JP3612966B2 - Cemented carbide, method for producing the same and cemented carbide tool - Google Patents
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【０００１】
【発明の属する技術分野】
この発明は、切削工具、ビットなどの耐衝撃工具、ロールや製缶工具などの塑性加工用工具に用いられる、硬度と靱性のバランスに優れた炭化タングステン（以下「ＷＣ」と称する）基超硬合金に関する。
【０００２】
【従来の技術】
従来より、ＷＣを主体とした結晶粒と、ＣｏあるいはＮｉのような鉄族金属を主体とする結合相からなる超硬合金は、その優れた硬度、靱性、剛性率のため、各種の切削工具や耐摩工具などに用いられてきた。しかし、近年、超硬合金の用途が拡大するにつれて、一段と優れた硬度、靱性を有するＷＣ超硬合金へのニーズが高まってきた。
【０００３】
このようなニーズに対して、特開平２−４７２３９号公報、特開平２−１３８４３４号公報、特開平２−２７４８２７号公報、特開平５−３３９６５９号公報では、ＷＣ結晶粒の粒形状を板状とし、従来の超硬合金よりもさらに硬度と靱性に優れたものとする提案がなされている。
【０００４】
上記特開平５−３３９６５９号公報には、超硬合金中に存在するＷＣ結晶粒の１５％以上が１〜１０μｍの最大寸法で最小寸法の２倍以上である板状のＷＣ結晶粒からなるものが開示されている。また、特開平７−２７８７１９号公報、あるいは特開平８−１９９２８５号公報には、最小寸法に対する最大寸法の比（以下アスペクト比と称す。すなわち、ＷＣを主体とする結晶粒と鉄族金属を主体とする結合相からなる超硬合金が板状のＷＣ結晶粒を含有している場合、超硬合金の任意の断面を走査型電子顕微鏡で観察したとき、該任意断面での個々の板状ＷＣ結晶粒の最大寸法の最小寸法に対する比率をいう。）が、３〜２０である板状ＷＣ結晶粒を含有しているものが開示されている。
【０００５】
【発明が解決しようとする課題】
上記のような提案では、合金の特性をある程度向上させることができたが、特殊な原料粉末や製造方法を用いるため製造コストが増大していた。また、板状ＷＣ結晶粒の生成量も不安定であり、その結果、合金特性が不安定なものであった。
【０００６】
しかもこれらの板状ＷＣ結晶粒の生成で靱性の改善はある程度達成されたが、一部の粗大化しすぎた板状ＷＣ結晶粒の強度は粗大化していないＷＣ結晶粒と比較して必ずしも高くなく、超硬合金自体の強度のばらつきを大きくする要因となっていた。また、ＷＣ結晶粒が粗大化すると合金は低硬度となるため、さらに硬度と靱性に優れたＷＣ超硬合金の開発が望まれていた。
【０００７】
この発明は、上記のような課題を解決するためになされたものである。この発明の目的は、強度のばらつきが小さく、かつ硬度および靱性に優れた超硬合金および超硬工具を提供することにある。
【０００８】
【課題を解決するための手段】
この発明に係る超硬合金は、ＷＣを主体とする結晶粒と、鉄族金属を主体とする結合相からなる。そして、ＷＣ結晶粒の少なくとも一部の内部に、ＩＶａ，Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体であって硬質相の本来の主体であるＷＣ以外のものからなる化合物（以下、単に「上記化合物」と称した場合には本化合物のことを意味する）が存在している。
【０００９】
本願の発明者らは、上記の目的を達成すべく種々の研究を行ない、強度のばらつきが小さく、硬度および靱性に優れた超硬合金を製造することに成功した。具体的には、本願の発明者らは、板状ＷＣ結晶粒の少なくとも一部に上述の化合物が存在することにより、ＷＣ結晶粒内に歪みが生じ、この歪みがＷＣ結晶粒の強化に役立つことを知得した。
【００１０】
なお、ＷＣ結晶粒内にＴｉの化合物を分散させてＷＣ結晶粒に圧縮応力を生じさせた複合硬質セラミックス粒子が、特開平５−８５０号公報に開示されている。しかし、この方法で作製された粉末は、固相焼結用原料としては適するものの、本発明のような液相焼結では十分その効果を発揮できない。これは、液相焼結中に原料が溶解再析出するために効果が半減するものと考えられる。本発明では、特開平５−８５０号公報の場合のように予め特殊な原料を作製することなく、液相焼結中に上記のような構造のＷＣ結晶粒を安価に作製することができる。しかも、特開平５−８５０号公報では、ＷＣ結晶粒の強化に体積率で１０％以上７０％以下のＴｉの化合物の分散が必要であるが、本発明では面積率で１０％以下の化合物の分散量でも、ＷＣ結晶粒の強化が可能となった。また、上記化合物が結晶粒内に存在するＷＣ結晶粒の面積率は、すべてのＷＣ結晶粒面積の１０％以上が好ましく、特に好ましいのは３０％を超える場合である。
【００１１】
上記化合物は、特に、Ｔｉ，Ｚｒ，Ｈｆ，Ｗの炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなることが好ましい。なかでも、Ｚｒの炭化物、窒化物もしくは炭窒化物であると、靱性および強度向上の効果が大きい。
【００１２】
これは、Ｔｉ，Ｚｒ，Ｈｆ，Ｗの炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物は、ＷＣ結晶粒内に取込まれやすく、本発明の効果を発揮しやすいからである。さらに、Ｔｉ，Ｚｒ，Ｈｆの超硬合金全体に対する含有量は、１０重量％以下であることが好ましい。より好ましくは、上記含有量は、５重量％以下である。これは、Ｔｉ，Ｚｒ，Ｈｆの含有量が多すぎると焼結性が低下し、超硬合金の強度が低下するためである。
【００１３】
なお、上記化合物は、ＷＣ結晶粒内にのみ存在する必要はなく、ＷＣ結晶粒内と結合相内の両方に存在していてもよい。また、上記化合物の粒径（多角形の場合は対角線の最大長さで示し、三角形の場合は辺の最大長さとした。ＷＣ結晶粒の粒径も同じ。）は、１μｍ未満である場合にＷＣ結晶粒の強化が行なわれやすく、靱性が大幅に向上する。特に好ましいのは、上記化合物の粒径が０．３μｍ以下の場合である。
【００１４】
また、上記超硬合金におけるＶａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体の重量％をＷａとし、ＩＶａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体の重量％をＷｂとしたときに、Ｗａ／Ｗｂの値が０〜０．２である場合には特に優れた靱性と硬度のバランスを示す。
【００１５】
これは、Ｔｉ，Ｚｒ，ＨｆなどのＩＶａ族元素の炭化物、窒化物、炭窒化物若しくはそれらの固溶体からなる化合物はＷＣ結晶粒内に取込まれやすいのに対し、Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物はＷＣ結晶粒内に取込まれにくく、さらに焼結時のＷＣ結晶粒成長を抑制する働きがあるからである。そこで、Ｗａ／Ｗｂの値を０〜０．２とした場合に、本発明の効果を発揮させやすいためこのように限定した。
【００１６】
また、前述の理由で、Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの１種の固溶体の含有量が結合相の重量に対し１０重量％以下とした場合には、Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物のＷＣ結晶粒内への取込が行なわれやすくなる。
【００１７】
次に、超硬合金の断面組織において、粒径が１μｍ以下のＷＣ結晶粒の面積率が、すべてのＷＣ結晶粒面積の１０〜４０％で、粒径が１μｍを超えるＷＣ結晶粒の面積率が６０〜９０％である場合、上記化合物が１μｍを超える粒径のＷＣ結晶粒内に主に存在すると、特に優れた硬度と靱性とを有する超硬合金が得られる。
【００１８】
ここで、粒径が１μｍ以下のＷＣ結晶粒の面積率をすべてのＷＣ結晶粒の面積の１０〜４０％と限定したのは、１０％よりも少ないと硬度が低下し、４０％よりも多いと靱性が低下するためである。また、粒径が１μｍを超えるＷＣ結晶粒の面積率を６０〜９０％と規定したのは、６０％よりも少ないと靱性が低下し、９０％よりも多いと硬度が低下するためである。
【００１９】
また、断面組織上の形状がアスペクト比で２以上のＷＣ結晶粒内に上記化合物が存在する場合には、特に優れた硬度と靱性とを示す。これは、ＷＣ結晶粒が板状に粗粒化した場合に、通常生じる硬度の低下が上記化合物がＷＣ結晶粒内に存在することによって緩和されること、粗粒化による靱性向上効果、ＷＣ結晶粒の強化が顕著になったこと等に起因するものと考えられる。
