JP2015117391A - Iron-based sintered alloy, method for producing the same, and high-carbon iron-based powder - Google Patents
Iron-based sintered alloy, method for producing the same, and high-carbon iron-based powder Download PDFInfo
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Description
本発明は、機械的特性または寸法安定性に優れた鉄基焼結合金と、その鉄基焼結合金を効率的に得ることができる鉄基焼結合金の製造方法と、その製造方法等に利用できる高炭素鉄系粉末に関する。 The present invention relates to an iron-based sintered alloy having excellent mechanical properties or dimensional stability, a method for producing an iron-based sintered alloy capable of efficiently obtaining the iron-based sintered alloy, a method for producing the same, and the like. The present invention relates to usable high carbon iron-based powder.
製造コストを削減するために、鉄系粉末の成形体を焼結させた鉄基焼結部材が利用される。この鉄基焼結部材は最終形状に近いため、機械加工の削減や歩留りの向上等によって製造コストを低減し得る。 In order to reduce the manufacturing cost, an iron-based sintered member obtained by sintering an iron-based powder compact is used. Since this iron-based sintered member is close to the final shape, the manufacturing cost can be reduced by reducing machining or improving yield.
ところで、このような鉄基焼結部材は、通常、その機械的特性を高めるために炭素(C)を含む合金(以下、鉄基焼結合金という。)からなり、その炭素源は黒鉛粉末(Gr粉末)として添加されるのが一般的である。 By the way, such an iron-based sintered member is usually made of an alloy containing carbon (C) (hereinafter referred to as an iron-based sintered alloy) in order to enhance its mechanical properties, and its carbon source is graphite powder ( Gr powder) is generally added.
黒鉛粉末と純鉄粉または鉄合金粉からなるベース粉末(以下、適宜「鉄源粉末」という。)との混合粉末からなる成形体を焼結させると、その昇温中にCOガスが発生することが知られている。このようなガスは、焼結体の構成粒子の結合(ネック形成)を阻害したり、焼結体を変形させたりし得る。しかし、焼結炉内で緩やかに昇温した後に一定温度で長時間保持する通常の焼結方法の場合、ガスの発生も緩やかであり、成形体等の内部で発生したガスは成形体等の内部にできた微細な開気孔を通じて成形体外へ放出される。このため、従来の焼結方法を行う限り、鉄基焼結合金の炭素源として黒鉛粉末を用いても、不都合を生じることは少なかった。 When a molded body made of a mixed powder of graphite powder and a base powder made of pure iron powder or iron alloy powder (hereinafter referred to as “iron source powder” as appropriate) is sintered, CO gas is generated during the temperature rise. It is known. Such a gas may inhibit the bonding (neck formation) of the constituent particles of the sintered body or may deform the sintered body. However, in the case of a normal sintering method in which the temperature is gradually raised in the sintering furnace and then maintained at a constant temperature for a long time, the gas generation is also slow, and the gas generated inside the molded body etc. It is discharged out of the molded body through fine open pores formed inside. For this reason, as long as the conventional sintering method is performed, even if graphite powder is used as the carbon source of the iron-based sintered alloy, there is little inconvenience.
ところが、焼結過程に要する時間を短縮して生産性の向上を図るために、従来の焼結炉による加熱に替えて、高周波誘導加熱(適宜、単に誘導加熱という。)、通電加熱、放電加熱などによる急速加熱を行うことが提案されている。これに関連した記載が下記の特許文献にある。 However, in order to shorten the time required for the sintering process and improve productivity, high-frequency induction heating (appropriately simply referred to as induction heating), current heating, discharge heating is used instead of heating by a conventional sintering furnace. It has been proposed to carry out rapid heating by such means. There is a description related to this in the following patent document.
特許文献1は、加熱促進材を圧粉体の内部に配置して誘導加熱することを提案している。これにより、加熱当初に圧粉体の抵抗値を大きくする内部潤滑剤が早期に脱漏され、圧粉体が焼結温度へ到達するまでの時間(昇温時間)の短縮が図られる。 Patent Document 1 proposes that a heating accelerator is disposed inside the green compact and induction heated. As a result, the internal lubricant that increases the resistance value of the green compact at the beginning of heating is quickly leaked, and the time until the green compact reaches the sintering temperature (temperature increase time) is shortened.
もっとも、内部潤滑剤の脱蝋後に圧粉体の温度が急激に上昇すると、圧粉体中に含まれる黒鉛粉末が周囲のOと反応して多量のCOガスが圧粉体中に急激に発生する。このようなガスは、放出が追いつかずに焼結体内に封入された状態となり、構成粒子間のネック形成等を妨げたり、焼結前後の寸法変化を大きくさせ得る。 However, if the temperature of the green compact rapidly rises after dewaxing of the internal lubricant, the graphite powder contained in the green compact reacts with the surrounding O, and a large amount of CO gas is rapidly generated in the green compact. To do. Such a gas is in a state of being enclosed in the sintered body without catching up the release, which may prevent formation of a neck between constituent particles or increase the dimensional change before and after sintering.
特許文献2は、黒鉛粉末と鉄系粉末からなる圧粉体を誘導加熱する際に生じる上述した問題を回避するため、昇温途中で一定時間保持する処理(第2活性化処理)を行い、圧粉体の内部に発生したガスを放出させている。しかし、このような方法では、誘導加熱を用いても、焼結工程に要する時間を十分に短縮することは当然できない。 Patent Document 2 performs a process (second activation process) for holding for a certain period of time during a temperature rise in order to avoid the above-described problem that occurs when induction compacting a green compact composed of graphite powder and iron-based powder. The gas generated inside the green compact is released. However, in such a method, even if induction heating is used, it is naturally not possible to sufficiently shorten the time required for the sintering process.
また、高密度成形された圧粉体(例えば、密度が7.2g/cm3以上)の場合、そもそも内部で発生したガスを放出するための開気孔が乏しいため、特許文献2のような保持時間を設けてもあまり意味がない。このため、誘導加熱等を用いた急速加熱により鉄基焼結合金を短時間で焼結する製造方法は、少なくとも工業レベルで実用化されていなかった。 Further, in the case of a green compact molded with a high density (for example, a density of 7.2 g / cm 3 or more), the open pores for releasing the gas generated inside are scarce in the first place. It doesn't make much sense to have time. For this reason, a manufacturing method for sintering an iron-based sintered alloy in a short time by rapid heating using induction heating or the like has not been put into practical use at least on an industrial level.
本発明は、このような事情に鑑みて為されたものであり、誘導加熱等による成形体の急速加熱や焼結時間の大幅な短縮を現実に可能とする鉄基焼結合金の製造方法を提供することを目的とする。また、その製造方法に適した高炭素鉄系粉末と、その製造方法により得られる鉄基焼結合金も併せて提供することを目的とする。 The present invention has been made in view of such circumstances, and provides a method for producing an iron-based sintered alloy that can actually rapidly heat a molded body by induction heating or the like and greatly reduce the sintering time. The purpose is to provide. Another object of the present invention is to provide a high carbon iron-based powder suitable for the production method and an iron-based sintered alloy obtained by the production method.
本発明者はこの課題を解決すべく鋭意研究し、試行錯誤を重ねた結果、鉄基焼結合金の重要な合金元素である炭素の供給形態を見直し、黒鉛粉末に替えて鉄合金または鉄化合物からなる高炭素鉄系粉末を炭素源粉末として用いることを着想した。この高炭素鉄系粉末を用いることにより、成形体を急速加熱して高特性で高精度な焼結体を極短時間で得ることに成功した。この成果を発展させることにより、以降に述べる本発明を完成するに至った。 As a result of extensive research and trial and error, the present inventor has reviewed the supply form of carbon, which is an important alloy element of the iron-based sintered alloy, and replaced the graphite powder with an iron alloy or an iron compound. The idea was to use a high-carbon iron-based powder consisting of as a carbon source powder. By using this high-carbon iron-based powder, we succeeded in obtaining a sintered body with high characteristics and high accuracy in a very short time by rapidly heating the compact. By developing this result, the present invention described below has been completed.
《鉄基焼結合金の製造方法》
(1)本発明の鉄基焼結合金の製造方法は、鉄源粉末と炭素源粉末を少なくとも含む混合粉末を加圧成形した成形体を得る成形工程と、該成形体を加熱した焼結体を得る焼結工程と、を備える鉄基焼結合金の製造方法であって、前記炭素源粉末の少なくとも一種は、Cを5質量%(以下、単に「%」で表す。)以上含む鉄合金または鉄化合物からなる高炭素鉄系粉末であることを特徴とする。
《Method for producing iron-based sintered alloy》
(1) The method for producing an iron-based sintered alloy according to the present invention includes a molding step for obtaining a molded body obtained by pressure molding a mixed powder containing at least an iron source powder and a carbon source powder, and a sintered body obtained by heating the molded body. And an iron-based sintered alloy manufacturing method comprising: at least one of the carbon source powders including 5 mass% (hereinafter simply referred to as “%”) or more of C. Or it is the high carbon iron-type powder which consists of an iron compound, It is characterized by the above-mentioned.
