JP2004285421A

JP2004285421A - Cermet

Info

Publication number: JP2004285421A
Application number: JP2003079752A
Authority: JP
Inventors: Takashi Umemura; 崇梅村; Nobuo Hojo; 伸夫北條; Satoshi Kinoshita; 聡木下
Original assignee: Tungaloy Corp
Current assignee: Tungaloy Corp
Priority date: 2003-03-24
Filing date: 2003-03-24
Publication date: 2004-10-14
Anticipated expiration: 2023-03-24
Also published as: JP4280525B2

Abstract

<P>PROBLEM TO BE SOLVED: To improve the wear resistance of a cutting tool made of cermet, and to suppress the fusion of the material to be machined in cast iron working. <P>SOLUTION: In cast iron working, the nitrogen-containing ratio in the core part is controlled to a suitable range, so that resistances to fusion and chemical reactivity with cast iron are improved, and further, the area ratio in the peripheral part of the cored structure is increased, so that its chemical reactivity with cast iron is improved. Namely, the cermet has a hard phase, and the hard phase consists of the core part of titanium carbonitride in which the ratio of nitrogen to the total of nitrogen and carbon, (N/(N+C)) satisfies 0.2≤(N/(N+C))≤0.5 by atom, and the peripheral part of a compound carbonitride solid solution of at least one kind selected from the group 4a, 5a and 6a metals in the Periodic Table other than titanium, and titanium. Provided that the average particle diameter of the core material is denoted as a, and the average particle diameter of the peripheral part as b, 3≤(b/a)≤8 is satisfied, and the average particle diameter of the hard phase is controlled to 2 to 7 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明に属する技術分野】
この発明は、耐摩耗性、耐溶着性にすぐれる炭窒化チタン系サーメットおよびその製造方法に関するものである。
【０００２】
【従来の技術】
ＴｉＣ−ＴｉＮ−Ｎｉを基本組成とする窒素含有サーメットは、ＴｉＣ−Ｎｉを基本組成とした窒素を含まないサーメットに比べて強度および耐塑性変形性に優れる傾向にある。そのため、高窒素含有サーメットの切削工具が提案されている（例えば、特許文献１参照）。
【０００３】
また、Ｔｉ（Ｃ，Ｎ）中の窒素量（Ｎ／（Ｃ＋Ｎ））が０．７以上からなる窒素に富む粒径１．５μｍ以下の有芯構造の高窒素含有サーメットが提案されている（例えば、特許文献２参照）。
【０００４】
【特許文献１】特公昭６３−３０１７号公報
【特許文献２】特表平８−５０８０６６号公報
【０００５】
【発明が解決しようとする課題】
