JP4483595B2 - Iron-based powder mixture for high-strength sintered parts - Google Patents
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- Powder Metallurgy (AREA)
Description
本発明は、粉末冶金用鉄基粉末混合物に関し、特に自動車用の高強度焼結部品の製造に適用して好適なものである。 The present invention relates to an iron-based powder mixture for powder metallurgy, and is particularly suitable for application to the production of high-strength sintered parts for automobiles.
金属粉を金型内で加圧−成形したのち、焼結して焼結体とする粉末冶金法は、複雑な形状の機械部品も精度よく製造することができるため、高い寸法精度が要求されるギヤ等の自動車用部品の製造に広く利用されている。
金属粉として鉄粉を用いる場合には、通常、鉄粉にCu粉や黒鉛粉等の合金成分を混合し、さらに成形性を向上させるための潤滑剤を 0.8〜1.2 質量％程度混合した後、成形し、ついで焼結を行うことにより、 5.0〜7.2Mg/m3程度の密度を有する焼結体としている。
また、これらの自動車用部品には、高強度であることが要求されている。そこで、一層の強度向上のために、合金元素を添加した焼結体に、さらに焼入−焼戻等の熱処理を施して製品化することが一般的に行われている。
The powder metallurgy method, in which metal powder is pressed and molded in a mold and then sintered to form a sintered body, can be used to accurately manufacture mechanical parts with complex shapes, so high dimensional accuracy is required. It is widely used in the manufacture of automotive parts such as gears.
When using iron powder as the metal powder, usually, alloy components such as Cu powder and graphite powder are mixed with the iron powder, and further, about 0.8 to 1.2% by mass of a lubricant for improving formability is mixed. By molding and then sintering, a sintered body having a density of about 5.0 to 7.2 Mg / m 3 is obtained.
Further, these automotive parts are required to have high strength. Therefore, in order to further improve the strength, it is a common practice to produce a product by further subjecting a sintered body to which an alloy element is added to a heat treatment such as quenching and tempering.
例えば、特許文献１には、高強度粉末冶金部品用原料粉として、Ｃ，Ｎ，Si，Al，Ｏを低減すると共に、Mn，Cr，Mo，Ｖのうちから選んだ１種または２種以上の元素を予合金成分として含有させ、残部はFeおよび不可避的不純物の組成になる、圧縮性、成形性および熱処理特性に優れる合金鋼粉が提案されている。 For example, in Patent Document 1, as raw material powder for high-strength powder metallurgy parts, C, N, Si, Al, and O are reduced, and one or more selected from Mn, Cr, Mo, and V are selected. These alloy steel powders having excellent compressibility, formability and heat treatment characteristics have been proposed in which the above elements are contained as a prealloy component and the balance is composed of Fe and inevitable impurities.
また、特許文献２には、自動車用高強度部品用原料粉として、鉄粉の表面にCu，Ni，Moの粉末を同時に付着拡散させた、熱処理における寸法変化のばらつきの小さい部分合金化合金鋼粉が提案されている。 Further, Patent Document 2 discloses a partially alloyed alloy steel with small variation in dimensional change during heat treatment, in which Cu, Ni, and Mo powders are simultaneously adhered and diffused on the surface of iron powder as raw material powder for high-strength parts for automobiles. Powder has been proposed.
ところで、最近では、焼結部品の製造に際し、製造コスト低減のために、弱酸化性雰囲気中で焼結温度を低下させた低温焼結や、焼結後における熱処理の省略が指向されている。
そのため、かような低温焼結を実施した場合であっても、あるいはその後の熱処理を省略したとしても、高強度の焼結部品が確保できる原料粉の開発が要望されている。
Recently, when manufacturing sintered parts, in order to reduce manufacturing costs, low-temperature sintering in which the sintering temperature is lowered in a weakly oxidizing atmosphere and heat treatment after sintering have been omitted.
Therefore, there is a demand for the development of raw material powder that can secure a high-strength sintered part even when such low-temperature sintering is performed or even if the subsequent heat treatment is omitted.
しかしながら、特許文献１に記載されたような、Cr，Mnなどの易酸化性合金元素を溶鋼の状態で予合金化させた予合金化合金鋼粉を用いて、弱酸化性雰囲気中で焼結すると、予合金化された合金元素が酸化されて、所望の強度を有する焼結部品が得られないという問題があった。
この点、特許文献２に記載のような、鉄粉に、NiやMo，Cu等の合金元素を部分合金化させた部分合金化合金鋼粉を用いた場合には、合金元素の酸化という問題はないが、この部分合金化合金鋼粉は、圧縮性が低いだけでなく、焼結後の熱処理によって高強度の確保を意図しているため、焼結のままでは引張強さ：800 MPa 以上の高強度を達成できないという問題があった。
However, as described in Patent Document 1, sintering is performed in a weakly oxidizing atmosphere by using a prealloyed alloy steel powder obtained by prealloying an easily oxidizable alloy element such as Cr or Mn in a molten steel state. Then, there is a problem that the prealloyed alloy element is oxidized and a sintered part having a desired strength cannot be obtained.
In this regard, as described in Patent Document 2, when a partially alloyed alloy steel powder obtained by partially alloying an alloy element such as Ni, Mo, or Cu is used for the iron powder, there is a problem of oxidation of the alloy element. However, this partially alloyed alloy steel powder is not only low in compressibility but also intended to ensure high strength by heat treatment after sintering. There was a problem that the high strength of could not be achieved.
このような問題に対し、特許文献３では、質量比率で、Ni：３〜５％、Mo：0.4 〜0.7 ％、残部Feからなる組成の合金粉末に、Cu粉を１〜２％、Ni粉を１〜３％、黒鉛粉を焼結後のＣ量が 0.2〜0.7 ％になるように混合した混合粉末を、圧縮成形し、得られた圧粉体を非酸化性雰囲気中で焼結し、その際、焼結炉中で５〜20℃/minの速度で冷却することからなる鉄系焼結合金の製造方法が提案されている。 In order to solve such a problem, in Patent Document 3, by mass ratio, Ni: 3 to 5%, Mo: 0.4 to 0.7%, and an alloy powder composed of the remaining Fe, Cu powder is 1 to 2%, Ni powder. 1 to 3% and graphite powder mixed so that the C content after sintering is 0.2 to 0.7%, compression molded, and the resulting green compact is sintered in a non-oxidizing atmosphere. At that time, a method for producing an iron-based sintered alloy comprising cooling in a sintering furnace at a rate of 5 to 20 ° C./min has been proposed.
