JPS649367B2

JPS649367B2 -

Info

Publication number: JPS649367B2
Application number: JP8184281A
Authority: JP
Inventors: Hiroki Shimizu; Yoshio Naruse
Original assignee: Teikoku Piston Ring Co Ltd
Current assignee: TPR Co Ltd
Priority date: 1981-05-30
Filing date: 1981-05-30
Publication date: 1989-02-17
Also published as: JPS57200765A

Description

[Detailed description of the invention]

本発明は、二層焼結合金製弁座の製造方法に関
するものである。更に詳しく述べるならば、本発
明は耐脱落性にすぐれ、内燃機関用に有用な、二
層焼結合金製弁座の製造方法に関するものであ
る。内燃機関用弁座は、近年内燃機関に対する排出
ガス規制の高度化および高出力の要望が高まるに
つれて、ますます苛酷な条件下に耐えることが要
求されるようになつている。このため、従来の弁
座はCo、Mo、および／又は、Ｗなどの高価な合
金元素を多量に使用して製造されていた。しかし
ながら、一方では、省資源の要求が高まり、上記
の高価な合金元素の使用を節約することが要望さ
れている。上記の諸要望に対応するために、最近、弁座の
摺接面を形成する層を、高合金焼結合金材料をも
つて形成し、その他の基層を、低合金焼結合金材
料をもつて形成して、いわゆる二層焼結合金製弁
座が提案されている。上述のような、従来の二層焼結合金製弁座にお
いて、基層の役割は、弁と摺接する面を形成する
摺接層をバツクアツプするものであり、併せて、
高価な合金元素の使用量を低減することにある。
ところが、従来の二層焼結合金製弁座は、クリー
プ変形が大きく、耐脱落性が低いという欠点があ
つた。内燃機関用弁座は、耐磨耗性および耐熱性にす
ぐれていることが要求されるが、それに加えて、
クリープ変形が小さく、シリンダヘツドからの脱
落が少ないことも強く要求されている。一般に弁
座は、0.07〜0.15mmの締代でシリンダヘツドに圧
入、又は、焼ばめされ、高負荷および高温のもと
で使用される。シリンダヘツドが鋳鉄製であり、
弁座が鉄系焼結合金製の場合、シリンダヘツドの
熱膨張係数が、弁座のそれにくらべてやや小さい
か、或はほぼ同一である。このため、内燃機関作
動時の熱負荷により、弁座にクリープ変形（いわ
ゆるヘタリ）を生じ、内燃機関が停止してシリン
ダヘツドが冷却したとき、しばしば弁座がシリン
ダヘツドから脱落することがある。上記のような脱落を防止するためには、二層弁
座の摺接層は勿論、その基層も、クリープ変形が
小さく耐脱落性が高いことが必要である。すなわ
ち、二層弁座の基層は、単に摺接層をバツクアツ
プするに足る高強度を有していることだけでは不
十分であつて、耐クリープ性と耐脱落性とを有し
ていなければならない。また、従来の鉄系焼結合金弁座においては、通
常、焼結された合金粒子間に空孔が内在してい
る。このような弁座が、高温で使用されると、弁
座内の空孔の周囲の部分が、酸化され、このた
め、合金粒子間の金属結合の割合が低下し、弁座
の実作用圧縮応力が高くなる。この現象は、弁座
のクリープ変形を大きくし、従つて、弁座がシリ
ンダヘツドから脱落する原因となる。上記のよう
な問題点を解消するためには、弁座内の空孔を封
孔することが必要である。本発明の目的は、高耐熱性および高耐摩耗性に
加えて、クリープ変形が小さく、シリンダヘツド
からの耐脱落性の高い、二層焼結合金製弁座を製
造する方法を提供することにある。本発明の他の目的は、耐高温圧縮性の高い基層
を有する二層焼結合金製弁座を製造する方法を提
供することにある。本発明の更に他の目的は、封孔処理によつて、
耐酸化性の高い二層焼結合金製弁座を製造する方
法を提供することである。上記の目的を達成する本発明の二層焼結合金製
弁座の製造方法は、弁に摺接する面を形成してい
る摺接層と、それを支持している基層とからな
り、前記摺接層と基層とを、(1)５〜35％（重量）
の、下記組成：Ｃ１〜４％（重量） Cr 10〜30％（重量） Ni ２〜15％（重量） Mo 10〜30％（重量） Co 20〜40％（重量） Nb １〜５％（重量） Fe 残部（重量）を有する特殊合金粉末と、0.5〜1.5％（重量）の
黒鉛粉末と、残部の鉄粉末とからなる摺接層用混
合粉末と、(2)0.5〜５％（重量）のNiと、0.5〜５
％（重量）のCrと、および0.5〜５％（重量）の
Moとからなる群から選ばれた少くとも１員（但
し、２員以上の混合物の場合、それらの合計重量
は10％以下である。）と、0.5〜1.5％（重量）の
黒鉛粉末と、残部の鉄粉末とからなる基層用混合
粉末とを、所望形状に積層し、前記積層された両
混合粉末を同時に加圧成形し、焼結して１体の焼
結体に形成し、前記焼結体に、弁座総重量の５〜
25％のCu又はCu合金を溶浸し、そして、前記溶
浸焼結体に、400℃からA₁変態点までの温度の焼
なまし熱処理を施す、ことによつて形成すること
を特徴とするものである。本発明の方法において弁座の摺接層は、５〜35
重量％の特殊合金粉末と、0.5〜1.5重量％の黒鉛
粉末と残部の鉄粉末とからなる摺接層用混合粉末
を用いて作られる。前記特殊粉末は下記組成：Ｃ１〜４重量％ Cr 10〜30 〃 Ni ２〜15 〃 Mo 10〜30 〃 Co 20〜40 〃 Nb １〜５〃 Fe 残部〃を有するものである。上記組成中、Ｃは、Cr，
MoおよびNbと結合して耐摩耗性の高い複合炭化
物を形成する。Ｃの含有率は１〜４重量％であ
る。この含有率が１重量％未満のときは、得られ
る耐摩耗性複合炭化物の量が不十分となり、４重
量％をこえると得られる複合炭化物の析出粒子が
粗大化する。 CrおよびMoは、Nbとともに上記復合炭化物
を形成して、摺接層の耐摩耗性の向上に寄与す
る。また、CrおよびMoは、焼結の際に、焼結合
金の基地に拡散固溶して、摺接層の耐熱性向上に
寄与する。CrおよびMoの含有率は、それぞれ10
〜30重量％である。CrおよびMoの含有率が、そ
れぞれ10重量％未満のときは、上記耐摩耗性およ
び耐熱性向上に対する寄与が不十分であり、ま
た、30％をこえると、合金作成の際のインゴツト
の鋳造性が悪化し、かつ、得られる合金が高価と
なり経済的に不利になる。 Nbは、それ自身で炭化物Nbc，或は、Nb（C.
N）を形成するとともに、CrおよびMoと複合炭
化物を形成する。このとき、Nbは、炭化物粒子
の微細化にすぐれた効果を発揮する。Nbの含有
率は１〜５重量％である。Nbの含有率が１％未
満のときは、上記の効果が不十分であり、また５
％を越えると、得られるNb炭化物の粒子が粗大
化するので好ましくない。 NiおよびCoは、それぞれ、焼結の際に、焼結
合金の基地に拡散固溶し、摺接層の耐熱性向上に
寄与する。NiおよびCoの含有率は、それぞれ２
〜15重量％、および20〜40重量％である。Niお
よびCoの含有率が、それぞれの下限値に満ない
ときは、上記耐熱性向上効果が不十分であり、ま
た、上記上限値を越えても、上記効果は、格別増
進せず、却つて経済的に不利となる。上記特殊合金は、焼結の際に、焼結体の基地に
分散して、それ自体で摺接層の耐摩耗性の向上に
寄与するとともに、この特殊合金粒子中のNi，
