JP6310495B2 - Tool manufacturing method - Google Patents

Tool manufacturing method Download PDF

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JP6310495B2
JP6310495B2 JP2016082966A JP2016082966A JP6310495B2 JP 6310495 B2 JP6310495 B2 JP 6310495B2 JP 2016082966 A JP2016082966 A JP 2016082966A JP 2016082966 A JP2016082966 A JP 2016082966A JP 6310495 B2 JP6310495 B2 JP 6310495B2
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layer
tool
cooling hole
treatment
base material
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JP2016204754A (en
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拓哉 村▲崎▼
拓哉 村▲崎▼
豊 宮嶋
豊 宮嶋
英資 白石
英資 白石
雅稔 鳴海
雅稔 鳴海
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Hitachi Metals Ltd
Hitachi Metals Tool Steel Ltd
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Hitachi Metals Ltd
Hitachi Metals Tool Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising
    • C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
    • C23C8/18—Oxidising of ferrous surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/20—Accessories: Details
    • B22D17/22—Dies; Die plates; Die supports; Cooling equipment for dies; Accessories for loosening and ejecting castings from dies
    • B22D17/2218—Cooling or heating equipment for dies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
    • B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
    • B23P15/24—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass dies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C33/00—Moulds or cores; Details thereof or accessories therefor
    • B29C33/02—Moulds or cores; Details thereof or accessories therefor with incorporated heating or cooling means
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/04—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)
  • Hard Magnetic Materials (AREA)

Description

本発明は、作業面と、冷却水を通すための冷却孔とを有する工具、およびその製造方法に関するものである。   The present invention relates to a tool having a work surface and a cooling hole for passing cooling water, and a method for manufacturing the tool.

一般的に、各種の工具は、それが加工や成形、搬送等の対象とする素材と接する「作業面」を有している。そして、これら工具のうち、使用中に高温になるものは、その使用中において作業面や工具の全体が冷却される。
作業面を有する工具として、例えば、金型がある。ダイカスト用やプラスチック成形用の金型は、溶融した金属やプラスチック等を成形するための作業面（すなわち、成形後の製品形状に応じた型彫面）を有している。ホットプレス用の金型は、加熱した鋼板をプレス成形して、その成形した鋼板を冷却するための作業面を有している。また、金型以外の工具として、例えば、スリーブ、ブッシュ、プランジャーチップ、鋳抜きピンといった鋳造用工具も、溶融した金属を押し出したり、鋳造品に穴を成形したりするための作業面を有している。このような工具は、使用中において、作業面や工具の全体が冷却される。そして、この冷却のために、通常、工具の内部には、冷却水を通すための冷却孔が設けられており、この冷却孔に冷却水を通すことで、使用中の工具を冷却している。 In general, various tools have a “work surface” in contact with a material to be processed, molded, conveyed, or the like. Of these tools, those that become hot during use cool down the work surface and the entire tool during use.
An example of a tool having a work surface is a mold. Molds for die casting and plastic molding have a work surface for molding molten metal, plastic, or the like (that is, a mold engraving surface corresponding to the product shape after molding). A mold for hot pressing has a work surface for press-forming a heated steel sheet and cooling the formed steel sheet. In addition, as tools other than molds, for example, casting tools such as sleeves, bushes, plunger tips, and core pins have work surfaces for extruding molten metal and forming holes in cast products. doing. In such a tool, the work surface and the entire tool are cooled during use. For this cooling, a cooling hole for passing cooling water is usually provided inside the tool, and the tool in use is cooled by passing cooling water through the cooling hole. .

上記の冷却孔に冷却水を通しているとき、この冷却水と接する冷却孔の表面は、冷却水との接触によって腐食する（錆びる）ことが懸念される。そして、冷却孔の表面の腐食が進むと、それによって発生した錆が冷却孔に詰まって、冷却水の流量が低下する。場合によっては、応力腐食割れ（Ｓｔｒｅｓｓ Ｃｏｒｒｏｓｉｏｎ Ｃｒａｃｋｉｎｇ；ＳＣＣ）が生じて、冷却孔の表面から工具の割れに至る場合もある。この対策として、冷却孔の表面に窒化処理を行う手法が提案されている（特許文献１）。特許文献１によれば、冷却孔の表面に窒化層を形成することで、冷却孔の表面に圧縮残留応力を付与し、応力腐食割れを起点とする割れ（亀裂）を防ぐことができる。   When cooling water is passed through the cooling holes, there is a concern that the surfaces of the cooling holes in contact with the cooling water are corroded (rusted) by contact with the cooling water. And if the surface corrosion of a cooling hole progresses, the rust produced | generated by that will clog a cooling hole, and the flow volume of cooling water will fall. In some cases, stress corrosion cracking (SCC) may occur, leading to tool cracking from the surface of the cooling hole. As a countermeasure against this, a method of performing nitriding treatment on the surface of the cooling hole has been proposed (Patent Document 1). According to Patent Document 1, by forming a nitride layer on the surface of the cooling hole, compressive residual stress can be applied to the surface of the cooling hole, and cracking (cracking) starting from stress corrosion cracking can be prevented.

特開２０１３−１５９８３１号公報JP2013-159831A

冷却孔の表面に窒化処理を行う手法は、冷却孔の表面に発生した応力腐食割れを起点とする亀裂の発生の抑制に一定の効果を有するようである。しかし、この亀裂の発生を抑制する前には、その発生に繋がる「腐食自体を抑える効果（つまり、耐錆性）」について、窒化層の場合、改善の余地があった。耐錆性に劣り、冷却孔の表面に顕著な錆が発生すると、その錆の発生による冷却孔の詰まりも心配される。また、窒化層の場合、冷却孔の表面に、一旦、応力腐食割れが発生すると、それが亀裂に進展するときの「亀裂進展速度」が大きく、総合的な「耐食性」の向上に改善の余地があった。
本発明の目的は、冷却孔の表面の耐食性に優れた工具およびその製造方法を提供することである。 The technique of performing nitriding treatment on the surface of the cooling hole seems to have a certain effect in suppressing the occurrence of cracks starting from stress corrosion cracks generated on the surface of the cooling hole. However, before suppressing the occurrence of cracks, there was room for improvement in the case of a nitrided layer with respect to the “effect of suppressing corrosion itself (that is, rust resistance)” leading to the occurrence of cracks. If the rust resistance is inferior and remarkable rust is generated on the surface of the cooling hole, the cooling hole may be clogged due to the rust. In the case of a nitrided layer, once a stress corrosion crack occurs on the surface of the cooling hole, the “crack growth rate” is large when it develops into a crack, and there is room for improvement in improving the overall “corrosion resistance”. was there.
The objective of this invention is providing the tool excellent in the corrosion resistance of the surface of a cooling hole, and its manufacturing method.