高窒素含有サーメットは、鋼切削加工時の耐熱衝撃性および耐塑性変形性および耐溶着性には優れた性能を発揮するものの、鋳鉄の切削加工時の耐摩耗性に劣るという問題がある。ＴｉＣＮ中の窒素量（Ｎ／（Ｃ＋Ｎ））が０．７以上からなる窒素に富む粒径１．５μｍ以下の有芯構造のサーメットは、有芯構造を有する硬質相が微粒となり、硬質相の周辺部が薄く鋳鉄と反応しやすいため、鋳鉄の切削工具として用いた場合、耐摩耗性が低いという問題がある。
【０００６】
近年、鋳鉄、焼結金属、チタン合金などの硬質材料の加工において、高能率加工が望まれるようになってきた。そこで、本発明は、鋳鉄、焼結金属、チタン合金などの硬質材料の加工において、従来のサーメットよりも優れた耐摩耗性、耐溶着性を示すサーメットとその製造方法を提供することを目的とする。
【０００７】
【課題を解決しようとするための手段】
本発明者らは、サーメット製切削工具、特に鋳鉄加工におけるサーメット製切削工具の工具寿命の延長を目的に、耐摩耗性の向上と被削材溶着の抑制の軽減について検討していたところ、有芯構造を有する硬質相における複合炭化物からなる周辺部の面積割合が多いほど、鋳鉄との耐化学反応性が向上すること、前記有芯構造を有する硬質相におけるＴｉの炭窒化物からなる芯部の窒素含有比率が適切な範囲であると鋳鉄との耐溶着性および耐化学反応性に優れることを見出した。
【０００８】
本発明のサーメットは、周期律表４ａ、５ａ、６ａ族金属の炭化物、窒化物、炭窒化物およびこれら固溶体の中から選ばれた少なくとも１種からなる硬質相：７０〜９７重量％と、鉄族金属の中から選ばれた少なくとも１種を主成分とする結合相：残部とからなるサーメットであって、該硬質相は、炭窒化チタンに含まれる窒素と炭素の合計に対する窒素の割合（Ｎ／（Ｎ＋Ｃ））が原子比で０．２≦（Ｎ／（Ｎ＋Ｃ））≦０．５である炭窒化チタンの芯部とチタン以外の周期律表４ａ、５ａ、６ａ族金属の中から選ばれた少なくとも１種とチタンとの複合炭窒化物固溶体の周辺部からなり、該芯部の平均粒径をａ、該周辺部の平均粒径をｂと表したとき、３≦（ｂ／ａ）≦８であり、該硬質相の平均粒径が２〜７μｍであることを特徴とする。
【０００９】
本発明サーメットは、周期律表４ａ、５ａ、６ａ族金属の炭化物、窒化物、炭窒化物およびこれらの固溶体の中から選ばれた少なくとも１種からなる硬質相：７０〜９７重量％と、鉄族金属の中から選ばれた少なくとも１種を主成分とする結合相：残部からなる焼結合金である。硬質相が７０重量％未満であると、耐摩耗性が低下し、硬質相が９７重量％を超えると耐欠損性が低下すると共に、相対的に残部の結合相量が減少するため焼結性が低下する。そこで、硬質相：７０〜９７重量％と結合相：残部と定めた。
【００１０】
硬質相の平均粒径は２〜７μｍとした。これは、平均粒径が２μｍ未満であると、耐化学反応性が低下し、鋳鉄などの硬質材料の切削において耐摩耗性が低下るためであり、平均粒径が７μｍを超えると抗折力強度が低下し、鋳鉄などの硬質材料の切削において耐欠損性が低下するためである。好ましくは、耐摩耗性と強度を保つため、硬質相の平均粒径は２〜５μｍがよい。
【００１１】
硬質相には、芯部と周辺部からなる有芯構造の硬質相と周辺部のみからなる硬質相がある。有芯構造の硬質相は、炭窒化チタンからなる芯部とチタン以外の周期律表４ａ、５ａ、６ａ族金属の中から選ばれた少なくとも１種とチタンとの複合炭窒化物固溶体の周辺部で構成される。芯部を成す炭窒化チタンとして、具体的には、Ｔｉ（Ｃ，Ｎ）を挙げることができる。周辺部を成すチタン以外の周期律表４ａ，５ａ，６ａ族金属の中から選ばれた少なくとも１種とチタンとの複合炭窒化物固溶体として、具体的には、（Ｔｉ，Ｍｏ）（Ｃ，Ｎ），（Ｔｉ，Ｍｏ，Ｗ）（Ｃ，Ｎ），（Ｔｉ，Ｔａ，Ｗ，Ｍｏ）（Ｃ，Ｎ）などを挙げることができる。
【００１２】
有芯構造の硬質相の芯部を構成する炭窒化チタンに含まれる窒素と炭素の合計に対する窒素の割合（Ｎ／（Ｎ＋Ｃ））が原子比で０．２未満であると、鉄系材料に対する耐溶着性が低下する。窒素の割合（Ｎ／（Ｎ＋Ｃ））が０．５を超えると鋳鉄との耐化学反応性が低下する。したがって、炭窒化チタンに含まれる窒素の割合（Ｎ／（Ｎ＋Ｃ））を０．２≦（Ｎ／（Ｎ＋Ｃ））≦０．５と定めた。
好ましくは、耐溶着性と耐化学反応性を保つため、（Ｎ／（Ｎ＋Ｃ））を０．３≦（Ｎ／（Ｎ＋Ｃ））≦０．４とするとよい。
【００１３】
周辺部のみの硬質相は、有芯構造の周辺部と同様に、チタン以外の周期律表４ａ，５ａ，６ａ族金属の中から選ばれた少なくとも１種とチタンとの複合炭窒化物固溶体からなる。具体的には、（Ｔｉ，Ｍｏ）（Ｃ，Ｎ），（Ｔｉ，Ｍｏ，Ｗ）（Ｃ，Ｎ），（Ｔｉ，Ｔａ，Ｗ，Ｍｏ）（Ｃ，Ｎ）などを挙げることができる。
