JPH0541693B2

JPH0541693B2 -

Info

Publication number: JPH0541693B2
Application number: JP1092671A
Authority: JP
Inventors: Naohisa Takahashi; Noryuki Kaneko; Koichiro Hayashi; Hiroyuki Endo
Original assignee: Hitachi Powdered Metals Co Ltd; Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd; Resonac Corp
Priority date: 1989-04-12
Filing date: 1989-04-12
Publication date: 1993-06-24
Also published as: JPH02270943A

Description

[Detailed description of the invention]

この発明は高温で腐蝕性の雰囲気というような
過酷な環境で用いられる軸受用に適する焼結合金
およびその製造方法に関するものである。［従来の問題点］自動車、自動二輪車などの内燃機関では、その
排気装置内に排気制御用の弁を設けて出力特性の
最適化を図る場合があるが、その弁の軸を支える
軸受に問題があつた。即ち、排気ガスは一般に500℃以上の高温にな
るため軸受に潤滑油を使用できず、排気ガスに
種々の腐蝕性成分を含むことと相侯つて軸受の摩
耗が促進される。そのため通常の条件では優れた
特性を示す黒鉛はもとより、耐熱材料として一般
的なステンレス鋼でも所要の設計寿命に達せず、
新しい材料の開発が望まれていた。［課題を解決するための手段］この発明は上述の背景に基づいてなされたもの
で、基本的にはステンレス鋼の系統ではあるが、
その製造に粉末冶金の手法を用いることで最適な
組成および合金組織を実現させ、それにより過酷
な環境での耐摩耗性を向上させたものである。即ち、この発明に係る焼結合金（以下特に付言
しない限り、組成は重量基準。）は、全体組成が炭素：1.5〜４％、Si：0.1〜0.8％ Cr：13〜25％、Ni：５〜21％ Mo：1.3〜10.7％、Co：３〜19％および鉄：残部からなり、かつその合金組織
は、金属炭化物が分散したニツケル・クロム系ス
テンレス鋼からなるマトリツクスの間に５〜30％
のケイ素、クロムおよびモリブデンを含有する粒
状のコバルト合金相と遊離炭素が分散した組織を
呈することを特徴とするものである。またこの様な合金組織を確実に実現させる製造
方法の発明は、組成がNi：８〜22％、Cr：16〜
26％および鉄：残部；またはNi：８〜22％、
Cr：16〜26％、Mo：３％以下および鉄：残部の
オーステナイト系ステンレス鋼粉に、Si：2.2〜
2.6％、Cr：7.5〜8.6％、Mo：27〜29％および
Co：残部のコバルト合金粉５〜30％と黒鉛粉1.5
〜４％を配合した混合粉を原料として用いること
をその骨子とするものである。［作用］以下、上述の合金組成と金属組織の作用効果に
ついて説明する。本発明の基本構想は、マトリツクスをオーステ
ナイト系ステンレス鋼として耐熱性を負担させる
とともにそのマトリツクス中にクロムを主とする
金属炭化物を分散させて基地の強化を図り、更に
硬質のコバルト系金属間化合物粒子を分散させて
凝着摩耗に対する抵抗力を増す一方、遊離黒鉛の
固体潤滑作用によつて耐摩擦摩耗性の強化を図る
ことにある。オーステナイト系ステンレス鋼は、ニツケルと
クロムの含有量がNi：８〜22％、Cr：16〜26％
の範囲のものが用いられる。更に、このオーステナイト系ステンレス鋼は、
Moを２〜３％を含有するもの（例えばJISの
SUS316L）でもよい。Moが３％を超えるステン
レス鋼種およびCuを含む鋼種は、硬さが高く、
粉末の圧縮性が悪いので好ましくない。同様の理
由で、炭素量の少ない鋼粉が好ましい。ステンレス鋼中のNiおよびCrは、鉄基地に固
溶しその耐蝕性および耐熱性を向上する元素であ
る。その組成範囲は例えば原著者ゾツフイーの
「ステンレス鋼入門」（昭和48年特殊鋼倶楽部発
行）に記載されているように、夫々下限値より少
ない場合にはその特性が不十分であり、上限値よ
り多くしてもそれ以上の効果を生じない。このマトリツクス中の金属炭化物は、混合粉中
の黒鉛とステンレス鋼中の主としてクロムの反応
で生成され、鏡検するとマトリツクスのほぼ全域
に、点状および迷路のような線状を呈している。コバルト系の金属間化合物は球状に近い形をし
ていて、その硬さは、マイクロビツカース硬さで
700程度である。これには通常、Si：2.2〜2.6％、
Cr：7.5〜8.6％、Mo：27〜29％およびCo：残部
の市販の合金粉が好ましく、比較的柔らかい基地