本発明は、作業面と、冷却水を通すための冷却孔とを有する工具であって、この冷却孔の冷却水と接する表面にマグネタイト層を有する工具である。
このとき、冷却孔の冷却水と接する表面が有する上記のマグネタイト層が、工具の母材と接していることが好ましい。また、作業面には、工具の母材よりも硬さが高い硬質層を有することが好ましい。 The present invention is a tool having a work surface and a cooling hole for allowing cooling water to pass therethrough, and a tool having a magnetite layer on the surface of the cooling hole in contact with the cooling water.
At this time, it is preferable that the magnetite layer on the surface of the cooling hole in contact with the cooling water is in contact with the base material of the tool. Moreover, it is preferable that the work surface has a hard layer whose hardness is higher than that of the base material of the tool.

そして、本発明は、作業面と、冷却水を通すための冷却孔とを有する工具の製造方法であって、冷却孔が形成された工具を用意し、４８０〜６００℃の水蒸気に曝すことによる酸化処理を行って、その冷却孔の冷却水と接する表面にマグネタイト層を形成する工具の製造方法である。
このとき、冷却孔の冷却水と接する表面にマグネタイト層を形成する上記の酸化処理を、工具の母材の直上に行うことが好ましい。また、上記の酸化処理の後に、作業面に表面硬化処理を行って、この作業面に、工具の母材よりも硬さが高い硬質層を形成することが好ましい。 And this invention is a manufacturing method of the tool which has a work surface and the cooling hole for letting a cooling water pass, Comprising: By preparing the tool in which the cooling hole was formed, it exposes to 480-600 degreeC water vapor | steam. It is a manufacturing method of the tool which performs an oxidation process and forms a magnetite layer in the surface which contacts the cooling water of the cooling hole.
At this time, it is preferable that the oxidation treatment for forming a magnetite layer on the surface of the cooling hole in contact with the cooling water is performed directly on the base material of the tool. Moreover, it is preferable to perform a surface hardening process on the work surface after the above oxidation treatment to form a hard layer having a higher hardness than the base material of the tool on the work surface.

本発明によれば、工具が有する冷却孔について、その表面の耐食性を向上することができる。   According to the present invention, the corrosion resistance of the surface of the cooling hole of the tool can be improved.

本発明例の試料について、その表面処理層の断面の一例を示す光学顕微鏡写真である。It is an optical microscope photograph which shows an example of the cross section of the surface treatment layer about the sample of this invention example. 本発明例の試料について、その表面処理層の断面の一例を示す光学顕微鏡写真である。It is an optical microscope photograph which shows an example of the cross section of the surface treatment layer about the sample of this invention example. 比較例の試料について、その表面処理層の断面の一例を示す光学顕微鏡写真である。It is an optical microscope photograph which shows an example of the cross section of the surface treatment layer about the sample of a comparative example. 本発明例の試料について、その表面処理層の断面の一例を示す走査型電子顕微鏡写真である。It is a scanning electron micrograph which shows an example of the cross section of the surface treatment layer about the sample of the example of the present invention. 図４の断面について、エネルギー分散型Ｘ線分析（ＥＤＸ）による元素分析の結果を示す図である。It is a figure which shows the result of the elemental analysis by energy dispersive X-ray analysis (EDX) about the cross section of FIG. 本発明例の試料について、その表面処理層をグロー放電発光分光分析（ＧＤＳ）したときの成分プロファイルの一例を示す図である。It is a figure which shows an example of a component profile when the surface treatment layer is subjected to glow discharge emission spectrometry (GDS) for the sample of the present invention. 本発明例および比較例の試料について、その表面の腐食状況を示す図面代用写真である。It is a drawing substitute photograph which shows the corrosion condition of the surface about the sample of this invention example and a comparative example. 本発明例の試料について、その表面にさらに窒化処理を行ったときの、表面処理層の断面の一例を示す光学顕微鏡写真である。It is an optical microscope photograph which shows an example of the cross section of a surface treatment layer when the surface of the sample of this invention example is further nitrided. 実施例３で行った応力腐食割れ試験の概況を示す図である。It is a figure which shows the general condition of the stress corrosion cracking test done in Example 3. 図９の応力腐食割れ試験を行ったときの、本発明例および比較例の試料における亀裂発生サイクル数を示す図である。It is a figure which shows the crack generation cycle number in the sample of the example of this invention and a comparative example when the stress corrosion cracking test of FIG. 9 is done.

（１）本発明は、作業面と、冷却水を通すための冷却孔とを有する工具である。
各種の工具は、それが加工や成形、搬送等の対象とする素材と接する「作業面」を有している。そして、これら工具において、使用中に高温になるものは、例えば、その内部に、作業面や工具の全体を冷却するための「冷却水を通すための冷却孔」を有している。このような工具として、例えば、ダイカスト用やプラスチック成形用、ホットプレス用の金型がある。また、スリーブ、ブッシュ、プランジャーチップ、鋳抜きピンといった鋳造用工具がある。そして、上記の冷却孔に通される冷却水の種類として、例えば、水そのものの他に、水に防錆剤が含まれたアルカリ性冷却水等がある。 (1) The present invention is a tool having a work surface and a cooling hole for passing cooling water.
Each type of tool has a “work surface” that comes into contact with a material to be processed, molded, conveyed, or the like. Of these tools, those that become hot during use have, for example, “cooling holes for passing cooling water” for cooling the work surface and the entire tool. Examples of such a tool include a die for die casting, plastic molding, and hot pressing. Further, there are casting tools such as a sleeve, a bush, a plunger tip, and a core pin. And as a kind of cooling water passed through said cooling hole, there exist alkaline cooling water etc. in which the rust preventive agent was contained in water other than water itself, for example.