(2)本発明の製造方法では、炭素源粉末としてCを高濃度に含有した鉄合金または鉄化合物からなる高炭素鉄系粉末を用いている。これにより、例えば成形体を急速加熱した場合でも、その昇温過程中に成形体内部でCOガスが急激に発生することが抑止される。この結果、本発明の製造方法によれば、焼結工程時の昇温速度の大小や成形体密度の高低に拘わらず、機械的特性や寸法安定性に優れた鉄基焼結合金を安定して得ることができる。 (2) In the production method of the present invention, a high carbon iron-based powder made of an iron alloy or iron compound containing C at a high concentration is used as the carbon source powder. As a result, for example, even when the molded body is rapidly heated, the sudden generation of CO gas in the molded body during the temperature rising process is suppressed. As a result, according to the production method of the present invention, it is possible to stabilize an iron-based sintered alloy having excellent mechanical properties and dimensional stability regardless of the rate of temperature rise during the sintering process and the density of the compact. Can be obtained.
(3)本発明に係る高炭素鉄系粉末が、上述したような優れた作用効果を発揮する理由は必ずしも定かではないが、焼結工程中におけるCの拡散挙動が高炭素鉄系粉末と黒鉛粉末とで異なるためと考えられる。具体的にいうと、次のように考えられる。黒鉛粉末の場合、その粒子(黒鉛粒子)はCのみからなる。このため、黒鉛粒子の最表面から接触している鉄源粒子へCが固相拡散すると、その拡散に伴い、その最表面(接触界面)近傍において黒鉛粒子の一部が消失することになる。そして、その黒鉛粒子の残部が、鉄源粒子との接触を断たれて成形体中でCOガス化することになる。 (3) The reason why the high carbon iron-based powder according to the present invention exhibits the above-described excellent effects is not necessarily known, but the diffusion behavior of C during the sintering process is high carbon iron-based powder and graphite. This is probably because it differs from powder. Specifically, it can be considered as follows. In the case of graphite powder, the particles (graphite particles) consist only of C. For this reason, when C is solid-phase diffused from the outermost surface of the graphite particles to the iron source particles that are in contact, a part of the graphite particles disappears in the vicinity of the outermost surface (contact interface). Then, the remainder of the graphite particles are cut off from contact with the iron source particles and become CO gas in the molded body.
一方、高炭素鉄系粉末の場合、その粒子(高炭素鉄系粒子)はC以外の主成分(Fe等)により基本的に構成されている。このため、高炭素鉄系粒子から鉄源粒子へCが拡散しても、高炭素鉄系粒子の接触界面近傍に空孔が生じることはなく、高炭素鉄系粒子と鉄源粒子の接触状態は維持されたままとなる。その結果、高炭素鉄系粒子中のCは容易にCOガス化せず、高炭素鉄系粒子から鉄源粒子へ安定的に固相拡散し続ける。 On the other hand, in the case of high carbon iron-based powder, the particles (high carbon iron-based particles) are basically composed of main components other than C (Fe and the like). For this reason, even if C diffuses from the high carbon iron-based particles to the iron source particles, no voids are generated near the contact interface of the high carbon iron-based particles, and the contact state between the high carbon iron-based particles and the iron source particles. Remains maintained. As a result, C in the high carbon iron-based particles is not easily converted to CO gas and continues to stably solid-phase diffuse from the high carbon iron-based particles to the iron source particles.
このようなCの拡散挙動の相違により、高炭素鉄系粉末を用いると、成形体を急速加熱した場合でも、急激なCOガスの発生が十分に抑制されたと考えられる。こうして本発明の製造方法によると、急速加熱・短時間焼結をした場合であっても、黒鉛粉末を用いた場合のようにCOガスにより鉄源粉末の粒子界面が押し広げられてネック形成(構成粒子間の結合)が妨げられたり、膨れが生じたりすることもなく、機械的特性(強度、延性、靱性等)または寸法安定性に優れる焼結体(鉄基焼結合金)が得られるようになったと考えられる。 Due to the difference in the diffusion behavior of C, it is considered that when a high carbon iron-based powder is used, the rapid generation of CO gas is sufficiently suppressed even when the compact is rapidly heated. Thus, according to the manufacturing method of the present invention, even when rapid heating and short-time sintering are performed, the particle interface of the iron source powder is expanded by the CO gas as in the case of using graphite powder, thereby forming a neck ( A sintered body (iron-based sintered alloy) excellent in mechanical properties (strength, ductility, toughness, etc.) or dimensional stability can be obtained without interfering with bonding between constituent particles) and without causing swelling. It is thought that it came to be.
《鉄基焼結合金と高炭素鉄系粉末》
(1)本発明は、上述した製造方法のみならず、それにより得られる鉄基焼結合金としても把握できる。
《Iron-based sintered alloy and high-carbon iron-based powder》
(1) The present invention can be grasped not only as the above-described manufacturing method but also as an iron-based sintered alloy obtained thereby.
(2)また本発明は、全体を100%として、Cを5%以上含む鉄合金または鉄化合物からなることを特徴とする高炭素鉄系粉末としても把握できる。この高炭素鉄系粉末の代表的な用途は上述した鉄基焼結合金の製造方法であるが、他の用途(例えば、常温付近で、きわめて硬い物質であるため、耐摩耗性を要求される機械部品の製造や砥石の製造等)に用いることも可能である。従って、ここでいう本発明の高炭素鉄系粉末は、その用途が焼結用炭素源粉末に限定されるものではない。 (2) Moreover, this invention can be grasped | ascertained also as a high carbon iron type | system | group powder characterized by consisting of the iron alloy or iron compound which contains 5% or more of C as a whole. A typical application of this high carbon iron-based powder is the above-described method for producing an iron-based sintered alloy, but other applications (for example, an extremely hard substance near room temperature, wear resistance is required. It can also be used for manufacturing machine parts and grinding wheels. Therefore, the use of the high carbon iron-based powder of the present invention is not limited to the carbon source powder for sintering.
《その他》
(1)本明細書でいう「鉄基焼結合金」はその形態を問わず、例えば、インゴット状、棒状、管状、板状等の素材であっても良いし、最終製品またはそれに近い部材(鉄基焼結部材)であっても良い。なお本明細書では、鉄基焼結合金が素材(バルク)であるか特定形状をした部材であるかを問わず、鉄基焼結合金を単に焼結体ともいう。
<Others>
(1) The “iron-based sintered alloy” referred to in the present specification may be a material such as an ingot shape, a rod shape, a tubular shape, a plate shape, etc. (Iron-based sintered member). In this specification, regardless of whether the iron-based sintered alloy is a material (bulk) or a member having a specific shape, the iron-based sintered alloy is also simply referred to as a sintered body.
(2)特に断らない限り本明細書でいう「x〜y」は下限値xおよび上限値yを含む。本明細書に記載した種々の数値または数値範囲に含まれる任意の数値を新たな下限値または上限値として「a〜b」のような範囲を新設し得る。 (2) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. A range such as “a to b” can be newly established with any numerical value included in various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.
本明細書で説明する内容は、鉄基焼結合金または高炭素鉄系粉末のみならず、それらの製造方法にも該当し得る。製造方法に関する構成要素は、プロダクトバイプロセスクレームとして理解すれば物に関する構成要素ともなり得る。上述した本発明の構成要素に、本明細書中から任意に選択した一つまたは二つ以上の構成要素を付加し得る。いずれの実施形態が最良であるか否かは、対象、要求性能等によって異なる。 The contents described in this specification can be applied not only to iron-based sintered alloys or high-carbon iron-based powders but also to their production methods. A component related to a manufacturing method can be a component related to an object if understood as a product-by-process claim. One or two or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. Which embodiment is the best depends on the target, required performance, and the like.
《原料粉末/混合粉末》
本発明に係る焼結体は、原料粉末を所望組成に配合した混合粉末の成形体を焼結させてなる。混合粉末は主に鉄源粉末と炭素源粉末からなるが、適宜、それら以外の改質粉末、内部潤滑剤等を含んでもよい。以下、各粉末について詳述する。
<< Raw material powder / Mixed powder >>
The sintered body according to the present invention is obtained by sintering a compact of a mixed powder obtained by blending raw material powder into a desired composition. The mixed powder is mainly composed of an iron source powder and a carbon source powder, but may optionally contain other modified powders, an internal lubricant, and the like. Hereinafter, each powder will be described in detail.