Co，およびCrなどの成分元素の一部が、この特
殊合金粒子のまわりのFe相中に拡散固溶して、
その結果摺接層の焼結体基地の耐熱性を向上させ
る。摺接層用混合粉末中の特殊合金粉末の含有率
は、５〜35重量％である。その含有率が５重量％
未満のときは、得られる摺接層の耐摩耗性および
耐熱性が不満足なものとなり、また35重量％を越
えると、混合粉末の成形性を低下させる。摺接層用混合粉末中の黒鉛粉末の含有率は、
0.5〜1.5重量％である。この含有率が0.5重量％未
満では、得られる摺接層中のフエライトの析出量
が過大となり、摺接層の耐摩耗性が不十分とな
る。また、1.5重量％を越えると、セメンタイト
が、網目状に析出するようになり、得られる摺接
層が脆弱となる。本発明の方法において、弁座の基層（摺接層を
バツクアツプするバツクアツプ層）は、それぞれ
0.5〜５重量％のNi，Cr，およびMoからなる群
から選ばれた少くとも１員（２員以上の場合、そ
の合計重量は10％以下）を粉末と、0.5〜1.5重量
％の黒鉛粉末と、残部の鉄とからなる混合粉末を
用いて形成される。基層用混合粉末中のNi，Cr，およびMoは、そ
れぞれ、焼結体基地の高温における強度を向上さ
せ、後に述べる封孔の効果と相まつて、基層の耐
クリープ性を向上させ、それによつて、得られる
弁座の耐脱落性を向上させる。Ni，CrおよびMo
の含有率は、それぞれ、0.5〜５重量％である。
これらの含有率が、それぞれ0.5重量％未満にな
ると、上記効果が不十分となり、また５重量％を
こえると、上記効果が飽和し、却つて、経済的に
不利となる。Ni，CrおよびMoの２種以上が用い
られるときは、それらの合計重量は10％以下であ
る。10％をこえて用いても、その効果が飽和して
しまうため、却つて経済的に不利になる。基層用混合粉末中の黒鉛粉末は、摺接層用混合
粉末中の黒鉛粉末と同様の効果を発揮するもの
で、その含有率も、0.5〜1.5重量％である。摺接層用混合粉末と、基層用混合粉末とは、所
望形状・寸法の金型中で二層に積層され、この積
層された両混合粉末は同時加圧形成され、そして
焼結されて、１体の焼結体に形成される。このと
き摺接層用混合粉末と、基層用混合粉末との重量
比および、摺接層と基層との体積比には、格別の
限定はなく、弁座の用途に応じて任意に定めるこ
とができる。上記加圧成形工程において、加圧は５〜７ト
ン／cm²の範囲で行われることが好ましく、また焼
結工程における焼結温度は、1080〜1150℃の範囲
で行われることが好ましい。上述のようにして得られた、前記二層焼結合金
製弁座に対し、その内部空孔を封孔するために、
Cu又はCu合金により溶浸する。この溶浸処理に
用いられるCu合金としては、例えばCu−Fe−
Mn系合金、Cu−Fe−Mu−Zn系合金又は、cu−
Co−Zn系合金などがある。溶浸処理は、1080〜
1150℃の範囲で行われるのが好ましく、溶浸され
る金属の量は、弁座総重量に対し、５〜25％の範
囲である。溶浸量が５％未満では、外部と連通し
た空孔が多数残存し、酸化防止の効果が不十分で
ある。また、溶浸量が25％を越えると、得られる
弁座の密度が過大となり、かつ得られる弁座中の
Cu又はCu合金の含有率が過大となるため、弁座
の高温における強度が低下し、クリープ変形が大
きくなり、耐脱落性が低下する。焼結操作と溶浸操作とは、一工程で同時に行わ
れてもよい。上記溶浸処理により、得られる弁座
の内部酸化が防止され、従つて、弁座の高温にお
ける強度低下が防止される。また、Cu又はCu合
金の溶浸は、弁座の熱伝導率を高め、それにより
弁座の熱負荷を低減することができる。一般に、上記焼結および溶浸処理の弁座、特に
摺接層中の基地は、残留オーステナイト構造にあ
るため、このまま高温にさらされると、その構造
に変態を生ずる。オーステナイトは、熱膨張係数
が大きく、また、その変態により寸法変化を生ず
るので、弁座の耐脱落性が低下する。そこで、溶浸処理後、弁座に400℃からA₁変態
点までの温度の焼なまし熱処理を施し、残留オー
ステナイトを分解して安定化する。熱処理温度が
400℃未満では、オーステナイトの分解が進行し
ないので、好ましくなく、また、A₁変態点をこ
える熱処理温度では、空冷すると、再び残留オー
ステナイトに戻るので好ましくない。以下、本発明方法を実施例によつて更に詳しく
説明する。実施例中、弁座の耐脱落性は、下記のようにし
てテストした。第１図は、耐脱落性テストに用いられた治具で
あつて、鋳鉄製円筒形治具２は、外径85mm、内径
30mm、高さ30mmを有し、その内壁上部に供試弁座
１を挿入するための段状部を有していた。供試弁
座１は、摺接層１ａと基層１ｂとからなり、その
外径は34mm、内径は25mm、高さは８mmであつた。第１図に示されているように、治具２に供試弁
座を挿入する際、治具２の段状部内径と、供試弁
座１の外径との差（締代）は、0.12mmとした。供
試弁座１を治具２の段状部に常温で圧入し、これ
を500℃で約15時間加熱し、次にこれを室温迄空
冷した。次に、弁座１を治具２から抜き出すとき
の荷重を側定した。また、耐摩耗性テストは、下記のようにして行
われた。供試弁座を、鋳鉄製シリンダヘツドを有
する水冷式４気筒（2200c.c.）デイーゼルエンジン
の吸気および排気弁座として組付け、これに
4200rpm、全負荷の条件で300時間の耐久テスト
を行い、吸気弁座および排気弁座について、その
摩耗量をそれぞれ４気筒分の平均値で示した。実施例１〜７および比較例１〜11 実施例１〜７および比較例１〜９の各々におい
て、第１表に示された組成を有する摺接層用混合
粉末および基層用混合粉末を使用した。摺接層用
混合粉末中に含まれた特殊合金粉は下記のように
して製造されたものであつた。下記組成：Ｃ２％ Cr 20％ Ni ８％ Mo 20％ Co 34％ Nb ２％ Fe 残部の特殊合金粉末を製造するために、金属混合物を
高周波誘導炉で溶解し板状体に鋳造し、この板状
体をスタンプミルで粉砕し、ふるい分けして−
150メツシユサイズの粉末とした。摺接層用混合粉末と、基層用混合粉末との使用
量は製品中の摺接層と基層との厚さの比が４：６
になるようにした。上記両混合粉末を金型内で積
層し、両混合粉末を同時に加圧成形して、その圧
粉体密度が6.7ｇ／cm³となるようにした。この成
形物を1130℃で40分間、分解アンモニアガス中で
加熱焼結して、１体の焼結体を得た。この焼結工程と同時に、下記組成： Fe 3.8％ Mn 2.2％ Zn 2.2％ Cu 残部のCu合金の溶浸処理を行つた。溶浸量は第１表
に示されている通りであつた。前記焼結・溶浸された弁座体に、600℃で１時
間の焼なまし加熱処理を施し、空冷した。前記弁座に所要の機械仕上を施し、耐脱落性テ
ストに供した。別に、比較例10および11において、現在、デイ
ーゼルエンジン用に使用されている、耐熱鋼
（SUH4）および特殊鋳鋼（1.8C−14Cr−4Mo−
0.3V−残部Fe）により作成された弁座について、