（２）本発明は、上記した冷却孔の、冷却水と接する表面にマグネタイト層を有する工具である。
工具は、各種の金属材料を母材に用いて製造されている。そして、この金属材料の中でも、工具鋼は、機械的特性に優れており、工具の母材に多用されている。工具鋼には、例えば「合金工具鋼鋼材」がある。合金工具鋼鋼材とは、炭素の他に、クロム、モリブデン、バナジウム等の合金元素を含む工具鋼であり、例えば、ＪＩＳ−Ｇ−４４０４に規格されている、ＳＫＤ６１等のような工具鋼である。そして、このような金属材料を母材に用いてなる工具が、上記した（１）の「冷却水を通すための冷却孔」を有していると、その使用中において、冷却水と接している冷却孔の表面が腐食することが懸念される。
この冷却孔の表面が腐食するという課題に対し、冷却孔の表面が「金属材料まま」の工具の場合、その冷却水と接している表面には著しい錆が発生した。そして、この冷却孔の表面に「窒化層」を有していた従来の工具であっても、錆の発生を十分に抑制する点で改善の余地があった。 (2) The present invention is a tool having a magnetite layer on the surface of the cooling hole that comes into contact with the cooling water.
The tool is manufactured using various metal materials as a base material. Among these metal materials, tool steel is excellent in mechanical properties and is frequently used as a base material for tools. An example of tool steel is “alloy tool steel”. The alloy tool steel material is a tool steel containing alloy elements such as chromium, molybdenum, vanadium in addition to carbon, for example, a tool steel such as SKD61 standardized in JIS-G-4404. . And if the tool using such a metal material as a base material has the “cooling hole for passing cooling water” described in (1) above, it will come into contact with the cooling water during its use. There is a concern that the surface of the cooling holes that are present will corrode.
In contrast to the problem that the surface of the cooling hole corrodes, in the case of a tool in which the surface of the cooling hole is “as metal”, significant rust was generated on the surface in contact with the cooling water. Even in the conventional tool having a “nitriding layer” on the surface of the cooling hole, there is room for improvement in terms of sufficiently suppressing the generation of rust.

そして、工具の総合的な「耐食性」を向上させるという面では、上記した冷却孔の表面の腐食自体を抑制する「耐錆性」に加えて、冷却孔の表面に発生した応力腐食割れの亀裂進展速度を小さく抑える「耐亀裂進展性」を向上させることが重要である。そして、冷却孔の表面に「窒化層」を有した従来の工具の場合、冷却孔の表面が「金属材料まま」の工具の場合に比べて、上記の亀裂進展速度が大きくなることを知見した。また、冷却孔の表面が「金属材料まま」の工具であっても、作業面に窒化処理を行ったものは、冷却孔の表面における上記の亀裂進展速度が大きくなることを知見した。
この亀裂進展速度が大きくなる原因は、窒化処理等によって、冷却孔の表面硬さが上昇することにあると思われる。これについては、冷却孔の表面に窒化処理を行わない工具であっても、作業面に窒化処理を行ったものは、同様と思われる。つまり、冷却孔の開口位置は、例えば、工具の作業面と対抗する面（工具の側面や裏面）にあるところ、工具の作業面に窒化処理を行えば、そのときの反応ガスが、冷却孔の開口位置を通じて、その表面にも侵入し、冷却孔の表面も少なからず硬化する。そして、冷却孔の表面に窒化処理を行ったときと同様に、冷却孔の表面硬さが少なからず上昇して、冷却孔の表面における亀裂進展速度が大きくなる。 And in terms of improving the overall "corrosion resistance" of the tool, in addition to the above-mentioned "rust resistance" that suppresses the corrosion of the surface of the cooling hole, cracks of stress corrosion cracks that have occurred on the surface of the cooling hole It is important to improve the “crack resistance” that keeps the growth rate small. And in the case of a conventional tool having a “nitride layer” on the surface of the cooling hole, it was found that the crack growth rate is higher than that of a tool in which the surface of the cooling hole is “as metal”. . Further, it was found that even when the surface of the cooling hole is a “metal material as it is” tool, when the work surface is subjected to nitriding treatment, the above-mentioned crack growth rate on the surface of the cooling hole is increased.
The cause of the increase in the crack growth rate seems to be that the surface hardness of the cooling hole is increased by nitriding treatment or the like. About this, even if it is a tool which does not perform nitriding on the surface of a cooling hole, what performed nitriding on the work surface seems to be the same. That is, the opening position of the cooling hole is, for example, on a surface (a side surface or the back surface of the tool) that opposes the work surface of the tool, and if the nitriding process is performed on the work surface of the tool, the reaction gas at that time The surface of the cooling hole penetrates through the opening position, and the surface of the cooling hole is hardened. As in the case where nitriding is performed on the surface of the cooling hole, the surface hardness of the cooling hole is increased to some extent, and the crack growth rate on the surface of the cooling hole is increased.

そこで、本発明では、冷却孔の表面の腐食を抑制すると同時に、冷却孔の表面に発生した応力腐食割れの進展も抑制できる手法を検討した。その結果、冷却水と接する冷却孔の表面に「マグネタイト層」を有することが効果的であることを突きとめた。マグネタイトとは、Ｆｅ３Ｏ４の化学式を有する、スピネル型の鉄酸化物である。そして、緻密な構造を有し、冷却水に対する耐錆性が高い物質である。このマグネタイト層を、冷却水と接する、工具の冷却孔の表面に有することで、冷却孔の表面の耐錆性が向上して、冷却孔の表面の腐食を効果的に抑制することができる。
そして、一般的な窒化処理によって工具鋼に形成された窒化層の硬さが、約１０００ＨＶであるのに対して、工具の表面に形成された上記のマグネタイト層の硬さは、１０００ＨＶ未満であり（例えば、約６００ＨＶ程度であり）、窒化層の硬さよりも低い。これによって、冷却孔の表面に発生した応力腐食割れの亀裂進展速度も小さく抑えることができ、耐亀裂進展性を向上することができる。 In view of this, in the present invention, a method that can suppress the corrosion of the surface of the cooling hole and at the same time suppress the progress of stress corrosion cracks generated on the surface of the cooling hole has been studied. As a result, it has been found that it is effective to have a “magnetite layer” on the surface of the cooling hole in contact with the cooling water. Magnetite is a spinel-type iron oxide having the chemical formula of Fe 3 O 4 . And it is a substance having a dense structure and high rust resistance against cooling water. By having this magnetite layer on the surface of the cooling hole of the tool in contact with the cooling water, the rust resistance of the surface of the cooling hole is improved, and corrosion of the surface of the cooling hole can be effectively suppressed.
The hardness of the nitride layer formed on the tool steel by a general nitriding treatment is about 1000 HV, whereas the hardness of the magnetite layer formed on the surface of the tool is less than 1000 HV. (For example, about 600 HV), which is lower than the hardness of the nitride layer. Thus, the crack propagation rate of stress corrosion cracking occurring on the surface of the cooling hole can also be reduced, it is possible to improve the resistance to crack growth resistance.

