JP3651285B2

JP3651285B2 - Cubic boron nitride-containing brazing composite material and method for producing the same

Info

Publication number: JP3651285B2
Application number: JP29896098A
Authority: JP
Inventors: 秀樹森口; 明彦池ヶ谷; 克典都築
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1998-10-20
Filing date: 1998-10-20
Publication date: 2005-05-25
Anticipated expiration: 2018-10-20
Also published as: JP2000129387A

Description

【０００１】
【発明の属する技術分野】
本発明は超硬およびサーメットの少なくとも一方と立方晶窒化硼素粒子とを複合化したロウ付けに最適な複合材料に関するものである。
【０００２】
【従来の技術】
近年、WC基超硬合金はその優れた靭性、耐摩粍性によりその適用分野を大幅に広げてきている。その適用範囲の拡大のため、特開平7−300375号公報、特開平9−194909号公報には超硬合金を積層構造にしたり、鋼と同時焼結することで、溶接可能とするなどの提案がなされている。しかしながら、これらの方法は従来の超硬合金と比較してコストが高くなるなどの問題点を有し、特殊な用途でしかその特性を発揮することができなかった。
【０００３】
また、立方晶窒化硼素焼結体も超硬合金を大幅に上回る耐摩耗性により、その適用分野を増大してきている。しかしながら従来の立方晶窒化硼素焼結体は超高圧発生容器により製造されるため、製造コストが極めて高く、また大径品が作製できないなど形状面でも制約が大きい上、その強度、靭性は超硬合金と比較して劣るため、限定された用途でしかその優れた性能を発揮することができなかった。
【０００４】
これに対して、本発明者らは上記問題点を解決するため、超硬合金マトリックス中に立方晶窒化硼素を分散した焼結体を超高圧発生容器を用いずに通電加圧焼結により製造する方法を提案（特開平9−194978号公報）し、安価で耐摩耗性に優れた焼結体を作製することができるようになった。
【０００５】
【発明が解決しようとする課題】
立方晶窒化硼素の含有量が50％を越える立方晶窒化硼素焼結体は、一般に超高圧容器を用いて製造されるときにWC基超硬合金を基体として焼結接合している。これは立方晶窒化硼素焼結体を耐摩材料として使用する場合に鋼などでできた構造物や機械本体との接合が立方晶窒化硼素焼結体と直接接合することができず、超硬合金を同時焼結して、超硬合金と鋼間をロウ付け処理することで接合力を確保するためである。しかしながら、立方晶窒化硼素焼結体は立方晶窒化硼素の含有量が一般に80体積％以上と大きく、立方晶窒化硼素の熱膨張係数は超硬合金や鋼のそれと比較すると小さいことから、両者の熱膨張係数差が大きく、ロウ付け加工時に発生した熱応力により焼結体に割れを生じやすい。そのため、焼結体の長さまたは径を30mm以下に小さくすることで応力緩和しながらロウ付け接合を行っている。
【０００６】
超硬合金については、特開平7−300375号公報において、超硬合金を積層構造とし、焼結炉内に温度傾斜を設けることで残留応力の発生の少ない溶接可能な超硬合金が提案されたり、特開平9−194909号公報には鋼と同時焼結することで溶接可能な超硬合金が提案されている。これらの提案で超硬合金の適用範囲は確かに拡大したが、これらの材料では耐摩耗性の大きな改善が見られないため、特殊な焼結法や特殊な黒鉛型を採用したことによるコスト増が大きく、その適用範囲は限定されたものであった。また、溶接による直接接合法は溶接加工時の熱により立方晶窒化硼素の劣化が起こりやすいと言う問題もある。その上、鋼と同時焼結することで黒鉛型が大型化し、コスト増となる問題点もあった。
【０００７】
従って、本発明の主目的は、立方晶窒化硼素を分散した複合材料を、鋼製の機械本体もしくは固定用の鋼製治具にロウ付け接合する際、発生する熱応力による欠けを抑制できる焼結体とその製造方法とを提供することにある。
【０００８】
【課題を解決するための手段】
本発明者らは上記の目的に鑑み種々の試験・検討を行った結果、立方晶窒化硼素粒子を含む硬質材料の下層に超硬合金およびサーメットの少なくとも一方からなる硬質材料を積層して接合し、その積層数や最上層の立方晶窒化硼素粒子の粒径、含有量、最下層の金属結合相量、WCの平均粒度などを最適化することで、各層の熱膨張係数を上層から下層に向かって大きくなるように配置し、最下層を鋼にロウ付け接合するのに好適な焼結体が作製できることを見出して本発明に至ったものである。
【０００９】
すなわち、本発明のロウ付け用複合材料は、線膨張係数が異なる硬質材料を3層以上積層した立方晶窒化硼素含有ロウ付け用複合材料において、各層の線膨張係数が最上層から最下層に向かうに従って大きくなる順に構成されている。ここで、立方晶窒化硼素粒子は最上層にのみ含有されており、最上層は平均粒径0.5〜100μmの立方晶窒化硼素粒子を10〜50体積％含有し、残部が超硬合金およびサーメットの少なくとも一方を主体とする。また、最下層はWCを主体とする硬質相と、25〜70体積％の鉄族金属を主体とする結合相とからなる。なお、各層の厚みを薄くし、各層の組成変化を僅かづつとすることで、硬質材料の厚さ方向における線膨張係数の変化が実質的に連続する構成も本発明に含む。
【００１０】
硬質材料の積層数を3層以上としたのは、積層数が3層未満では鋼とロウ付けする際に鋼と最下層の熱膨張係数差または最上層と最下層の熱膨張係数差が大きくなりすぎて大きな熱応力が発生し、亀裂または割れが生じやすくなるためである。
【００１１】
立方晶窒化硼素の含有量を10〜50体積％としたのは10体積％より立方晶窒化硼素が少ないと立方晶窒化硼素を含有させたことによる特性向上の効果が現れにくく、50体積％より立方晶窒化硼素が多いとロウ付け時の割れ発生が起こりやすくなるためである。特に好ましいのは15〜40体積％である。また、立方晶窒化硼素粒子の粒径を0.5〜100μｍとしたのは、0.5μｍよりも粒径が小さいと優れた耐摩耗性が得られないためであり、100μｍよりも大きいとロウ付け時の割れ発生が起こりやすくなるためである。特に好ましいのは1〜60μｍである。