【００２０】
また、上記粒径が１μｍを超えるＷＣ結晶粒のうち、断面組織上の形状がアスペクト比で２以上のものを３０％以上含む場合には特に靱性が向上する。通常、アスペクト比が２以上と大きくなると硬度が低下するが、上記化合物が粒内に存在している場合には、硬度の低下が抑制される。そのため、靱性と硬度に特に優れた超硬合金を製造することができる。なお、ＷＣ結晶粒内に上記化合物が存在する効果は、アスペクト比が１〜２の場合でも期待できる。
【００２１】
この発明に係る超硬合金の製造方法は、下記の工程を備える。すなわち、平均粒径が０．６〜１μｍのＷＣ粉末（原料Ａ）と、平均粒径が原料Ａの２倍以上となるＷＣ粉末（原料Ｂ）と、Ｃｏ，Ｎｉ，Ｃｒ，Ｆｅ，Ｍｏから選ばれた少なくとも１種の金属の粉末（原料Ｃ）と、ＩＶａ，Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはこれらの固溶体であって平均粒径が０．０１〜０．５μｍのもの（原料Ｄ）を各々原料粉末として用い、好ましくは１５００℃以上の温度で焼結する。それにより本発明に係る超硬合金を安定して製造することができる。なお、上記原料Ａ，Ｂ，Ｄの平均粒径は、粉砕、混合工程で上記の値となってもよい。
【００２２】
また、上述の方法では、特開平２−４７２３９号公報、特開平２−１３８４３４号公報、特開平２−２７４８２７号公報のように特殊な原料粉末を用いる必要がない。さらに、特開平５−３３９６５９号公報のようにＷＣ粉末を０．５μｍ以下まで粉砕する必要もない。それにより、市販されているＷＣ原料粒径に近いＷＣ粉末を過度に粉砕することなく利用でき、余分な粉砕時の粉砕・混合装置（アトライタ）からの異物混入やＷＣ粉末の酸化現象を抑制できる。その結果、優れた特性の超硬合金を安価に安定して製造することができる。
【００２３】
上記本方法により、安定して板状ＷＣ結晶粒を含有する超硬合金を製造できる原因は、板状ＷＣ結晶粒が成長する機構としてＷＣの液相への溶解再析出現象（微粒ＷＣが液相中に溶解し、粗粒ＷＣ上に再析出する現象）が主であると考えられる。また、粉砕、混合後の原料ＷＣ粉末の平均粒径（フィッシャーサブシーブサイザ粒径とも称され、ＪＩＳ Ｈ ２１１６による装置で測定した平均粒径のことである。以下同じ。）が２倍以上、好ましくは３倍以上異なる２種類のＷＣ粉末を原料として用いることも寄与し得るものと考えられる。このような平均粒径の異なる２種類のＷＣ粉末を原料として用いることにより、ＷＣの溶解再析出のための駆動力が向上し、板状ＷＣ結晶粒が生成しやすくなる。そればかりでなく、原料Ｂとして添加した粗粒ＷＣが原料粉末内に均一に存在し、粒成長の種結晶として作用する。それにより、局所的な板状ＷＣの成長が抑制され、粉末ロットや焼結ロットなどの違いに関係なく、板状ＷＣ結晶粒が焼結体内で安定して生成され得る。
【００２４】
従来の製造法でも何らかの問題で粉砕工程で均一な粉砕が行なわれず、結果的にＷＣ粒度分布が大きくなることで板状ＷＣ結晶粒の生成が促進され、α２と呼ばれる異常に粗大なＷＣ結晶粒が生成されることは報告されていた。しかし、粗粒側のＷＣの粒度管理がなされていないため、安定した板状ＷＣ結晶粒の生成が行なえなかった。これに対し、本発明に係る方法では、原料Ａと原料Ｂの配合比および原料Ａと原料Ｂの平均粒度差を管理することで、ＷＣ結晶粒の形状、粒度分布などの組織制御が可能となる。また、本発明の方法では、欠陥の少ない特性の優れた粗粒ＷＣを原料Ｂとして用いた場合、このＷＣが種結晶となって溶解再析出現象により成長する。それにより、半導体製造で有名なブリッジマン法のように、欠陥の少ない特性の優れた板状ＷＣを生成させることができる。さらに、上記のように粒度の異なる２種類のＷＣ粉末を使用することにより、原料ＤがＷＣ粒内に取込まれやすくなる。
【００２５】
なお、原料Ａ、原料ＢのＷＣ粉末には、市販のＷＣ原料をそのまま用いることもできる。また、予備粉砕により、粒度調整（原料Ａは０．６〜１μｍ、原料Ｂはその２倍以上の平均粒径）した粉末を用いて、ボールミルなどにより軽混合して用いたり、混合、粉砕工程で狙いとする粒度となるような平均粒径の異なる２種類以上の市販ＷＣ粉末を用いてもよい。
【００２６】
また、平均粒径０．０１〜０．５μｍの原料Ｄもしくは粉砕、混合工程で平均粒径が０．０１〜０．５μｍとなる原料Ｄを原料粉末として用いることにより、ＷＣの溶解再析出時に原料ＤがＷＣ結晶粒内に取込まれやすくなる。それにより、安定して本発明の超硬合金を作製することができる。このように平均粒径の小さい原料を準備するには、通常の粉砕法以外にゾルゲル法などの液相合成法やＰＶＤやＣＶＤなどの気相合成法により作製された原料粉末を使用することもできる。なお、ここで原料Ｄの平均粒径を０．０１〜０．５μｍとしたのは、０．０１μｍよりも小さくすることは工業的に難しく、０．５μｍよりも大きくすると原料ＤをＷＣ結晶粒へ取込みにくくなるためである。
【００２７】
なお、原料Ａの重量ＷＡと原料Ｂの重量ＷＢの比ＷＡ／ＷＢが０．５〜３０であるときに、特に優れた性能の超硬合金を得ることができる。より好ましくは、ＷＡ／ＷＢが１〜１０である。ＷＡ／ＷＢが０．５より小さい場合にはアスペクト比が２より大きい板状ＷＣ結晶粒を生成しにくくなる。また、ＷＡ／ＷＢが３０よりも大きい場合には、板状ＷＣ結晶粒の生成が不安定となり、局所的に粗大な板状ＷＣ結晶粒が生成しやすくなる。その上、ＷＣ結晶粒内に上記化合物が取込まれにくくなる。
【００２８】
また、原料Ａの少なくとも一部に使用済超硬合金をリサイクル法（亜鉛処理法や高温処理法等による）でリサイクルしたＷＣ粉末を使用することができる。それにより、安価に本発明の超硬合金が製造できるばかりでなく、地球環境保護の観点からタングステン（Ｗ）鉱山の無益な採掘を抑制できる。従来より、超硬合金のリサイクル粉末を使用することは試みられてきたが、ごく一部に使用されるだけで全面的な採用はなされていないのが現状であった。
【００２９】
リサイクルは、一般に亜鉛処理法で行われるが、リサイクルＷＣ粉末の粒度はリサイクルする使用済超硬合金のＷＣ結晶粒度に依存するため、特定の粒度のＷＣ原料を作製することはできない。高温処理法でも、処理時にＷＣ結晶粒が部分的に粒成長するため、その後粉砕したとしてもＷＣ粉末の粒度分布の幅が非常に大きくなる。このため、これらのリサイクル粉末を使用して超硬合金を作製すると、ＷＣ結晶粒度分布を管理することができないため、性能のばらつきが大きくなるという問題があった。
【００３０】
これに対し、本発明に係る製造方法では、リサイクル原料である使用済超硬合金から再生された粒径０．６〜１μｍの範囲のリサイクル粉末を、焼結過程で液相中に溶解させ、より平均粒径の大きい原料Ｂ上に再析出させている。それにより、作製した焼結体の板状ＷＣ結晶の粒径を原料ＢのＷＣ粉末粒度で制御することとなる。そのため、リサイクル粉末の粒度が最終焼結体の粒径を決定することにならず、前述の問題を回避できる。しかも、本方法では前述したように微粒原料Ａは、液相に溶解後、粗粒原料Ｂ上に析出するので板状ＷＣの特性は粗粒原料Ｂの特性に依存することとなる。そのため、特性が不安定なリサイクル原料を用いた場合でも、優れた特性を有する焼結体を作製できる。
【００３１】
上記リサイクル原料である使用済超硬合金を粉砕したリサイクル粉末から生じたＷＣ粉末の重量ＷＲと原料Ａの重量ＷＡの比ＷＲ／ＷＡが０．３〜１（好ましくは０．５〜１）である場合には、特に安価に本発明の超硬合金を作製できるほか、地球環境保護の観点からも好ましい超硬合金が得られる。
【００３２】
以上のような超硬合金からなる工具等の製品の表面に、さらにＩＶａ，Ｖａ，ＶＩａ族元素，Ａｌから選ばれた少なくとも１種の炭化物、窒化物、酸化物、ホウ化物およびこれらの固溶体、あるいはダイヤモンド、ＤＬＣ、ＣＢＮから選ばれた少なくとも１層以上からなる被覆膜を設け、これらを切削工具や耐摩工具として用いた場合に、合金母材が優れた硬度と靱性のバランスを有するため、特に優れた性能を発揮する。
【００３３】
特に、２０μｍ以上の被覆膜を従来のＷＣ基超硬合金上に被覆した場合には、被覆膜が亀裂の発生を助長（グリフィスの予亀裂の働き）すると考えられる。そのため、超硬合金における耐欠損性の低下が見られた。しかし、本発明に係る超硬合金では、ＷＣ結晶粒内に上記化合物が析出し、ＷＣ結晶粒が強化されているため、亀裂の進展が起こりにくく優れた耐欠損性が得られることが判明した。