耐脱落性テストを行つた。結果を第１表に示す。 The present invention relates to a method for manufacturing a valve seat made of a double-layer sintered alloy. More specifically, the present invention relates to a method for manufacturing a valve seat made of a double-layer sintered alloy, which has excellent drop-off resistance and is useful for internal combustion engines. In recent years, valve seats for internal combustion engines are required to withstand increasingly severe conditions as exhaust gas regulations for internal combustion engines have become more sophisticated and demands for higher output have increased. For this reason, conventional valve seats have been manufactured using large amounts of expensive alloying elements such as Co, Mo, and/or W. However, on the other hand, there is an increasing demand for resource conservation, and it is desired to economize on the use of the above-mentioned expensive alloying elements. In order to meet the above demands, recently the layer that forms the sliding surface of the valve seat is made of a high alloy sintered alloy material, and the other base layer is made of a low alloy sintered alloy material. A valve seat made of a so-called double-layer sintered alloy has been proposed. In the conventional two-layer sintered alloy valve seat as described above, the role of the base layer is to back up the sliding contact layer that forms the surface that comes into sliding contact with the valve.
The objective is to reduce the amount of expensive alloying elements used.
However, conventional valve seats made of two-layer sintered alloys have the drawbacks of large creep deformation and low drop-off resistance. Valve seats for internal combustion engines are required to have excellent wear resistance and heat resistance, but in addition,
There is also a strong demand for small creep deformation and less chance of falling off from the cylinder head. Generally, the valve seat is press-fitted or shrink-fitted into the cylinder head with an interference of 0.07 to 0.15 mm, and is used under high loads and high temperatures. The cylinder head is made of cast iron,
When the valve seat is made of iron-based sintered alloy, the coefficient of thermal expansion of the cylinder head is slightly smaller than that of the valve seat, or is almost the same. Therefore, the thermal load during operation of the internal combustion engine causes creep deformation (so-called settling) in the valve seat, and when the internal combustion engine is stopped and the cylinder head cools down, the valve seat often falls off from the cylinder head. In order to prevent the above-mentioned falling off, not only the sliding contact layer of the two-layer valve seat but also its base layer must have low creep deformation and high resistance to falling off. In other words, it is not enough for the base layer of a two-layer valve seat to simply have a high enough strength to back up the sliding contact layer; it must also have creep resistance and drop-off resistance. . Furthermore, in conventional iron-based sintered alloy valve seats, pores are usually present between the sintered alloy particles. When such a valve seat is used at high temperatures, the area around the pores in the valve seat is oxidized, which reduces the proportion of metal bonding between alloy particles and reduces the actual compression of the valve seat. Stress increases. This phenomenon increases the creep deformation of the valve seat and therefore causes the valve seat to fall off from the cylinder head. In order to solve the above