【００１４】
芯部の平均粒径ａに対する周辺部の平均粒径ｂの粒径比（ｂ／ａ）の平均が、３未満であると鋳鉄との耐化学反応性が低下し、鋳鉄などの硬質材料の切削において耐摩耗性が低下する。ここで周辺部の平均粒径ｂは、有芯構造の硬質相および／または周辺部のみからなる硬質相の周辺部の平均粒径を測定することで求められる。いずれの硬質相も外側が周辺部であるため、硬質相の平均粒径が周辺部の平均粒径ｂとなる。（ｂ／ａ）の平均が８を超えると、靱性および強度が低下し、鋳鉄などの硬質材料の切削において耐欠損性が低下する。したがって、粒径比（ｂ／ａ）を３≦（ｂ／ａ）≦８の範囲とした。その中でも耐化学反応性と靱性および強度を保つため、４≦（ｂ／ａ）≦７が好ましい。
【００１５】
サーメットの断面観察面における芯部の面積率が２面積％未満であると、鉄系材料に対する耐溶着性が低下し、切削工具として用いた場合、耐摩耗性および被削材の加工面の仕上げ面粗さが低下する傾向が見られる。面積率が、２０面積％を超えると、鋳鉄に対する耐反応性が低下し、具体的には、鋳鉄などの切削において耐摩耗性が低下する傾向が見られる。芯部の面積率は２〜２０面積％であると好ましく、その中でも、耐摩耗性と加工材の仕上げ面粗さを保つため、３〜１５面積％がさらに好ましい。なお、芯部の面積率は、サーメットの断面組織観察面における芯部の面積率を示す。
【００１６】
結合相は、鉄族金属の中から選ばれた少なくとも１種を主成分とする金属である。ここで、鉄族金属とは、コバルト、鉄、ニッケルをいう。鉄族金属を主成分とする結合相は、鉄族金属、または、鉄族金属に硬質相成分を０．１〜２０重量％固溶した合金を示す。結合相としては、鉄を主成分とした金属よりもコバルトおよび／またはニッケルを主成分とした金属の方が耐熱性、耐食性、および硬質相とのぬれ性が高いため好ましい。
【００１７】
サーメットのＭｏ含有量は、０．５〜３．５重量％であると耐摩耗性向上効果が顕著となる。これは、Ｍｏ_２Ｃを添加した場合、焼結過程の液相出現温度が低下するため、焼結初期の炭窒化チタンの粒成長を抑制できるためである。Ｍｏ含有量は、０．５重量％未満であるとその効果が見られず、３．５重量％を超えると、耐化学反応性が低下する傾向がみられ、そのため耐摩耗性が低下する傾向が見られることから、Ｍｏ含有量は０．５〜３．５重量％が好ましく、耐摩耗性向上効果と耐化学反応性を高く保つため、１〜２重量％とするとさらに好ましい。
【００１８】
本発明のサーメットは、優れた耐摩耗性、耐化学安定性を利用して、耐摩耗部品、金型、切削工具として用いられることができるが、その中でも切削工具として用いられることが好ましい。本発明のサーメットは鋳鉄に対する耐化学安定性が優れているため、鋳鉄用切削工具として用いられることは特に好ましい。
【００１９】
本発明のサーメットの製造方法としては、（Ａ）炭窒化チタンに含まれる窒素と炭素の合計に対する窒素の割合（Ｎ／（Ｎ＋Ｃ））が原子比で０．２≦（Ｎ／（Ｎ＋Ｃ））≦０．５である炭窒化チタン粉末：５０〜７５重量％と、周期律表４ａ，５ａ，６ａ族金属の化合物の中から選ばれた少なくとも１種の粉末：２０〜４０重量％と、鉄族金属の中から選ばれた少なくとも１種の粉末：３〜３０重量％とからなり合計で１００重量％となる混合物を得る工程、（Ｂ）混合物を１２００〜１２８０℃の所定温度まで昇温する工程、（Ｃ）混合物を１２００〜１２８０℃の範囲の所定温度で水素、炭化水素およびこれらの混合ガス雰囲気中で所定時間保持する工程、（Ｄ）混合物を１２００〜１２８０℃の範囲の所定温度から１４５０〜１５５０℃の範囲の焼結温度まで昇温する工程、（Ｅ）混合物を１４５０〜１５５０℃の範囲の焼結温度で所定時間保持して焼結する工程を含むことを特徴とする。
【００２０】
具体的には、炭窒化チタンに含まれる窒素と炭素の合計に対する窒素の割合（Ｎ／（Ｎ＋Ｃ））が原子比で０．２≦（Ｎ／（Ｎ＋Ｃ））≦０．５である炭窒化チタン粉末：５０〜７５重量％と、周期律表４ａ，５ａ，６ａ族金属の炭化物、窒化物、炭窒化物およびこれらの固溶体の中から選ばれた少なくとも１種の化合物の粉末：２０〜４０重量％と、ニッケルまたはコバルトの粉末：３〜３０重量％とからなり合計で１００重量％となる混合物を得る工程と、混合物を室温から１０００℃までを６７Ｐａの真空中で昇温し、混合物を１０００℃から１２００〜１２５０℃の範囲の所定温度まで０．０１３３〜１３．３Ｐａの高真空中で昇温する工程、混合物を１２００〜１２８０℃の範囲の所定温度でＨ_２、ＣＨ_４およびこれらの混合ガス雰囲気中で６６５〜２６６００Ｐａの圧力で０．５〜２時間保持する工程、混合物を１２００〜１２８０℃の範囲の所定温度から１４５０〜１５５０℃の範囲の焼結温度まで昇温する工程、混合物を１４５０〜１５５０℃の範囲の所定の焼結温度で圧力１．３３〜１３３００Ｐａの真空中または窒素雰囲気中、０．５〜２時間保持して焼結する工程を経てサーメットを作製するとよい。
