of the sintered member, or a shape suitable for cutting in a later step (eg, cylindrical or cylindrical). For the production of a green compact, it is possible to use a suitable molding device capable of molding the above-mentioned shape. In particular, use of a press forming apparatus capable of uniaxially pressing along the axial direction of a cylinder or a cylinder is preferable because it is easy to obtain the above-described compacted powder molded product. The uniaxial pressing includes using a die provided with a die having openings at the top and bottom and an upper punch and a lower punch fitted in the openings at the top and the bottom. The raw material powder is filled in the cavity of the die in the mold, and the raw material powder in the cavity is compressed by the upper punch and the lower punch to produce a green compact.

　成形圧力（面圧）を１５６０ＭＰａ（≒１６ｔｏｎ／ｃｍ^２）以上とすると、上述のような緻密な圧粉成形体を作製できる。成形圧力が大きいほど圧粉成形体の相対密度を高め易く、１６６０ＭＰａ（≒１７ｔｏｎ／ｃｍ^２）以上、更に１７６０ＭＰａ（≒１８ｔｏｎ／ｃｍ^２）以上、１８６０ＭＰａ（≒１９ｔｏｎ／ｃｍ^２）以上、１９６０ＭＰａ（≒２０ｔｏｎ／ｃｍ^２）以上とすることができる。原料粉末に上述の鉄合金粉を含む場合には、成形圧力を高めにすると成形性に優れる。 When the molding pressure (surface pressure) is set to 1560 MPa (ton16 ton / cm ² ) or more, the above-described compacted compact can be produced. The relative density of the green compact tends to be increased as the compacting pressure is increased, and 1660 MPa (≒ 17 ton / cm ² ) or more, and further 1760 MPa (≒ 18 ton / cm ² ) or more, 1860 MPa (ton 19 ton / cm ² ) or more It can be ²⁰ ton / cm ² or more. When the above-mentioned iron alloy powder is contained in the raw material powder, when the molding pressure is increased, the moldability is excellent.

　上述の金型の内周面（上述のダイの内周面やパンチの押圧面）に潤滑剤を塗布すると、原料粉末が金型に焼付くことを防止でき、緻密な圧粉成形体を成形し易く好ましい。潤滑剤には、例えば、高級脂肪酸、金属石鹸、脂肪酸アミド、高級脂肪酸アミドなどが利用できる。 When a lubricant is applied to the inner peripheral surface of the above-mentioned mold (the inner peripheral surface of the above-mentioned die or the pressing surface of the punch), the raw material powder can be prevented from sticking to the mold, and a compact powder compact is formed. Easy to do and preferred. As the lubricant, for example, higher fatty acids, metal soaps, fatty acid amides, higher fatty acid amides and the like can be used.

《焼結工程》
　この工程では、圧粉成形体を焼結して、相対密度が９７％以上であり、かつＮｉの濃度分布が上述の特定の範囲を満たす焼結材を作製する。焼結時、圧粉成形体は収縮するため、上述のように圧粉成形体の相対密度を９６％以上、更に９７％以上とすれば、相対密度が９７％以上である焼結材をより確実に作製できる。圧粉成形体の相対密度が上述のように非常に高密度であると、焼結時の収縮量は小さいものの、焼結材の相対密度を圧粉成形体の相対密度超とすることができる。 << Sintering process >>
In this step, the green compact is sintered to produce a sintered material having a relative density of 97% or more and a concentration distribution of Ni satisfying the above-described specific range. Since the green compact shrinks during sintering, if the relative density of the green compact is 96% or more, and further 97% or more as described above, a sintered material having a relative density of 97% or more is used. It can be manufactured reliably. If the relative density of the green compact is very high density as described above, although the amount of shrinkage during sintering is small, the relative density of the sintered material can be made greater than the relative density of the green compact. .

　焼結条件は、原料粉末の組成に応じて適宜選択するとよい。
　焼結温度は、例えば、１１００℃以上１４００℃以下、更に１１１０℃以上１３００℃以下、１１２０℃以上１２５０℃以下が挙げられる。
　焼結時間は、例えば、１５分以上１５０分以下、更に２０分以上６０分以下が挙げられる。
　焼結時の雰囲気は、窒素雰囲気などの不活性雰囲気が挙げられる。
　その他、焼結条件は、公知の条件を参照できる。 The sintering conditions may be appropriately selected according to the composition of the raw material powder.
The sintering temperature is, for example, 1100 ° C. or more and 1400 ° C. or less, and further 1110 ° C. or more and 1300 ° C. or less, 1120 ° C. or more and 1250 ° C. or less.
The sintering time is, for example, 15 minutes or more and 150 minutes or less, and further 20 minutes or more and 60 minutes or less.
The atmosphere at the time of sintering includes an inert atmosphere such as a nitrogen atmosphere.
For other sintering conditions, known conditions can be referred to.

《その他の工程》
　焼結工程後に、以下の成形体加工工程、熱処理工程、及び仕上げ加工工程の少なくとも一つの工程を行うことが挙げられる。 << Other process >>
After the sintering step, at least one of the following compact processing step, heat treatment step, and finish processing step may be performed.

〈成形体加工工程〉
　この工程は、上述の成形工程後、焼結工程前に、圧粉成形体に切削加工を施す。切削加工には、加工内容に応じた適宜な切削工具を用いるとよい。焼結前の圧粉成形体に切削加工を施すと、焼結材や溶製材に比較して加工し易い。特に、この圧粉成形体は、焼結材や溶製材に比較すると軟らかいものの、相対密度が上述のように高く緻密であり、ある程度強度に優れるため、切削加工による欠けや亀裂の発生も抑制し易い。切削加工は、例えば、転削加工（穴あけ加工を含む）、旋削加工などが挙げられる。 Molded body processing process
In this step, the green compact is subjected to cutting after the above-described forming step and before the sintering step. For cutting, it is preferable to use an appropriate cutting tool according to the processing content. When the green compact before sintering is cut, it is easier to process as compared to a sintered material or a molten material. In particular, although this compact is soft as compared with sintered materials and ingots, the relative density is high as described above and dense, and since it is excellent in strength to some extent, generation of chips and cracks due to cutting is also suppressed. easy. Examples of cutting include milling (including drilling), turning, and the like.

　切削加工に供する前に、有機バインダー（例、パラフィンや各種のワックスなど）を溶かした揮発性溶液や、ポリエチレンなどの熱可塑性樹脂の溶液を圧粉成形体の表面に塗布したり、上記溶液に圧粉成形体を浸漬したりすると、切削加工時に圧粉成形体の表層が割れたり欠けたりすることを抑制し易い。 Before being subjected to cutting, a volatile solution in which an organic binder (eg, paraffin or various waxes) is dissolved, or a solution of a thermoplastic resin such as polyethylene is applied to the surface of the green compact or the above solution When the green compact is immersed, it is easy to suppress cracking or chipping of the surface layer of the green compact during cutting.