また、特許文献４には、重量比率で、Ni：0.5 〜３質量％およびMo：0.7 超〜４質量、残部Feおよび不可避的不純物の組成になる合金粉末に、Ni粉を１〜５質量％、Cu粉を 0.5〜３質量％、黒鉛粉を0.2 〜0.9 質量％混合させた鉄基混合粉が提案されている。 Further, Patent Document 4 discloses that Ni powder is contained in an alloy powder having a composition of Ni: 0.5 to 3 mass% and Mo: more than 0.7 to 4 mass, the balance Fe and inevitable impurities in a weight ratio of 1 to 5 mass%. An iron-based mixed powder in which 0.5 to 3% by mass of Cu powder and 0.2 to 0.9% by mass of graphite powder are mixed has been proposed.
しかしながら、上記特許文献３および特許文献４に記載された技術では、いずれも合金鋼粉中にNiが予合金化されているため、焼入れ性は高いものの、合金鋼粉の圧縮性が低下することから、高い圧粉体密度が得られず、そのため高強度の焼結体が得られないという問題があった。
また、いずれの文献でも、潤滑剤を 0.8％程度添加しているため、脱ろう時間の短い焼結条件では、焼結の初期段階まで脱ろうに費やされ、実質的な焼結時間が短くなるため、高強度の焼結体が得られないという問題があることも判明した。
However, in the techniques described in Patent Document 3 and Patent Document 4 described above, since Ni is pre-alloyed in the alloy steel powder, the hardenability is high, but the compressibility of the alloy steel powder is reduced. Therefore, there has been a problem that a high green compact density cannot be obtained, and thus a high-strength sintered body cannot be obtained.
Also, in all of the documents, about 0.8% of the lubricant is added, so under the sintering conditions with a short dewaxing time, the dewaxing time is spent up to the initial stage of sintering, and the substantial sintering time is short. Therefore, it has also been found that there is a problem that a high-strength sintered body cannot be obtained.
本発明は、上記の実状に鑑み開発されたもので、高い圧粉体密度が得られ、また脱ろう時間の短い厳しい焼結条件下でも、焼結のままで引張強さが 800 MPa以上の高強度焼結体を得ることができる鉄基粉末混合物を提案することを目的とする。 The present invention has been developed in view of the above-mentioned circumstances, and can obtain a high green compact density and has a tensile strength of 800 MPa or more as it is sintered even under severe sintering conditions with a short dewaxing time. The object is to propose an iron-based powder mixture from which a high-strength sintered body can be obtained.
さて、発明者らは、上記の課題を解決すべく、鉄基粉末混合物に添加する潤滑剤の種類および添加方法について鋭意検討を重ねた。
その結果、鉄基粉末混合物に添加する潤滑剤として遊離潤滑剤を用い、かつこの遊離潤滑剤の粒度分布を適切に制御することにより、圧粉成形時における抜出力を上昇させることなしに、潤滑剤の添加量を効果的に低減することができ、その結果、圧粉体密度が向上するだけでなく、焼結時における潤滑剤の脱ろう効率も向上するため、焼結体の強度が有利に向上するとの知見を得た。
本発明は、上記の知見に基づき、さらに検討を加えた末に、完成されたものである。
Now, in order to solve the above-mentioned problems, the inventors have intensively studied the kind of lubricant added to the iron-based powder mixture and the addition method.
As a result, a free lubricant is used as a lubricant to be added to the iron-based powder mixture, and the particle size distribution of the free lubricant is appropriately controlled, thereby increasing lubrication without increasing the output during compacting. The amount of additive added can be effectively reduced. As a result, not only the density of the green compact is improved, but also the dewaxing efficiency of the lubricant during sintering is improved, so the strength of the sintered body is advantageous. I got the knowledge that it would improve.
The present invention has been completed after further studies based on the above findings.
すなわち、本発明の要旨構成は次のとおりである。
NiおよびMoを予合金化した合金鋼粉の表面に、Ni粉、Cu粉および黒鉛粉を有機結合剤により付着させた鉄基粉末：100 質量部に対し、遊離潤滑剤を0.05〜0.6 質量部混合した鉄基粉末混合物であって、該遊離潤滑剤の少なくとも20質量％が、粒径：５〜80μm の一次粒子を凝集して造粒した粒径：10〜200 μm の二次粒子からなり、前記合金鋼粉におけるNiおよびMoの予合金化率が、Ni：0.5 〜３質量％、Mo：0.7 超〜４質量％であり、また前記鉄基粉末におけるNi粉、Cu粉および黒鉛粉の配合率が、Ni粉：0.5 〜５質量％、Cu粉：0.5 〜３質量％、黒鉛粉：0.2 〜1.0 質量％であることを特徴とする高強度焼結部品用の鉄基粉末混合物。
That is, the gist configuration of the present invention is as follows.
Iron-based powder with Ni powder, Cu powder and graphite powder adhered to the surface of alloy steel powder prealloyed with Ni and Mo by organic binder: 0.05 to 0.6 parts by mass of free lubricant with respect to 100 parts by mass A mixed iron-based powder mixture, wherein at least 20% by mass of the free lubricant is composed of secondary particles having a particle size of 10 to 200 μm formed by agglomerating primary particles having a particle size of 5 to 80 μm. The prealloying rate of Ni and Mo in the alloy steel powder is Ni: 0.5-3 mass%, Mo: more than 0.7-4 mass%, and the Ni powder, Cu powder and graphite powder in the iron-based powder An iron-based powder mixture for high-strength sintered parts, characterized in that the blending ratio is Ni powder: 0.5 to 5% by mass, Cu powder: 0.5 to 3% by mass, and graphite powder: 0.2 to 1.0% by mass.