なお、立方晶窒化硼素粒子は最上層にのみ含有されるが、これは最上層以外に立方晶窒化硼素粒子が含まれると、ロウ付け時の割れ発生が起こりやすくなるためである。
次に最上層の厚みは0.1〜４mmであることが好ましい。これは、４mmよりも厚いと、ロウ付け時の割れが起こりやすいためであり、0.1mmよりも薄いと優れた耐摩耗性が得られにくくなるためである。特に好ましい厚みは0.5〜3mmである。
【００１２】
最上層の立方晶窒化硼素粒子には200〜1500MPaの圧縮残留応力が導入されていることが好ましい。これによりロウ付け時の引っ張りの熱応力が発生しても打ち消す方向に働くため、ロウ付け時の割れの発生が抑制される。また、この圧縮残留応力によリ立方晶窒化硼素粒子の脱落が抑制され、優れた耐摩粍性の複合材料とできる。この圧縮残留応力の値が200MPaを下回るとロウ付け時の割れ抑制や立方晶窒化硼素粒子の脱落防止の効果が得られにくく、1500MPaを上回ると焼結体の強度が低下する。特に好ましいのは300〜1000MPaのときである。
【００１３】
なお、この最上層のマトリックスである硬質合金の結合相にはCoが好ましいが、耐食性を向上させたい場合にはNiやCrで置き換えても構わない。また、WCの少なくとも一部を周期律表第IVa、Va、VIa族元素の炭化物、窒化物又は炭窒化物、例えばTiC、TiCN、TiN、Mo₂C、TaC、NbCなどで置き換えても構わない。
【００１４】
次に、最下層のWC基超硬合金中の結合相は25〜70体積％の鉄族金属を含有する。これは、25体積％未満であるとロウ付け時の熱応力による割れ発生の抑制効果が小さく、70体積％を越えると超硬合金としての優れた性能が低下するためである。鉄族金属としてはロウ付け時の割れ抑制の観点からCoを主体とすることが好ましく、NiやFeなどを一部に用いても構わない。また、結合相中には周期律表第IVa、Va、VIa族元素、例えばCr、Ta、Ti、Zrなどが固溶されていると強度の観点から好ましい。なお、硬質相であるWCの一部をTiの炭化物、窒化物又は炭窒化物で置き換えても構わないが、最も好ましいのはWCとCoもしくはWCとCrが固溶したCoからなる超硬合金である。
【００１５】
WCの結晶粒径は1〜5μmであることがロウ付け時の割れ発生抑制および亀裂進展抑制の観点から好ましい。特に好ましいのはWCの平均粒径が1〜3μmのときである。
【００１６】
また、前記最下層のWCの平均粒径よりも、前記最上層中のWCの平均粒径を小さくすると、最上層の耐摩耗性向上と最下層の耐熱亀裂性向上が両立し、かつ最上層の焼結性も焼結中に生成した液相の毛細管現象がWCの微粒化で起こりやすくなって向上するため好ましい。特に、最上層のWCの平均粒径が１μmよりも小さいと、前記効果が顕著となり好ましい。
【００１７】
さらに、前記最下層のHv硬度が1000kg／m²以下であるようにすると、特に優れた耐熱亀裂性を有することができ、ロウ付け加工性が向上する。なお、本発明の複合材料は、ロウ付け加工前に金属や合金を複合材料の最下面にコーティングやメタライズし、ロウ付け作業性、ロウ付け強度を高めることができる。
【００１８】
以上のような構造とすることで、従来の超高圧装置で作製された立方晶窒化硼素焼結体では難しかったロウ付け面の最大長さが50mm以上の耐摩材料のロウ付けが熱亀裂の発生なしで行うことができる。そのため、作業性の向上やロウ付けコストの低減、ロウ付け時の寸法精度向上による加工取りしろの低減により、立方晶窒化硼素粒子を含む難削性硬質材料の研削加工コストの低減が可能となる。また、超高圧装置を使用しないことによる大幅な製造コストの低減およびその優れた耐摩耗性により、従来の超硬合金や立方晶窒化硼素焼結体よりも優れたコストパフォーマンスが期待できるようになる。
【００１９】
本発明の複合材料は内径50mm以上、好ましくは80mm以上の黒鉛型を用いて、通電加圧焼結法によって製造されることが好ましい。すなわち、所定の組成に混合した各層の原料粉末を線膨張係数が最上層から最下層に向かうに従って大きくなる順に黒鉛型に装填し、通電加圧焼結により黒鉛型内の原料粉末を焼結することで焼結体を得る。この製造法によれば、超高圧発生容器を使わずとも立方晶窒化硼素粒子を含有する硬質材料の作製が可能であり、製造コストの低減および大サイズの焼結体の製造が可能となる。また、低温での短時間焼結が可能であるので、組成の異なる硬質材料を2層以上と立方晶窒化硼素を含有する硬質材料を積層した状態で組成の変動を極力少なくして同時焼結することが可能である。
【００２０】
なお、この焼結法を用いた場合の好ましい製造条件は以下の通りである。すなわち、焼結温度は硬質材料に液相が生成する温度であることが好ましく、前記焼結温度での保持時間が20秒以上10分以内、加圧力が5〜100MPaの条件で通電加圧焼結して製造されると好ましい。ここで、液相生成温度での保持時間は20秒以上10分以内が好ましい。これは、20秒よりも液相生成温度での焼結時間が短いと緻密化が不十分であり、10分よりも長いと立方晶窒化硼素の劣化が起こりやすいためである。特に、前記通電加圧焼結が1〜100msecのパルス電流を用いて行われた場合には、非常に緻密で立方晶窒化硼素の脱落が生じにくい焼結体を得ることができる。
【００２１】
本発明の複合材料は以上に記載したように、大サイズの焼結体でも良好なロウ付け加工が可能で耐摩耗性と靭性に優れるため、超硬合金や超高圧発生容器を用いて製造される立方晶窒化硼素焼結体と比較して、コストパフォーマンスに優れる。特に鋼にロウ付け接合して用いられる耐摩耗材料として使用されたときに、その優れた性能を発揮できる。
【００２２】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
（実施例1）
平均粒径3μmのWC粉末、平均粒径1μmのCo、Ni、Cr粉末、平均粒径2μmのTiCN粉末、平均粒径30μmの立方晶窒化硼素（cBN）粉末を準備し、表1の組成に配合後、ボールミルを用いて混合し、焼結用粉末を用意した。このようにして準備した粉末を各層の厚みが焼結後に2mmとなるように表1の順に積層して、内径80mmの黒鉛型に充填し、0.01Torr以下の真空中で圧力20MPaを付加しながら、パルス電流を流して通電加圧焼結した。昇温パターンは10分間で1330℃まで昇温、その温度で1分間保持して、30℃／minの速度で冷却した。このようにして得られた焼結体No.1-1〜No.1-11は直径が80mm、各層の厚みが2mmで総厚みが4〜8mmの焼結体で、割れもなく良好な外観を呈していた。
【００２３】
【表１】

