JP4184147B2 - NITRIDED TOOL, DIE AND ITS MANUFACTURING METHOD - Google Patents
NITRIDED TOOL, DIE AND ITS MANUFACTURING METHOD Download PDFInfo
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- JP4184147B2 JP4184147B2 JP2003127663A JP2003127663A JP4184147B2 JP 4184147 B2 JP4184147 B2 JP 4184147B2 JP 2003127663 A JP2003127663 A JP 2003127663A JP 2003127663 A JP2003127663 A JP 2003127663A JP 4184147 B2 JP4184147 B2 JP 4184147B2
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- mold
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- decarburization
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Description
【0001】
【発明の属する技術分野】
本発明は、窒化処理を適用する冷間、熱間の鍛造型、プレス型などの金型全般、および工具や治具並びにそれらの製造方法に関するものである。
【0002】
【従来の技術】
近年、冷間、温熱間用途における部品のニアネットシェイプ化に伴う金型負荷の増大に対応すべく、各種表面処理が実施されている。広くは、金型の耐摩耗性、耐焼付き性、耐ヒートチェック性を付与するために、イオン法、ガス法および塩浴法などによる単一の窒化処理が適用されている。例えば特開平2−232353号公報(特許文献1)に開示されているように、窒化処理後、高周波焼入れで所要部位を再硬化させる方法や、特開平3−267358号公報(特許文献2)に開示されているように、機械加工仕上げのされた金型の成形に用いる面にプラズマを作用させることで低温で表面をクリーニングし活性化する工程と、窒素を含んだガスをプラズマ化しこれを用いて金型表面を改質し窒化処理する工程と、窒素を含んだガスの他に少なくとも1種以上の成膜用ガスをプラズマ化しこれを窒化処理した金型の表面に作用させ、窒化層よりも硬さの大きい硬質膜を形成する工程とからなる金型の表面処理方法が提案されている。
【0003】
さらに、特開平7−138733号公報(特許文献3)に開示されているように、窒化処理後の再加熱により、窒素化合物の消失および窒素の拡散・固溶を図り、深い硬化層を得る方法や特開2003−13199号公報(特許文献4)に開示されているように、鋼材表面に、一定温度で一定時間の窒化処理を行い、窒化層を形成させた後、さらに一定温度で一定時間の酸化処理を行い、鋼材表面の所定部の全域を均一な酸化皮膜により被覆し、鋼材に耐溶損性を付与した鋼材表面の改質方法が提案されている。
【0004】
【引用文献】
(1)(特開平2−232353号公報)
(2)特許文献2(特開平3−267358号公報)
(3)特許文献3(特開平7−138733号公報)
(4)特許文献4(特開2003−13199号公報)
【0005】
【発明が解決しようとする課題】
しかしながら、上述した特許文献1の方法は、硬度は得られるが、窒化層の脆化対策が不十分であり、また、特許文献2の方法では、用途と設備が限定され、Al窒化物で硬質膜形成がされる。また、特許文献3の方法では、窒化に伴う脆化物の消失が不十分である。さらに、特許文献4の方法では、窒化層の脆化対策は不十分で、金型の強度や靱性が低下するという問題がある。このように、従来の金型は焼入焼戻後に窒化処理を実施して、金型表面に硬化層を形成することで、金型寿命の向上に一定の改善効果を挙げている。しかしながら、窒化の際に窒化層中に生成・成長された脆弱な炭窒化物および表面付近で形成された化合物層により、早期割れに至るケースもあり、窒化による金型寿命の改善効果が充分に得られていないのが実状である。
【0006】
【課題を解決するための手段】
上述したような問題を解消するために、発明者らは、安定した金型寿命の向上を目標とし、従来の窒化処理による窒化層の脆さについて調査検討を行なった結果、本発明は脱炭処理の後に窒化処理を行なう方法(以下、脱炭窒化処理という)により窒化層の脆さを改善できることを見出した。具体的には、鋼材を金型に仕上加工し、焼入焼戻を行い、一定温度で一定温度の脱炭処理を行なった後に、窒化処理を行なう方法である。本発明では、窒化の前処理として高温酸化雰囲気による脱炭処理を行い、窒化層相当部位の炭素を低減させて金型表面に脱炭層を形成することで、窒化時に窒化層中での窒素の固溶・拡散が容易にして、より深くまで高硬度が得られるようになる。さらに、窒化層中において、脆弱な炭窒化物の生成、成長が抑制され、金型使用中の割れや欠けが抑制できる製造方法を提供するものである。
