JP3715775B2 - High speed cutting tool - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、鋼や鋳鉄等の被削材を高速で旋削加工するのに適した高速切削用工具に関するものである。
【０００２】
【従来の技術】
従来から、切削工具としては、超硬合金、サーメット等の金属−セラミック系材料に加え、アルミナ、窒化ケイ素等のセラミックスが用いられている。これらの中で、アルミナ系切削工具は、高硬度、耐高温、耐環境性などの優れた特性により、切削工具として注目されてきた。
【０００３】
従来から、アルミナ質焼結体を切削工具として採用した場合、アルミナ単味の焼結体では、高速切削条件下で使用される場合に、摩耗により寿命が短い、あるいはチッピング等が生じるなどの問題があることから、アルミナに対してＴｉＣやＴｉＮ等の金属窒化物、炭化物、炭窒化物粒子を分散したり（例えば特開平７−９７２５５号）、ＺｒＯ2 を分散させる方法が用いられ、硬度と靭性を向上することにより耐摩耗性や耐チッピング性等をを改善する効果が確認されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、上述の従来のアルミナ質切削工具は、低速切削条件ではある程度の長寿命性を有するが、２５０ｍ／ｍｉｎ以上の高速切削条件では、工具と被削材の間の摩擦により接触面の温度が１２００℃以上に温度上昇するため、分散粒子として添加された金属の窒化物、炭化物、炭窒化物粒子は被削材と反応して、クレータ摩耗を著しく加速する問題があった。また、ＺｒＯ2 分散系においては、高速切削時に軟化したり、変形する等の問題があった。
【０００５】
従って、本発明は、高速切削条件下でも優れた耐摩耗性を具備し、高速切削において優れた長寿命化が可能な切削工具を提供することを目的とするものである。
【０００６】
【課題を解決するための手段】
本発明者は、アルミナ質切削工具の高温での安定性を損なうことなく、表面部の硬度を大幅に改善して耐摩耗性を向上するための方法について検討を重ねた結果、被削材と接触する切削工具表面のアルミナ結晶粒子を微細化するとともに、その結晶粒子内に、Ｔｉ含有酸化物やＭｇ含有酸化物を析出させることにより、上記目的が達成できることを見いだした。
【０００７】
即ち、本発明の高速切削用工具は、第１の形態として、Ａｌ2 Ｏ3 を６０〜９９重量％、Ｔｉを酸化物換算で０．２〜５重量％、希土類元素、Ｚｒ、Ｈｆ、Ｍｏ、ＷおよびＳｉの群から選ばれる少なくとも１種を酸化物換算による合量で０．３〜３５重量％の割合で含有するアルミナ質焼結体からなる工具であって、少なくとも被削材との接触面におけるアルミナ結晶粒子の平均粒径が１０μｍ以下であり、該接触面から０．０１ｍｍ以上の深さに亘り、前記アルミナ結晶粒子内に平均粒径０．３μｍ以下のＴｉを含む酸化物粒子が分散していることを特徴とするものである。
【０００８】
また、第２の形態として、Ａｌ2 Ｏ3 を６０〜９９重量％、Ｔｉを酸化物換算で０．２〜５重量％、Ｍｇを酸化物換算で０．１〜３重量％、希土類元素、Ｚｒ、Ｈｆ、Ｍｏ、ＷおよびＳｉの群から選ばれる少なくとも１種を酸化物換算による合量で０．３〜３５重量％の割合で含有するアルミナ質焼結体からなる工具であって、少なくとも被削材との接触面におけるアルミナ結晶粒子の平均粒径が１０μｍ以下であり、該接触面から０．０１ｍｍ以上の深さに亘り、前記アルミナ結晶粒子内に平均粒径０．３μｍ以下のＭｇを含む酸化物粒子が分散していることを特徴とするものである。
【０００９】
【発明の実施の形態】
本発明の高速切削用工具における大きな特徴は、工具を形成するアルミナ質焼結体における被削材と接触する表面のアルミナ結晶粒子の平均粒径が１０μｍ以下であることに加え、そのアルミナ結晶粒子内に、平均粒径が０．３μｍ以下のＴｉを含む酸化物粒子、またはＭｇを含む酸化物粒子が分散している点にある。