【００２４】
次に、これらの焼結体からワイヤカット装置を用いて長さ70mm、幅10mmの短冊状の試験片を切りだし、ワイヤカット面を＃200のダイヤモンド砥石を用いて平面研削後、S45C製鋼材に銀ロウ（住友電工製SA4）とフラックス（硝酸25％、硼砂30％、酸性フッ化カリ45％）を用いて、高周波炉で大気中、500℃以上に加熱しながら最下層と鋼材のロウ付け接合を行った。その結果を表2に示す。
【００２５】
【表２】

【００２６】
本発明品であるNo.1-2、1-3、1-6、1-7、1-8、1-11の試料には熱亀裂や割れもなく、鋼に対し良好に接着していることが確認できた。一方、本発明品でないNo.1-1、1-4、1-5、1-9、1-10の試料にはロウ付け時に発生したと思われる熱亀裂や割れが発生し、良好なロウ付けができなかった。No.1-1は硬質材料が2層しかなく、No.1-4、1-5は線膨張係数の配列が下層に向かうに従って大きくなっていない。また、No.1-9は最下層におけるCo量が多すぎ、No.10は最下層の硬質相がWCを主体として構成されていない。
【００２７】
（実施例2）
実施例1で作製したNo.1-2と同じ構造の焼結体を最上層の立方晶窒化硼素粒径のみ表3に示すように変化させて、試料No.2-1〜2-8を実施例1と同様にして作製した。さらに、これらの試料から、実施例1と同様に長さ70mm、幅10mmの短冊状の試験片を切りだし、ワイヤカット面を＃200のダイヤモンド砥石を用いて平面研削後、SK5製鋼材に銀ロウ（住友電工製SA3）とフラックス（硝酸25％、硼砂30％、酸性フッ化カリ45％）を用いて、高周波炉で大気中、500℃以上に加熱しながら最下層と鋼材のロウ付け接合を行ない、熱亀裂の発生の有無を評価した。
【００２８】
【表３】

【００２９】
次に、上記の鋼にロウ付けした円盤状試験片の最上面に垂直方向から100μmのSiC粉末を用いて、5kg／cm²で、60分間のサンドブラストを行い、エロージョンテストを行った。標準試料として、No.1-2最上層のマトリックスであるWC−Coと同じ組成比、同じ平均粒径の粉末を実施例1の条件で通電加圧焼結し、この焼結体（No.2-9）の摩耗量を100としたときの、No.2-1〜2-9の焼結体の摩耗量を測定した。
【００３０】
これらの評価結果も表3中に示す。立方晶窒化硼素の平均粒径が0.5〜100μmの範囲にあり、本発明品であるNo.2-2、2-3、2-4、2-5、2-6の試料には熱亀裂や割れもなく、鋼に対し良好に接着していることが確認できた。しかも優れた耐摩粍性も同時に有していることが確認できた。中でも1〜60μmの範囲にあるNo.2-2、2-3、2-4の試料は特に優れた耐摩耗性を有していることがわかる。
【００３１】
（実施例3）
実施例1で用いた粉末を用いて、表4の組成と構造を持つ焼結体No.3-1〜3-7を実施例1と同様にして作製した。なお、各層の厚みは1.5mm、総厚みは4.5mmとした。なお、No.3-1の試料のみ単層で総厚みは4.5mmである。
【００３２】
【表４】

【００３３】
これらの試料の最上面を＃400のダイヤモンド砥石で平面研削後、＃400のダイヤモンド電着砥石で研磨し、この面の中央部をX線を用いて最上層の立方晶窒化硼素粒子が有する応力の測定をsin²φ法により行った。用いたX線の線源はCo−Kα線で立方晶窒化硼素のヤング率を71GPa、ポアソン比を0.2として応力値を算出した。その結果を表5中に記す。
【００３４】
【表５】

