JP4540791B2

JP4540791B2 - Cermet for cutting tools

Info

Publication number: JP4540791B2
Application number: JP2000094463A
Authority: JP
Inventors: 伸夫北條
Original assignee: Tungaloy Corp
Current assignee: Tungaloy Corp
Priority date: 2000-03-30
Filing date: 2000-03-30
Publication date: 2010-09-08
Anticipated expiration: 2020-03-30
Also published as: JP2001277008A

Description

【０００１】
【発明の属する技術分野】
耐摩耗性と耐欠損性が要求される切削工具で、特に高速切削領域での耐摩耗性、耐熱衝撃性にすぐれる切削工具用サーメットおよびその製造方法に関する
【０００２】
【従来の技術】
従来のサーメットは、切削状況の変化への対策としていくつかの発明が提案されてきた。具体的には、微粒化を目的とした窒素添加、サーメット中の窒素量制御、有芯構造および組成制御、粒径制御、粒径分布制御などの発明が提案されている。
【０００３】
有芯構造に関して例えば特表平８―５０８０６６号公報では、（Ｔｉ，Ｗ，Ｔａ，Ｎｂ）Ｃおよび／または（Ｔｉ，Ｗ，Ｔａ）ＣとＴｉＣＮとＷとＣｏを含有し、ＴｉＣＮ中の窒素量Ｎ／（Ｃ＋Ｎ）が０．７以上からなる窒素に富むサーメットが提案されている。ただし、粒径を１．５μm以下と限定しているため、高温領域での耐熱衝撃性が劣り、現在の高速切削条件における切削性能は不十分であった。また特開平９―１７４３０６号公報では、Ｔｉの炭窒化物と、周期率表第４ａ、５ａ、６ａ族炭化物、窒化物、炭窒化物からなる硬質相と鉄族金属を含む結合相からなり、Ｎ／（Ｃ＋Ｎ）比が０．４〜０．７のサーメットであって、有芯構造の粒子で囲まれた芯のない粒子または１μｍ以下の微粒粒子の凝集体が点在したことが提案されている。ここでは、凝集部を形成させるための条件として、Ｔｉ化合物の粒径を０．５〜２μｍとしているため高温領域での耐熱衝撃性が劣り、現在の高速切削条件における切削性能は不十分であった。粗粒の硬質相を特徴とするサーメットとして特公昭６１―４１１号公報、特公昭６１―２２２０１６号公報があり、両公報ともに７μｍ以上のＴｉＣを１〜３０ｖｏｌ％添加することで耐摩耗性の向上を提案している。また、特開昭６１―１２８４６号公報では、粒径５〜１０μmの粒子を含み、平均粒径３〜８μmであるサーメットが提案されている。これらはいずれも、Ｔｉ化合物が低窒素なサーメットに関するものであった。
【０００４】
さらに、特開平５―１８６８４３号公報では、硬質成分の平均粒径が１μm未満のより微細化されたマトリックスの中に、コアのための平均粒径が２〜８μmのコア・リム構造を有する硬質成分粒子を１０〜５０体積％含み、微細マトリックス粒子とコア・リム構造粒子の平均粒子径の差が１．５μm以上である炭窒化物焼結合金が提案されているが、低窒素であるために実施例にも記載されているような切削領域では効果を発揮するものの、より高温領域での熱塑性変形性および耐熱衝撃性が劣り、現在の高速切削条件における工具性能としては不十分であった。
【０００５】
また、コア・リム構造の硬質相を含むサーメットについては、古くはアメリカ特許第３９７１６５６号が開示されてより日本においても種々提案されてきており、その中でも特にコアに着目した特許が提案されている。例えば、特開平１０―２８７９４６号公報ではコアが粒子全体の３０面積％以上の粒子と、コアが粒子全体の３０面積％未満の粒子との比を０．３〜０．８と限定しているが、粒径の絶対値や窒素含有量の影響が大きい切削条件の領域では所望の効果が得られない問題があった。特開平１０―２９８６９７号公報では黒芯の面積が０．１〜０．７μm²と０．８〜２．５μm²の範囲にピークを持つことが開示されているが、請求範囲で限定された硬質粒子の芯は比較的微細であるため、高温領域での耐熱衝撃性が劣り、現在の高速切削条件における切削性能は不十分であった。