【００３４】
【発明の実施の形態】
以下、この発明の実施の形態について、図１，図２および表１〜表１４を用いて説明する。
【００３５】
（実施の形態１）
原料粉末として粉砕効率の高いアトライタを用いて粉砕した平均粒径０．７μｍのＷＣ粉末（原料Ａ）と、同様の粉砕により平均粒径２μｍのＷＣ粉末（原料Ｂ）を準備した。また、平均粒径１．５μｍのＣＯ粉末、平均粒径１．３μｍのＮｉ粉末、平均粒径０．３μｍのＺｒＣ粉末、平均粒径０．５μｍのＴｉＣ粉末、平均粒径０．５μｍのＨｆＣ粉末、平均粒径０．３μｍのＮｂＣ粉末、平均粒径０．４μｍのＴａＣ粉末、平均粒径０．３μｍのＣｒ３ Ｃ２ 粉末、平均粒径０．５μｍのＺｒＮ粉末、平均粒径０．５μｍの（Ｗ，Ｔｉ）（Ｃ，Ｎ）固溶体粉末、平均粒径０．５μｍの（Ｗ，Ｚｒ）Ｃ固溶体粉末、平均粒径０．５μｍの（Ｔａ，Ｎｂ）Ｃ固溶体粉末を加えて、表１の組成に配合し、通常のボールミルを用いてアセトン溶媒中で２時間の混合を行った。その後、スプレードライヤによって造粒を行った。
【００３６】
【表１】
上記の表１において、原料ＮｏおよびＷａ／Ｗｂの列の数字以外の数字は、ｗｔ％を示す。また、表１には、Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体の重量％をＷａとし、ＩＶａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体の重量％をＷｂとしたときのＷａ／Ｗｂの値が示されている。
【００３８】
これらの粉末を１ｔｏｎ／ｃｍ２ の圧力で金型を用いてプレスし、真空中で１５５０℃で１時間保持して焼結を行う。それにより、ＩＳＯ型番ＣＮＭＧ１２０４０８の形状（ＪＩＳ Ｇ ４０５３に準拠した菱形スローアウェイチップ）の焼結体を作製した。焼結体は、♯２５０のダイヤモンド砥石で研削加工され、ダイヤモンドペーストを用いてラッピング処理が施される。その後、ダイヤモンド製のビッカース圧子を用いて５０ｋｇ荷重で硬度と、同圧子の圧痕隅に生じる亀裂長より求めるＩｎｄｅｎｔａｔｉｏｎ Ｆｒａｃｔｕｒｅ法による破壊靱性の値ＫＩＣ（ＭＰａｍ１／２ ）を測定した。
【００３９】
また、本発明との比較のために従来例による平均粒径６μｍのＷＣ粉末と、平均粒径１．５μｍのＣｏ粉末、平均粒径１．３μｍのＮｉ粉末、平均粒径２μｍのＺｒＣ粉末、平均粒径１．５μｍのＴｉＣ粉末、平均粒径２μｍのＨｆＣ粉末、平均粒径２μｍのＮｂＣ粉末、平均粒径１．５μｍのＴａＣ粉末、平均粒径２μｍのＣｒ３ Ｃ２ 粉末、平均粒径１．５μｍのＺｒＮ粉末、平均粒径２μｍの（Ｗ，Ｔｉ）（Ｃ，Ｎ）固溶体粉末、平均粒径１．５μｍの（Ｗ，Ｚｒ）Ｃ固溶体粉末、平均粒径１．８μｍの（Ｔａ，Ｎｂ）Ｃ固溶体粉末をアトライタで７時間混合し、同様にして造粒した粉末も作製した。この粉末を１ｔｏｎ／ｃｍ２ の圧力で金型を用いてプレスし、真空中で１４００℃で１時間保持して焼結を行った。そして、焼結体の硬度、破壊靱性を同様の方法で測定した。
【００４０】
また、ＷＣ結晶粒内にＩＶａ，Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物が存在しているかどうかを測定した。すなわち、走査型電子顕微鏡もしくは透過電子顕微鏡用の試料を作製し、ＥＤＸ（Ｅｎｅｒｇｙ ｄｉｓｐｅｒｓｉｖｅ Ｘ−ｒａｙ Ｓｐｅｃｔｒｏｍｅｔｅｒの略称であって、半導体検出器を用いて電気的に分光選別するエネルギ分散型の蛍光Ｘ線分析）にて元素分析した。そして、ＴｉとＣが検出された際には、その物質はＴｉＣであるとした。これらの測定結果を表２に示す。なお、表２の試料番号において、Ｎｏ．１−１〜１０が本発明に係る方法により作製された焼結体を示し、Ｎｏ．２−１〜１０が従来のＷＣ粉末により作製された焼結体を示している。
【００４１】
【表２】
表２において、○印は、本発明に該当していることを示している。表２の結果より、本発明の方法で作製した試料には、ＷＣ結晶粒内にＩＶａ，Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物が存在し、これらの試料の硬度、破壊靱性は従来の方法で作製した試料と比較して優れた値を示していることがわかる。
【００４３】
図１に示される写真は、試料１−１の走査電子顕微鏡写真である。図１において、灰色で四角く見える結晶がＷＣ結晶粒１であり、黒く見えるのが結合相２であるＣｏ相であり、ＷＣ結晶粒内に灰色に見える析出物（化合物３）はＴｉの炭化物である。この写真より、試料１−１のＷＣ結晶粒１内に存在する上記化合物３の粒径は約０．１μｍであって、０．３μｍ以下であることがわかる。また、上記化合物３を内部に有するＷＣ結晶粒の面積に対する上記化合物３の面積が１０％以下であることもわかる。本発明では、このような断面組織を用いて、ＷＣ結晶粒内の化合物の存在の有無を判定した。
【００４４】
同様にして、表２の１−２〜１−８の試料には、Ｔｉ、Ｚｒ、Ｈｆ，Ｗの炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物がＷＣ結晶粒内に存在していることが確認できた。１−９、１−１０の試料には、Ｔｉ、Ｚｒ、Ｈｆ、Ｗの炭化物、窒化物、炭窒化物もしくはそれらの固溶体以外のＩＶａ，Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物が存在していることが確認できた。
【００４５】
１−１〜１−８までの試料の特性値は従来の方法による２−１〜２−８の試料の特性値と比較して優れた値を示し、その向上割合は１−９〜１−１０の本発明の試料が従来の方法による試料２−９〜２−１０の特性値に対して向上した値と比較して大きいことも判明した。すなわち、ＷＣ結晶粒内に存在する化合物としては、Ｔｉ、Ｚｒ、Ｈｆ、Ｗの炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物が好ましく、特にＺｒの炭化物、窒化物がＷＣ結晶粒内に存在していた試料１−２は非常に優れた合金特性を示すことも確認できた。
【００４６】
中でも、Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体の重量％をＷａとし、ＩＶａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体の重量％をＷｂとしたときにＷａ／Ｗｂの値が０〜０．２の範囲にある１−１〜１−６の試料が、従来の方法による試料２−１〜２−６と比較して特に優れた特性を示すことも確認できた。
【００４７】
（実施の形態２）
実施の形態１で作製した原料Ｎｏ．８とＩＶａ，Ｖａ，ＶＩａ族元素の炭化物であるＴｉＣ、ＴａＣ、Ｃｒ３ Ｃ２ の量が異なる原料Ｎｏ．１１〜１５を準備し（表３）、実施の形態１と同様にして焼結体を作製し、硬度および破壊靱性の測定を行った。その結果を表４に示す。また、ＷＣ結晶粒内の上記化合物の有無について、実施の形態１と同様に調べたところ、いずれの試料にもＷＣ結晶粒内に上記化合物が存在することが確認できた。
【００４８】
【表３】
表３の割合（％）は、Ｖａ，ＶＩａ族元素の炭化物、窒化物、炭窒化物もしくはそれらの固溶体（ＷＣを除く）の含有量の、結合相の重量に対する割合（％）である。なお、原料Ｎｏ、割合およびＷａ／Ｗｂの列の数字以外の数字は、ｗｔ％を示す。
【００５０】
【表４】
表４の結果より、ＴａＣ，Ｃｒ３ Ｃ２ の合計添加量が結合相の量に対して１０ｗｔ％以下である試料Ｎｏ．１−１２〜１−１５の合金特性は優れており、中でもＴａＣ、Ｃｒ３ Ｃ２ の添加量が結合相に固溶できる量より少ない試料１−１４、１−１５は特に優れた合金特性を示すことが確認できた。
【００５２】
（実施の形態３）
実施の形態１と同様にして、原料Ａと原料Ｂの配合比の異なる原料Ｎｏ．１６〜２３を表５に示す組成で準備した。これらの粉末を１ｔｏｎ／ｃｍ２ の圧力で金型を用いてプレスし、真空中で１５００℃で１時間保持して焼結を行った。それにより、ＩＳＯ型番ＣＮＭＧ１２０４０８の形状の焼結体を作製した。
【００５３】
【表５】
表５の原料Ｎｏ．およびＷＡ／ＷＢの列の数字以外の数字は、ｗｔ％を示す。次に、これらの試料の硬度および破壊靱性を、実施の形態１の場合と同様の方法で測定した。その測定結果を表６に示す。また、これらの試料を平面研削、鏡面研磨後に走査電子顕微鏡で５０００倍にて写真撮影した。この写真を画像処理装置を用いて粒径が１μｍを超えるＷＣ結晶粒と粒径が１μｍ以下のＷＣ結晶粒に分類し、それぞれの面積率を測定した結果についても表６中に記載した。さらに、これらのＷＣ結晶粒のうち、粒径が１μｍを超えるＷＣ結晶粒のうちのアスペクト比が２以上であるものの面積割合を同様にして測定し、その結果についても表６中に記載した。なお、ＷＣ結晶粒内へのＺｒＣ、ＺｒＮ、ＴｉＣ化合物の有無については実施の形態１と同様にして調べた。その結果、３−１６、３−２３以外の試料については、いずれもＷＣ結晶粒内に上記化合物が存在していることが確認できた。