本発明の鉄基粉末混合物を原料として使用することにより、高密度の高強度焼結部品を得ることができる。
また、本発明の鉄基粉末混合物は、比較的低い焼結温度でも焼結が促進され、高強度の焼結部品を得ることができる。
By using the iron-based powder mixture of the present invention as a raw material, a high-density, high-strength sintered part can be obtained.
Moreover, the iron-based powder mixture of the present invention can be sintered at a relatively low sintering temperature, and a high-strength sintered part can be obtained.
以下、本発明を具体的に説明する。
まず、本発明の主原料である鉄基粉末について説明する。本発明では、強度向上のための合金元素として、Ni，Mo，CuおよびＣ（黒鉛）を選択した。これら合金元素は、炭化水素変成ガス雰囲気中で焼結を行っても、酸化することがなく、強度を効率良く向上させることができる。
これらの合金元素のうち、Niは、粉体として用いた場合の焼結の活性化による空孔の微細化、および粉体と予合金化のいずれかを用いた場合の基地強化のために、粉体による添加と予合金化による添加の両方とする。
また、Cuは、焼結時に液相を形成して焼結を促進させるために、粉体で添加する。
さらに、Moは基地強化のために添加される。ただし、粉体で添加すると拡散しにくく、予合金化しても圧縮性の低下が少ないため、予合金化により添加する。
また、Ｃは焼結体の強度向上のために粉体（黒鉛粉）で添加する。予合金化によるＣは鋼粉を硬化させて圧縮性を低下させるので0.02質量％以下に制限するとよい。
The present invention will be specifically described below.
First, the iron-based powder that is the main raw material of the present invention will be described. In the present invention, Ni, Mo, Cu and C (graphite) were selected as alloy elements for improving the strength. Even if these alloy elements are sintered in a hydrocarbon-modified gas atmosphere, they are not oxidized and the strength can be improved efficiently.
Among these alloy elements, Ni is used for finer pores due to activation of sintering when used as powder, and for strengthening the base when using either powder and pre-alloying. Both addition by powder and addition by pre-alloying.
Further, Cu is added as a powder to form a liquid phase during sintering and promote sintering.
In addition, Mo is added to strengthen the base. However, when added as a powder, it is difficult to diffuse, and even if prealloyed, there is little decrease in compressibility, so it is added by prealloying.
C is added as a powder (graphite powder) to improve the strength of the sintered body. C by pre-alloying hardens the steel powder and lowers the compressibility, so it should be limited to 0.02% by mass or less.
本発明における合金鋼粉は、所定量の合金元素を含有する溶鋼を、溶製したのち、例えば水アトマイズにより製造することができる。水アトマイズは、通常公知の装置および方法を用いて行えばよく、特に限定されることはない。なお、この予合金化合金鋼粉は、水アトマイズ後、常法に従い、仕上還元処理、ついで解砕処理が施されるのは言うまでもない。 The alloy steel powder in the present invention can be manufactured by, for example, water atomization after melting molten steel containing a predetermined amount of alloy elements. Water atomization may be performed using a generally known apparatus and method, and is not particularly limited. Needless to say, the prealloyed alloy steel powder is subjected to finish reduction treatment and then pulverization treatment in accordance with a conventional method after water atomization.
上述した予合金化合金鋼粉におけるNiおよびMoの好適含有量は次のとおりである。
Ni：0.5 〜３質量％
Niは、マルテンサイト変態開始温度を低温側に移行させることにより、基地組織を微細化して、強度を向上させる有用元素である。しかしながら、Niの予合金化量が 0.5質量％未満では強度の向上効果が充分ではなく、一方３質量％を超えて予合金化させると鋼粉が著しく硬化し、圧縮性が著しく低下して、強度および靭性がともに低下する。このため、Niの予合金化量は 0.5〜３質量％の範囲に限定した。好ましくは 0.5〜２質量％の範囲である。
The preferred contents of Ni and Mo in the prealloyed alloy steel powder described above are as follows.
Ni: 0.5-3 mass%
Ni is a useful element that refines the matrix structure and improves the strength by shifting the martensitic transformation start temperature to the low temperature side. However, if the prealloyed amount of Ni is less than 0.5% by mass, the effect of improving the strength is not sufficient. On the other hand, if prealloyed exceeding 3% by mass, the steel powder is hardened significantly, and the compressibility is significantly reduced. Both strength and toughness are reduced. For this reason, the pre-alloying amount of Ni was limited to the range of 0.5 to 3% by mass. Preferably it is the range of 0.5-2 mass%.
Mo：0.7 超〜４質量％
Moは、固溶強化および変態強化により強度を向上させる有用元素であり、しかも予合金化しても圧縮性の低下は少ない。しかしながら、Moの予合金化量が 0.7質量％以下では強度を向上させる効果が十分でなく、一方４質量％を超えて予合金化させると鋼粉が硬化し、圧縮性が著しく低下して、強度および靭性がともに低下する。このため、Moの予合金化量は 0.7超〜４質量％の範囲に限定した。好ましくは 0.7超〜３質量％の範囲である。
Mo: More than 0.7 to 4% by mass
Mo is a useful element that improves strength by solid solution strengthening and transformation strengthening, and even when pre-alloyed, there is little decrease in compressibility. However, when the prealloyed amount of Mo is 0.7% by mass or less, the effect of improving the strength is not sufficient. On the other hand, when prealloyed exceeding 4% by mass, the steel powder is hardened, and the compressibility is significantly reduced. Both strength and toughness are reduced. For this reason, the prealloying amount of Mo was limited to the range of more than 0.7 to 4% by mass. Preferably, it is in the range of more than 0.7 to 3% by mass.