【０００６】
【発明が解決しようとする課題】
上記のように、従来のサーメットでは耐摩耗性と耐欠損性を共に向上させることは難しく、特に近年の高速切削に対応できる高温領域での機械的な要求特性と熱的な要求特性を同時に満足させることは困難であった。
【０００７】
【課題を解決するための手段】
本発明はこれらの課題を解決すべく種々の検討を行なった結果、主として周期率表４ａ族金属の炭化物、窒化物、炭窒化物および相互固溶体の１種以上の芯部を有する粒子の窒素量と炭素量の原子比が０.４≦窒素/(窒素＋炭素)≦０.９５であって、かつ、該焼結体の組織は、芯部の粒径が３μm以上である粒子の芯部面積が全硬質相の３面積％以上、かつ2μm以上である粒子の芯部面積が全硬質相の１０面積％以上であることを特徴とするサーメットが、極めて優れた耐摩耗性と耐欠損性を兼ね備えることが明らかとなったものである。さらに、芯部粒径が３μm以上である粒子の芯部面積が有芯構造である全硬質相芯部の１０面積％以上、かつ2μm以上である粒子の芯部面積が有芯構造である全硬質相芯部の３０面積％以上であることでさらに高温特性が向上することを明らかにした。加えて、０．５μｍ以下の芯部を持つ粒子により結合相のミーンフリーパスを短くなり耐熱衝撃性が向上することが明らかとなった。
【０００８】
また、上記の主として周期率表４ａ族金属の炭化物、窒化物、炭窒化物および相互固溶体の１種以上の芯部を有する粒子の芯部の径が３μm以上の分布幅とすることによって、高温領域で要求される強度と硬度を兼ね備えるものである。さらに、主として周期率表４ａ族金属の炭化物、窒化物、炭窒化物および相互固溶体の１種以上の芯部を有する粒子の平均粒径をＡ、主として周期率表５ａ、６ａ族金属の炭化物、窒化物、炭窒化物および相互固溶体の１種以上からなる芯部を有する粒子の平均粒径をＢとした場合、Ｂ／Ａ≦０．５とした焼結体組織にすることにより、強度および耐欠損性が向上するものである。これらのサーメットは平均粒径６μm以上で、かつ０．４≦窒素/(窒素＋炭素)≦０．９５である炭窒化チタン粉末を原料として配合し、高温かつ高窒素雰囲気下で焼結することにより従来には得られなかったサーメットが実現されたものである。
【０００９】
【発明の実施態様】
従来の高窒素サーメットでは窒素量の増加に伴って焼結性が低下するため、原料粉末粒径や焼結条件を調整して組織を微粒化して焼結してきた。微粒化しない場合では焼結後の焼結体強度が低下するため、切削工具として用いた場合に従来の焼結条件では所望の強度が得られなかった。本発明は、高速切削で要求される高温特性の向上に特に着目して種々の試験を行った結果、従来の焼結条件では得られなかった粗粒であってかつ高窒素な芯部が形成された硬質相を有する焼結体が得られたものである。主として周期率表４ａ族金属の炭化物、窒化物、炭窒化物の１種以上の芯部を有する粒子を高窒素にするのには焼結性の点からは微粒な方が所望の特性が得られやすいが、それに対してあえて粗粒にする目的は、高温での耐熱衝撃性を向上させることが極めて高速切削での切削性能に対して効果が高いことが明らかになったためである。なおかつ高窒素としたために低窒素合金に比較して靭性が向上した。さらに窒素量が多いほど金属や酸素との反応性が低下するため、従来のサーメットよりも化学的な耐摩耗性の向上をも実現したものである。
【００１０】