【００３５】
さらに、これらの試料から直径60mmの円盤状の試験片をワイヤカット装置で切りだし、実施例1と同様にワイヤカット面を＃200のダイヤモンド砥石を用いて平面研削後、SCM435製鋼材にロウ材（Ag40%,Cu30%,In５%,Zn25%）銀ロウ（住友電工製SA3）とフラックス（硝酸25％、硼砂30％、酸性フッ化カリ45％）を用いて、真空炉中で650℃程度に加熱しながら最下層と鋼材のロウ付け接合を行った。その結果を表5に示すが、本発明品の積層構造を有するNo.3-2〜3-7の試料には熱亀裂や割れもなく、鋼に対し良好に接着していることが確認できた。
【００３６】
次に、上記の鋼にロウ付けした円盤状試験片の最上面に垂直方向から100μmのSiC粉末を用いて、5kg／cm²で、60分間のサンドブラストを行い、エロージョンテストを行った。なお、No.3-1の試料に関しては良好なロウ付けができていなかったため、ロウ付け前の試験片を用いて評価を行った。No.3-1の摩耗量（重量減少量）を100としたときの各試料の摩耗量を評価し、その結果を表5中に記載した。
【００３７】
表5の結果より、立方晶窒化硼素粒子に導入された圧縮応力値が200〜1500MPaの範囲にあるNo.3-2〜3-6の試料は、圧縮応力値がこの範囲外にある試料No.3-1、3-7よりも優れた耐摩耗性を有し、中でも圧縮応力値が500〜1000MPaの範囲にあるNo.3-3〜3-5の試料は特に優れた耐摩耗性を有することがわかる。
【００３８】
（実施例4）
平均粒径0.5〜10μmのWC粉末、平均粒経1μmのCo、Ni粉末、平均粒径15μmの立方晶窒化硼素粉末を準備し、表6の組成に配合後、ボールミルを用いて混合し、焼結用粉末を用意した。このようにして準備した粉末を各層の厚みが焼結後に1mmとなるように表6の順に積層して、内径100mmの黒鉛型に充填し、0.01Torr以下の真空中で圧力30MPaを付加しながら、パルス電流を流して通電加圧焼結した。昇温パターンは6分間で1350℃まで昇温、その温度で1分間保持して、50℃／minの速度で冷却した。このようにして得られた焼結体No.4-1〜4-9は直径が60mm、各層の厚みが３mmで総厚みが12mmの焼結体で、割れもなく良好な外観を呈していた。
【００３９】
【表６】

【００４０】
次に、この焼結体の一部をダイヤモンド砥石を用いて切断し、厚み方向の断面を平面研削後、鏡面研磨し、最下層のHv硬度をダイヤモンド製のビッカース圧子を用いて荷重50kgで測定するとともに、最上層と最下層の中に含まれるWCの平均粒径をフルマンの式により算出した。その結果を表7中に記載した。
【００４１】
【表７】