【００５５】
【表６】
表６の結果より、原料Ａの重量ＷＡと原料Ｂの重量ＷＢの比ＷＡ／ＷＢが０．５〜３０の範囲にある３−１８〜３−２１の試料は、粒径が１μｍ以下のＷＣ結晶粒の面積率が１０〜４０％の範囲内にあり、優れた硬度と破壊靱性のバランスを有している。中でも、粒径が１μｍを超えるＷＣ結晶粒のうちのアスペクト比が２以上であるＷＣ結晶粒を、面積率で３０％以上を有する試料３−２０と３−２１は、特に優れた合金特性を示すことがわかる。
【００５７】
（実施の形態４）
実施の形態１で作製した試料１−１〜１−１０および試料２−１〜２−１０のＣＮＭＧ１２０４０８形状のチップに０．０５Ｒのホーニング処理を行った後、表７に示す被覆膜を形成した。そして、丸棒材の円周方向に４本の溝を設けた図２に示す形状のＳＣＭ４３５製被削材４を下記条件で切削テストし、欠損するまでの時間を測定した。その結果を表７に示す。なお、表７の被覆膜中のＤＬＣはダイヤモンドライクカーボン、ＣＶＤは化学蒸着法、ＰＶＤは物理蒸着法を示す。
【００５８】
切削条件 切削速度：１００ｍ／ｍｉｎ
送り ：０．４ｍｍ／ｒｅｖ
切り込み：２ｍｍ
切削形態：乾式
【００５９】
【表７】
表７の欠損に至るまでの時間を測定した結果より、本発明の試料Ｎｏ．１−１〜１−５に被覆膜を形成した工具は従来の方法の試料Ｎｏ．２−１〜２−５に被覆膜を形成した工具よりも優れた性能を示すことがわかる。なお、表７中のダイヤモンドを立方晶窒化ホウ素（ＣＢＮ）にしても同様の結果を得ることができた。このように、本発明の超硬合金に被覆膜を形成した試料は優れた特性を発揮できることがわかる。
【００６１】
（実施の形態５）
実施の形態１で作製したＮｏ．１の原料粉末と同一の組成で、原料Ａの一部に使用済超硬合金を亜鉛処理法もしくは高温処理法で処理したリサイクルＷＣ粉末を使用した原料Ｎｏ．２４〜２８（表８）を作製した。これらを実施の形態１と同一の方法で焼結し、硬度、破壊靱性、ＷＣ結晶粒内の上記化合物の有無を実施の形態１と同様の方法で測定した。その結果を表９に示す。
【００６２】
【表８】
【表９】
表９の結果より、亜鉛処理法、高温処理法でリサイクルした粉末を使用した試料２４〜２８の合金特性は、リサイクル粉末を用いない試料１と同等の優れた特性を示していることがわかる。このように、本発明の方法では、従来、合金特性が劣るため少量しか使用できなかったリサイクル粉末をＷＣ粉末の主成分として使用できる。それにより、これまでの超硬合金の製造法と比較して低コストで地球環境保護に好ましい超硬合金が得られる。
【００６５】
（実施の形態６）
原料Ａとして平均粒径０．９μｍのＷＣ粉末、原料Ｂとして平均粒径４μｍのＷＣ粉末、原料Ｃとして平均粒径１．５μｍのＣｏ粉末、平均１．８μｍのＣｒ粉末、原料Ｄとして平均粒径０．１μｍ、０．５μｍ、０．９μｍのＺｒＣＮ粉末を用いて、表１０の組成に配合した原料Ｎｏ．２９〜３２を作製した。
【００６６】
【表１０】
表１０の原料Ｎｏの列の数字以外の数字は、ｗｔ％を示す。原料Ｎｏ．２９〜３２の粉末を用いて、実施の形態１と同様にして、プレス、焼結を行ない、ＩＳＯ型番ＣＮＭＧ１２０４０８の形状の焼結体を作製した。次に、実施の形態４と同様の手法で、これらの試料の切削テストを行ない、欠損するまでの時間の測定を行なった。測定結果を表１１中に示す。また、これらの試料を平面研削、鏡面研磨後に、走査電子顕微鏡で５０００倍にて写真撮影したところ、ＷＣ結晶粒に上記化合物が存在していることが確認できた。また、この化合物の組成は、ＥＤＸ分析により、Ｚｒの炭窒化物であることも確認できた。さらに、この写真を用いて、画像処理装置により、写真内のＷＣ結晶粒の総面積とそれらの中で結晶粒内に上記化合物の存在が認められる結晶粒の面積を測定し、結晶粒内に上記化合物が存在するＷＣ結晶粒の面積率を算出した。その結果を表１１に示す。
【００６８】
【表１１】
表１１の結果より、ＺｒＣＮ粉末には微粒原料を用いた方が、ＺｒＣＮを結晶粒内に取込むＷＣ結晶粒の面積率が高くなり、結晶粒内に上記化合物が存在するＷＣ結晶粒の面積率が多いほど耐欠損性も向上することがわかる。中でも、結晶粒内に上記化合物が存在するＷＣ結晶粒の面積率が１０％を超えると急激に耐欠損性が向上することも確認できた。
【００７０】
（実施の形態７）
表１２に示す組成の粉末を用いて、ボールミルによりアセトン溶媒中で２時間の混合を行なった。その後、この粉末を乾燥させ、１ｔｏｎ／ｃｍ２ の圧力で金型を用いてプレスし、真空中で１５００℃の温度下で１時間保持して焼結を行なった。それにより実施の形態１と同じＣＮＭＧ１２０４０８の形状の焼結体Ｎｏ．３−４〜３−６を作製した。なお、これらの焼結体にはＷＣ結晶粒内に表１３に示す化合物が存在することが、透過型電子顕微鏡でＥＤＸもしくはＸ線定性分析を行なうことで確認できた。次に、これらの試料の硬度および破壊靱性を実施の形態１と同様の方法で測定した。その結果を表１４に示す。
【００７１】
【表１２】
【表１３】
【表１４】
表１４の結果より、Ｚｒ化合物がＷＣ結晶粒内に析出した試料Ｎｏ．３−４〜３−６の試料は、Ｔｉ化合物がＷＣ結晶粒内に析出した試料Ｎｏ．３−１〜３−３の試料よりも優れた硬度と破壊靱性のバランスを有することが確認できた。さらに、この焼結体を平面研削、外周研削し、さらに０．０５Ｒのホーニング処理を行なった後、下層から順に０．５μｍＴｉＮ、５μｍＴｉＣＮ、３μｍＴｉＣ、２μｍアルミナ、０．５μｍＴｉＮの被覆膜をＣＶＤ法でコーティングした。これらの試料を用いて、実施の形態４で用いた被削材を下記の条件で切削し、欠損するまでの時間を測定した。その結果を表１４に示す。
【００７５】
【００７６】
【発明の効果】
以上説明したように、本発明によれば、ＩＶａ，Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体からなる化合物がＷＣ結晶粒の中に生成されることにより、強度に優れたＷＣ結晶となり、特にその効果はＷＣ結晶粒が板状である場合に顕著となる。その結果、強度と靱性に優れた超硬合金を提供することができる。
【図面の簡単な説明】
【図１】超硬合金の走査電子顕微鏡写真を示す図（複写）である。
【図２】切削試験に用いた被削材の断面形状を示す図である。
【符号の説明】
１ ＷＣ結晶粒
２ 結合相
３ 化合物
４ 被削材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tungsten carbide (hereinafter referred to as “WC”) based carbide that is used in cutting tools, impact resistant tools such as bits, and plastic working tools such as rolls and canning tools, and has an excellent balance between hardness and toughness. Regarding alloys.
[0002]
[Prior art]
Conventionally, cemented carbides composed of crystal grains mainly composed of WC and binder phases mainly composed of iron group metals such as Co or Ni have various cutting tools due to their excellent hardness, toughness and rigidity. It has been used for anti-wear tools. However, in recent years, as the use of cemented carbide has expanded, the need for a WC cemented carbide having further superior hardness and toughness has increased.
