JP2005226141A - Method for manufacturing graphite-dispersed sintered member - Google Patents
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本発明は、黒鉛分散焼結部材の製造方法に係り、特に、摺動特性および被削性に優れ、その結果各種摺動部材等に好適な黒鉛分散焼結部材の製造技術に関する。 The present invention relates to a method for producing a graphite dispersed sintered member, and in particular, to a technique for producing a graphite dispersed sintered member that is excellent in sliding characteristics and machinability, and is therefore suitable for various sliding members.
鋳鉄は、安価なことから構造材料として多用されているが、基地中に黒鉛が分散して摺動特性が良好なことから摺動材料としても多用されている。このように、特に摺動材料としても好適に使用されている鋳鉄は、２〜６質量％超の炭素を含有するとともに、１〜５質量％程度、多いものでは１５質量％までの珪素を含有する。このような組成に起因して、鋳鉄には、珪素の黒鉛排出作用（黒鉛安定化作用）がある。この作用により、鉄基地に固溶する炭素量が低減され、過剰なセメンタイトの析出が抑制される。その結果、鋳鉄の組織は、パーライト、フェライトまたはこれらの混合相となり、余剰の炭素を遊離黒鉛として析出させることができる。このような鋳鉄においては、基地中に分散する遊離黒鉛が固体潤滑剤として機能することで、良好な摺動特性が実現される。以上のような特性を有する鋳鉄を使用して機械部品等を製造する場合には、通常、鋳造法が用いられるが、量産性に富む粉末冶金法においても種々の検討がなされている。 Cast iron is widely used as a structural material because it is inexpensive, but it is also frequently used as a sliding material because graphite is dispersed in the matrix and has good sliding characteristics. As described above, cast iron that is also preferably used as a sliding material contains more than 2 to 6% by mass of carbon, and about 1 to 5% by mass, and most of which contains up to 15% by mass of silicon. To do. Due to such a composition, cast iron has silicon graphite discharging action (graphite stabilizing action). By this action, the amount of carbon dissolved in the iron base is reduced, and excessive precipitation of cementite is suppressed. As a result, the structure of cast iron becomes pearlite, ferrite or a mixed phase thereof, and excess carbon can be precipitated as free graphite. In such cast iron, the free graphite dispersed in the matrix functions as a solid lubricant, so that good sliding characteristics are realized. In the case of producing machine parts or the like using cast iron having the above characteristics, a casting method is usually used, but various studies have been made also in a powder metallurgy method having high mass productivity.
すなわち、例えば、鉄粉末に３〜８質量％の黒鉛粉末と１〜５質量％の珪素粉末とを添加混合して混合粉末を形成し、または鉄粉末に３〜８質量％の黒鉛粉末と珪素成分として１〜５質量％の珪素鉄合金粉末とを添加混合して混合粉末を形成し、次いでこれらの混合粉末を所要の形状に成形して圧粉体を形成した後、これらの圧粉体を中性または還元性雰囲気に調整した加熱炉内で１１００〜１１５０℃の温度で３０〜６０分焼結する製造方法、並びにこのような製造方法により得られた焼結摺動部材が提案されている（特許文献１参照）。この技術は、珪素を珪素粉末あるいはフェロシリコン粉末の形態で付与し、珪素を鉄基地中に拡散させることにより、上記の鋳鉄組織を粉末冶金法で得ようとするものである。 That is, for example, 3-8 mass% graphite powder and 1-5 mass% silicon powder are added to iron powder and mixed to form a mixed powder, or 3-8 mass% graphite powder and silicon are added to iron powder. After adding and mixing 1 to 5% by mass of silicon iron alloy powder as a component to form a mixed powder, these mixed powders are molded into a required shape to form a green compact, and then these green compacts Proposed is a method for sintering in a heating furnace adjusted to a neutral or reducing atmosphere at a temperature of 1100 to 1150 ° C. for 30 to 60 minutes, and a sintered sliding member obtained by such a manufacturing method. (See Patent Document 1). In this technique, silicon is applied in the form of silicon powder or ferrosilicon powder, and silicon is diffused into the iron matrix, so that the cast iron structure is obtained by the powder metallurgy method.
しかしながら、特許文献１に記載されている技術のように、珪素の供給源として珪素粉末を用いた場合には、珪素粉末が酸化され易いことから、珪素粉末の保管状況によっては珪素粉末の酸化量が著しく変動するおそれがある。この酸化量分の酸素は焼結時に黒鉛粉末の炭素と化合してＣＯガスとして離脱する。このため、部材中に残留する炭素量がその分減少することとなり、珪素粉末の酸化量が変動すると析出する遊離黒鉛の分散量が変動したり、遊離黒鉛が十分に析出しない等の、遊離黒鉛析出量に関する安定性を損なうという問題が生じる。したがって、例えば、遊離黒鉛が十分に析出しない場合には、遊離黒鉛が固体潤滑剤として十分に機能し得ないため、焼結部材において優れた摺動性が得られない。 However, when the silicon powder is used as the silicon supply source as in the technique described in Patent Document 1, the silicon powder is easily oxidized. Therefore, depending on the storage state of the silicon powder, the oxidation amount of the silicon powder May fluctuate significantly. This oxidation amount of oxygen combines with the carbon of the graphite powder during sintering and leaves as CO gas. For this reason, the amount of carbon remaining in the member is reduced by that amount, and the amount of free graphite that precipitates fluctuates when the oxidation amount of the silicon powder fluctuates, or the free graphite does not precipitate sufficiently. There arises a problem that the stability relating to the amount of precipitation is impaired. Therefore, for example, when free graphite does not sufficiently precipitate, the free graphite cannot sufficiently function as a solid lubricant, so that excellent slidability cannot be obtained in the sintered member.