[炭素源粉末]
(1)本発明に係る炭素源粉末の少なくとも一部は、高炭素鉄系粉末からなる。高炭素鉄系粉末は、Cを5%以上、6%以上さらには6.5%以上含む鉄合金または鉄化合物からなる粒子(適宜、高炭素鉄系粒子という。)であると好ましい。C量が過少では、焼結体中のC量が不十分となり、また多くの高炭素鉄系粉末が必要となって不経済である。一方、そのC量の上限値は問わないが、C量が過多な粉末の製造は容易ではない。なお、ここでいうC量は、高炭素鉄系粉末全体(それを構成する鉄合金または鉄化合物からなる粒子全体)を100質量%としたときの割合である。
[Carbon source powder]
(1) At least a part of the carbon source powder according to the present invention is made of a high carbon iron-based powder. The high carbon iron-based powder is preferably particles made of an iron alloy or an iron compound containing 5% or more, 6% or more, and further 6.5% or more of C (referred to as high carbon iron-based particles as appropriate). If the amount of C is too small, the amount of C in the sintered body becomes insufficient, and a lot of high carbon iron-based powder is required, which is uneconomical. On the other hand, the upper limit of the amount of C is not limited, but it is not easy to produce a powder having an excessive amount of C. In addition, C amount here is a ratio when the whole high carbon iron-type powder (the whole particle | grains which consist of the iron alloy or iron compound which comprises it) is 100 mass%.
高炭素鉄系粒子は、全体としてCを高濃度に含む鉄合金または鉄化合物からなる限り、その微細組織やCの存在形態は特に問わない。例えば、Cの一部は、Fe中に固溶していてもよいし、セメンタイトを形成していてもよいし、さらにはC粒子として高炭素鉄系粒子中に析出していてもよい。 As long as the high carbon iron-based particles are composed of an iron alloy or an iron compound containing C at a high concentration as a whole, the microstructure and the existence form of C are not particularly limited. For example, a part of C may be dissolved in Fe, may form cementite, or may be precipitated in high carbon iron-based particles as C particles.
もっとも、高炭素鉄系粉末は、セメンタイト型鉄化合物を有する粒子からなると好ましい。セメンタイト型鉄化合物は準安定相であり、焼結工程の昇温初期(低温域)には化合物状態で存在するが、焼結温度付近の高温域になると、Fe(γ相)とC(炭素)に分解し易い。従って、焼結工程中にCOガスの発生を抑えつつ、Cを成形体または焼結体の構成粒子へ素早く拡散させる上で、セメンタイト型鉄化合物の粉末は炭素源粉末として好ましい。 However, the high-carbon iron-based powder is preferably made of particles having a cementite-type iron compound. The cementite-type iron compound is a metastable phase and exists in the compound state in the early stage of temperature increase (low temperature range) in the sintering process, but when it reaches a high temperature range near the sintering temperature, Fe (γ phase) and C (carbon) ). Therefore, cementite-type iron compound powder is preferred as the carbon source powder in order to quickly diffuse C into the constituent particles of the compact or sintered body while suppressing generation of CO gas during the sintering process.
本明細書でいうセメンタイト型鉄化合物は、Fe3Cの他、そのFeの一部がCr、Mo、Mnなどの他の金属元素で置換されたものでもよい。要するに、M3C(M:金属元素)で表される化合物を本明細書ではセメンタイト型鉄化合物という。また、そのセメンタイト型鉄化合物は、α−Feと層状をなしたパーライト組織を形成していてもよい。つまり本発明に係る高炭素鉄系粉末は、セメンタイト型鉄化合物からなる場合(セメンタイト型鉄化合物が主相の場合)でもよいし、セメンタイト型鉄化合物とα−Feの複合組織からなる場合でもよい。 The cementite-type iron compound referred to in the present specification may be one in which a part of Fe is substituted with other metal elements such as Cr, Mo, Mn in addition to Fe 3 C. In short, a compound represented by M 3 C (M: metal element) is referred to as a cementite-type iron compound in this specification. The cementite-type iron compound may form a layered pearlite structure with α-Fe. That is, the high carbon iron-based powder according to the present invention may be composed of a cementite type iron compound (when the cementite type iron compound is the main phase), or may be composed of a composite structure of the cementite type iron compound and α-Fe. .
(2)本発明に係る高炭素鉄系粉末は、その製造方法を問わない。但し、純鉄粉と黒鉛粉末のみから、純粋なFe3Cからなる高炭素鉄系粉末を効率的に製造することは容易ではない。そこで、Cr、Mo、Mnなどの合金元素を含む鉄合金粉と黒鉛粉末を用いると、比較的容易にM3C(M:Fe、Cr、Mo、Mn、Siなど)のセメンタイト型鉄化合物からなる高炭素鉄系粉末を得ることができる。その鉄合金粉は、高炭素鉄系粉末となる混合粉末全体を100%として、例えば、Cr:0.5〜5%さらには0.8〜3.5%、Mo:0.1〜2%さらには0.3〜1.5%、Mn:0.05〜1%さらには0.3〜0.8%、Si:0.1〜0.8%さらには0.2〜0.6%の一種以上を含むと好ましい。このような鉄合金粉と黒鉛粉末の混合粉末(高炭素混合粉末)を焼成、粉砕等することにより高炭素鉄系粉末は得られる。 (2) The production method of the high carbon iron-based powder according to the present invention is not limited. However, it is not easy to efficiently produce a high carbon iron-based powder composed of pure Fe 3 C from pure iron powder and graphite powder alone. Therefore, when iron alloy powder and graphite powder containing alloy elements such as Cr, Mo, Mn, etc. are used, it is relatively easy to form M 3 C (M: Fe, Cr, Mo, Mn, Si, etc.) cementite type iron compounds. A high carbon iron-based powder can be obtained. The iron alloy powder is, for example, Cr: 0.5 to 5%, further 0.8 to 3.5%, Mo: 0.1 to 2%, based on 100% of the entire mixed powder that becomes a high carbon iron-based powder. Furthermore, 0.3 to 1.5%, Mn: 0.05 to 1%, further 0.3 to 0.8%, Si: 0.1 to 0.8%, further 0.2 to 0.6% It is preferable to include one or more of the above. A high-carbon iron-based powder can be obtained by firing, pulverizing, or the like of such a mixed powder of iron alloy powder and graphite powder (high carbon mixed powder).
(3)高炭素鉄系粉末の粒度は問わないが、粒度が過大になると、焼結体中に比較的大きな残留気孔が形成され易くなり、焼結体の強度や延性の低下を招く。そこで高炭素鉄系粉末の粒度は75μm以下、65μm以下、55μm以下さらには50μm以下であると好ましい。一方、その粒度が過小になると、高炭素鉄系粉末の生産性や取扱性等が低下し得るため、敢えていうと高炭素鉄系粉末の粒度は5μm以上、10μm以上さらには15μm以上であると好ましい。 (3) The particle size of the high-carbon iron-based powder is not limited, but if the particle size is excessive, relatively large residual pores are easily formed in the sintered body, resulting in a decrease in strength and ductility of the sintered body. Therefore, the particle size of the high carbon iron-based powder is preferably 75 μm or less, 65 μm or less, 55 μm or less, and further 50 μm or less. On the other hand, if the particle size is too small, the productivity and handleability of the high carbon iron-based powder may be lowered. Therefore, the particle size of the high carbon iron-based powder is 5 μm or more, 10 μm or more, and further 15 μm or more. preferable.
なお、本明細書でいう粉末の「粒度」は、篩い分けにより特定され、その篩いの公称目開き(メッシュサイズ)により表現される。例えば、粒度がaμm以下の粉末とは、公称目開きがaμmの篩いを通過した粒子からなる粉末を意味する。その他、篩いを用いた分級や粒度の特定はJIS Z 8801に準拠する。 The “particle size” of the powder in the present specification is specified by sieving, and is expressed by the nominal opening (mesh size) of the sieving. For example, a powder having a particle size of a μm or less means a powder composed of particles that have passed through a sieve having a nominal opening of a μm. In addition, classification using a sieve and identification of particle size are based on JIS Z8801.