【0007】
その発明の要旨とするところは、
(1)工具の製造において、窒化処理前に900〜1100℃の酸化雰囲気で0.5〜2.0時間保持の脱炭処理を行った後窒化処理をすることを特徴とする工具の製造方法。
(2)金型の製造において、金型表面からの脱炭深さd=30〜500μmで900〜1100℃の酸化雰囲気で0.5〜2.0時間保持の脱炭処理を行った後窒化処理をすることを特徴とする金型の製造方法。
(3)前記(1)に記載の方法によって製造された窒化した工具。
(4)前記(2)に記載の方法によって製造された窒化した金型である。
【0008】
【発明の実施の形態】
以下、本発明について詳細に説明する。
上述したように、本発明は、窒化の前処理として高温酸化雰囲気による脱炭処理を行い、窒化層相当部位の炭素を低減させて金型表面に脱炭層を形成することで、窒化時に窒化層中での窒素の固溶・拡散が容易にして、より深くまで高硬度が得られるようになる。さらに、窒化層中において、脆弱な炭窒化物の生成、成長が抑制され、金型使用中の割れや欠けが抑制できる。従って、窒化処理を行なう前に、大気、酸素中で酸化処理を行い金型表面を脱炭処理しておくような、従来技術である酸窒化処理としての、酸素添加アンモニア雰囲気による窒素を活性化させ、窒化を迅速に行なうものとは方法が異なり、金型表面を脱炭させておくことで、窒化時の窒素の侵入・拡散が容易となり、より高硬度が得られるようになる。また、炭窒化物や化合物の生成・成長を抑制し、窒化層の脆化が抑えられるため、金型寿命の向上を大幅に向上させることがでる。
【0009】
なお、脱炭処理は焼入焼戻を兼ねて行なうことも可能であり、この際焼入時の酸化雰囲気を制御することで、所定の脱炭層の深さや硬さを得ることができる。また、本発明の対象とする鋼材は、JISで規定された炭素鋼、合金鋼、高速度鋼やその他改良鋼種に代表される、いわゆる一般的に工具鋼と呼ばれる鋼である。本発明において、金型表面からの脱炭深さd=30〜500μmで脱炭処理を行なう理由は、脱炭深さdが30μm未満では従来同様に、単一窒化と同じ程度にしか硬化しない。また、500μmを超えると脱炭し過ぎて、硬さ、疲労限が共に低下することから、その範囲を30〜500μmとした。好ましくは、50〜300μmとする。
【0010】
【実施例】
以下、本発明について実施例によって具体的に説明する。
表1に示す鋼を100kg真空誘導溶解炉を用いて溶解し、鋼塊に鋳造し、1000〜1150℃に加熱し、φ30mmに圧鍛した鋼材を供試材とした。この試験片を小野式回転曲げ疲労試験片(JIS Z2274 1−8試験片)を作製し、1030℃、空冷による焼入れ、530℃、空冷×2回の焼戻し、引続いて900〜1100℃の酸化雰囲気で0.5〜2.0時間保持の脱炭処理を行い、その後窒化処理を行なった。
【0011】
【表1】
【0012】
図1は、脱炭窒化と従来窒化の硬さを比較した図である。この図1は、表1に示す鋼種Aを焼入焼戻し、脱炭した場合、および従来の単一窒化処理と、本発明の脱炭窒化処理を行なった場合の表面付近の硬度分布を示したものである。すなわち、A鋼について、脱炭させた後に、従来の単一窒化処理、および本発明の脱炭窒化処理を行なった硬度比較では、本発明に係る脱炭窒化処理が、より硬く、より深い窒化層が得られることが判る。この時、脱炭深さと硬度は、5%HCl+アルコールで腐食したミクロ組織の観察およびビッカース硬度計により測定した。
【0013】
B鋼、C鋼についても、同様の処理を行い調査した結果および疲労試験の結果を、A鋼と合わせて表2に示す。疲労限は、小野式回転曲げ試験機により、107 サイクル付近で疲労破壊に至る限界荷重を測定したものである。本発明の脱炭窒化処理によって、窒化層は、より硬く、深くなる傾向がいずれの鋼種でも見られ、疲労限も改善された。
【0014】
【表2】
【0015】
【発明の効果】
以上述べたように、本発明による窒化処理の前に、脱炭処理を行なうことで、窒化層をより硬く、深くすることができ、同時に窒化層中の脆弱な炭窒化物の生成が抑制されるため、金型寿命が大幅に改善させる極めて優れた効果を奏するものである。
【図面の簡単な説明】
【図1】脱炭窒化と従来窒化の硬さを比較した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to general dies such as cold and hot forging dies and press dies to which nitriding treatment is applied, tools and jigs, and methods for producing them.