また、珪素供給源としてフェロシリコン粉末を用いた場合には、上述した珪素の酸化による遊離黒鉛析出量の変動の問題は回避できる。しかしながら、珪素は少量で鉄基地の塑性を低下させ、硬さを増加させる元素であるため、原料の混合粉末の圧縮性を低下させるおそれがある。例えば、全体として珪素が３質量％となるように珪素量が２０質量％のフェロシリコン粉末を用いる場合には、１５質量％もの硬質のフェロシリコン粉末を与える必要があり、このため、混合粉末全体としての圧縮性が著しく低下する。この圧縮性の低下は、成形体密度、ひいては焼結体密度の低下をもたらし、その結果、焼結部材表面の硬度を低下させ、焼結部材において優れた摺動性が得られない。 Further, when ferrosilicon powder is used as the silicon supply source, the above-described problem of fluctuations in the amount of free graphite deposited due to silicon oxidation can be avoided. However, since silicon is an element that decreases the plasticity of the iron base and increases the hardness in a small amount, there is a possibility that the compressibility of the mixed powder of the raw material may be decreased. For example, when using a ferrosilicon powder having a silicon content of 20% by mass so that silicon is 3% by mass as a whole, it is necessary to provide a hard ferrosilicon powder of 15% by mass. As a result, the compressibility is significantly reduced. This decrease in compressibility results in a decrease in the density of the compact, and consequently the density of the sintered body. As a result, the hardness of the surface of the sintered member is decreased, and excellent slidability cannot be obtained in the sintered member.
さらに、上記特許文献１にしたがって、珪素供給源として珪素粉末を用いる場合には、遊離黒鉛析出量に関する安定性が低いことにより、遊離黒鉛が固体潤滑剤として十分に機能せず、このため、優れた被削性も得れない。また、珪素供給源としてフェロシリコン粉末を用いる場合にも、混合粉末全体の圧縮性の低下に伴う焼結部材表面の硬度の低下により、優れた被削性を実現することができない。 Furthermore, when using silicon powder as the silicon supply source according to the above-mentioned Patent Document 1, free graphite does not function sufficiently as a solid lubricant due to low stability with respect to the amount of free graphite deposited. High machinability cannot be obtained. Even when ferrosilicon powder is used as the silicon supply source, excellent machinability cannot be realized due to a decrease in hardness of the surface of the sintered member accompanying a decrease in compressibility of the entire mixed powder.
よって、本発明は、上記事情に鑑みてなされたものであり、全体組成中の炭素量が１質量％以上で、過剰なセメンタイトが析出せず、パーライトとフェライトとの少なくとも一方の基地中に、遊離黒鉛が分散する鋳鉄組織を呈する黒鉛分散焼結部材の製造を前提としており、供給源としての珪素の保管が容易で、安定した黒鉛析出量を確保することができ、しかも混合粉末全体の圧縮性を低下させずに、鉄基地中に遊離黒鉛を十分に分散させることにより、優れた摺動特性と被削性とを実現する黒鉛分散焼結部材の製造方法を提供することを目的としている。 Therefore, the present invention has been made in view of the above circumstances, the amount of carbon in the overall composition is 1% by mass or more, excessive cementite does not precipitate, in at least one base of pearlite and ferrite, Based on the premise of producing a graphite dispersion sintered member exhibiting a cast iron structure in which free graphite is dispersed, it is easy to store silicon as a supply source, and a stable amount of graphite precipitation can be secured, and the entire mixed powder is compressed. An object of the present invention is to provide a method for producing a graphite-dispersed sintered member that realizes excellent sliding characteristics and machinability by sufficiently dispersing free graphite in an iron base without lowering the workability. .
本発明者らは、上述したような、所望の黒鉛分散焼結部材の製造方法について鋭意研究を重ねた。その結果、従来のように珪素供給源として珪素粉末やフェロシリコン粉末を用いる代わりに炭化珪素粉末を用いるとともに、雰囲気および焼結温度の適正化を併せて図ることで、炭化珪素が分解して珪素が鉄基地中に拡散し、これにより、珪素による黒鉛排出作用が効果的に奏されるとともに、炭化珪素から分解した炭素も遊離黒鉛として析出し、その結果、鉄基地中に遊離黒鉛が安定的に分散する黒鉛分散焼結部材が得られるとの知見を得た。本発明は、上記知見に鑑みてなされたものである。 The inventors of the present invention have made extensive studies on a method for producing a desired graphite dispersion sintered member as described above. As a result, silicon carbide powder is used in place of silicon powder or ferrosilicon powder as a silicon supply source as in the past, and the atmosphere and sintering temperature are optimized together, so that silicon carbide decomposes and silicon Diffuses into the iron base, thereby effectively exerting the graphite discharging action by silicon, and carbon decomposed from silicon carbide also precipitates as free graphite. As a result, the free graphite is stable in the iron base. The knowledge that a graphite dispersion sintered member that disperses in the powder is obtained. The present invention has been made in view of the above findings.
