JP4537501B2

JP4537501B2 - Cemented carbide and method for producing the same

Info

Publication number: JP4537501B2
Application number: JP21986997A
Authority: JP
Inventors: 裕明後藤; 典光木本; 寿康石崎
Original assignee: Sumitomo Electric Hardmetal Corp
Current assignee: Sumitomo Electric Hardmetal Corp
Priority date: 1997-07-30
Filing date: 1997-07-30
Publication date: 2010-09-01
Anticipated expiration: 2017-07-30
Also published as: JPH1150182A

Description

【０００１】
【発明の属する技術分野】
本発明は特に衝撃強度を向上できる超硬合金とその製造方法に関するものである。
【０００２】
【従来の技術】
超硬合金の衝撃強度や靱性と剛性・硬度とは相反関係にあり、両者を両立させることは難しい。この点を改善する技術として、▲１▼特公平5-20492 号公報，▲２▼特開昭58-39764号公報，▲３▼特公昭61-4899 号公報記載のものが知られている。これらは主に焼結温度からの冷却速度を特定することにより靱性と強度の両立を図っている。
【０００３】
【発明が解決しようとする課題】
しかし、上記のいずれの技術でも衝撃強度や靱性と剛性・硬度との両立は十分とはいえず、衝撃強度不足による破損や靱性不足による亀裂の発生、剛性・硬度不足による塑性変形に対応できる材料が要望されていた。また、１４００℃程度の焼結温度からの急冷では熱衝撃が大き過ぎ、超硬合金に割れが発生する可能性が強い。さらに、焼結温度から急冷した場合、その急冷効果を維持するには、後にＨＩＰ処理を行うことができないという問題があった。
【０００４】
従って、本発明の主目的は、靱性と強度、特に衝撃強度とを両立できる超硬合金とその製造方法を提供することにある。
【０００５】
【課題を解決するための手段】
本発明は超硬合金中のＣｏの結晶構造および固溶量を制御することにより上記の目的を達成する。すなわち、本発明超硬合金は、ＷＣを主体とする硬質相がＣｏを含む鉄族金属の結合相中に分散された超硬合金において、前記Ｃｏの結晶構造が次式を満たすことを特徴とする。
０≦Ｉ(Co・hcp)／Ｉ(Co・fcc)≦０．１
ただし、Ｉ(Co・hcp)はhcp構造のＣｏの(101)面におけるＸ線回折強度で、Ｉ(Co・fcc)はfcc 構造のＣｏの(111)面におけるＸ線回折強度である。
【０００６】
ここで、Ｉ(Co・hcp)／Ｉ(Co・fcc)のより好ましい範囲は０．０１〜０．０５である。さらにＣｏの格子定数が３．５７０以上であることが好ましい。なお、結合相量は１０〜３０ｗｔ％程度が好適である。
【０００７】
「Ｉ(Co・hcp)／Ｉ(Co・fcc)」が０．１を越えると、脆弱なhcp 構造のＣｏが増えて靱性が不足する。そのため、このような超硬合金を鍛造工具に用いた場合、亀裂が発生しやすく、工具寿命が短くなってしまう。さらに、格子定数が３．５７０未満であるとＣｏ中へのＷの固溶量が少ないことを意味し、やはり靱性不足となりやすい。
【０００８】
また、本発明超硬合金の製造方法は、ＷＣを主体とする硬質相とＣｏを含む鉄族金属の結合相とを焼結して冷却する工程と、この冷却後に焼結体を液相出現直下の温度まで加熱し、液体中に浸漬して急冷する工程とを含むことを特徴とする。
【０００９】
液相出現直下の温度としては１２００〜１３００℃程度が好適である。また、急冷速度は１０００℃／ｍｉｎ以上とすることが望ましい。急冷する際に焼結体を浸漬する液体は特に限定されない。例えば、水や油が挙げられる。なお、硬質相と結合相とを焼結した後に必要に応じてＨＩＰ処理を行ってもよい。
【００１０】
一般に、超硬合金製品は次の工程により製造される。
原料粉末の混合→プレス→中間焼結→成形→焼結→（ＨＩＰ）→検査
すなわち、混合した原料をプレスして例えばブロック状に成形し、７００℃程度で中間焼結する。そして、中間焼結体を所定の工具形状に成形して１４００℃程度で焼結を行う。さらに焼結体中の空隙を減少させるため、焼結の後にＨＩＰ（例えば１３４０℃程度）を行うこともある。
【００１１】
前述した従来の技術▲１▼〜▲３▼ではおもに焼結温度から冷却する際の速度に着目ししている。本発明では焼結温度からの冷却は特に規定せず、一旦冷却された後に再度加熱してから急冷することを特徴とする。
【００１２】
このような急冷はＣｏの結晶構造の変態温度域（４１３℃前後）をごく短時間で通過することにより、(1) 高温で安定相であるfcc 構造からhcp 構造へ相変態させることなく固化する，(2) 急冷直前にＣｏへ固溶しているＷを冷却中に析出させることなく固化する、ことに有効である。
【００１３】
液相出現温度直下の温度より急冷を開始するのは、Ｃｏ中にＷを多量に固溶でき、かつfcc →hcp の変態温度に最も近い温度条件だからである。１４００℃程度の焼結温度近辺の温度からの急冷では熱衝撃が大きく、割れが発生する場合がある。具体的な再加熱温度は１２００〜１３００℃程度、特に１２２０〜１２８０℃程度が好適である。
【００１４】
また、従来の技術▲１▼〜▲３▼では焼結温度からの冷却を急冷としており、冷却後にＨＩＰを行なうと急冷効果が失われるため、焼結に引き続いてＨＩＰを行うことが難しい。しかし、本発明では後に再加熱してから急冷するため、焼結と再加熱との間にＨＩＰを行ってより緻密な超硬合金を得ることもできる。
【００１５】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
市販のＷＣ粉末（平均粒径６．５μｍと３μｍ）とＣｏ粉末（平均粒径１．２μｍ）を表１に示す組成に配合し、アトライターで湿式混合した後、乾燥した粉末を作製した。この粉末を１ｔ／cm² の圧力でプレスし、１３８０℃〜１４００℃にて６０分間焼結してから除冷した超硬合金試験片を作製した。これらの試験片のうち、いくつかはさらにＨＩＰ処理（１３４０℃，１ｔ／cm² ，Ａｒガス雰囲気）を施した。焼結またはＨＩＰ処理を施して冷却された試験片は、予め１２５０℃に加熱した電気炉内に１５分間保持した後、炉から取り出して直ちに（３０秒以内）に水中に浸漬して、急冷処理が施された。なお、上記急冷処理を行わなかったものと、従来のガス冷却を施したものとを比較例とした。ガス冷却は窒素ガス導入により冷却を行うもので、冷却速度はせいぜい５００℃／ｍｉｎである。
【００１６】
そして、得られた試験片について、Ｘ線回折によりＣｏの結晶構造（Ｉ(Co・hcp)／Ｉ(Co・fcc)），格子定数，衝撃強度，硬度，抗折力の分析・測定を行った。その結果を表２に示す。
【００１７】
【表１】

