JP2016035105A - Mixed powder for iron-based powder metallurgy, iron-based sintered alloy and sintered machine component, and method for producing iron-based sintered alloy - Google Patents
Mixed powder for iron-based powder metallurgy, iron-based sintered alloy and sintered machine component, and method for producing iron-based sintered alloy Download PDFInfo
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本発明は、粉末冶金技術に供して好適な鉄基粉末冶金用混合粉、鉄基焼結合金および焼結機械部品、並びに鉄基焼結合金の製造方法に関するものであって、特に、かかる鉄基粉末冶金用混合粉を用いた圧粉体を焼結した際の鉄基焼結合金の寸法変化の変動の低減を図ろうとするものである。 The present invention relates to a mixed powder for iron-based powder metallurgy suitable for use in powder metallurgy technology, an iron-based sintered alloy and a sintered machine part, and a method for producing the iron-based sintered alloy. An object of the present invention is to reduce the variation of the dimensional change of the iron-based sintered alloy when the green compact using the mixed powder for base powder metallurgy is sintered.
粉末冶金法によって製造される焼結機械部品は、少ない仕上げ加工量で最終部品形状が得られるため、特に、複雑形状の部品において、高生産性を実現できることを最大のメリットとしている。従って、その製造工程における寸法変化の制御が重要である。 Since sintered machine parts manufactured by the powder metallurgy method can obtain the final part shape with a small amount of finishing processing, the greatest merit is that high productivity can be achieved especially in parts having complex shapes. Therefore, control of dimensional changes in the manufacturing process is important.
粉末冶金法において、鉄、銅、カーボン系の焼結合金は、輸送機械などの機械部品として最も広く用いられている成分系であって、鉄、銅、黒鉛の粉末を混合したのち、粉末成形に必要な潤滑材粉末を添加し、さらに、成形、焼結することで得ることができる。 In powder metallurgy, iron, copper, and carbon-based sintered alloys are the most widely used component parts for machine parts such as transport machinery. After mixing iron, copper, and graphite powders, powder molding It can be obtained by adding the necessary lubricant powder to the above, and further molding and sintering.
ここで、鉄、銅、カーボン系焼結合金の焼結工程では、黒鉛粉から鉄粉へのカーボン拡散、銅粉の溶融と鉄生地への拡散、そして鉄の相変態と焼結の進行とが相次いで起こるため、図１に示すように、それぞれの工程で極めて複雑な寸法変化挙動を示す。なお、図中、ΔＡは、最終的な寸法変化量を示す。 Here, in the sintering process of iron, copper, and carbon-based sintered alloy, carbon diffusion from graphite powder to iron powder, melting of copper powder and diffusion to iron dough, and iron phase transformation and progress of sintering 1 occur one after another, and as shown in FIG. 1, each process exhibits extremely complicated dimensional change behavior. In the figure, ΔA represents the final dimensional change.
この複雑な寸法変化挙動に対し、特許文献１では、銅粉中のPb含有量を0.05wt％以下とすることで、焼結中の寸法変化率を制御できるとしている。 In contrast to this complicated dimensional change behavior, Patent Document 1 states that the dimensional change rate during sintering can be controlled by setting the Pb content in the copper powder to 0.05 wt% or less.
しかしながら、近年の材料費の高騰、また、焼結機械部品の寸法精度向上に対する要求の増大、切削屑の処理にかかる環境問題等を考慮すると、特許文献１に記載された技術であっても、未だ十分な寸法変化制御をしているとは言いがたい。 However, considering the recent increase in material costs, an increase in demand for improvement in dimensional accuracy of sintered machine parts, environmental problems related to processing of cutting waste, etc., even with the technique described in Patent Document 1, It is hard to say that the dimensional change control is still sufficient.