【００１０】
切削工具の被削材との接触面において、少なくともアルミナ結晶粒内に上記微細な酸化物粒子を分散することにより、準粒界構造が形成され、硬度が著しく向上されるとともに、脱粒による摩耗を効果的に抑制できる。また、上記Ｔｉ含有酸化物粒子、Ｍｇ含有酸化物粒子としては、具体的には、ＴｉＯ2 、Ａｌ2 ＴｉＯ5 、ＲＥ2 Ｔｉ2 Ｏ7 （ＲＥは希土類元素）、ＭｇＯ、ＭｇＡｌ2 Ｏ4 などが挙げられる。
【００１１】
これらの酸化物は、いずれも化学的、熱的安定性に優れ、工具の耐酸化性を損なうことがないだけではなく、高温強度、高温硬度を大幅に改善する効果もある。よって、本発明の切削工具は、優れた耐フランク摩耗、耐クレータ摩耗特性を有し、高速切削条件下でも長い使用寿命を有する。また、この酸化物粒子は、アルミナ結晶粒内およびアルミナ結晶粒界にも析出する場合もある。
【００１２】
本発明によれば、上記ＴｉあるいはＭｇを含む酸化物粒子の平均粒径は０．３μｍ以下、特に０．２μｍ以下であることが必要である。これは、ＴｉあるいはＭｇを含む酸化物粒子の析出による耐摩耗性を改善する効果を十分に発揮させるために必要である。
【００１３】
即ち、アルミナ結晶粒内あるいは粒界に分散するＴｉまたはＭｇを含む酸化物粒子の粒径が小さい場合は、分散粒子同士の間隔が小さく、また、アルミナ結晶との間に結晶的整合性を保つことにより界面部の歪みが大きく、大きな硬化効果をもたらすことができる。従って、平均粒径が０．３μｍよりも大きいと、強化効果が低下するだけでなく、母相との界面にクラックが生成することにより耐摩耗性を劣化させることがある。
【００１４】
また、本発明によれば、工具中に含有されるＴｉ量が酸化物（ＴｉＯ2 ）換算で０．２〜５重量％、特に０．５〜３重量％であることが重要である。工具中に含まれるＴｉの含有量が０．２重量％よりも少なければ、アルミナ結晶粒子内への分散粒子の体積分率が少なく、耐摩耗性を改善する効果が小さい。逆にＴｉが５重量％よりも多く含まれると、アルミナ結晶粒子の粒界に粗大なＡｌ2 ＴｉＯ5 相が形成され、アルミナ結晶粒子との熱膨張差により微小なクラックが発生し、工具の耐欠損性を低下させることがある。
【００１５】
また、さらにＭｇを含有する場合、Ｍｇ含有量はＭｇＯに換算で０．１〜３重量％、特に０．１〜２重量％であることが必要である。Ｍｇの含有量が０．１重量％よりも少なければ、アルミナ結晶粒子内への分散粒子の体積分率が少なく、耐摩耗性を改善する効果が小さく、逆にＭｇが３重量％を越えて含まれると、焼結を阻害し、緻密な焼結体が得られにくくなる。
【００１６】
また、被削材との接触面におけるアルミナ結晶粒子径は、小さいほど良いが、本発明の切削工具では、平均粒径が１０μｍ以下であることがよい。特に、切削工具としての耐欠損性を高める上では、材料が高強度であるとともに、均質であることが望ましい。かかる観点から、アルミナの平均粒径は特に６μｍ以下であることが望ましく、さらには最大粒子径が３０μｍ以下、特に２０μｍ以下であることがさらに望ましい。なお、アルミナ結晶粒子径は、アルミナ結晶粒子が柱状体である場合には、長径の平均値である。
【００１７】
本発明の工具においては、表面の高度を向上させる上で、被削材との接触面から０．０１ｍｍ以上、特に０．０２ｍｍ以上の深さに亘り、上記ＴｉあるいはＭｇを含む酸化物粒子がアルミナ結晶粒内に析出していることが必要であるが、上記析出領域は、表面のみならず、工具の中心部まで析出していてもよい。
【００１８】