【００２１】
本発明のサーメットの製造方法の工程（Ｂ）において混合物を１３．３Ｐａ以下の真空中で昇温することで液相出現前の固相状態で硬質相の核となるＴｉ（Ｃ，Ｎ）粒子の脱窒、脱炭を促進させることで、Ｔｉ（Ｃ，Ｎ）中に原子空孔を多量に出現させる。また、同工程（Ｄ）において硬質相の脱ガスを促進させるとともに、Ｈ_２、ＣＨ_４およびこれらの混合ガス雰囲気中で炭化させ、Ｔｉ（Ｃ，Ｎ）粒子表面近傍の炭素比率を増加させる。工程（Ｅ）は、液相出現温度より高い焼結温度で焼結することで、Ｔｉに富む芯部を包囲してなる周辺組織の粒成長を促進させ、粗大化を促す働きを有する。さらに、工程（Ｄ）において出現させた硬質相中の多量の原子空孔に、主にＴｉ（Ｃ，Ｎ）の芯部を包囲してなる周辺部（複合炭窒化物固溶体）成分原子を置換させることで、周辺部の粗大化をさらに促進させる。
【００２２】
【発明の実施の形態】
本発明のサーメットの硬質相の芯部を形成する炭窒化チタンの窒素と炭素の原子量は、芯部１０粒子をオージェ電子分光法にてそれぞれ測定し、窒素と炭素の合計に対する窒素の割合を原子比で求める。硬質相の芯部と周辺部あるいは結合相は、走査型電子顕微鏡（ＳＥＭ）の反射２次電子像の色調の差で識別するのが良い。具体的には、サーメットを断面研磨し、その断面組織をＳＥＭにて５０００倍の倍率で反射２次電子像を求め、Ｔｉに富む芯部の平均粒径ａ、周辺部の平均粒径ｂを測定し、（ｂ／ａ）の比率を求めるのが良い。ここで、Ｔｉに富む芯部の粒度ａは前記により観察された反射２次電子像より、Ｔｉに富む芯部の長手方向およびそれに垂直な方向の長さを画像解析ソフトにより求め、それら全数の平均値によりａを求めた。
【００２３】
周辺部の平均粒径ｂは、前記により観察された反射２次電子像より、Ｆｕｌｌｍａｎの式を用いて求めるとよい。ここで、Ｆｕｌｌｍａｎの式は、サーメットの硬質相の平均粒径をｄｍとし、断面研摩面の任意の直線によってヒットされる単位長さ当たりの硬質相数をＮＬ、任意の単位面積内に含まれる硬質相数をＮＳとした場合、式１によって平均粒径を算出する方法である。
【式１】ｄｍ＝（４／π）×（ＮＬ／ＮＳ）
またＴｉに富む芯部の面積率は、市販の画像解析ソフトにより求めるとよい。サーメット中のＭｏ含有量（重量％）は、断面研磨面を蛍光Ｘ線分析器で測定し、その強度から定量化するのがよい。
【００２４】
【実施例】
平均粒径１．５μｍのＴｉＣ粉末、Ｔｉ（Ｃ，Ｎ）粉末（重量比でＴｉＣ／ＴｉＮ＝１０／０〜４／６）と、その他の原料粉末としてＷＣ，ＮｂＣ，Ｍｏ，Ｎｉ，Ｃｏの各粉末を表１の割合になるように秤量し、ステンレス製ポットにアセトン溶媒と超硬合金製ボールと共に装入し、混合および強粉砕を行った。得られた混合物（混合粉末）をＪＩＳ−Ｂ４１２０に記載のＳＰＭＮ１２０３０８形状用金型でもって、１９６ＭＰａ圧力でプレス成形し、成形体を作製した。
【００２５】
成形体を、（ａ）室温から１０００℃までを６７Ｐａの真空雰囲気で昇温し、（ｂ）１２５０℃まで昇温を表１に記載の圧力（Ｐａ）および速度（℃／ｍｉｎ）の真空中で行い、（ｃ）１２５０℃で表２に記載の雰囲気および圧力（Ｐａ）中で１時間保持をし、（ｄ）昇温速度１℃／ｍｉｎで１５５０℃の焼結温度まで圧力１．３３〜１３３３ＰａのＮ_２雰囲気で昇温し、１時間保持を行い、（ｅ）その後、Ｎ_２雰囲気中で室温まで冷却を行い、発明品１〜７および比較品１〜５を作製した。
【００２６】
こうして得られた発明品１〜７、比較品１〜５のサーメットチップを中央で切断し、切断面を研削した後、１μｍのダイヤモンドペーストによりラップ加工を行った。ラップ加工面を走査型電子顕微鏡にて５０００倍の倍率で観察し、試料表面より深さ方向に０．５ｍｍ以上入った試料内部の断面組織について反射２次電子像を求めた。Ｔｉに富む芯部の平均粒径をａ、Ｔｉに富む芯部を包囲してなる周辺部の平均粒径をｂと表したとき、上記に示す方法で（ｂ／ａ）の比率を求め、さらに硬質相の平均粒径を求めた。また画像解析ソフトにより、Ｔｉに富む芯部の面積率を求めた。芯部Ｔｉ（Ｃ，Ｎ）の窒素と炭素の原子含有量をオージェ分析により求め、窒素と炭素の合計に対する窒素の割合（Ｎ／（Ｃ＋Ｎ））を原子比で求めた。また、試料表面より深さ方向に０．５ｍｍ以上入った試料内部のラップ加工面について蛍光Ｘ線分析を行い、Ｍｏ含有量を求めた。これらの結果は表３に記載した。
【００２７】
【表１】