合金鋼粉において、上記した成分以外は、Feおよび不可避的不純物である。不可避的不純物のうち、SiやMn，Ｓ，Ｐ等は、それぞれSi：0.1 質量％以下、Mn：0.3 質量％以下、Ｓ：0.02質量％以下、Ｐ：0.02質量％以下で許容できる。 In the alloy steel powder, other than the above-described components are Fe and inevitable impurities. Among the inevitable impurities, Si, Mn, S, P, etc. are acceptable at Si: 0.1% by mass or less, Mn: 0.3% by mass or less, S: 0.02% by mass or less, and P: 0.02% by mass or less, respectively.
次に、合金鋼粉の表面に、有機結合剤によりNi粉、Cu粉および黒鉛粉を付着させた鉄基粉末において、Ni粉、Cu粉および黒鉛粉の配合率を前記の範囲に限定した理由について説明する。
なお、鉄基粉末における各成分の配合率は、合金鋼粉、Ni粉、Cu粉、黒鉛粉および有機結合剤の合計量（鉄基粉末全体）に対する質量％で表示する。
Next, in the iron-based powder in which Ni powder, Cu powder and graphite powder are adhered to the surface of the alloy steel powder by an organic binder, the reason why the mixing ratio of Ni powder, Cu powder and graphite powder is limited to the above range Will be described.
In addition, the compounding rate of each component in iron-based powder is displayed by the mass% with respect to the total amount (whole iron-based powder) of alloy steel powder, Ni powder, Cu powder, graphite powder, and an organic binder.
Ni粉：0.5 〜５質量％
Ni粉は、焼結を活性化し、空孔を微細化して、強度を向上させるために添加する。しかしながら、Ni粉の配合率が 0.5質量％に満たないと焼結を活性化させる効果が十分でなく、一方５質量％を超えると残留オーステナイトが著しく増加して、強度の低下を招く。このため、Ni粉の配合率は 0.5〜５質量％の範囲に限定した。好ましくは２〜４質量％の範囲である。
なお、Ni粉としては、熱分解法により作製したカルボニルニッケル粉、Ni酸化物を還元して作製したNi粉など公知のものを用いればよい。
Ni powder: 0.5-5% by mass
Ni powder is added to activate sintering, refine pores, and improve strength. However, if the Ni powder content is less than 0.5% by mass, the effect of activating the sintering is not sufficient. On the other hand, if it exceeds 5% by mass, the retained austenite is remarkably increased and the strength is lowered. For this reason, the compounding rate of Ni powder was limited to the range of 0.5-5 mass%. Preferably it is the range of 2-4 mass%.
In addition, as Ni powder, what is necessary is just to use carbonyl nickel powder produced by the thermal decomposition method, Ni powder produced by reducing Ni oxide, and the like.
Cu粉：0.5 〜３質量％
Cu粉は、焼結時に液相形成により空孔を球状化して焼結を促進し、強度を向上させるため添加する。しかしながら、Cu粉の配合率が 0.5質量％未満では強度を向上させる効果が十分でなく、一方３質量％を超えると脆化する。このため、Cuの配合率は 0.5〜３質量％の範囲とした。好ましくは１〜２質量％の範囲である。
なお、Cu粉としては、電解Cu粉やアトマイズCu粉など公知のものを用いればよい。
Cu powder: 0.5-3 mass%
Cu powder is added to spheroidize the pores by forming a liquid phase during sintering to promote sintering and improve strength. However, when the Cu powder content is less than 0.5% by mass, the effect of improving the strength is not sufficient, while when it exceeds 3% by mass, the material becomes brittle. For this reason, the compounding ratio of Cu was made into the range of 0.5-3 mass%. Preferably it is the range of 1-2 mass%.
In addition, as Cu powder, what is necessary is just to use well-known things, such as electrolytic Cu powder and atomized Cu powder.
黒鉛粉：0.2 〜1.0 質量％
黒鉛粉は、焼結時に鉄粉中に拡散して固溶強化により強度を高くする元素である。しかしながら、黒鉛粉の配合率が 0.2質量％未満では強度を向上させる効果が十分でなく、一方 1.0質量％を超えると、初析セメンタイトが粒界に析出し、強度が低下する。このため、黒鉛粉の配合率は 0.2〜1.0 質量％の範囲とした。
Graphite powder: 0.2 to 1.0 mass%
Graphite powder is an element that diffuses into iron powder during sintering and increases strength by solid solution strengthening. However, if the blending ratio of the graphite powder is less than 0.2% by mass, the effect of improving the strength is not sufficient. On the other hand, if it exceeds 1.0% by mass, pro-eutectoid cementite precipitates at the grain boundaries and the strength decreases. For this reason, the blending ratio of the graphite powder is set in the range of 0.2 to 1.0% by mass.
鉄基粉末の作製に際しては、Ni粉、Cu粉、黒鉛粉等の粉体は、合金鋼粉の表面に有機結合剤により付着させる。というのは、Ni粉やCu粉、黒鉛粉は合金鋼粉よりも微粉であるため、これらを単に混合しただけでは、輸送時やホッパへの装入・排出時、さらには金型充填時に、偏析が起こり易いため、焼結体の寸法や強度のばらつきが生じ易いからである。
この点、かような黒鉛粉等を予め合金鋼粉の表面に付着させておけば、上記のような偏析、ひいては焼結体における寸法や強度のばらつきを有利に解消することができる。
ここに、有機結合剤の添加量は、鉄基粉末に対する配合率で0.05〜0.3 質量％程度とするのが好適である。
In producing the iron-based powder, powders such as Ni powder, Cu powder, and graphite powder are attached to the surface of the alloy steel powder by an organic binder. This is because Ni powder, Cu powder, and graphite powder are finer than alloy steel powder, so simply mixing them can be used for transportation, charging / discharging to the hopper, and filling the mold. This is because segregation is likely to occur, and variations in the size and strength of the sintered body are likely to occur.
By preliminarily attaching such graphite powder or the like to the surface of the alloy steel powder, it is possible to advantageously eliminate the segregation as described above, and thus the variation in size and strength in the sintered body.
Here, the addition amount of the organic binder is preferably about 0.05 to 0.3% by mass with respect to the iron-based powder.