　その他、切削加工は、圧粉成形体に作用する引張応力を打ち消す方向に、圧粉成形体に圧縮応力を付与しながら行うと、圧粉成形体の割れや欠けを抑制し易い。 In addition, if cutting is performed while applying compressive stress to the powder compact in a direction that cancels out the tensile stress acting on the powder compact, it is easy to suppress cracking and chipping of the powder compact.

〈熱処理工程〉
　この工程は、焼結材に焼入れ焼戻しを施す。焼入れによってマルテンサイト組織とし、焼戻しによってマルテンサイト組織を安定化させる。焼入れ焼戻しによって、特に硬度及び靭性を向上でき、焼結のままの場合と比較して機械的特性により優れる焼結部材とすることができる。特に、焼入れ焼戻し前の焼結材は上述のようにＮｉの濃度分布が０．２％超２１％未満であることから、焼入れ焼戻し後の熱処理材（実施形態の焼結部材の一例）は残留オーステナイトを低減でき、上記熱処理材全体が実質的にマルテンサイト組織（焼戻しマルテンサイト組織）からなる焼結部材をより確実に製造できる。 Heat treatment process
In this process, the sintered material is subjected to quenching and tempering. Quenching produces a martensitic structure and tempering stabilizes the martensitic structure. By quenching and tempering, hardness and toughness can be particularly improved, and it is possible to obtain a sintered member which is more excellent in mechanical characteristics than in the case of as it is sintered. In particular, since the sintered material before quenching and tempering has a concentration distribution of Ni of more than 0.2% and less than 21% as described above, the heat-treated material after quenching and tempering (an example of the sintered member of the embodiment) remains Austenite can be reduced, and a sintered member in which the entire heat-treated material substantially has a martensitic structure (tempered martensitic structure) can be manufactured more reliably.

　焼入れは、代表的には、浸炭焼入れを行うことが挙げられる。
　浸炭条件は、カーボンポテンシャル（Ｃ．Ｐ．）を０．８質量％以上１．４質量％以下、処理温度を９１０℃以上９５０℃以下、処理時間を６０分以上１５０分以下とすることが挙げられる。
　オーステナイト化条件は、処理温度を８５０℃以上１０００℃以下、処理時間を１０分以上１５０分以下とし、その後油冷又は水冷にて急冷することが挙げられる。 The quenching typically includes carburizing and quenching.
Carburizing conditions include that carbon potential (C.P.) is 0.8 mass% or more and 1.4 mass% or less, treatment temperature is 910 ° C. or more and 950 ° C. or less, and treatment time is 60 minutes or more and 150 minutes or less Be
The austenitizing conditions include a treatment temperature of 850 ° C. or more and 1000 ° C. or less, a treatment time of 10 minutes or more and 150 minutes or less, and then quenching by oil cooling or water cooling.

　焼戻し条件は、処理温度を１５０℃以上２３０℃以下、処理時間を６０分以上１５０分以下とすることが挙げられる。 The tempering conditions include that the treatment temperature is 150 ° C. or more and 230 ° C. or less, and the treatment time is 60 minutes or more and 150 minutes or less.

　なお、焼入れ焼戻し前の焼結材におけるＮｉの濃度分布は、焼入れ焼戻しによって実質的に変化しない。従って、焼入れ焼戻し後の熱処理材におけるＮｉの濃度分布は、焼入れ焼戻し前の焼結材におけるＮｉの濃度分布と同様の範囲、即ち０．２％超２１％未満をとる。 Note that the concentration distribution of Ni in the sintered material before quenching and tempering does not substantially change by quenching and tempering. Therefore, the concentration distribution of Ni in the heat-treated material after quenching and tempering is in the same range as the concentration distribution of Ni in the sintered material before quenching and tempering, that is, more than 0.2% and less than 21%.

〈仕上げ加工工程〉
　この工程は、焼結材の表面粗さを小さくすると共に、焼結材の寸法を設計寸法に適合させるための加工を行う。仕上げ加工は、例えば、研磨加工などが挙げられる。 Finishing process
This process reduces the surface roughness of the sintered material and performs processing to make the dimension of the sintered material conform to the design dimensions. The finishing process may, for example, be polishing process.

　上述の焼結部材の製造方法によって製造された焼結部材は、その表面領域（代表的には、表面から内部に向かって厚さ１ｍｍの領域）において密度の変化が実質的に無く、密度が実質的に均一である。焼結材に転造加工を施していないからである。また、この焼結部材の金属組織は、金属粒子が引き伸ばされた流線状の組織が形成されていない。焼結材に鍛造加工を施していないからである。 The sintered member produced by the above-described method for producing a sintered member has substantially no density change in its surface area (typically, a region with a thickness of 1 mm from the surface to the inside), and has a density It is substantially uniform. This is because the sintered material is not rolled. Also, the metal structure of this sintered member does not have a streamlined structure in which metal particles are stretched. This is because the sintered material is not subjected to forging processing.

＜主な効果＞
　実施形態の焼結部材は、相対密度が非常に高く緻密である上に、Ｎｉを均一的に含むため、割れや破断の起点となり得る箇所が少ない。従って、実施形態の焼結部材は、静的強度に優れる上に、疲労強度にも優れる。高強度であることを以下の試験例で具体的に説明する。 <Main effects>
The sintered member of the embodiment has a very high relative density and is dense, and additionally contains Ni uniformly, so there are few places that can be the origin of cracking or breakage. Therefore, the sintered member of the embodiment is excellent not only in static strength but also in fatigue strength. The high strength is specifically described in the following test examples.

［試験例１］
　種々の相対密度の焼結部材を作製して、相対密度と引張強さとの関係を調べた。 [Test Example 1]
Sintered members of various relative densities were prepared to investigate the relationship between relative density and tensile strength.

　この試験では、原料粉末として、混合粉（原料Ｎｏ．２）、鉄合金粉（原料Ｎｏ．１）、混合粉と鉄合金粉とを含む複合粉であって、Ｎｉ粉の配合が異なるもの（原料Ｎｏ．３１，３２，３３）を用意し、各原料粉末を用いて、相対密度が異なる圧粉成形体を作製する。圧粉成形体の相対密度は、約９１％以上約９９％以下の範囲から選択する。所定の相対密度の圧粉成形体が得られるように、成形圧力を１５６０ＭＰａ（１６ｔｏｎ／ｃｍ^２）～１９６０ＭＰａ（２０ｔｏｎ／ｃｍ^２）の範囲から選択する。成形圧力が大きいほど、相対密度が高い圧粉成形体を得易い。また、圧粉成形体の相対密度が高いほど、相対密度が高い焼結部材を得易い。 In this test, a composite powder containing a mixed powder (raw material No. 2), an iron alloy powder (raw material No. 1), and a mixed powder and an iron alloy powder as raw material powders, wherein the composition of Ni powder is different ( Raw material Nos. 31, 32, and 33) are prepared, and powder compacts having different relative densities are produced using the respective raw material powders. The relative density of the green compact is selected from the range of about 91% to about 99%. The molding pressure is selected from the range of 1560 MPa (16 ton / cm ² ) to 1960 MPa (20 ton / cm ² ) so as to obtain a green compact having a predetermined relative density. The larger the molding pressure, the easier it is to obtain a green compact having a high relative density. Moreover, it is easy to obtain a sintered member with high relative density, so that the relative density of a compacting body is high.