【００１８】
【表２】

【００１９】
表２に示すように、いずれの実施例も硬度・抗折力に関しては比較例と同等であるが、衝撃強度は著しく向上していることがわかる。これは、結合相のＣｏの結晶構造が延性に富むfcc 構造となり、Ｃｏ中に多量にＷが固溶し、その結果格子定数が向上して強化されたためであると思われる。各実施例の冷却速度は、１２５０℃からほぼ常温まで冷却するのにせいぜい１０秒程度であったため、１２０℃／ｓｅｃ程度と推定される。
【００２０】
これに対し、比較例はいずれも衝撃強度が劣っている。すなわち、急冷処理を行わなかった比較例１〜６は全て衝撃強度，格子定数共に低い。また、窒素ガス導入によるガス冷却を行った比較例７，８は５００℃／ｍｉｎ程度の冷却を行ったにもかかわらず、実施例に匹敵する衝撃強度は得られなかった。
【００２１】
なお、急冷する際の冷却媒体を水ではなく油とした場合でも同様の結果が得られた。
【００２２】
（試験例）
表１の組成Ａの粉末を用いてφ２９−Ｌ１３７mmの温熱間鍛造用のパンチを作製した。作製条件は実施例１と同じように、プレス圧力：１ｔ／cm² ，焼結温度：１３８０℃〜１４００℃，焼結時間：６０分で、ＨＩＰ処理後に急冷処理を施した。比較として急冷処理を行わないパンチも作製した。これらのパンチを切削加工後、ワーク：ＳＣＭ１５，ワーク温度：１１００℃，サイクルタイム：７５ケ／ｍｉｎ，面圧：６５kg/mm²がかかる条件で鍛造工具として使用し、寿命までのショット数の計測と工具表面の観察とを行った。その結果を表３および図１，２に示す。
【００２３】
【表３】