[0003]
In response to such needs, in JP-A-2-47239, JP-A-2-138434, JP-A-2-274727, and JP-A-5-339659, the shape of the WC crystal grains is a plate shape. In addition, a proposal has been made to further improve the hardness and toughness of conventional cemented carbide.
[0004]
JP-A-5-339659 discloses that 15% or more of the WC crystal grains present in the cemented carbide are composed of plate-like WC crystal grains having a maximum dimension of 1 to 10 μm and at least twice the minimum dimension. Is disclosed. Japanese Patent Application Laid-Open No. 7-278719 or Japanese Patent Application Laid-Open No. 8-199285 discloses a ratio of the maximum dimension to the minimum dimension (hereinafter referred to as an aspect ratio. That is, a crystal grain mainly composed of WC and an iron group metal. When the cemented carbide composed of the binder phase contains plate-like WC crystal grains, when an arbitrary cross section of the cemented carbide is observed with a scanning electron microscope, each plate-like WC in the arbitrary cross section is observed. The ratio of the maximum size of the crystal grains to the minimum size is disclosed. It contains 3 to 20 plate-like WC crystal grains.
[0005]
[Problems to be solved by the invention]
In the above proposal, although the characteristics of the alloy could be improved to some extent, the manufacturing cost was increased due to the use of special raw material powders and manufacturing methods. Further, the amount of plate-like WC crystal grains produced was also unstable, and as a result, the alloy characteristics were unstable.
[0006]
Moreover, toughness has been improved to some extent by the generation of these plate-like WC crystal grains, but the strength of some of the excessively coarsened plate-like WC crystal grains is not necessarily high compared with the WC crystal grains not coarsened. It was a factor that increased the variation in strength of the cemented carbide itself. Further, since the alloy becomes low in hardness when the WC crystal grains are coarsened, it has been desired to develop a WC cemented carbide having further excellent hardness and toughness.
[0007]
The present invention has been made to solve the above-described problems. An object of the present invention is to provide a cemented carbide and a cemented carbide tool having a small variation in strength and excellent in hardness and toughness.
[0008]
[Means for Solving the Problems]
The cemented carbide according to the present invention comprises crystal grains mainly composed of WC and a binder phase mainly composed of iron group metals. In addition, at least a part of the WC crystal grains includes at least one kind of carbide, nitride, carbonitride, or a solid solution thereof selected from group IVa, Va, and VIa elements, and the main component of the hard phase. There is a compound composed of something other than a certain WC (hereinafter simply referred to as “the above compound” means this compound).
[0009]
The inventors of the present application have made various studies in order to achieve the above object, and succeeded in producing a cemented carbide having a small strength variation and excellent hardness and toughness. Specifically, the inventors of the present application show that the presence of the above-mentioned compound in at least a part of the plate-like WC crystal grains causes distortion in the WC crystal grains, and this distortion helps strengthen the WC crystal grains. I knew that.
[0010]
JP-A-5-850 discloses composite hard ceramic particles in which a Ti compound is dispersed in WC crystal grains and compressive stress is generated in the WC crystal grains. However, although the powder produced by this method is suitable as a raw material for solid phase sintering, the effect cannot be sufficiently exhibited by liquid phase sintering as in the present invention. This is considered to be half the effect because the raw material is dissolved and reprecipitated during liquid phase sintering. In the present invention, WC crystal grains having the structure as described above can be produced at low cost during liquid phase sintering without producing a special raw material in advance as in JP-A-5-850. Moreover, in JP-A-5-850, it is necessary to disperse the Ti compound in a volume ratio of 10% or more and 70% or less for strengthening the WC crystal grains, but in the present invention, the area ratio is 10%. Less than Even with the amount of the compound dispersed, WC crystal grains can be strengthened. Further, the area ratio of the WC crystal grains in which the above compound is present in the crystal grains is preferably 10% or more of all WC crystal grain areas, and more preferably 30%.
[0011]
In particular, the compound is preferably composed of Ti, Zr, Hf, W carbide, nitride, carbonitride, or a solid solution thereof. Among these, Zr carbide, nitride, or carbonitride has a great effect of improving toughness and strength.
[0012]
This is because Ti, Zr, Hf, and W carbides, nitrides, carbonitrides, or compounds composed of these solid solutions are easily taken into the WC crystal grains and easily exert the effects of the present invention. Furthermore, the content of Ti, Zr, and Hf with respect to the entire cemented carbide is preferably 10% by weight or less. More preferably, the content is 5% by weight or less. This is because if the content of Ti, Zr, and Hf is too large, the sinterability decreases and the strength of the cemented carbide decreases.
[0013]
In addition, the said compound does not need to exist only in a WC crystal grain, You may exist in both a WC crystal grain and a binder phase. In addition, when the particle size of the above compound is the maximum length of the diagonal line in the case of a polygon, and the maximum length of a side in the case of a triangle. The WC crystal grains are easily strengthened and the toughness is greatly improved. Particularly preferred is the case where the particle size of the compound is 0.3 μm or less.
[0014]
In addition, the weight% of at least one carbide, nitride, carbonitride or their solid solution selected from Va, VIa group elements in the cemented carbide is Wa, and at least one kind selected from IVa group elements is used. When the weight% of the carbide, nitride, carbonitride or their solid solution is Wb, a particularly excellent balance between toughness and hardness is exhibited when the value of Wa / Wb is 0 to 0.2.
[0015]
This is because carbides, nitrides, carbonitrides or their solid solution compounds of group IVa elements such as Ti, Zr, and Hf are easily incorporated into WC crystal grains, but are selected from group elements Va and VIa. This is because the compound composed of at least one kind of carbide, nitride, carbonitride, or a solid solution thereof is difficult to be taken into the WC crystal grains and further has a function of suppressing WC crystal grain growth during sintering. . In view of this, when the value of Wa / Wb is set to 0 to 0.2, the effect of the present invention is easily exhibited, and thus the above is limited.
[0016]
For the reasons described above, the content of at least one kind of carbide, nitride, carbonitride, or one kind of solid solution selected from Va and VIa group elements is 10% by weight or less based on the weight of the binder phase. In this case, at least one type of carbide, nitride, carbonitride selected from the group elements Va and VIa, or a compound made of a solid solution thereof is easily taken into the WC crystal grains.
[0017]
Next, in the cross-sectional structure of the cemented carbide, the area ratio of WC grains having a grain size of 1 μm or less is 10 to 40% of the area of all WC grains, and the area ratio of WC grains having a grain size exceeding 1 μm. Is 60 to 90%, the cemented carbide having particularly excellent hardness and toughness can be obtained when the above compound is mainly present in the WC crystal grains having a grain size exceeding 1 μm.
[0018]
Here, the reason why the area ratio of the WC crystal grains having a grain size of 1 μm or less was limited to 10 to 40% of the area of all the WC crystal grains is that the hardness is reduced when it is less than 10%, and is more than 40%. This is because the toughness decreases. Further, the reason why the area ratio of WC crystal grains having a grain size exceeding 1 μm is defined as 60 to 90% is that the toughness is lowered when it is less than 60%, and the hardness is lowered when it is more than 90%.
[0019]
Moreover, when the said compound exists in the WC crystal grain whose shape on a cross-sectional structure is 2 or more by aspect ratio, especially outstanding hardness and toughness are shown. This is because when the WC crystal grains are coarsened into a plate shape, the decrease in hardness that usually occurs is alleviated by the presence of the above-mentioned compounds in the WC crystal grains, the effect of improving toughness due to the coarsening, WC crystals This is thought to be due to the remarkable strengthening of grains.
[0020]
Further, among the WC crystal grains having a grain size of more than 1 μm, the toughness is particularly improved when the shape on the cross-sectional structure contains 30% or more having an aspect ratio of 2 or more. Usually, when the aspect ratio increases to 2 or more, the hardness decreases, but when the compound is present in the grains, the decrease in hardness is suppressed. Therefore, a cemented carbide having particularly excellent toughness and hardness can be produced. The effect of the presence of the compound in the WC crystal grains can be expected even when the aspect ratio is 1 to 2.
[0021]
The manufacturing method of the cemented carbide according to the present invention includes the following steps. That is, from WC powder (raw material A) having an average particle size of 0.6 to 1 μm, WC powder (raw material B) having an average particle size twice or more that of raw material A, and Co, Ni, Cr, Fe, and Mo. At least one selected metal powder (raw material C) and at least one carbide, nitride, carbonitride, or solid solution thereof selected from IVa, Va, VIa group elements, and having an average particle size Each of 0.01 to 0.5 μm (raw material D) is used as a raw material powder, and preferably sintered at a temperature of 1500 ° C. or higher. Thereby, the cemented carbide according to the present invention can be manufactured stably. The average particle diameter of the raw materials A, B, and D may be the above value in the pulverization and mixing process.
