JP2009167435A - Steel for cold-press die and die for cold-pressing - Google Patents

Steel for cold-press die and die for cold-pressing Download PDF

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JP2009167435A
JP2009167435A JP2008003524A JP2008003524A JP2009167435A JP 2009167435 A JP2009167435 A JP 2009167435A JP 2008003524 A JP2008003524 A JP 2008003524A JP 2008003524 A JP2008003524 A JP 2008003524A JP 2009167435 A JP2009167435 A JP 2009167435A
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steel
hardness
toughness
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JP5276330B2 (en
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Shogo Murakami
昌吾 村上
Tsuyoshi Tonomura
剛志 殿村
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Nippon Koshuha Steel Co Ltd
Kobe Steel Ltd
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Nippon Koshuha Steel Co Ltd
Kobe Steel Ltd
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Priority to PCT/JP2009/050097 priority patent/WO2009088027A1/en
Priority to CN2009800002926A priority patent/CN101743335B/en
Priority to US12/598,324 priority patent/US20100132429A1/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Heat Treatment Of Articles (AREA)
  • Mounting, Exchange, And Manufacturing Of Dies (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel for cold-press die, which is useful as a blank of the die for cold-pressing, in which the basic characteristics, such as the hardness, toughness and dimensional change with the heat-treatment, are provided and also, which is acceptable in terms of the roughness on the cutting-finish surface and the service life of a cutting tool. <P>SOLUTION: The steel contains 0.5-0.7% C, 5.0-7.0% Cr, 0.5-2.0% Si, 0.1-2.0% Mn, 0.001-0.010% Al, 0.25-1.00% Cu, 0.25-1.00% Ni, 0.5-3.0% Mo+0.5×W, ≤0.5% V, ≤0.05% P, ≤0.1% S, ≤0.005% O, in which a requirement of [C]×[Cr]≤4, a requirement of FP(parameter composed of ferritic generating elements)=[Si]/5+[Cr]/5+2×[Mo]+[W]+2×[V]+10×[Al]≤5.0 and a requirement of AP(parameter composed of austenitic generating elements)=[Mn]+3×([Cu]+[Ni])≤2.5 are satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、自動車用鋼板や家電用鋼板などを、冷間等でプレス成形（打ち抜き、曲げ、絞り、トリミングなど）する際に用いられる冷間プレス用金型の素材として有用な冷間金型用鋼と、その冷間プレス用金型に関するものである。   INDUSTRIAL APPLICABILITY The present invention is a cold mold useful as a material for a cold press mold used when press forming (punching, bending, drawing, trimming, etc.) of steel sheets for automobiles, steel sheets for household appliances, etc. Steel and its cold press mold.

自動車用鋼板や家電用鋼板などのプレス成形に用いられる冷間プレス用金型は、鋼板の高強度化に伴い、その寿命の改善が求められている。特に自動車用鋼板では、環境問題が考慮され、自動車の燃費を向上するために、引っ張り強度が５９０ＭＰａ以上のハイテン鋼板が採用されることが多くなってきており、今後その需要が益々高くなることが予想されている。   Cold stamping dies used for press forming of steel plates for automobiles, steel plates for household appliances, etc. are required to have an improved service life as the strength of the steel plates increases. Especially for automobile steel sheets, environmental issues are taken into consideration, and high-tensile steel sheets having a tensile strength of 590 MPa or more are increasingly employed in order to improve the fuel efficiency of automobiles. Expected.

そのハイテン鋼板をプレス成形するにあたり、表面処理を施された冷間プレス用金型の表面皮膜が、早期に損傷することで、型カジリやカジリと呼ばれるプレス成形時に焼きつく現象が発生し、冷間プレス用金型の金型寿命が極端に短くなるといった問題の発生が増加している。   When the high-tensile steel plate is press-formed, the surface film of the cold-press die that has been surface-treated is damaged early, causing a phenomenon of seizure during press-forming called mold galling or galling. The occurrence of problems such as extremely shortening the die life of the hot press die is increasing.

冷間プレス用金型は、母材となる冷間金型用鋼の表面に硬質皮膜処理を施すことで製造される。母材となる冷間金型用鋼は、一般に、焼鈍→切削加工→焼入焼戻処理という工程を経て製造される。   A cold press mold is manufactured by applying a hard coating to the surface of a cold mold steel as a base material. Cold mold steel as a base material is generally manufactured through a process of annealing → cutting → quenching and tempering.

冷間金型用鋼として、従来から、ＪＩＳ ＳＫＤ１１などの高Ｃ高Ｃｒの合金工具鋼や、更に耐摩耗性が改善されたＪＩＳ ＳＫＨ５１などの高速度工具鋼が汎用されている。これらの工具鋼では、Ｃｒ系炭化物やＭｏ、Ｗ、Ｖ系炭化物の析出硬化により硬度の向上を図っている。更には、ＪＩＳ ＳＫＨ５１が含有するＣ、Ｍｏ、Ｗ、Ｖなどの合金元素を低減することで、靭性、耐摩耗性の両方を向上させたマトリックスハイスと呼ばれる低合金高速度工具鋼も、冷間金型用鋼に使用されている。また、これら冷間金型用鋼の更なる特性の改善を図ったものとして特許文献１に記載の技術や、特許文献２に記載の技術も提案されている。   Conventionally, as steel for cold molds, a high C high Cr alloy tool steel such as JIS SKD11 and a high speed tool steel such as JIS SKH51 with improved wear resistance have been widely used. In these tool steels, the hardness is improved by precipitation hardening of Cr-based carbides, Mo, W, and V-based carbides. Furthermore, low alloy high-speed tool steel called matrix high speed, which has improved both toughness and wear resistance by reducing alloy elements such as C, Mo, W and V contained in JIS SKH51, Used in mold steel. Moreover, the technique of patent document 1 and the technique of patent document 2 are proposed as what aimed at the further improvement of the characteristic of these steel for cold molds.

特許文献１には、被削性や耐摩耗性といった必要特性を阻害せずに、優れた変寸抑制特性と高硬度特性、耐カジリ性を得ることを目的として、適正量のＮｉやＡｌを添加し、それに応じた適正量のＣｕを添加すると共に、更にＣ及びＣｒの含有量を調整して組織中の炭化物分布を微細に分散した冷間ダイス鋼が開示されている。   In Patent Document 1, an appropriate amount of Ni or Al is added for the purpose of obtaining excellent dimension suppressing properties, high hardness properties, and galling resistance without impairing necessary properties such as machinability and wear resistance. A cold die steel is disclosed in which the addition of an appropriate amount of Cu according to the addition and further adjusting the C and Cr contents to finely disperse the carbide distribution in the structure.

また、特許文献２には、従来のマトリックスハイスより焼き入れ温度を低くしても、熱処理後の硬さ、靭性などの特性が従来のマトリックスハイスと同程度の特性が得られることを目的として、焼き戻し状態でＭ２３Ｃ６型炭化物が２〜５ｖｏｌ％生成する組織を有し、かつＭＣ型炭化物及びＭ６Ｃ型炭化物の少なくともいずれかが分散析出した焼入れ焼戻し組織を有する合金工具鋼が開示されている。 Further, in Patent Document 2, even if the quenching temperature is lower than that of the conventional matrix high speed, characteristics such as hardness and toughness after heat treatment can be obtained at the same level as the conventional matrix high speed. Disclosed is an alloy tool steel having a structure in which 2 to 5 vol% of M 23 C 6 type carbide is generated in a tempered state and having a quenched and tempered structure in which at least one of MC type carbide and M 6 C type carbide is dispersed and precipitated. Has been.

特開２００６−１６９６２４号公報JP 2006-169624 A 特開２００４−１６９１７７号公報JP 2004-169177 A

冷間プレス用金型は、母材となる冷間金型用鋼の表面に硬質皮膜処理を施すことで製造される。この硬質皮膜処理としては、熱拡散によってＶＣでなる皮膜を形成するＴＤ処理、主にＴｉＣでなる皮膜を形成するＣＶＤ処理、主にＴｉＮでなる皮膜を形成するＰＶＤ処理等がある。これらの硬質皮膜処理は、金型ユーザーやプレスメーカーの事情に応じて適宜採用されている。そのため、何れの硬質皮膜処理にも対応することができる冷間金型用鋼が開発されることが求められている。また、当然のことではあるが、冷間プレス用金型には、硬さや靭性、熱処理変寸といった基本特性を確保することも求められている。   A cold press mold is manufactured by applying a hard coating to the surface of a cold mold steel as a base material. As this hard film treatment, there are a TD process for forming a film made of VC by thermal diffusion, a CVD process for forming a film made mainly of TiC, a PVD process for forming a film made mainly of TiN, and the like. These hard coating treatments are appropriately employed depending on the circumstances of the mold user and the press manufacturer. Therefore, it is required to develop cold mold steel that can cope with any hard coating treatment. Needless to say, the cold press mold is also required to ensure basic characteristics such as hardness, toughness, and heat treatment size change.