本発明では特に粒子を有芯構造として、その芯部の大きさが極めて切削性能に大きな影響を与えることが明らかとなったものであり、主として周期率表４ａ族金属の炭化物、窒化物、炭窒化物および相互固溶体の１種以上の芯部を有する粒子は、粒子の窒素／（窒素＋炭素）原子比が０．４以上０．９５以下であって、該焼結体の組織は、芯部の粒径が３μm以上である粒子の芯部面積が全硬質相の３面積％以上、かつ２μm以上である粒子の芯部面積が全硬質相の１０面積％以上有すれば所望の効果が認められ、上記限定事項を満足しない焼結体では、特に着目した高速領域での切削性能が劣るものであった。これは従来の微粒芯部を有するサーメットに比べて、粒子の脱落が起こりにくく硬質相のなかでも耐摩耗性に寄与する芯部の比率が高いため優れた耐摩耗性を示し、かつ個々粒子の中間相間の接着強度が向上したことにより、熱衝撃によるクラックに対して優れた耐欠損性を有しているためと思われる。その芯部の窒素量は０．４未満では高温特性が劣化し、０．９５以上では所望の耐摩耗性が得られないため０．４以上０．９５以下と限定したが、０．４５以上０．７以下が好ましく、０．５以上０．６４以下がさらに好ましい。また、芯部の粒径が３μm以上である粒子の芯部面積が有芯構造である全硬質相芯部の１０面積％以上、かつ2μm以上である粒子の芯部面積が有芯構造である全硬質相芯部の３０面積％以上となるように、粗い芯をもつ粒子の比率を上記の条件を満足する焼結体では、粗粒の粒子によって熱衝撃クラックの進展を遅らせるため、耐熱衝撃性が向上するものである。
【００１１】
さらに、０．５μｍ以下の芯部を持つ粒子により結合相のミーンフリーパスを短くさせることにより、耐熱衝撃性性が向上するが、芯部面積が全硬質相の５面積％より多い焼結体では高温領域での特性を低下させ、２面積％以下では所望の特性が得られないため２〜５面積％と限定した。そのことより、０．５μｍ以下の芯部を持つ粒子の５０％以上を結合相と接していることを限定した。また、芯の大きさの粒径分布は、３μm未満では切削応力の変動および熱衝撃による負荷に対する所望の性能が得られないため、３μm以上と限定したが、５〜１０μmであることがより好ましい。
【００１２】
主として周期率表４ａ族金属の炭化物、窒化物、炭窒化物および相互固溶体の１種以上の芯部を有する粒子の平均粒径をＡ、主として周期率表５ａ、６ａ族金属の炭化物、窒化物、炭窒化物の１種以上からなる芯部を有する粒子の平均粒径をＢとした場合、Ｂ／Ａが０．５より大きい場合は高温での耐熱塑性変形性が劣るため０．５以下と限定した。
【００１３】
本発明の切削工具用サーメットを得るには原料粉が高窒素であることは当然であるが、さらに平均粒径が６μm以上の原料粉を配合することによって所望の特性が得られることが本件で明らかとなった。平均粒径が６μmより細かい原料粉を用いても混合時間や焼結時間を短縮することで粗い芯を有する焼結体が得られるが、そのようにして得られた焼結体では、混合時間が短い条件では分散が悪いため耐摩耗性と耐欠損性の切削性能のバラツキが大きく、焼結時間が短い条件では欠陥が残りやすいことにより強度が低下し、欠損に係る工具寿命のバラツキが極めて大きくなるため、平均粒径が６μm以上のＴｉＣＮ粉として原料に使用すると限定したが、さらに粗い8μｍ以上のＴｉＣＮ粉を用いることが好ましい。焼結条件は高温かつ高窒素雰囲気下で行うことで、高窒素かつ３μm以上の粗粒の芯を有する焼結体が得られたものである。
【００１４】
【実施例】
市販されている平均粒子径が１〜２μmのＷＣ、（Ｗ，Ｔｉ）Ｃの複合炭化物（重量比でＷＣ／ＴｉＣ＝７０／３０）、ＴａＣ、Ｍｏ₂Ｃ、ＺｒＣ、Ｃｏ、Ｎｉと発明品として平均粒径１０μmのＴｉＣ、ＴｉＮ、ＴｉＣＮ（重量比でＴｉＣ／ＴｉＮ＝４０／６０〜５０／５０）、比較品として平均粒径１．５μｍのＴｉＣ、ＴｉＮ、ＴｉＣＮ（重量比でＴｉＣ／ＴｉＮ＝４０／６０〜５０／５０）の各原料粉末を表１に示した配合組成に秤量し、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、２０時間混合した。
得られた混合粉末をＪＩＳ−Ｂ４１２０に記載のＳＰＭＮ１２０３０８形状用金型でもって、１９６ＭＰａの圧力でプレス成形した。得られた粉末成形体を雰囲気圧力０．１３〜２．６ｋＰａの窒素気流中で温度１７７３〜１８７３Ｋ、保持時間１時間の条件で焼結を行ない、本発明品１〜６および比較品１〜６を得た。