に分散させると凝着摩耗を緩和させる作用があ
る。コバルト合金粉の添加量は５〜30％の範囲が好
ましく、その量が５％未満では作用効果が低下す
る。一方30％を越えると焼結合金が硬くなり過ぎ
て相手部材を損傷したり、あるいは混合粉の圧縮
性が悪くなるため焼結体の密度や強度が低くな
り、好ましくない。黒鉛粉は1.5〜４％添加する。この内の一部は
焼結中に前述のマトリツクス中の主としてクロム
と炭化物を形成し、残余は遊離炭素の形態で空孔
および粒界に残留する。添加量が1.5％未満では
遊離炭素が少なく潤滑効果が認められない。一方
添加量が４％を越えると焼結体の強度が低くなる
ので好ましくない。本発明の合金においては焼結温度は1100℃〜
1120℃が最適であり、1130℃を上限とする。その
理由は、この合金の特徴とする金属組織を確保す
るためである。即ち、その特徴の一つは、多量に
配合した黒鉛を遊離炭素の形態で残すことにあ
る。焼結温度がこれ以上に高くなると炭素の拡散
が著しく促進され、遊離炭素量が急減する一方、
マトリツクスの炭化物が粗大化して、耐摩耗性を
劣化させる。他の特徴は、原料粉に配合したケイ
素、クロムおよびモリブデンを含有する粒状のコ
バルト合金粉をそのまま合金相として残存、分散
させることにある。この合金粉は、多量の炭素と
共存する状態で、高温で、特に1140℃以上で焼結
すると拡散し、消失するので、凝着摩耗を緩和さ
せることができない。これらの理由から、焼結温
度は1130℃以下に止めなければならない。焼結合金の空孔量は特に限定しないが、通常の
焼結合金と同様に、材料の機械強度を考慮すると
約25％以下、即ち、焼結密度に換算すると5.9
ｇ／cm³以上であることが望ましい。実施例１先ず原料粉として第１表の試料１〜６の欄に示
す組成で粒度100メツシユ以下のオーステナイト
系ステンレス鋼粉６種；組成がSi：2.5％、Cr：
8.1％、Mo：27.8％およびCo：残部で粒度が100
メツシユ以下のコバルト合金粉；それに平均粒径
が5μの天然黒鉛粉を準備した。次にこれらの原料粉を第１表に示す割合に配合
し、成形潤滑剤として１％のステアリン酸亜鉛を
添加して充分に混合した。そして、夫々の混合粉
を成形圧力6t／cm²で所定の形状に圧縮成形後、分
解アンモニアガス雰囲気炉中温度1100℃で30分間
焼結し、焼結密度6.1ｇ／cm³の圧環強度測定用お
よび摩耗試験用の各試料（試料番号１〜15）を作
製した。摩耗試験用試料の形状は内径８mm、外形
13mm、全長35mmの軸受形である。また、比較のためにSUS304ステンレス鋼（溶
製材）のブロツクおよび黒鉛のブロツクから試料
を作成し、夫々試料16，17とした。摩耗試験は、温度500℃に保つた軸受試料に
SUS304ステンレス鋼（9Ni−19Cr）の軸を挿入
し、この軸に１Kgの荷重を加えた状態で軸を10mm
のストロークで軸方向に毎分60回往復動させ、30
時間経過後、軸受と軸の摩耗量を測定した。各試料についての圧環強さ、摩耗量の試験結果
ならびに摩耗試験における凝着状況は、第１表に
示す通りである。試料番号１〜６は、コバルト合金粉と黒鉛粉の
添加量を一定としてステンレス鋼粉の組成の影響
を見たもので、試料１〜４はその組成、合金組織
ともこの発明の範囲内にあり、試料、相手軸とも
に摩耗が少ない優れた結果を示している。これに
対して、試料５はステンレス鋼粉中のCr量が、
試料６はNi量が範囲外であり、これらは試料、
相手軸ともに摩耗量が多くなつている。試料番号７〜15は、ステンレス鋼粉の種類を最
良の結果が得られた試料３で用いたものに一定し
て、コバルト合金粉と黒鉛粉の添加量を変えてそ
の影響を見たものである。その結果を試料３と比
較すると、コバルト合金粉は試料７，８が示すよ
うに、減少すると圧環強さは向上するものの耐摩
耗性は低下し、増加すると圧環強さは低下するが
耐摩耗性は向上する。黒鉛粉も試料９，10が示す
通り、コバルト合金粉の場合と同様の傾向を示し
ている。ただし、試料７〜10はその特性が後述の
比較材や従来材に比べて著しく高く、充分実用で
きる域にある。これに対して試料11はコバルト合金粉を更に減
量したため全体組成中のモリブデンとコバルトが
範囲外（不足）になり、また、試料12は更に増量
したためコバルトが範囲外（過剰）になつたもの
で、両者とも試料および相手軸の摩耗が増加して
いる。試料13，14は黒鉛に関するものであり、黒
鉛の場合は相手軸に対する影響は少ないものの、
自己の摩耗量は、不足、過剰のとちらの場合も多
くなつている。試料15は、コバルト合金粉も黒鉛粉も省いてス
テンレス鋼粉単味を焼結したもので、圧環強さは
高いが、試料自身および相手軸の摩耗が全試料の
中で最も多くなつている。なお、コバルト合金粉
の添加量が不足の試料11、黒鉛粉の添加量が不足
の試料13ならびにこの試料15の場合に、摩擦によ