更には、冷間プレス用金型には、切削加工中のむしれ発生といった問題もある。むしれが発生すると切削仕上げ面粗さが大きくなるため、熱処理後のラッピング作業が困難となり、更には金型寿命の低減を招く。また、切削工具寿命も短くなり、製造コストが増大する。これらの問題を解消するためには、問題の発生原因であるＡｌ系介在物(Ａｌ２Ｏ３、ＡｌＮ）の析出を抑制する必要があるが、Ａｌ系介在物を析出する元素であるＡｌの含有量を低減すると、逆に、硬さ低下、靭性低下、熱処理変寸量の増大といった基本特性に悪影響を及ぼすおそれがある。よって、これらの基本特性を確保した上で、切削仕上げ面粗さや切削工具寿命といった面でも問題がない冷間プレス用金型が開発されることが待ち望まれている。 Furthermore, the cold press mold has a problem that stagnation occurs during cutting. When peeling occurs, the finished surface roughness becomes large, so that the lapping work after the heat treatment becomes difficult, and further the life of the mold is reduced. In addition, the cutting tool life is shortened and the manufacturing cost is increased. In order to solve these problems, it is necessary to suppress the precipitation of Al-based inclusions (Al 2 O 3 , AlN) that is the cause of the problem. On the other hand, when the content is reduced, there is a risk of adversely affecting basic properties such as hardness reduction, toughness reduction, and heat treatment dimensional change. Therefore, it is desired to develop a cold press die that ensures these basic characteristics and has no problems in terms of cutting finish surface roughness and cutting tool life.

本発明は、これら従来の問題を解決せんとしてなされたもので、硬さ、靭性、熱処理変寸といった求められる基本特性を備えた上に、様々な硬質皮膜処理にも対応することができ、更には、切削仕上げ面粗さや切削工具寿命といった面でも問題のない冷間プレス用金型の素材として有用な冷間金型用鋼と、その冷間プレス用金型を提供することを課題とするものである。   The present invention has been made as a solution to these conventional problems, and has the required basic properties such as hardness, toughness, heat treatment size change, and can also handle various hard coating treatments. An object of the present invention is to provide a steel for cold mold that is useful as a material for a cold press mold that has no problems in terms of roughness of the finished surface and cutting tool life, and to provide a cold press mold. Is.

請求項１記載の発明は、質量％で、Ｃ：０．５〜０．７％、Ｃｒ：５．０〜７．０％、Ｓｉ：０．５〜２．０％、Ｍｎ：０．１〜２．０％、Ａｌ：０．００１〜０．０１０％、Ｃｕ：０．２５〜１．００％、Ｎｉ：０．２５〜１．００％、Ｎ：０．００３〜０．０２５％、Ｍｏ＋０．５×Ｗ：０．５〜３．０％、Ｐ：０．０５％以下（０％を含まない）、Ｓ：０．１％以下（０％を含まない）、Ｏ：０．００５％以下（０％を含まない）を含有し、残部が鉄及び不可避的不純物であって、且つ、［Ｃ］×［Ｃｒ］≦４という要件を満足し、更に、ＦＰ（フェライト生成元素からなるパラメータ）が、［Ｓｉ］／５＋［Ｃｒ］／５＋２×［Ｍｏ］＋［Ｗ］＋２×［Ｖ］＋１０×［Ａｌ］≦５．０という要件を満足し、ＡＰ（オーステナイト生成元素からなるパラメータ）が、［Ｍｎ］＋３×（［Ｃｕ］＋［Ｎｉ］）≦２．５という要件を満足することを特徴とする冷間金型用鋼である。
但し、上式で［ ］は、各元素の含有量（質量％）を示す。 Invention of Claim 1 is the mass%, C: 0.5-0.7%, Cr: 5.0-7.0%, Si: 0.5-2.0%, Mn: 0.1 -2.0%, Al: 0.001-0.010%, Cu: 0.25-1.00%, Ni: 0.25-1.00%, N: 0.003-0.025%, Mo + 0.5 × W: 0.5 to 3.0%, P: 0.05% or less (not including 0%), S: 0.1% or less (not including 0%), O: 0.005 % Or less (excluding 0%), the balance being iron and inevitable impurities and satisfying the requirement of [C] × [Cr] ≦ 4, and further comprising FP (ferrite-forming element) Parameter) satisfies the requirement of [Si] / 5 + [Cr] / 5 + 2 × [Mo] + [W] + 2 × [V] + 10 × [Al] ≦ 5.0, and AP (austenite forming element) Is a cold mold steel characterized by satisfying the requirement of [Mn] + 3 × ([Cu] + [Ni]) ≦ 2.5.
However, in the above formula, [] indicates the content (% by mass) of each element.

請求項２記載の発明は、更に、Ｖ：０．５％以下（０％を含む）を含有する請求項１記載の冷間金型用鋼である。   Invention of Claim 2 is steel for cold mold of Claim 1 which contains V: 0.5% or less (0% is included) further.

請求項３記載の発明は、更に、Ｔｉ、Ｚｒ、Ｈｆ、Ｔａ、Ｎｂからなる群から選択される少なくとも１種の元素を、合計０．５％以下含有する請求項１または２記載の冷間金型用鋼である。   The invention according to claim 3 further includes at least one element selected from the group consisting of Ti, Zr, Hf, Ta, and Nb in a total amount of 0.5% or less. Steel for molds.

請求項４記載の発明は、更に、Ｃｏを１０％以下含有する請求項１乃至３のいずれかに記載の冷間金型用鋼である。   Invention of Claim 4 is steel for cold mold | die in any one of Claim 1 thru | or 3 which contains Co 10% or less further.

請求項５記載の発明は、請求項１乃至４のいずれかに記載の冷間金型用鋼を用いて得られる冷間プレス用金型である。   A fifth aspect of the present invention is a cold press mold obtained by using the cold mold steel according to any one of the first to fourth aspects.

本発明の冷間金型用鋼を冷間プレス用金型の素材に用いることで、硬さ、靭性、熱処理変寸といった求められる基本特性を備えた上に、様々な硬質皮膜処理にも対応することができ、更には、切削仕上げ面粗さや切削工具寿命といった面でも問題のない冷間プレス用金型を得ることができる。また、その冷間金型用鋼を用いて得られる冷間プレス用金型は、特に、引っ張り強度が５９０ＭＰａ以上のハイテン鋼板の成形用として好適に用いることができる。   By using the steel for cold molds of the present invention as a material for cold stamping molds, it has the required basic properties such as hardness, toughness, heat treatment size change, and also supports various hard coating treatments. Furthermore, it is possible to obtain a cold press die that is free from problems in terms of the finished surface roughness and cutting tool life. In addition, a cold press die obtained by using the cold die steel can be suitably used particularly for forming a high-tensile steel plate having a tensile strength of 590 MPa or more.

以下、本発明を実施形態に基づいて更に詳細に説明する。   Hereinafter, the present invention will be described in more detail based on embodiments.

本発明者は、まず、従来のＪＩＳ ＳＫＤ１１やマトリックスハイスを素材に用いた冷間プレス用金型において、ＰＶＤ処理によって形成されたＴｉＮ皮膜が損傷して、カジリが発生する原因を鋭意探求した。   The present inventor first eagerly investigated the cause of galling caused by damage to the TiN film formed by PVD treatment in a cold press mold using conventional JIS SKD11 or matrix high speed.

探求の結果、ＴｉＮ皮膜にカジリが発生する原因は、母材となる冷間金型用鋼に生成される粗大なＣｒ系炭化物であり、そのＣｒ系炭化物が起点となって、カジリが発生することを見出した。そのＣｒ系炭化物によるＴｉＮ皮膜の損傷のメカニズムは、図１に示す通りである。   As a result of the search, the cause of galling in the TiN film is the coarse Cr-based carbide produced in the cold mold steel used as the base material, and galling is generated starting from the Cr-based carbide. I found out. The mechanism of damage of the TiN film by the Cr-based carbide is as shown in FIG.

まず、図１（ａ）に示すように、母材となる冷間金型用鋼１の表面に硬質皮膜処理を施すことで、表面にＴｉＮ皮膜２を形成した冷間プレス用金型を準備する。この冷間金型用鋼１が、ＪＩＳ ＳＫＤ１１やマトリックスハイスを素材として形成されている場合、母材である冷間金型用鋼１の表面には粗大なＣｒ系炭化物３が析出している。この冷間プレス用金型を用いてプレス成形する際に、図１（ｂ）に示すように、被成形物が矢印方向に摺動すると、ＴｉＮ皮膜２にはクラック４が発生する。このクラック４が発生する部位は、ＴｉＮ皮膜２の下方の母材にＣｒ系炭化物３が析出している部位である。更に、被成形物を摺動すると、図１（ｃ）に示すように、そのクラック４が起点となって、ＴｉＮ皮膜２に剥離が生じ、カジリが発生する。   First, as shown in FIG. 1 (a), a cold press mold having a TiN film 2 formed on its surface is prepared by applying a hard film treatment to the surface of the cold mold steel 1 as a base material. To do. When this cold mold steel 1 is made of JIS SKD11 or matrix high speed steel, coarse Cr-based carbides 3 are deposited on the surface of the cold mold steel 1 as a base material. . When press molding is performed using this cold press die, as shown in FIG. 1B, when the molding slides in the direction of the arrow, a crack 4 is generated in the TiN film 2. The part where the crack 4 is generated is a part where the Cr-based carbide 3 is deposited on the base material below the TiN film 2. Furthermore, when the molding is slid, as shown in FIG. 1 (c), the crack 4 is the starting point, and the TiN film 2 is peeled off, which causes galling.