problems, it is necessary to seal the holes in the valve seat. An object of the present invention is to provide a method for manufacturing a valve seat made of a double-layer sintered alloy that has high heat resistance and high wear resistance, small creep deformation, and high resistance to falling off from a cylinder head. be. Another object of the present invention is to provide a method for manufacturing a two-layer sintered alloy valve seat having a base layer with high resistance to high temperature compression. Still another object of the present invention is to, by sealing treatment,
An object of the present invention is to provide a method for manufacturing a valve seat made of a double-layer sintered alloy with high oxidation resistance. A method for manufacturing a two-layer sintered metal valve seat of the present invention that achieves the above object comprises a sliding contact layer forming a surface that slides on the valve, and a base layer supporting the sliding contact layer, and a base layer supporting the sliding contact layer. The contact layer and the base layer are (1) 5 to 35% (by weight)
The following composition: C 1-4% (weight) Cr 10-30% (weight) Ni 2-15% (weight) Mo 10-30% (weight) Co 20-40% (weight) Nb 1-5% (weight) Special alloy powder with Fe balance (weight), 0.5 to 1.5% (weight) graphite powder, and balance iron powder mixed powder for sliding contact layer, (2) 0.5 to 5% (weight) of Ni and 0.5 to 5
% (wt) Cr and 0.5-5% (wt)
at least one member selected from the group consisting of Mo (however, in the case of a mixture of two or more members, the total weight is 10% or less), and 0.5 to 1.5% (by weight) of graphite powder; The mixed powder for the base layer consisting of the remaining iron powder is laminated in a desired shape, the laminated mixed powders are simultaneously pressure-molded, and sintered to form a single sintered body. In conclusion, the total weight of the valve seat is 5~
It is characterized by being formed by infiltrating 25% Cu or Cu alloy, and subjecting the infiltrated sintered body to annealing heat treatment at a temperature from 400°C to the _A1 transformation point. It is something. In the method of the present invention, the sliding contact layer of the valve seat is 5 to 35
It is made using a mixed powder for the sliding contact layer consisting of % by weight of special alloy powder, 0.5 to 1.5% by weight of graphite powder, and the balance iron powder. The special powder has the following composition: C 1 to 4% by weight Cr 10 to 30 Ni 2 to 15 Mo 10 to 30 Co 20 to 40 Nb 1 to 5 Fe balance. In the above composition, C is Cr,
Combines with Mo and Nb to form a composite carbide with high wear resistance. The content of C is 1 to 4% by weight. If this content is less than 1% by weight, the amount of the wear-resistant composite carbide obtained will be insufficient, and if it exceeds 4% by weight, the precipitated particles of the composite carbide obtained will become coarse. Cr and Mo form the above-mentioned condensation carbide together with Nb and contribute to improving the wear resistance of the sliding contact layer. Furthermore, during sintering, Cr and Mo diffuse into the base of the sintered alloy and form a solid solution, contributing to improving the heat resistance of the sliding contact layer. The content of Cr and Mo is 10 each.