る凝着現象が認められた。試料16はステンレス鋼SUS304の溶製材で、焼
結材（試料15）ほどではないが試料、軸とも摩耗
が多く、凝着も認められた。試料17の黒鉛材は、相手軸を傷付けることはな
いが試料自体の摩耗が多く、試験の途中で割れを
生じたため摩耗試験を中断した。 The present invention relates to a sintered alloy suitable for bearings used in harsh environments such as high-temperature and corrosive atmospheres, and a method for manufacturing the same. [Conventional problems] In internal combustion engines such as automobiles and motorcycles, exhaust control valves are sometimes installed in the exhaust system to optimize output characteristics, but there are problems with the bearings that support the valve shafts. It was hot. That is, the exhaust gas generally has a high temperature of 500° C. or higher, so lubricating oil cannot be used for the bearings, and since the exhaust gas contains various corrosive components, the wear of the bearings is accelerated. For this reason, not only graphite, which has excellent properties under normal conditions, but also stainless steel, which is a common heat-resistant material, cannot reach the required design life.
The development of new materials was desired. [Means for Solving the Problem] This invention was made based on the above-mentioned background, and although it is basically a stainless steel system,
By using a powder metallurgy method in its production, we were able to achieve an optimal composition and alloy structure, thereby improving wear resistance in harsh environments. That is, the sintered alloy according to the present invention (hereinafter, unless otherwise specified, the composition is based on weight) has an overall composition of carbon: 1.5 to 4%, Si: 0.1 to 0.8%, Cr: 13 to 25%, Ni: 5. ~21% Mo: 1.3~10.7%, Co: 3~19%, and iron: the balance, and the alloy structure is 5~30% between a matrix of nickel-chromium stainless steel with metal carbides dispersed.
It is characterized by exhibiting a structure in which a granular cobalt alloy phase containing silicon, chromium, and molybdenum and free carbon are dispersed. In addition, the invention of a manufacturing method that reliably realizes such an alloy structure has a composition of Ni: 8-22% and Cr: 16-16%.