以上説明したように、ＴｉＮ皮膜のカジリ発生の原因はＣｒ系炭化物である。本発明者は、このＣｒ系炭化物の生成を抑制することで、ＴｉＮ皮膜の剥離を防止でき、金型寿命が極端に短くなるといった問題を発生することを抑制できることを見出した。   As described above, the cause of galling in the TiN film is Cr-based carbide. The present inventor has found that by suppressing the formation of this Cr-based carbide, it is possible to prevent the TiN film from peeling off and to suppress the occurrence of problems such as extremely shortening the mold life.

母材となる冷間金型用鋼の表面に析出する粗大なＣｒ系炭化物３の生成を抑制して、ＰＶＤ処理によって形成したＴｉＮ皮膜の寿命を長くするためには、鋼中のＣの含有量とＣｒの含有量を低減させれば良い。しかし、Ｃの含有量を低減させ過ぎると、冷間金型用鋼の表面に、ＴＤ処理によるＶＣ皮膜や、ＣＶＤ処理によるＴｉＣ皮膜を形成することが難しくなる。そこで、本発明では、Ｃの含有量を０．５〜０．７質量％、Ｃｒの含有量を５．０〜７．０質量％とした上で、それらの含有量の積を規定することによって、冷間金型用鋼の表面に粗大なＣｒ系炭化物３を析出させず、且つ一方で、必要とする十分な厚みのＶＣ皮膜やＴｉＣ皮膜を形成することを可能とした。   In order to suppress the formation of coarse Cr-based carbide 3 precipitated on the surface of the cold mold steel as a base material and to prolong the life of the TiN film formed by PVD treatment, the inclusion of C in the steel The amount and the Cr content may be reduced. However, if the C content is excessively reduced, it becomes difficult to form a VC film by TD treatment or a TiC film by CVD treatment on the surface of the steel for cold mold. Therefore, in the present invention, the C content is set to 0.5 to 0.7 mass%, the Cr content is set to 5.0 to 7.0 mass%, and the product of these contents is specified. Thus, the coarse Cr carbide 3 is not deposited on the surface of the cold mold steel, and on the other hand, it is possible to form a VC film or a TiC film having a sufficient thickness as required.

また、本発明では、Ｓｉ、Ｃｒ、Ｍｏ、Ｗ、Ｖ、Ａｌといったフェライト生成元素からなるパラメータと、Ｍｎ、Ｃｕ、Ｎｉといったオーステナイト生成元素からなるパラメータも規定した。   In the present invention, parameters composed of ferrite-generating elements such as Si, Cr, Mo, W, V, and Al and parameters composed of austenite-generating elements such as Mn, Cu, and Ni are also defined.

Ｓｉ、Ｃｒ、Ｍｏ、Ｗ、Ｖ、Ａｌといったフェライト生成元素の合計含有量が多過ぎた場合、冷間金型用鋼の硬さと靭性のバランスが崩れると共に、切削加工仕上げ面精度も悪化する。そこで、本発明では、フェライト生成元素からなるパラメータ（ＦＰ）を数式化し、その式を満足するようにフェライト生成元素の合計含有量を規定することで、冷間金型用鋼の硬さと靭性のバランスを良好にする共に、切削加工仕上げ面精度も向上させた。   When the total content of ferrite-forming elements such as Si, Cr, Mo, W, V, and Al is too large, the balance between hardness and toughness of the steel for cold mold is lost, and the accuracy of the finished surface of the cutting work is also deteriorated. Therefore, in the present invention, the parameter (FP) composed of the ferrite-forming element is formulated into a mathematical formula, and the total content of the ferrite-forming elements is defined so as to satisfy the formula, thereby reducing the hardness and toughness of the steel for cold mold. In addition to improving the balance, the machined surface accuracy was improved.

また、Ｍｎ、Ｃｕ、Ｎｉといったオーステナイト生成元素の合計含有量が多過ぎた場合、残留オーステナイトが多くなることにより熱処理変寸量のばらつきが増大すると共に、切削時の工具寿命が短くなる。そこで、本発明では、オーステナイト生成元素からなるパラメータ（ＡＰ）を数式化し、その式を満足するようにオーステナイト生成元素の合計含有量を規定することで、鋼中の残留オーステナイトを少なくして熱処理変寸量のばらつきを減少させると共に、切削時の工具寿命を長くした。   In addition, when the total content of austenite-generating elements such as Mn, Cu, and Ni is too large, the amount of retained austenite increases, resulting in an increase in variation in heat treatment size change and a shortened tool life during cutting. Therefore, in the present invention, the parameter (AP) composed of an austenite-forming element is formulated and the total content of austenite-forming elements is defined so as to satisfy the formula, thereby reducing the residual austenite in the steel and changing the heat treatment. The variation in dimensions was reduced and the tool life during cutting was extended.

以下、本発明の冷間金型用鋼中の化学成分の含有量の範囲限定理由について、元素毎に詳細に説明する。尚、本明細書中に記載する％は全て質量％を示す。   Hereinafter, the reason for limiting the range of the content of chemical components in the steel for cold mold according to the present invention will be described in detail for each element. In addition, all% described in this specification shows the mass%.

Ｃ：０．５〜０．７％
Ｃは、硬さ及び耐摩耗性を確保し、ＨＡＺ軟化の抑制にも寄与する元素である。また、金型母材の表面に、ＴＤ処理によるＶＣ皮膜や、ＣＶＤ処理によるＴｉＣ皮膜といった炭化物皮膜を形成する場合、Ｃの含有量が少ないと皮膜の厚さが薄くなるなどの問題もある。これらを勘案し、上記作用を有効に発揮させるためにＣの含有量の下限を０．５％とした。また、その下限は０．５５％であることが好ましい。但し、その含有量が過剰であると、粗大なＣｒ系炭化物が生成して、ＰＶＤ処理で形成されるＴｉＮ皮膜が剥離し易くなる。また、Ｃの含有量が過剰であると、残留オーステナイトが増加し、高温で焼戻処理を行わないと所望の硬さが得られないほか、焼戻処理後に膨張するなどして変寸が大きくなる。更に、Ｃの含有量が過剰であると靭性にも悪影響を及ぼす。よって、Ｃの含有量の上限を０．７％とした。また、その上限は０．６５％であることが好ましい。 C: 0.5 to 0.7%
C is an element that ensures hardness and wear resistance and contributes to the suppression of HAZ softening. In addition, when a carbide film such as a VC film by TD treatment or a TiC film by CVD treatment is formed on the surface of the mold base material, there is a problem that the thickness of the film becomes thin if the C content is small. Considering these, the lower limit of the C content is set to 0.5% in order to effectively exhibit the above-described action. The lower limit is preferably 0.55%. However, if the content is excessive, coarse Cr-based carbides are generated, and the TiN film formed by the PVD process is easily peeled off. In addition, if the C content is excessive, retained austenite increases, and the desired hardness cannot be obtained unless tempering is performed at a high temperature. In addition, the size changes greatly due to expansion after tempering. Become. Furthermore, if the C content is excessive, the toughness is also adversely affected. Therefore, the upper limit of the C content is set to 0.7%. The upper limit is preferably 0.65%.

Ｃｒ：５．０〜７．０％
Ｃｒは、所定の硬さを確保するために有用な元素である。詳しくは、Ｃｒの含有量が少な過ぎると、焼入性が不足してベイナイトが一部生成するため、硬さが低下し、耐摩耗性を確保することができない。更に、Ｃｒは金型の耐食性を確保するためにも有用な元素である。そこでＣｒの含有量の下限を５．０％とした。また、その下限は５．５％であることが好ましい。但し、その含有量が過剰であると、粗大なＣｒ系炭化物が多量に生成して、ＰＶＤ処理で形成されるＴｉＮ皮膜が剥離し易くなる。また、Ｃｒの含有量が過剰であると、熱処理後の収縮によって硬質皮膜の耐久性が低下する。更に、Ｃｒの含有量が過剰であると靭性にも悪影響を及ぼす。そこでＣｒの含有量の上限を７．０％とした。また、その上限は６．５％であることが好ましい。 Cr: 5.0-7.0%
Cr is an element useful for ensuring a predetermined hardness. Specifically, if the Cr content is too small, the hardenability is insufficient and a portion of bainite is generated, so that the hardness is lowered and the wear resistance cannot be ensured. Furthermore, Cr is an element useful for ensuring the corrosion resistance of the mold. Therefore, the lower limit of the Cr content is set to 5.0%. Further, the lower limit is preferably 5.5%. However, if the content is excessive, a large amount of coarse Cr-based carbide is generated, and the TiN film formed by the PVD treatment is easily peeled off. On the other hand, if the Cr content is excessive, the durability of the hard coating is reduced by shrinkage after heat treatment. Furthermore, if the Cr content is excessive, the toughness is also adversely affected. Therefore, the upper limit of the Cr content is set to 7.0%. Moreover, it is preferable that the upper limit is 6.5%.