さらに、本発明の切削工具中には、希土類元素、Ｚｒ、Ｈｆ、Ｍｏ、ＷおよびＳｉの群から選ばれる少なくとも１種を酸化物換算による合量で０．３〜３５重量％、特に１〜１５重量％の割合で含有することが重要である。これは、希土類元素、Ｚｒ、Ｈｆ、Ｍｏ、Ｗの各酸化物は化学的安定性に優れ、アルミナの結晶粒成長を抑制し、工具の強度を向上する効果を有し、Ｓｉの酸化物の存在は、アルミナ結晶の異方性成長を促進することにより、工具の靭性を著しく改善することができる。従って、本発明によれば、上記成分の含有量が０．３重量％よりも少ないと、粒成長によって強度が低下し、３５重量％よりも多いと、硬度あるいは靱性が低下する。希土類元素としては、Ｙ、Ｅｒ，Ｙｂ、Ｌｕ、Ｄｙ、Ｈｏ等が挙げられる。
【００１９】
また、本発明の切削工具は、相対密度が９８％以上、特に９９％以上の緻密質であることが望ましい。これは相対密度が上記よりも小さいと、アルミナ結晶粒内へのＴｉあるいはＭｇ含有酸化物が析出しても、残存する空孔によって摩耗が加速し、切削特性が劣化してしまう恐れがあるためであり、また、切削工具における耐欠損性を高める上では、焼結体中の最大ボイド径が５μｍ以下であることが望ましく、最大ボイド径が５μｍを越えると、耐摩耗性、耐欠損性が低下するためである。
【００２０】
本発明の切削工具を製造するには、先ず、平均粒径が０．１〜１μｍのアルミナ粉末に、Ｔｉ成分を酸化物換算で０．２〜５重量％、さらにはＭｇ成分を酸化物換算で０．１〜３重量％、そして、希土類元素、Ｚｒ、Ｈｆ、Ｍｏ、ＷおよびＳｉの群から選ばれる少なくとも１種の酸化物を０．３〜３５重量％の割合で添加混合する。各成分としては、酸化物粉末、金属粉末、有機塩類、無機塩類およびその溶液のいずれでもよい。
【００２１】
上記の混合物を、所望の成形手段、例えば、金型プレス、冷間静水圧プレス、鋳込成形、射出成形、押出し成形等により切削工具形状に成形する。
【００２２】
次に、この成形体を公知の焼結法、例えば、ホットプレス法、常圧焼成法、ガス加圧焼成法、マイクロ波加熱焼成法、さらにこれらの焼成後に熱間静水圧処理（ＨＩＰ）処理、およびガラスシール後（ＨＩＰ）処理する等、種々の焼結手法によって焼結する。
【００２３】
本発明によれば、焼成にあたり、まず、Ｔｉがアルミナ結晶中に固溶可能な還元性雰囲気中で熱処理した後、固溶体からＴｉが酸化物として析出可能な酸化雰囲気で熱処理することにより、アルミナ結晶粒内にＴｉ含有酸化物を微細な結晶粒子として析出させることができる。
【００２４】
また、Ｔｉに加え、Ｍｇを含む場合には、Ｔｉ：Ｍｇ原子比を１：１に制御し、アルミナ結晶中に固溶可能な酸化性雰囲気中で熱処理した後、固溶体から、Ｍｇが酸化物として析出可能な還元雰囲気で熱処理することにより、アルミナ結晶粒内にＭｇ含有酸化物を析出させることができる。成形体は上記いずれの熱処理工程において緻密に焼成してもよいし、別の焼結工程で緻密化させてもよい。
Ｔｉ化合物をアルミナに添加する場合、Ｔｉは還元性雰囲気で熱処理すると、Ｔｉのイオン価数が３＋となりアルミナ結晶に対する溶解度が高くなり、固溶体を形成する。そして、この固溶体を酸化性雰囲気で処理することによりＴｉのイオン価数が４＋に戻り、アルミナ結晶への溶解度が低下する結果、Ｔｉは、主にＴｉＯ2 、Ａｌ2 ＴｉＯ5 として析出させることができる。
【００２５】
また、ＴｉとＭｇを含む化合物を同時にアルミナに添加する場合に、酸化性雰囲気で処理すると、ＴｉとＭｇは同モル比でアルミナ結晶中に同時に固溶できる。そして、この固溶体を還元雰囲気で処理することによりＴｉのイオン価数が３＋となり、単独で優先にアルミナ中に溶解する。Ｍｇは単独でアルミナに溶解できないため、主にＭｇＡｌ2 Ｏ4 の形で析出させることができる。
【００２６】
上記の還元性雰囲気とは、水素含有雰囲気、不活性ガス雰囲気、高真空など酸素分圧が１０-6ａｔｍ以下の雰囲気でよい。また、酸化性雰囲気中の処理は大気中で行えば良い。なお、上記固溶、あるいは析出処理時の温度が低ければ目的の組織を形成することができず、温度が高ければ、アルミナ結晶粒および析出粒子の粗大化を発生させてしまう。かかる見地から、固溶、析出時の温度は、１１００〜１６００℃の範囲が好適である。