上記のマグネタイト層の厚さは、本発明の耐食性の向上効果を十分に得る上で、１μｍ以上とすることが好ましい。なお、厚さの上限については、特段の限定を要しない。但し、後述する酸化処理の際の処理温度や処理時間に照らし合わせて、５μｍ程度が上限になり得る。
上記のマグネタイト層は、工具が有する冷却孔の表面に、４８０〜６００℃の水蒸気に曝すことによる酸化処理を行うことによって、形成することが可能である。また、処理時間は、１〜３時間程度とすることが好ましい。これら酸化処理は、炉を用いた通常の方法（例えば、「酸化処理」として知られている公知の方法）によって行うことができる。この酸化処理として、例えば、ホモ処理（ｈｏｍｏｔｒｅａｔｍｅｎｔ）がある。 The thickness of the magnetite layer is preferably 1 μm or more in order to sufficiently obtain the effect of improving the corrosion resistance of the present invention. In addition, about the upper limit of thickness, the limitation in particular is not required. However, the upper limit may be about 5 μm in light of the processing temperature and processing time in the oxidation processing described later.
The magnetite layer can be formed by subjecting the surface of the cooling hole of the tool to oxidation treatment by exposure to water vapor at 480 to 600 ° C. The treatment time is preferably about 1 to 3 hours. These oxidation treatments can be performed by an ordinary method using a furnace (for example, a known method known as “oxidation treatment”). As this oxidation treatment, for example, there is a homotreatment.

（３）好ましくは、本発明は、冷却孔の冷却水と接する表面が有する上記のマグネタイト層が、工具の母材と接している工具である。
上記の（２）において、冷却孔の表面にマグネタイト層を形成するとき、その形成前の母材の表面に、上記のマグネタイト層とは別の、「その他の表面処理層（表面被覆層を含む）」が形成されていると、マグネタイト層の有する耐食性の向上効果が少なからず低下するかも知れない。そして、上記したその他の表面処理層が、例えば、窒化層といったような、工具の母材よりも硬さが高い硬質層であると、その上にマグネタイト層が形成されていても、冷却孔の表面における亀裂進展速度が大きくなり得る。よって、本発明に係るマグネタイト層は、その工具の母材との間にその他の表面処理層を介さずに、母材と接するように、母材の直上に形成することが好ましい。これによって、本発明の優れた耐食性を、高いレベルで維持することができる。 (3) Preferably, this invention is a tool in which said magnetite layer which the surface which contact | connects the cooling water of a cooling hole has is in contact with the base material of a tool.
In the above (2), when the magnetite layer is formed on the surface of the cooling hole, “other surface treatment layer (including the surface coating layer) other than the magnetite layer is formed on the surface of the base material before the formation. ) "May decrease the effect of improving the corrosion resistance of the magnetite layer. If the other surface treatment layer described above is a hard layer having a higher hardness than the base material of the tool, such as a nitride layer, for example, even if a magnetite layer is formed thereon, the cooling hole The crack growth rate at the surface can be large. Therefore, the magnetite layer according to the present invention is preferably formed immediately above the base material so as to be in contact with the base material without interposing any other surface treatment layer between the base material of the tool. As a result, the excellent corrosion resistance of the present invention can be maintained at a high level.

（４）好ましくは、本発明は、作業面に、工具の母材よりも硬さが高い硬質層を有する工具である。
本発明の工具においては、その冷却孔の冷却水と接する表面には上記のマグネタイト層を形成した上で、作業面には、上記のマグネタイト層とは別の、その他の表面処理層（表面被覆層を含む）を形成することができる。これにより、本発明の工具では、その冷却孔の表面でマグネタイト層の形成による耐食性の向上効果を阻害することなく、作業面にその他の特性を付与することができる。 (4) Preferably, this invention is a tool which has a hard layer whose hardness is higher than the base material of a tool on a work surface.
In the tool of the present invention, the magnetite layer is formed on the surface of the cooling hole in contact with the cooling water, and another surface treatment layer (surface coating layer) other than the magnetite layer is formed on the work surface. Layer). Thereby, in the tool of this invention, other characteristics can be provided to a work surface, without inhibiting the corrosion-resistant improvement effect by formation of a magnetite layer in the surface of the cooling hole.

そして、上記したその他の表面処理層において、一般的に、工具の作業面には、各種の硬質層が形成される場合が多い。硬質層とは、工具の母材よりも硬さが高い層のことであり、例えば、窒化処理や炭化処理といった表面硬化処理によって形成される窒化層や炭化層が挙げられる。また、物理蒸着法や化学蒸着法といった被覆処理による表面硬化処理で形成される窒化皮膜や炭化皮膜、更には、ＤＬＣ皮膜等の硬質皮膜が挙げられる。そして、本発明の工具において、その作業面が上記の硬質層を有することで、冷却孔の表面では優れた耐食性を維持して、作業面には優れた強度を付与することができる。また、これらの硬質層は、使用中の工具において、その作業面が接する素材との反応の抑制にも効果的である。   In the other surface treatment layers described above, various hard layers are often formed on the work surface of the tool. The hard layer is a layer having a hardness higher than that of the base material of the tool, and examples thereof include a nitride layer and a carbonized layer formed by a surface hardening process such as a nitriding process and a carbonizing process. In addition, a nitride film or a carbonized film formed by a surface hardening process such as a physical vapor deposition method or a chemical vapor deposition method, and a hard film such as a DLC film may be used. And in the tool of this invention, the work surface has said hard layer, Therefore The outstanding corrosion resistance can be maintained on the surface of a cooling hole, and the outstanding intensity | strength can be provided to a work surface. In addition, these hard layers are also effective in suppressing reaction with a material that is in contact with the work surface of a tool in use.