Ｓｉ：０．５〜２．０％
Ｓｉは、製鋼時の脱酸元素として有用であり、硬さの向上と被削性確保に寄与する元素である。また、Ｓｉはマトリックスのマルテンサイトの焼戻し軟化を抑え、ＨＡＺ軟化の抑制に有用である。このような作用を有効に発揮するため、Ｓｉの含有量の下限を０．５％とした。その含有量は、好ましくは１．０％以上、より好ましくは１．２％以上である。但し、その含有量が過剰であると靭性が低下する。また、偏析が大きくなり、熱処理後の変寸が大きくなる。よってＳｉの含有量の上限を２．０％とした。その含有量は、好ましくは１．８５％以下である。 Si: 0.5 to 2.0%
Si is useful as a deoxidizing element at the time of steelmaking, and is an element that contributes to improving hardness and securing machinability. Moreover, Si suppresses the temper softening of the martensite of the matrix and is useful for suppressing the HAZ softening. In order to effectively exhibit such an action, the lower limit of the Si content is set to 0.5%. The content is preferably 1.0% or more, more preferably 1.2% or more. However, if the content is excessive, the toughness decreases. Moreover, segregation increases and the size after heat treatment increases. Therefore, the upper limit of the Si content is set to 2.0%. The content is preferably 1.85% or less.

Ｍｎ：０．１〜２．０％
Ｍｎは、焼入性確保に有用な元素である。しかし、その含有量が過剰であると、残留オーステナイトが増加するため、高温で焼戻処理を行わないと所望の硬さが得られなくなるほか、靭性も低下する。これらを勘案して、Ｍｎの含有量を０．１〜２．０％の範囲に定めた。Ｍｎの含有量の下限は、好ましくは０．１５％であり、その上限は、好ましくは１．０％、より好ましくは０．５％、更に好ましくは０．３５％である。 Mn: 0.1 to 2.0%
Mn is an element useful for ensuring hardenability. However, if the content is excessive, retained austenite increases, so that the desired hardness cannot be obtained unless tempering is performed at a high temperature, and the toughness also decreases. Taking these into consideration, the content of Mn is set in the range of 0.1 to 2.0%. The lower limit of the Mn content is preferably 0.15%, and the upper limit is preferably 1.0%, more preferably 0.5%, and still more preferably 0.35%.

Ａｌ：０．００１〜０．０１０％
Ａｌは、脱酸剤として有用な元素である。しかし、含有量が０．００１％未満であると、その効果は十分に得ることはできない。従って、Ａｌの含有量の下限を０．００１％とした。その下限は好ましくは０．００２％である。一方、Ａｌ２Ｏ３や粗大なＡｌＮといったＡｌ系介在物は、切削中にむしれの原因となり、切削仕上げ面精度を低下させるため、Ａｌの含有量の上限を０．０１０％とした。その上限は、好ましくは０．００８％である。 Al: 0.001 to 0.010%
Al is an element useful as a deoxidizer. However, if the content is less than 0.001%, the effect cannot be sufficiently obtained. Therefore, the lower limit of the Al content is set to 0.001%. The lower limit is preferably 0.002%. On the other hand, Al-based inclusions such as Al 2 O 3 and coarse AlN cause peeling during cutting and reduce the accuracy of the finished surface of the cut. Therefore, the upper limit of the Al content is set to 0.010%. The upper limit is preferably 0.008%.

Ｃｕ：０．２５〜１．００％
Ｃｕは、ε−Ｃｕの析出強化による硬さ向上を図るために必要な元素であり、ＨＡＺ軟化の抑制にも寄与する。但し、その含有量が過剰であると、靭性が低下し、また、鍛造割れが発生し易くなる。そこでＣｕの含有量の上限を１．００％とした。また、その上限は０．８０％であることが好ましい。また、Ｃｕの含有量の下限は０．２５％である。また、その下限は０．３０％であることが好ましい。 Cu: 0.25 to 1.00%
Cu is an element necessary for improving hardness by precipitation strengthening of ε-Cu, and contributes to suppression of HAZ softening. However, if the content is excessive, toughness is reduced and forging cracks are likely to occur. Therefore, the upper limit of the Cu content is set to 1.00%. The upper limit is preferably 0.80%. Further, the lower limit of the Cu content is 0.25%. The lower limit is preferably 0.30%.

Ｎｉ：０．２５〜１．００％
Ｎｉは、Ｎｉ３ＡｌなどのＡｌ−Ｎｉ系金属間化合物の析出強化による硬さ向上を図るために必要な元素であり、ＨＡＺ軟化の抑制にも寄与する。また、ＮｉはＣｕと併用することにより、Ｃｕの過剰添加による熱間脆性を抑制し、鍛造時の割れを防止することもできる。但し、その含有量が過剰であると、残留オーステナイトが増加して高温で焼戻処理をしないと所定の硬さを確保できないほか、熱処理後に膨張してしまう。また、Ｎｉの含有量が過剰であると、靭性も低下する。これらを勘案して、Ｎｉの含有量を０．２５〜１．００％の範囲に定めた。Ｎｉの含有量の下限は、好ましくは０．３０％であり、その上限は、好ましくは０．８０％である。 Ni: 0.25 to 1.00%
Ni is an element necessary for improving the hardness by precipitation strengthening of Al—Ni-based intermetallic compounds such as Ni 3 Al, and contributes to suppression of HAZ softening. Ni can also be used in combination with Cu to suppress hot brittleness due to excessive addition of Cu and to prevent cracking during forging. However, if the content is excessive, the retained austenite increases, and unless it is tempered at a high temperature, a predetermined hardness cannot be secured, and it expands after the heat treatment. Further, if the Ni content is excessive, toughness is also lowered. Taking these into consideration, the content of Ni is set in the range of 0.25 to 1.00%. The lower limit of the Ni content is preferably 0.30%, and the upper limit is preferably 0.80%.

Ｎ：０．００３〜０．０２５％
Ｎは、Ａｌと共にＡｌＮ析出物を形成して、焼入時の結晶粒粗大化を防止して、優れた靭性を達成するために重要な元素である。優れた靭性を達成するためにＮの含有量の下限を０．００３％とした。その下限は０．００４％であることが好ましい。また、Ｎの含有量の上限を０．０２５％とした。その上限は０．０１７％であることが好ましい。 N: 0.003 to 0.025%
N is an important element for forming an AlN precipitate together with Al to prevent crystal grain coarsening during quenching and achieving excellent toughness. In order to achieve excellent toughness, the lower limit of the N content was 0.003%. The lower limit is preferably 0.004%. Further, the upper limit of the N content was 0.025%. The upper limit is preferably 0.017%.

Ｍｏ＋０．５Ｗ：０．５〜３．０％
ＭｏとＷは、何れもＭ３Ｃ型炭化物、Ｍ６Ｃ型炭化物を形成するほか、Ｎｉ３Ｍｏ系金属間化合物などを形成し、析出強化に寄与する元素である。但し、これらの含有量が過剰であると、前記の炭化物などが過剰に生成し、靭性の低下を招くほか、熱処理後の変寸が大きくなる。そこで、Ｍｏ＋０．５×Ｗの式に当てはめた場合のＭｏとＷの合計含有量を０．５〜３．０％の範囲に定めた。Ｍｏ単独の含有量も、０．５〜３．０％の範囲が好ましい。また、Ｗ単独の含有量は、２．０％以下（０％を含む）であることが好ましい。即ち、Ｍｏが必須元素、Ｗが選択元素である。但し、Ｗ単独の含有量の下限は、０．０２％であることがより好ましい。また、Ｍｏ単独の含有量の下限は０．７％、上限は２．５％であることが更に好ましい。Ｗ単独の含有量の下限は０．０５％、上限は１．５％であることが更に好ましい。 Mo + 0.5W: 0.5-3.0%
Mo and W are elements that contribute to precipitation strengthening by forming M 3 C type carbides and M 6 C type carbides as well as forming Ni 3 Mo intermetallic compounds. However, if these contents are excessive, the above carbides and the like are excessively generated, resulting in a decrease in toughness, and a change in size after heat treatment becomes large. Therefore, the total content of Mo and W when applied to the formula of Mo + 0.5 × W is determined in the range of 0.5 to 3.0%. The content of Mo alone is also preferably in the range of 0.5 to 3.0%. The content of W alone is preferably 2.0% or less (including 0%). That is, Mo is an essential element and W is a selective element. However, the lower limit of the content of W alone is more preferably 0.02%. Further, the lower limit of the content of Mo alone is more preferably 0.7%, and the upper limit is more preferably 2.5%. More preferably, the lower limit of the content of W alone is 0.05%, and the upper limit is 1.5%.