[0002]
[Prior art]
In recent years, various surface treatments have been performed in order to cope with an increase in mold load accompanying the near net shaping of parts in cold and warm applications. In general, a single nitriding treatment by an ion method, a gas method, a salt bath method, or the like is applied to impart wear resistance, seizure resistance, and heat check resistance of a mold. For example, as disclosed in JP-A-2-232353 (Patent Document 1), a method of re-curing a required part by induction hardening after nitriding treatment, or JP-A-3-267358 (Patent Document 2) As disclosed, a plasma is applied to the surface used to mold a machine-finished mold to clean and activate the surface at a low temperature, and a gas containing nitrogen is converted into plasma and used. A step of modifying and nitriding the mold surface, and plasma forming at least one kind of film forming gas in addition to the nitrogen-containing gas, and causing this to act on the surface of the nitrided mold, In addition, a surface treatment method for a mold including a step of forming a hard film having a high hardness has been proposed.
[0003]
Further, as disclosed in JP-A-7-138733 (Patent Document 3), a method of obtaining a deep hardened layer by eliminating nitrogen compounds and diffusing / solid-dissolving nitrogen by reheating after nitriding treatment As disclosed in Japanese Patent Laid-Open No. 2003-13199 (Patent Document 4), a steel material surface is subjected to nitriding treatment at a constant temperature for a fixed time to form a nitride layer, and then at a fixed temperature for a fixed time. There has been proposed a method for reforming the surface of a steel material in which the entire surface of a predetermined portion of the surface of the steel material is covered with a uniform oxide film, and the steel material is imparted with a corrosion resistance.
[0004]
[Cited document]
(1) (JP-A-2-232353)
(2) Patent Document 2 (Japanese Patent Laid-Open No. 3-267358)
(3) Patent Document 3 (Japanese Patent Laid-Open No. 7-138733)
(4) Patent Document 4 (Japanese Patent Laid-Open No. 2003-13199)
[0005]
[Problems to be solved by the invention]
However, although the method of Patent Document 1 described above can obtain hardness, the countermeasure against embrittlement of the nitride layer is insufficient, and the method of Patent Document 2 has limited applications and facilities, and is hard with Al nitride. A film is formed. Moreover, in the method of Patent Document 3, the disappearance of the embrittlement due to nitriding is insufficient. Furthermore, the method of Patent Document 4 has a problem that the countermeasure for embrittlement of the nitride layer is insufficient and the strength and toughness of the mold are lowered. As described above, the conventional mold performs a nitriding treatment after quenching and tempering, and forms a hardened layer on the mold surface, thereby providing a certain improvement effect in improving the mold life. However, the brittle carbonitride produced and grown in the nitride layer during nitriding and the compound layer formed in the vicinity of the surface may lead to early cracking. The actual situation is not obtained.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have conducted a study on the brittleness of the nitrided layer by the conventional nitriding treatment with the goal of improving the stable mold life. It has been found that the brittleness of the nitrided layer can be improved by a method of performing nitriding after the treatment (hereinafter referred to as decarbonitriding). Specifically, the steel material is finished into a mold, quenched and tempered, decarburized at a constant temperature, and then subjected to nitriding. In the present invention, a decarburization process in a high-temperature oxidizing atmosphere is performed as a pretreatment for nitriding, and the carbon corresponding to the nitrided layer is reduced to form a decarburized layer on the mold surface. Solid solution / diffusion is facilitated and high hardness can be obtained deeper. Furthermore, the present invention provides a production method in which the formation and growth of fragile carbonitrides in the nitride layer is suppressed, and cracks and chips during use of the mold can be suppressed.
[0007]
The gist of the invention is that
(1) In the manufacture of a tool, a nitriding treatment is performed after performing a decarburization treatment that is held for 0.5 to 2.0 hours in an oxidizing atmosphere at 900 to 1100 ° C. before the nitriding treatment. .
(2) In the manufacture of a mold, nitriding was performed after decarburization treatment was performed for 0.5 to 2.0 hours in an oxidizing atmosphere of 900 to 1100 ° C. at a decarburization depth d = 30 to 500 μm from the mold surface. A manufacturing method of a metal mold characterized by performing processing.