上記した有機結合剤については、その種類が特に限定されるものではないが、次のものがとりわけ有利に適合する。
(1) 金属石鹸（ステアリン酸亜鉛、ステアリン酸リチウム、ステアリン酸カルシウムなど）
(2) 金属石鹸と脂肪酸の共融混合物（ステアリン酸、オレイン酸など）
(3) 脂肪酸アミド（ステアリン酸アミド、エチレンビスステアロアミド、エルカ酸アミドなど）
(4) 金属石鹸と脂肪酸アミドの共融混合物
(5) 熱可塑性樹脂（ポリエチレン、ポリプロピレンを含むポリオレフィン、ポリアミド、ポリスチレンなど）
なお、これらは単独で使用しても、また複合して使用してもよいのは言うまでもない。
The types of the above-mentioned organic binders are not particularly limited, but the following are particularly advantageously adapted.
(1) Metal soap (zinc stearate, lithium stearate, calcium stearate, etc.)
(2) Eutectic mixture of metal soap and fatty acid (stearic acid, oleic acid, etc.)
(3) Fatty acid amides (stearic acid amide, ethylenebisstearamide, erucic acid amide, etc.)
(4) Eutectic mixture of metal soap and fatty acid amide
(5) Thermoplastic resin (polyolefin including polyethylene, polypropylene, polyamide, polystyrene, etc.)
Needless to say, these may be used alone or in combination.
さて、上記したような鉄基粉末に対し、成形時における粉末同士および粉末と金型との間の摩擦の低減、さらには成形後の金型からの抜出力の低下を目的として適量の潤滑剤を添加する。
本発明では、かような潤滑剤として遊離潤滑剤を使用するわけであるが、本発明において最も重要なことは、上記した遊離潤滑剤中に一次粒子が凝集して造粒された二次粒子をある程度以上残存させることである。
Now, with respect to the iron-based powder as described above, an appropriate amount of lubricant for the purpose of reducing the friction between the powders at the time of molding and between the powder and the mold, and further reducing the extraction force from the mold after molding. Add.
In the present invention, a free lubricant is used as such a lubricant, but the most important thing in the present invention is that secondary particles obtained by agglomerating primary particles in the above-described free lubricant are granulated. Is left to some extent.
すなわち、発明者らの研究によれば、鉄基粉末に対して遊離潤滑剤を混合する際、せん断力を適切に制御して、二次粒子をある程度以上の残存させることにより、少量の潤滑剤でも金型からの抜出力を効果的に低下させることができ、また潤滑剤量を少なくできるため圧粉体密度の有利な向上が達成されることが究明されたのである。 That is, according to the study by the inventors, when mixing a free lubricant with an iron-based powder, a small amount of lubricant can be obtained by appropriately controlling the shearing force and leaving the secondary particles to a certain extent. However, it has been determined that an advantageous improvement in the density of the green compact can be achieved because the output from the mold can be effectively reduced and the amount of lubricant can be reduced.
この理由については、まだ明確に解明されたわけではないが、遊離潤滑剤中に比較的粒径が大きい二次粒子を存在させると、鉄基粉末混合物を圧粉成形金型に装入した場合、金型壁面とそれに接する鉄基粉末との空隙にも二次粒子が侵入し、この二次粒子がほぐれる（さらに小さい二次粒子あるいは一次粒子に分割される）ことにより潤滑効果が格段に向上して、金型からの抜出力が低下するものと考えられる。
また、潤滑剤は、鉄基粉末に比べて比重が小さいため、少なくするほど圧粉体密度は向上する。
本発明では、少量の遊離潤滑剤で抜出力が低下するため、従来、鉄基粉末混合物全体で 0.8〜1.2 質量％程度添加していた潤滑剤量を、鉄基粉末：100 質量部に対し0.05〜0.6 質量部まで低減することができ、その分圧粉体密度の向上を図ることができる。さらに、潤滑剤量を低減したため、脱ろう性が改善され、脱ろう時間の短い厳しい焼結条件でも、高強度の焼結体を得ることができる。
The reason for this is not yet clearly understood, but when secondary particles having a relatively large particle size are present in the free lubricant, when the iron-based powder mixture is charged into a compacting mold, The secondary particles also enter the voids between the mold wall and the iron-based powder that touches the mold wall, and the secondary particles are loosened (divided into smaller secondary particles or primary particles), which significantly improves the lubrication effect. Therefore, it is considered that the output from the mold is reduced.
Further, since the specific gravity of the lubricant is smaller than that of the iron-based powder, the green compact density is improved as the lubricant is decreased.
In the present invention, since the unloading power is reduced with a small amount of free lubricant, the amount of lubricant conventionally added in an amount of about 0.8 to 1.2% by mass in the entire iron-based powder mixture is 0.05% with respect to 100 parts by mass of iron-based powder. It can reduce to -0.6 mass part, and the improvement of the partial pressure powder density can be aimed at. Furthermore, since the amount of lubricant is reduced, the dewaxing property is improved, and a high-strength sintered body can be obtained even under severe sintering conditions with a short dewaxing time.
ここに、一次粒子については、粒径を５〜80μm の範囲に制限する必要がある。というのは、一次粒子の粒径すなわち一次粒径が５μm に満たないと、凝集力が強くなり、二次粒子が成形時にほぐれ難くなって金型とのかじりが起こり、あるいは抜出力が高くなり、一方80μm を超えると、成形体中に潤滑剤粒子に起因した粗大な空孔が残留して圧粉体密度の低下を招き、焼結体強度を低下させてしまうからである。好ましくは５〜60μm である。
また、二次粒子については、その粒径を10〜200 μm の範囲に制限する必要がある。というのは、二次粒子の粒径すなわち二次粒径が10μm に満たないと、金型壁面と鉄基粉末との間に入り込む潤滑剤量が少なくなって、抜出力を十分に低下させることができず、一方 200μm を超えると、成形体中に潤滑剤粒子に起因した粗大な空孔が残留する結果、圧粉体密度の低下を招き、その結果、焼結体強度も低下してしまうからである。好ましくは10〜100 μm である。
なお、二次粒子への造粒は、スプレードライ法、マルメライザー等公知の方法を利用することができる。
Here, for primary particles, it is necessary to limit the particle size to a range of 5 to 80 μm. This is because if the particle size of the primary particles, that is, the primary particle size is less than 5 μm, the cohesive force becomes strong, the secondary particles are difficult to loosen during molding, and galling with the mold occurs, or the extraction force is high. On the other hand, if the thickness exceeds 80 μm, coarse pores resulting from the lubricant particles remain in the molded body, leading to a reduction in the green density and a reduction in the strength of the sintered body. Preferably 5 ~60μm.