(4)本発明に係る炭素源粉末は、高炭素鉄系粉末以外に、黒鉛粉末など他種粉末をさらに含むものでもよい。また高炭素鉄系粉末は、一種からなる場合に限らず、複数種からなる場合でもよい。組成の異なる複数種の高炭素鉄系粉末を用意し、焼結体の所望組成に応じて適切な高炭素鉄系粉末を適宜選択して用いると、焼結体となる混合粉末の配合が容易となり得る。 (4) The carbon source powder according to the present invention may further include other kinds of powder such as graphite powder in addition to the high carbon iron-based powder. Further, the high carbon iron-based powder is not limited to a single type, and may be a plurality of types. When multiple types of high-carbon iron-based powders with different compositions are prepared, and appropriate high-carbon iron-based powders are selected and used according to the desired composition of the sintered body, it is easy to mix the mixed powder that will be the sintered body Can be.
例えば、炭素源粉末として高炭素鉄系粉末と他の炭素粉末(例えば黒鉛粉末)を併用する場合、混合粉末全体を100%としてC:0.4〜1%さらには0.5〜0.8%となるように各粉末を配合すると好ましい。この際、高炭素鉄系粉末は混合粉末全体の50%以上、60%以上さらには70%以上であると好ましい。特に、高密度成形体を急速加熱して短時間焼結させる場合ほど、高炭素鉄系粉末の割合を高めるとよい。 For example, when a high carbon iron-based powder and other carbon powder (for example, graphite powder) are used in combination as the carbon source powder, C: 0.4 to 1%, further 0.5 to 0.8 It is preferable to blend each powder so as to be%. At this time, the high carbon iron-based powder is preferably 50% or more, 60% or more, further 70% or more of the entire mixed powder. In particular, the proportion of the high carbon iron-based powder is preferably increased as the high-density molded body is rapidly heated and sintered for a short time.
[鉄源粉末]
鉄源粉末は、純鉄粉または鉄合金粉の一種以上からなる。例えば、鉄源粉末は、純鉄粉と一種以上の鉄合金粉の混合粉末でもよいし、二種以上の鉄合金粉からなってもよい。鉄合金粉を構成する合金元素として、Cr、Mo、V、Mn、SiさらにはCなどがある。鉄源粉末の全体組成や構成は、鉄基焼結合金の所望組成に適したものであると好ましい。鉄源粉末の粒度は、250μm以下さらには200μm以下であると、焼結体の機械的特性の向上を図れて好ましい。焼結体となる混合粉末全体に対する鉄源粉末の割合は、例えば85質量%以上さらには90質量%以上であると、特性に優れた焼結体が比較的低コストで効率的に生産され得る。
[Iron source powder]
The iron source powder is composed of one or more of pure iron powder or iron alloy powder. For example, the iron source powder may be a mixed powder of pure iron powder and one or more types of iron alloy powder, or may be composed of two or more types of iron alloy powder. Examples of alloy elements constituting the iron alloy powder include Cr, Mo, V, Mn, Si, and C. The overall composition and configuration of the iron source powder is preferably suitable for the desired composition of the iron-based sintered alloy. When the particle size of the iron source powder is 250 μm or less, further 200 μm or less, it is preferable to improve the mechanical properties of the sintered body. When the ratio of the iron source powder to the entire mixed powder to be a sintered body is, for example, 85% by mass or more, further 90% by mass or more, a sintered body having excellent characteristics can be efficiently produced at a relatively low cost. .
[改質粉末]
焼結体となる混合粉末は、鉄源粉末および炭素源粉末以外に、適宜、改質粉末は含んでもよい。改質粉末は、Feを含有するものでも含有しないものでもよい。このような改質粉末として、例えば、FeとMnとSiの合金粉末(FeMS粉末)またはFeとMnとSiとCの合金粉末(FeMSC粉末)などがある。FeMS粉末またはFeMSC粉末は、Oとの親和力が高く酸化物生成自由エネルギーも低いため、焼結時にOゲッターとして機能し、焼結体の機械的特性(強度、靱性、延性等)の向上や寸法安定性の向上(焼結前後の寸法変化の抑制)に寄与し得る。なお、各粉末中には、当然ながら、コスト的または技術的に除去困難な不可避不純物が含まれる。
[Modified powder]
The mixed powder to be a sintered body may appropriately include a modified powder in addition to the iron source powder and the carbon source powder. The modified powder may or may not contain Fe. Examples of such a modified powder include an alloy powder of Fe, Mn, and Si (FeMS powder) or an alloy powder of Fe, Mn, Si, and C (FeMSC powder). FeMS powder or FeMSC powder has high affinity with O and low free energy for oxide formation, so it functions as an O getter during sintering, improving the mechanical properties (strength, toughness, ductility, etc.) and dimensions of the sintered body It can contribute to improvement of stability (suppression of dimensional change before and after sintering). Each powder naturally contains inevitable impurities that are difficult to remove costly or technically.
《製造方法》
(1)成形工程
成形工程は、鉄源粉末と炭素源粉末を含む混合粉末を加圧成形して成形体を得る工程である。この際、得られる成形体の密度(ρ)や成形圧力は問わないが、敢えていうと、機械的特性に優れた焼結体を得るため、成形体密度は6.8g/cm3以上、7g/cm3以上さらには7.3g/cm3以上であると好ましい。成形圧力は、所望する成形体密度や混合粉末の組成または構成により適宜選択されるが、例えば、400〜1600MPaさらには600〜1200MPaの範囲内で調整され得る。なお、本発明の製造方法によれば、焼結工程中におけるCOガスの内部発生が大幅に抑制されるため、例えば、開気孔が殆どない高密度な成形体も急速加熱による短時間焼結が可能である。
"Production method"
(1) Molding step The molding step is a step of obtaining a molded body by pressure molding a mixed powder containing an iron source powder and a carbon source powder. At this time, the density (ρ) and the molding pressure of the molded body to be obtained are not limited. However, in order to obtain a sintered body having excellent mechanical properties, the molded body density is 6.8 g / cm 3 or more and 7 g. / Cm 3 or more, more preferably 7.3 g / cm 3 or more. The molding pressure is appropriately selected depending on the desired density of the compact and the composition or configuration of the mixed powder, and can be adjusted, for example, within a range of 400 to 1600 MPa or even 600 to 1200 MPa. According to the production method of the present invention, the internal generation of CO gas during the sintering process is greatly suppressed. For example, a high-density molded body having almost no open pores can be sintered in a short time by rapid heating. Is possible.
成形工程は、冷間成形(室温成形)でも温間成形でも良い。また、混合粉末と金型との潤滑は、内部潤滑剤を混合粉末に添加して行ってもよいし、金型潤滑により行ってもよい。金型潤滑を行う場合、金型潤滑温間加圧成形法(詳細は特許3309970号公報等を参照)によると好ましい。なお、焼結工程の加熱方法にも依るが、例えば、誘導加熱を行う場合なら、昇温初期における成形体の抵抗値を高める内部潤滑剤の使用量は少ないほど好ましい。そして、内部潤滑剤を含まない混合粉末を高圧で加圧成形できる金型潤滑温間加圧成形法により成形工程を行うとより好ましい。 The forming process may be cold forming (room temperature forming) or warm forming. Further, the lubrication between the mixed powder and the mold may be performed by adding an internal lubricant to the mixed powder, or may be performed by mold lubrication. When performing mold lubrication, it is preferable to use a mold lubrication warm pressure molding method (refer to Japanese Patent No. 3309970 for details). Although depending on the heating method of the sintering step, for example, when induction heating is performed, it is preferable that the amount of the internal lubricant used to increase the resistance value of the molded body at the early stage of temperature rise is as small as possible. And it is more preferable to perform the molding process by a mold lubrication warm pressure molding method capable of pressure molding the mixed powder not containing the internal lubricant at a high pressure.
(2)焼結工程
焼結工程は、成形体を加熱して焼結体を得る工程である。この際、焼結炉を用いた従来の加熱方法を用いることもできるが、誘導加熱方法等を用いると、成形体の急速加熱・短時間焼結により焼結体の生産性向上や省エネルギー化を図ることができる。
(2) Sintering process A sintering process is a process of heating a molded object and obtaining a sintered compact. At this time, a conventional heating method using a sintering furnace can be used. However, when an induction heating method or the like is used, productivity of the sintered body is improved and energy saving is achieved by rapid heating and short-time sintering of the molded body. Can be planned.