【００２７】
そして、得られた焼結体表面を研磨加工して、被削材との接触面の表面粗さ（Ｒｍａｘ）が１μｍ以下、特に０．５μｍ以下となるように研磨加工する。さらには、刃先部をホーニング加工することによりさらに耐摩耗性を高めることができる。
【００２８】
このようにして得られる焼結体は、ＪＩＳＲ１６０１における１２００℃の４点曲げ強度が４００ＭＰａ以上の優れた高温強度を具備するとともに、表面のビッカース硬度も１８ＧＰａ以上の優れた機械的特性を具備する。
【００２９】
従って、本発明の切削工具は、特に、鋼や鋳鉄などの仕上げ加工などのように、切削速度２５０ｍ／ｍｉｎ以上の高速旋削加工用として最も有用である。
【００３０】
【実施例】
平均粒径０．５μｍのアルミナ粉末に、平均粒径０．７μｍの酸化チタン（ＴｉＯ2 ）粉末、平均粒径が０．６μｍの水酸化マグネシウム（Ｍｇ（ＯＨ）2 ）粉末、平均粒径１．０μｍの希土類元素（Ｙ、Ｙｂ、Ｌｕ）酸化物粉末、平均粒径０．５μｍのＺｒＯ2 、ＨｆＯ2 、ＭｏＯ3 、ＷＯ3 、ＳｉＯ2 、ＴｉＣＮ粉末を用い、表１、２に示す組成になるように秤量混合して混合粉末を得た。
【００３１】
そして、この混合粉末を１ｔ／ｃｍ2 の圧力で工具形状に金型成形し、さらに３ｔ／ｃｍ2 の圧力で静水圧処理を加えて成形体を作製した後、表１、２に示す各種条件で固溶処理および析出処理を行った。
【００３２】
得られた各焼結体に対して、アルキメデス法により相対密度を算出し、さらに断面を鏡面加工し、エッチング後の走査型電子顕微鏡写真に対して画像解析を行い、被削材の接触面に観察されるアルミナ結晶の平均粒径および表面における最大ボイド径を求めた。また、ＴｉあるいはＭｇ含有酸化物の析出相が存在する領域の深さおよび析出粒子の粒径を透過型電子顕微鏡写真より求めた。機械的特性として、焼結体鏡面のビッカース硬度（荷重１ｋｇ）を測定した。これらの結果を表３、４に示す。
【００３３】
また、上記と同様にしてＪＩＳＲ１６０１の規格に基づく抗折試験片を作製して、１２００℃における強度を測定し、表３、４に示した。
【００３４】
各焼結体をそれぞれを形状ＳＮＧＮ１２０４０８（幅０．１ｍｍ×傾斜角２５°）のホーニング加工し、表面粗さＲｍａｘを０．５μｍとして、
被削材 ＳＫＤ１１（ＨＣＲ６０〜６２）
切削速度 ３００ｍ／ｍｉｎ
切り込み ０．５ｍｍ
送り ０．１ｍｍ／ｒｅｖ
の乾式による外周連続旋削試験を行い、フランク摩耗量（ＶＢ）が約３ｍｍとなるまでの時間とその時点でのフランク摩耗量を測定し，結果を表３，４に示した。
【００３５】
【表１】
【表２】
【表３】
【表４】
表１〜４より本発明に基づいて得られた切削工具は、３００ｍ／ｍｉｎもの高速切削条件下でも３０分以上の切削寿命を有し、優れた耐摩耗性とともに、優れた長寿命を示した。
【００４０】
これに対して、ＴｉＣＮ粒子を分散させた試料Ｎo.１７は、２０分でクレータ摩耗が原因で破損に至った。また、それ以外の本発明の条件を逸脱する試料Ｎo.１６、１８〜２２では、いずれも硬度が低く、切削寿命が２０分以内で寿命判定となった。
【００４１】
【発明の効果】
以上詳述した通り、本発明の高速切削用工具は、その被削材との接触面においてアルミナ結晶粒子内にＴｉあるいはＭｇ含有酸化物粒子を分散させることにより、材料の化学的安定性を損なうことなしに、表面硬度を大幅に改善するとともに、高温強度も高めることができる結果、鋼や鋳鉄などの旋削による高速切削加工においても優れた耐摩耗特性を具備する長寿命の切削工具を提供できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high speed cutting tool suitable for turning a work material such as steel or cast iron at high speed.