すなわち、本発明の一の黒鉛分散焼結部材の製造方法（第１発明）は、鉄基原料粉末に、３．３〜５質量％の炭化珪素粉末を添加して混合し、混合粉末を所定形状に成形した後、非酸化性雰囲気中１１００〜１２５０℃で焼結して、炭化珪素粉末を分解させるとともに、鉄基地中に遊離黒鉛を分散させることを特徴としている。また、本発明の他の黒鉛分散焼結部材の製造方法（第２発明）は、鉄基原料粉末に、０．７〜５質量％の炭化珪素粉末と、０．８〜５質量％の黒鉛粉末とを添加して混合し、混合粉末を所定形状に成形した後、非酸化性雰囲気中１１００〜１２５０℃で焼結して、炭化珪素粉末を分解させるとともに、鉄基地中に遊離黒鉛を分散させることを特徴としている。 That is, in the method for producing a graphite-dispersed sintered member of the present invention (first invention), 3.3 to 5% by mass of silicon carbide powder is added to and mixed with the iron-based raw material powder, and the mixed powder is predetermined. After being formed into a shape, it is sintered at 1100 to 1250 ° C. in a non-oxidizing atmosphere to decompose the silicon carbide powder and to disperse free graphite in the iron matrix. Moreover, the manufacturing method (2nd invention) of the other graphite dispersion | distribution sintered member of this invention is the iron-based raw material powder, 0.7-5 mass% silicon carbide powder, and 0.8-5 mass% graphite. After adding and mixing the powder, the mixed powder is molded into a predetermined shape, then sintered in a non-oxidizing atmosphere at 1100 to 1250 ° C. to decompose the silicon carbide powder and disperse the free graphite in the iron base It is characterized by letting.
ここで、鉄基原料粉末とは、粉末冶金法で一般に用いられる、鉄を主成分とする原料粉末を意味し、
(１)実質的に純粋な鉄粉末、
(２)鉄を主成分とし、他の元素と予め合金化した鉄合金粉末、
(３)鉄を主成分とし、他の元素あるいは合金が拡散結合されている部分拡散鉄合金粉末、または
(４)上記(１)〜(３)の少なくとも１種の粉末に、他の元素からなる粉末もしくは合金粉末を混合した混合粉末
等を示す。
Here, the iron-based raw material powder means a raw material powder mainly containing iron, which is generally used in powder metallurgy.
(1) substantially pure iron powder,
(2) Iron alloy powder mainly composed of iron and prealloyed with other elements,
(3) Partially diffused iron alloy powder mainly composed of iron and diffusion-bonded with other elements or alloys, or
(4) A mixed powder obtained by mixing at least one powder of (1) to (3) above with a powder of another element or an alloy powder is shown.
本発明の黒鉛分散焼結部材の製造方法は、珪素供給源として炭化珪素粉末を用いるもので、安定した黒鉛析出量が確保でき、しかも原料粉末の圧縮性の低下も僅かで、摺動特性や被削性に優れた黒鉛分散焼結部材を簡便に製造することが可能となる。また、本発明の製法により得られた焼結部材は、鉄基表面に好適に遊離黒鉛が分散していることから、優れた摺動特性と被削性とを有するものである。 The method for producing a graphite-dispersed sintered member of the present invention uses silicon carbide powder as a silicon supply source, can secure a stable amount of graphite precipitation, and has a slight decrease in compressibility of the raw material powder. It becomes possible to easily produce a graphite dispersion sintered member having excellent machinability. The sintered member obtained by the production method of the present invention has excellent sliding characteristics and machinability because free graphite is suitably dispersed on the iron base surface.
以下に、本発明の好適な実施形態を詳細に説明する。
本発明は、珪素供給源として炭化珪素粉末を用いることを最大の特徴としている。炭化珪素粉末は、単体では極めて安定で、高温でも容易には分解しないと考えられていたが、本発明者等は、鉄基原料粉末に炭化珪素粉末を与えた場合、焼結時に炭化珪素粉末が分解して焼結後に残留しないという現象に遭遇した。また、この焼結体を分析したところ、炭化珪素は、珪素と炭素とに分解して炭化珪素の珪素分が鉄基地に拡散して珪素による黒鉛排出作用が効果的に奏されるとともに、残余の炭素分が遊離黒鉛として析出して、炭化珪素として残留しないことを見出した。したがって、本発明の製造方法において得られる黒鉛分散焼結部材においては、炭化珪素は全て分解し、炭化珪素としては残留していない。
Hereinafter, preferred embodiments of the present invention will be described in detail.
The greatest feature of the present invention is the use of silicon carbide powder as a silicon supply source. Although silicon carbide powder was considered to be extremely stable as a simple substance and not easily decomposed even at high temperatures, the present inventors, when given silicon carbide powder to iron-based raw material powder, silicon carbide powder during sintering We encountered a phenomenon in which the material decomposes and does not remain after sintering. Further, when this sintered body was analyzed, silicon carbide was decomposed into silicon and carbon, and the silicon content of silicon carbide diffused into the iron base, and the graphite discharging action by silicon was effectively exhibited, and the remaining It was found that the carbon content of was precipitated as free graphite and did not remain as silicon carbide. Therefore, in the graphite dispersion sintered member obtained by the manufacturing method of the present invention, all silicon carbide is decomposed and does not remain as silicon carbide.