本発明は、上記した現状に鑑み開発されたもので、上記した従来技術の問題点を克服し、焼結体としたときの寸法変化の低減が可能な鉄基粉末冶金用混合粉、および鉄基焼結合金、並びに焼結機械部品の製造方法を提案することを目的とする。 The present invention has been developed in view of the above-described present situation, overcomes the problems of the prior art described above, and can reduce the dimensional change when the sintered body is formed. It aims at proposing the manufacturing method of a base sintered alloy and a sintered machine part.
さて、発明者は、上記の目的を達成するために、鉄基粉末冶金用混合粉の原料となる鉄基粉末の合金成分およびその添加手段について種々検討を重ね、以下に述べる知見を得た。 Now, in order to achieve the above object, the inventor has made various studies on the alloy component of the iron-based powder, which is a raw material of the mixed powder for iron-based powder metallurgy, and the means for adding it, and has obtained the following knowledge.
すなわち、鉄、銅、カーボン系焼結合金を用いる焼結機械部品の製造においては、その焼結工程で、銅の融点に至るまでの昇温時のカーボンの拡散（浸炭）が、寸法精度に影響することは知られていた。しかしながら、このカーボンの拡散は、鉄粉、銅粉、黒鉛粉等の粉末特性や、粉末成形、焼結などの条件等、種々の要因によって変動するために、最終的な焼結体の寸法変化を正確に把握することは困難であった。 In other words, in the manufacture of sintered machine parts using iron, copper, and carbon-based sintered alloys, the diffusion of carbon (carburization) at the time of temperature rise up to the melting point of copper in the sintering process increases the dimensional accuracy. It was known to affect. However, this carbon diffusion varies depending on various factors such as powder characteristics of iron powder, copper powder, graphite powder, etc., conditions such as powder molding, sintering, etc. It was difficult to grasp accurately.
そこで、発明者は、鉄、銅、カーボン系焼結合金の焼結過程における寸法の変動要因について、再度検討したところ、銅粉の溶融時に発生する銅膨張現象が、焼結過程における寸法の変動に対し、最も大きな影響を及ぼす因子であることを突き止めた。
そして、この銅膨張現象に対してさらに詳細に検討したところ、焼結工程における銅の融点まで昇温するに先立って、原料鉄粉中に十分な量のカーボンを拡散させておくことで、焼結体の膨張を抑制できることを知得した。
本発明は、上記知見に基づいてなされたものである。
Therefore, the inventor reexamined the dimensional variation factors in the sintering process of iron, copper, and carbon-based sintered alloys, and found that the copper expansion phenomenon that occurs when the copper powder melts is due to the dimensional variation in the sintering process. On the other hand, it was found that it is the factor that has the greatest influence.
Further, when the copper expansion phenomenon was examined in more detail, prior to raising the temperature to the melting point of copper in the sintering process, a sufficient amount of carbon was diffused in the raw iron powder, so It was found that the expansion of the knot can be suppressed.
The present invention has been made 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。
１．鉄粉、銅粉、黒鉛粉および潤滑材を含み、鉄粉、銅粉、および黒鉛粉の合計量１００質量％に対して0.05〜１質量％の炭酸塩を含有する鉄基粉末冶金用混合粉。
That is, the gist configuration of the present invention is as follows.
1. Mixed powder for iron-based powder metallurgy containing iron powder, copper powder, graphite powder and lubricant, and containing 0.05 to 1% by mass of carbonate with respect to 100% by mass of the total amount of iron powder, copper powder and graphite powder .
２．前記鉄粉が還元鉄粉またはアトマイズ鉄粉である前記１に記載の鉄基粉末冶金用混合粉。 2. 2. The iron-based powder metallurgy mixed powder according to 1, wherein the iron powder is reduced iron powder or atomized iron powder.
３．前記炭酸塩が炭酸カルシウムである前記１または２に記載の鉄基粉末冶金用混合粉。 3. The mixed powder for iron-based powder metallurgy according to 1 or 2, wherein the carbonate is calcium carbonate.