Ｐ：０．０５％以下（０％を含まない）
Ｐは、溶解原料中に不可避的に存在する元素であり、靭性を阻害する元素である。そのため、Ｐの含有量の上限を０．０５％とした。その上限は、好ましくは０．０２％である。 P: 0.05% or less (excluding 0%)
P is an element that is unavoidably present in the melting raw material and is an element that inhibits toughness. Therefore, the upper limit of the P content is set to 0.05%. The upper limit is preferably 0.02%.

Ｓ：０．１％以下（０％を含まない）
Ｓは、被削性確保に有用な元素である。被削性確保の観点からはＳを、好ましくは０．００２％以上、より好ましくは０．００４％以上の含有量とすることが推奨される。しかし、その含有量が過剰であると溶接割れが発生する。そこでＳの含有量の上限を０．１％とした。Ｓの含有量の上限は、好ましくは０．０７％、より好ましくは０．０５％、更に好ましくは０．０２５％である。 S: 0.1% or less (excluding 0%)
S is an element useful for ensuring machinability. From the viewpoint of securing machinability, it is recommended that S is a content of preferably 0.002% or more, more preferably 0.004% or more. However, if the content is excessive, weld cracks occur. Therefore, the upper limit of the S content is set to 0.1%. The upper limit of the S content is preferably 0.07%, more preferably 0.05%, and still more preferably 0.025%.

Ｏ：０．００５％以下（０％を含まない）
Ｏは、溶鋼中に含まれる元素で、不可避的に鋼中に含まれる。Ｏの含有量が高いと、Ｓｉ、Ａｌなどと反応し、酸化物系の介在物を形成する。そのため、Ｏの含有量の上限を０．００５％とした。その上限は、好ましくは０．００３％、より好ましくは０．００２％である。 O: 0.005% or less (excluding 0%)
O is an element contained in molten steel and is inevitably contained in steel. When the content of O is high, it reacts with Si, Al, etc. to form oxide inclusions. Therefore, the upper limit of the O content is set to 0.005%. The upper limit is preferably 0.003%, more preferably 0.002%.

更に、本発明は、先に説明した各数式を満足することを必須要件としている。尚、各数式に示す［ ］は、各元素の含有量（質量％）を示す。   Furthermore, the present invention makes it essential to satisfy each mathematical formula described above. In addition, [] shown to each numerical formula shows content (mass%) of each element.

［Ｃ］×［Ｃｒ］≦４
上記数式は、粗大なＣｒ系炭化物の生成抑制を目的として設定した数式である。Ｃの含有量とＣｒの含有量の積が４を超えると、硬質皮膜の耐久性が低下するほか、熱処理後の変寸が大きくなる。尚、粗大なＣｒ系炭化物の生成抑制や、熱処理後の変寸抑制の観点からは、Ｃの含有量とＣｒの含有量の積は出来るだけ小さいことが好ましいが、ＣやＣｒの添加による上記作用を有効に発揮させることなども勘案すると、この積の下限は、概ね０．８であることが好ましい。 [C] × [Cr] ≦ 4
The above formula is a formula set for the purpose of suppressing the formation of coarse Cr-based carbides. When the product of the content of C and the content of Cr exceeds 4, the durability of the hard coating is reduced and the size after heat treatment is increased. In addition, from the viewpoint of suppressing the formation of coarse Cr-based carbides and suppressing the change in size after heat treatment, the product of the C content and the Cr content is preferably as small as possible, but the above-described addition of C and Cr In consideration of effectively exhibiting the action, the lower limit of this product is preferably approximately 0.8.

ＦＰ＝［Ｓｉ］／５＋［Ｃｒ］／５＋２×［Ｍｏ］＋［Ｗ］＋２×［Ｖ］＋１０×［Ａｌ］≦５．０
上記数式は、Ｓｉ、Ｃｒ、Ｍｏ、Ｗ、Ｖ、Ａｌといったフェライト生成元素の合計含有量をパラメータ化し規定した数式である。このパラメータ（ＦＰ）が、５．０より大きくなると、冷間金型用鋼の硬さと靭性のバランスが崩れると共に、切削加工仕上げ面精度も悪化する。このパラメータ（ＦＰ）は、４．８以下であることがより好ましい。 FP = [Si] / 5 + [Cr] / 5 + 2 × [Mo] + [W] + 2 × [V] + 10 × [Al] ≦ 5.0
The above mathematical formula is a mathematical formula defining and parameterizing the total content of ferrite-forming elements such as Si, Cr, Mo, W, V, and Al. If this parameter (FP) is larger than 5.0, the balance between hardness and toughness of the steel for cold mold is lost, and the accuracy of the finished surface of the machining work is also deteriorated. This parameter (FP) is more preferably 4.8 or less.

ＡＰ＝［Ｍｎ］＋３×（［Ｃｕ］＋［Ｎｉ］）≦２．５
上記数式は、Ｍｎ、Ｃｕ、Ｎｉといったオーステナイト生成元素の合計含有量をパラメータ化し規定した数式である。このパラメータ（ＡＰ）が、２．５より大きくなると、残留オーステナイトが多くなり、熱処理変寸量のばらつきが増大すると共に、切削時の工具寿命が短くなる。このパラメータ（ＡＰ）は、２．３以下であることがより好ましい。 AP = [Mn] + 3 × ([Cu] + [Ni]) ≦ 2.5
The above formula is a formula that defines and defines the total content of austenite-generating elements such as Mn, Cu, and Ni. When this parameter (AP) is larger than 2.5, the retained austenite increases, the variation in the heat treatment sizing amount increases, and the tool life during cutting decreases. This parameter (AP) is more preferably 2.3 or less.

本発明の冷間金型用鋼中の基本成分に関する要件は以上の通りである。残部は鉄及び不可避的不純物である。また、本発明では、他の特性改善を目的として、更に以下の選択成分を含有させても良い。   The requirements regarding the basic components in the cold mold steel of the present invention are as described above. The balance is iron and inevitable impurities. In the present invention, the following selective components may be further contained for the purpose of improving other characteristics.

Ｖ：０．５％以下（０％を含む）
Ｖは、ＶＣなどの炭化物を形成して硬さ向上に寄与するほか、ＨＡＺ軟化の抑制に有効な元素である。また、母材表面に、ガス窒化、塩溶窒化、プラズマ窒化などの窒化処理を施して拡散硬化層を形成する場合に、表面硬さの向上や硬化層深さの上昇に有効な元素である。このような作用を有効に発揮させるためには、Ｖの含有量は、概ね０．０５％以上添加することが好ましい。但し、その含有量が過剰であると、固溶Ｃ量が低下し、母相であるマルテンサイト組織の硬さ低下を招くほか、靭性が低下する。そこでＶの含有量の上限を０．５％とした。Ｖの含有量の上限は、好ましくは０．４％、より好ましくは０．３％である。 V: 0.5% or less (including 0%)
V is an element effective for suppressing HAZ softening, in addition to forming carbides such as VC and contributing to improvement in hardness. In addition, it is an effective element for improving the surface hardness and increasing the depth of the hardened layer when a diffusion hardened layer is formed on the surface of the base material by nitriding such as gas nitriding, salt nitriding, plasma nitriding, etc. . In order to effectively exhibit such an action, it is preferable to add approximately 0.05% or more of the V content. However, if the content is excessive, the amount of solute C is reduced, the hardness of the martensite structure that is the parent phase is reduced, and the toughness is reduced. Therefore, the upper limit of the V content is set to 0.5%. The upper limit of the V content is preferably 0.4%, more preferably 0.3%.

Ｔｉ、Ｚｒ、Ｈｆ、Ｔａ、Ｎｂからなる群から選択される少なくとも１種の元素：合計０．５％以下
これらの元素は、何れも窒化物形成元素であり、これら元素の窒化物及びＡｌＮの微細分散化に寄与し、その結果、結晶粒の粗大化を防止して靭性の向上に寄与する元素である。以上のような作用を有効に発揮させるため、概ね、Ｔｉを０．０１％以上、Ｚｒを０．０２％以上、Ｈｆを０．０４％以上、Ｔａを０．０４％以上、Ｎｂを０．０２％以上、含有させることが好ましい。但し、これらの合計含有量が過剰であると、固溶Ｃ量が低下してマルテンサイトの硬さ低下を招く。そこでこれらの元素の合計含有量を０．５％以下とした。これらの元素の合計含有量は、好ましくは０．４％以下、更に好ましくは０．３％以下である。尚、これらの元素は、単独で含有させても良く、２種以上を併せて含有させても良い。 At least one element selected from the group consisting of Ti, Zr, Hf, Ta, and Nb: 0.5% or less in total These elements are all nitride-forming elements, and nitrides of these elements and AlN It is an element that contributes to fine dispersion and, as a result, prevents coarsening of crystal grains and contributes to improvement of toughness. In order to effectively exhibit the above-described actions, in general, Ti is 0.01% or more, Zr is 0.02% or more, Hf is 0.04% or more, Ta is 0.04% or more, and Nb is 0.0. It is preferable to contain 02% or more. However, when these total contents are excessive, the amount of solid solution C falls and the hardness of a martensite falls. Therefore, the total content of these elements is set to 0.5% or less. The total content of these elements is preferably 0.4% or less, more preferably 0.3% or less. In addition, these elements may be contained alone or in combination of two or more.