　各原料粉末は、Ｆｅ－５質量％Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎ－０．３質量％Ｃという基本組成を満たすように、配合割合などを調整して用いる。この試験では、各原料粉末は、潤滑剤及び有機バインダーを含有していない（内部潤滑せず）。 Each raw material powder is used by adjusting the blending ratio and the like so as to satisfy the basic composition of Fe-5% by mass Ni-0.5% by mass Mo-0.2% by mass Mn-0.3% by mass C. In this test, each raw material powder does not contain a lubricant and an organic binder (without internal lubrication).

　原料Ｎｏ．１の粉末は、純鉄粉、純Ｎｉ粉、純Ｍｏ粉、純Ｍｎ粉、純Ｃ粉を混合したものである。
　原料Ｎｏ．２の粉末は、Ｆｅ－５質量％Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎという組成の鉄合金粉と、純Ｃ粉とを混合したものである。
　原料Ｎｏ．３１の粉末は、Ｆｅ－３質量％Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎという組成の鉄合金粉と、純Ｎｉ粉と、純Ｃ粉とを混合したものである。
　原料Ｎｏ．３２の粉末は、Ｆｅ－２質量％Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎという組成の鉄合金粉と、純Ｎｉ粉と、純Ｃ粉とを混合したものである。
　原料Ｎｏ．３３の粉末は、Ｆｅ－０．５質量％Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎという組成の鉄合金粉と、純Ｎｉ粉と、純Ｃ粉とを混合したものである。 Raw material No. The powder of 1 is a mixture of pure iron powder, pure Ni powder, pure Mo powder, pure Mn powder and pure C powder.
Raw material No. The powder of No. 2 is a mixture of iron alloy powder having a composition of Fe-5% by mass Ni-0.5% by mass Mo-0.2% by mass Mn and pure C powder.
Raw material No. The powder of No. 31 is a mixture of an iron alloy powder having a composition of Fe-3 mass% Ni-0.5 mass% Mo-0.2 mass% Mn, a pure Ni powder and a pure C powder.
Raw material No. The powder of No. 32 is a mixture of an iron alloy powder having a composition of Fe-2 mass% Ni-0.5 mass% Mo-0.2 mass% Mn, a pure Ni powder, and a pure C powder.
Raw material No. The powder of 33 is a mixture of iron alloy powder having a composition of Fe-0.5 mass% Ni-0.5 mass% Mo-0.2 mass% Mn, pure Ni powder, and pure C powder. .

　ここでは、純鉄粉、鉄合金粉、Ｎｉ粉、Ｍｏ粉、Ｍｎ粉といった金属粉末はいずれも水アトマイズ法などの公知の方法により作製したものである。純鉄粉の平均粒径（Ｄ５０）は７５μｍ、鉄合金粉の平均粒径（Ｄ５０）は７０μｍ、Ｎｉ粉の平均粒径（Ｄ５０）は５μｍ、Ｍｏ粉及びＭｎ粉の平均粒径（Ｄ５０）は１０μｍ、Ｃ粉の平均粒径（Ｄ５０）は５μｍである。上述の金属粉末に適宜、還元処理などを施して酸素の含有量を低減する。 Here, metal powders such as pure iron powder, iron alloy powder, Ni powder, Mo powder, and Mn powder are all produced by a known method such as water atomization. Average particle size (D50) of pure iron powder is 75μm, average particle size of iron alloy powder (D50) is 70μm, average particle size of Ni powder (D50) is 5μm, average particle size of Mo powder and Mn powder (D50) Is 10 μm, and the average particle size (D50) of C powder is 5 μm. The above-described metal powder is appropriately subjected to reduction treatment or the like to reduce the content of oxygen.

　原料粉末を加圧成形して円柱状の圧粉成形体を作製する。圧粉成形体の作製には、一軸加圧が可能な金型を用いる。この金型におけるダイの内周面に潤滑剤としてミリスチン酸のアルコール溶液を塗布する（外部潤滑有り）。 The raw material powder is pressure-formed to produce a cylindrical compact. For production of the green compact, a mold capable of uniaxial pressing is used. An alcohol solution of myristic acid is applied as a lubricant to the inner peripheral surface of the die in this mold (with external lubrication).

　作製した各圧粉成形体を焼結し、得られた円柱状の焼結材に切削加工を施して、所定の引張試験片の形状に加工し、その後に熱処理を施し、得られた熱処理材を各試料の焼結部材とする。ここでの熱処理は、浸炭焼入れ焼戻しとする。焼結条件、浸炭焼入れ条件、焼戻し条件は以下の通りである。
（焼結）１１３０℃×３０分、窒素雰囲気
（浸炭焼入れ）９３０℃×９０分、カーボンポテンシャル：１．２質量％⇒８５０℃×３０分⇒油冷
（焼戻し）２００℃×９０分 Each of the produced green compacts is sintered, and the obtained cylindrical sintered material is subjected to cutting, processed into a predetermined tensile test piece shape, and thereafter subjected to heat treatment, and the obtained heat treated material As a sintered member of each sample. The heat treatment here is carburizing, quenching and tempering. The sintering conditions, the carburizing and quenching conditions, and the tempering conditions are as follows.
(Sintering) 1130 ° C. × 30 minutes, nitrogen atmosphere (carburizing and quenching) 930 ° C. × 90 minutes, carbon potential: 1.2 mass% → 850 ° C. × 30 minutes → oil cold (tempering) 200 ° C. × 90 minutes

　作製した各試料の焼結部材について、相対密度、引張強さを測定した。その結果を表１及び図１に示す。
　表１では、相対密度ごとに試料Ｎｏ．を付す。以下の説明では、各焼結部材を、試料Ｎｏ．と原料Ｎｏ．とを合わせた番号で呼ぶ。例えば、「試料Ｎｏ．５－１」の焼結部材とは、原料Ｎｏ．１の粉末を用いて作製され、相対密度が９９％である焼結部材を意味する。
　図１は、横軸が焼結部材の相対密度（％）、縦軸が焼結部材の引張強さ（ＭＰａ）を示すグラフである。図１では、後述する溶製材（相対密度１００％）の引張強さも示す。 The relative density and tensile strength were measured for the sintered members of each of the produced samples. The results are shown in Table 1 and FIG.
In Table 1, for each relative density, sample no. Attach. In the following description, each sintered member is designated as a sample No. And the raw material No. We call with number that united. For example, a sintered member of “sample No. 5-1” is a raw material No. This means a sintered member produced using the powder of 1 and having a relative density of 99%.
FIG. 1 is a graph in which the horizontal axis represents the relative density (%) of the sintered member, and the vertical axis represents the tensile strength (MPa) of the sintered member. FIG. 1 also shows the tensile strength of a molten material (relative density 100%) described later.