４．前記鉄粉、銅粉、および黒鉛粉の合計量１００質量％に対して、0.05〜１質量％の硼砂および／または硼酸を添加した前記１〜３のいずれかに記載の鉄基粉末冶金用混合粉。 4). The iron-based powder metallurgy mixture according to any one of 1 to 3 above, wherein 0.05 to 1% by mass of borax and / or boric acid is added to 100% by mass of the total amount of the iron powder, copper powder, and graphite powder. powder.
５．前記炭酸塩の比表面積が0.5m2/g以上である、前記１〜４のいずれかに記載の鉄基粉末冶金用混合粉。 5. The mixed powder for iron-based powder metallurgy according to any one of 1 to 4 above, wherein the carbonate has a specific surface area of 0.5 m 2 / g or more.
６．前記１〜５のいずれかに記載の鉄基粉末冶金用混合粉を原料とする鉄基焼結合金。 6). An iron-based sintered alloy using the iron-based powder metallurgy mixed powder according to any one of 1 to 5 as a raw material.
７．前記鉄基粉末冶金用混合粉中の炭酸塩含有量（CBｐ）と前記鉄基焼結合金中の炭酸塩含有量（CBｓ）との比率（CBｓ/CBｐ）×100が２％以下である前記６に記載の鉄基焼結合金。 7). The ratio (CB s / CB p ) × 100 of the carbonate content (CB p ) in the iron-based powder metallurgy mixed powder and the carbonate content (CB s ) in the iron-based sintered alloy is 2%. 6. The iron-based sintered alloy according to 6, wherein
８．前記１〜５のいずれかに記載の鉄基粉末冶金用混合粉を、圧縮成形により成形体とし、室温から400〜700℃まで、１分当たり100℃以下の平均昇温速度で加熱し、昇温も含め15分以上加熱保持して潤滑材成分を除去（脱脂）した後、焼結温度まで昇温する鉄基焼結合金の製造方法。 8). The mixed powder for iron-based powder metallurgy according to any one of 1 to 5 above is formed into a compact by compression molding, and heated from room temperature to 400 to 700 ° C at an average temperature increase rate of 100 ° C or less per minute. A method for producing an iron-based sintered alloy in which the temperature is raised to the sintering temperature after removing (degreasing) the lubricant component by heating and holding for 15 minutes or more including the temperature.
９．前記６または７に記載の鉄基焼結合金を用いる焼結機械部品。 9. A sintered machine part using the iron-based sintered alloy according to 6 or 7 above.
本発明によれば、焼結時の寸法精度の悪化が効果的に抑制されるので、焼結機械部品の製造において、仕上げ加工の加工量をより少なくすることができ、もって粉末冶金法のメリットを最大限拡大することができる。 According to the present invention, since deterioration of dimensional accuracy during sintering is effectively suppressed, the amount of finishing processing can be reduced in the manufacture of sintered machine parts, and thus the merit of the powder metallurgy method Can be maximized.
以下、本発明を具体的に説明する。
本発明の鉄基粉末冶金用混合粉は、鉄粉、銅粉、黒鉛粉および潤滑材を含む混合粉に対し、炭酸塩を含有することを特徴としている。
Hereinafter, the present invention will be specifically described.
The mixed powder for iron-based powder metallurgy according to the present invention is characterized by containing a carbonate with respect to the mixed powder containing iron powder, copper powder, graphite powder and a lubricant.
具体的には、鉄粉と銅粉と黒鉛粉との合計量：100質量％に対して、0.05〜１質量％の炭酸塩を含有させることを特徴としている。
すなわち、本発明では、炭酸塩を、上記所定の範囲で含有することにより、混合粉成形体を焼結した際の寸法変化を効果的に小さくすることができる。なお、上記含有量の好適範囲は、0.1〜0.3質量％である。
また、炭酸塩の種類は、以下に説明する二酸化炭素の熱解離が生じるものであれば特に限定されないが、入手のしやすさ等から炭酸カルシウムや、炭酸リチウム、炭酸ナトリウム、炭酸カリウム、炭酸マグネシウムなどが好ましい。
Specifically, 0.05 to 1% by mass of carbonate is contained with respect to the total amount of iron powder, copper powder and graphite powder: 100% by mass.