【００２８】
【表２】

【００２９】
表１の条件により得られた焼結体は＃２３０のダイヤモンド砥石にて上下面を研削加工し、さらに逃げ面切れ刃稜線部に０．１５ｍｍ×３０°のホーニング処理を施して、下記条件の切削試験により逃げ面摩耗量の比較試験を行った。その結果を表３に示す。
【００３０】
切削試験条件１（摩耗試験）
被削材：ＦＣＤ４５０
切削速度：１８０ｍ／ｍｉｎ
切り込み：０．２ｍｍ
送り：０．２ｍｍ／ｒｅｖ
切削油：ＷＥＴ
切削時間：５０ｍｉｎ
【００３１】
切削試験条件２（欠損試験）
被削材：ＦＣＤ４５０
切削速度：２２０ｍｍ／ｒｅｖ
切り込み：０．２ｍｍ
送り：０．２ｍｍ／ｒｅｖ
切削油：ＷＥＴ
５秒切削−５秒休止の繰り返し
繰り返し数１００回で試験終了
試験回数は各サンプル３回
【００３２】
【表３】

（溶着）は、被削材が溶着する事に起因して、欠損した。
【００３３】
【発明の効果】
上記の結果から明らかのように、発明品１〜７のような硬質相の芯部の窒素の割合（Ｎ／（Ｎ＋Ｃ））が原子比で０．２≦（Ｎ／（Ｎ＋Ｃ））≦０．５であって、かつ平均粒径が２〜７μｍであり、芯部の平均粒径をａ、周辺部の平均粒径をｂと表したとき、３≦（ｂ／ａ）≦８である硬質相を有する本発明のサーメットは、従来のサーメットに比べ、鋳鉄の切削において優れた耐摩耗性、耐欠損性および耐溶着性を示す。これは、低窒素含有サーメットが高窒素含有サーメットに比べ、鋳鉄との耐化学反応性に優れるため、切削時の溶着などによる摩耗及び欠損に優れた効果を示すためである。また、Ｔｉに富む芯部を可能な限り細かくし、硬質相の平均粒径を２〜７μｍとすることで、耐欠損性を向上させることが可能となった。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a titanium carbonitride cermet having excellent wear resistance and welding resistance, and a method for producing the same.
[0002]
[Prior art]
Nitrogen-containing cermets having a basic composition of TiC-TiN-Ni tend to be superior in strength and plastic deformation resistance to cermets containing no nitrogen and having a basic composition of TiC-Ni. Therefore, a cutting tool of a high nitrogen-containing cermet has been proposed (for example, see Patent Document 1).
[0003]
Further, a nitrogen-rich cermet having a cored structure having a particle size of 1.5 μm or less and having a nitrogen content (N / (C + N)) of 0.7 or more in Ti (C, N) has been proposed ( For example, see Patent Document 2).
[0004]
[Patent Document 1] Japanese Patent Publication No. Sho 63-3017 [Patent Document 2] Japanese Patent Publication No. Hei 8-508066 [0005]
[Problems to be solved by the invention]
The high nitrogen-containing cermet exhibits excellent performance in heat shock resistance, plastic deformation resistance and welding resistance during steel cutting, but has a problem in that it has poor wear resistance during cutting of cast iron. The nitrogen-rich cored cermet having a particle size of 1.5 μm or less in which the nitrogen content (N / (C + N)) in TiCN is 0.7 or more has a hard phase having a cored structure in which fine particles are formed. Since the peripheral portion is thin and easily reacts with cast iron, when used as a cutting tool for cast iron, there is a problem that wear resistance is low.
[0006]
In recent years, in the processing of hard materials such as cast iron, sintered metal, and titanium alloy, high-efficiency processing has been desired. Therefore, an object of the present invention is to provide a cermet exhibiting abrasion resistance and welding resistance superior to conventional cermets in the processing of hard materials such as cast iron, sintered metal, and titanium alloy, and a method for producing the same. I do.
[0007]
[Means for solving the problem]
The present inventors have studied the improvement of wear resistance and the reduction of suppression of work material welding for the purpose of extending the tool life of cermet cutting tools, particularly cermet cutting tools in cast iron processing. The larger the area ratio of the peripheral portion made of the composite carbide in the hard phase having the core structure, the more the chemical reactivity with cast iron is improved, and the core portion made of Ti carbonitride in the hard phase having the cored structure It has been found that, when the nitrogen content ratio is within an appropriate range, the alloy has excellent resistance to welding and chemical reaction with cast iron.
[0008]
The cermet of the present invention comprises 70 to 97% by weight of a hard phase composed of at least one selected from carbides, nitrides, carbonitrides, and solid solutions of metals of Groups 4a, 5a, and 6a in the periodic table; A cermet comprising at least one binder phase selected from group III metals as a main component: the balance, wherein the hard phase is a ratio of nitrogen (N) to the total of nitrogen and carbon contained in titanium carbonitride. / (N + C)) is selected from metals of the periodic table 4a, 5a and 6a other than titanium and the core of titanium carbonitride having an atomic ratio of 0.2 ≦ (N / (N + C)) ≦ 0.5. When the average particle size of the core portion is represented by a and the average particle size of the peripheral portion is represented by b, 3 ≦ (b / a ) ≦ 8, and the average particle size of the hard phase is 2 to 7 μm. .
[0009]
The cermet of the present invention comprises 70 to 97% by weight of a hard phase composed of at least one selected from carbides, nitrides, carbonitrides and solid solutions of metals belonging to groups 4a, 5a and 6a of the periodic table; It is a sintered alloy composed of a binder phase containing at least one selected from group metals as a main component: the remainder. When the hard phase is less than 70% by weight, the wear resistance is reduced. When the hard phase is more than 97% by weight, the fracture resistance is reduced, and the amount of the remaining binder phase is relatively reduced. Decreases. Therefore, the hard phase was determined to be 70 to 97% by weight and the binder phase was determined to be the balance.
[0010]
The average particle size of the hard phase was 2 to 7 μm. This is because, if the average particle size is less than 2 μm, the chemical reactivity decreases, and the wear resistance decreases when cutting hard materials such as cast iron. This is because the strength is reduced and the fracture resistance is reduced in cutting hard materials such as cast iron. Preferably, in order to maintain abrasion resistance and strength, the average particle size of the hard phase is preferably 2 to 5 μm.
[0011]
The hard phase includes a hard phase having a cored structure including a core portion and a peripheral portion, and a hard phase including only a peripheral portion. The hard phase having a cored structure includes a core portion made of titanium carbonitride and a peripheral portion of a composite carbonitride solid solution of titanium and at least one selected from metals of Group 4a, 5a, and 6a other than titanium. It consists of. Specific examples of the titanium carbonitride forming the core include Ti (C, N). As a composite carbonitride solid solution of titanium and at least one selected from metals of the periodic table 4a, 5a and 6a other than titanium constituting the peripheral portion, specifically, (Ti, Mo) (C, N), (Ti, Mo, W) (C, N), (Ti, Ta, W, Mo) (C, N), and the like.
[0012]