　焼結部材の相対密度は、（焼結部材の見かけ密度／焼結部材の真密度）×１００によって求める。焼結部材の見かけ密度は、アルキメデス法に準拠して求める。詳しくは、焼結部材における空中での質量と純水中での質量とを測定し、「（純水の密度×空中での質量）／（空中での質量－純水中での質量）」によって、焼結部材の見かけ密度を算出する。
焼結部材の真密度は、例えば、ＩＣＰ－ＯＥＳなどによって焼結部材の成分分析を行って各元素の含有割合を求め、この含有割合と、各元素の密度と、焼結部材の質量とを用いて算出することが挙げられる。この試験では、原料粉末の基本組成から焼結部材の真密度を求めることができる。ここでの焼結部材の真密度は、７．８２ｇ／ｃｍ^３である。 The relative density of the sintered member is determined by (apparent density of sintered member / true density of sintered member) × 100. The apparent density of the sintered member is determined in accordance with the Archimedes method. Specifically, the mass in air and the mass in pure water in the sintered member are measured, and "(density of pure water x mass in air) / (mass in air-mass in pure water)" The apparent density of the sintered member is calculated by
The true density of the sintered member is, for example, component analysis of the sintered member by ICP-OES or the like to determine the content ratio of each element, and the content ratio, the density of each element, and the mass of the sintered member It can be mentioned that it is calculated using. In this test, the true density of the sintered member can be determined from the basic composition of the raw material powder. The true density of the sintered member here is 7.82 g / cm ³ .

　引張強さは、汎用の引張試験機を用いて引張試験を行って測定する。試験片は、細幅部と、細幅部の両端に形成される太幅部とで構成される平板状とする。試験片の厚みを５ｍｍ、長さを７２ｍｍとする。細幅部は、中央部と、中央部から太幅部にかけて形成される円弧状の側面を有する肩部とで構成される。中央部の長さを３２ｍｍ、中央の幅を５．７ｍｍ、両端の幅を５．９６ｍｍ、肩部の側面の半径Ｒを２５ｍｍ、太幅部の幅を８．７ｍｍとする。この試験片は、日本粉末冶金工業会の規格、ＪＰＭＡ　Ｍ　０４－１９９２　焼結金属材料引張試験片に準ずるものである。 The tensile strength is measured by conducting a tensile test using a general purpose tensile tester. A test piece is made into the flat form comprised by the narrow part and the wide part formed in the both ends of a narrow part. The thickness of the test piece is 5 mm and the length is 72 mm. The narrow portion is composed of a central portion and a shoulder having an arc-shaped side surface formed from the central portion to the wide portion. The length of the central part is 32 mm, the width of the central part is 5.7 mm, the width of both ends is 5.96 mm, the radius R of the side of the shoulder is 25 mm, and the width of the wide part is 8.7 mm. This test piece conforms to the standard of the Japan Powder Metallurgy Industry Association, JPMA M 04-1992 Sintered Metal Material Tensile Test Piece.

　比較として、上述の基本組成を有する溶製材（相対密度１００％）を用意し、上述の試験片を作製して、引張強さを測定したところ、１６９５ＭＰａである。 As a comparison, when a molten material (relative density 100%) having the above-described basic composition is prepared, the above-described test piece is produced, and the tensile strength is measured, it is 1695 MPa.

　作製した各試料の焼結部材について、Ｎｉの局所的な濃度分布（含有量）を以下のようにして測定した。
　相対密度が９９％である試料Ｎｏ．５－１，Ｎｏ．５－３１～３３，Ｎｏ．５－２の焼結部材について、任意の断面を複数とる（ｎ≧３）。また、断面ごとに一つずつ、測定視野（４００μｍ×５００μｍ）をとる。各測定視野内のＮｉの含有量をＳＥＭ－ＥＤＸ装置で測定し、各測定視野内におけるＮｉの含有量のうち、最大値と最小値とを調べる。ＳＥＭ‐ＥＤＸ装置で用いる電子線は半径約５μｍ程度である。つまり空間分解能は約５μｍφである。複数（ｎ≧３）の各測定視野の最大値、最小値のうち、更に最大の値、最小の値を、各試料の焼結部材におけるＮｉの最大値、最小値とし、表２に示す。 The local concentration distribution (content) of Ni was measured as follows about the sintered member of each sample produced.
Sample No. 1 having a relative density of 99%. 5-1, no. 5-31 to 33, no. A plurality of arbitrary cross sections are taken for the sintered member 5-2 (n ≧ 3). In addition, one measurement field (400 μm × 500 μm) is taken for each cross section. The content of Ni in each measurement field of view is measured by the SEM-EDX apparatus, and the maximum value and the minimum value of the content of Ni in each measurement field of view are checked. The electron beam used in the SEM-EDX apparatus has a radius of about 5 μm. That is, the spatial resolution is about 5 μmφ. The maximum value and the minimum value among the maximum value and the minimum value of each of the plurality (n ≧ 3) of measurement fields are shown in Table 2 as the maximum value and the minimum value of Ni in the sintered member of each sample.

　なお、相対密度が９１％～９７％である焼結部材におけるＮｉの濃度分布は、相対密度が９９％である焼結部材における原料Ｎｏ．が同じもののＮｉの濃度分布と概ね同様である。例えば、原料Ｎｏ．３３の粉末を用いて作製され、相対密度が９５％である試料Ｎｏ．３－３３の焼結部材のＮｉの濃度分布は、試料Ｎｏ．５－３３のＮｉの濃度分布と概ね同様な値である。 The concentration distribution of Ni in the sintered member having a relative density of 91% to 97% is similar to that of the raw material No. 1 in the sintered member having a relative density of 99%. Is the same as the concentration distribution of Ni in the same thing. For example, the raw material No. Sample No. 3 made using 33 powders and having a relative density of 95%. The distribution of concentration of Ni of the sintered member of 3-33 is the same as that of sample No. The value is almost the same as the concentration distribution of Ni in 5-33.