図１（ａ）は、本発明の一の製造方法により得た黒鉛分散焼結部材（純鉄粉末に３．３質量％の炭化珪素粉末のみを添加して焼結したもの）の、金属組織の顕微鏡観察写真である。同図によれば、炭素分として炭化珪素粉末しか添加していないにもかかわらず、鉄基地がパーライトとなっており、炭化珪素粉末が炭素と珪素に分解し、鉄基地中に炭素が拡散していることが判る。また、炭化珪素粉末３．３質量％は炭素分として約１質量％に相当するが、同図ではセメンタイトは観察されず、気孔中に遊離黒鉛の残留も確認されることから分解した珪素も鉄基地に拡散し黒鉛排出に作用していることが判る。さらに金属組織中に炭化珪素と思しき相は確認されない。 FIG. 1 (a) shows a metal structure of a graphite dispersion sintered member (sintered by adding only 3.3% by mass of silicon carbide powder to pure iron powder) obtained by one manufacturing method of the present invention. It is a microscopic observation photograph. According to the figure, even though only silicon carbide powder is added as carbon, the iron base is pearlite, the silicon carbide powder decomposes into carbon and silicon, and the carbon diffuses into the iron base. You can see that In addition, although 3.3% by mass of silicon carbide powder corresponds to about 1% by mass as carbon content, no cementite is observed in the figure, and the presence of free graphite in the pores is also confirmed. It can be seen that it diffuses into the base and acts on graphite discharge. Furthermore, a phase that seems to be silicon carbide is not confirmed in the metal structure.
また、図１（ｂ）は、本発明の他の製造方法により得た黒鉛分散焼結部材（純鉄粉末に４．０質量％の炭化珪素粉末のみを添加して焼結したもの）の、金属組織の顕微鏡観察写真で、図１（ａ）のものより炭化珪素粉末の添加量を増加させたものである。同図によれば、図１（ａ）の場合と同様に炭化珪素が分解した珪素と炭素（一部）が鉄基地中に拡散している様子が明らかで、鉄基地中に拡散した珪素量が図１（ａ）のものより多いことから、この時の炭素分は１．２質量％に相当するにもかかわらずセメンタイトの析出は確認されないばかりか、鉄基地中にフェライトの分散が認められる。なお、図１（ａ）と同様に金属組織中に炭化珪素と思しき相が存在しないことも判る。 FIG. 1 (b) shows a graphite dispersed sintered member obtained by another production method of the present invention (sintered by adding only 4.0% by mass of silicon carbide powder to pure iron powder). In the microscope observation photograph of a metal structure, the addition amount of silicon carbide powder is increased from that in FIG. According to the figure, it is clear that silicon and carbon (partially) decomposed from silicon carbide are diffused in the iron base as in FIG. 1A, and the amount of silicon diffused in the iron base. 1 is larger than that in FIG. 1 (a), so that although the carbon content at this time corresponds to 1.2% by mass, precipitation of cementite is not confirmed, and ferrite is dispersed in the iron matrix. . In addition, it turns out that the phase considered to be silicon carbide does not exist in a metal structure similarly to Fig.1 (a).
これらの図より炭化珪素が決して安定ではなく焼結過程で分解すること、および炭化珪素が分解した珪素と炭素の一部が鉄基地中に拡散して基地組織をパーライトまたはパーライトとフェライトの混合相とし、珪素による黒鉛排出作用により残部の炭素は遊離黒鉛として分散する鋳鉄組織が得られることが明らかである。 From these figures, silicon carbide is never stable and decomposes during the sintering process, and part of silicon and carbon decomposed by silicon carbide diffuses into the iron matrix, and the matrix structure is pearlite or a mixed phase of pearlite and ferrite. It is apparent that a cast iron structure in which the remaining carbon is dispersed as free graphite is obtained by the graphite discharging action by silicon.
このように、炭化珪素が焼結時になぜ分解するかについての詳細なメカニズムは未解明である。しかしながら、焼結時において、鉄基粉末表面は高温で、かつ酸化被膜が除去された極めて活性な状態にあるため、炭化珪素が触媒として作用して分解が生じると考えられる。ちなみに、炭化珪素のような従来安定と考えられてきた物質の中には、焼結環境において必ずしも安定ではなく、分解し易いものも存在する。例えば、特開２０００−６４００２号公報等に記載された発明も、そのような従来安定と考えられてきた物質（この場合は硫化物）が焼結環境で分解することに鑑みてなされたものである。 Thus, the detailed mechanism of why silicon carbide decomposes during sintering is not yet elucidated. However, at the time of sintering, the surface of the iron-based powder is at a high temperature and is in an extremely active state from which the oxide film has been removed. Therefore, it is considered that silicon carbide acts as a catalyst and decomposition occurs. Incidentally, some materials that have been conventionally considered to be stable, such as silicon carbide, are not always stable in the sintering environment and are easily decomposed. For example, the invention described in Japanese Patent Application Laid-Open No. 2000-64002 is also made in view of the fact that such a substance (in this case, sulfide) that has been considered stable in the past is decomposed in a sintering environment. is there.
このように、本発明の製造方法にしたがう焼結過程で分解する炭化珪素粉末は、常温では極めて安定であるため、珪素粉末のように酸化しない。このため、長期間保管しても酸化等の問題は生じない。また、炭化珪素粉末中の珪素量は７０質量％と高濃度である。このため、炭化珪素粉末は硬質ではあるが、混合粉末に占める添加量自体が低減できることから、混合粉末自体の圧縮性の低下も僅かである。 Thus, the silicon carbide powder that decomposes during the sintering process according to the manufacturing method of the present invention is extremely stable at room temperature, and thus does not oxidize like silicon powder. For this reason, problems such as oxidation do not occur even when stored for a long period of time. The silicon content in the silicon carbide powder is as high as 70% by mass. For this reason, although silicon carbide powder is hard, since the addition amount itself which occupies for mixed powder can be reduced, the fall of compressibility of mixed powder itself is also slight.