That is, in the present invention, by containing the carbonate in the above predetermined range, the dimensional change when the mixed powder molded body is sintered can be effectively reduced. In addition, the suitable range of the said content is 0.1-0.3 mass%.
The type of carbonate is not particularly limited as long as the thermal dissociation of carbon dioxide described below occurs, but calcium carbonate, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate are easily available. Etc. are preferable.
ここで、上記の寸法変化を効果的に小さくできる効果について、発明者は、以下のように考えている。
以下の式（１）〜（３）に示されるように、本発明では、炭酸カルシウムの熱分解により生じる二酸化炭素（ＣＯ２）が、黒鉛粉からの浸炭性ガス（一酸化炭素：ＣＯ）の生成を助けるため、鉄粉へのカーボン（Ｃ＊）の拡散が促進される。そして、鉄粉へのカーボンの拡散が促進されることで、銅融点に到達する時点の鉄中のカーボン濃度が安定する。その結果、銅膨張が抑制され、寸法精度の悪化を防止することができるのである。
ＣａＣＯ３→ＣａＯ＋ＣＯ２ ・・・（１）
Ｃ（黒鉛）＋ＣＯ２→２ＣＯ ・・・（２）
２ＣＯ→ＣＯ２＋Ｃ＊ ・・・（３）
Here, the inventor considers the effect of effectively reducing the above dimensional change as follows.
As shown in the following formulas (1) to (3), in the present invention, carbon dioxide (CO 2 ) generated by thermal decomposition of calcium carbonate is a carburizing gas (carbon monoxide: CO) from graphite powder. In order to assist the generation, diffusion of carbon (C * ) into the iron powder is promoted. And the carbon density | concentration in iron at the time of reaching | attaining copper melting | fusing point is stabilized by the spreading | diffusion of the carbon to an iron powder. As a result, copper expansion is suppressed, and deterioration of dimensional accuracy can be prevented.
CaCO 3 → CaO + CO 2 (1)
C (graphite) + CO 2 → 2CO (2)
2CO → CO 2 + C * (3)
また、炭酸カルシウムなどの炭酸塩には、さまざまな粒子径のものが市販されているが、前記式（２）の反応によって黒鉛からの浸炭ガス生成を十分に促進するためには、炭酸塩の反応界面の大きさを表す指標である比表面積が0.5m2/g以上であることが好ましい。炭酸塩の比表面積が0.5m2/g以上であれば、一般的な焼結プロセスの処理時間内に十分な前記式（１）〜（３）の反応が起こり、浸炭を促進する作用が得られ易いからである。
なお、本発明における炭酸塩の比表面積の上限に制限はないが、混合粉の流動性が悪化するため、10m2/g程度以下とするのが好ましい。
In addition, carbonates such as calcium carbonate having various particle sizes are commercially available. In order to sufficiently promote carburizing gas generation from graphite by the reaction of the above formula (2), The specific surface area, which is an index representing the size of the reaction interface, is preferably 0.5 m 2 / g or more. If the specific surface area of the carbonate is 0.5 m 2 / g or more, sufficient reactions of the above formulas (1) to (3) occur within the processing time of a general sintering process, and an effect of promoting carburization is obtained. It is because it is easy to be done.
In addition, although there is no restriction | limiting in the upper limit of the specific surface area of the carbonate in this invention, Since the fluidity | liquidity of mixed powder deteriorates, it is preferable to set it as about 10 m < 2 > / g or less.