上記の表面硬化処理について、各種の処理条件には、従来のものを適用することができる。そして、窒化処理を行うのであれば、例えば、ガス軟窒化処理の場合、窒素ガス中にアンモニアガスを３０〜６０体積％程度添加して、５００〜６００℃の温度域で１時間以上保持する条件を適用できる。窒化処理を行うと、まず、母材上に窒素拡散層が形成される。そして、窒化処理を続けることで、窒素拡散層の構造が窒素化合物層の構造に移行する。なお、窒素化合物層は「白層」と呼ばれる脆化層として扱われ、窒化処理後に除去されるのが一般的である。   About said surface hardening process, a conventional thing can be applied to various process conditions. If nitriding treatment is performed, for example, in the case of gas soft nitriding treatment, ammonia gas is added in an amount of about 30 to 60% by volume in nitrogen gas, and the condition is maintained at 500 to 600 ° C. for 1 hour or more Can be applied. When nitriding is performed, first, a nitrogen diffusion layer is formed on the base material. Then, by continuing the nitriding treatment, the structure of the nitrogen diffusion layer shifts to the structure of the nitrogen compound layer. The nitrogen compound layer is handled as an embrittlement layer called “white layer” and is generally removed after nitriding.

このとき、先述した冷却孔の表面にマグネタイト層を形成する酸化処理の前に、上記の表面硬化処理を行うと、この表面硬化処理が作業面のみの表面硬化を狙ったものであっても、そのときの反応ガスが冷却孔の表面に侵入して、冷却孔の表面も少なからず硬化させ得る。マグネタイト層との間に、硬質層が介在する場合であっても、耐食性向上および亀裂進展速度抑制の効果は期待されるが、冷却孔の表面が硬化すると亀裂進展速度抑制には不利になるため、工具の母材と上記のマグネタイト層との間には、硬質層が介在しないことが好ましい。したがって、工具の作業面に上記の硬質層を形成する場合は、先に、冷却孔の表面にマグネタイト層を形成する酸化処理を行ってから、作業面に表面硬化処理を行って、作業面に硬質層を形成することが好ましい。   At this time, before the oxidation treatment for forming the magnetite layer on the surface of the cooling holes, the surface hardening treatment is performed, even if this surface hardening treatment is aimed at surface hardening of only the work surface, At that time, the reaction gas enters the surface of the cooling hole, and the surface of the cooling hole can be hardened. Even if a hard layer is interposed between the magnetite layer, the effect of improving corrosion resistance and suppressing the crack growth rate is expected, but if the surface of the cooling hole is hardened, it will be disadvantageous for suppressing the crack growth rate. It is preferable that no hard layer is interposed between the base material of the tool and the magnetite layer. Therefore, when the hard layer is formed on the work surface of the tool, first, an oxidation treatment is performed to form a magnetite layer on the surface of the cooling hole, and then a surface hardening treatment is performed on the work surface. It is preferable to form a hard layer.

そして、先に、冷却孔の表面にマグネタイト層を形成したときに、このマグネタイト層が作業面にも形成されていたのであれば、マグネタイト層の硬さは低いので、切削加工やショットブラスト等によって、マグネタイト層を作業面から容易に除去することができる。マグネタイト層は緻密な構造を有する。よって、作業面に、例えば、窒化層を形成しようとした場合、この作業面に先に形成されているマグネタイト層は、窒化処理における窒素の母材への侵入を妨げて、窒素拡散層および窒素化合物層の形成を抑制する働きがある。よって、表面硬化処理を行う前の作業面に、マグネタイト層が形成されているときは、これを除去しておくことが好ましい。そして、このマグネタイト層が除去された作業面に、上記の表面処理を行うことで、作業面に必要な特性を付与することができる。そして、上記の表面処理を表面硬化処理とすることで、作業面に優れた強度を付与することができる。   If the magnetite layer is also formed on the work surface when the magnetite layer is first formed on the surface of the cooling hole, the hardness of the magnetite layer is low, so cutting or shot blasting etc. The magnetite layer can be easily removed from the work surface. The magnetite layer has a dense structure. Therefore, for example, when a nitride layer is to be formed on the work surface, the magnetite layer previously formed on the work surface prevents the nitrogen from entering the base material in the nitriding treatment, and thus the nitrogen diffusion layer and the nitrogen It functions to suppress the formation of the compound layer. Therefore, when the magnetite layer is formed on the work surface before the surface hardening treatment, it is preferable to remove it. Then, by performing the above-described surface treatment on the work surface from which the magnetite layer has been removed, necessary characteristics can be imparted to the work surface. And the intensity | strength excellent in the working surface can be provided by making said surface treatment into a surface hardening process.

本発明の工具において、上記のマグネタイト層は、その冷却孔の「冷却水と接する」表面に形成されたものである。そして、このマグネタイト層の上に硬質層が、例えば、窒化層が形成されていると、亀裂進展速度の上昇を助長する。
但し、この場合において、マグネタイト層は、窒化処理における窒素の母材への侵入を妨げて、窒化層の形成を抑制する働きがあることは上述の通りである。よって、冷却孔の表面にマグネタイト層を形成した後に、作業面に窒化処理を行った場合、そのときの反応ガス（窒素）が冷却孔の表面にも達して、この位置の母材に侵入しようとしても、冷却孔の表面に窒化層が形成されることが抑制される。また、上記の窒化層（窒化皮膜）を、物理蒸着法で形成する場合でも、その物理蒸着法が有する被覆特性の面から、工具の冷却孔のような「深い孔」の表面に皮膜が形成されることは、容易に回避することができる。これらによって、本発明の工具は、その冷却孔の表面で優れた耐食性を有して、かつ、作業面は優れた強度を有することができる。 In the tool of the present invention, the magnetite layer is formed on the surface of the cooling hole “contacting with the cooling water”. Then, if a hard layer, for example, a nitride layer is formed on the magnetite layer, an increase in the crack growth rate is promoted.
However, in this case, as described above, the magnetite layer has a function of inhibiting the penetration of nitrogen into the base material in the nitriding treatment and suppressing the formation of the nitride layer. Therefore, when a nitriding treatment is performed on the work surface after forming a magnetite layer on the surface of the cooling hole, the reaction gas (nitrogen) at that time will reach the surface of the cooling hole and enter the base material at this position. However, the formation of a nitride layer on the surface of the cooling hole is suppressed. In addition, even when the above nitrided layer (nitride film) is formed by physical vapor deposition, a film is formed on the surface of the “deep hole” such as a cooling hole of a tool from the viewpoint of the coating characteristics of the physical vapor deposition method. It can be easily avoided. By these, the tool of the present invention has excellent corrosion resistance on the surface of the cooling hole, and the work surface can have excellent strength.