[0022]
In the above-described method, there is no need to use a special raw material powder as in JP-A-2-47239, JP-A-2-138434, and JP-A-2-274748. Furthermore, it is not necessary to pulverize the WC powder to 0.5 μm or less as disclosed in JP-A-5-339659. As a result, commercially available WC powder having a particle diameter close to that of the WC material can be used without excessively pulverizing, and contamination of foreign matters from an excessive pulverization / mixing device (attritor) and oxidation phenomenon of WC powder can be suppressed. . As a result, a cemented carbide having excellent characteristics can be stably produced at a low cost.
[0023]
The reason why a cemented carbide containing plate-like WC crystal grains can be produced stably by the above-described method is as follows. The mechanism of growth of plate-like WC crystal grains is the phenomenon of dissolution and reprecipitation into the liquid phase of WC (fine WC is a liquid It is considered that the phenomenon of dissolution in the phase and reprecipitation on the coarse WC) is the main. In addition, the average particle size of the raw material WC powder after pulverization and mixing (also referred to as “Fischer sub-sieve sizer particle size, which is an average particle size measured with an apparatus according to JIS H 2116. The same shall apply hereinafter.) It is considered that the use of two types of WC powders that are preferably three times or more different as raw materials can also contribute. By using such two types of WC powders having different average particle diameters as raw materials, the driving force for dissolution and reprecipitation of WC is improved, and plate-like WC crystal grains are easily generated. In addition, the coarse WC added as the raw material B exists uniformly in the raw material powder, and acts as a seed crystal for grain growth. Thereby, local growth of the plate-like WC is suppressed, and plate-like WC crystal grains can be stably generated in the sintered body regardless of the difference between the powder lot and the sintered lot.
[0024]
Even in the conventional manufacturing method, uniform crushing is not performed in the crushing process due to some problem, and as a result, the generation of plate-like WC crystal grains is promoted by increasing the WC grain size distribution, and abnormally coarse WC crystal grains called α2 Has been reported to be generated. However, since the grain size of the WC on the coarse grain side is not controlled, stable plate-like WC crystal grains cannot be generated. On the other hand, in the method according to the present invention, by controlling the blending ratio of raw material A and raw material B and the average particle size difference between raw material A and raw material B, it is possible to control the structure such as the shape of WC crystal grains and the particle size distribution. Become. Further, in the method of the present invention, when coarse WC having excellent characteristics with few defects is used as the raw material B, this WC becomes a seed crystal and grows by dissolution reprecipitation phenomenon. As a result, a plate-like WC having excellent characteristics with few defects can be generated as in the Bridgman method, which is famous for semiconductor manufacturing. Furthermore, by using two types of WC powders having different particle sizes as described above, the raw material D is easily taken into the WC grains.
[0025]
A commercially available WC raw material can be used as it is for the WC powder of the raw material A and the raw material B. In addition, the powder whose particle size has been adjusted by pre-grinding (the raw material A is 0.6 to 1 μm and the raw material B is twice or more the average particle size) is used by lightly mixing with a ball mill or the like, or a mixing and grinding process Two or more types of commercially available WC powders having different average particle sizes so as to obtain a target particle size may be used.
[0026]
In addition, by using the raw material D having an average particle diameter of 0.01 to 0.5 μm or the raw material D having an average particle diameter of 0.01 to 0.5 μm in the pulverization and mixing process as a raw material powder, The raw material D is easily taken into the WC crystal grains. Thereby, the cemented carbide of the present invention can be produced stably. In order to prepare a raw material with a small average particle size in this way, it is also possible to use a raw material powder produced by a liquid phase synthesis method such as a sol-gel method or a gas phase synthesis method such as PVD or CVD in addition to a normal pulverization method. it can. Here, the average particle size of the raw material D is set to 0.01 to 0.5 μm. It is industrially difficult to make the raw material D smaller than 0.01 μm, and when it is larger than 0.5 μm, the raw material D is converted into WC crystal grains. It is because it becomes difficult to take in.
[0027]
In addition, when the ratio WA / WB of the weight WA of the raw material A and the weight WB of the raw material B is 0.5 to 30, a cemented carbide having particularly excellent performance can be obtained. More preferably, WA / WB is 1-10. When WA / WB is smaller than 0.5, it becomes difficult to generate plate-like WC crystal grains having an aspect ratio larger than 2. When WA / WB is larger than 30, the generation of plate-like WC crystal grains becomes unstable, and locally coarse plate-like WC crystal grains are likely to be generated. In addition, the above compound is less likely to be taken into the WC crystal grains.
[0028]
Moreover, WC powder which recycled the used cemented carbide alloy by the recycle method (by a zinc treatment method, a high temperature treatment method, etc.) can be used for at least a part of the raw material A. Thereby, not only the cemented carbide of the present invention can be produced at low cost, but also the useless mining of the tungsten (W) mine can be suppressed from the viewpoint of protecting the global environment. In the past, attempts have been made to use cemented carbide recycled powder, but the present situation is that only a small portion of the powder has been used and has not been fully adopted.
[0029]
Recycling is generally performed by a zinc treatment method. However, since the particle size of the recycled WC powder depends on the WC crystal particle size of the used cemented carbide to be recycled, a WC raw material having a specific particle size cannot be produced. Even in the high temperature treatment method, the WC crystal grains partially grow during the treatment, and therefore the width of the particle size distribution of the WC powder becomes very large even if pulverized thereafter. For this reason, when a cemented carbide is produced using these recycled powders, the WC crystal grain size distribution cannot be managed, and there is a problem that the dispersion of performance becomes large.
[0030]
On the other hand, in the production method according to the present invention, the recycled powder having a particle size of 0.6 to 1 μm regenerated from the used cemented carbide which is a recycled raw material is dissolved in the liquid phase in the sintering process, It is reprecipitated on the raw material B having a larger average particle diameter. Thereby, the particle size of the plate-like WC crystal of the produced sintered body is controlled by the WC powder particle size of the raw material B. Therefore, the particle size of the recycled powder does not determine the particle size of the final sintered body, and the aforementioned problem can be avoided. Moreover, in the present method, as described above, the fine raw material A is dissolved in the liquid phase and then deposited on the coarse raw material B. Therefore, the characteristics of the plate-like WC depend on the characteristics of the coarse raw material B. Therefore, even when a recycled material having unstable characteristics is used, a sintered body having excellent characteristics can be produced.
[0031]
The ratio WR / WA of the weight WR of the WC powder generated from the recycled powder obtained by pulverizing the used cemented carbide which is the recycled raw material and the weight WA of the raw material A is 0.3 to 1 (preferably 0.5 to 1). In some cases, the cemented carbide of the present invention can be produced at a particularly low cost, and a cemented carbide preferable from the viewpoint of protecting the global environment can be obtained.
[0032]
Further, at least one kind of carbide, nitride, oxide, boride and solid solution thereof selected from IVa, Va, VIa group elements and Al are provided on the surface of a product such as a tool made of the above cemented carbide. Alternatively, when a coating film composed of at least one layer selected from diamond, DLC, and CBN is provided, and these are used as a cutting tool or an anti-abrasion tool, the alloy base material has an excellent balance of hardness and toughness. Particularly excellent performance.
[0033]
In particular, when a coating film of 20 μm or more is coated on a conventional WC-based cemented carbide, it is considered that the coating film promotes the generation of cracks (the action of pre-cracking of Griffith). Therefore, the fracture resistance of the cemented carbide was reduced. However, in the cemented carbide according to the present invention, it has been found that the above compound is precipitated in the WC crystal grains and the WC crystal grains are strengthened, so that crack progress hardly occurs and excellent fracture resistance is obtained. .
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS. 1 and 2 and Tables 1 to 14.
[0035]
(Embodiment 1)
A WC powder (raw material A) having an average particle diameter of 0.7 μm pulverized using an attritor with high pulverization efficiency as a raw material powder and a WC powder (raw material B) having an average particle diameter of 2 μm were prepared by the same pulverization. Also, CO powder with an average particle size of 1.5 μm, Ni powder with an average particle size of 1.3 μm, ZrC powder with an average particle size of 0.3 μm, TiC powder with an average particle size of 0.5 μm, HfC with an average particle size of 0.5 μm Powder, NbC powder with an average particle size of 0.3 μm, TaC powder with an average particle size of 0.4 μm, Cr with an average particle size of 0.3 μm 3 C 2 Powder, ZrN powder with an average particle size of 0.5 μm, (W, Ti) (C, N) solid solution powder with an average particle size of 0.5 μm, (W, Zr) C solid solution powder with an average particle size of 0.5 μm, average particle A (Ta, Nb) C solid solution powder having a diameter of 0.5 μm was added and blended with the composition shown in Table 1, followed by mixing in an acetone solvent for 2 hours using a normal ball mill. Thereafter, granulation was performed by a spray dryer.
[0036]
[Table 1]
In Table 1 above, numbers other than the numbers in the raw material No and Wa / Wb columns indicate wt%. Table 1 also shows that the weight percent of at least one carbide, nitride, carbonitride or solid solution thereof selected from Va, VIa group elements is Wa, and at least one kind selected from group IVa elements. The value of Wa / Wb is shown when the weight% of carbide, nitride, carbonitride or their solid solution is Wb.