【００４２】
さらに、これらの試料から50mm×40mmの角状の試験片をワイヤカット装置を用いて切り出し、実施例1と同様にワイヤカット面を＃200のダイヤモンド砥石を用いて平面研削後、S45C製鋼材にロウ材（JIS：BAg-4）を用いて、真空炉中で800℃程度に加熱しながら最下層と鋼材のロウ付け接合を行った。その結果を表7に示す。本発明品の積層構造を有するNo.4-1〜4-9の試料にはいずれも熱亀裂や割れもなく、鋼に対し良好に接着していることが確認できた。
【００４３】
このようにして鋼にロウ付け接合したNo.4-1〜4-9の角状試験片における最上面の黒皮を＃400のダイヤモンド砥石を用いて平面研削し、これらの面に対して垂直方向からφ20mmの超硬ボールを用いて15Jの衝撃エネルギー与える試験を行った。この破壊衝撃試験では、衝撃を5回与える度に試験片の破壊の有無を確認しながら試験片が破壊するまで繰り返し、試験片が破壊するまでに要した破壊衝撃回数を計測した。その結果も表7に示す。
【００４４】
また、前述の方法で同様に作製した鋼にロウ付け接合したNo.4-1〜4-9の角状試験片の最上面に垂直方向から100μmのSiC粉末を用いて、5kg／cm²で60分間のサンドブラストを行い、エロージョンテストを行った。なお、No.4-3の摩耗量（重量減少量）を100としたときの各試料の摩耗量を評価し、その結果を表７中に記載した。
【００４５】
表7の結果より、最下層のHv硬度が1000kg／m²以下であるNo.4-2〜4-9の試料は最下層の硬度が1000kg／m²より大きいNo.4-1の試料よりも優れた耐衝撃性を示している。中でも最下層のWCの平均粒径が1〜5μmの範囲にあるNo.4-2、4-3、4-4、4-6、4-7、4-8、4-9の試料は特に優れた耐衝撃性を示した。また、最下層中のWCの平均粒径よりも最上層中のWCの平均粒度が小さいNo.4-6、4-7の試料の耐エロージョン性能は最上層と最下層のWCの平均粒径が等しいNo.4-3の試料よりも優れている。中でも最上層のWCの平均粒径が1μmよりも小さいNo.4-6の試料の耐エロージョン性能は特に優れていることが確認できた。
【００４６】
【発明の効果】
以上説明したように、本発明複合材料によれば、最上層を硬度に優れた立方晶窒化硼素含有硬質材料で構成し、下層に向かって線膨張係数が大きくなるような積層構造の焼結体とすることで、この複合材料を鋼材料にロウ付けする際の熱応力に伴う割れを抑制し、鋼材料との接着性を高めることができる。
【００４７】
また、本発明製造方法によれば、超高圧発生容器を使わずとも立方晶窒化硼素粒子を含有する硬質材料の作製が可能であり、製造コストの低減および大サイズの焼結体の製造が可能となる。また、低温での短時間焼結が可能であり、各層間の組成の変動を極力少なくして複数層を同時焼結することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite material optimum for brazing in which at least one of cemented carbide and cermet and cubic boron nitride particles are combined.
[0002]
[Prior art]
In recent years, WC-based cemented carbide has greatly expanded its application field due to its excellent toughness and abrasion resistance. In order to expand its application range, JP-A-7-300375 and JP-A-9-194909 propose that a cemented carbide alloy can be made into a laminated structure or can be welded by simultaneous sintering with steel. Has been made. However, these methods have problems such as higher costs as compared with conventional cemented carbides, and have been able to exhibit their properties only for special applications.
[0003]
In addition, the cubic boron nitride sintered body has been increasing its application field due to its wear resistance significantly exceeding that of cemented carbide. However, since conventional cubic boron nitride sintered bodies are manufactured using an ultra-high pressure generating container, the manufacturing cost is extremely high, and large-diameter products cannot be produced. Since it is inferior to an alloy, its superior performance could be exhibited only in limited applications.
[0004]
On the other hand, in order to solve the above problems, the present inventors manufactured a sintered body in which cubic boron nitride is dispersed in a cemented carbide matrix by means of electric pressure sintering without using an ultrahigh pressure generating vessel. A method for this purpose has been proposed (Japanese Patent Laid-Open No. 9-194978), and it has become possible to produce a sintered body that is inexpensive and excellent in wear resistance.
[0005]
[Problems to be solved by the invention]
A cubic boron nitride sintered body having a cubic boron nitride content exceeding 50% is generally sintered and bonded using a WC-based cemented carbide as a base when manufactured using an ultrahigh pressure vessel. This is because when a cubic boron nitride sintered body is used as a wear-resistant material, the structure and the machine body made of steel cannot be directly joined to the cubic boron nitride sintered body. This is because the bonding strength is ensured by simultaneously sintering and brazing between the cemented carbide and the steel. However, the cubic boron nitride sintered body generally has a large cubic boron nitride content of 80% by volume or more, and the thermal expansion coefficient of cubic boron nitride is small compared to that of cemented carbide or steel. The difference in thermal expansion coefficient is large, and cracks are likely to occur in the sintered body due to thermal stress generated during brazing. Therefore, brazing joining is performed while reducing stress by reducing the length or diameter of the sintered body to 30 mm or less.
[0006]
Regarding cemented carbide, JP-A-7-300375 proposes a cemented cemented carbide that can be welded with less residual stress by making the cemented carbide a laminated structure and providing a temperature gradient in the sintering furnace. JP-A-9-194909 proposes a cemented carbide that can be welded by simultaneous sintering with steel. Although these proposals have certainly expanded the range of cemented carbide applications, these materials do not show significant improvement in wear resistance, so the cost increases due to the use of special sintering methods and special graphite molds. The application range was limited. Further, the direct joining method by welding also has a problem that cubic boron nitride is likely to be deteriorated by heat during welding. In addition, the graphite mold becomes large due to simultaneous sintering with steel, resulting in increased costs.
[0007]
Therefore, the main object of the present invention is to suppress the chipping caused by thermal stress generated when brazing a composite material in which cubic boron nitride is dispersed to a steel machine body or a fixing steel jig. The object of the present invention is to provide a combined body and a method for producing the same.
[0008]
[Means for Solving the Problems]
As a result of various tests and examinations in view of the above object, the present inventors have laminated and joined a hard material made of at least one of cemented carbide and cermet under the hard material containing cubic boron nitride particles. By optimizing the number of layers, the particle size and content of cubic boron nitride particles in the uppermost layer, the amount of metal binding phase in the lowermost layer, the average particle size of WC, etc., the thermal expansion coefficient of each layer is changed from the upper layer to the lower layer. It has been found that a sintered body suitable for brazing and joining the lowermost layer to steel can be produced by arranging the layers so as to become larger toward the present invention.
[0009]
That is, the brazing composite material of the present invention is a cubic boron nitride-containing brazing composite material in which three or more layers of hard materials having different linear expansion coefficients are laminated, and the linear expansion coefficient of each layer is from the uppermost layer to the lowermost layer. According to the order of increasing. Here, the cubic boron nitride particles are contained only in the uppermost layer, and the uppermost layer contains 10 to 50% by volume of cubic boron nitride particles having an average particle size of 0.5 to 100 μm, with the balance being cemented carbide and cermet. At least one is the subject. The lowermost layer is composed of a hard phase mainly composed of WC and a binder phase mainly composed of 25 to 70% by volume of iron group metal. In addition, the present invention includes a configuration in which the change of the linear expansion coefficient in the thickness direction of the hard material is substantially continuous by reducing the thickness of each layer and slightly changing the composition of each layer.
[0010]
The reason why the number of laminated hard materials is 3 or more is that if the number of laminated layers is less than 3, the difference in thermal expansion coefficient between the steel and the bottom layer or the difference in thermal expansion coefficient between the top layer and the bottom layer is large when brazing to steel. This is because too much thermal stress is generated and cracks or cracks are likely to occur.
[0011]
The content of cubic boron nitride is 10 to 50% by volume. If the amount of cubic boron nitride is less than 10% by volume, the effect of improving the characteristics due to the inclusion of cubic boron nitride is less likely to appear, and from 50% by volume. This is because when there is a large amount of cubic boron nitride, cracks are likely to occur during brazing. Particularly preferred is 15 to 40% by volume. Further, the cubic boron nitride particles have a particle size of 0.5 to 100 μm because excellent wear resistance cannot be obtained if the particle size is smaller than 0.5 μm. This is because cracking tends to occur. Particularly preferred is 1 to 60 μm.