【００１５】
【表１】
焼結体配合組成

配合量：mass％、発明品焼結温度：1873K、比較品焼結温度：1773K
【００１６】
こうして得られた本発明品１〜６、比較品１〜６のサーメットチップを切断し、逃げ面側の断面を研削した後、1μmのダイヤモンドペーストにより表面から０．２ｍｍの内部までラップ加工を行なった。加工面を光学顕微鏡で１５００倍に拡大して観察し、画像解析装置で芯部が３μm以上である粒子と芯部が２μm以上である粒子の芯部の面積％を、５視野測定して平均値を求めた。また、該芯部のＮおよびＣ量をＷＤＳにより測定した。
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、さらに切れ刃稜線部に０．１５×―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評価を行なった。結果を表２に示す。
【００１７】
切削試験条件1（摩耗試験）
被削材：Ｓ４８Ｃ
切削速度：２４０ｍ／ｍｉｎ
切り込み：１．５ｍｍ
送り：０．３２ｍｍ／ｒｅｖ.
切削油：使用せず（乾式切削）
切削時間：２０ｍｉｎ
【００１８】
切削試験条件２（欠損試験）
被削材 SNCM439
切削速度２４０m/min
切り込み１mm
送り 0.2 mm/rev.
切削油：WET（水溶性）
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
【００１９】
【表２】
試験結果

※１比較品５は焼結時の温度が低いために欠陥を多く含み、所望の性能を得られなかった。
【００２０】
【発明の効果】
上記の結果から明らかなように、発明品１〜６のような高窒素であってかつ３μm以上の粗粒な芯部を有する硬質相の芯部面積が全硬質相の３面積％以上、かつ2μm以上の粗粒な芯部を有する硬質相の芯部面積が全硬質相の１０面積％以上含まれるサーメットは、比較品１〜６に示したような従来の微粒芯部を有するサーメットに比べて、粒子の脱落が起こりにくく硬質相のなかでも耐摩耗性に寄与する芯部の比率が高いため優れた耐摩耗性を示し、かつ、個々粒子の中間相間の接着強度が向上したことにより、熱衝撃によるクラックに対して優れた耐欠損性を示している。[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool that requires wear resistance and fracture resistance, and particularly to a cermet for a cutting tool that has excellent wear resistance and thermal shock resistance in a high-speed cutting region, and a manufacturing method thereof.
[Prior art]
Several inventions have been proposed for conventional cermets as countermeasures against changes in cutting conditions. Specifically, inventions such as nitrogen addition for the purpose of atomization, control of the amount of nitrogen in the cermet, cored structure and composition control, particle size control, particle size distribution control have been proposed.