焼結工程に係る昇温速度、焼結温度、その保持時間、冷却速度等は適宜設定され得る。本発明に係る高炭素鉄系粉末を用いる場合、昇温速度は、例えば、5℃/秒以上、10℃/秒以上、15℃/秒以上、20℃/秒以上、30℃/秒以上さらには40℃/秒以上とすることができる。このように本発明に係る焼結工程は、成形体を急速加熱する急速加熱過程を含むと好適である。ちなみに、従来の焼結炉を用いた加熱方法の場合、昇温速度は高々0.5℃/秒以下程度に過ぎなかった。なお、本明細書でいう昇温速度は、成形体の温度が、加熱開始時(t0)の初期温度(T0)から所望の焼結温度(T1)になる時(t1)までにおける温度の時間変化率である(T1−T0/t1−t0)。 The heating rate, sintering temperature, holding time, cooling rate, and the like related to the sintering process can be appropriately set. When the high carbon iron-based powder according to the present invention is used, the rate of temperature rise is, for example, 5 ° C./second or more, 10 ° C./second or more, 15 ° C./second or more, 20 ° C./second or more, 30 ° C./second or more Can be 40 ° C./second or more. Thus, it is preferable that the sintering process according to the present invention includes a rapid heating process in which the compact is rapidly heated. Incidentally, in the case of a heating method using a conventional sintering furnace, the rate of temperature increase was at most about 0.5 ° C./second or less. In this specification, the rate of temperature increase is the time of temperature from the initial temperature (T0) at the start of heating (t0) to the desired sintering temperature (T1) (t1). It is the rate of change (T1-T0 / t1-t0).
焼結温度は、例えば、1050℃〜1350℃以上さらには1100〜1300℃が好ましい。焼結温度が過小では焼結体の機械的特性が不十分となり、焼結温度が過大では非効率であると共に、焼結体の機械的特性や寸法安定性を却って劣化させ得る。焼結温度の保持時間は適宜選択され得るが、本発明に係る高炭素鉄系粉末を用いた場合、極短時間でも機械的特性に優れた焼結体を得ることができる。例えば、高炭素鉄系粉末を用いた場合、保持時間が1〜20分間、2〜10分間さらには3〜5分間でも、黒鉛粉末を用いて保持時間を30分間以上とした場合と同等な機械的特性が得られる。さらに誘導加熱等により急速加熱を行えば、焼結工程中の加熱開始から加熱終了までに要する合計時間も大幅に短縮できる。例えば、その合計時間を1〜30分間、2〜20分間さらには3〜10分間とすることも可能となる。 For example, the sintering temperature is preferably 1050 ° C. to 1350 ° C. or higher, and more preferably 1100 to 1300 ° C. If the sintering temperature is too low, the mechanical properties of the sintered body will be insufficient, and if the sintering temperature is too high, it will be inefficient, and the mechanical properties and dimensional stability of the sintered body may be deteriorated. The holding time of the sintering temperature can be appropriately selected, but when the high carbon iron-based powder according to the present invention is used, a sintered body having excellent mechanical properties can be obtained even in a very short time. For example, when a high carbon iron-based powder is used, even if the holding time is 1 to 20 minutes, 2 to 10 minutes, or even 3 to 5 minutes, the same machine as when the holding time is set to 30 minutes or more using graphite powder Characteristics are obtained. Furthermore, if rapid heating is performed by induction heating or the like, the total time required from the start of heating to the end of heating during the sintering process can be greatly shortened. For example, the total time can be set to 1 to 30 minutes, 2 to 20 minutes, or 3 to 10 minutes.
その他、焼結雰囲気は、真空雰囲気、不活性ガス雰囲気、窒素ガス雰囲気等の酸化防止雰囲気でなされると好ましい。また、加熱終了後の冷却過程では、焼結体を徐冷しても急冷してもよい。この際の冷却速度は問わないが、例えば、20〜200℃/分(0.4〜3.3℃/秒)とするとよい。なお、焼結温度から続けて急冷すれば、焼入れ(シンターハードニング)により高強度化された焼結体を効率的に得ることもできる。 In addition, the sintering atmosphere is preferably an oxidation-preventing atmosphere such as a vacuum atmosphere, an inert gas atmosphere, or a nitrogen gas atmosphere. Moreover, in the cooling process after completion of heating, the sintered body may be gradually cooled or rapidly cooled. Although the cooling rate in this case is not ask | required, it is good to set it as 20-200 degreeC / min (0.4-3.3 degreeC / second), for example. In addition, if it cools continuously from sintering temperature, the sintered compact strengthened by quenching (sinter hardening) can also be obtained efficiently.
《鉄基焼結合金》
本発明の鉄基焼結合金は、必須元素であるFeおよびC以外に、適宜、Cr、Mo、V、Mn、Siなど合金元素を一種以上含むと好ましい。この場合、例えば、全体を100%として、Cr:0.05〜2%さらには0.1〜1.5%、Mo:0.05〜1%さらには0.1〜0.5%、V、MnまたはSi:合計で0.05〜1%さらには0.1〜0.7%とするとよい。なお、鉄基焼結合金に係る組成は、ほぼそのまま混合粉末全体の組成としても把握できる。
《Iron-based sintered alloy》
The iron-based sintered alloy of the present invention preferably contains one or more alloy elements such as Cr, Mo, V, Mn, and Si in addition to the essential elements Fe and C. In this case, for example, assuming that the whole is 100%, Cr: 0.05-2%, further 0.1-1.5%, Mo: 0.05-1%, further 0.1-0.5%, V , Mn or Si: 0.05 to 1% in total, further 0.1 to 0.7% is preferable. Note that the composition of the iron-based sintered alloy can be grasped as it is as the composition of the entire mixed powder.
《用途》
本発明の鉄基焼結合金は、前述したように素材(バルク材)でもよいが、通常は、所望形状をした鉄基焼結部材であることが多い。このような鉄基焼結部材は、種々考えられるが、例えば、各種プーリー、変速機のシンクロハブ、エンジンのコンロッド、ハブスリーブ、スプロケット、リングギヤ、パーキングギヤ、ピニオンギヤ、サンギヤ、ドライブギヤ、ドリブンギヤ、リダクションギヤ等がある。なお、鉄基焼結部材は、その要求仕様に応じて、適宜、焼鈍、焼準、時効、調質(焼入れ、焼き戻し)、浸炭、窒化等の熱処理や種々の加工が施され得る。
<Application>
The iron-based sintered alloy of the present invention may be a raw material (bulk material) as described above, but is usually an iron-based sintered member having a desired shape. Various types of such iron-based sintered members are conceivable. For example, various pulleys, transmission sync hubs, engine connecting rods, hub sleeves, sprockets, ring gears, parking gears, pinion gears, sun gears, drive gears, driven gears, reductions. There are gears. The iron-based sintered member can be appropriately subjected to heat treatment such as annealing, normalizing, aging, tempering (quenching, tempering), carburizing, nitriding, and various processes according to the required specifications.
炭素源粉末を種々変更した混合粉末を加圧成形した成形体を焼結した試料(鉄基焼結合金)を多数製作し、それら試料を観察、測定および評価した。これらに基づき、本発明をより具体的に説明する。 A number of samples (iron-based sintered alloys) obtained by sintering compacts obtained by pressure-molding mixed powders obtained by variously changing the carbon source powder were manufactured, and these samples were observed, measured, and evaluated. Based on these, the present invention will be described more specifically.
《高炭素鉄系粉末の製造》
個別に調製した表1に示す複数種の鉄合金粉と黒鉛(Gr)粉末(日本黒鉛社製JCPB、平均粒径:5μm)とを用意した。これらの粉末を表1に示す割合でそれぞれ配合した後、ボールミル式回転混合により高炭素混合粉末を調整した。なお、表1に示した配合組成は、高炭素混合粉末全体を100質量%(適宜、単に%で表す。)としたときの黒鉛粉末の割合であり、残部は鉄合金粉である。また、表1に示した各鉄合金粉の組成は、その鉄合金粉の全体を100質量%としたときの各合金元素の割合であり、その残部はFeである。さらに、各鉄合金粉の粒度も表1に併せて示した。本実施例でいう粒度も、前述したようにJIS Z 8801に準拠した篩分けにより特定される。
<Manufacture of high carbon iron-based powder>
A plurality of types of iron alloy powders and graphite (Gr) powders (JCPB manufactured by Nippon Graphite Co., Ltd., average particle diameter: 5 μm) shown in Table 1 prepared individually were prepared. After blending these powders in the proportions shown in Table 1, high carbon mixed powders were prepared by ball mill rotary mixing. In addition, the compounding composition shown in Table 1 is the ratio of the graphite powder when the high carbon mixed powder is 100% by mass (appropriately expressed simply as%), and the balance is the iron alloy powder. Moreover, the composition of each iron alloy powder shown in Table 1 is the ratio of each alloy element when the total amount of the iron alloy powder is 100% by mass, and the remainder is Fe. Furthermore, the particle size of each iron alloy powder is also shown in Table 1. The particle size referred to in the present embodiment is also specified by sieving based on JIS Z 8801 as described above.