炭化珪素添加量が０．７質量％に満たないと、鉄基地に固溶する珪素が乏しくなり、遊離黒鉛が十分に析出しない。一方、炭化珪素量が５質量％を超えると、Ｆｅ−Ｓｉ−Ｃ共晶液相の発生が著しくなって焼結部材の型くずれが生じ、寸法精度が極めて低くなる。よって、珪素添加量の観点から、炭化珪素粉末の添加量は０．７〜５質量とする必要がある。なお、この炭化珪素添加量は、全体中の珪素量としては０．５〜３．５質量％に相当し、全体中の炭素量としては０．２〜１．５質量％に相当する。 If the amount of silicon carbide added is less than 0.7% by mass, the silicon dissolved in the iron base becomes insufficient, and free graphite is not sufficiently precipitated. On the other hand, when the amount of silicon carbide exceeds 5% by mass, the generation of the Fe—Si—C eutectic liquid phase becomes remarkable, and the sintered member is deformed, resulting in extremely low dimensional accuracy. Therefore, from the viewpoint of the silicon addition amount, the addition amount of the silicon carbide powder needs to be 0.7 to 5 mass. The amount of silicon carbide added corresponds to 0.5 to 3.5 mass% as the amount of silicon in the whole, and corresponds to 0.2 to 1.5 mass% as the amount of carbon in the whole.
次に、炭素量としては、摺動特性の観点によって必要な遊離黒鉛分散量を得るため、焼結部材の炭素量として１質量％を目標とする。しかしながら、上記の適正な珪素量の観点によって決定した炭化珪素粉末添加量では炭素量の欠乏が生じる。このため、必要な炭素量を炭化珪素粉末のみで与える場合には、炭化珪素粉末添加量の下限値を３．３質量％とする。また、炭素の欠乏分を黒鉛粉末の形態で添加して補う場合には、炭化珪素粉末添加量の下限値は０．７質量％とすることができる。ただし、黒鉛粉末の添加量が５質量％を超えると混合粉末の圧縮性が低下し、見掛け密度も低下する結果、焼結体強度が低下するため、黒鉛粉末を添加する場合には、その添加量は５質量％以下に止めるべきである。 Next, as the amount of carbon, in order to obtain a required amount of free graphite dispersion from the viewpoint of sliding characteristics, the target carbon amount of the sintered member is 1% by mass. However, the carbon amount deficiency occurs at the silicon carbide powder addition amount determined from the viewpoint of the appropriate silicon amount. For this reason, when the required amount of carbon is given only by silicon carbide powder, the lower limit of the amount of silicon carbide powder added is 3.3 mass%. When the carbon deficiency is added in the form of graphite powder, the lower limit value of the silicon carbide powder addition amount can be set to 0.7% by mass. However, if the added amount of graphite powder exceeds 5% by mass, the compressibility of the mixed powder decreases and the apparent density also decreases, resulting in a decrease in the strength of the sintered body. The amount should be kept below 5% by weight.
したがって、必要な珪素量と炭素量とを得るにあたり、炭素供給源として炭化珪素粉末のみとする場合には、上記第１発明の如く、鉄基原料粉末に炭化珪素粉末を３．３〜５質量％配合して混合した混合粉末を用いればよい。 Therefore, when only the silicon carbide powder is used as the carbon supply source for obtaining the necessary silicon amount and carbon amount, 3.3 to 5 mass of silicon carbide powder is added to the iron-based raw material powder as in the first invention. It is sufficient to use a mixed powder prepared by mixing and mixing%.
また、必要な珪素量と炭素量とを得るにあたり、炭素供給源に炭化珪素粉末と黒鉛粉末とを併用する場合には、上記第２発明の如く、鉄基原料粉末に炭化珪素粉末を０．７〜５質量％と黒鉛粉末を０．８〜５質量％配合して混合した混合粉末を用いればよい。 In addition, when silicon carbide powder and graphite powder are used in combination as a carbon supply source in obtaining the necessary silicon amount and carbon amount, the silicon carbide powder is added to the iron-based raw material powder in an amount of 0.0. What is necessary is just to use the mixed powder which mix | blended and mixed 7-5 mass% and graphite powder 0.8-5 mass%.
さらに、焼結は、非酸化性雰囲気中１１００〜１２５０℃で行う。焼結温度が１１００℃に満たないと、焼結部材の強度が低くなる他、上記の炭化珪素の分解が不十分となって遊離黒鉛の分散量が低下する。一方、１２５０℃を超えて焼結すると、焼結部材の型くずれが生じて寸法精度が低下する。また、雰囲気は非酸化性雰囲気とする必要がある。雰囲気を酸化性雰囲気とすると、酸化性雰囲気に含まれる酸素が焼結部材の炭素と結合して一酸化炭素ガスとして離脱し、遊離黒鉛量が低下するからである。さらに、焼結時間は３０〜１２０分が適当である。焼結時間が３０分に満たない場合には、粉末間の拡散が不十分となり、強度が低下する。一方、１２０分を超えて焼結した場合には、強度の向上の割に寸法精度の低下が著しい。 Furthermore, sintering is performed at 1100 to 1250 ° C. in a non-oxidizing atmosphere. When the sintering temperature is less than 1100 ° C., the strength of the sintered member is lowered, and the above-described decomposition of silicon carbide is insufficient and the amount of free graphite dispersed is lowered. On the other hand, when sintering is performed at a temperature exceeding 1250 ° C., the sintered member is deformed and the dimensional accuracy is lowered. The atmosphere must be a non-oxidizing atmosphere. This is because if the atmosphere is an oxidizing atmosphere, oxygen contained in the oxidizing atmosphere is combined with the carbon of the sintered member and separated as carbon monoxide gas, thereby reducing the amount of free graphite. Furthermore, the sintering time is suitably 30 to 120 minutes. When the sintering time is less than 30 minutes, the diffusion between the powders becomes insufficient and the strength is lowered. On the other hand, in the case of sintering for more than 120 minutes, the reduction in dimensional accuracy is remarkable for the improvement in strength.