[0003]
With regard to the cored structure, for example, JP-T-8-508066 discloses (Ti, W, Ta, Nb) C and / or (Ti, W, Ta) C, TiCN, W and Co, and nitrogen in TiCN. Nitrogen-rich cermets with a quantity N / (C + N) of 0.7 or more have been proposed. However, since the particle size is limited to 1.5 μm or less, the thermal shock resistance in the high temperature region is inferior, and the cutting performance under the current high-speed cutting conditions is insufficient. In JP-A-9-174306, Ti carbonitride, periodic table 4a, 5a, 6a group carbide, nitride, consisting of a hard phase composed of carbonitride and a binder phase containing an iron group metal, It is proposed that the cermet has an N / (C + N) ratio of 0.4 to 0.7 and is dotted with agglomerates of coreless particles or fine particles of 1 μm or less surrounded by cored particles. ing. Here, as a condition for forming the agglomerated part, since the particle size of the Ti compound is 0.5-2 μm, the thermal shock resistance in the high temperature region is inferior, and the cutting performance under the current high-speed cutting conditions is insufficient. It was. Japanese Patent Publication No. 61-411 and Japanese Patent Publication No. 61-222016 are cermets characterized by a coarse hard phase, and both publications improve wear resistance by adding 1-30 vol% of TiC of 7 μm or more. Has proposed. Japanese Patent Laid-Open No. 61-12846 proposes a cermet containing particles having a particle diameter of 5 to 10 μm and having an average particle diameter of 3 to 8 μm. These all relate to cermets in which the Ti compound is low nitrogen.
[0004]
Further, in Japanese Patent Application Laid-Open No. 5-186843, a hard component having a core-rim structure having an average particle size of 2 to 8 μm for a core in a more refined matrix having an average particle size of a hard component of less than 1 μm. A carbonitride sintered alloy containing 10 to 50% by volume of component particles and having a difference in average particle size between the fine matrix particles and the core / rim structure particles of 1.5 μm or more has been proposed. Although it is effective in the cutting region as described in the examples, it is inferior in thermoplastic deformation and thermal shock resistance in a higher temperature region, and is insufficient as a tool performance under the current high-speed cutting conditions. .
[0005]
In addition, cermets containing a hard phase with a core-rim structure have been proposed in Japan since the disclosure of US Pat. No. 3,971,656, and among them, patents focusing on the core have been proposed. . For example, in Japanese Patent Laid-Open No. 10-287946, the ratio of particles having a core of 30 area% or more of the whole particle and particles having a core of less than 30 area% of the whole particle is limited to 0.3 to 0.8. However, there is a problem that a desired effect cannot be obtained in a region of cutting conditions where the influence of the absolute value of the particle size or the nitrogen content is large. Japanese Patent Laid-Open No. 10-298697 discloses that the area of the black core has peaks in the range of 0.1 to 0.7 μm ² and 0.8 to 2.5 μm ² , but is limited by the claims. Since the core of the hard particles is relatively fine, the thermal shock resistance in a high temperature region is inferior, and the cutting performance under the current high-speed cutting conditions is insufficient.
[0006]
[Problems to be solved by the invention]
As mentioned above, it is difficult to improve both wear resistance and fracture resistance with conventional cermets, and satisfy both the mechanical and thermal requirements in the high temperature range that can handle high-speed cutting in recent years. It was difficult to do.