ＪＩＳ−Ｇ−４４０４（合金工具鋼鋼材）に規定されるＳＫＤ６１の熱間工具鋼を母材に用いて、これを直径２６ｍｍ×高さ１０ｍｍの形状の試験片に加工した。次に、この試験片に焼入れ焼戻しを行って、試験片の硬さを約４５ＨＲＣに調整した。そして、これらの試験片の直径２６ｍｍの面に、表面粗さを同一とするため、ショットブラストを行った後、表１に示す条件の窒化処理および酸化処理による表面処理を順次行って、耐錆性を評価するための試料１〜４を作製した。このとき、これら耐錆性を評価するための試料とは別に、上記と同じ条件で作製した、表面処理後の表面処理層の状態を評価するための試料も準備した。
表１において、試料１、２で行った酸化処理は、水蒸気の雰囲気で行うホモ処理とした。試料２、３で行った窒化処理は、ガス軟窒化処理であり、窒素ガスとアンモニアガスとの体積割合が２：１になるように流量を調整した雰囲気ガス中で、５２０℃に加熱して２．５時間の保持を行ったものである。なお、試料４は、一切の表面処理を行わず、上記のショットブラストを行った後の母材のままとした。 Using a hot tool steel of SKD61 defined in JIS-G-4404 (alloy tool steel) as a base material, this was processed into a test piece having a diameter of 26 mm and a height of 10 mm. Next, the test piece was quenched and tempered to adjust the hardness of the test piece to about 45 HRC. Then, in order to make the surface roughness the same on the surface of these test pieces having a diameter of 26 mm, after performing shot blasting, surface treatment by nitriding treatment and oxidation treatment under the conditions shown in Table 1 was sequentially carried out to prevent rust resistance. Samples 1 to 4 for evaluating the properties were prepared. At this time, a sample for evaluating the state of the surface treatment layer after the surface treatment, prepared under the same conditions as described above, was prepared separately from the sample for evaluating the rust resistance.
In Table 1, the oxidation treatment performed on samples 1 and 2 was a homotreatment performed in an atmosphere of water vapor. The nitriding treatment performed on Samples 2 and 3 is gas soft nitriding treatment, which is performed by heating to 520 ° C. in an atmospheric gas whose flow rate is adjusted so that the volume ratio of nitrogen gas to ammonia gas is 2: 1. This was a 2.5 hour holding. Note that Sample 4 was not subjected to any surface treatment and remained as a base material after the above shot blasting.

図１〜３は、それぞれ順に、試料１〜３の上記した表面処理後の表面に形成された表面処理層の断面を示す光学顕微鏡写真(×４００倍)である。図１〜３の各視野において、右側が母材である。試料１（図１）は、母材４の表面（つまり、直上）に酸化物層１が形成されていた。試料２（図２）は、母材４の表面に、母材中に窒素が拡散した窒素拡散層３が形成され、その上に、白黒の濃淡で区別された窒素化合物層２が形成されていた。そして、この窒素化合物層２の上に、マグネタイト層の酸化物層１が形成されていた。なお、試料３（図３）は、母材４の表面に、上記の窒素拡散層３と窒素化合物層２とが形成されていた。そして、表面処理が行われた後の試料１〜３の表面硬さは、試料１、２で約６００ＨＶであり、試料３で約１０００ＨＶであった。   1 to 3 are optical micrographs (× 400 magnifications) showing the cross section of the surface treatment layer formed on the surface of the samples 1 to 3 after the surface treatment described above in order. 1-3, the right side is a base material. In the sample 1 (FIG. 1), the oxide layer 1 was formed on the surface of the base material 4 (that is, directly above). In the sample 2 (FIG. 2), a nitrogen diffusion layer 3 in which nitrogen is diffused in the base material is formed on the surface of the base material 4, and a nitrogen compound layer 2 distinguished by black and white shading is formed thereon. It was. A magnetite oxide layer 1 was formed on the nitrogen compound layer 2. In Sample 3 (FIG. 3), the nitrogen diffusion layer 3 and the nitrogen compound layer 2 described above were formed on the surface of the base material 4. The surface hardness of Samples 1 to 3 after the surface treatment was about 600 HV for Samples 1 and 2 and about 1000 HV for Sample 3.

図４は、試料１の表面処理層の断面を示す走査型電子顕微鏡写真（×３０００倍）である。また、図５は、図４の表面処理層の断面における、ＥＤＸによる元素分析の結果である。そして、図６は、試料１の表面処理層における、ＧＤＳによる成分プロファイル分析の結果である。図６において、横軸は、表面処理層の表面からの距離であり、縦軸は、その距離の位置における「表面処理層全体に占める各元素の質量％」である。母材４の表面には、鉄（Ｆｅ）と酸素（Ｏ）とでなり、上記の表面処理層の全体に占めるＦｅの質量が７５％を超える酸化物層１が形成されていた。そして、Ｘ線回折試験より、この酸化物層１がマグネタイト（Ｆｅ３Ｏ４）であることを確認した。母材４の表面に形成されている酸化物層１の厚さは、約２μｍであった。なお、試料１の表面処理層において、微量に検出されるクロム（Ｃｒ）は、母材（ＳＫＤ６１）が含んでいたクロムである。 4 is a scanning electron micrograph (× 3000 magnification) showing a cross section of the surface treatment layer of Sample 1. FIG. FIG. 5 shows the results of elemental analysis by EDX in the cross section of the surface treatment layer of FIG. FIG. 6 shows the result of component profile analysis by GDS in the surface treatment layer of Sample 1. In FIG. 6, the horizontal axis represents the distance from the surface of the surface treatment layer, and the vertical axis represents “mass% of each element in the entire surface treatment layer” at the position of the distance. On the surface of the base material 4, an oxide layer 1 made of iron (Fe) and oxygen (O) and having a mass of Fe exceeding 75% in the entire surface treatment layer was formed. Then, from X-ray diffraction analysis, the oxide layer 1 was confirmed to be magnetite (Fe 3 O 4). The thickness of the oxide layer 1 formed on the surface of the base material 4 was about 2 μm. Note that chromium (Cr) detected in a trace amount in the surface treatment layer of Sample 1 is chromium contained in the base material (SKD61).