【００２４】
本発明超硬合金によるパンチは寿命までのショット数が１４５０００回と格段に多く、工具の表面も図１に示すように熱亀裂の発生が見られない。すなわち、本発明超硬合金の工具は従来工具に比べて２〜１０倍の寿命を有することがわかる。これに対して急冷を行わなかったパンチは３５０００ショットで図２に示すように多数の熱亀裂が生じて使用不能となった。
【００２５】
【発明の効果】
以上説明したように、本発明超硬合金は衝撃強度と硬度とを両立でき、高い衝撃強度が求められる鍛造工具などへの利用が期待される。また、本発明方法は本発明超硬合金を製造するのに最適な方法である。
【図面の簡単な説明】
【図１】本発明超硬合金を用いたパンチの鍛造加工後における打撃面を示す模式図。
【図２】従来の超硬合金を用いたパンチの鍛造加工後における打撃面を示す模式図。[0001]
BACKGROUND OF THE INVENTION
The present invention particularly relates to a cemented carbide capable of improving impact strength and a method for producing the same.
[0002]
[Prior art]
The impact strength, toughness and rigidity / hardness of cemented carbide are in a contradictory relationship, making it difficult to achieve both. As techniques for improving this point, those described in (1) Japanese Patent Publication No. 5-20492, (2) Japanese Unexamined Patent Publication No. 58-39764, and (3) Japanese Patent Publication No. 61-4899 are known. These aim to achieve both toughness and strength mainly by specifying the cooling rate from the sintering temperature.
[0003]
[Problems to be solved by the invention]
However, none of the above technologies provides sufficient balance between impact strength, toughness, rigidity and hardness, and materials that can handle damage due to insufficient impact strength, cracks due to insufficient toughness, and plastic deformation due to insufficient rigidity and hardness. Was requested. Moreover, in the rapid cooling from the sintering temperature of about 1400 ° C., the thermal shock is too large, and there is a strong possibility that the cemented carbide will crack. Furthermore, when quenching from the sintering temperature, there is a problem that the HIP treatment cannot be performed later in order to maintain the quenching effect.
[0004]
Accordingly, a main object of the present invention is to provide a cemented carbide capable of achieving both toughness and strength, particularly impact strength, and a method for producing the same.
[0005]
[Means for Solving the Problems]
The present invention achieves the above object by controlling the crystal structure and solid solution amount of Co in the cemented carbide. That is, the cemented carbide of the present invention is characterized in that, in a cemented carbide in which a hard phase mainly composed of WC is dispersed in a binding phase of an iron group metal containing Co, the crystal structure of the Co satisfies the following formula: To do.
0 ≦ I (Co · hcp) / I (Co · fcc) ≦ 0.1
Here, I (Co · hcp) is the X-ray diffraction intensity in the (101) plane of Co in the hcp structure, and I (Co · fcc) is the X-ray diffraction intensity in the (111) plane of Co in the fcc structure.
[0006]
Here, a more preferable range of I (Co · hcp) / I (Co · fcc) is 0.01 to 0.05. Furthermore, the lattice constant of Co is preferably 3.570 or more. In addition, about 10-30 wt% is suitable for the amount of binder phases.
[0007]
When “I (Co · hcp) / I (Co · fcc)” exceeds 0.1, Co having a weak hcp structure increases and the toughness is insufficient. Therefore, when such a cemented carbide is used for a forging tool, cracks are likely to occur and the tool life is shortened. Further, if the lattice constant is less than 3.570, it means that the solid solution amount of W in Co is small, and the toughness tends to be insufficient.
[0008]
In addition, the method of manufacturing the cemented carbide according to the present invention includes a step of sintering and cooling a hard phase mainly composed of WC and a binding phase of an iron group metal containing Co, and a liquid phase appears after the cooling. And a step of heating to a temperature immediately below and immersing in a liquid and quenching.
[0009]