(3) tool was nitrided produced by the method according to (1).
(4) A nitrided mold manufactured by the method described in (2) above.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
As described above, the present invention performs a decarburization process in a high-temperature oxidizing atmosphere as a pretreatment for nitriding, reduces the carbon corresponding to the nitrided layer, and forms a decarburized layer on the mold surface, so that a nitrided layer is formed during nitriding. The solid solution / diffusion of nitrogen therein is facilitated, and high hardness can be obtained deeper. Furthermore, the formation and growth of fragile carbonitrides are suppressed in the nitride layer, and cracks and chips during use of the mold can be suppressed. Therefore, prior to nitriding treatment, activation of nitrogen in oxygen-added ammonia atmosphere as a conventional oxynitriding treatment, in which the mold surface is decarburized by oxidizing treatment in air and oxygen However, the method is different from that in which nitridation is performed rapidly, and by decarburizing the mold surface, nitrogen intrusion / diffusion during nitridation is facilitated and higher hardness can be obtained. Further, since the formation / growth of carbonitrides and compounds is suppressed and embrittlement of the nitrided layer is suppressed, the improvement of the mold life can be greatly improved.
[0009]
The decarburization treatment can also be performed as quenching and tempering. At this time, the depth and hardness of a predetermined decarburized layer can be obtained by controlling the oxidizing atmosphere during quenching. In addition, the steel material that is the subject of the present invention is a steel that is generally called a tool steel, typified by carbon steel, alloy steel, high-speed steel, and other improved steel types defined by JIS. In the present invention, the reason for performing the decarburization treatment at the decarburization depth d = 30 to 500 μm from the mold surface is that when the decarburization depth d is less than 30 μm, it is hardened only to the same extent as in the conventional nitriding. . Moreover, since it will decarburize too much when it exceeds 500 micrometers, both hardness and a fatigue limit will fall, The range was 30-500 micrometers. Preferably, it is 50 to 300 μm.
[0010]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
Steels shown in Table 1 were melted using a 100 kg vacuum induction melting furnace, cast into steel ingots, heated to 1000 to 1150 ° C., and forged to φ30 mm as test materials. This test piece was prepared as an Ono-type rotating bending fatigue test piece (JIS Z2274 1-8 test piece), quenched at 1030 ° C., air-cooled, 530 ° C., air-cooled × twice, and subsequently oxidized at 900-1100 ° C. Decarburization treatment was performed for 0.5 to 2.0 hours in an atmosphere, and then nitriding treatment was performed.
[0011]
[Table 1]
[0012]
FIG. 1 is a diagram comparing the hardness of decarburizing and conventional nitriding. FIG. 1 shows the hardness distribution near the surface when the steel type A shown in Table 1 is quenched and tempered and decarburized, and when the conventional single nitriding treatment and the decarburizing and nitriding treatment of the present invention are performed. Is. That is, for steel A, after decarburization, in the hardness comparison in which the conventional single nitriding treatment and the decarburizing treatment of the present invention were performed, the decarburizing treatment according to the present invention was harder and deeper. It can be seen that a layer is obtained. At this time, the decarburization depth and hardness were measured by observation of a microstructure corroded with 5% HCl + alcohol and a Vickers hardness meter.
[0013]
For Steel B and Steel C, Table 2 shows the results of the same treatment and investigation and the results of fatigue tests together with Steel A. The fatigue limit is a value obtained by measuring a limit load that leads to fatigue failure in the vicinity of 10 7 cycles by an Ono rotary bending tester. By the decarburization and nitriding treatment of the present invention, the tendency of the nitrided layer to become harder and deeper was observed in any steel type, and the fatigue limit was improved.
[0014]
[Table 2]
[0015]
【The invention's effect】
As described above, by performing the decarburization treatment before the nitriding treatment according to the present invention, the nitrided layer can be made harder and deeper, and at the same time, the formation of fragile carbonitride in the nitrided layer is suppressed. Therefore, an extremely excellent effect of greatly improving the mold life is achieved.
[Brief description of the drawings]
FIG. 1 is a diagram comparing the hardness of decarbonizing and conventional nitriding.
Claims (4)
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JP7495099B2 (en) | 2020-03-02 | 2024-06-04 | エジソンハード株式会社 | Heat treatment method, mold manufacturing method |
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