[0002]
[Prior art]
Conventionally, ceramics such as alumina and silicon nitride have been used as cutting tools in addition to metal-ceramic materials such as cemented carbide and cermet. Among these, alumina-based cutting tools have attracted attention as cutting tools because of their excellent properties such as high hardness, high temperature resistance, and environmental resistance.
[0003]
Conventionally, when an alumina sintered body is used as a cutting tool, problems such as short life due to wear or chipping, etc. occur when using a simple sintered alumina body under high-speed cutting conditions. Therefore, a method of dispersing metal nitride, carbide, carbonitride particles such as TiC and TiN in alumina (for example, JP-A-7-97255), or a method of dispersing ZrO 2 is used. The effect of improving wear resistance, chipping resistance, etc. by improving toughness has been confirmed.
[0004]
[Problems to be solved by the invention]
However, the above-described conventional alumina cutting tool has a certain long life under low-speed cutting conditions. However, under high-speed cutting conditions of 250 m / min or more, the temperature of the contact surface is increased due to friction between the tool and the work material. Since the temperature rises to 1200 ° C. or more, the metal nitride, carbide, and carbonitride particles added as dispersed particles react with the work material, and there is a problem of significantly accelerating crater wear. In addition, the ZrO 2 dispersion has problems such as softening and deformation during high-speed cutting.
[0005]
Accordingly, an object of the present invention is to provide a cutting tool that has excellent wear resistance even under high-speed cutting conditions and can have a long life in high-speed cutting.
[0006]
[Means for Solving the Problems]
As a result of repeated investigations on a method for greatly improving the hardness of the surface portion and improving the wear resistance without impairing the stability of the alumina cutting tool at high temperatures, It has been found that the above object can be achieved by refining alumina crystal particles on the surface of the cutting tool to be contacted and precipitating Ti-containing oxide or Mg-containing oxide in the crystal particles.
[0007]
That is, the high-speed cutting tool of the present invention has, as a first form, 60 to 99% by weight of Al 2 O 3 and 0.2 to 5% by weight of Ti in terms of oxide, rare earth elements, Zr, Hf, Mo. , A tool composed of an alumina sintered body containing at least one selected from the group of W and Si in a proportion of 0.3 to 35% by weight in terms of oxide, and at least a work material The average particle diameter of the alumina crystal particles on the contact surface is 10 μm or less, and the oxide particles containing Ti having an average particle diameter of 0.3 μm or less in the alumina crystal particles over a depth of 0.01 mm or more from the contact surface Are dispersed.
[0008]
Further, as the second form, Al 2 O 3 is 60 to 99% by weight, Ti is 0.2 to 5% by weight in terms of oxide, Mg is 0.1 to 3% by weight in terms of oxide, a rare earth element, A tool comprising an alumina sintered body containing at least one selected from the group consisting of Zr, Hf, Mo, W and Si in a ratio of 0.3 to 35% by weight in terms of the total amount in terms of oxide, The average particle diameter of the alumina crystal particles at the contact surface with the work material is 10 μm or less, and the Mg has an average particle diameter of 0.3 μm or less in the alumina crystal particles over a depth of 0.01 mm or more from the contact surface. The oxide particles containing are dispersed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A major feature of the high-speed cutting tool of the present invention is that the alumina crystal particles on the surface of the alumina sintered body forming the tool in contact with the work material have an average particle size of 10 μm or less, and the alumina crystal particles The oxide particles containing Ti having an average particle diameter of 0.3 μm or less or the oxide particles containing Mg are dispersed therein.