　その他、作製した各試料の焼結部材について、酸素の含有量を測定したところ、いずれも２０００質量ｐｐｍ以下である。酸素の含有量の測定は、試料を不活性ガス中で加熱して溶融して酸素を抽出し、抽出した酸素を測定する不活性ガス融解赤外線吸収法を用いる。この測定には市販の酸素分析装置を利用できる。なお、各試料の焼結部材について、その全体組成をＩＣＰ－ＯＥＳにて測定したところ、上述の原料粉末の基本組成と概ね同様である。 In addition, when content of oxygen was measured about the sintering member of each produced sample, it is 2000 mass ppm or less in all. The measurement of the content of oxygen uses an inert gas melting infrared absorption method in which a sample is heated in an inert gas and melted to extract oxygen, and the extracted oxygen is measured. A commercially available oxygen analyzer can be used for this measurement. In addition, when the entire composition of the sintered member of each sample was measured by ICP-OES, it was almost the same as the basic composition of the above-mentioned raw material powder.

　表１，図１に示すように、相対密度が９７％未満の範囲では、相対密度が高いほど、引張強さが高くなり比例的に大きくなることが分かる。しかし、相対密度が９７％以上の範囲では、原料Ｎｏ．が同じものごとに着目すれば、相対密度が高くなっても、引張強さの変化が非常に小さいことが分かる。このことから、相対密度が９７％以上の焼結部材では、相対密度をより高めることによる引張強さの更なる向上が難しいといえる。相対密度をより高めて、気孔をより少なくしても引張強さを向上し難いことから、相対密度が９７％以上の焼結部材では、気孔以外の原因によって、割れや破断が生じ得ると考えられる。気孔以外の原因として、表１，図１から製造条件の相違、ここでは特に原料粉末の相違が考えられる。 As shown in Table 1 and FIG. 1, when the relative density is less than 97%, it can be seen that the higher the relative density, the higher the tensile strength and the proportionally higher. However, when the relative density is in the range of 97% or more, the raw materials No. It can be seen that the change in tensile strength is very small even if the relative density is high, focusing on the same thing. From this, it can be said that in the sintered member having a relative density of 97% or more, it is difficult to further improve the tensile strength by increasing the relative density. Since it is difficult to improve the tensile strength even if the relative density is further increased and the number of pores is further reduced, it is considered that in sintered members having a relative density of 97% or more, cracking or breakage may occur due to causes other than the pores. Be As causes other than pores, differences in manufacturing conditions can be considered from Table 1 and FIG. 1, particularly differences in raw material powders here.

　製造条件の相違は、焼結部材の組成や組織に相違が生じ得ると考えられる。そこで、相対密度が９９％と高いにも関わらず、引張強さが１４５０ＭＰａ未満である試料Ｎｏ．５－２の組織を調べた。原料粉末に混合粉を用いた試料Ｎｏ．５－２の焼結部材について、その断面をＳＥＭ－ＥＢＳＤ装置で組織解析を行った。この解析箇所におけるＮｉの含有量をＳＥＭ－ＥＤＸ装置で測定し、Ｎｉマッピング像を得た。Ｎｉマッピング像においては、色が濃いほど（モノクロ画像では暗いほど）Ｎｉの含有量が少なく、色が薄いほど（モノクロ画像では明るいほど）Ｎｉの含有量が多いこと示す。 It is considered that differences in manufacturing conditions may cause differences in the composition and structure of the sintered member. Then, although the relative density is as high as 99%, sample No. 1 having a tensile strength of less than 1450 MPa. We examined the organization of 5-2. Sample No. 1 using mixed powder as raw material powder. The cross-sections of the sintered members of 5-2 were analyzed by SEM-EBSD. The content of Ni at this analysis point was measured by a SEM-EDX apparatus to obtain a Ni mapping image. In the Ni mapping image, the darker the color (darker in the monochrome image), the smaller the content of Ni, and the lighter the color (brighter the monochrome image), the higher the content of Ni.

　組織解析像において、緑色の領域（モノクロ画像では薄いグレーの領域）は、面心立方格子（ｆｃｃ）である、その他の赤色の領域（モノクロ画像では濃いグレーの領域）は概ね体心立方格子（ｂｃｃ）である。ｆｃｃ領域は、残留オーステナイトであり、ｂｃｃ領域はマルテンサイトである。そして、ｆｃｃ領域はＮｉマッピング像では明るく見え、Ｎｉの含有量が局所的に高いことが分かる。反面、ｂｃｃ領域はＮｉマッピング像では暗く見え、Ｎｉの含有量が局所的に低い箇所が存在する。即ち、試料Ｎｏ．５－２の焼結部材は、Ｎｉが不均一に存在すると言える。このような不均一組成によって強度の低下を招き易くなり、焼入れ焼戻しを行うと強度に劣る残留オーステナイトを含み易く、引張強さが更に低下し易くなったと考えられる。 In the tissue analysis image, the green area (light gray area in monochrome image) is a face-centered cubic lattice (fcc), and the other red area (dark gray area in monochrome image) is a body-centered cubic lattice ( bcc). The fcc region is retained austenite and the bcc region is martensite. Then, the fcc region appears bright in the Ni mapping image, and it can be seen that the content of Ni is locally high. On the other hand, the bcc region appears dark in the Ni mapping image, and there are locations where the content of Ni is locally low. That is, sample no. It can be said that Ni is unevenly present in the sintered member 5-2. It is considered that such nonuniform composition tends to cause a reduction in strength, and when quenching and tempering is performed, retained austenite which is inferior in strength is easily included, and the tensile strength is further easily reduced.

　以上の知見を踏まえて、相対密度が９７％以上であり、Ｎｉの濃度分布が０．２質量％超２１質量％未満である試料Ｎｏ．４－１，Ｎｏ．４－３３，Ｎｏ．５－１，Ｎｏ．５－３１～Ｎｏ．５－３３（以下、均一試料群と呼ぶ）の焼結部材はいずれも、引張強さが１４６０ＭＰａ以上、更に１５００ＭＰａ以上、１５５０ＭＰａ以上と高く、静的強度に優れる。特に、試料Ｎｏ．４－１，Ｎｏ．５－１の焼結部材はいずれも、引張強さが１６９２ＭＰａ以上であり、溶製材（１６９５ＭＰａ）と同等程度以上の強度を有する。 Based on the above findings, Sample No. 1 having a relative density of 97% or more and a concentration distribution of Ni of more than 0.2% by mass and less than 21% by mass. 4-1, No. 4-33, no. 5-1, no. 5-31 to No. The sintered members of 5-33 (hereinafter referred to as uniform sample group) all have high tensile strength of 1460 MPa or more, further 1500 MPa or more, 1550 MPa or more, and are excellent in static strength. In particular, sample no. 4-1, No. Each of the sintered members 5-1 has a tensile strength of 1692 MPa or more and a strength equal to or higher than that of the ingot material (1695 MPa).