26% and iron: balance; or Ni: 8-22%,
Cr: 16 to 26%, Mo: 3% or less, iron: remaining austenitic stainless steel powder, Si: 2.2 to
2.6%, Cr: 7.5~8.6%, Mo: 27~29% and
Co: remaining cobalt alloy powder 5-30% and graphite powder 1.5%
The gist of the method is to use a mixed powder containing ~4% as a raw material. [Function] Hereinafter, the function and effect of the above-mentioned alloy composition and metal structure will be explained. The basic concept of the present invention is to use austenitic stainless steel for the matrix to provide heat resistance, and to strengthen the base by dispersing metal carbides mainly composed of chromium in the matrix, and to further strengthen the matrix by using hard cobalt-based intermetallic compound particles. The objective is to increase the resistance to adhesive wear by dispersing the graphite, and to strengthen the friction and wear resistance by the solid lubricating action of free graphite. Austenitic stainless steel has a nickel and chromium content of Ni: 8 to 22% and Cr: 16 to 26%.
Those within the range of are used. Furthermore, this austenitic stainless steel is
Those containing 2 to 3% Mo (for example, JIS
SUS316L) may be used. Stainless steel types with Mo content exceeding 3% and steel types containing Cu have high hardness.
This is not preferred because the compressibility of the powder is poor. For the same reason, steel powder with a low carbon content is preferred. Ni and Cr in stainless steel are elements that form a solid solution in the iron matrix and improve its corrosion resistance and heat resistance. The composition range is, for example, as described in the original author Zotsufi's "Introduction to Stainless Steel" (published by the Special Steel Club in 1971), if it is less than the lower limit, the properties are insufficient, and if it is less than the upper limit. Even if the amount is increased, no further effect will be produced. The metal carbide in this matrix is produced by a reaction between the graphite in the mixed powder and the chromium in the stainless steel, and when examined under a microscope, it appears dotted and labyrinth-like lines over almost the entire area of the matrix. Cobalt-based intermetallic compounds have an almost spherical shape, and their hardness is measured by the microbits hardness.
It is about 700. This typically includes Si: 2.2-2.6%;
A commercially available alloy powder containing Cr: 7.5 to 8.6%, Mo: 27 to 29%, and Co: the balance is preferred, and when dispersed in a relatively soft base, it has the effect of alleviating adhesive wear. The amount of cobalt alloy powder added is preferably in the range of 5 to 30%, and if the amount is less than 5%, the effect will decrease. On the other hand, if it exceeds 30%, the sintered alloy becomes too hard and may damage the mating member, or the compressibility of the mixed powder becomes poor, resulting in a low density and strength of the sintered body, which is not preferable. Graphite powder is added in an amount of 1.5 to 4%. A portion of this forms carbides during sintering, primarily with chromium in the aforementioned matrix, and the remainder remains in the form of free carbon in the pores and grain boundaries. If the amount added is less than 1.5%, there is little free carbon and no lubricating effect is observed. On the other hand, if the amount added exceeds 4%, the strength of the sintered body decreases, which is not preferable. In the alloy of the present invention, the sintering temperature is 1100℃~
The optimum temperature is 1120°C, and the upper limit is 1130°C. The reason for this is to ensure the characteristic metal structure of this alloy. That is, one of its characteristics is that a large amount of graphite blended remains in the form of free carbon. If the sintering temperature is higher than this, carbon diffusion will be significantly promoted and the amount of free carbon will decrease rapidly.
The carbides in the matrix become coarse and the wear resistance deteriorates. Another feature is that the granular cobalt alloy powder containing silicon, chromium, and molybdenum blended into the raw material powder remains and is dispersed as an alloy phase. When this alloy powder coexists with a large amount of carbon and is sintered at high temperatures, particularly at 1140° C. or higher, it diffuses and disappears, making it impossible to alleviate adhesive wear. For these reasons, the sintering temperature must be kept below 1130°C. The amount of pores in the sintered alloy is not particularly limited, but as with normal sintered alloys, considering the mechanical strength of the material, it is approximately 25% or less, or 5.9 when converted to sintered density.
It is desirable that it is at least g/cm ³ . Example 1 First, six types of austenitic stainless steel powders having a particle size of 100 mesh or less with the compositions shown in the columns of Samples 1 to 6 in Table 1 were used as raw material powder; the composition was Si: 2.5%, Cr:
8.1%, Mo: 27.8% and Co: balance with particle size of 100
Cobalt alloy powder with a mesh size or smaller; and natural graphite powder with an average particle size of 5μ were prepared. Next, these raw material powders were blended in the proportions shown in Table 1, 1% zinc stearate was added as a molding lubricant, and the mixture was thoroughly mixed. After compression molding each mixed powder into a predetermined shape at a molding pressure of 6 t/cm ² , it was sintered in a decomposed ammonia gas atmosphere furnace at a temperature of 1100°C for 30 minutes, and the radial crushing strength was measured at a sintered density of 6.1 g/cm ³ Samples (sample numbers 1 to 15) were prepared for use and wear tests. The shape of the sample for the wear test is 8 mm in inner diameter and outer diameter.