Ｃｏ：１０％以下
Ｃｏは、Ｍｓ点を高め、残留オーステナイトの低減化に有効な元素であり、これにより硬さを向上させることができる。この作用を有効に発揮させるため、Ｃｏの含有量を、概ね、１％以上とすることが好ましい。但し、その含有量が過剰であると、コストなどの上昇を招くため、上限を１０％とした。Ｃｏの含有量の上限は、好ましくは５．５％である。 Co: 10% or less Co is an element that increases the Ms point and is effective in reducing retained austenite, and can thereby improve the hardness. In order to effectively exhibit this action, the Co content is preferably approximately 1% or more. However, if the content is excessive, the cost is increased, so the upper limit is made 10%. The upper limit of the Co content is preferably 5.5%.

以上記載した要件を満足した冷間金型用鋼を用いて、冷間プレス用金型が製造される。この冷間プレス用金型の製造方法の一例を説明すると、例えば、本発明の冷間金型用鋼を溶製後、熱間鍛造してから、焼鈍（例えば、約７００℃で７時間保持した後、約１７℃／ｈｒの平均冷却速度で約４００℃まで炉冷した後、放冷）を行って軟化した後、切削加工などによって所定の形状に粗加工を行ってから、９５０〜１１５０℃の温度で焼入処理し、更に４００〜５３０℃で焼戻処理を行って所望の硬さを付与することで、冷間プレス用金型を製造する。   A cold press die is manufactured using the cold die steel that satisfies the requirements described above. An example of the manufacturing method of this cold press mold will be described. For example, after the cold mold steel of the present invention is melted, it is hot forged and then annealed (for example, held at about 700 ° C. for 7 hours). Then, after furnace cooling to about 400 ° C. at an average cooling rate of about 17 ° C./hr, and then softening by performing cooling, rough processing into a predetermined shape by cutting or the like is performed, and then 950 to 1150. A die for cold pressing is manufactured by quenching at a temperature of ° C. and further tempering at 400 to 530 ° C. to give a desired hardness.

以下、実施例を挙げて本発明をより具体的に説明する。本実施例では、表１に記載した計２６種の成分組成の鋼種（Ｎｏ．１は、冷間金型用鋼として従来から用いられているＪＩＳ ＳＫＤ１１）を用い、真空誘導溶解炉で１５０ｋｇのインゴットを溶製した後、９００〜１１５０℃に加熱し、４０ｍｍＴ×７５ｍｍＷ×約２０００ｍｍＬの板を鍛造し、その後、約６０℃／ｈｒの平均冷却速度で徐冷を行った。１００℃以下の温度まで冷却した後、再び、約８５０℃の温度まで加熱し、約５０℃／ｈｒの平均冷却速度で徐冷を行った（焼鈍）。以上のようにして得られた焼鈍材を用いて、以下の種々の試験を行った。   Hereinafter, the present invention will be described more specifically with reference to examples. In this example, a total of 26 types of steel compositions described in Table 1 (No. 1 is JIS SKD11 conventionally used as a steel for cold molds) and 150 kg in a vacuum induction melting furnace are used. After melting the ingot, it was heated to 900 to 1150 ° C., a plate of 40 mmT × 75 mmW × about 2000 mmL was forged, and then gradually cooled at an average cooling rate of about 60 ° C./hr. After cooling to a temperature of 100 ° C. or lower, the mixture was again heated to a temperature of about 850 ° C. and gradually cooled at an average cooling rate of about 50 ° C./hr (annealing). The following various tests were conducted using the annealed material obtained as described above.

（１）最大硬さの測定
前記した焼鈍材から、２０ｍｍＴ×２０ｍｍＷ×１５ｍｍＬサイズの試験片を切り出して硬さ測定用試験片とし、この試験片に、「焼入処理：１０３０℃で１２０分間加熱→空冷→焼戻処理：４５０〜５２０℃で１８０分間保持→放冷」という熱処理を施した。焼戻温度を４５０〜５２０℃範囲内で変化させたときの硬さをビッカーズ硬度計（ＡＫＡＳＨＩ社製の規格ＡＶＫ、荷重５ｋｇ）で測定し、その最大硬さを調べた。本試験では、測定で得られた最大硬さが６５０ＨＶ以上のものを合格とした。その試験結果を表２に示す。 (1) Measurement of maximum hardness From the above-mentioned annealed material, a test piece of 20 mm T × 20 mm W × 15 mm L size was cut out to obtain a test piece for hardness measurement, and this test piece was subjected to “quenching treatment: heated at 1030 ° C. for 120 minutes. → Air cooling → Tempering treatment: Heat treatment at 450 to 520 ° C. for 180 minutes → cooling was performed. The hardness when the tempering temperature was changed within the range of 450 to 520 ° C. was measured with a Vickers hardness meter (standard AVK manufactured by AKASHI, load 5 kg), and the maximum hardness was examined. In this test, those having a maximum hardness of 650 HV or more obtained by measurement were regarded as acceptable. The test results are shown in Table 2.

（２）シャルピー衝撃値の測定（靭性の測定）
上記した焼鈍材に対し、「焼入処理：１０３０℃で１２０分間加熱→空冷→焼戻処理：４５０〜５２０℃で１８０分間保持→空冷または放冷」という熱処理を施した。次に、図２に示すような、１０ｍｍＲのＲノッチ部を有する試験片を切り出して靭性測定用試験片（シャルピー衝撃試験片）とした。この試験片を用いてシャルピー衝撃試験を実施し、室温での吸収エネルギー（シャルピー衝撃値）を測定した。シャルピー衝撃試験片は各の鋼種毎に３本ずつ採取し、これらの平均値をシャルピー衝撃値とした。本試験では、測定で得られたシャルピー衝撃値が２０Ｊ以上のものを合格とした。その試験結果を表２に示す。 (2) Measurement of Charpy impact value (measurement of toughness)
The above annealed material was subjected to a heat treatment of “quenching treatment: heating at 1030 ° C. for 120 minutes → air cooling → tempering treatment: holding at 450 to 520 ° C. for 180 minutes → air cooling or standing cooling”. Next, a test piece having an R notch portion of 10 mmR as shown in FIG. 2 was cut out to obtain a test piece for toughness measurement (Charpy impact test piece). A Charpy impact test was performed using this test piece, and the absorbed energy (Charpy impact value) at room temperature was measured. Three Charpy impact test specimens were collected for each steel type, and the average value of these specimens was taken as the Charpy impact value. In this test, a Charpy impact value obtained by measurement of 20 J or more was regarded as acceptable. The test results are shown in Table 2.

（３）切削仕上げ面粗さの調査
前記した焼鈍材を試験体とし、ボールエンドミルで仕上げ加工を行い、切削仕上げ面粗さを調べた。試験条件は以下の通りである。
機械：ＭＯＲＩ（ＢＴ４０、５．５ｋｗ）
工具：三菱 ＳＲＦＨ３０Ｓ３２Ｍ φ３０
チップ：三菱 ＳＲＦＴ３０ ＶＰ１０ＭＦ φ３０
突出長：１１８ｍｍ
切削方向：ダウンカット
切削速度：２５０ｍｍ／ｍｉｎ
送り速度：０．３１ｍｍ／ｒｅｖ
切込み：Ａｄ０．３ｍｍ、Ｒｄ０．７ｍｍ
切削油：なし（エアブロー）
加工距離：２５７．１ｍ (3) Investigation of cutting finish surface roughness The above-mentioned annealed material was used as a specimen, and finishing was performed with a ball end mill, and the cutting finish surface roughness was examined. The test conditions are as follows.
Machine: MORI (BT40, 5.5kw)
Tool: Mitsubishi SRFH30S32M φ30
Chip: Mitsubishi SRFT30 VP10MF φ30
Protrusion length: 118mm
Cutting direction: Down cut Cutting speed: 250 mm / min
Feeding speed: 0.31mm / rev
Cutting depth: Ad0.3mm, Rd0.7mm
Cutting oil: None (Air blow)
Processing distance: 257.1m

切削仕上げ面粗さＲａは、試験体の１０ｍｍの長さ範囲を５箇所調査して得られた値の平均値とした。本試験では、試験で得られた切削仕上げ面粗さＲａが０．４０ｍｍ以下のものを合格とした。その試験結果を表２に示す。   The cutting finish surface roughness Ra was an average value of values obtained by examining five 10 mm length ranges of the specimen. In this test, the cutting finish surface roughness Ra obtained by the test was 0.40 mm or less. The test results are shown in Table 2.