純鉄粉末に、炭化珪素粉末のみを表１に示す割合で添加混合し、得られた混合粉末をφ７．８×２０の円柱形状に５００ＭＰａで圧粉成形した後、１１８０℃で焼結して試料番号０１〜０６の試料を作製した。これらの試料について、溶解法にて遊離黒鉛量を測定した。また、リングオンディスク摩擦摩耗試験機で摩擦試験を行った後の試料の摩耗量を測定した。これらの結果を表１に併記する。 Only silicon carbide powder was added to and mixed with pure iron powder in the ratio shown in Table 1, and the obtained mixed powder was compacted into a cylindrical shape of φ7.8 × 20 at 500 MPa, and then sintered at 1180 ° C. Samples with sample numbers 01 to 06 were prepared. For these samples, the amount of free graphite was measured by a dissolution method. Further, the amount of wear of the sample after the friction test was conducted with a ring-on-disk friction and wear tester was measured. These results are also shown in Table 1.
表１より、炭化珪素粉末の添加量が３．３質量％以上（試料番号０３〜０６）の場合には、遊離黒鉛の析出が認められ、炭化珪素粉末の添加量が０．７０質量％（試料番号０１）の場合に比して摩耗量が１／２以下となっている。また、炭化珪素粉末の添加量が増加するにしたがい、析出する遊離黒鉛量が増加し、摩耗量も減少している。ただし、炭化珪素粉末の添加量が５質量％を超えた（試料番号０６）の場合には、Ｆｅ−Ｓｉ−Ｃ共晶液相の発生量が多すぎて溶融し、焼結部材の型くずれが著しいため、遊離黒鉛量および摩耗量の測定を中止した。
From Table 1, when the addition amount of silicon carbide powder is 3.3 mass% or more (
以上のように遊離黒鉛の析出が認められた試料番号０３〜０５の試料、および溶融した試料番号０６の試料について金属組織を観察した。その結果を図２に示す。図２より、試料番号０３の試料は、全面パーライト組織となっており、炭化珪素粉末が珪素と炭素に分解したことがはっきりと判る。また、気孔中には黒鉛の存在が認められた。試料番号０４の試料では、炭化珪素粉末の添加量が試料番号０３の試料に比して増加したことにより、パーライト基地中にフェライト相が点在している。炭化珪素粉末の添加量をさらに増加した試料番号０５の試料では、炭化珪素粉末の添加量のさらなる増加により、フェライト相の増大、およびＦｅ−Ｓｉ−Ｃ共晶液相の発生による気孔の球状化が見られる。さらに、炭化珪素粉末の添加量が７質量％の試料番号０６の試料では、Ｆｅ−Ｓｉ−Ｃ共晶液相の発生量が多すぎて気孔が消失しており、片状黒鉛をフェライト相が取り囲み、残部がパーライトの鋳鉄のような組織を呈している。
As described above, the metal structures of the sample Nos. 03 to 05 in which the precipitation of free graphite was observed and the molten sample No. 06 were observed. The result is shown in FIG. From FIG. 2, it is clear that the sample of
以上の結果より、炭化珪素粉末が焼結過程で珪素と炭素とに分解し、両者が鉄基地に拡散すること、および基地に拡散した珪素の影響で炭素が遊離黒鉛として析出することが確認された。したがって、炭素供給源として炭化珪素粉末のみを用いる場合、その添加量が３．３質量％以上で遊離黒鉛が析出し、それに伴い耐摩耗性の向上が確認された。ただし、炭化珪素粉末の添加量が５質量％を超えるとＦｅ−Ｓｉ−Ｃ共晶液相の発生量が過多となり、焼結部材の型くずれが著しくなるため、炭化珪素粉末の添加量の上限値を５質量％に止める必要がある。 From the above results, it was confirmed that the silicon carbide powder decomposed into silicon and carbon during the sintering process, both diffused to the iron base, and carbon precipitated as free graphite under the influence of the silicon diffused to the base. It was. Therefore, when only silicon carbide powder was used as a carbon supply source, free graphite precipitated when the amount added was 3.3% by mass or more, and as a result, improved wear resistance was confirmed. However, if the amount of silicon carbide powder added exceeds 5% by mass, the amount of Fe-Si-C eutectic liquid phase generated will be excessive, and the shape of the sintered member will be severely deformed. Must be stopped at 5% by mass.