[0010]
By dispersing the fine oxide particles in at least the alumina crystal grains at the contact surface of the cutting tool with the work material, a quasi-grain boundary structure is formed, the hardness is remarkably improved, and wear due to degranulation is reduced. It can be effectively suppressed. Specific examples of the Ti-containing oxide particles and Mg-containing oxide particles include TiO 2 , Al 2 TiO 5 , RE 2 Ti 2 O 7 (RE is a rare earth element), MgO, MgAl 2 O 4 and the like. Is mentioned.
[0011]
These oxides are both excellent in chemical and thermal stability and do not impair the oxidation resistance of the tool, but also have the effect of greatly improving the high temperature strength and the high temperature hardness. Therefore, the cutting tool of the present invention has excellent flank wear resistance and crater wear resistance, and has a long service life even under high-speed cutting conditions. In addition, the oxide particles may be precipitated in the alumina crystal grains and the alumina crystal grain boundaries.
[0012]
According to the present invention, the average particle diameter of the oxide particles containing Ti or Mg needs to be 0.3 μm or less, particularly 0.2 μm or less. This is necessary to sufficiently exhibit the effect of improving the wear resistance due to the precipitation of oxide particles containing Ti or Mg.
[0013]
That is, when the particle size of the oxide particles containing Ti or Mg dispersed in the alumina crystal grains or in the grain boundaries is small, the distance between the dispersed particles is small, and the crystal matching with the alumina crystal is maintained. As a result, the distortion of the interface is large, and a great curing effect can be brought about. Therefore, when the average particle size is larger than 0.3 μm, not only the strengthening effect is lowered, but also the wear resistance may be deteriorated by generating cracks at the interface with the parent phase.
[0014]
Further, according to the present invention, it is important that the amount of Ti contained in the tool is 0.2 to 5% by weight, particularly 0.5 to 3% by weight in terms of oxide (TiO 2 ). If the Ti content contained in the tool is less than 0.2% by weight, the volume fraction of dispersed particles in the alumina crystal particles is small, and the effect of improving the wear resistance is small. Conversely, if Ti is contained in an amount of more than 5% by weight, a coarse Al 2 TiO 5 phase is formed at the grain boundary of the alumina crystal particles, and micro cracks are generated due to the difference in thermal expansion from the alumina crystal particles, and the tool Defect resistance may be reduced.
[0015]
Further, when Mg is further contained, the Mg content needs to be 0.1 to 3% by weight, particularly 0.1 to 2% by weight in terms of MgO. If the Mg content is less than 0.1% by weight, the volume fraction of dispersed particles in the alumina crystal particles is small, and the effect of improving the wear resistance is small. Conversely, Mg exceeds 3% by weight. If it is contained, sintering is inhibited, and it becomes difficult to obtain a dense sintered body.
[0016]
Further, the smaller the alumina crystal particle diameter at the contact surface with the work material, the better. However, in the cutting tool of the present invention, the average particle diameter is preferably 10 μm or less. In particular, in order to increase the fracture resistance as a cutting tool, it is desirable that the material has high strength and is homogeneous. From this viewpoint, the average particle size of alumina is particularly preferably 6 μm or less, and further preferably the maximum particle size is 30 μm or less, particularly 20 μm or less. The alumina crystal particle diameter is an average value of the long diameter when the alumina crystal particles are columnar bodies.
[0017]
In the tool of the present invention, in order to improve the altitude of the surface, the oxide particles containing Ti or Mg have a depth of 0.01 mm or more, particularly 0.02 mm or more from the contact surface with the work material. Although it is necessary to deposit in the alumina crystal grain, the said precipitation area | region may precipitate not only to the surface but to the center part of a tool.
[0018]
Further, in the cutting tool of the present invention, at least one selected from the group of rare earth elements, Zr, Hf, Mo, W and Si is 0.3 to 35% by weight in terms of oxide, particularly 1 to It is important to contain it in a proportion of 15% by weight. This is because the oxides of rare earth elements, Zr, Hf, Mo, and W are excellent in chemical stability, have the effect of suppressing the crystal grain growth of alumina, and improving the strength of the tool. The presence can significantly improve tool toughness by promoting anisotropic growth of alumina crystals. Therefore, according to the present invention, when the content of the above components is less than 0.3% by weight, the strength decreases due to grain growth, and when it exceeds 35% by weight, the hardness or toughness decreases. Examples of rare earth elements include Y, Er, Yb, Lu, Dy, and Ho.