（４）切削工具寿命の判定
前記した焼鈍材を試験体とし、高送りカッタによる粗加工を行い、切削工具の寿命を調査した。試験条件は以下の通りである。
機械：ＯＫＫ（ＢＴ５０、７．５ｋｗ）
工具：三菱 ＡＪＸ１４８Ｒ５０３ＳＡ４２Ｓ φ５０
チップ：ＪＯＭＷ１４０５２０ＺＤＳＲ−ＦＴ ＶＰ１５ＴＦ
切削速度：１０ｍ／ｍｉｎ
送り量：１．０ｍｍ／ｒｅｖ
切込み：Ａｄ１ｍｍ、Ｒｄ３５ｍｍ
突出長：８０ｍｍ
切削油：なし（エアブロー）
寿命判定：工具摩耗、チッピング (4) Judgment of cutting tool life The above-mentioned annealed material was used as a test specimen, rough machining was performed with a high-feed cutter, and the cutting tool life was investigated. The test conditions are as follows.
Machine: OKK (BT50, 7.5kw)
Tool: Mitsubishi AJX148R503SA42S φ50
Chip: JOMW140520ZDSR-FT VP15TF
Cutting speed: 10 m / min
Feed amount: 1.0mm / rev
Cutting depth: Ad1mm, Rd35mm
Projection length: 80mm
Cutting oil: None (Air blow)
Life judgment: Tool wear, chipping

切削工具寿命は、ＪＩＳ ＳＫＤ１１を素材とした試験体（Ｎｏ．１）を用いて粗加工を行ったときの切削工具の寿命を「１」とした場合、各々の試験体を用いて粗加工を行ったときの切削工具の寿命が、ＳＫＤ１１を素材とした試験体（Ｎｏ．１）を用いて粗加工を行ったときの切削工具の寿命の何倍になるかで判定した。この判定値が４．０以上になるものを合格とした。その試験結果を表２に示す。   When the life of the cutting tool is “1” when roughing is performed using a specimen (No. 1) made of JIS SKD11 as a raw material, the cutting tool life is roughened using each specimen. The life of the cutting tool when performed was determined by how many times the life of the cutting tool when roughing was performed using a test body (No. 1) made of SKD11. The determination value of 4.0 or higher was regarded as acceptable. The test results are shown in Table 2.

（５）最大熱処理変寸量の測定
前記した焼鈍材から、４０ｍｍＴ×７５ｍｍＷ×１００ｍｍＬのブロックを、焼鈍材毎に６個ずつ切り出して最大熱処理変寸量測定用の試験体とし、この試験体に、図３に示すような条件で熱処理を施した。最大熱処理変寸量は、６個の試験体の熱処理前後の寸法変化量から求めた。試験体毎に直交する３方向（ｘ方向、ｙ方向、ｚ方向）の寸法変化量を夫々求め、得られた３方向×６個の絶対値のうち最大の数値を、最大熱処理変寸量とした。本試験では、この最大熱処理変寸量が０．０８以下のものを合格とした。その試験結果を表２に示す。 (5) Measurement of maximum heat treatment change amount From the above-mentioned annealed material, 6 blocks of 40 mm T × 75 mm W × 100 mm L are cut out for each anneal material to make a test piece for measuring the maximum heat treatment change amount. The heat treatment was performed under the conditions shown in FIG. The maximum heat treatment change amount was determined from the dimensional change amount before and after the heat treatment of six specimens. The amount of dimensional change in three directions (x direction, y direction, z direction) orthogonal to each specimen is obtained, and the maximum numerical value among the obtained three directions × 6 absolute values is the maximum heat treatment dimensional change amount. did. In this test, this maximum heat treatment dimension change amount was 0.08 or less. The test results are shown in Table 2.

Figure 2009167435
Figure 2009167435

Figure 2009167435
Figure 2009167435

表１及び表２に記載したように、各化学成分の含有量、Ｃの含有量とＣｒの含有量の積、フェライト生成元素からなるパラメータ、オーステナイト生成元素からなるパラメータの全てが本発明の要件を満足する発明例であるＮｏ．７〜９、１１、１５〜２０は、最大硬さ、シャルピー衝撃値、切削仕上げ面粗さ、切削工具寿命、最大熱処理変寸量の全てが合格判定基準の範囲内となった。これに対し、本発明の要件を１つでも満たさない比較例であるＮｏ．１〜６、１０、１２〜１４、２１〜２６は、合格判定基準を最低１つは外し、何らかの不具合を有している。   As described in Table 1 and Table 2, the contents of each chemical component, the product of the content of C and the content of Cr, the parameter composed of a ferrite-forming element, and the parameter composed of an austenite-forming element are all requirements of the present invention. No. which is an example of the invention satisfying 7-9, 11, 15-20, all of maximum hardness, Charpy impact value, cutting finish surface roughness, cutting tool life, and maximum heat treatment change amount were within the range of acceptance criteria. On the other hand, No. 1 which is a comparative example which does not satisfy even one requirement of the present invention. 1 to 6, 10, 12 to 14, 21 to 26 have at least one acceptance criterion and have some defects.

Ｎｏ．１〜６、１０、１２〜１４、２１〜２６の比較例は、前記した本発明の要件のうち、１つ或いは２つ以上の要件を外すことで、何らかの不具合を有しているが、前記に記載した要件毎に特徴のあるものを比較例とした。以下、本発明に規定した要件毎に該当する比較例を説明する。   No. The comparative examples 1 to 6, 10, 12 to 14, and 21 to 26 have some problems by removing one or more of the requirements of the present invention described above. A characteristic example for each requirement described in the above was used as a comparative example. Hereinafter, a comparative example corresponding to each requirement defined in the present invention will be described.

Ｃの含有量とＣｒの含有量が多過ぎる比較例がＮｏ．１とＮｏ．２、逆にＣの含有量とＣｒの含有量が少な過ぎる比較例がＮｏ．３とＮｏ．４である。これらの含有量が多過ぎる比較例、少な過ぎる比較例ともに、シャルピー衝撃値（靭性）、切削仕上げ面粗さ、切削工具寿命、最大熱処理変寸量の全て、或いは何れかで合格判定基準を外れた。   A comparative example in which the content of C and the content of Cr are excessive is No. 1 and No. 2, on the contrary, the comparative example in which the content of C and the content of Cr are too small is No. 3 and no. 4. Both the comparative examples with too much content and the comparative examples with too little content deviate from the acceptance criteria in all or any of Charpy impact value (toughness), cutting finish surface roughness, cutting tool life, maximum heat treatment dimension change amount. It was.

Ｓｉの含有量が多過ぎる比較例がＮｏ．２１、逆に少な過ぎる比較例がＮｏ．１である。特にその含有量が過剰であるＮｏ．２１では、靭性が大きく低下し、シャルピー衝撃値で合格判定基準を外れた。また、合格判定基準の範囲内ではあるが、熱処理後の変寸が比較的大きくなった。   The comparative example with too much Si content is No. 21, on the contrary, there are too few comparative examples. 1. In particular, No. whose content is excessive. In No. 21, the toughness was greatly reduced, and the Charpy impact value deviated from the acceptance criterion. Moreover, although it was within the range of the acceptance criterion, the size change after the heat treatment became relatively large.

Ｍｎの含有量が多過ぎる比較例がＮｏ．２２である。この比較例では、靭性が大きく低下し、シャルピー衝撃値で合格判定基準を外れた。更に、切削工具寿命、最大熱処理変寸量でも合格判定基準を外れている。   The comparative example with too much Mn content is No. 22. In this comparative example, the toughness was greatly lowered and the Charpy impact value deviated from the acceptance criterion. Furthermore, the cutting tool life and the maximum heat treatment size change are also outside the acceptance criteria.

Ａｌの含有量が多過ぎる比較例がＮｏ．１０、逆に少な過ぎる比較例がＮｏ．６である。Ａｌ含有量が多過ぎる比較例のＮｏ．１０では、ボールエンドミルで仕上げ加工をした際にむしれが発生し、切削仕上げ面精度が悪化した。また、少な過ぎる比較例のＮｏ．６では、シャルピー衝撃値で合格判定基準を外れた。   A comparative example with too much Al content is No. 10, on the contrary, there are too few comparative examples. 6. No. of comparative example having too much Al content. In No. 10, peeling occurred when finishing with a ball end mill, and the accuracy of the finished surface was deteriorated. In addition, the comparative example No. In 6, the Charpy impact value deviated from the acceptance criterion.