~30% by weight. When the content of Cr and Mo is less than 10% by weight each, their contribution to improving the wear resistance and heat resistance is insufficient, and when it exceeds 30%, the castability of the ingot during alloy production is reduced. In addition, the resulting alloy becomes expensive, which is economically disadvantageous. Nb itself is carbide Nbc or Nb(C.
N) and forms composite carbides with Cr and Mo. At this time, Nb exhibits an excellent effect on making carbide particles finer. The content of Nb is 1 to 5% by weight. When the Nb content is less than 1%, the above effects are insufficient, and
%, the resulting Nb carbide particles become coarse, which is not preferable. During sintering, Ni and Co each diffuse into a solid solution in the base of the sintered alloy and contribute to improving the heat resistance of the sliding contact layer. The content of Ni and Co is 2
~15% by weight, and 20-40% by weight. When the content rates of Ni and Co are less than their respective lower limits, the heat resistance improvement effect described above is insufficient, and even if they exceed the above upper limit values, the above effects do not improve significantly, and on the contrary, It will be economically disadvantageous. The above-mentioned special alloy is dispersed in the base of the sintered body during sintering, and contributes to improving the wear resistance of the sliding contact layer.
Some of the component elements such as Co and Cr diffuse into the Fe phase around this special alloy particle,
As a result, the heat resistance of the sintered base of the sliding contact layer is improved. The content of the special alloy powder in the mixed powder for the sliding contact layer is 5 to 35% by weight. Its content is 5% by weight
If it is less than 35% by weight, the wear resistance and heat resistance of the resulting sliding contact layer will be unsatisfactory, and if it exceeds 35% by weight, the moldability of the mixed powder will be reduced. The content of graphite powder in the mixed powder for sliding contact layer is:
It is 0.5-1.5% by weight. If this content is less than 0.5% by weight, the amount of ferrite precipitated in the resulting sliding contact layer will be excessive, resulting in insufficient wear resistance of the sliding contact layer. Moreover, if it exceeds 1.5% by weight, cementite will begin to precipitate in a network shape, and the resulting sliding contact layer will become brittle. In the method of the present invention, the base layer of the valve seat (backup layer that backs up the sliding contact layer) is
0.5 to 5% by weight of at least one member selected from the group consisting of Ni, Cr, and Mo (in the case of 2 or more members, the total weight is 10% or less) and 0.5 to 1.5% by weight of graphite powder. and the balance is iron. Ni, Cr, and Mo in the mixed powder for the base layer each improve the strength of the sintered body base at high temperatures, and together with the sealing effect described later, they improve the creep resistance of the base layer, thereby increasing the strength of the base layer. , improving the falling-off resistance of the resulting valve seat. Ni, Cr and Mo
The content of each is 0.5 to 5% by weight.