[0019]
In addition, the cutting tool of the present invention is desirably a dense material having a relative density of 98% or more, particularly 99% or more. This is because if the relative density is smaller than the above, even if Ti- or Mg-containing oxides are precipitated in the alumina crystal grains, there is a risk that the wear will accelerate due to the remaining pores and the cutting characteristics may deteriorate. In order to increase the fracture resistance in a cutting tool, it is desirable that the maximum void diameter in the sintered body is 5 μm or less. If the maximum void diameter exceeds 5 μm, the wear resistance and fracture resistance are improved. It is because it falls.
[0020]
To manufacture the cutting tool of the present invention, first, alumina powder having an average particle size of 0.1 to 1 μm, Ti component is 0.2 to 5% by weight in terms of oxide, and Mg component is in terms of oxide. 0.1 to 3 wt%, and at least one oxide selected from the group consisting of rare earth elements, Zr, Hf, Mo, W and Si is added and mixed at a ratio of 0.3 to 35 wt%. Each component may be any of oxide powder, metal powder, organic salts, inorganic salts and solutions thereof.
[0021]
The above mixture is formed into a cutting tool shape by a desired forming means such as a die press, cold isostatic pressing, cast molding, injection molding, extrusion molding and the like.
[0022]
Next, the molded body is subjected to a known sintering method, for example, a hot press method, an atmospheric pressure firing method, a gas pressure firing method, a microwave heating firing method, and a hot isostatic treatment (HIP) treatment after firing. , And after glass sealing (HIP) treatment.
[0023]
According to the present invention, in firing, first, heat treatment is performed in a reducing atmosphere in which Ti can be dissolved in the alumina crystal, and then heat treatment is performed in an oxidizing atmosphere in which Ti can be precipitated as an oxide from the solid solution. Ti-containing oxides can be precipitated as fine crystal grains in the grains.
[0024]
When Mg is contained in addition to Ti, the Ti: Mg atomic ratio is controlled to 1: 1, heat treatment is performed in an oxidizing atmosphere capable of solid solution in alumina crystals, and then Mg is oxidized from the solid solution. As a heat treatment in a reducing atmosphere capable of precipitating, an Mg-containing oxide can be precipitated in the alumina crystal grains. The molded body may be densely fired in any of the above heat treatment steps, or may be densified in another sintering step.
When a Ti compound is added to alumina, when Ti is heat-treated in a reducing atmosphere, the ionic valence of Ti becomes 3+ and the solubility with respect to alumina crystals increases, forming a solid solution. When this solid solution is treated in an oxidizing atmosphere, the ionic valence of Ti returns to 4+ and the solubility in alumina crystals decreases. As a result, Ti can be precipitated mainly as TiO 2 and Al 2 TiO 5. it can.
[0025]
Further, when a compound containing Ti and Mg is simultaneously added to alumina, when treated in an oxidizing atmosphere, Ti and Mg can be simultaneously dissolved in the alumina crystal at the same molar ratio. Then, by treating this solid solution in a reducing atmosphere, the ionic valence of Ti becomes 3+ and is preferentially dissolved in alumina. Since Mg cannot be dissolved alone in alumina, it can be precipitated mainly in the form of MgAl 2 O 4 .
[0026]
The reducing atmosphere may be an atmosphere having an oxygen partial pressure of 10 −6 atm or less, such as a hydrogen-containing atmosphere, an inert gas atmosphere, or a high vacuum. Further, the treatment in the oxidizing atmosphere may be performed in the air. Note that if the temperature during the solid solution or precipitation treatment is low, the target structure cannot be formed. If the temperature is high, the alumina crystal grains and the precipitated particles are coarsened. From this standpoint, the temperature during solid solution and precipitation is preferably in the range of 1100 to 1600 ° C.
[0027]
Then, the surface of the obtained sintered body is polished and polished so that the surface roughness (Rmax) of the contact surface with the work material is 1 μm or less, particularly 0.5 μm or less. Furthermore, the wear resistance can be further enhanced by honing the blade edge portion.