そして、試料１〜４の耐錆性を評価した。耐錆性は、上記の表面処理層を形成した試料（または表面処理層を形成しなかった試料）を、２１日間（＝５０４時間）水道水に浸漬して、その浸漬後の表面に発生した錆の程度で評価した。錆の程度は、試料の直径２６ｍｍの面において、その面に占める錆の面積率（％）とした。結果を表２に示す。
また、浸漬後の各試料の直径２６ｍｍの表面を、図７に示す（図７において、（Ａ）試料１、（Ｂ）試料２、（Ｃ）試料３、（Ｄ）試料４である）。 And the rust resistance of samples 1-4 was evaluated. Rust resistance occurred on the surface after immersion of the sample with the surface treatment layer (or the sample without the surface treatment layer) immersed in tap water for 21 days (= 504 hours). Evaluation was based on the degree of rust. The degree of rust was defined as the area ratio (%) of rust in the surface of the sample having a diameter of 26 mm. The results are shown in Table 2.
Further, the surface of each sample having a diameter of 26 mm after immersion is shown in FIG. 7 (in FIG. 7, (A) Sample 1, (B) Sample 2, (C) Sample 3, (D) Sample 4).

表２の通り、表面処理を行わず、母材のままとした試料４の場合、その直径２６ｍｍの全面に錆が生じていた（図７（Ｄ）参照）。そして、母材の表面に窒化層を有した試料３の場合、試料４に比べて、錆の発生が大幅に抑えられていた。しかし、直径２６ｍｍの表面には、面積率が５％程度の錆が発生していた（図７（Ｃ）参照）。
これに対して、母材の表面にマグネタイト層の酸化物層を有した本発明の試料１、２の場合、その直径２６ｍｍの表面に錆の発生が確認されず（図７（Ａ）、（Ｂ）参照）、優れた耐錆性を示した。 As shown in Table 2, in the case of Sample 4 which was not subjected to surface treatment and remained as a base material, rust was generated on the entire surface with a diameter of 26 mm (see FIG. 7D). In the case of Sample 3 having a nitride layer on the surface of the base material, the generation of rust was significantly suppressed as compared with Sample 4. However, rust having an area ratio of about 5% was generated on the surface having a diameter of 26 mm (see FIG. 7C).
On the other hand, in the case of Samples 1 and 2 of the present invention having the magnetite layer oxide layer on the surface of the base material, the occurrence of rust was not confirmed on the surface having a diameter of 26 mm (FIG. 7 (A), ( B)) and excellent rust resistance.

実施例１の表面処理を行った後の試料１について、その表面に形成したマグネタイト層の酸化物層１の上に、さらに、窒化処理を行った。窒化処理の条件は、実施例１で試料３に行ったものと同じである。
図８は、上記した窒化処理後の、試料１の表面処理層の断面を示す光学顕微鏡写真(×４００倍)である。図８において、「Ｍ」で示される層は、断面観察用の試料作製のために施したメッキ処理層であり、試料１の表面処理層とは関係ない。そして、図８より、試料１の表面処理層には、その既存の酸化物層１の上に窒化処理を行ったにも関わらず、この窒化処理による窒化層（窒素拡散層や窒素化合物層）が形成されておらず、最表面は酸化物層１のままである。これは、マグネタイト層の酸化物層１が、窒化処理時の窒素の母材４への侵入を妨げて、窒素拡散層および窒素化合物層の形成に至らなかったものと推定する。 The sample 1 after the surface treatment of Example 1 was further subjected to nitriding treatment on the oxide layer 1 of the magnetite layer formed on the surface. The conditions of the nitriding treatment are the same as those performed on the sample 3 in Example 1.
FIG. 8 is an optical micrograph (× 400) showing a cross section of the surface treatment layer of Sample 1 after the above nitriding treatment. In FIG. 8, a layer indicated by “M” is a plating layer applied for preparing a sample for cross-sectional observation, and is not related to the surface treatment layer of the sample 1. Then, from FIG. 8, the surface treatment layer of Sample 1 was nitrided by this nitriding treatment (nitrogen diffusion layer or nitrogen compound layer) even though nitriding treatment was performed on the existing oxide layer 1. Is not formed, and the outermost surface remains the oxide layer 1. This is presumably because the oxide layer 1 of the magnetite layer hindered the penetration of nitrogen into the base material 4 during the nitriding treatment, and did not lead to the formation of the nitrogen diffusion layer and the nitrogen compound layer.