It is a bearing type with a length of 13mm and a total length of 35mm. In addition, for comparison, samples were prepared from SUS304 stainless steel (molten material) blocks and graphite blocks, and were designated Samples 16 and 17, respectively. The wear test was performed on bearing samples kept at a temperature of 500℃.
Insert a SUS304 stainless steel (9Ni-19Cr) shaft, and with a 1Kg load applied to this shaft, extend the shaft 10mm.
It reciprocates in the axial direction 60 times per minute with a stroke of 30
After time had elapsed, the amount of wear on the bearing and shaft was measured. The test results of the radial crushing strength and amount of wear for each sample, as well as the adhesion status in the wear test, are shown in Table 1. Sample numbers 1 to 6 were used to examine the influence of the composition of stainless steel powder while keeping the amounts of cobalt alloy powder and graphite powder constant, and samples 1 to 4 are within the scope of this invention in both their composition and alloy structure. , showing excellent results with little wear on both the sample and the mating shaft. On the other hand, in sample 5, the amount of Cr in the stainless steel powder was
Sample 6 has a Ni amount outside the range, and these samples
The amount of wear on both mating shafts is increasing. For samples 7 to 15, the type of stainless steel powder used was the same as that used in sample 3, which gave the best results, and the amount of cobalt alloy powder and graphite powder added was changed to see the effect. be. Comparing the results with Sample 3, as shown in Samples 7 and 8, when cobalt alloy powder decreases, the radial crushing strength improves but the wear resistance decreases, and when it increases, the radial crushing strength decreases but the wear resistance decreases. will improve. Graphite powder also shows the same tendency as the cobalt alloy powder, as shown by samples 9 and 10. However, the characteristics of Samples 7 to 10 are significantly higher than those of the comparative materials and conventional materials described below, and are in a range that is sufficiently practical. On the other hand, in sample 11, the amount of cobalt alloy powder was further reduced, so molybdenum and cobalt in the overall composition were out of range (insufficient), and in sample 12, the amount was further increased, so cobalt was out of range (in excess). In both cases, the wear of the sample and the mating shaft increased. Samples 13 and 14 are related to graphite, and in the case of graphite, although the effect on the mating shaft is small,
The amount of self-wear is becoming more and more often both insufficient and excessive. Sample 15 is made by sintering only stainless steel powder without cobalt alloy powder or graphite powder, and has high radial crushing strength, but the wear of the sample itself and the mating shaft is the highest among all samples. . Incidentally, adhesion due to friction was observed in sample 11 in which the amount of cobalt alloy powder added was insufficient, sample 13 in which the amount of graphite powder was added was insufficient, and sample 15. Sample 16 is a melted stainless steel SUS304, and although not as severe as the sintered material (sample 15), both the sample and the shaft had a lot of wear, and adhesion was also observed. Although the graphite material of sample 17 did not damage the mating shaft, the sample itself suffered a lot of wear and cracking occurred during the test, so the wear test was discontinued.