For secondary particles, the particle size must be limited to a range of 10 to 200 μm. This is because if the particle size of the secondary particles, that is, the secondary particle size is less than 10 μm, the amount of lubricant entering between the mold wall surface and the iron-based powder is reduced, and the output power is sufficiently reduced. On the other hand, if it exceeds 200 μm, coarse pores resulting from the lubricant particles remain in the molded body, resulting in a reduction in the green compact density, resulting in a decrease in the strength of the sintered body. Because. Preferably it is 10-100 micrometers.
In addition, the granulation to a secondary particle can utilize well-known methods, such as a spray-dry method and a malmerizer.
そして、上記した粒径が10〜200 μm の二次粒子を、遊離潤滑剤全体に対して少なくとも20質量％の比率で含有させるのである。
というのは、二次粒子の比率が20質量％に満たないと、金型壁面とそれに接する鉄基粉末との空隙に侵入する二次粒子の量が少なすぎ、金型とのかじりが起こり、あるいは抜出力が高くなるからである。
以上の粒径は、レーザー回折式の粒度分布計で測定する平均粒径とする。二次粒子の比率は走査電子顕微鏡で二次粒子が100 個以上観察できる視野で、算出した二次粒子の面積率とする。
The secondary particles having a particle size of 10 to 200 μm are contained at a ratio of at least 20 mass% with respect to the entire free lubricant.
This is because if the ratio of the secondary particles is less than 20% by mass, the amount of secondary particles entering the voids between the mold wall surface and the iron-based powder in contact therewith is too small, and galling with the mold occurs. Alternatively, the output is increased.
The above particle diameter is an average particle diameter measured with a laser diffraction particle size distribution meter. The ratio of secondary particles is the calculated area ratio of secondary particles in a visual field where 100 or more secondary particles can be observed with a scanning electron microscope.
また、上記した遊離潤滑剤は、鉄基粉末：100 質量部に対し、0.05〜0.6 質量部の範囲で添加する必要がある。
というのは、鉄基粉末に対する遊離潤滑剤の混合量が0.05質量部に満たないと十分な潤滑効果が得られず，一方 0.6質量部を超えると高い圧粉体密度が得られず、また、脱ろう時間の短い厳しい焼結条件では、高強度の焼結体が得られることができないという弊害を生じるからである。好ましくは 0.1〜0.4 質量部である。
Moreover, it is necessary to add the above-mentioned free lubricant in the range of 0.05 to 0.6 parts by mass with respect to 100 parts by mass of the iron-based powder.
This is because if the amount of the free lubricant mixed with the iron-based powder is less than 0.05 parts by mass, a sufficient lubricating effect cannot be obtained, while if it exceeds 0.6 parts by mass, a high green compact density cannot be obtained. This is because, under severe sintering conditions with a short dewaxing time, there is a disadvantage that a high-strength sintered body cannot be obtained. Preferably it is 0.1-0.4 mass part.
なお、本発明の遊離潤滑剤としては、その種類が特に限定されるものではないが、次のものがとりわけ有利に適合する。
(1) 金属石鹸（ステアリン酸亜鉛、ステアリン酸リチウム、ステアリン酸カルシウムなど）
(2) 金属石鹸と脂肪酸の共融混合物（ステアリン酸、オレイン酸など）
(3) 脂肪酸アミド（ステアリン酸アミド、エチレンビスステアロアミド、エルカ酸アミド、オレイン酸アミドなど）
(4) 金属石鹸と脂肪酸アミドの共融混合物
(5) 熱可塑性樹脂（ポリエチレン、ポリプロピレンを含むポリオレフィン、ポリアミド、ポリスチレンなど）
なお、これらは単独で使用しても、また複合して使用してもよいのは言うまでもない。 その他、必要に応じてシリカやTiO2微粉等を混合しても良い。
The type of the free lubricant of the present invention is not particularly limited, but the following are particularly advantageous.
(1) Metal soap (zinc stearate, lithium stearate, calcium stearate, etc.)
(2) Eutectic mixture of metal soap and fatty acid (stearic acid, oleic acid, etc.)
(3) Fatty acid amides (stearic acid amide, ethylenebisstearamide, erucic acid amide, oleic acid amide, etc.)
(4) Eutectic mixture of metal soap and fatty acid amide
(5) Thermoplastic resin (polyolefin including polyethylene, polypropylene, polyamide, polystyrene, etc.)
Needless to say, these may be used alone or in combination. In addition, silica or TiO 2 fine powder may be mixed as necessary.
次に、本発明の製造条件について説明する。
まず、本発明では、合金鋼粉の表面に、有機結合剤により、Ni粉、Cu粉および黒鉛粉を付着させる。そのためには、合金鋼粉、Ni粉、Cu粉および黒鉛粉を混合した鉄基粉末中に適量の有機結合剤を加えたのち、有機結合剤の融点以上に加熱して、合金鋼粉の表面にNi粉、Cu粉および黒鉛粉を付着させる。
ここに、加熱温度は有機結合剤の種類によって異なるけれども、有機結合剤としてエチレンビスステアロアミド（融点：148 ℃）を用いた場合には、 150〜160 ℃程度で十分である。
Next, the manufacturing conditions of the present invention will be described.