混合粉における銅粉の配合量は、0.1〜５質量％とすることが好ましい。
混合粉へ配合された銅粉は、焼結時に液相となり、鉄粉へ拡散し、焼結部品の強度を増加させ焼結収縮を防止する効果を有する。混合粉における銅粉の配合量が、0.1質量％未満では、その効果が認められない一方で、５質量％を超えると焼結中の寸法変化が大きくなって、所望の寸法精度が得られない。このため、混合粉１００質量％中、銅粉の配合量は、0.1〜５質量％の範囲とするのが好ましい。
It is preferable that the compounding quantity of the copper powder in mixed powder shall be 0.1-5 mass%.
The copper powder blended into the mixed powder becomes a liquid phase during sintering, diffuses into the iron powder, and has an effect of increasing the strength of the sintered part and preventing sintering shrinkage. If the blending amount of the copper powder in the mixed powder is less than 0.1% by mass, the effect is not recognized. On the other hand, if it exceeds 5% by mass, the dimensional change during sintering becomes large and the desired dimensional accuracy cannot be obtained. . For this reason, it is preferable to make the compounding quantity of copper powder into the range of 0.1-5 mass% in 100 mass% of mixed powder.
混合粉における黒鉛粉の配合量は、２質量％以下とすることが好ましい。
黒鉛粉は、焼結中に鉄粉へ容易に拡散し、合金化して、焼結体の強度を上昇することができるため、必要に応じ配合するが、２質量％を超える黒鉛粉の添加は、焼結体の寸法精度が劣化するため、２質量％以下とする。なお、黒鉛粉は、鱗片状の天然黒鉛粉が好適である。また、配合量の下限は、0.1質量％程度が好ましい。このため、混合粉１００質量％中、黒鉛粉の配合量は、0.1〜２質量％の範囲とするのが好ましい。
The blending amount of the graphite powder in the mixed powder is preferably 2% by mass or less.
Graphite powder easily diffuses into iron powder during sintering and can be alloyed to increase the strength of the sintered body. Therefore, it is blended as necessary, but the addition of graphite powder exceeding 2 mass% Since the dimensional accuracy of the sintered body deteriorates, it is set to 2% by mass or less. The graphite powder is preferably scaly natural graphite powder. Further, the lower limit of the amount is preferably about 0.1% by mass. For this reason, it is preferable to make the compounding quantity of graphite powder into the range of 0.1-2 mass% in 100 mass% of mixed powder.
本発明で使用する鉄粉（鉄系粉）は、還元鉄粉、アトマイズ鉄粉、電解鉄粉等いずれも好適に適用でき、とくに限定する必要はないが、表面に不純物が少ない還元鉄粉や、製造の容易なアトマイズ鉄粉が好適である。 As the iron powder (iron-based powder) used in the present invention, any of reduced iron powder, atomized iron powder, electrolytic iron powder, etc. can be suitably applied, and there is no particular limitation. Atomized iron powder that is easy to manufacture is suitable.
その他、混合粉には、潤滑材を添加する。潤滑材としては、粉末冶金に常用されるものであれば特に限定されないが、ステアリン酸亜鉛、ワックスなどが好適である。なお、添加量に関しても特に限定はされず、常法に従う。 In addition, a lubricant is added to the mixed powder. The lubricant is not particularly limited as long as it is commonly used in powder metallurgy, but zinc stearate, wax, and the like are preferable. In addition, there is no limitation in particular regarding addition amount, and it follows a conventional method.
本発明では、上記混合粉に対し、所定の炭酸塩を添加することで、鉄基粉末冶金用混合粉を得ることができる。そして、この鉄基粉末冶金用混合粉を、成形、焼結等の工程を経るといった、鉄基焼結合金を得るための常法に従うことで、仕上げ加工の加工量が少なく、かつ焼結体の強度と靭性が共に向上した鉄基焼結合金を得ることができる。
なお、上記した組成の鉄基粉末冶金用混合粉は、圧縮成形により、所定の寸法の成形体とされ、非酸化性雰囲気で焼結するのが、焼結体の寸法制御に関してより有利である。
In the present invention, a mixed powder for iron-based powder metallurgy can be obtained by adding a predetermined carbonate to the mixed powder. And, according to a conventional method for obtaining an iron-based sintered alloy, such as forming, sintering, etc., through this mixed powder for iron-based powder metallurgy, the amount of finish processing is small, and the sintered body An iron-based sintered alloy with improved strength and toughness can be obtained.