Note that the cubic boron nitride particles are contained only in the uppermost layer, because if the cubic boron nitride particles are contained in addition to the uppermost layer, cracks are likely to occur during brazing.
Next, the thickness of the uppermost layer is preferably 0.1 to 4 mm. This is because if it is thicker than 4 mm, cracks are likely to occur during brazing, and if it is thinner than 0.1 mm, it is difficult to obtain excellent wear resistance. A particularly preferred thickness is 0.5 to 3 mm.
[0012]
It is preferable that a compressive residual stress of 200 to 1500 MPa is introduced into the uppermost cubic boron nitride particles. As a result, even if a tensile thermal stress is generated during brazing, it works in the direction to cancel out, so that cracking during brazing is suppressed. In addition, dropping of the cubic boron nitride particles is suppressed by this compressive residual stress, and an excellent wear-resistant composite material can be obtained. If the value of this compressive residual stress is less than 200 MPa, it is difficult to obtain the effect of suppressing cracking during brazing and preventing the cubic boron nitride particles from falling off, and if it exceeds 1500 MPa, the strength of the sintered body decreases. Particularly preferred is 300 to 1000 MPa.
[0013]
Note that Co is preferable for the binder phase of the hard alloy which is the uppermost layer matrix, but Ni or Cr may be substituted for improving the corrosion resistance. Further, at least a part of WC may be replaced with carbides, nitrides or carbonitrides of group IVa, Va, VIa elements of the periodic table, such as TiC, TiCN, TiN, Mo ₂ C, TaC, NbC, etc. .
[0014]
Next, the binder phase in the lowermost WC-based cemented carbide contains 25 to 70% by volume of an iron group metal. This is because if it is less than 25% by volume, the effect of suppressing cracking due to thermal stress during brazing is small, and if it exceeds 70% by volume, the excellent performance as a cemented carbide decreases. The iron group metal is preferably mainly composed of Co from the viewpoint of suppressing cracking during brazing, and Ni, Fe, or the like may be used in part. In addition, it is preferable from the viewpoint of strength that a group IVa, Va, or VIa group element such as Cr, Ta, Ti, or Zr in the periodic table is dissolved in the binder phase. A part of WC, which is a hard phase, may be replaced by Ti carbide, nitride or carbonitride, but the most preferable is a cemented carbide made of Co in which WC and Co or WC and Cr are dissolved. It is.
[0015]
The crystal grain size of WC is preferably 1 to 5 μm from the viewpoint of suppressing crack generation and crack progress during brazing. Particularly preferred is when the average particle size of WC is 1 to 3 μm.
[0016]
Further, if the average particle diameter of the WC in the uppermost layer is made smaller than the average particle diameter of the WC in the lowermost layer, both the improvement of the wear resistance of the uppermost layer and the improvement of the thermal crack resistance of the lowermost layer are achieved, and the uppermost layer The sinterability of the liquid phase is also preferable because the liquid phase capillary phenomenon generated during sintering is likely to occur due to the atomization of WC. In particular, it is preferable that the average particle diameter of the WC of the uppermost layer is smaller than 1 μm because the above effect becomes remarkable.
[0017]
Furthermore, when the Hv hardness of the lowermost layer is 1000 kg / m ² or less, it can have particularly excellent thermal crack resistance and brazing workability is improved. Note that the composite material of the present invention can be coated or metallized with a metal or an alloy on the lowermost surface of the composite material before brazing to improve brazing workability and brazing strength.
[0018]
With the above structure, brazing of a wear-resistant material with a maximum brazing surface length of 50 mm or more, which was difficult with a cubic boron nitride sintered body produced by a conventional ultra-high pressure device, caused thermal cracks. Can be done without. Therefore, it is possible to reduce the grinding cost of hard-to-cut hard materials containing cubic boron nitride particles by improving workability, reducing brazing cost, and reducing machining allowance by improving dimensional accuracy during brazing. . In addition, the cost performance superior to conventional cemented carbides and cubic boron nitride sintered bodies can be expected due to the significant reduction in manufacturing cost and the superior wear resistance by not using ultra-high pressure equipment. .
[0019]
The composite material of the present invention is preferably produced by an electric current pressure sintering method using a graphite mold having an inner diameter of 50 mm or more, preferably 80 mm or more. That is, the raw material powder of each layer mixed in a predetermined composition is loaded into the graphite mold in the order in which the linear expansion coefficient increases from the uppermost layer to the lowermost layer, and the raw material powder in the graphite mold is sintered by electric pressure sintering. Thus, a sintered body is obtained. According to this manufacturing method, it is possible to produce a hard material containing cubic boron nitride particles without using an ultra-high pressure generating vessel, and it is possible to reduce the production cost and produce a large-sized sintered body. In addition, since sintering can be performed at low temperatures for a short time, simultaneous sintering is possible with as little variation in composition as possible in a state where two or more layers of hard materials having different compositions and a hard material containing cubic boron nitride are laminated. Is possible.
[0020]
In addition, the preferable manufacturing conditions at the time of using this sintering method are as follows. That is, the sintering temperature is preferably a temperature at which a liquid phase is generated in the hard material, and the holding time at the sintering temperature is not less than 20 seconds and not more than 10 minutes, and the pressurizing pressure is 5 to 100 MPa. It is preferable to produce by ligation. Here, the holding time at the liquid phase generation temperature is preferably 20 seconds or more and 10 minutes or less. This is because if the sintering time at the liquid phase generation temperature is shorter than 20 seconds, densification is insufficient, and if it is longer than 10 minutes, cubic boron nitride is likely to deteriorate. In particular, when the energization and pressure sintering is performed using a pulse current of 1 to 100 msec, it is possible to obtain a sintered body that is very dense and in which cubic boron nitride does not easily fall off.
[0021]
As described above, the composite material of the present invention can be produced by using a cemented carbide or an ultra-high pressure generation container because it can be brazed well even in a large-sized sintered body and has excellent wear resistance and toughness. Excellent cost performance compared to cubic boron nitride sintered bodies. In particular, when used as a wear-resistant material used by brazing to steel, its excellent performance can be exhibited.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
(Example 1)
Prepare WC powder with an average particle size of 3 μm, Co, Ni, Cr powder with an average particle size of 1 μm, TiCN powder with an average particle size of 2 μm, and cubic boron nitride (cBN) powder with an average particle size of 30 μm. After blending, the mixture was mixed using a ball mill to prepare a powder for sintering. The powder thus prepared was laminated in the order of Table 1 so that the thickness of each layer was 2 mm after sintering, filled in a graphite mold having an inner diameter of 80 mm, and a pressure of 20 MPa was applied in a vacuum of 0.01 Torr or less. Then, a pulsed current was passed to conduct pressure sintering. The heating pattern was raised to 1330 ° C. in 10 minutes, held at that temperature for 1 minute, and cooled at a rate of 30 ° C./min. The sintered bodies No. 1-1 to No. 1-11 thus obtained are sintered bodies having a diameter of 80 mm, a thickness of each layer of 2 mm, and a total thickness of 4 to 8 mm. Was presenting.
[0023]
[Table 1]