各高炭素混合粉末をルツボに入れて、窒素雰囲気中で900〜1100℃×90分間加熱した。加熱後の高炭素混合粉末を粉砕して、所望の粒度(32μm以下)に篩い分けした。こうして表1に示す9種類の高炭素混合粉末(P1〜P9)を得た。 Each high carbon mixed powder was put in a crucible and heated in a nitrogen atmosphere at 900 to 1100 ° C. for 90 minutes. The high carbon mixed powder after heating was pulverized and sieved to a desired particle size (32 μm or less). Thus, nine types of high carbon mixed powders (P1 to P9) shown in Table 1 were obtained.
《試料の製造》
(1)原料粉末
原料粉末として、炭素源粉末である高炭素混合粉末および黒鉛粉末と、鉄源粉末である純鉄粉(ヘガネスAB社製ASC100.29、粒度:−212μm)および3種類の鉄合金粉とを用意した。用意した鉄合金粉は、Fe−0.5%Mo(ヘガネスコーポレーション社製、粒度:−212μm)、Fe−0.3%V−0.3%Mo(試作粉末、粒度:−180μm)、Fe−1.5%Cr−0.2%Mo(ヘガネスAB社製、粒度:−212μm)である。なお、純鉄粉および鉄合金粉は、水噴霧アトマイズ粉である。
<Production of sample>
(1) Raw material powder As raw material powder, high carbon mixed powder and graphite powder as carbon source powder, pure iron powder as iron source powder (ASC 100.29 manufactured by Höganäs AB, particle size: -212 μm) and three types of iron Alloy powder was prepared. The prepared iron alloy powders are Fe-0.5% Mo (manufactured by Höganäs Corporation, particle size: -212 μm), Fe-0.3% V-0.3% Mo (prototype powder, particle size: -180 μm). Fe-1.5% Cr-0.2% Mo (manufactured by Höganäs AB, particle size: -212 μm). The pure iron powder and the iron alloy powder are water spray atomized powders.
(2)混合粉末
各粉末を全体に対するC量が0.6%となるように配合した後、ボールミル式回転混合を30分間行い、均一な混合粉末を得た(混合工程)。
(2) Mixed powder After blending each powder so that the C content relative to the whole was 0.6%, ball mill type rotary mixing was performed for 30 minutes to obtain a uniform mixed powder (mixing step).
(3)成形工程
成形工程は、所望形状(φ14mm×12mm)に応じたキャビティを有する金型を用意して、金型潤滑温間加圧成形法により行った。成形温度(金型温度)は150℃とし、加熱した金型の内周面に高級脂肪酸系潤滑剤であるステアリン酸リチウム(LiSt)を塗布して行った。成形圧力は、成形体密度が7.0g/cm3または7.5g/cm3の成形体が得られるように400〜1050MPa内で調整した。なお、金型潤滑温間加圧成形法の詳細は特許3309970号公報の記載を参考にした。また成形体密度は、成形体の寸法と重量から算出した。
(3) Molding step The molding step was carried out by preparing a mold having a cavity corresponding to a desired shape (φ14 mm × 12 mm) and performing a mold lubrication warm pressure molding method. The molding temperature (mold temperature) was 150 ° C., and lithium stearate (LiSt), which is a higher fatty acid lubricant, was applied to the inner peripheral surface of the heated mold. The molding pressure was adjusted within 400 to 1050 MPa so as to obtain a molded body having a molded body density of 7.0 g / cm 3 or 7.5 g / cm 3 . The details of the mold lubrication warm pressing method were referred to the description in Japanese Patent No. 3309970. The density of the compact was calculated from the dimensions and weight of the compact.
(4)焼結工程
各成形体を高周波加熱装置(日鉄住金テクノロジー株式会社製サーメックマスタZ)を用いて加熱した。この際、昇温速度:2〜50℃/秒、焼結温度:800〜1250℃、各焼結温度で保持する時間(保持時間):10〜600秒の範囲で種々調整した。特に断らない場合は、昇温速度:50℃/秒、焼結温度:1200℃、保持時間:180秒(3分)とした。いずれの場合も保持時間経過後の降温速度(冷却速度)は100℃/分とした。なお、加熱雰囲気は、Arガス分圧:0.05Paの真空雰囲気(Arパーシャル雰囲気)とした。
(4) Sintering process Each molded object was heated using the high frequency heating apparatus (Thermec Master Z by Nippon Steel & Sumikin Technology Co., Ltd.). At this time, various adjustments were made in the range of temperature rising rate: 2 to 50 ° C./second, sintering temperature: 800 to 1250 ° C., and holding time at each sintering temperature (holding time): 10 to 600 seconds. Unless otherwise specified, the heating rate was 50 ° C./second, the sintering temperature was 1200 ° C., and the holding time was 180 seconds (3 minutes). In either case, the temperature lowering rate (cooling rate) after elapse of the holding time was 100 ° C./min. The heating atmosphere was an Ar gas partial pressure: 0.05 Pa vacuum atmosphere (Ar partial atmosphere).
比較のため、一部の成形体は窒素ガス雰囲気中のバッチ式焼結炉で加熱した。この際、昇温速度:0.33℃/秒、焼結温度:1200℃、保持時間:30分間、降温速度:100℃/分とした。 For comparison, some of the compacts were heated in a batch sintering furnace in a nitrogen gas atmosphere. At this time, the heating rate was 0.33 ° C./second, the sintering temperature was 1200 ° C., the holding time was 30 minutes, and the cooling rate was 100 ° C./min.
こうして表2〜8に示す種々の焼結体(鉄基焼結合金)からなる試料を得た。各試料の組成(混合粉末の配合組成)、工程内容(製造条件)は、各表に示した。なお、表2〜表8に示した炭素源粉末量は、焼結体となる混合粉末全体を100質量%としたときの割合である。この点で、上述した表1に示す炭素源粉末の割合と異なる。 Thus, samples made of various sintered bodies (iron-based sintered alloys) shown in Tables 2 to 8 were obtained. The composition of each sample (blended composition of the mixed powder) and the process content (manufacturing conditions) are shown in each table. In addition, the amount of carbon source powder shown in Tables 2 to 8 is a ratio when the entire mixed powder serving as a sintered body is 100% by mass. This is different from the ratio of the carbon source powder shown in Table 1 described above.
《測定》
(1)寸法変化
各試料に係る成形体と焼結体の直径(基準寸法:φ14mm)をそれぞれ測定することにより、焼結前後の寸法変化を求めた。こうして得られた結果は各表に併せて示した。
<Measurement>
(1) Dimensional change The dimensional change before and after sintering was calculated | required by measuring the diameter (reference | standard dimension: (phi) 14mm) of the molded object and sintered compact which concern on each sample, respectively. The results thus obtained are also shown in each table.
(2)各焼結体を機械加工して、外径:φ13mm×内径:φ8mm×厚さ:3mmのリング状試験片をそれぞれ製作した。こうして得られたリング状試験片に対して圧縮試験を行うことにより、各試料(焼結体)の圧環強度および破壊時の変位量を求めた。なお、圧縮試験はクロスヘッドスピード:0.4mm/分で行った。こうして得られた結果も各表に併せて示した。 (2) Each sintered body was machined to produce ring-shaped test pieces each having an outer diameter: φ13 mm × inner diameter: φ8 mm × thickness: 3 mm. By carrying out a compression test on the ring-shaped test piece thus obtained, the crushing strength and the displacement amount at break of each sample (sintered body) were obtained. The compression test was performed at a crosshead speed of 0.4 mm / min. The results thus obtained are also shown in each table.
《評価・観察》
(1)高炭素鉄系粉末
表1に示した高炭素鉄系粉末の一部について、その構成粒子の断面(研磨面)を光学顕微鏡により観察して得られた金属組織写真を図1Aに示した。各写真中、白色部分はセメンタイト相であり、灰色部分はパーライト相である。図1Aから、高炭素鉄系粉末の構成粒子は、セメンタイト相(セメンタイト型鉄化合物)が主体であることがわかった。これは、高炭素混合粉末中の黒鉛粉末が6.7質量%以上の場合(P2粉末)でも同様であった。
<< Evaluation / Observation >>
(1) High carbon iron-based powder FIG. 1A shows a metal structure photograph obtained by observing the cross section (polished surface) of the constituent particles of a part of the high carbon iron-based powder shown in Table 1 with an optical microscope. It was. In each photograph, the white part is the cementite phase and the gray part is the pearlite phase. FIG. 1A shows that the constituent particles of the high-carbon iron-based powder are mainly composed of a cementite phase (cementite-type iron compound). This was the same even when the graphite powder in the high carbon mixed powder was 6.7% by mass or more (P2 powder).