ＳＫＤ６１の母材を、縦１５ｍｍ×横１６ｍｍ×高さ６０ｍｍの直方体の形状に機械加工した。そして、この直方体の高さ方向の中心部に直径９．５ｍｍの貫通孔を空けて、作業面と、冷却水を通すための冷却孔とを有する工具状の試験片を作製した（硬さ約４５ＨＲＣ）。そして、この試験片の上記した貫通孔（冷却孔）の表面に、実施例１と同じ条件の表面処理を行って、応力腐食割れ試験を行ったときの上記した貫通孔の表面の耐亀裂進展性を評価するための試料１〜４を作製した。なお、試料４は、表面処理を行っていない、母材のままの試料である。
そして、工具の使用環境に応じて、試料１〜４の試験片の貫通孔に３．５％ＮａＣｌ水溶液を通水させ、かつ、試験片の外部から最大１０００ＭＰａ、応力比０．１、周波数２Ｈｚの周期的な応力を付加する応力腐食割れ試験を実施した。図９は、応力腐食割れ試験の概況を示す図である。そして、試験片の貫通孔の表面に、図９に示す亀裂が発生するまでのサイクル数を測定した。そして、この応力腐食割れ試験を、各試料につき２回実施し、測定された亀裂発生サイクル数を平均して、耐亀裂進展性を評価した。 The base material of SKD61 was machined into a rectangular parallelepiped shape of 15 mm long × 16 mm wide × 60 mm high. Then, a through-hole having a diameter of 9.5 mm was formed in the center of the rectangular parallelepiped in the height direction, and a tool-like test piece having a work surface and a cooling hole for allowing cooling water to pass therethrough was produced (hardness of about 45HRC). Then, the surface of the through hole (cooling hole) of the test piece is subjected to a surface treatment under the same conditions as in Example 1, and the crack resistance progress of the surface of the through hole when the stress corrosion cracking test is performed. Samples 1 to 4 for evaluating the properties were prepared. In addition, the sample 4 is a sample with the base material which is not surface-treated.
Then, depending on the usage environment of the tool, a 3.5% NaCl aqueous solution is passed through the through holes of the specimens of Samples 1 to 4, and a maximum of 1000 MPa, a stress ratio of 0.1, and a frequency of 2 Hz from the outside of the specimen. A stress corrosion cracking test was conducted to add periodic stresses. FIG. 9 is a diagram showing an overview of the stress corrosion cracking test. And the cycle number until the crack shown in FIG. 9 generate | occur | produced on the surface of the through-hole of a test piece was measured. Then, this stress corrosion cracking test was performed twice for each sample, and the crack propagation resistance was evaluated by averaging the number of crack generation cycles measured.

図１０に、試料１〜４の亀裂発生サイクル数を示す。表面処理を行わず、貫通孔の表面が母材のままの試料４の場合、その亀裂発生サイクル数は約２０，０００回であった。そして、貫通孔の表面に窒化層を有した試料３の亀裂発生サイクル数は約１１，０００回であり、試料４に比べて、耐亀裂進展性が低下した。これは、窒化層の形成によって、貫通孔の表面硬さが高くなったことが原因と考えられる。
これに対して、貫通孔の表面にマグネタイト層の酸化物層を有した本発明の試料１、２の場合、良好な亀裂発生サイクル数を得た。まず、母材とマグネタイト層との間に窒化層を有した試料２では、亀裂発生サイクル数が約２５，０００回であり、試料４に比べて、耐亀裂進展性が向上した。そして、母材の直上に、窒化層を介さずに、マグネタイト層を形成した試料１では、そのマグネタイト層の優れた耐錆性に加えて、硬さの高い窒化層が介在しないことから、亀裂発生サイクル数が約１３０，０００回に上昇して、耐亀裂進展性がさらに向上した。 FIG. 10 shows the number of crack generation cycles of Samples 1 to 4. In the case of Sample 4 where the surface treatment was not performed and the surface of the through-hole was a base material, the number of crack generation cycles was about 20,000. And the crack generation cycle number of the sample 3 which had the nitride layer on the surface of the through-hole was about 11,000 times, and the crack progress resistance fell compared with the sample 4. This is considered to be because the surface hardness of the through hole is increased by the formation of the nitride layer.
On the other hand, in the case of Samples 1 and 2 of the present invention having a magnetite oxide layer on the surface of the through-hole, a good crack generation cycle number was obtained. First, in Sample 2 having a nitride layer between the base material and the magnetite layer, the number of crack generation cycles was about 25,000 times, and the crack propagation resistance was improved as compared with Sample 4. And, in the sample 1 in which the magnetite layer is formed without a nitride layer directly above the base material, in addition to the excellent rust resistance of the magnetite layer, a high hardness nitride layer does not intervene. The number of generation cycles increased to about 130,000 times, and the crack growth resistance was further improved.

１ 酸化物層
２ 窒素化合物層
３ 窒素拡散層
４ 母材
Ｍ メッキ処理層 1 Oxide layer 2 Nitrogen compound layer 3 Nitrogen diffusion layer 4 Base material M Plating treatment layer

Claims (5)

作業面と、冷却水を通すための冷却孔とを有する工具の製造方法であって、前記冷却孔が形成された工具を用意し、４８０〜６００℃の水蒸気に曝すことによる酸化処理を行って、前記冷却孔の冷却水と接する表面にマグネタイト層を形成した後に、前記作業面に表面硬化処理を行って、前記作業面に、前記工具の母材よりも硬さが高い硬質層を形成することを特徴とする工具の製造方法。 A method of manufacturing a tool having a work surface and a cooling hole for passing cooling water, the tool having the cooling hole formed therein is prepared and subjected to oxidation treatment by exposure to water vapor at 480 to 600 ° C. After forming a magnetite layer on the surface of the cooling hole in contact with the cooling water , surface hardening treatment is performed on the work surface to form a hard layer having a hardness higher than that of the base material of the tool on the work surface. The manufacturing method of the tool characterized by the above-mentioned. 前記酸化処理の処理時間を１〜３時間とすることを特徴とする請求項１に記載の工具の製造方法。 The method for manufacturing a tool according to claim 1 , wherein a treatment time of the oxidation treatment is 1 to 3 hours. 前記冷却孔の冷却水と接する表面にマグネタイト層を形成する酸化処理を、前記工具の母材の直上に行うことを特徴とする請求項１または２に記載の工具の製造方法。 The method for manufacturing a tool according to claim 1 or 2 , wherein an oxidation treatment for forming a magnetite layer on a surface of the cooling hole in contact with the cooling water is performed immediately above the base material of the tool. 前記硬質層が、窒化層であることを特徴とする請求項１ないし３のいずれかに記載の工具の製造方法。 The hard layer is, the manufacturing method of a tool according to any one of claims 1 to 3, characterized in that a nitride layer. 前記マグネタイト層が、前記冷却孔の冷却水と接する表面の最表面にあることを特徴とする請求項４に記載の工具の製造方法。 The tool manufacturing method according to claim 4 , wherein the magnetite layer is on the outermost surface of the cooling hole in contact with the cooling water.
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