[0038]
1 ton / cm of these powders 2 Is pressed using a mold at a pressure of 1, and held in a vacuum at 1550 ° C. for 1 hour for sintering. Thereby, the sintered compact of the shape of ISO type | model number CNMG120408 (the rhombus throwaway chip based on JISG4053) was produced. The sintered body is ground with a # 250 diamond grindstone and lapped with a diamond paste. After that, the fracture toughness value K obtained by the Indentation Fracture method K obtained from the hardness at 50 kg load using a diamond Vickers indenter and the crack length generated at the indentation corner of the indenter IC (MPam 1/2 ) Was measured.
[0039]
For comparison with the present invention, a WC powder having an average particle diameter of 6 μm according to the prior art, a Co powder having an average particle diameter of 1.5 μm, a Ni powder having an average particle diameter of 1.3 μm, a ZrC powder having an average particle diameter of 2 μm, TiC powder with an average particle size of 1.5 μm, HfC powder with an average particle size of 2 μm, NbC powder with an average particle size of 2 μm, TaC powder with an average particle size of 1.5 μm, Cr with an average particle size of 2 μm 3 C 2 Powder, ZrN powder with an average particle size of 1.5 μm, (W, Ti) (C, N) solid solution powder with an average particle size of 2 μm, (W, Zr) C solid solution powder with an average particle size of 1.5 μm, average particle size of 1 .8 μm (Ta, Nb) C solid solution powder was mixed with an attritor for 7 hours to produce a granulated powder in the same manner. 1 ton / cm of this powder 2 The sample was pressed using a mold at a pressure of 1 and held at 1400 ° C. in a vacuum for 1 hour for sintering. Then, the hardness and fracture toughness of the sintered body were measured by the same method.
[0040]
Further, it was measured whether or not a compound composed of at least one kind of carbide, nitride, carbonitride, or a solid solution thereof selected from IVa, Va, VIa group elements was present in the WC crystal grains. In other words, an energy dispersive X-ray fluorescence X-ray is produced by preparing a sample for a scanning electron microscope or a transmission electron microscope, and is electrically abbreviated as EDX (Energy dispersive X-ray Spectrometer). Analysis). When Ti and C were detected, the substance was TiC. These measurement results are shown in Table 2. In the sample numbers in Table 2, No. 1-1 to 10 represent sintered bodies produced by the method according to the present invention. Reference numerals 2-1 to 10 represent sintered bodies made of conventional WC powder.
[0041]
[Table 2]
In Table 2, the ◯ marks indicate that the present invention is applicable. From the results of Table 2, the sample produced by the method of the present invention includes at least one carbide, nitride, carbonitride, or a solid solution thereof selected from IVa, Va, and VIa group elements in the WC crystal grains. It can be seen that the hardness and fracture toughness of these samples show superior values compared to the samples prepared by the conventional method.
[0043]
The photograph shown in FIG. 1 is a scanning electron micrograph of Sample 1-1. In FIG. 1, the gray and square crystals are WC crystal grains 1, the black crystals are Co phases that are the binder phase 2, and the precipitates (compound 3) that appear gray in the WC crystal grains are Ti carbides. is there. From this photograph, it can be seen that the particle size of the compound 3 present in the WC crystal grain 1 of the sample 1-1 is about 0.1 μm and is 0.3 μm or less. Moreover, it turns out that the area of the said compound 3 with respect to the area of the WC crystal grain which has the said compound 3 inside is 10% or less. In the present invention, using such a cross-sectional structure, the presence or absence of the compound in the WC crystal grains was determined.
[0044]
Similarly, in the samples of 1-2 to 1-8 in Table 2, compounds composed of carbides, nitrides, carbonitrides or their solid solutions of Ti, Zr, Hf, and W exist in the WC crystal grains. It was confirmed that Samples 1-9 and 1-10 include at least one carbide selected from Ti, Zr, Hf, W carbides, nitrides, carbonitrides or IVa, Va, VIa group elements other than solid solutions thereof. It was confirmed that a compound composed of nitride, carbonitride, or a solid solution thereof was present.
[0045]
The characteristic values of the samples 1-1 to 1-8 are superior to those of the samples 2-1 to 2-8 according to the conventional method, and the improvement ratio is 1-9 to 1-1- It was also found that ten samples of the present invention were large compared to the improved values for the characteristic values of samples 2-9 to 2-10 by the conventional method. That is, the compound present in the WC crystal grains is preferably a compound composed of Ti, Zr, Hf, W carbide, nitride, carbonitride, or a solid solution thereof. In particular, Zr carbide and nitride are WC crystal grains. It was also confirmed that Sample 1-2, which was present inside, exhibited very excellent alloy characteristics.
[0046]
Among them, the weight% of at least one carbide, nitride, carbonitride, or solid solution thereof selected from Va, VIa group elements is Wa, and at least one carbide, nitride selected from group IVa elements, Samples 1-1 to 1-6 in which the value of Wa / Wb is in the range of 0 to 0.2 when the weight% of the carbonitride or their solid solution is Wb are the samples 2-1 by the conventional method. It was also confirmed that particularly excellent characteristics were exhibited as compared with ˜2-6.
[0047]
(Embodiment 2)
The raw material No. produced in the first embodiment was used. 8 and carbides of IVa, Va, VIa group elements TiC, TaC, Cr 3 C 2 Raw material No. with different amounts of 11 to 15 were prepared (Table 3), and sintered bodies were produced in the same manner as in the first embodiment, and the hardness and fracture toughness were measured. The results are shown in Table 4. Moreover, when the presence or absence of the compound in the WC crystal grain was examined in the same manner as in Embodiment 1, it was confirmed that the compound was present in the WC crystal grain in any sample.
[0048]
[Table 3]
The ratio (%) in Table 3 is the ratio (%) of the content of the carbide, nitride, carbonitride or their solid solution (excluding WC) of the Va, VIa group element to the weight of the binder phase. The numbers other than the numbers in the raw material No., ratio, and Wa / Wb columns indicate wt%.
[0050]
[Table 4]
From the results in Table 4, TaC, Cr 3 C 2 Sample No. having a total addition amount of 10 wt. The alloy characteristics of 1-12 to 1-15 are excellent, especially TaC, Cr 3 C 2 It was confirmed that Samples 1-14 and 1-15, in which the added amount of A was less than the amount that can be dissolved in the binder phase, showed particularly excellent alloy characteristics.
[0052]
(Embodiment 3)
In the same manner as in the first embodiment, the raw material Nos. With different mixing ratios of the raw material A and the raw material B are as follows. 16-23 were prepared with the composition shown in Table 5. 1 ton / cm of these powders 2 Was pressed using a mold at a pressure of 1, and held at 1500 ° C. for 1 hour in a vacuum for sintering. Thereby, the sintered compact of the shape of ISO model number CNMG120408 was produced.
[0053]
[Table 5]
Raw material No. in Table 5 The numbers other than those in the WA / WB column indicate wt%. Next, the hardness and fracture toughness of these samples were measured by the same method as in the first embodiment. The measurement results are shown in Table 6. Moreover, these samples were photographed with a scanning electron microscope at a magnification of 5000 after surface grinding and mirror polishing. This photograph was classified into WC crystal grains having a grain size exceeding 1 μm and WC crystal grains having a grain size of 1 μm or less using an image processing apparatus, and the results of measuring the respective area ratios are also shown in Table 6. Furthermore, among these WC crystal grains, the area ratio of those having an aspect ratio of 2 or more among the WC crystal grains having a grain size exceeding 1 μm was measured in the same manner, and the results are also shown in Table 6. The presence or absence of ZrC, ZrN, and TiC compounds in the WC crystal grains was examined in the same manner as in the first embodiment. As a result, it was confirmed that the samples other than 3-16 and 3-23 were present in the WC crystal grains.
[0055]
[Table 6]
From the results in Table 6, the samples of 3-18 to 3-21 in which the ratio WA / WB of the weight WA of the raw material A and the weight WB of the raw material B is in the range of 0.5 to 30 are WC having a particle size of 1 μm or less. The area ratio of crystal grains is in the range of 10 to 40%, and has an excellent balance between hardness and fracture toughness. Among them, samples 3-20 and 3-21 having an area ratio of 30% or more of WC crystal grains having an aspect ratio of 2 or more among WC crystal grains having a grain size exceeding 1 μm have particularly excellent alloy characteristics. You can see that
[0057]
(Embodiment 4)
A CNR120408 shaped chip of Samples 1-1 to 1-10 and Samples 2-1 to 2-10 produced in Embodiment 1 was subjected to a honing treatment of 0.05R, and then a coating film shown in Table 7 was formed. did. Then, the
[0058]
Cutting conditions Cutting speed: 100 m / min
Feeding: 0.4mm / rev
Cutting depth: 2mm
Cutting form: Dry
[0059]
[Table 7]
From the result of measuring the time until the defect in Table 7, the sample No. A tool in which a coating film is formed on 1-1 to 1-5 is the sample No. It turns out that the performance superior to the tool which formed the coating film in 2-1 to 2-5 is shown. Similar results could be obtained even if the diamond in Table 7 was cubic boron nitride (CBN). Thus, it turns out that the sample which formed the coating film in the cemented carbide alloy of this invention can exhibit the outstanding characteristic.