また、粉末P1に係る高炭素混合粉末(加熱前)と高炭素鉄系粉末(加熱後)をそれぞれX線回折(XRD)により観察した様子を図1Bに示した。図1Bからも、加熱前には存在しなかったセメンタイト相が加熱後に多量に生成されており、高炭素鉄系粉末の構成粒子が主にセメンタイト相(Fe3C相)からなることが確認された。 Further, FIG. 1B shows a state in which the high carbon mixed powder (before heating) and the high carbon iron-based powder (after heating) according to the powder P1 are observed by X-ray diffraction (XRD). Also from FIG. 1B, it was confirmed that the cementite phase which did not exist before heating was produced in large quantities after heating, and that the constituent particles of the high carbon iron-based powder mainly consisted of cementite phase (Fe 3 C phase). It was.
(2)昇温速度の影響
表2に示す各試料の特性と、各試料の圧環強度(適宜、単に「強度」という。)を比較した図2A、各試料の破壊時の変位量(適宜、単に「変位量」または「延性」という。)を比較した図2Bおよび各試料の焼結前後の寸法変化(適宜、単に「寸法変化」という。)を比較した図2Cとから、昇温速度に関して次のことがわかる。
(2) Effect of temperature rise rate FIG. 2A comparing the characteristics of each sample shown in Table 2 and the crushing strength of each sample (simply referred to as “strength” as appropriate), From FIG. 2B, which is simply referred to as “displacement amount” or “ductility”), and FIG. 2C, which compares dimensional changes before and after sintering of each sample (simply referred to as “dimensional change” where appropriate), the temperature increase rate is related. You can see the following:
炭素源が高炭素鉄系粉末(P1粉末)である試料は、昇温速度が非常に大きくなっても、優れた強度や延性を示し、その寸法変化も十分に小さかった。一方、炭素源が黒鉛粉末である試料は、昇温速度が非常に大きくなると、強度および延性が大きく劣化し、寸法変化も大きくなった。 The sample in which the carbon source was a high carbon iron-based powder (P1 powder) showed excellent strength and ductility even when the rate of temperature increase was very large, and its dimensional change was sufficiently small. On the other hand, in the sample in which the carbon source is graphite powder, the strength and ductility deteriorated greatly and the dimensional change also increased when the heating rate was very large.
このような傾向は、各試料の破面を走査型電子顕微鏡(SEM)により観察した組織写真(図2D)からもわかる。つまり、炭素源が高炭素鉄系粉末である試料は、鉄粉粒子の隣接間に未結合部が殆ど観られなかったが、炭素源が黒鉛粉末である試料は、鉄粉粒子の隣接間に未結合部が多く観られた。この理由として、炭素源に黒鉛粉末を用いた場合、昇温速度が大きいために焼結開始後からCOガスが急激に発生し、そのガスが放出されることなく成形体内部で高圧となって鉄粉粒子間を押し広げ、鉄粉粒子同士の結合(ネック形成)を妨げたことが考えられる。 Such a tendency can also be seen from a structural photograph (FIG. 2D) obtained by observing the fracture surface of each sample with a scanning electron microscope (SEM). That is, in the sample in which the carbon source is a high carbon iron-based powder, almost no unbonded portion was observed between adjacent iron powder particles, but in the sample in which the carbon source was graphite powder, Many unbonded parts were seen. The reason for this is that when graphite powder is used as the carbon source, CO gas is abruptly generated after the start of sintering due to the high rate of temperature rise, and the pressure is increased inside the compact without being released. It is conceivable that the iron powder particles are spread and hindered from binding (neck formation) between the iron powder particles.
(3)焼結温度の影響
表3に示す各試料の特性と、それらの強度および延性をそれぞれグラフに示した図3Aおよび図3Bから、焼結温度に関して次のことがわかる。焼結温度(加熱温度)が900℃までは、炭素源粉末の相違が焼結体の強度または延性に及ぼす影響は少ない。しかし、焼結温度が950℃以上になると、炭素源粉末の相違が焼結体の強度または延性に顕著に影響している。つまり、黒鉛粉末を炭素源とした試料では、焼結温度を上昇させても強度や延性の向上はあまり望めない。一方、高炭素鉄系粉末を炭素源とした試料では、焼結温度の上昇に伴い、強度および延性が大幅に上昇して、機械的特性に非常に優れた焼結体(鉄基焼結合金)が得られることがわかった。
(3) Influence of sintering temperature From FIG. 3A and FIG. 3B, in which the characteristics of each sample shown in Table 3 and their strength and ductility are shown in graphs, the following can be understood with respect to the sintering temperature. When the sintering temperature (heating temperature) is up to 900 ° C., the difference in the carbon source powder has little influence on the strength or ductility of the sintered body. However, when the sintering temperature is 950 ° C. or higher, the difference in the carbon source powder significantly affects the strength or ductility of the sintered body. That is, in a sample using graphite powder as a carbon source, improvement in strength and ductility cannot be expected much even if the sintering temperature is increased. On the other hand, in a sample using high carbon iron-based powder as a carbon source, as the sintering temperature rises, the strength and ductility greatly increase, and a sintered body (iron-based sintered alloy) with excellent mechanical properties. ) Was obtained.
このような傾向は、各試料の金属組織を観察したSEM写真(図3Cおよび図3D)からもわかる。例えば、1050℃または1150℃の組織を比較すると、黒鉛粉末を用いた試料では高炭素鉄系粉末を用いた試料よりも、炭素拡散が進行してパーライト相(灰色部分)の比率がより大きくなっている。このような炭素の拡散速度差が焼結時におけるCOガスの発生挙動に影響し、ひいては鉄粉粒子の結合(ネック形成)に影響して、上述したような結果になったと考えられる。 Such a tendency can be seen from SEM photographs (FIGS. 3C and 3D) in which the metal structure of each sample is observed. For example, when comparing the structures at 1050 ° C. or 1150 ° C., the carbon diffusion proceeds and the ratio of the pearlite phase (gray portion) becomes larger in the sample using the graphite powder than in the sample using the high carbon iron-based powder. ing. Such a difference in the diffusion rate of carbon affects the generation behavior of CO gas during sintering, and consequently influences the binding (neck formation) of iron powder particles, and it is considered that the above-described results are obtained.
(4)保持時間の影響
表4に示す各試料の特性と、それらの強度および延性をそれぞれグラフに示した図4Aおよび図4Bから、保持時間に関して次のことがわかる。黒鉛粉末を炭素源とした試料では、成形体を一定の加熱温度(焼結温度)に保持する時間(保持時間)を長くしても、強度や延性は緩やかにしか向上しない。一方、高炭素鉄系粉末を炭素源とした試料では、保持時間を僅か180秒(3分)程度とするだけで、十分な強度および延性の焼結体が得られることがわかる。その強度や延性は、従来の焼結炉でゆっくり加熱して保持時間を1800秒(30分)とした焼結体と同程度となることもわかった。ちなみに、高炭素鉄系粉末を炭素源とした試料では、緩慢加熱後に長時間保持して得られた焼結体(試料P46)でも、十分に高い強度および延性が発揮されることも確認された。
(4) Influence of holding time From FIG. 4A and FIG. 4B, in which the characteristics of each sample shown in Table 4 and their strength and ductility are shown in graphs, the following can be understood with respect to holding time. In a sample using graphite powder as a carbon source, even if the time (holding time) for holding the compact at a constant heating temperature (sintering temperature) is increased, the strength and ductility are improved only moderately. On the other hand, in the sample using high carbon iron-based powder as the carbon source, it can be seen that a sintered body having sufficient strength and ductility can be obtained only by holding the holding time only about 180 seconds (3 minutes). It was also found that the strength and ductility were comparable to those of a sintered body heated slowly in a conventional sintering furnace and having a holding time of 1800 seconds (30 minutes). Incidentally, it was also confirmed that a sample using high carbon iron-based powder as a carbon source exhibited sufficiently high strength and ductility even with a sintered body (sample P46) obtained by holding for a long time after slow heating. .
(5)高炭素鉄系粉末と黒鉛粉末の配合割合の影響
表5に示す各試料の特性と、それらの強度および延性をそれぞれ棒グラフで示した図5Aおよび図5Bから、高炭素鉄系粉末と黒鉛粉末の配合割合に関して次のことがわかる。急速加熱・短時間焼結を行う場合、高炭素鉄系粉末の割合が多いと、黒鉛粉末を併用した場合でも、強度および延性に優れた焼結体が得られることがわかった。具体的には、炭素源粉末の1/4程度(50%以下、40%以下さらには30%以下)を黒鉛粉末としても、残部が高炭素鉄系粉末であれば、急速加熱・短時間焼結により十分に高強度・高延性な焼結体が得られることもわかった。
(5) Effect of blending ratio of high carbon iron-based powder and graphite powder From FIG. 5A and FIG. 5B in which the characteristics of each sample shown in Table 5 and their strength and ductility are shown by bar graphs, respectively, The following can be understood with respect to the blending ratio of the graphite powder. When performing rapid heating and short-time sintering, it was found that if the proportion of high carbon iron-based powder is large, a sintered body excellent in strength and ductility can be obtained even when graphite powder is used in combination. Specifically, even if about 1/4 (50% or less, 40% or less, or 30% or less) of the carbon source powder is used as the graphite powder, if the balance is a high carbon iron-based powder, rapid heating and short-time firing are performed. It has also been found that a sintered body with sufficiently high strength and high ductility can be obtained by sintering.