[0007]
[Means for Solving the Problems]
As a result of various investigations to solve these problems, the present invention mainly has a nitrogen content of particles having one or more cores of carbides, nitrides, carbonitrides and mutual solid solutions of Group 4a metals in the periodic table. And the atomic ratio of the amount of carbon is 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95, and the structure of the sintered body is a core of a particle having a core having a particle size of 3 μm or more. A cermet with an area of 3% by area or more of the entire hard phase and a core area of particles of 2 μm or more of 10% by area or more of the entire hard phase has excellent wear resistance and fracture resistance. It has become clear that it has both. Furthermore, the core area of the particles having a core particle diameter of 3 μm or more is 10 area% or more of the total hard phase core part having a cored structure, and the core area of the particles having a core diameter of 2 μm or more is the cored structure. It has been clarified that the high temperature characteristics are further improved by being 30% by area or more of the hard phase core part. In addition, it has been clarified that particles having a core of 0.5 μm or less shorten the mean free path of the binder phase and improve the thermal shock resistance.
[0008]
Further, by setting the diameter of the core part of the particles having one or more kinds of cores of carbides, nitrides, carbonitrides and mutual solids of the periodic table 4a metal to a distribution width of 3 μm or more, It combines strength and hardness required in the region. Furthermore, the average particle size of the particles having one or more cores of periodic table 4a group metal carbide, nitride, carbonitride and mutual solid solution is A, mainly periodic table 5a, 6a group metal carbide, When the average particle size of the particles having a core portion composed of one or more of nitride, carbonitride, and mutual solid solution is B, by making a sintered body structure with B / A ≦ 0.5, strength and This improves the fracture resistance. These cermets should be blended with titanium carbonitride powder having an average particle size of 6 μm or more and 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95 as a raw material and sintered in a high temperature and high nitrogen atmosphere. Thus, a cermet that was not obtained in the past has been realized.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In conventional high nitrogen cermets, the sinterability decreases with an increase in the amount of nitrogen. Therefore, the raw material powder particle size and the sintering conditions are adjusted to make the structure finer and sinter. When the particles are not atomized, the strength of the sintered body after sintering is lowered. Therefore, when used as a cutting tool, the desired strength cannot be obtained under conventional sintering conditions. As a result of various tests focusing on improving the high-temperature characteristics required for high-speed cutting, the present invention forms coarse and high-nitrogen cores that could not be obtained under conventional sintering conditions. A sintered body having the hard phase thus obtained is obtained. In order to make particles having one or more cores of group 4a metal carbides, nitrides, and carbonitrides of high periodicity mainly from the viewpoint of sinterability, finer particles have desirable characteristics. However, the purpose of coarse graining is that it has become clear that improving the thermal shock resistance at high temperatures is highly effective for cutting performance in extremely high-speed cutting. In addition, because of the high nitrogen, the toughness improved compared to the low nitrogen alloy. Furthermore, since the reactivity with a metal and oxygen falls, so that there is much nitrogen amount, the improvement of chemical abrasion resistance is also implement | achieved rather than the conventional cermet.
[0010]
In the present invention, it has been clarified that the particle has a cored structure, and the size of the core part has a great influence on the cutting performance. Mainly, the periodic table 4a group metal carbide, nitride, charcoal The particles having one or more cores of nitride and mutual solid solution have a nitrogen / (nitrogen + carbon) atomic ratio of the particles of 0.4 or more and 0.95 or less, and the structure of the sintered body is the core If the core area of a particle having a particle size of 3 μm or more is 3 area% or more of the entire hard phase and the core area of a particle having a particle diameter of 2 μm or more is 10 area% or more of the entire hard phase, a desired effect is obtained. The sintered body that was recognized and did not satisfy the above-mentioned limitations was inferior in cutting performance in a particularly high speed region. This is superior to conventional cermets with fine-grained cores, and it has excellent wear resistance due to the high proportion of cores that contribute to wear resistance even in the hard phase. This is probably because the adhesive strength between the intermediate phases has improved, and thus it has excellent fracture resistance against cracks caused by thermal shock. If the nitrogen content of the core is less than 0.4, the high temperature characteristics deteriorate, and if it is 0.95 or more, the desired wear resistance cannot be obtained, so it is limited to 0.4 or more and 0.95 or less. 0.7 or less is preferable and 0.5 or more and 0.64 or less are more preferable. In addition, the core area of the particles whose core part particle size is 3 μm or more is 10 area% or more of the total hard phase core part having a cored structure, and the core part area of particles having a core part structure of 2 μm or more is the cored structure. In a sintered body that satisfies the above-mentioned conditions for the ratio of particles having a rough core so that it is 30 area% or more of the total hard phase core portion, the progress of thermal shock cracks is delayed by the coarse particles. The property is improved.