[0061]
(Embodiment 5)
No. 1 manufactured in the first embodiment. A raw material No. 1 using a recycled WC powder having the same composition as the raw material powder of No. 1 and using a used cemented carbide alloy as a part of the raw material A treated by a zinc treatment method or a high temperature treatment method. 24-28 (Table 8) were produced. These were sintered by the same method as in the first embodiment, and the hardness, fracture toughness, and presence / absence of the compound in the WC crystal grains were measured by the same method as in the first embodiment. The results are shown in Table 9.
[0062]
[Table 8]
[Table 9]
From the results of Table 9, it can be seen that the alloy characteristics of Samples 24-28 using powders recycled by the zinc treatment method and the high temperature treatment method show excellent characteristics equivalent to those of Sample 1 using no recycled powder. As described above, in the method of the present invention, the recycled powder, which has conventionally been used only in a small amount due to poor alloy properties, can be used as the main component of the WC powder. As a result, a cemented carbide preferable for global environmental protection can be obtained at a lower cost than conventional cemented carbide manufacturing methods.
[0065]
(Embodiment 6)
WC powder with an average particle size of 0.9 μm as raw material A, WC powder with an average particle size of 4 μm as raw material B, Co powder with an average particle size of 1.5 μm as raw material C, Cr powder with an average particle size of 1.8 μm, and average particles as raw material D The raw material No. which mix | blended with the composition of Table 10 using the ZrCN powder of diameter 0.1 micrometer, 0.5 micrometer, and 0.9 micrometer. 29-32 were produced.
[0066]
[Table 10]
The numbers other than the numbers in the raw material No column in Table 10 indicate wt%. Raw material No. Using the powders 29 to 32, pressing and sintering were performed in the same manner as in Embodiment 1 to produce a sintered body having the shape of ISO model number CNMG120408. Next, a cutting test of these samples was performed by the same method as in the fourth embodiment, and the time until loss was measured. The measurement results are shown in Table 11. Moreover, when these samples were photographed with a scanning electron microscope at a magnification of 5000 after surface grinding and mirror polishing, it was confirmed that the compound was present in the WC crystal grains. The composition of this compound was also confirmed to be Zr carbonitride by EDX analysis. Furthermore, using this photograph, the total area of the WC crystal grains in the photograph and the area of the crystal grains in which the presence of the above-mentioned compound is recognized are measured by using an image processing apparatus. The area ratio of WC crystal grains in which the compound was present was calculated. The results are shown in Table 11.
[0068]
[Table 11]
From the results of Table 11, the area ratio of the WC crystal grains in which ZrCN is incorporated into the crystal grains is higher when the finer raw material is used for the ZrCN powder, and the area of the WC crystal grains in which the above compounds are present in the crystal grains. It can be seen that the greater the rate, the better the fracture resistance. In particular, it was also confirmed that when the area ratio of WC crystal grains in which the above-described compound is present in the crystal grains exceeds 10%, the fracture resistance is rapidly improved.
[0070]
(Embodiment 7)
The powders having the compositions shown in Table 12 were mixed in an acetone solvent for 2 hours by a ball mill. The powder is then dried and 1 ton / cm 2 Was pressed using a mold at a pressure of 1, and held in a vacuum at a temperature of 1500 ° C. for 1 hour for sintering. Thereby, the sintered body No. 1 having the same shape of CNMG120408 as in the first embodiment is used. 3-4 to 3-6 were produced. In these sintered bodies, it was confirmed by performing EDX or X-ray qualitative analysis with a transmission electron microscope that the compounds shown in Table 13 were present in the WC crystal grains. Next, the hardness and fracture toughness of these samples were measured by the same method as in the first embodiment. The results are shown in Table 14.
[0071]
[Table 12]
[Table 13]
[Table 14]
From the results shown in Table 14, the sample No. in which the Zr compound was precipitated in the WC crystal grains. Samples Nos. 3-4 to 3-6 are sample Nos. In which the Ti compound was precipitated in the WC crystal grains. It was confirmed that the balance of hardness and fracture toughness was superior to those of samples 3-1 to 3-3. Further, this sintered body was subjected to surface grinding and outer periphery grinding, and further subjected to 0.05R honing treatment, and then a 0.5 μm TiN, 5 μm TiCN, 3 μm TiC, 2 μm alumina, 0.5 μm TiN coating film was sequentially formed from the lower layer by the CVD method. Coated with. Using these samples, the work material used in
[0075]
[0076]
【The invention's effect】
As described above, according to the present invention, a compound composed of at least one carbide, nitride, carbonitride, or a solid solution thereof selected from IVa, Va, and VIa group elements is generated in the WC crystal grains. As a result, the WC crystal is excellent in strength, and the effect is particularly remarkable when the WC crystal grains are plate-like. As a result, a cemented carbide excellent in strength and toughness can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram (copy) showing a scanning electron micrograph of a cemented carbide.
FIG. 2 is a diagram showing a cross-sectional shape of a work material used in a cutting test.
[Explanation of symbols]
1 WC grain
2 bonded phase
3 compounds
4 Work material
Claims (11)
前記超硬合金の断面組織において、前記化合物を内部に有する前記炭化タングステン結晶粒の面積に対する前記化合物の面積が１０％以下であり、
前記化合物の平均粒径が０．３μｍ未満であり、
前記化合物が、チタン（Ｔｉ）、ジルコニウム（Ｚｒ）、ハフニウム（Ｈｆ）、タングステン（Ｗ）の少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体であって前記炭化タングステン以外のものからなり、
前記Ｖａ，ＶＩａ族元素から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体であって前記炭化タングステン以外のものからなる化合物の重量％をＷａとし、前記ＩＶａ族元素もしくはタングステン（Ｗ）から選ばれた少なくとも１種の炭化物、窒化物、炭窒化物もしくはそれらの固溶体であって前記炭化タングステン以外のものからなる化合物の重量％をＷｂとしたときに、Ｗａ／Ｗｂの値が０〜０．２である、超硬合金。In a cemented carbide comprising a crystal grain mainly composed of tungsten carbide (WC) and a binder phase mainly composed of iron group metal, it is selected from IVa, Va, and VIa group elements inside at least a part of the tungsten carbide crystal grains. There is at least one carbide, nitride, carbonitride, or a solid solution thereof and a compound other than tungsten carbide,
In the cross-sectional structure of the cemented carbide, the area of the compound with respect to the area of the tungsten carbide crystal grains having the compound inside is 10% or less,
The average particle size of the compound is less than 0.3 μm;
The compound is titanium (Ti), zirconium (Zr), hafnium (Hf), tungsten (W) at least one carbide, nitride, carbonitride, or a solid solution thereof other than the tungsten carbide. Become
At least one carbide, nitride, carbonitride, or a solid solution thereof selected from the Va, VIa group elements, and a compound composed of other than the tungsten carbide is represented by Wa, and the IVa group element or When the weight% of the compound consisting of at least one carbide, nitride, carbonitride, or a solid solution thereof selected from tungsten (W) and other than tungsten carbide is Wb, Wa / Wb A cemented carbide having a value of 0 to 0.2 .
前記超硬合金の断面組織において、粒径が１μｍ以下の前記炭化タングステン結晶粒の面積率が、すべての前記炭化タングステン結晶粒面積の１０〜４０％で、粒径が１μｍを超える前記炭化タングステン結晶粒の面積率が、すべての前記炭化タングステン結晶粒面積の６０〜９０％であり、
粒径が１μｍを超える前記炭化タングステン結晶粒のうち断面組織上の形状がアスペクト比で２以上であるものを３０％以上含むことを特徴とする、超硬合金。In a cemented carbide comprising a crystal grain mainly composed of tungsten carbide (WC) and a binder phase mainly composed of iron group metal, it is selected from IVa, Va, and VIa group elements inside at least a part of the tungsten carbide crystal grains. There is at least one carbide, nitride, carbonitride, or a solid solution thereof and a compound other than tungsten carbide,
The tungsten carbide crystal in which the area ratio of the tungsten carbide crystal grains having a grain size of 1 μm or less in the cross-sectional structure of the cemented carbide is 10 to 40% of all the tungsten carbide crystal grain areas and the grain size exceeds 1 μm. grain area ratio, Ri 60% to 90% der of all the tungsten carbide crystal grains area,
A cemented carbide comprising 30% or more of the tungsten carbide crystal grains having a grain size of more than 1 μm and having a cross-sectional shape of 2 or more in aspect ratio .
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| JP32586197A JP3612966B2 (en) | 1996-12-16 | 1997-11-27 | Cemented carbide, method for producing the same and cemented carbide tool |
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| JP32586197A JP3612966B2 (en) | 1996-12-16 | 1997-11-27 | Cemented carbide, method for producing the same and cemented carbide tool |
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| EP2607512B1 (en) * | 2011-12-21 | 2017-02-22 | Sandvik Intellectual Property AB | Method of making a cemented carbide |
| KR102584679B1 (en) * | 2021-09-10 | 2023-10-05 | 한국야금 주식회사 | Cemented carbide for cutting tools and method for manufacturing the same |
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