このような傾向は、成形体密度が高い場合(7.5g/cm3)でも低い場合(7.0g/cm3)でも同様であったが、成形体密度が高い場合ほど顕著であった。これは急速加熱した際に生じるCOガスが成形体中の開気孔を経由して放出される程度を反映していると考えられる。具体的にいうと、成形体密度が低い場合、黒鉛粉末の割合が大きくても、成形体内部に発生したCOガスは開気孔から放出され得るため、鉄粉粒子のネック形成はさほど阻害されない。しかし、成形体密度が高い場合、黒鉛粉末の割合が大きくなると、成形体内部に発生した多量のCOガスは開気孔から放出され難くなり、鉄粉粒子のネック形成が大きく阻害され得る。従って、成形体密度が高い場合ほど、高炭素鉄系粉末の割合を大きくすると好ましいといえる。 Such a tendency was the same whether the compact density was high (7.5 g / cm 3 ) or low (7.0 g / cm 3 ), but the tendency was more remarkable as the compact density was higher. This is considered to reflect the extent to which the CO gas generated upon rapid heating is released via the open pores in the molded body. Specifically, when the density of the compact is low, even if the proportion of the graphite powder is large, the CO gas generated inside the compact can be released from the open pores, so that the neck formation of the iron powder particles is not hindered so much. However, when the density of the compact is high, if the ratio of the graphite powder increases, a large amount of CO gas generated inside the compact becomes difficult to be released from the open pores, and the neck formation of the iron powder particles can be greatly inhibited. Therefore, it can be said that it is preferable to increase the proportion of the high carbon iron-based powder as the density of the compact is higher.
(6)鉄源粉末組成の影響
表6に示す各試料の特性と、それらの強度を棒グラフで示した図6Aおよび図6Bから、鉄源粉末の組成に関して次のことがわかる。鉄源粉末が純鉄粉でも鉄合金粉でも、上述した場合と同様に、高炭素鉄系粉末を用いた試料の方が黒鉛粉末を用いた試料よりも優れた強度や延性を発揮した。そして、このような傾向は成形体密度が高いほど顕著であった。なお、いずれの試料でも合金元素(Mo、V、Cr等)の合計量が増加するほど、高強度、高延性となることも確認された。
(6) Influence of iron source powder composition From FIG. 6A and FIG. 6B in which the characteristics of each sample shown in Table 6 and their strengths are shown in bar graphs, the following can be understood with respect to the composition of the iron source powder. Whether the iron source powder is a pure iron powder or an iron alloy powder, the sample using the high-carbon iron-based powder exhibited better strength and ductility than the sample using the graphite powder, as described above. And such a tendency was so remarkable that the molded object density was high. In any sample, it was confirmed that the higher the total amount of alloying elements (Mo, V, Cr, etc.), the higher the strength and the higher the ductility.
(7)高炭素鉄系粉末の組成の影響
表7に示す各試料の特性と、それらの強度を棒グラフで示した図7Aおよび図7Bから、高炭素鉄系粉末の組成に関して次のことがわかる。高炭素鉄系粉末の組成が変化しても、いずれの試料も優れた強度や延性を発揮した。このような傾向は成形体密度が高いほど顕著であった。
(7) Effect of composition of high carbon iron-based powder From FIG. 7A and FIG. 7B in which the characteristics of each sample shown in Table 7 and their strengths are shown in bar graphs, the following can be understood with respect to the composition of the high carbon iron-based powder. . All samples exhibited excellent strength and ductility even when the composition of the high-carbon iron-based powder changed. Such a tendency was more prominent as the density of the molded body was higher.
また、表7に示す各試料と同等な組成となるように、炭素源である黒鉛粉末と各種の鉄合金粉(平均粒径10μm以下)と純鉄粉を配合した混合粉末からなる焼結体も同様に製作した。こうして得られた各試料の特性を表8に示した。また、これら各試料の強度を示す棒グラフを図7Aおよび図7Bに併記した。その際、焼結体の全体組成が同一となる試料に係る棒グラフを隣接して配置した(例えば、表7の試料H1と表8の試料HM1)。 Further, a sintered body comprising a mixed powder in which graphite powder as a carbon source, various iron alloy powders (average particle size of 10 μm or less) and pure iron powder are blended so as to have a composition equivalent to each sample shown in Table 7. Was made in the same way. The characteristics of each sample thus obtained are shown in Table 8. Moreover, the bar graph which shows the intensity | strength of each of these samples was written together in FIG. 7A and FIG. 7B. In that case, the bar graph which concerns on the sample with the same whole composition of a sintered compact was arrange | positioned adjacently (for example, sample H1 of Table 7, and sample HM1 of Table 8).
上述した場合と同様に、いずれの組成に係る試料でも、高炭素鉄系粉末を用いた試料の方が黒鉛粉末を用いた試料よりも優れた強度を発揮した。このような傾向も成形体密度が高いほど顕著であった。 As in the case described above, the sample using any of the compositions exhibited a strength superior to that of the sample using the graphite powder. Such a tendency was more remarkable as the density of the molded body was higher.
また、同組成であるが粒度の異なるP1粉末、P3粉末、P4粉末およびP5粉末をそれぞれ用いて、表7に示す試料L1と同様に製造した焼結体の金属組織を光学顕微鏡で観察した様子を図8に示した。これから、急速加熱・短時間焼結により焼結させた場合、高炭素鉄系粉末の粒度が大きくなるほど、Fe−C系共晶液相の生成に由来した大きな残留気孔が発生することがわかる。そして、P5粉末のように粒度45μm以上の粒子からなる高炭素鉄系粉末を炭素源粉末として用いると、その残留気孔がかなり粗大になることもわかった。このように残留気孔が大きくなると、焼結体の機械的特性(特に延性)の低下を招き得ると考えられる。 In addition, using the P1 powder, P3 powder, P4 powder and P5 powder having the same composition but different particle sizes, the metal structure of the sintered body produced in the same manner as the sample L1 shown in Table 7 was observed with an optical microscope. Is shown in FIG. From this, it can be seen that when sintered by rapid heating and short-time sintering, the larger the particle size of the high carbon iron-based powder, the larger residual pores derived from the formation of the Fe—C-based eutectic liquid phase. And when the high carbon iron type powder which consists of particle | grains with a particle size of 45 micrometers or more like P5 powder was used as a carbon source powder, it turned out that the residual pore becomes quite coarse. When the residual pores become large in this way, it is considered that the mechanical properties (particularly ductility) of the sintered body may be reduced.
Claims (13)
該成形体を加熱した焼結体を得る焼結工程と、
を備える鉄基焼結合金の製造方法であって、
前記炭素源粉末の少なくとも一種は、Cを5質量%(以下、単に「%」で表す。)以上含む鉄合金または鉄化合物からなる高炭素鉄系粉末であることを特徴とする鉄基焼結合金の製造方法。 A molding step of obtaining a molded body obtained by pressure molding a mixed powder containing at least an iron source powder and a carbon source powder;
A sintering step for obtaining a sintered body obtained by heating the molded body;
A method for producing an iron-based sintered alloy comprising:
At least one of the carbon source powders is a high-carbon iron-based powder composed of an iron alloy or an iron compound containing 5% by mass or more of C (hereinafter simply expressed as “%”). Gold manufacturing method.
Cr:0.5〜5%、
Mo:0.1〜2%、
Mn:0.05〜1% 3. The method for producing an iron-based sintered alloy according to claim 1, wherein the high-carbon iron-based powder includes one or more of the following components with the entire powder as 100%.
Cr: 0.5-5%
Mo: 0.1 to 2%,
Mn: 0.05 to 1%
Cr:0.05〜2%、
Mo:0.05〜1%、
V、MnまたはSi:合計で0.05〜1% The said mixed powder is a manufacturing method of the iron-based sintered alloy in any one of Claims 1-5 which makes this mixed powder 100% the whole and contains one or more of the following components.
Cr: 0.05-2%
Mo: 0.05 to 1%
V, Mn or Si: 0.05 to 1% in total
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