When these contents are less than 0.5% by weight, the above-mentioned effects become insufficient, and when they exceed 5% by weight, the above-mentioned effects become saturated, which becomes economically disadvantageous. When two or more of Ni, Cr and Mo are used, their total weight is 10% or less. Even if it is used in excess of 10%, the effect will be saturated and it will be economically disadvantageous. The graphite powder in the mixed powder for the base layer exhibits the same effect as the graphite powder in the mixed powder for the sliding contact layer, and its content is 0.5 to 1.5% by weight. The mixed powder for the sliding contact layer and the mixed powder for the base layer are laminated in two layers in a mold having a desired shape and size, and both of the laminated mixed powders are simultaneously pressed and formed, and then sintered. It is formed into a single sintered body. At this time, there are no particular limitations on the weight ratio of the mixed powder for the sliding contact layer and the mixed powder for the base layer, and the volume ratio between the sliding contact layer and the base layer, and they can be arbitrarily determined depending on the purpose of the valve seat. can. In the pressure forming step, the pressure is preferably carried out in a range of 5 to 7 tons/cm ² , and the sintering temperature in the sintering step is preferably carried out in a range of 1080 to 1150°C. In order to seal the internal pores of the two-layer sintered metal valve seat obtained as described above,
Infiltrated with Cu or Cu alloy. Examples of Cu alloys used in this infiltration treatment include Cu-Fe-
Mn alloy, Cu-Fe-Mu-Zn alloy or cu-
Examples include Co-Zn alloys. Infiltration treatment is 1080～
Preferably it is carried out at a temperature in the range of 1150°C, and the amount of metal infiltrated is in the range of 5 to 25%, based on the total weight of the valve seat. When the amount of infiltration is less than 5%, many pores communicating with the outside remain, and the effect of preventing oxidation is insufficient. Additionally, if the amount of infiltration exceeds 25%, the density of the valve seat obtained will be excessive, and the density of the valve seat obtained will be too high.
Because the content of Cu or Cu alloy becomes excessive, the strength of the valve seat at high temperatures decreases, creep deformation increases, and fall-off resistance decreases. The sintering operation and the infiltration operation may be performed simultaneously in one step. The above-mentioned infiltration treatment prevents internal oxidation of the resulting valve seat, and therefore prevents the strength of the valve seat from decreasing at high temperatures. Infiltration of Cu or Cu alloy can also increase the thermal conductivity of the valve seat, thereby reducing the thermal load on the valve seat. Generally, the valve seat subjected to the sintering and infiltration treatment, particularly the base in the sliding contact layer, has a retained austenite structure, so if it is exposed to high temperatures as it is, the structure will undergo transformation. Austenite has a large coefficient of thermal expansion and undergoes dimensional changes due to its transformation, which reduces the resistance to falling off of the valve seat. Therefore, after the infiltration treatment, the valve seat is subjected to annealing heat treatment at a temperature from 400℃ to the _A1 transformation point to decompose and stabilize residual austenite. Heat treatment temperature
If the temperature is less than 400°C, the decomposition of austenite will not proceed, which is undesirable, and if the heat treatment temperature exceeds the _A1 transformation point, it will return to residual austenite when air-cooled, which is undesirable. Hereinafter, the method of the present invention will be explained in more detail with reference to Examples. In the examples, the falling-off resistance of the valve seat was tested as follows. Figure 1 shows the jig used for the drop-off resistance test, and cast iron cylindrical jig 2 has an outer diameter of 85 mm and an inner diameter of
It had a height of 30 mm and a stepped portion on the upper part of its inner wall into which the test valve seat 1 was inserted. The test valve seat 1 consisted of a sliding contact layer 1a and a base layer 1b, and had an outer diameter of 34 mm, an inner diameter of 25 mm, and a height of 8 mm. As shown in Fig. 1, when inserting the test valve seat into the jig 2, the difference (tightness) between the inner diameter of the stepped part of the jig 2 and the outer diameter of the test valve seat 1 is , 0.12mm. The test valve seat 1 was press-fitted into the stepped portion of the jig 2 at room temperature, heated at 500° C. for about 15 hours, and then air-cooled to room temperature. Next, the load when extracting the valve seat 1 from the jig 2 was determined. Further, the wear resistance test was conducted as follows. The test valve seats were assembled as intake and exhaust valve seats for a water-cooled four-cylinder (2200 c.c.) diesel engine with a cast iron cylinder head.