[0011]
Furthermore, the thermal shock resistance is improved by shortening the mean free path of the binder phase with particles having a core of 0.5 μm or less, but the sintered body has a core area larger than 5 area% of the total hard phase. Then, the characteristics in the high temperature region were lowered, and since desired characteristics could not be obtained at 2 area% or less, it was limited to 2 to 5 area%. From this, it was limited that 50% or more of the particles having a core of 0.5 μm or less were in contact with the binder phase. Further, the particle size distribution of the core size is limited to 3 μm or more because desired performance with respect to load due to fluctuations in cutting stress and thermal shock cannot be obtained if it is less than 3 μm, but it is more preferably 5 to 10 μm. .
[0012]
The average particle size of the particles having one or more cores of group 4a metal carbide, nitride, carbonitride, and mutual solid solution is mainly A, and the period table 5a, group 6a metal carbide, nitride When the average particle diameter of the particles having a core portion composed of one or more types of carbonitride is B, if B / A is larger than 0.5, the heat plastic deformation at high temperatures is inferior, so that it is 0.5 or less. And limited.
[0013]
In order to obtain the cermet for a cutting tool of the present invention, it is natural that the raw material powder is high nitrogen, but it is the present case that desired characteristics can be obtained by further blending the raw material powder having an average particle size of 6 μm or more. It became clear. Even if a raw material powder having an average particle size smaller than 6 μm is used, a sintered body having a coarse core can be obtained by shortening the mixing time and the sintering time. However, the dispersion of the wear resistance and fracture resistance is large due to poor dispersion under short conditions, and the strength decreases due to the fact that defects tend to remain under conditions where the sintering time is short, resulting in extreme variations in tool life related to fracture. Since it becomes large, it was limited to use it as a raw material as a TiCN powder having an average particle diameter of 6 μm or more, but it is preferable to use a coarser TiCN powder of 8 μm or more. Sintering is performed under a high temperature and high nitrogen atmosphere to obtain a sintered body having a high-nitrogen and coarse core of 3 μm or more.
[0014]
【Example】
Commercially available WC having an average particle size of 1 to 2 μm, composite carbide of (W, Ti) C (weight ratio WC / TiC = 70/30), TaC, Mo ₂ C, ZrC, Co, Ni and invention products TiC, TiN, TiCN having an average particle size of 10 μm (TiC / TiN = 40/60 to 50/50 by weight ratio), and TiC, TiN, TiCN having an average particle size of 1.5 μm (TiC / TiN by weight ratio) as comparative products = 40/60 to 50/50), each raw material powder was weighed to the blending composition shown in Table 1, and placed in a stainless steel pot together with an acetone solvent and a cemented carbide ball and mixed for 20 hours.
The obtained mixed powder was press-molded at a pressure of 196 MPa using a SPMN120308 shape mold described in JIS-B4120. The obtained powder compact was sintered in a nitrogen stream at an atmospheric pressure of 0.13 to 2.6 kPa under conditions of a temperature of 1773 to 1873 K and a holding time of 1 hour. Got.
[0015]
[Table 1]
Sintered body composition

Compounding amount: mass%, invention product sintering temperature: 1873K, comparative product sintering temperature: 1773K
[0016]
After cutting the cermet chips of the present invention products 1 to 6 and comparative products 1 to 6 thus obtained and grinding the cross section on the flank side, lapping is performed from the surface to the inside of 0.2 mm with a 1 μm diamond paste. It was. The processed surface was magnified 1500 times with an optical microscope and observed with an image analyzer, and the area% of the core portion of the particle having a core portion of 3 μm or more and the core portion of the particle having a core portion of 2 μm or more was measured by 5 visual fields and averaged. The value was determined. In addition, the N and C contents of the core were measured by WDS.