　均一試料群の焼結部材が上述のように高強度である理由の一つとして、焼結部材全体に亘ってＮｉが均一的に存在することが挙げられる。このことは、相対密度が９９％である試料Ｎｏ．５について、原料Ｎｏ．１，Ｎｏ．３１～３３，Ｎｏ．２を比較することから裏付けられる。試料Ｎｏ．５－１，Ｎｏ．５－３１～Ｎｏ．５－３３，Ｎｏ．５－２の順に、Ｎｉの濃度分布の幅が小さく、Ｎｉ量における最大値と最小値との差が小さい。具体的には、試料Ｎｏ．５－１では、上記差が実質的に無く、焼結部材の全体に亘ってＮｉが均一的に存在するといえる。試料Ｎｏ．５－３１～Ｎｏ．５－３３では順に、上記幅が３質量％～８質量％及び上記差が５質量％、上記幅が２質量％～１０質量％及び上記差が８質量％、上記幅が０．５質量％～１６質量％及び上記差が１０質量％超と大きくなっている。試料Ｎｏ．５－２では、上記差が２０質量％以上であり、Ｎｉが不均一に存在するといえる。 One of the reasons why the sintered members of the uniform sample group have high strength as described above is that Ni is uniformly present throughout the sintered members. This indicates that the sample No. 1 with a relative density of 99%. Regarding No. 5, the raw material No. 1, No. 31-33, no. This is corroborated by comparing the two. Sample No. 5-1, no. 5-31 to No. 5-33, no. In the order of 5-2, the width of the concentration distribution of Ni is small, and the difference between the maximum value and the minimum value of the Ni amount is small. Specifically, sample nos. In 5-1, the above difference is not substantially present, and it can be said that Ni is uniformly present throughout the sintered member. Sample No. 5-31 to No. In 5-33, the width is 3% to 8% by mass, the difference is 5% by mass, the width is 2% to 10% by mass, the difference is 8% by mass, and the width is 0.5% by mass. The difference is as large as ̃16% by mass and more than 10% by mass. Sample No. In 5-2, the difference is 20% by mass or more, and it can be said that Ni is nonuniformly present.

　鉄合金粉を用いた試料Ｎｏ．５－１と、混合粉を用いた試料Ｎｏ．５－２について、その断面をＳＥＭで観察し、この観察箇所におけるＮｉの含有量をＳＥＭ－ＥＤＸ装置で測定した。試料Ｎｏ．５－１の焼結部材では、Ｎｉマッピング像の全体が暗く、Ｎｉが全体的に一様に存在することが分かった。このようなＮｉの分布状態から、試料Ｎｏ．５－１の焼結部材は、残留オーステナイトが実質的に存在せず、その全体に亘ってマルテンサイト組織を有すると考えられる。また、このことから、相対密度が９７％以上であり、上述のようにＮｉの濃度分布の幅が小さい試料Ｎｏ．５－３１～Ｎｏ．５－３３の焼結部材は、残留オーステナイトを若干含み得るものの、概ねマルテンサイト組織を有すると考えられる。 Sample No. 1 using iron alloy powder. 5-1 and sample No. 1 using mixed powder. The cross section of No. 5-2 was observed by SEM, and the content of Ni at this observation point was measured by an SEM-EDX apparatus. Sample No. In the sintered member of 5-1, it was found that the whole of the Ni mapping image was dark and Ni was uniformly present. From such a distribution of Ni, sample no. The sintered component 5-1 is considered to be substantially free of retained austenite and to have a martensitic structure throughout its entirety. Moreover, from this, the relative density is 97% or more, and the width of the concentration distribution of Ni is small as described above. 5-31 to No. The 5-33 sintered member is considered to have a generally martensitic structure although it may contain some retained austenite.

　一方、試料Ｎｏ．５－２の焼結部材では、明るく見える箇所も暗く見える箇所も見られ、Ｎｉが全体的に不均一に存在することが分かった。 On the other hand, for sample no. In the sintered member 5-2, the bright and dark spots were also observed, and it was found that Ni was present unevenly as a whole.

　上述のように、この試験から、相対密度が９７％以上の焼結部材では、Ｎｉの濃度分布が０．２質量％超２１質量％未満を満たすことで、引張強さがより高く、好ましくは同じ組成の溶製材と同等程度の引張強さを有し、強度に優れることが示された。 As described above, according to this test, in a sintered member having a relative density of 97% or more, the tensile strength is higher, preferably by satisfying the concentration distribution of Ni by more than 0.2% by mass and less than 21% by mass. It was shown that it had an equivalent tensile strength to a molten material of the same composition and was excellent in strength.

　また、この試験から、相対密度が９７％以上であって、Ｎｉの濃度分布が０．２質量％超２１質量％未満を満たす焼結部材は、原料粉末に鉄合金粉を含むと（ここでは、原料Ｎｏ．１，Ｎｏ．３１～３３を用いると）、製造し易いといえる。特に、原料Ｎｏ．１の粉末を用いること、即ち、鉄合金粉を主として用いることが好ましいといえる。 In addition, according to this test, when a sintered member having a relative density of 97% or more and a concentration distribution of Ni satisfying more than 0.2% by mass but less than 21% by mass contains iron alloy powder in the raw material powder (here The raw materials Nos. 1 and 31 to 33 can be said to be easy to manufacture. In particular, no. It is preferable to use the powder of 1, that is, to use mainly iron alloy powder.

［試験例２］
　Ｎｉの含有量を変化させて、引張強さに対する影響を調べた。 [Test Example 2]
The content of Ni was varied to examine the influence on tensile strength.

　ここでは、試験例１で作製した試料Ｎｏ．５－１に対して、原料粉末に用いる鉄合金粉中のＮｉの含有量を異ならせた点を除いて、試験例１と同様にして焼結部材を作製する。
試料Ｎｏ．２－１は、Ｆｅ－０．５質量％Ｍｏ－０．２質量％Ｍｎという組成の鉄合金粉と、純Ｃ粉とを混合したものであり、原料粉末にＮｉを含まない。なお、試験例２における試料Ｎｏ．２－１は、試験例１（表２）におけるＮｏ．２－１とは異なる試料である。 Here, for the sample No. 1 produced in Test Example 1. A sintered member is produced in the same manner as in Test Example 1 except that the content of Ni in the iron alloy powder used as the raw material powder is different from 5-1.
Sample No. 2-1 is a mixture of an iron alloy powder having a composition of Fe-0.5 mass% Mo-0.2 mass% Mn and a pure C powder, and the raw material powder does not contain Ni. Sample No. 1 in Test Example 2 2-1 is No. 1 in Test Example 1 (Table 2). It is a sample different from 2-1.