If the atomic ratio (N / (N + C)) of nitrogen to the total of nitrogen and carbon contained in the titanium carbonitride constituting the core of the hard phase having a cored structure is less than 0.2, the iron-based material is The welding resistance decreases. When the ratio of nitrogen (N / (N + C)) exceeds 0.5, the chemical reaction resistance with cast iron decreases. Therefore, the ratio of nitrogen (N / (N + C)) contained in titanium carbonitride was set to 0.2 ≦ (N / (N + C)) ≦ 0.5.
Preferably, (N / (N + C)) should be set to 0.3 ≦ (N / (N + C)) ≦ 0.4 in order to maintain the welding resistance and the chemical reaction resistance.
[0013]
The hard phase only in the peripheral portion, like the peripheral portion of the cored structure, is made of a complex carbonitride solid solution of titanium and at least one selected from metals of the periodic table 4a, 5a, and 6a other than titanium. Become. Specifically, (Ti, Mo) (C, N), (Ti, Mo, W) (C, N), (Ti, Ta, W, Mo) (C, N) and the like can be mentioned.
[0014]
When the average of the particle diameter ratio (b / a) of the average particle diameter b of the peripheral part to the average particle diameter a of the core part is less than 3, the chemical reaction resistance with cast iron is reduced, and hard material such as cast iron Wear resistance decreases in cutting. Here, the average particle size b at the peripheral portion is determined by measuring the average particle size at the peripheral portion of the hard phase having the cored structure and / or the hard phase including only the peripheral portion. Since the outer side of each hard phase is the peripheral portion, the average particle size of the hard phase is the average particle size b of the peripheral portion. If the average of (b / a) exceeds 8, the toughness and strength decrease, and the fracture resistance in cutting hard materials such as cast iron decreases. Therefore, the particle size ratio (b / a) was set in the range of 3 ≦ (b / a) ≦ 8. Among them, 4 ≦ (b / a) ≦ 7 is preferable in order to maintain chemical resistance, toughness, and strength.
[0015]
If the area ratio of the core on the cross-section observation surface of the cermet is less than 2% by area, the welding resistance to iron-based materials is reduced, and when used as a cutting tool, the wear resistance and the finish of the machined surface of the work material are reduced. There is a tendency for the surface roughness to decrease. When the area ratio exceeds 20 area%, the reaction resistance to cast iron decreases, and specifically, the wear resistance in cutting of cast iron or the like tends to decrease. The area ratio of the core is preferably 2 to 20% by area, and more preferably 3 to 15% by area in order to maintain the wear resistance and the finished surface roughness of the processed material. The area ratio of the core indicates the area ratio of the core on the cross-sectional structure observation surface of the cermet.
[0016]
The binder phase is a metal mainly composed of at least one selected from iron group metals. Here, the iron group metal refers to cobalt, iron, and nickel. The binder phase mainly composed of an iron group metal indicates an iron group metal or an alloy in which a hard phase component is solid-dissolved in an iron group metal in an amount of 0.1 to 20% by weight. As the binder phase, a metal containing cobalt and / or nickel as a main component is preferable to a metal containing iron as a main component because of its higher heat resistance, corrosion resistance, and wettability with a hard phase.
[0017]
When the Mo content of the cermet is 0.5 to 3.5% by weight, the effect of improving the wear resistance becomes remarkable. This is because, when Mo ₂ C is added, the liquid phase appearance temperature in the sintering process is lowered, so that the grain growth of titanium carbonitride in the early stage of sintering can be suppressed. If the Mo content is less than 0.5% by weight, the effect is not seen, and if it exceeds 3.5% by weight, the chemical reactivity tends to decrease, and therefore the wear resistance tends to decrease. Is preferable, the Mo content is preferably 0.5 to 3.5% by weight, and more preferably 1 to 2% by weight in order to keep the abrasion resistance improving effect and the chemical reactivity high.
[0018]
The cermet of the present invention can be used as wear-resistant parts, dies, and cutting tools by utilizing excellent wear resistance and chemical stability, and among them, it is preferable to be used as a cutting tool. Since the cermet of the present invention has excellent chemical stability against cast iron, it is particularly preferable to use it as a cutting tool for cast iron.
[0019]
In the method for producing the cermet of the present invention, (A) the ratio of nitrogen (N / (N + C)) to the total of nitrogen and carbon contained in titanium carbonitride is 0.2 ≦ (N / (N + C)) in atomic ratio. Titanium carbonitride powder with ≦ 0.5: 50-75% by weight, and at least one powder selected from compounds of metals of Group 4a, 5a, 6a of the periodic table: 20-40% by weight, and iron Obtaining a mixture comprising at least one powder selected from group metals: 3 to 30% by weight and totaling 100% by weight; (B) heating the mixture to a predetermined temperature of 1200 to 1280 ° C. (C) maintaining the mixture at a predetermined temperature in the range of 1200 to 1280 ° C for a predetermined time in an atmosphere of hydrogen, hydrocarbon or a mixture of these gases, and (D) maintaining the mixture at a predetermined temperature in the range of 1200 to 1280 ° C. 1450-155 A step of raising the temperature to the sintering temperature in the range of ° C., characterized in that it comprises a step of sintering and holds a predetermined time at a sintering temperature in the range of 1,450-1,550 ° C. (E) a mixture.
[0020]