純鉄粉末に炭化珪素粉末と黒鉛粉末とを、炭素量が２質量％となるよう表２に示す割合で添加混合した混合粉末を用い、実施例１と同様にして試料番号０７〜１３の試料を作製するとともに、同様に遊離黒鉛量および摩耗量を測定した。これらの結果を表２に併記する。 Samples of sample numbers 07 to 13 were used in the same manner as in Example 1 using a mixed powder obtained by adding silicon carbide powder and graphite powder to pure iron powder at a ratio shown in Table 2 so that the carbon content was 2% by mass. In the same manner, the amount of free graphite and the amount of wear were measured. These results are also shown in Table 2.
表２より、炭化珪素粉末に加えて黒鉛粉末を用いる場合には、炭化珪素粉末の添加量が０．７質量％以上で十分な遊離黒鉛の析出が認められ、併せて摩耗量も微少なものとなることが判る。また、遊離黒鉛の析出は、炭化珪素粉末の添加量の増加にしたがい増加し、これに伴って摩耗量も減少している。ただし、炭化珪素粉末の添加量が５質量％を超えると、Ｆｅ−Ｓｉ−Ｃ共晶液相の発生量が過多となって焼結部材の型くずれが著しくなっている。なお、試料番号０７の試料について組織観察を行ったところ、基地に固溶する珪素量が乏しく、セメンタイトが多量に析出していることが確認された。以上より、炭素供給源に炭化珪素粉末と黒鉛粉末とを併用する場合の炭化珪素粉末の添加量が０．７質量％以上の場合には、遊離黒鉛の十分な析出および摩耗量の著しい減少が確認された。また、この場合の炭化珪素粉末の添加量の上限値は５質量％に止めることが必要であるも併せて確認された。 From Table 2, when graphite powder is used in addition to silicon carbide powder, precipitation of sufficient free graphite is recognized when the amount of silicon carbide powder added is 0.7% by mass or more, and the amount of wear is also small. It turns out that it becomes. In addition, the precipitation of free graphite increases as the amount of silicon carbide powder added increases, and the amount of wear decreases accordingly. However, if the amount of silicon carbide powder added exceeds 5% by mass, the amount of Fe—Si—C eutectic liquid phase generated becomes excessive, and the shape of the sintered member is significantly lost. Note that, when the structure of the sample of sample number 07 was observed, it was confirmed that the amount of silicon dissolved in the matrix was small and a large amount of cementite was precipitated. From the above, when the addition amount of silicon carbide powder in the case where silicon carbide powder and graphite powder are used in combination in the carbon supply source is 0.7% by mass or more, sufficient precipitation of free graphite and a significant decrease in the amount of wear are caused. confirmed. In addition, it was confirmed that the upper limit of the amount of silicon carbide powder added in this case needs to be limited to 5% by mass.
炭素供給源として炭化珪素粉末と黒鉛粉末とを併用して用いる場合において、黒鉛粉末の添加量の影響を調査するため、実施例２で好適であることが確認された炭化珪素粉末添加量の下限値（０．７質量％）の炭化珪素粉末に、表３に示す割合で黒鉛粉末の添加量を変化させた混合粉末を用い、実施例２と同様にして試料番号１４〜１９の試料を作製し、遊離黒鉛量および摩耗量を測定した。これらの結果を試料番号０８の試料とともに表３に併記する。 In the case where silicon carbide powder and graphite powder are used in combination as a carbon supply source, the lower limit of the silicon carbide powder addition amount confirmed to be suitable in Example 2 in order to investigate the influence of the addition amount of graphite powder. Samples Nos. 14 to 19 were prepared in the same manner as in Example 2 by using mixed powder in which the addition amount of graphite powder was changed in the ratio shown in Table 3 to silicon carbide powder having a value (0.7 mass%). The amount of free graphite and the amount of wear were measured. These results are shown in Table 3 together with the sample No. 08.
表３より、炭化珪素粉末の添加量が上記下限値の０．７質量％において、黒鉛粉末の添加量が０．８質量％以上で十分な遊離黒鉛の析出が認められ、併せて摩耗量の低減も認められる。また、黒鉛粉末の添加量が増加するにしたがい遊離黒鉛の析出量が増加し、摩耗量の低減が認められる。ただし、黒鉛粉末の添加量が５質量％を超える試料番号１９の試料では、圧縮性が低下することに伴い焼結後の基地強度が低下した結果、十分な遊離黒鉛の析出が認められるにもかかわらず、摩耗量が増加に転じている。したがって、黒鉛粉末の添加は０．８質量％以上の添加で効果があるが、５質量％までに止めるべきである。 From Table 3, when the addition amount of silicon carbide powder is 0.7% by mass of the above lower limit value, sufficient free graphite is precipitated when the addition amount of graphite powder is 0.8% by mass or more, and the amount of wear is also reduced. Reduction is also observed. Further, as the amount of graphite powder added increases, the amount of free graphite deposited increases, and a reduction in wear is observed. However, in the sample of Sample No. 19 in which the amount of graphite powder added exceeds 5% by mass, as the compressive strength decreases, the matrix strength after sintering decreases, and as a result, sufficient precipitation of free graphite is observed. Regardless, the amount of wear has begun to increase. Therefore, the addition of graphite powder is effective when added in an amount of 0.8% by mass or more, but should be stopped by 5% by mass.