[0028]
The sintered body obtained in this way has excellent high-temperature strength with a 4-point bending strength at 1200 ° C. of 400 MPa or higher in JIS R1601 and also has excellent mechanical properties with a surface Vickers hardness of 18 GPa or higher.
[0029]
Therefore, the cutting tool of the present invention is most useful for high-speed turning with a cutting speed of 250 m / min or more, particularly for finishing of steel or cast iron.
[0030]
【Example】
Alumina powder having an average particle size of 0.5 μm, titanium oxide (TiO 2 ) powder having an average particle size of 0.7 μm, magnesium hydroxide (Mg (OH) 2 ) powder having an average particle size of 0.6 μm, average particle size of 1 Compositions shown in Tables 1 and 2 using 0.0 μm rare earth element (Y, Yb, Lu) oxide powder, ZrO 2 , HfO 2 , MoO 3 , WO 3 , SiO 2 , TiCN powder having an average particle size of 0.5 μm Weighed and mixed to obtain a mixed powder.
[0031]
Then, this mixed powder was molded into a tool shape at a pressure of 1 t / cm 2 , and further subjected to hydrostatic pressure treatment at a pressure of 3 t / cm 2 to produce a molded body. The solid solution treatment and the precipitation treatment were performed.
[0032]
For each of the obtained sintered bodies, the relative density was calculated by Archimedes method, the cross section was further mirror-finished, image analysis was performed on the scanning electron micrograph after etching, and the contact surface of the work material was The average particle diameter of the observed alumina crystal and the maximum void diameter on the surface were determined. Further, the depth of the region where the precipitation phase of the Ti- or Mg-containing oxide exists and the particle size of the precipitated particles were determined from a transmission electron micrograph. As mechanical properties, the Vickers hardness (load 1 kg) of the mirror surface of the sintered body was measured. These results are shown in Tables 3 and 4.
[0033]
Moreover, the bending test piece based on the specification of JISR1601 was produced similarly to the above, the intensity | strength in 1200 degreeC was measured, and it showed to Table 3, 4.
[0034]
Each sintered body is honed with a shape SNGN120408 (width 0.1 mm × tilt angle 25 °), and the surface roughness Rmax is 0.5 μm.
Work Material SKD11 (HCR60-62)
Cutting speed 300m / min
Cut 0.5mm
Feed 0.1mm / rev
The dry outer peripheral continuous turning test was conducted, and the time until the flank wear amount (VB) reached about 3 mm and the flank wear amount at that time were measured. The results are shown in Tables 3 and 4.
[0035]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
The cutting tools obtained according to the present invention from Tables 1 to 4 have a cutting life of 30 minutes or more even under high-speed cutting conditions as high as 300 m / min, and show an excellent long life together with excellent wear resistance. .
[0040]
On the other hand, Sample No. 17 in which TiCN particles were dispersed was damaged in 20 minutes due to crater wear. Moreover, in the samples No. 16 and 18-22 that deviate from the conditions of the present invention other than that, the hardness was low and the cutting life was judged within 20 minutes.
[0041]
【The invention's effect】
As described above in detail, the high-speed cutting tool of the present invention impairs the chemical stability of the material by dispersing Ti or Mg-containing oxide particles in the alumina crystal particles at the contact surface with the work material. As a result, the surface hardness can be greatly improved and the high-temperature strength can be increased. As a result, it is possible to provide a long-life cutting tool having excellent wear resistance even in high-speed cutting by turning of steel or cast iron. .
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03713298A JP3715775B2 (en) | 1998-02-19 | 1998-02-19 | High speed cutting tool |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03713298A JP3715775B2 (en) | 1998-02-19 | 1998-02-19 | High speed cutting tool |
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| Publication Number | Publication Date |
|---|---|
| JPH11235605A JPH11235605A (en) | 1999-08-31 |
| JP3715775B2 true JP3715775B2 (en) | 2005-11-16 |
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| JP03713298A Expired - Fee Related JP3715775B2 (en) | 1998-02-19 | 1998-02-19 | High speed cutting tool |
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| JP4883885B2 (en) * | 2004-01-28 | 2012-02-22 | 京セラ株式会社 | Biomaterial, method for manufacturing the same, and artificial joint |
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