【表】実施例２次に実施例１の摩耗試験で好成績を示した試料
２と試料３の本発明材について、実機に近い条件
で、溶製ステンレス材（試料16）および黒鉛材
（試料17）との比較試験を行なつた。その結果は
以下の通りである。試験装置は大型自動二輪車の排気管を利用した
もので、その管内にはステンレス鋼SUS304（9Ni
−19Cr）製の排気制御弁が装着されている。試
験の対象部品はこの弁の軸を支える軸受で、その
寸法は内径10mm、外形17mm、全長20mmである。従
つて各試料はこの寸法に作られているが、それぞ
れの製造条件は実施例１の場合と同一である。排気制御弁の軸は、駆動機構により0.5秒で半
回転正転、0.5秒間停止、0.5秒で半回転逆転、0.5
秒間停止を１サイクルとする揺動を反復するよう
設定され、同時に、軸には１Kgの荷重が負荷され
ている。そして、排気管内にはプロパン燃焼ガス
を連続して流し、軸受の近傍を温度500℃に常時
保つてある。この試験装置の軸受部に各試料を順に装着して
５万回揺動させた結果は、試料16の溶製ステンレ
ス材が81μ（軸の摩耗は51μ）、試料17の黒鉛材が
124μ（軸は摩耗せず）も摩耗したのに対して、試
料２、試料３の本発明材の摩耗はどちらも7μ（軸
の摩耗は2μ）に過ぎず、その優れた耐摩耗性を
実証した。以上に詳述した通り、本発明によれば、従来の
材質が早期に劣化、摩耗するような過酷な条件、
例えば高温の排気ガス中での使用に耐え得る軸受
を容易に得ることができる。従つてこの発明は、
その様な用途の装置の設計を可能にすると同時に
焼結合金の用途を拡大したものでもある。[Table] Example 2 Next, the materials of the present invention, Samples 2 and 3, which showed good results in the wear test of Example 1, were tested under conditions close to those of the actual machine. ). The results are as follows. The test device used the exhaust pipe of a large motorcycle, and inside the pipe was stainless steel SUS304 (9Ni).
-19Cr) exhaust control valve is installed. The part to be tested is the bearing that supports the shaft of this valve, and its dimensions are 10 mm in inner diameter, 17 mm in outer diameter, and 20 mm in total length. Therefore, each sample was manufactured to these dimensions, but the manufacturing conditions for each were the same as in Example 1. The shaft of the exhaust control valve rotates forward for half a turn in 0.5 seconds, stops for 0.5 seconds, reverses for half a turn in 0.5 seconds, and rotates in the reverse direction for 0.5 seconds.
It is set to repeat rocking with one cycle of stopping for seconds, and at the same time, a load of 1 kg is applied to the shaft. Propane combustion gas is continuously flowed into the exhaust pipe to keep the area near the bearing at a constant temperature of 500°C. Each sample was sequentially mounted on the bearing of this test device and swung 50,000 times.The results showed that sample 16, a molten stainless steel material, had a wear of 81μ (shaft wear was 51μ), and sample 17, a graphite material.
The wear was 124μ (shaft not worn), whereas the inventive material of Samples 2 and 3 only wore 7μ (shaft wear was 2μ), demonstrating their excellent wear resistance. did. As detailed above, according to the present invention, it is possible to overcome harsh conditions where conventional materials deteriorate and wear out quickly.
For example, a bearing that can withstand use in high-temperature exhaust gas can be easily obtained. Therefore, this invention
This makes it possible to design equipment for such uses, and at the same time expands the uses of sintered alloys.

Claims

[Claims] In terms of 1% by weight, the total composition is: Carbon: 1.5-4%, Si: 0.1-0.8%, Cr: 13-25%, Ni: 5-21%, Mo: 1.3-10.7%, Co: The alloy structure consists of granular cobalt containing 5 to 30% silicon, chromium, and molybdenum between a matrix of nickel-chromium stainless steel in which metal carbides are dispersed. A sintered alloy for bearings that can withstand high temperatures and is characterized by a structure in which alloy phases and free carbon are dispersed. 2 1.5% to 4% graphite powder, 5 to 30% by weight
In the method for producing a sintered alloy, the composition of the cobalt alloy powder is Si: 2.2 to 2.6%, Cr: 7.5 to 8.6%, Mo：27～29
%, Co: the remaining alloy powder, the austenitic stainless steel powder has a composition of Ni: 8-22%,
Cr: 16 to 26% and iron: balance; or Ni: 8 to 22%, Cr: 16 to 26%, Mo: 3% or less, and iron: balance using alloy powder, sintering at a low temperature of 1130℃ or less. The overall composition in weight percent is: Carbon: 1.5-4%, Si: 0.1-0.8%, Cr: 13-25%, Ni: 5-21%, Mo: 1.3-10.7%, Co: A granular cobalt alloy containing 5 to 30% silicon, chromium, and molybdenum between a matrix of nickel-chromium stainless steel in which metal carbides are dispersed. A method for manufacturing a sintered alloy for bearings that can withstand high temperatures and exhibits a structure in which phases and free carbon are dispersed.