First, in this invention, Ni powder, Cu powder, and graphite powder are made to adhere to the surface of alloy steel powder with an organic binder. For this purpose, an appropriate amount of organic binder is added to the iron-based powder mixed with alloy steel powder, Ni powder, Cu powder and graphite powder, and then heated to the melting point of the organic binder or higher to obtain the surface of the alloy steel powder. Ni powder, Cu powder and graphite powder are adhered to the surface.
Here, although the heating temperature varies depending on the kind of the organic binder, when ethylene bisstearamide (melting point: 148 ° C.) is used as the organic binder, about 150 to 160 ° C. is sufficient.
ついで、上記のようにして得た合金鋼粉の表面に黒鉛粉等を付着させた鉄基粉末中に、遊離潤滑剤を適量添加したのち、遊離潤滑剤の二次粒子が破壊しないせん断力の混合機を使用して混合を実施する。
かような混合機としては、容器回転式、機械撹拌式、流動撹拌式および無撹拌式等の、混合粉体に与えるせん断力が小さい混合機が好適である。容器回転式混合機では、水平円筒型、傾斜円筒型、Ｖ型、二重円錐型および連続Ｖ型が好ましく、撹拌羽が内蔵されている混合機も好適に使用できる。機械撹拌式混合機では、リボン型、スクリュー型、複軸パドル型、円錐形スクリュー型および回転円板型が好ましい。流動撹拌式混合機では、流動床式、旋回流動式、ジェットポンプ式が好ましい。
Then, after adding an appropriate amount of free lubricant to the iron-based powder with the graphite powder and the like adhered to the surface of the alloy steel powder obtained as described above, the shearing force of the secondary particles of the free lubricant does not break. Mixing is performed using a mixer.
As such a mixer, a mixer having a small shearing force applied to the mixed powder, such as a container rotating type, a mechanical stirring type, a flow stirring type and a non-stirring type, is preferable. In the container rotation type mixer, a horizontal cylinder type, an inclined cylinder type, a V type, a double cone type and a continuous V type are preferable, and a mixer having a built-in stirring blade can also be suitably used. In the mechanical stirring mixer, a ribbon type, a screw type, a biaxial paddle type, a conical screw type and a rotating disk type are preferable. In the fluid agitation mixer, a fluid bed type, a swirl type, and a jet pump type are preferable.
混合機の条件は、例えば、上記したＶ型容器回転式混合機を使用する場合、粒径が10〜200 μm の二次粒子を少なくとも20質量％残存させるためには、２リットルの容器の回転数を10〜100 rpm とすることが好適である。ただし、混合条件は、上記の範囲に限定されるものではなく、遊離潤滑剤の二次粒子の凝集強度に応じて、適宜決定されるものである。 The condition of the mixer is, for example, when using the above-mentioned V-type container rotary mixer, in order to leave at least 20% by mass of secondary particles having a particle size of 10 to 200 μm, a 2 liter container is rotated. The number is preferably 10 to 100 rpm. However, the mixing conditions are not limited to the above range, and are appropriately determined according to the aggregation strength of the secondary particles of the free lubricant.
成形方法については、従来公知の方法いずれもが適合する。
例えば、鉄基粉末混合物を室温とし、金型を50〜70℃に加熱する方法は、粉末の取り扱いが容易で、圧粉体密度がさらに向上するため好適である。
また、粉末、金型ともに 120〜130 ℃に加熱する温間成形も使用することができる。
Any conventionally known method is suitable for the molding method.
For example, a method in which the iron-based powder mixture is brought to room temperature and the mold is heated to 50 to 70 ° C. is preferable because the powder can be easily handled and the green density is further improved.
Also, warm molding in which both the powder and the mold are heated to 120 to 130 ° C. can be used.
なお、本発明の鉄基粉末混合物は、弱酸化性であるRXガス雰囲気中にて1100〜1200℃の低温焼結を施しても、焼結のままで 800 MPa以上の高強度を有する焼結体とすることができる。しかしながら、この条件に限定されるものではなく、N2，酸化性のAXガス等他の雰囲気中で高温焼結を行うこともできることは言うまでもない。 It should be noted that the iron-based powder mixture of the present invention is a sintered material having a high strength of 800 MPa or more as it is sintered even when subjected to low temperature sintering at 1100 to 1200 ° C. in an RX gas atmosphere that is weakly oxidizing. It can be a body. However, it is not limited to this condition, and it goes without saying that high-temperature sintering can be performed in other atmospheres such as N 2 and oxidizing AX gas.
Ni：2.1 質量％およびMo：1.0 質量％を含有し、残部はFeおよび不可避的不純物の組成になる溶鋼を、溶製し、水アトマイズ法で粉体とした後、仕上還元処理を施して、予合金鋼粉とした。ついで、この予合金鋼粉に、Ni粉：２質量％、Cu粉：1.5 質量％および黒鉛粉：0.6 質量％を配合し、さらに表１に示す有機結合剤を添加したのち、該有機結合剤の融点以上に加熱して合金鋼粉の表面にNi粉、Cu粉、黒鉛粉を付着させ、ついで表１に示す遊離潤滑剤を添加してＶ型混合機に入れ、15分間混合した。 Ni: 2.1% by mass and Mo: 1.0% by mass, with the balance being Fe and the inevitable impurities composition, the molten steel is melted and powdered by the water atomization method, and then subjected to a finish reduction treatment. Pre-alloyed steel powder. Next, Ni powder: 2% by mass, Cu powder: 1.5% by mass, and graphite powder: 0.6% by mass are added to the prealloyed steel powder, and after adding the organic binder shown in Table 1, the organic binder is added. The powder was heated to a melting point of or higher and Ni powder, Cu powder, and graphite powder were adhered to the surface of the alloy steel powder, and then the free lubricant shown in Table 1 was added and placed in a V-type mixer and mixed for 15 minutes.