The temperature immediately below the appearance of the liquid phase is preferably about 1200 to 1300 ° C. The rapid cooling rate is desirably 1000 ° C./min or more. The liquid in which the sintered body is immersed during the rapid cooling is not particularly limited. For example, water and oil are mentioned. In addition, you may perform a HIP process as needed, after sintering a hard phase and a binder phase.
[0010]
In general, a cemented carbide product is manufactured by the following process.
Mixing of raw material powder → press → intermediate sintering → molding → sintering → (HIP) → inspection In other words, the mixed raw material is pressed into a block shape, for example, and sintered at about 700 ° C. Then, the intermediate sintered body is formed into a predetermined tool shape and sintered at about 1400 ° C. Further, in order to reduce the voids in the sintered body, HIP (for example, about 1340 ° C.) may be performed after the sintering.
[0011]
In the conventional techniques {circle around (1)} to {circle around (3)} described above, attention is paid mainly to the speed at the time of cooling from the sintering temperature. In the present invention, cooling from the sintering temperature is not particularly defined, and it is characterized in that it is once cooled and then heated again and then rapidly cooled.
[0012]
Such rapid cooling passes through the transformation temperature region (around 413 ° C) of the Co crystal structure in a very short time, and (1) solidifies without transformation from the fcc structure, which is a stable phase, to the hcp structure at high temperatures. (2) It is effective to solidify the W dissolved in Co immediately before quenching without being precipitated during cooling.
[0013]
The reason why the rapid cooling is started from a temperature immediately below the liquid phase appearance temperature is that it can dissolve a large amount of W in Co and is the temperature condition closest to the transformation temperature of fcc → hcp. In rapid cooling from a temperature in the vicinity of the sintering temperature of about 1400 ° C., the thermal shock is large and cracks may occur. The specific reheating temperature is preferably about 1200 to 1300 ° C, particularly about 1220 to 1280 ° C.
[0014]
Further, in the conventional techniques (1) to (3), the cooling from the sintering temperature is rapid cooling, and if the HIP is performed after the cooling, the rapid cooling effect is lost, so that it is difficult to perform the HIP following the sintering. However, in the present invention, since reheating is performed after reheating later, HIP is performed between sintering and reheating so that a denser cemented carbide can be obtained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
Commercially available WC powders (average particle size 6.5 μm and 3 μm) and Co powder (average particle size 1.2 μm) were blended in the composition shown in Table 1, wet-mixed with an attritor, and then dried powder was prepared. This powder was pressed at a pressure of 1 t / cm ² , sintered at 1380 ° C. to 1400 ° C. for 60 minutes, and then cooled to prepare a cemented carbide specimen. Some of these test pieces were further subjected to HIP treatment (1340 ° C., 1 t / cm ² , Ar gas atmosphere). The specimen cooled by sintering or HIP treatment is kept in an electric furnace preheated to 1250 ° C. for 15 minutes, then taken out of the furnace and immediately immersed in water (within 30 seconds) for rapid cooling treatment. Was given. In addition, the thing which did not perform the said rapid cooling process and the thing which performed the conventional gas cooling were made into the comparative example. Gas cooling is performed by introducing nitrogen gas, and the cooling rate is at most 500 ° C./min.
[0016]
The obtained test piece is analyzed and measured for Co crystal structure (I (Co · hcp) / I (Co · fcc)), lattice constant, impact strength, hardness, and bending strength by X-ray diffraction. It was. The results are shown in Table 2.
[0017]
[Table 1]