More specifically, the ratio of nitrogen (N / (N + C)) to the total of nitrogen and carbon contained in titanium carbonitride is atomic ratio of 0.2 ≦ (N / (N + C)) ≦ 0.5. Titanium powder: 50 to 75% by weight and powder of at least one compound selected from carbides, nitrides, carbonitrides, and solid solutions of metals of Groups 4a, 5a, and 6a of the periodic table: 20 to 40 A mixture comprising 3% to 30% by weight of nickel or cobalt powder to obtain a total of 100% by weight; and heating the mixture from room temperature to 1000 ° C. in a vacuum of 67 Pa. Elevating the temperature from 1000 ° C. to a predetermined temperature in the range of 1200 to 1250 ° C. in a high vacuum of 0.0133 to 13.3 Pa, and heating the mixture at a predetermined temperature in the range of 1200 to 1280 ° C. with H ₂ , CH ₄ and the like. Mixed gas A step of holding the mixture at a pressure of 665 to 26600 Pa for 0.5 to 2 hours in an atmosphere, a step of raising the temperature of the mixture from a predetermined temperature in the range of 1200 to 1280 ° C. to a sintering temperature in the range of 1450 to 1550 ° C., The cermet may be produced through a step of sintering at a predetermined sintering temperature in the range of 〜1550 ° C. in a vacuum or a nitrogen atmosphere at a pressure of 1.33 to 13300 Pa for 0.5 to 2 hours.
[0021]
In the step (B) of the method for producing a cermet of the present invention, the temperature of the mixture is raised in a vacuum of 13.3 Pa or less, whereby Ti (C, N) particles serving as nuclei of a hard phase in a solid state before a liquid phase appears. Promotes denitrification and decarburization of Ti, thereby generating a large amount of atomic vacancies in Ti (C, N). In the same step (D), degassing of the hard phase is promoted, and carbonization is performed in an atmosphere of H ₂ , CH _4, or a mixed gas thereof to increase the carbon ratio near the surface of the Ti (C, N) particles. In the step (E), sintering is performed at a sintering temperature higher than the liquid phase appearance temperature, thereby promoting the grain growth of the peripheral structure surrounding the Ti-rich core and promoting the coarsening. Further, the peripheral (composite carbonitride solid solution) component atoms mainly surrounding the core of Ti (C, N) are substituted for the large number of atomic vacancies in the hard phase appearing in the step (D). This further promotes the coarsening of the peripheral portion.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
The atomic weights of nitrogen and carbon of titanium carbonitride forming the core of the hard phase of the cermet of the present invention were measured by Auger electron spectroscopy on 10 core particles, and the ratio of nitrogen to the total of nitrogen and carbon was determined by atom. Calculate by ratio. The core part and the peripheral part or the binder phase of the hard phase may be identified by the difference in the color tone of the reflected secondary electron image of the scanning electron microscope (SEM). Specifically, the cermet was polished in cross section, and the cross-sectional structure thereof was subjected to SEM to obtain a reflected secondary electron image at a magnification of 5000 times, and the average particle diameter a of the core portion rich in Ti and the average particle size b of the peripheral portion were determined. It is better to measure and obtain the ratio of (b / a). Here, the grain size a of the Ti-rich core portion is obtained from the reflected secondary electron image observed as described above, and the length of the Ti-rich core portion in the longitudinal direction and the direction perpendicular thereto is obtained by image analysis software. A was determined from the average value.
[0023]
The average particle size b of the peripheral portion may be obtained from the reflected secondary electron image observed as described above, using Fullman's formula. Here, Fullman's equation is that the average particle size of the hard phase of the cermet is dm, the number of hard phases per unit length hit by an arbitrary straight line on the cross-section polished surface is NL, and is included in an arbitrary unit area. When the number of hard phases is NS, the average particle size is calculated by Equation 1.
[Formula 1] dm = (4 / π) × (NL / NS)
The area ratio of the core portion rich in Ti may be obtained by using commercially available image analysis software. The Mo content (% by weight) in the cermet is preferably measured from the polished surface of the cross section with a fluorescent X-ray analyzer and quantified based on the intensity.
[0024]
【Example】
TiC powder and Ti (C, N) powder having an average particle size of 1.5 μm (TiC / TiN = 10/0 to 4/6 by weight ratio) and WC, NbC, Mo, Ni and Co as other raw material powders Each powder was weighed so as to have the ratio shown in Table 1, charged into a stainless steel pot together with an acetone solvent and a cemented carbide ball, and mixed and strongly pulverized. The obtained mixture (mixed powder) was press-formed at a pressure of 196 MPa using a SPMN120308 shape mold described in JIS-B4120 to produce a formed body.
[0025]
The molded body is heated (a) from room temperature to 1000 ° C. in a vacuum atmosphere of 67 Pa, and (b) heated to 1250 ° C. in a vacuum at a pressure (Pa) and a speed (° C./min) described in Table 1. (C) Hold at 1250 ° C. for 1 hour in the atmosphere and pressure (Pa) described in Table 2, and (d) Pressure 1.33 to a sintering temperature of 1550 ° C. at a rate of 1 ° C./min. The temperature was raised in an N ₂ atmosphere of １３1333 Pa and held for 1 hour, and then (e), then cooled to room temperature in an N ₂ atmosphere to produce invention products 1 to 7 and comparative products 1 to 5.
[0026]
The cermet chips of Invention Products 1 to 7 and Comparative Products 1 to 5 thus obtained were cut at the center, the cut surfaces were ground, and then lapping was performed with a 1 μm diamond paste. The lapping surface was observed with a scanning electron microscope at a magnification of 5000 times, and a reflected secondary electron image was obtained for a cross-sectional structure inside the sample that was 0.5 mm or more in the depth direction from the sample surface. When the average particle size of the Ti-rich core portion is represented by a, and the average particle size of the peripheral portion surrounding the Ti-rich core portion is represented by b, the ratio of (b / a) is obtained by the method described above. Further, the average particle size of the hard phase was determined. The area ratio of the Ti-rich core was determined by image analysis software. The atomic contents of nitrogen and carbon of the core Ti (C, N) were determined by Auger analysis, and the ratio of nitrogen to the total of nitrogen and carbon (N / (C + N)) was determined by the atomic ratio. In addition, X-ray fluorescence analysis was performed on the wrapped surface inside the sample, which was 0.5 mm or more in the depth direction from the sample surface, to determine the Mo content. These results are shown in Table 3.
[0027]
[Table 1]