得られた鉄基粉末混合物を、日本粉末冶金工業会（JAMA）のM04-1992に準拠して、成形圧力：686 MPa で引張試験片形状に成形した。ついで、これらの成形体に、RXガス雰囲気中で、特に脱ろうのための保持はせずに、昇温速度：60℃／分、1130℃×20分、冷却速度：60℃／分の条件で焼結を施し、焼結体とした。焼結後、大気中にて 180℃、60分の焼戻し処理を施した。
かくして得られた焼結体の密度および引張強さについて調べた結果を、表１に併記する。
なお、焼結体の密度はJIS Z 2501、引張強さはJIS Z 2550に従い測定した。
The obtained iron-based powder mixture was molded into a tensile test piece shape at a molding pressure of 686 MPa in accordance with M04-1992 of Japan Powder Metallurgy Association (JAMA). Next, these compacts were not held for dewaxing in an RX gas atmosphere, and the conditions were as follows: heating rate: 60 ° C./min, 1130 ° C. × 20 min, cooling rate: 60 ° C./min Was sintered to obtain a sintered body. After sintering, a tempering treatment was performed in the atmosphere at 180 ° C. for 60 minutes.
The results of examining the density and tensile strength of the sintered body thus obtained are also shown in Table 1.
The density of the sintered body was measured according to JIS Z 2501, and the tensile strength was measured according to JIS Z 2550.
同表に示したとおり、本発明に従い、潤滑剤として粒度分布を適切に制御した遊離潤滑剤を用いた場合には、遊離潤滑剤の添加量が0.6 質量部以下という少ない量で、引張強さが830 MPa以上の高強度焼結体を得ることができた。一方、一次粒径および二次粒径が小さいNo.11および二次粒子比率の小さいNo.13では、かじりが起こって成形ができず、一次粒径と二次粒径が大きいNo.12および遊離潤滑剤の添加量が過多のNo.14は引張強さが780 MPa以下と小さくなった。 As shown in the table, in accordance with the present invention, when using a free lubricant whose particle size distribution is appropriately controlled as a lubricant, the amount of free lubricant added is as small as 0.6 parts by mass or less, and the tensile strength is reduced. Was able to obtain a high-strength sintered body having a thickness of 830 MPa or more. On the other hand, No. 11 with a small primary particle size and secondary particle size and No. 13 with a small secondary particle ratio cannot be molded due to galling, and No. 12 with a large primary particle size and secondary particle size. No. 14 with an excessive amount of free lubricant added had a tensile strength of 780 MPa or less.
表２に示す量のMo，Niを予合金化した合金溶鋼を、溶製し、水アトマイズ法で粉体とした後、仕上還元処理を施して、予合金鋼粉とした。ついで、これらの予合金鋼粉に、表２に示す量のNi粉、Cu粉、黒鉛粉を配合し、さらに有機結合剤として、ステアリン酸アミド：0.1 質量％とエチレンビスステアロアミド：0.1 質量％を加えた後、 150℃に加熱して合金鋼粉の表面にNi粉、Cu粉、黒鉛粉を付着させ、ついで遊離潤滑剤は表１のNo.6と同じものを同じ添加量で用い、Ｖ型混合機に入れ、15分間混合した。
得られた鉄基粉末混合物を、実施例１と同様にして成形、焼結して得た焼結体の密度および引張強さについて調べた結果を、表２に併記する。
An alloy molten steel in which Mo and Ni in amounts shown in Table 2 were pre-alloyed was melted and powdered by the water atomization method, and then subjected to a finish reduction treatment to obtain a pre-alloyed steel powder. Next, Ni powder, Cu powder and graphite powder in the amounts shown in Table 2 were blended with these pre-alloyed steel powders, and stearamide: 0.1% by mass and ethylene bisstearamide: 0.1% as organic binders. %, Then heat to 150 ° C to adhere Ni powder, Cu powder and graphite powder to the surface of the alloy steel powder, and then use the same free lubricant as No. 6 in Table 1 in the same amount. And placed in a V-type mixer for 15 minutes.
Table 2 shows the results of examining the density and tensile strength of the sintered body obtained by molding and sintering the obtained iron-based powder mixture in the same manner as in Example 1.
同表から明らかなように、Ni，Moの予合金化率およびNi粉、Cu粉および黒鉛粉の混合割合が本発明の範囲を満足する鉄基粉末混合物を用いた場合にはいずれも、焼結体の引張強さが 840 MPa以上という高強度焼結体を得ることができた。
これに対し、No.1, 5, 9, 13, 16の比較例はそれぞれ、合金鋼粉中のMo量、Ni量、鉄基粉末中のNi粉量、Cu粉量、黒鉛粉量が少なく、強度向上の効果が小さいため、高強度焼結体が得られていない。
また、No.4, 8 はそれぞれ、合金鋼粉中のMo, Ni量が多すぎ、鋼粉粒子が硬化するため、焼結体密度が著しく低下し、高強度が得られていない。
No.12 は、鉄基粉末中のNi粉量が多すぎ、残留オーステナイトが著しく多くなるため、高強度が得られていない。
No.15 は、鉄基粉末中のCu粉量が多すぎるため、高強度が得られていない。
No.18 は、鉄基粉末中の黒鉛粉量が多すぎ、セメンタイトが焼結体の結晶粒界に析出するため、高強度が得られていない。
As is clear from the table, when using an iron-based powder mixture in which the prealloying ratio of Ni and Mo and the mixing ratio of Ni powder, Cu powder and graphite powder satisfy the scope of the present invention, A high-strength sintered body with a tensile strength of 840 MPa or more was obtained.
On the other hand, the comparative examples of No. 1, 5, 9, 13, and 16 each have a small amount of Mo, Ni, iron, Ni, Cu, and graphite in the alloy steel powder. Since the effect of improving the strength is small, a high-strength sintered body has not been obtained.
In Nos. 4 and 8, the amounts of Mo and Ni in the alloy steel powder are too large, and the steel powder particles are hardened, so the density of the sintered body is remarkably lowered and high strength is not obtained.
No. 12 does not have high strength because the amount of Ni powder in the iron-based powder is too large and the retained austenite increases remarkably.
No. 15 does not have high strength because the amount of Cu powder in the iron-based powder is too large.
No. 18 does not have high strength because the amount of graphite powder in the iron-based powder is too large and cementite precipitates at the grain boundaries of the sintered body.
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