The iron-based powder metallurgy mixed powder having the above composition is formed into a compact having a predetermined size by compression molding, and sintering in a non-oxidizing atmosphere is more advantageous in terms of controlling the size of the sintered compact. .
また、本発明では、さらに、硼砂および／または硼酸を添加した鉄基粉末冶金用混合粉を用いて、これを成形し、焼結を行う際に、鉄粉表面の酸化層を溶融する、いわゆるフラックス効果を誘発することによって、浸炭反応の妨げとなる鉄粉表面の炭素拡散バリアを除去することができる。
この際、硼砂および／または硼酸の添加量が過大であると、焼結合金の組織に黒鉛を析出させ、強度を低下させる。そこで、硼砂および／または硼酸を添加する場合は、粉末冶金用混合粉に対し、鉄粉、銅粉、および黒鉛粉の合計量１００質量％に対する外添加で0.05〜１質量％の範囲で添加することが好ましい。
Further, in the present invention, a so-called mixed powder for iron-based powder metallurgy to which borax and / or boric acid is added is molded, and when the sintering is performed, the oxide layer on the surface of the iron powder is melted. By inducing the flux effect, the carbon diffusion barrier on the surface of the iron powder that hinders the carburization reaction can be removed.
At this time, if the amount of borax and / or boric acid added is excessive, graphite is precipitated in the structure of the sintered alloy and the strength is lowered. Therefore, when adding borax and / or boric acid, it is added in the range of 0.05 to 1% by mass with respect to 100% by mass of the total amount of iron powder, copper powder, and graphite powder with respect to the mixed powder for powder metallurgy. It is preferable.
さらに、本発明に従う鉄基焼結合金を得るための焼結条件は、室温から400〜700℃まで、１分当たり100℃以下の平均昇温速度で加熱し、潤滑材がほぼ完全に溶融、蒸発して除去されるまで、昇温も含め15分以上加熱保持したのち、焼結温度まで昇温する。なお、上記焼結温度は、1000〜1250℃程度の範囲が好ましい。 Furthermore, the sintering conditions for obtaining the iron-based sintered alloy according to the present invention are heating from room temperature to 400 to 700 ° C. at an average heating rate of 100 ° C. or less per minute, and the lubricant is almost completely melted. Heat and hold for 15 minutes or more, including the temperature rise, until evaporated and removed, and then raise the temperature to the sintering temperature. The sintering temperature is preferably in the range of about 1000 to 1250 ° C.
上記条件で焼結を行った場合、潤滑材成分がほぼ完全に除去（脱脂）されて、鉄粉表面が潤滑材成分に覆われていない状態が得られるので、その後の昇温中にフラックス成分の溶融による鉄粉表面の酸化物等の浸炭阻害物質の除去や、炭酸塩の分解による二酸化炭素の生成により活発化される黒鉛粉から鉄粉への浸炭などが円滑に行われるため、有利である。 When sintering is performed under the above conditions, the lubricant component is almost completely removed (degreased), and the iron powder surface is not covered with the lubricant component. It is advantageous because the carburization inhibitor such as oxides on the surface of iron powder by melting of the iron powder and the carburization from graphite powder to iron powder activated by the production of carbon dioxide by decomposition of carbonate are performed smoothly. is there.