　作製した各試料の焼結部材について、試験例１と同様にして引張強さ（ＭＰａ）を測定し、結果を表３及び図２に示す。図２は、横軸が焼結部材の全体組成（鉄基合金全体）におけるＮｉの含有量（Ｎｉ量、質量％）、縦軸が焼結部材の引張強さ（ＭＰａ）を示すグラフである。 The tensile strength (MPa) of the sintered members of each of the produced samples was measured in the same manner as in Test Example 1, and the results are shown in Table 3 and FIG. FIG. 2 is a graph in which the abscissa represents the content (Ni amount, mass%) of Ni in the overall composition of the sintered member (entire iron-based alloy) and the ordinate represents the tensile strength (MPa) of the sintered member .

　作製した各試料の焼結部材について、Ｎｉの局所的な濃度分布（含有量）を試験例１と同様にして調べ、結果を表３に示す。その他、各試料の焼結部材について、試験例１と同様にして測定したところ、相対密度は９９％、酸素の含有量は２０００質量ｐｐｍ以下、全体組成は原料粉末の基本組成（Ｆｅ－（表３の値）Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎ－０．３質量％Ｃ）と概ね同様である。 The local concentration distribution (content) of Ni was examined in the same manner as in Test Example 1 with respect to the sintered members of each of the manufactured samples, and the results are shown in Table 3. In addition, the sintered members of each sample were measured in the same manner as in Test Example 1. As a result, the relative density was 99%, the oxygen content was 2000 mass ppm or less, and the overall composition was the basic composition of the raw material powder (Fe-( Value of 3) substantially the same as Ni-0.5% by mass Mo-0.2% by mass Mn-0.3% by mass C).

　表３，図２に示すように、この試験では、相対密度が９７％以上であり、Ｎｉを均一的に含む焼結部材について、Ｎｉの局所的な濃度分布（含有量）は引張強さに影響を与えることが分かる。Ｎｉを含まないと引張強さが低い（試料Ｎｏ．２－１）。Ｎｉの含有量が多くなると引張強さが高くなる。ここではＮｉの含有量が１質量％以上であると引張強さが１４６０ＭＰａ以上である。特にＮｉの含有量が２質量％超８質量％未満であると、引張強さが１６００ＭＰａ以上となり、５質量％に近づくほど引張強さがより高く、５質量％で引張強さが最大になる（ピークをとる）ことが分かる。この理由は定かではないが、この試験結果から、相対密度が９７％以上であって、Ｎｉの濃度分布が０．２質量％超２１質量％未満を満たす焼結部材では、焼結部材の全体組成におけるＮｉの含有量を２質量％超８質量％未満、更には３質量％以上７質量％以下とすると、引張強さをより向上でき、１６００ＭＰａ以上の引張強さを有し得ることが示された。 As shown in Table 3 and FIG. 2, in this test, the local concentration distribution (content) of Ni is a tensile strength for a sintered member having a relative density of 97% or more and uniformly containing Ni. It turns out that it affects. The tensile strength is low when Ni is not contained (Sample No. 2-1). The tensile strength increases as the content of Ni increases. Here, when the content of Ni is 1% by mass or more, the tensile strength is 1460 MPa or more. In particular, if the content of Ni is more than 2% by mass and less than 8% by mass, the tensile strength is 1600 MPa or more, and the tensile strength becomes higher as it approaches 5% by mass, and the tensile strength becomes maximum at 5% by mass It can be seen that it takes a peak. Although the reason is not clear, according to the test results, in the sintered member having a relative density of 97% or more and a concentration distribution of Ni satisfying more than 0.2% by mass and less than 21% by mass, the entire sintered member When the content of Ni in the composition is more than 2% by mass and less than 8% by mass, and further 3% by mass or more and 7% by mass or less, tensile strength can be further improved, and tensile strength of 1600 MPa or more can be exhibited. It was done.

［試験例３］
　酸素の含有量を変化させて、引張強さに対する影響を調べた。 [Test Example 3]
The oxygen content was varied to examine the effect on tensile strength.

　ここでは、試験例１で作製した試料Ｎｏ．５－１に対して、原料粉末に用いる鉄合金粉に対する還元処理の度合いを異ならせた点を除いて、試験例１と同様にして焼結部材を作製する。 Here, for the sample No. 1 produced in Test Example 1. A sintered member is produced in the same manner as in Test Example 1 except that the degree of reduction treatment for the iron alloy powder used as the raw material powder is different from 5-1.

　作製した各試料の焼結部材について、試験例１と同様にして、酸素の含有量（酸素量、質量％）と引張強さ（ＭＰａ）とを測定し、結果を表４，図３に示す。図３は、横軸が焼結部材の全体組成における酸素の含有量（酸素量、質量ｐｐｍ）、縦軸が焼結部材の引張強さ（ＭＰａ）を示すグラフである。 With respect to the sintered members of each sample produced, the oxygen content (oxygen amount, mass%) and tensile strength (MPa) were measured in the same manner as in Test Example 1, and the results are shown in Table 4 and FIG. . FIG. 3 is a graph in which the horizontal axis represents the oxygen content (oxygen amount, mass ppm) in the overall composition of the sintered member, and the vertical axis represents the tensile strength (MPa) of the sintered member.

　また、作製した各試料の焼結部材について、Ｎｉの局所的な濃度分布（含有量）を試験例１と同様にして調べたところ、試料Ｎｏ．５－１のＮｉの局所的な濃度分布（含有量）と実質的に同じである。その他、各試料の焼結部材について、試験例１と同様にして測定したところ、相対密度は９９％、全体組成は原料粉末の基本組成（Ｆｅ－５質量％Ｎｉ－０．５質量％Ｍｏ－０．２質量％Ｍｎ－０．３質量％Ｃ）と概ね同様であり、実質的にマルテンサイト組織から構成されている。 Moreover, when the local concentration distribution (content) of Ni was investigated in the same manner as in Test Example 1 with respect to the sintered members of each of the manufactured samples, sample No. 1 was obtained. It is substantially the same as the local concentration distribution (content) of Ni 5-1. In addition, the sintered members of each sample were measured in the same manner as in Test Example 1. As a result, the relative density was 99%, and the overall composition was the basic composition of the raw material powder (Fe-5% by mass Ni-0.5% by mass Mo- It is substantially the same as 0.2% by mass Mn-0.3% by mass C), and substantially comprises a martensitic structure.