The upper and lower surfaces of the sintered body obtained under the conditions shown in Table 1 were ground with a # 230 diamond grindstone, and the cutting edge ridge was subjected to a honing treatment of 0.15 × −30 °, and cutting under the following conditions: A comparative evaluation of the amount of flank wear was performed by the test. The results are shown in Table 2.
[0017]
Cutting test condition 1 (Abrasion test)
Work material: S48C
Cutting speed: 240 m / min
Cutting depth: 1.5mm
Feed: 0.32 mm / rev.
Cutting oil: Not used (dry cutting)
Cutting time: 20 min
[0018]
Cutting test condition 2 (defect test)
Work material SNCM439
Cutting speed 240m / min
1mm depth of cut
Feed 0.2 mm / rev.
Cutting oil: WET (water-soluble)
5 seconds cutting-5 seconds pause repeat count 100 times, test end test number is 3 times for each sample
[Table 2]
Test results

* 1 Comparative product 5 contained many defects due to the low temperature during sintering, and the desired performance could not be obtained.
[0020]
【The invention's effect】
As is apparent from the above results, the core area of the hard phase having high nitrogen as in Inventions 1 to 6 and having a coarse core of 3 μm or more is 3 area% or more of the total hard phase, and The cermet in which the core area of the hard phase having a coarse core part of 2 μm or more is contained by 10% by area or more of the total hard phase is compared with the cermet having the conventional fine core part as shown in comparative products 1-6. In addition, since the ratio of the core that contributes to wear resistance is high in the hard phase, the particles are less likely to fall off and show excellent wear resistance, and the adhesive strength between the intermediate phases of the individual particles is improved. Excellent fracture resistance against cracks caused by thermal shock.

Claims

The main component is one or more of Ti carbide, nitride, carbonitride, and one of carbides, nitrides, carbonitrides of groups 4a, 5a, and 6a of the periodic table, and 1 of these solid solutions. In a titanium carbonitride-based alloy composed of 70 to 97% by weight of a hard phase containing at least seeds and a binder phase and unavoidable impurities consisting of one or more types of iron group metal in the balance, the hard phase is mainly composed of a periodic table 4a group metal. Particles having one or more cores of carbide, nitride, carbonitride and mutual solid solution, and mainly composed of one or more of periodic table 5a, group 6a metal carbide, nitride, carbonitride and mutual solid solution In a cermet composed of particles having a core and single-phase particles composed of one or more of carbides, nitrides, carbonitrides and mutual solids of 4a, 5a, and 6a in the periodic table, the group 4a metal in the periodic table Carbide, nitriding The atomic ratio of the nitrogen content and the carbon content of the particles having one or more core parts of carbonitride and mutual solid solution is 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95, and the structure of the sintered body is: The core area of particles having a core particle size of 3 μm or more is 3 area% or more of the entire hard phase, and the core area of particles having a particle diameter of 2 μm or more is 10 area% or more of the entire hard phase. Cermet for cutting tools

In the particles having one or more core parts of the carbides, nitrides, carbonitrides, and their mutual solid solutions, mainly the periodic table 4a group metal, the core area of the particles having a core particle diameter of 3 μm or more is A patent characterized in that the core area of a particle having a core structure of 10% by area or more of the entire hard core part and 2 μm or more is 30% by area or more of the core part having a core structure. The cermet for a cutting tool according to claim 1

The core area of particles having a core particle size of 0.5 μm or less in the particles having one or more cores of the carbides, nitrides, carbonitrides and their mutual solid solutions, mainly of the periodic table 4a group metals. 2. The cermet for a cutting tool according to claim 1, wherein the cermet is 2 to 5% by area of the total hard phase.