また、特に、前記鉄基粉末冶金用混合粉中の炭酸塩含有量をCBｐとし、前記鉄基焼結合金中の炭酸塩含有量をCBｓとした時、比率：（CBｓ/CBｐ）×100が２％以下となるように、焼結炉内のCO2濃度を下げた焼結条件に調整することで、より仕上げ加工の加工量が少なく、かつ焼結体の強度と靭性が共に向上した鉄基焼結合金を得ることができる。好ましくは、比率：（CBｓ/CBｐ）×100が１％以下である。一方、製造コストに問題なければ、（CBｓ/CBｐ）×100の下限は０％であってもよい。 In particular, when the carbonate content in the iron-based powder metallurgy mixed powder is CB p and the carbonate content in the iron-based sintered alloy is CB s , the ratio: (CB s / CB p ) By adjusting the sintering conditions to lower the CO 2 concentration in the sintering furnace so that x100 is 2% or less, the amount of finishing work is less, and the strength and toughness of the sintered body are reduced. Both improved iron-based sintered alloys can be obtained. Preferably, the ratio: (CB s / CB p ) × 100 is 1% or less. On the other hand, if there is no problem with the manufacturing cost, the lower limit of (CB s / CB p ) × 100 may be 0%.
さらに、本発明では、前記鉄基焼結合金を用いる焼結機械部品の製造方法であって、焼結機械部品の製造工程中、焼結工程までは、前記した鉄基焼結合金の製造条件に従うことで、仕上げ加工の加工量がより少ない焼結機械部品を製造することができる。なお、本発明で限定される製造条件以外の製造条件は、焼結機械部品を製造するための公知公用の製造条件に従えば良い。 Furthermore, in this invention, it is a manufacturing method of the sintered machine part using the said iron-based sintered alloy, Comprising: During the manufacturing process of a sintered machine part, it is the manufacturing conditions of an iron-based sintered alloy mentioned above until a sintering process. By following the above, it is possible to manufacture a sintered machine part having a smaller amount of finishing. In addition, what is necessary is just to follow the manufacturing conditions other than the manufacturing conditions limited by this invention in the well-known public use manufacturing conditions for manufacturing a sintered machine part.
アトマイズ鉄粉（JFEスチール(株)製、JIP−301A）：97.2質量％、電解銅粉：2.0質量％、天然黒鉛粉：0．8質量％に、潤滑材としてステアリン酸亜鉛：0.8質量％を外添加した鉄基粉末冶金用混合粉に、炭酸カルシウムなどを外添加（発明例）した。また、更に加えて硼砂を外添加した。
本実施例における適用設備／適用工程／適用作業、および、操業条件／加工条件は、以下のとおりである。
原料粉末を、Ｖミキサにて30分間均一に混合し、万能試験機（（株）島津製作所製、2000ｋＮオートグラフ）を用いて、35mm外径×14mm内径の金型に粉末を充填し、成形圧力：490MPaで高さ10mmとなるように圧粉成形したのち、ベルト幅６インチのメッシュベルト炉で1130℃のRXガス雰囲気中で焼結してサンプルを得た。各サンプルについて、外径寸法の金型に対する変化率（焼結後の外形寸法変化率）と、JIS Z 2507-2000に従って圧環強さを測定した。尚、それぞれ100個のサンプルについて、焼結後の外径寸法変化率を求め、標準偏差を算出した。
なお、上記焼結条件は、室温から400〜700℃の範囲まで、１分当たり100℃以下の平均昇温速度で加熱し、潤滑材がほぼ完全に溶融、蒸発して除去されるまで、昇温も含め15分以上加熱保持したのち、最終的に1130℃の焼結温度まで昇温した。ただし、比較例３については、室温から400〜700℃の範囲まで、昇温も含め10分間加熱保持したのち、最終的に1130℃の焼結温度まで昇温した。
ここで、本実施例では、比較例１の圧環強さ：684MPaに対し、圧環強さが９％以上低下（圧環強さ：622MPa以下）した場合、圧環強さ不足により不合格とした。
他方、焼結後の外形寸法変化率の標準偏差が0.015以下であれば、焼結体の外形寸法変化率のばらつきが小さく、合格とした。
Atomized iron powder (JFE Steel Co., Ltd., JIP-301A): 97.2 mass%, electrolytic copper powder: 2.0 mass%, natural graphite powder: 0.8 mass%, zinc stearate: 0.8 mass% as a lubricant Calcium carbonate or the like was externally added (invention example) to the externally added mixed powder for iron-based powder metallurgy. In addition, borax was added outside.