[0024]
Next, a 70 mm long and 10 mm wide strip-shaped test piece was cut out from these sintered bodies using a wire cutting device, and the wire cut surface was surface ground using a # 200 diamond grindstone, and then S45C steel product The bottom layer and steel brazing material are heated to 500 ° C or higher in a high-frequency furnace using silver brazing (SA4 made by Sumitomo Electric) and flux (nitric acid 25%, borax 30%, potassium acid fluoride 45%) Bonding was performed. The results are shown in Table 2.
[0025]
[Table 2]

[0026]
No. 1-2, 1-3, 1-6, 1-7, 1-8, 1-11 samples of the present invention have no thermal cracking or cracking and adhere well to steel I was able to confirm. On the other hand, samples No. 1-1, 1-4, 1-5, 1-9, 1-10, which are not products of the present invention, show thermal cracks and cracks that are thought to have occurred during brazing, resulting in good brazing. I couldn't attach it. No. 1-1 has only two layers of hard material, and Nos. 1-4 and 1-5 have a linear expansion coefficient arrangement that does not increase toward the lower layer. In No. 1-9, the amount of Co in the lowermost layer is too large, and in No. 10, the hard phase in the lowermost layer is not composed mainly of WC.
[0027]
(Example 2)
The sintered body having the same structure as No. 1-2 produced in Example 1 was changed only in the cubic boron nitride particle size of the uppermost layer as shown in Table 3, and Sample Nos. 2-1 to 2-8 were changed. It was produced in the same manner as in Example 1. Further, from these samples, a strip-shaped test piece having a length of 70 mm and a width of 10 mm was cut out in the same manner as in Example 1, and the wire-cut surface was subjected to surface grinding using a # 200 diamond grindstone, and then to SK5 steel material. Using brazing (SA3 made by Sumitomo Electric) and flux (nitric acid 25%, borax 30%, potassium acid fluoride 45%), brazing the bottom layer to the steel while heating to 500 ° C or higher in the air in a high frequency furnace And the presence or absence of thermal cracks was evaluated.
[0028]
[Table 3]

[0029]
Next, an erosion test was performed by sandblasting at 5 kg / cm ² for 60 minutes using SiC powder of 100 μm from the vertical direction on the uppermost surface of the disk-shaped test piece brazed to the steel. As a standard sample, a powder having the same composition ratio and the same average particle diameter as WC-Co, which is the matrix of No. 1-2 uppermost layer, was subjected to current and pressure sintering under the conditions of Example 1, and this sintered body (No. The amount of wear of the sintered bodies of Nos. 2-1 to 2-9 was measured when the amount of wear in 2-9) was 100.
[0030]
These evaluation results are also shown in Table 3. The average particle diameter of cubic boron nitride is in the range of 0.5 to 100 μm, and samples No. 2-2, 2-3, 2-4, 2-5, and 2-6 that are the present invention have thermal cracks and There was no crack and it was confirmed that the steel was well bonded to the steel. Moreover, it has been confirmed that it also has excellent abrasion resistance. In particular, it can be seen that the samples No. 2-2, 2-3 and 2-4 in the range of 1 to 60 μm have particularly excellent wear resistance.
[0031]
(Example 3)
Using the powder used in Example 1, sintered bodies No. 3-1 to 3-7 having the compositions and structures shown in Table 4 were produced in the same manner as in Example 1. The thickness of each layer was 1.5 mm, and the total thickness was 4.5 mm. Only the sample No. 3-1 is a single layer and the total thickness is 4.5 mm.
[0032]
[Table 4]

[0033]
The top surface of these samples is surface ground with a # 400 diamond grindstone, then polished with a # 400 diamond electrodeposited grindstone, and the central portion of this surface is stressed by the cubic boron nitride particles on the top layer using X-rays measurements were carried out by sin ² φ method. The X-ray source used was a Co—Kα ray, and the stress value was calculated assuming that the Young's modulus of cubic boron nitride was 71 GPa and the Poisson's ratio was 0.2. The results are shown in Table 5.
[0034]
[Table 5]

[0035]
Further, a disk-shaped test piece having a diameter of 60 mm was cut out from these samples with a wire-cutting device, and the surface of the wire-cut surface was ground using a # 200 diamond whetstone in the same manner as in Example 1, and then the SCM435 steel material was brazed. (Ag40%, Cu30%, In5%, Zn25%) Using silver solder (Sumitomo Electric SA3) and flux (nitric acid 25%, borax 30%, potassium acid fluoride 45%) in a vacuum furnace at around 650 ° C The bottom layer and the steel material were brazed and joined while heating. The results are shown in Table 5, and it can be confirmed that the samples No. 3-2 to 3-7 having a laminated structure of the present invention have no thermal cracks or cracks and are well bonded to steel. It was.
[0036]
Next, an erosion test was performed by sandblasting at 5 kg / cm ² for 60 minutes using SiC powder of 100 μm from the vertical direction on the uppermost surface of the disk-shaped test piece brazed to the steel. Since the sample No. 3-1 was not brazed well, the test piece before brazing was used for evaluation. The wear amount of each sample was evaluated when the wear amount (weight reduction amount) of No. 3-1 was 100, and the results are shown in Table 5.
[0037]
From the results of Table 5, the samples No. 3-2 to 3-6 in which the compressive stress value introduced into the cubic boron nitride particles is in the range of 200 to 1500 MPa are the sample Nos. In which the compressive stress value is outside this range. .3-1 and 3-7 have superior wear resistance, especially No. 3-3 to 3-5 samples with compression stress values in the range of 500 to 1000 MPa have particularly superior wear resistance. You can see that
[0038]
(Example 4)
Prepare WC powder with an average particle size of 0.5 to 10 μm, Co and Ni powder with an average particle size of 1 μm, and cubic boron nitride powder with an average particle size of 15 μm. After blending to the composition shown in Table 6, mixing using a ball mill and firing A powder for ligation was prepared. The powder thus prepared was laminated in the order of Table 6 so that the thickness of each layer was 1 mm after sintering, and filled in a graphite mold with an inner diameter of 100 mm, while applying a pressure of 30 MPa in a vacuum of 0.01 Torr or less. Then, a pulsed current was passed to conduct pressure sintering. The heating pattern was raised to 1350 ° C. in 6 minutes, held at that temperature for 1 minute, and cooled at a rate of 50 ° C./min. The sintered bodies No. 4-1 to 4-9 thus obtained were sintered bodies having a diameter of 60 mm, a thickness of each layer of 3 mm, and a total thickness of 12 mm, and exhibited a good appearance without cracks. .
[0039]
[Table 6]