[0028]
[Table 2]

[0029]
The sintered body obtained under the conditions shown in Table 1 was ground on the upper and lower surfaces with a # 230 diamond grindstone, and further subjected to a honing treatment of 0.15 mm × 30 ° on the flank of the flank cutting edge. A comparative test of the flank wear amount was performed by a cutting test. Table 3 shows the results.
[0030]
Cutting test condition 1 (wear test)
Work material: FCD450
Cutting speed: 180m / min
Cut: 0.2mm
Feed: 0.2mm / rev
Cutting oil: WET
Cutting time: 50min
[0031]
Cutting test condition 2 (breakage test)
Work material: FCD450
Cutting speed: 220mm / rev
Cut: 0.2mm
Feed: 0.2mm / rev
Cutting oil: WET
The number of repetitions of 5 seconds cutting and 5 seconds pause is 100, and the test is completed. The number of tests is 3 for each sample.
[Table 3]

(Welding) was lost due to welding of the work material.
[0033]
【The invention's effect】
As is clear from the above results, the ratio of nitrogen (N / (N + C)) in the core of the hard phase such as invention products 1 to 7 is 0.2 ≦ (N / (N + C)) ≦ 0 in atomic ratio. 0.5, the average particle diameter is 2 to 7 μm, and when the average particle diameter of the core is represented by a and the average particle diameter of the peripheral part is represented by b, 3 ≦ (b / a) ≦ 8. The cermet of the present invention having a hard phase exhibits superior wear resistance, chipping resistance and welding resistance in cutting cast iron, as compared with conventional cermets. This is because the low-nitrogen-containing cermet is superior to the high-nitrogen-containing cermet in chemical reaction resistance with cast iron, and thus exhibits an excellent effect on wear and breakage due to welding and the like during cutting. Further, by making the core portion rich in Ti as fine as possible and setting the average particle size of the hard phase to 2 to 7 μm, it became possible to improve the fracture resistance.

Claims

Hard phase consisting of at least one selected from the group consisting of carbides, nitrides, carbonitrides and solid solutions of metals of the periodic table 4a, 5a and 6a: 70 to 97% by weight, and selected from iron group metals A cermet comprising at least one binder phase having at least one kind as a main component and the balance, wherein the hard phase has a ratio of nitrogen (N / (N + C)) to the total of nitrogen and carbon contained in titanium carbonitride. A core of titanium carbonitride having an atomic ratio of 0.2 ≦ (N / (N + C)) ≦ 0.5 and at least one selected from metals of Group 4a, 5a, and 6a of the periodic table other than titanium; When the average particle size of the core portion is represented by a and the average particle size of the peripheral portion is represented by b, 3 ≦ (b / a) ≦ 8, comprising a peripheral portion of a composite carbonitride solid solution with titanium. A cermet wherein the hard phase has an average particle size of 2 to 7 μm.

The cermet according to claim 1, wherein the area ratio of the core is 2 to 20% by area.

The cermet according to claim 1, wherein the Mo content of the cermet is 0.5 to 3.5% by weight.

The cermet according to any one of claims 1 to 3, wherein the cermet is used as a cutting tool.

(A) Titanium carbonitride powder in which the atomic ratio of nitrogen (N / (N + C)) to the total of nitrogen and carbon contained in titanium carbonitride is 0.2 ≦ (N / (N + C)) ≦ 0.5 : 50 to 75% by weight, and at least one powder selected from compounds of metals of Groups 4a, 5a and 6a of the Periodic Table: 20 to 40% by weight and at least 1 powder selected from iron group metals Seed powder: a step of obtaining a mixture consisting of 3 to 30% by weight and a total of 100% by weight, (B) a step of raising the temperature of the mixture to a predetermined temperature of 1200 to 1280 ° C, and (C) a step of heating the mixture to 1200 to 1280 (D) maintaining the mixture at a predetermined temperature in the range of 1200 ° C. to 1280 ° C. to a sintering temperature in the range of 1450 to 1550 ° C. The process of raising the temperature to Method for manufacturing a cermet comprising sintering holding a predetermined time at a sintering temperature in the range of E) mixture 1,450 to 1,550 ° C..