A 300-hour durability test was conducted under the conditions of 4200 rpm and full load, and the amount of wear on the intake valve seat and exhaust valve seat was shown as an average value for 4 cylinders each. Examples 1 to 7 and Comparative Examples 1 to 11 In each of Examples 1 to 7 and Comparative Examples 1 to 9, mixed powder for sliding contact layer and mixed powder for base layer having the composition shown in Table 1 were used. . The special alloy powder contained in the mixed powder for the sliding contact layer was manufactured as follows. The following composition: C 2% Cr 20% Ni 8% Mo 20% Co 34% Nb 2% Fe To produce the remaining special alloy powder, the metal mixture was melted in a high frequency induction furnace and cast into a plate shape. Pulverize the plate with a stamp mill, sieve it and...
It was made into a powder of 150 mesh size. The amount of the mixed powder for the sliding contact layer and the mixed powder for the base layer is such that the ratio of the thickness of the sliding contact layer to the base layer in the product is 4:6.
I made it so that Both of the above mixed powders were laminated in a mold, and both mixed powders were simultaneously pressure-molded so that the green compact density was 6.7 g/cm ³ . This molded product was heated and sintered in decomposed ammonia gas at 1130° C. for 40 minutes to obtain a sintered body. Simultaneously with this sintering process, infiltration treatment was performed with a Cu alloy having the following composition: Fe 3.8% Mn 2.2% Zn 2.2% Cu with the remainder remaining. The amount of infiltration was as shown in Table 1. The sintered and infiltrated valve seat body was subjected to annealing heat treatment at 600° C. for 1 hour, and then cooled in air. The valve seat was given a required mechanical finish and subjected to a drop resistance test. Separately, in Comparative Examples 10 and 11, heat-resistant steel (SUH4) and special cast steel (1.8C-14Cr-4Mo-
Regarding the valve seat made by 0.3V - balance Fe),
A drop resistance test was conducted. The results are shown in Table 1.

【表】第１表から明らかなように、溶浸処理を施さな
い場合（比較例１，２）、基層が、Fe−Ｃ系の場
合（比較例３，４）、および基層中のCr，Mo，
Niの各含有率が0.5％未満の場合（比較例５，
６）、溶浸量が５％未満の場合（比較例７）およ
び溶浸量が、25％をこえる場合（比較例８）、い
づれも得られる弁座の耐脱落性は、不十分なもの
であつた。また基層中のCr，Mo，Niの合計含有
率を10％より大きくしても（比較例９，Cr＋Ni
＝11.8％）、実施例５（Cr＋Ni＝5.2％）にくらべ
て、耐脱落性向上の程度は極めて軽微であり、経
済的に、著るしく不利である。実施例１〜７の弁
座は、すべて、比較例10，11の弁座とほぼ同等の
耐脱落性を示し、満足すべきものであつた。実施例８〜11および比較例12〜17 実施例８〜11および比較例12〜17の各々におい
て、第２表記載の組成の摺接層用混合粉末、およ
び、基層用混合粉末を用い、実施例１と同様の方
法で焼結体を製造し、このとき、同時に第２表記
載の溶浸量で溶浸処理を行つた。用いられた特殊
合金および溶浸用Cu合金の組成は、実施例１記
載のものと同一であつた。焼結・溶浸された弁座体に対し、第２表記載の
温度で、１時間の焼なまし熱処理を施した。これらの弁座の耐脱落性テストの結果を第２表
に示す。[Table] As is clear from Table 1, when no infiltration treatment is performed (Comparative Examples 1 and 2), when the base layer is Fe-C type (Comparative Examples 3 and 4), and when Cr in the base layer is Mo,
When each content rate of Ni is less than 0.5% (Comparative Example 5,
6) When the amount of infiltration is less than 5% (Comparative Example 7) and when the amount of infiltration exceeds 25% (Comparative Example 8), the resulting valve seat has insufficient drop-off resistance. It was hot. Moreover, even if the total content of Cr, Mo, and Ni in the base layer is made larger than 10% (Comparative Example 9, Cr+Ni
= 11.8%), and compared to Example 5 (Cr+Ni = 5.2%), the degree of improvement in drop-off resistance is extremely small, which is economically disadvantageous. All of the valve seats of Examples 1 to 7 exhibited almost the same drop-off resistance as the valve seats of Comparative Examples 10 and 11, and were satisfactory. Examples 8 to 11 and Comparative Examples 12 to 17 In each of Examples 8 to 11 and Comparative Examples 12 to 17, the mixed powder for the sliding contact layer and the mixed powder for the base layer having the compositions listed in Table 2 were used. A sintered body was produced in the same manner as in Example 1, and at the same time an infiltration treatment was performed at the infiltration amount shown in Table 2. The compositions of the special alloy and infiltration Cu alloy used were the same as those described in Example 1. The sintered and infiltrated valve seat bodies were subjected to annealing heat treatment for 1 hour at the temperatures listed in Table 2. Table 2 shows the results of the falling-off resistance test of these valve seats.