[0018]
[Table 2]

[0019]
As shown in Table 2, it can be seen that all the examples have the same hardness and bending strength as the comparative examples, but the impact strength is remarkably improved. This is presumably because the Co crystal structure of the binder phase is an fcc structure rich in ductility, and a large amount of W is dissolved in the Co, resulting in an improvement in the lattice constant and strengthening. The cooling rate in each example was estimated to be about 120 ° C./sec because it was at most about 10 seconds for cooling from 1250 ° C. to almost normal temperature.
[0020]
On the other hand, all the comparative examples are inferior in impact strength. That is, all of Comparative Examples 1 to 6 where the rapid cooling treatment was not performed have low impact strength and lattice constant. Further, in Comparative Examples 7 and 8 in which gas cooling was performed by introducing nitrogen gas, the impact strength comparable to that of the example was not obtained although cooling was performed at about 500 ° C./min.
[0021]
The same result was obtained even when the cooling medium for the rapid cooling was oil instead of water.
[0022]
(Test example)
A punch for hot forging with a diameter of 29-L137 mm was prepared using the powder of composition A in Table 1. The production conditions were the same as in Example 1, press pressure: 1 t / cm ² , sintering temperature: 1380 ° C. to 1400 ° C., sintering time: 60 minutes, and rapid cooling treatment was performed after HIP treatment. As a comparison, a punch without a rapid cooling treatment was also produced. After these punches are cut, they are used as forging tools under conditions where workpiece: SCM15, workpiece temperature: 1100 ° C, cycle time: 75 pcs / min, surface pressure: 65 kg / mm ² , and the number of shots until the end of life is measured. And observation of the tool surface. The results are shown in Table 3 and FIGS.
[0023]
[Table 3]

[0024]
The punch made of the cemented carbide of the present invention has a remarkably large number of shots up to its lifetime of 145,000, and the surface of the tool does not show thermal cracks as shown in FIG. That is, it can be seen that the cemented carbide tool of the present invention has a life of 2 to 10 times that of the conventional tool. On the other hand, punches that were not rapidly cooled became unusable after 35,000 shots, as shown in FIG.
[0025]
【The invention's effect】
As described above, the cemented carbide according to the present invention can achieve both impact strength and hardness, and is expected to be used for forging tools and the like that require high impact strength. The method of the present invention is an optimum method for producing the cemented carbide of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a striking surface after forging a punch using the cemented carbide of the present invention.
FIG. 2 is a schematic diagram showing a striking surface after forging a punch using a conventional cemented carbide.

Claims

In a cemented carbide in which a hard phase mainly composed of WC is dispersed in a binder phase of an iron group metal containing Co,
The crystal structure of Co satisfies the following formula :
Further, a cemented carbide characterized in that the lattice constant of Co is 3.570 or more .
0 ≦ I (Co · hcp) / I (Co · fcc) ≦ 0.1
Here, I (Co · hcp) is the X-ray diffraction intensity in the (101) plane of Co in the hcp structure, and I (Co · fcc) is the X-ray diffraction intensity in the (111) plane of Co in the fcc structure.

Sintering and cooling a hard phase mainly composed of WC and a binder phase of an iron group metal containing Co;
And heating the sintered body to a temperature immediately below the appearance of the liquid phase after the cooling , and immediately immersing the sintered body in the liquid and quenching.

3. The method for producing a cemented carbide according to claim 2 , wherein the temperature immediately under the appearance of the liquid phase is 1200 to 1300 ° C.

3. The method for producing a cemented carbide according to claim 2, wherein the rapid cooling rate is 1000 ° C./min or more.