The application equipment / application process / application work and operation / processing conditions in this example are as follows.
The raw material powder is mixed uniformly for 30 minutes with a V mixer, and filled into a 35mm outer diameter x 14mm inner diameter mold using a universal testing machine (Shimadzu Corporation, 2000kN autograph) and molded. Pressure: 490 MPa, compacted to a height of 10 mm, and then sintered in an RX gas atmosphere at 1130 ° C. in a mesh belt furnace with a belt width of 6 inches to obtain a sample. For each sample, the crushing strength was measured in accordance with the rate of change of the outer diameter with respect to the mold (the rate of change in the external dimension after sintering) and JIS Z 2507-2000. For each of the 100 samples, the dimensional change rate after sintering was obtained, and the standard deviation was calculated.
The sintering conditions are as follows: from room temperature to 400 to 700 ° C., heated at an average heating rate of 100 ° C. or less per minute, until the lubricant is almost completely melted and evaporated and removed. After heating and holding for 15 minutes including the temperature, the temperature was finally raised to the sintering temperature of 1130 ° C. However, in Comparative Example 3, the temperature was raised from room temperature to 400 to 700 ° C. for 10 minutes including heating, and finally the temperature was raised to a sintering temperature of 1130 ° C.
Here, in this example, when the crushing strength decreased by 9% or more (crushing strength: 622 MPa or less) compared to the crushing strength: 684 MPa of Comparative Example 1, the crushing strength was judged to be rejected.
On the other hand, if the standard deviation of the rate of change in the outer dimension after sintering was 0.015 or less, the variation in the rate of change in the outer dimension of the sintered body was small, and it was accepted.
表１に示したように、本発明によれば、焼結体の外形寸法変化率のばらつきを有効に低減できると共に、焼結体圧環強さは、炭酸塩を添加しない場合と比較して、それ以上か、９％未満の低下に抑えられる。一方、炭酸塩を添加しないと、焼結体の外形寸法変化率のばらつきが有効に低減できない。また、炭酸塩の含有量が本発明の範囲を超えると、炭酸塩を添加しない場合と比較して９％以上の焼結体圧環強さの低下が起こる。 As shown in Table 1, according to the present invention, it is possible to effectively reduce the variation in the external dimension change rate of the sintered body, and the sintered body crushing strength is compared with the case where no carbonate is added, It is suppressed to a decrease of more than or less than 9%. On the other hand, if the carbonate is not added, the variation in the external dimension change rate of the sintered body cannot be effectively reduced. Moreover, when content of carbonate exceeds the range of this invention, compared with the case where carbonate is not added, the fall of a sintered compact rolling strength of 9% or more will occur.
また、表２に示したように、本発明によれば、鉄基粉末冶金用混合粉中の炭酸塩含有量（CBｐ）と前記鉄基焼結合金中の炭酸塩含有量（CBｓ）との比率（CBｓ/ CBｐ）×100を２％以下にすると、さらに焼結体の外形寸法変化率のばらつきを有効に低減することができる。
Further, as shown in Table 2, according to the present invention, the carbonate content (CB p ) in the iron-based powder metallurgy mixed powder and the carbonate content (CB s ) in the iron-based sintered alloy When the ratio (CB s / CB p ) × 100 is made 2% or less, the variation in the external dimensional change rate of the sintered body can be effectively reduced.
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