[0040]
Next, a part of this sintered body is cut with a diamond grindstone, the cross section in the thickness direction is surface ground and then mirror polished, and the Hv hardness of the lowest layer is measured with a diamond Vickers indenter at a load of 50 kg In addition, the average particle size of WC contained in the uppermost layer and the lowermost layer was calculated by the Fullman equation. The results are shown in Table 7.
[0041]
[Table 7]

[0042]
Further, a square test piece of 50 mm × 40 mm was cut out from these samples using a wire cutting device, and the wire cut surface was subjected to surface grinding using a # 200 diamond grindstone in the same manner as in Example 1, and then the S45C steel product was obtained. Using the brazing material (JIS: BAg-4), the lowermost layer and the steel material were brazed and joined while heating to about 800 ° C. in a vacuum furnace. The results are shown in Table 7. It was confirmed that none of the samples Nos. 4-1 to 4-9 having the laminated structure of the present invention had good thermal adhesion and adhesion to steel.
[0043]
The black skin of the top surface of the square test pieces of Nos. 4-1 to 4-9 brazed to the steel in this way was surface ground using a # 400 diamond grindstone and perpendicular to these surfaces. A test was conducted to give an impact energy of 15 J using a carbide ball of φ20mm from the direction. In this destructive impact test, the test was repeated until the test piece was broken while checking the presence or absence of the test piece every time an impact was applied five times, and the number of times of destructive impact required until the test piece was broken was measured. The results are also shown in Table 7.
[0044]
Also, using SiC powder of 100 μm from the vertical direction on the top surface of the square test pieces of No. 4-1 to 4-9 brazed to the steel produced in the same manner as described above, at 5 kg / cm ² An erosion test was performed by sandblasting for 60 minutes. The wear amount of each sample was evaluated when the wear amount (weight reduction amount) of No. 4-3 was 100, and the results are shown in Table 7.
[0045]
From the results of Table 7, the samples of No. 4-2 to 4-9 whose Hv hardness of the lowermost layer is 1000 kg / m ² or less are more than those of No. 4-1 whose hardness of the lowermost layer is higher than 1000 kg / m ^2. Also shows excellent impact resistance. Especially the samples of No.4-2, 4-3, 4-4, 4-6, 4-7, 4-8, 4-9 whose average particle size of WC in the lowermost layer is in the range of 1-5 μm Excellent impact resistance. In addition, the erosion resistance of the samples No. 4-6 and 4-7, in which the average particle size of WC in the uppermost layer is smaller than the average particle size of WC in the lowermost layer, is the average particle size of WC in the uppermost layer and the lowermost layer. Is superior to the No.4-3 sample with equal In particular, it was confirmed that the erosion resistance performance of the No. 4-6 sample having an average particle diameter of the uppermost WC smaller than 1 μm was particularly excellent.
[0046]
【The invention's effect】
As described above, according to the composite material of the present invention, the uppermost layer is composed of a cubic boron nitride-containing hard material having excellent hardness, and the sintered body has a laminated structure in which the linear expansion coefficient increases toward the lower layer. By doing this, it is possible to suppress cracking due to thermal stress when brazing the composite material to the steel material, and to enhance the adhesion to the steel material.
[0047]
In addition, according to the manufacturing method of the present invention, it is possible to manufacture a hard material containing cubic boron nitride particles without using an ultra-high pressure generating vessel, and it is possible to reduce manufacturing cost and manufacture a large size sintered body. It becomes. Moreover, it is possible to perform sintering at a low temperature for a short time, and it is possible to simultaneously sinter a plurality of layers while minimizing the variation of the composition between the layers.

Claims

In a cubic boron nitride-containing brazing composite material in which three or more layers of hard materials having different linear expansion coefficients are laminated,
The linear expansion coefficient of each layer is configured in order of increasing from the top layer to the bottom layer, cubic boron nitride particles are contained only in the top layer,
The uppermost layer contains 10 to 50% by volume of cubic boron nitride particles having an average particle size of 0.5 to 100 μm, and the balance is mainly composed of at least one of cemented carbide and cermet,
A cubic boron nitride-containing brazing composite material characterized in that the lowermost layer comprises a hard phase mainly composed of WC and a binder phase mainly composed of 25 to 70% by volume of an iron group metal.

The cubic boron nitride-containing brazing composite material according to claim 1, wherein the uppermost layer has a thickness of 0.1 to 4 mm.

2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein the cubic boron nitride particles have a compressive residual stress of 200 to 1500 MPa.

2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein an average particle diameter of the cubic boron nitride particles is 1 to 60 μm.

2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein an average particle diameter of the lowermost WC is 1 to 5 μm.

2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein an average particle diameter of the uppermost WC is smaller than an average particle diameter of the lowermost WC.

2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein an average particle diameter of WC of the uppermost layer is smaller than 1 μm.

^2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein the lowermost layer has an Hv hardness of 1000 kg / m ² or less.

2. The cubic boron nitride-containing brazing composite material according to claim 1, wherein the maximum length of the lowermost layer in the composite material is 50 mm or more.

Mixing the raw material powder of each layer of three or more layers;
Loading the raw material powder of each layer into the graphite mold in order of increasing linear expansion coefficient from the top layer to the bottom layer;
A step of sintering the raw material powder in the graphite mold by electric pressure sintering,
The uppermost raw material powder is 10-50 vol% of cubic boron nitride particles with an average particle size of 0.5-100 μm, the balance being WC, periodic table IVa, Va, VIa group element carbide, nitride and carbonitride Mainly at least one selected from the group and iron group metals,
The lowermost raw material powder consists of a hard phase mainly composed of WC and a binder phase mainly composed of 25 to 70% by volume of iron group metal,
A method for producing a cubic boron nitride-containing composite material for brazing, wherein the graphite mold has an inner diameter of 50 mm or more.