【表】第２表から明らかなように、焼なまし熱処理を
施さない場合（比較例12，15）焼なまし熱処理温
度が400℃未満の場合（比較例13，16）、焼なまし
熱処理温度がA₁変態点をこえる場合（比較例14，
17）は、いづれも耐脱落性が不良であつた。本発
明による実施例８〜11の弁座はいづれも良好な耐
脱落性を示した。実施例12〜15および比較例18〜19 実施例12〜15の各々において、実施例１と同様
の方法で、弁座を製造し、この弁座を、耐摩耗性
テストに供した。各実施例に用いられた摺接層用
および基層用混合粉末の組成および、溶浸合金の
組成と溶浸量は第３表に示されている通りであつ
た。比較例18および19において、比較例10および11
と同一弁座に対しても耐摩耗性テストを施した。これらのテスト結果を第３表に示す。[Table] As is clear from Table 2, when annealing heat treatment is not performed (Comparative Examples 12 and 15) and when the annealing heat treatment temperature is less than 400℃ (Comparative Examples 13 and 16), annealing heat treatment When the temperature exceeds the _A1 transformation point (Comparative Example 14,
17) had poor falling resistance. The valve seats of Examples 8 to 11 according to the present invention all exhibited good drop-off resistance. Examples 12 to 15 and Comparative Examples 18 to 19 In each of Examples 12 to 15, valve seats were manufactured in the same manner as in Example 1, and the valve seats were subjected to a wear resistance test. The composition of the mixed powder for the sliding contact layer and the base layer, the composition of the infiltration alloy, and the amount of infiltration used in each example were as shown in Table 3. In Comparative Examples 18 and 19, Comparative Examples 10 and 11
A wear resistance test was also conducted on the same valve seat. The results of these tests are shown in Table 3.

【表】第３表から明らかなように、本発明に係る実施
例12〜15の弁座はいづれも従来の弁座よりも良好
な耐摩耗性を示した。以上詳述したように本発明方法により製造され
た弁座は、耐脱落性、耐摩耗性、耐熱性に優れて
おり、特に鋳鉄製シリンダヘツド用弁座として優
れた性能を有するものである。[Table] As is clear from Table 3, the valve seats of Examples 12 to 15 according to the present invention all exhibited better wear resistance than the conventional valve seats. As detailed above, the valve seat manufactured by the method of the present invention has excellent drop-off resistance, wear resistance, and heat resistance, and has particularly excellent performance as a valve seat for a cast iron cylinder head.

[Brief explanation of drawings]

第１図は、弁座の耐脱落性テスト用治具の断面
説明図である。１……供試弁座、１ａ……摺接層、１ｂ……基
層、２……テスト用治具。 FIG. 1 is an explanatory cross-sectional view of a jig for testing the fall-off resistance of a valve seat. 1... Test valve seat, 1a... Sliding contact layer, 1b... Base layer, 2... Test jig.

Claims

[Claims] 1. When manufacturing a valve seat consisting of a sliding contact layer forming a surface that slides on the valve and a base layer supporting the sliding contact layer, the sliding contact layer and the base layer are formed by (1) )5~35% (weight)
The following composition: C 1-4% (weight) Cr 10-30% (weight) Ni 2-15% (weight) Mo 10-30% (weight) Co 20-40% (weight) Nb 1-5% (weight) Special alloy powder with Fe balance (weight), 0.5-1.5% (weight) of graphite powder, balance iron powder, (2) 0.5-5% (weight) of Ni and 0.5 to 5
% (by weight) of Cr, and at least one member selected from the group consisting of 0.5 to 5% Mo (however, in the case of a mixture of 2 or more members, the total weight thereof is 10% or less). A base layer mixed powder consisting of 0.5 to 1.5% (by weight) of graphite powder and the remainder iron powder is laminated into a desired shape, and both of the laminated mixed powders are simultaneously pressure-molded and sintered. The sintered body is infiltrated with Cu or Cu alloy in an amount of 5 to 25% of the total weight of the valve seat, and the infiltrated sintered body is heated with A ₁ from 400°C. A method for manufacturing a valve seat made of a double-layer sintered alloy, characterized in that the valve seat is formed by subjecting it to annealing heat treatment at a temperature up to transformation.