実施例２の試料番号０９の試料において、鉄基原料粉末として用いた純鉄粉末を、純鉄粉末に１．５質量％の純銅粉末の混合粉末に変更した場合、および、組成がＣｒ：３質量％、Ｍｏ：０．３質量％、Ｖ：０．３質量％で残部がＦｅの合金粉末に変更した場合の結果を表４に示す。 In the sample of sample number 09 of Example 2, when the pure iron powder used as the iron-based raw material powder is changed to a mixed powder of 1.5 mass% pure copper powder in pure iron powder, and the composition is Cr: 3 Table 4 shows the results in the case of changing to an alloy powder in which the balance is Fe and the balance is Fe: 0.3% by mass, Mo: 0.3% by mass, V: 0.3% by mass.
表４より、鉄基原料粉末として、純鉄粉末に他の元素の粉末を混合した混合粉末、または鉄を主成分とし他の元素と予め合金化した鉄合金粉末を用いても、純鉄粉末を用いた場合と同様に、炭化珪素粉末の分解が生じて遊離黒鉛が析出し、摩耗量も減少することが確認された。なお、試料番号２１の試料の場合は炭素の一部がクロム炭化物として使用された結果、純鉄粉末を用いた場合よりも遊離黒鉛析出量が減少しているが、十分な量の遊離黒鉛が析出しており、鉄基地が合金化されて強化されることから摩耗量は却って減少していることが判る。以上より、鉄基原料粉末は純鉄粉末に限らず、鉄粉末の混合粉末や鉄合金粉末においても同様に炭化珪素が分解して遊離黒鉛が析出し、摩耗量が低減できることが確認された。 From Table 4, pure iron powder can be used as the iron-based raw material powder by using a mixed powder obtained by mixing pure iron powder with a powder of another element, or an iron alloy powder pre-alloyed with other elements containing iron as a main component. It was confirmed that the decomposition of the silicon carbide powder occurred, free graphite was precipitated, and the amount of wear was reduced as in the case of using. In the case of the sample of sample number 21, as a result of using a part of carbon as chromium carbide, the amount of precipitated free graphite is reduced as compared with the case of using pure iron powder. It can be seen that the amount of wear is reduced because the iron base is alloyed and strengthened by alloying. From the above, it has been confirmed that the iron-based raw material powder is not limited to pure iron powder, but also in a mixed powder of iron powder or iron alloy powder, silicon carbide is decomposed and free graphite is precipitated to reduce the amount of wear.
以上のように、本発明の黒鉛分散焼結部材の製造方法によれば、珪素供給源として炭化珪素粉末を用いることから、珪素供給源としての珪素の酸化が防止されて長期保管が可能であり、しかも添加粉末に占める珪素濃度が高いため、混合粉末に占める珪素を含む添加粉末量を低減することができ、これにより混合粉末自体の圧縮性の低下が僅かであるという格別の効果が得られる。これにより、焼結部材の優れた摺動性等が実現される。また、本発明の製造方法によれば、鉄基原料粉末として、純鉄粉末、純鉄粉の混合粉末、および鉄合金粉末等のいずれを用いることもできる。よって、本発明は、各種摺動部材や快削性部材等の製造に好適である。 As described above, according to the method for producing a graphite dispersion sintered member of the present invention, since silicon carbide powder is used as a silicon supply source, oxidation of silicon as a silicon supply source is prevented and long-term storage is possible. In addition, since the silicon concentration in the additive powder is high, the amount of the additive powder containing silicon in the mixed powder can be reduced, thereby obtaining a special effect that the compressibility of the mixed powder itself is slightly reduced. . Thereby, the outstanding slidability etc. of a sintered member are implement | achieved. Further, according to the production method of the present invention, any of pure iron powder, mixed powder of pure iron powder, iron alloy powder, and the like can be used as the iron-based raw material powder. Therefore, the present invention is suitable for manufacturing various sliding members and free-cutting members.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010069020A3 (en) * | 2008-12-15 | 2010-08-12 | Whirpool S.A. | Composition of particulate materials for forming self- lubricating products in sintered steel, product in self- lubricating sintered steel and process for obtaining self-lubricating products in sintered steel |
| WO2011153573A2 (en) | 2010-06-10 | 2011-12-15 | Miba Sinter Austria Gmbh | Component having reduced metal adhesion |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010069020A3 (en) * | 2008-12-15 | 2010-08-12 | Whirpool S.A. | Composition of particulate materials for forming self- lubricating products in sintered steel, product in self- lubricating sintered steel and process for obtaining self-lubricating products in sintered steel |
| JP2012512320A (en) * | 2008-12-15 | 2012-05-31 | ワールプール・エシ・ア | Composition of particulate material to form a self-lubricating product made of sintered steel, self-lubricating product made of sintered steel, and method of obtaining self-lubricating product made of sintered steel |
| CN102497948A (en) * | 2008-12-15 | 2012-06-13 | 惠而浦股份有限公司 | Composition of particulate materials for forming self- lubricating products in sintered steel, product in self- lubricating sintered steel and process for obtaining self-lubricating products in sintered steel |
| WO2011153573A2 (en) | 2010-06-10 | 2011-12-15 | Miba Sinter Austria Gmbh | Component having reduced metal adhesion |
| WO2011153573A3 (en) * | 2010-06-10 | 2013-03-21 | Miba Sinter Austria Gmbh | Component having reduced metal adhesion |
| CN103180069A (en) * | 2010-06-10 | 2013-06-26 | 米巴烧结奥地利有限公司 | Component made of an iron-based sinter-alloy having reduced metal adhesion |
| US9255575B2 (en) | 2010-06-10 | 2016-02-09 | Miba Sinter Austria Gmbh | Component having reduced metal adhesion |
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