　表４，図３に示すように、この試験では、相対密度が９７％以上であり、Ｎｉを均一的に含む焼結部材について、酸素の含有量は引張強さに影響を与えることが分かる。この試験では、酸素の含有量が少ないほど、引張強さを高められることが分かる。表４，図３から酸素の含有量が３０００質量ｐｐｍ以下であれば、引張強さが１６００ＭＰａであり、高強度な焼結部材といえる。更に、酸素の含有量が３０００質量ｐｐｍ未満であれば、引張強さが１６５０ＭＰａ以上、更に１７００ＭＰａ程度であり、上述の溶製材と同等程度の強度を有することが分かる。この理由の一つは、酸素の含有量が少ないことで、割れや破断の起点となり得る酸化物が低減されたためと考えられる。この試験結果から、相対密度が９７％以上であって、Ｎｉの濃度分布が０．２質量％超２１質量％未満を満たす焼結部材では、焼結部材の全体組成における酸素の含有量を３０００質量ｐｐｍ未満、更に２０００質量ｐｐｍ以下とすると、引張強さを更に向上できることが示された。また、酸素の含有量は、原料粉末に適宜還元処理などして、酸素を除去することで調整できることが示された。 As shown in Table 4 and FIG. 3, in this test, it is found that the content of oxygen affects the tensile strength for a sintered member having a relative density of 97% or more and uniformly containing Ni. In this test, it is found that the lower the content of oxygen, the higher the tensile strength. From Table 4 and FIG. 3, when the content of oxygen is 3000 mass ppm or less, the tensile strength is 1600 MPa and it can be said that the sintered member is a high strength. Furthermore, if the content of oxygen is less than 3000 ppm by mass, it can be seen that the tensile strength is 1650 MPa or more, and further about 1700 MPa, and has the same level of strength as the molten material described above. One of the reasons for this is considered to be that the low content of oxygen reduces the oxide that can be a starting point of cracking and breakage. From this test result, in a sintered member having a relative density of 97% or more and a concentration distribution of Ni satisfying more than 0.2% by mass but less than 21% by mass, the content of oxygen in the entire composition of the sintered member is 3000 It was shown that the tensile strength can be further improved if the amount is less than mass ppm and further 2000 mass ppm or less. In addition, it was shown that the content of oxygen can be adjusted by removing oxygen by appropriately reducing the raw material powder.

　今回開示された実施の形態はすべての点で例示であって、どのような面からも制限的なものではないと理解されるべきである。本発明の範囲は上記した説明ではなく、請求の範囲によって規定され、請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。例えば、上述の試験例１～３において、組成を変更したり（Ｍｏ，Ｍｎの含有量の変更、ＳｉやＢを含むなど）、製造条件を変更したりすることができる。 It should be understood that the embodiments disclosed herein are illustrative in all respects and not restrictive in any respect. The scope of the present invention is not the above description, but is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. For example, in the above-described Test Examples 1 to 3, the composition can be changed (such as changing the content of Mo and Mn, containing Si and B, or the like) or the manufacturing conditions can be changed.

Claims (11)

1. 　鉄基合金からなる焼結部材であって、
   　　前記鉄基合金全体におけるＮｉの含有量が０．２質量％を超え１０質量％以下であり、Ｃの含有量が０質量％を超え２．０質量％以下であり、Ｍｏ，Ｍｎ，Ｃｒ，Ｂ，及びＳｉから選択される１種以上の元素が合計で０質量％を超え５．０質量％以下であり、残部がＦｅ及び不可避不純物であり、
   　　前記鉄基合金の局所的な領域におけるＮｉの含有量が０．２質量％を超え２１質量％未満であり、
   　相対密度が９７％以上である焼結部材。 A sintered member made of an iron-based alloy,
   The content of Ni in the entire iron-based alloy is more than 0.2% by mass and 10% by mass or less, the content of C is more than 0% by mass and 2.0% by mass or less, Mo, Mn, Cr, One or more elements selected from B and Si are more than 0% by mass and 5.0% by mass or less in total, and the balance is Fe and an unavoidable impurity,
   The content of Ni in the local region of the iron-based alloy is more than 0.2% by mass and less than 21% by mass,
   A sintered member having a relative density of 97% or more.
2. 　前記鉄基合金全体におけるＮｉの含有量が２質量％を超え８質量％未満である、請求項１に記載の焼結部材。 The sintered member according to claim 1, wherein the content of Ni in the entire iron-based alloy is more than 2% by mass and less than 8% by mass.
3. 　酸素の含有量が３０００質量ｐｐｍ未満である請求項１又は請求項２に記載の焼結部材。 The sintered member according to claim 1 or 2, wherein the content of oxygen is less than 3000 ppm by mass.
4. 　マルテンサイトからなる組織を有する請求項１から請求項３のいずれか１項に記載の焼結部材。 The sintered member according to any one of claims 1 to 3, which has a structure made of martensite.
5. 　前記鉄基合金全体におけるＮｉの含有量が２質量％を超え８質量％未満であり、
   酸素の含有量が３０００質量ｐｐｍ未満である、請求項１に記載の焼結部材。 The content of Ni in the entire iron-based alloy is more than 2% by mass and less than 8% by mass,
   The sintered member according to claim 1, wherein the content of oxygen is less than 3000 ppm by mass.
6. 　前記鉄基合金全体におけるＮｉの含有量が２質量％を超え８質量％未満であり、
   酸素の含有量が３０００質量ｐｐｍ未満であり、マルテンサイトからなる組織を有する請求項１に記載の焼結部材。 The content of Ni in the entire iron-based alloy is more than 2% by mass and less than 8% by mass,
   The sintered member according to claim 1, wherein the content of oxygen is less than 3000 ppm by mass, and it has a structure made of martensite.
7. 　前記鉄基合金全体におけるＮｉの含有量が４質量％を超え６質量％以下である、請求項２に記載の焼結部材。 The sintered member according to claim 2, wherein the content of Ni in the entire iron-based alloy is more than 4% by mass and 6% by mass or less.
8. 　酸素の含有量が２０００質量ｐｐｍ以下である、請求項３に記載の焼結部材。
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   The sintered member according to claim 3, wherein the content of oxygen is 2000 mass ppm or less.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
9. 前記鉄基合金全体におけるＣの含有量が０．２質量％以上０．８質量％以下である、請求項１から請求項８のいずれか１項に記載の焼結部材。 The sintered member according to any one of claims 1 to 8, wherein the content of C in the entire iron-based alloy is 0.2% by mass or more and 0.8% by mass or less.
10. 前記鉄基合金全体におけるＭｏの含有量が０．１５％質量以上０．８％質量以下であり、
    前記鉄基合金全体におけるＭｎの含有量が０．１５％質量以上０．８％質量以下である、請求項１から請求項９のいずれか１項に記載の焼結部材。 The content of Mo in the entire iron-based alloy is 0.15% by mass or more and 0.8% by mass or less,
    The sintered member according to any one of claims 1 to 9, wherein the content of Mn in the entire iron-based alloy is 0.15% by mass or more and 0.8% by mass or less.
11. 前記鉄基合金の局所的な領域におけるＮｉの含有量が１質量％以上１２質量％以下である、請求項１から請求項１０のいずれか１項に記載の焼結部材。 The sintered member according to any one of claims 1 to 10, wherein a content of Ni in a local region of the iron-based alloy is 1% by mass or more and 12% by mass or less.

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