Ｃｕの含有量が多過ぎる比較例がＮｏ．２３、逆に少な過ぎる比較例がＮｏ．５である。その含有量が過剰であるＮｏ．２３では、靭性が低下し、シャルピー衝撃値で合格判定基準を外れた。更に、切削工具寿命、最大熱処理変寸量でも合格判定基準を外れている。一方、含有量が少な過ぎる比較例のＮｏ．５でも、シャルピー衝撃値、最大熱処理変寸量で合格判定基準を外れた。   The comparative example with too much Cu content is No. 23, on the contrary, there are too few comparative examples. 5. No. whose content is excessive. In No. 23, the toughness decreased and the Charpy impact value deviated from the acceptance criterion. Furthermore, the cutting tool life and the maximum heat treatment size change are also outside the acceptance criteria. On the other hand, the comparative example No. 5 also deviated from the acceptance criteria in terms of Charpy impact value and maximum heat treatment change.

Ｎｉの含有量が多過ぎる比較例がＮｏ．２３、逆に少な過ぎる比較例がＮｏ．１である。その含有量が過剰であるＮｏ．２３では、シャルピー衝撃値、最大熱処理変寸量で合格判定基準を外れた。また、切削工具寿命でも合格判定基準を外れている。   A comparative example with too much Ni content is No. 23, on the contrary, there are too few comparative examples. 1. No. whose content is excessive. In No. 23, the acceptance criterion was exceeded by the Charpy impact value and the maximum heat treatment change amount. Also, the cutting tool life is out of the acceptance criteria.

Ｍｏ＋０．５Ｗから求められる数値が小さ過ぎる比較例がＮｏ．２４であり、その数値が本発明の範囲内ではあるが、境界値である最大の３．０％にあたる事例がＮｏ．２５である。Ｎｏ．２４では、最大硬さとシャルピー衝撃値で合格判定基準を外れた。また、Ｎｏ．２５では、他の要件を外した影響はあるが、シャルピー衝撃値が低下している。   A comparative example in which the numerical value obtained from Mo + 0.5W is too small is No. 24, and the numerical value is within the range of the present invention, but the case corresponding to the maximum of 3.0% which is the boundary value is No. 24. 25. No. In 24, the maximum hardness and Charpy impact value deviated from the acceptance criteria. No. 25, the Charpy impact value is lowered, although there is an influence that other requirements are removed.

Ｖの含有量が多過ぎる比較例がＮｏ．２６である。この比較例のＮｏ．２６では、Ｖの含有量が過剰であったため、靭性が低下し、シャルピー衝撃値で合格判定基準を外れた。また、切削仕上げ面粗さでも合格判定基準を外れた。   A comparative example with too much V content is No. 26. No. of this comparative example. In No. 26, since the content of V was excessive, the toughness was lowered, and the acceptance criterion was deviated by the Charpy impact value. Moreover, the acceptance criteria were also out of the finished surface roughness.

Ｃの含有量とＣｒの含有量の積が多過ぎる比較例が、Ｎｏ．１とＮｏ．２である。Ｎｏ．１とＮｏ．２は、この影響で、切削工具の寿命が著しく短くなったと共に、熱処理後の変寸が大きくなった。   A comparative example in which the product of the content of C and the content of Cr is too large is No. 1 and No. 2. No. 1 and No. In No. 2, due to this influence, the life of the cutting tool was remarkably shortened and the size after heat treatment was increased.

Ｎの含有量が多過ぎる比較例がＮｏ．２７である。その結果、靭性が低下し、シャルピー衝撃値で合格判定基準を外れた。   A comparative example with too much N content is No. 27. As a result, the toughness decreased and the Charpy impact value deviated from the acceptance criterion.

フェライト生成元素からなるパラメータが大き過ぎる比較例が、Ｎｏ．１〜４とＮｏ．２５である。この影響で、これらの比較例では、靭性のバランスが崩れたり、切削加工仕上げ面精度が悪化したりしている。特にこの要件のみを外したＮｏ．２５では、靭性が大きく低下し、シャルピー衝撃値で合格判定基準を外れた。   A comparative example in which the parameter composed of a ferrite-forming element is too large is No. 1-4 and No.1. 25. Due to this influence, in these comparative examples, the balance of toughness is lost or the accuracy of the finished surface of the cutting work is deteriorated. In particular, no. In No. 25, the toughness was greatly reduced and the Charpy impact value deviated from the acceptance criterion.

オーステナイト生成元素からなるパラメータが大き過ぎる比較例が、Ｎｏ．２〜５、Ｎｏ．１２、１３、２２、２３である。この影響で、これらの比較例では、残留オーステナイトが多くなり、熱処理変寸量が増大すると共に、切削時の工具寿命が短くなっている。特にこの要件のみを外したＮｏ．１２とＮｏ．１３では、切削工具寿命と最大熱処理変寸量のみで合格判定基準を外れている。   A comparative example in which a parameter composed of an austenite-forming element is too large is No. 2-5, no. 12, 13, 22, and 23. Due to this influence, in these comparative examples, the amount of retained austenite increases, the amount of heat treatment change increases, and the tool life during cutting is shortened. In particular, no. 12 and no. No. 13 is out of the acceptance criteria only by the cutting tool life and the maximum heat treatment change amount.

Ｃｒ系炭化物によるＴｉＮ皮膜の損傷のメカニズムを示すもので、（ａ）は元の冷間プレス用金型を示す縦断面図、（ｂ）は冷間プレス用金型のＴｉＮ皮膜にクラックが発生した状態を示す縦断面図、（ｃ）はそのクラックが起点となってＴｉＮ皮膜に剥離が発生した状態を示す縦断面図である。This shows the mechanism of damage to the TiN film by Cr carbide, (a) is a longitudinal sectional view showing the original cold press mold, (b) is a crack in the TiN film of the cold press mold The longitudinal cross-sectional view which shows the state which carried out, (c) is a longitudinal cross-sectional view which shows the state which peeling generate | occur | produced in the TiN membrane | film | coat from the crack. 実施例のシャルピー衝撃値の測定で用いたシャルピー衝撃試験片を示す説明図である。It is explanatory drawing which shows the Charpy impact test piece used by the measurement of the Charpy impact value of an Example. 実施例最大熱処理変寸量の測定で用いた試験体に、熱処理を施す際の熱処理条件を示す説明図である。It is explanatory drawing which shows the heat processing conditions at the time of heat-processing to the test body used by the measurement of the Example maximum heat processing size change amount.

符号の説明Explanation of symbols

１…冷間金型用鋼
２…ＴｉＮ皮膜
３…Ｃｒ系炭化物
４…クラック DESCRIPTION OF SYMBOLS 1 ... Cold mold steel 2 ... TiN film 3 ... Cr type carbide 4 ... Crack

Claims (5)

質量％で、Ｃ：０．５〜０．７％、Ｃｒ：５．０〜７．０％、Ｓｉ：０．５〜２．０％、Ｍｎ：０．１〜２．０％、Ａｌ：０．００１〜０．０１０％、Ｃｕ：０．２５〜１．００％、Ｎｉ：０．２５〜１．００％、Ｎ：０．００３〜０．０２５％、Ｍｏ＋０．５×Ｗ：０．５〜３．０％、Ｐ：０．０５％以下（０％を含まない）、Ｓ：０．１％以下（０％を含まない）、Ｏ：０．００５％以下（０％を含まない）を含有し、残部が鉄及び不可避的不純物であって、
且つ、［Ｃ］×［Ｃｒ］≦４という要件を満足し、
更に、ＦＰ（フェライト生成元素からなるパラメータ）が、［Ｓｉ］／５＋［Ｃｒ］／５＋２×［Ｍｏ］＋［Ｗ］＋２×［Ｖ］＋１０×［Ａｌ］≦５．０という要件を満足し、
ＡＰ（オーステナイト生成元素からなるパラメータ）が、［Ｍｎ］＋３×（［Ｃｕ］＋［Ｎｉ］）≦２．５という要件を満足することを特徴とする冷間金型用鋼。
但し、上式で［ ］は、各元素の含有量（質量％）を示す。 In mass%, C: 0.5 to 0.7%, Cr: 5.0 to 7.0%, Si: 0.5 to 2.0%, Mn: 0.1 to 2.0%, Al: 0.001 to 0.010%, Cu: 0.25 to 1.00%, Ni: 0.25 to 1.00%, N: 0.003 to 0.025%, Mo + 0.5 × W: 0.00. 5 to 3.0%, P: 0.05% or less (not including 0%), S: 0.1% or less (not including 0%), O: 0.005% or less (not including 0%) ), The balance being iron and inevitable impurities,
And satisfies the requirement of [C] × [Cr] ≦ 4,
Further, the FP (parameter made of ferrite-forming elements) satisfies the requirement of [Si] / 5 + [Cr] / 5 + 2 × [Mo] + [W] + 2 × [V] + 10 × [Al] ≦ 5.0. ,
A cold mold steel characterized in that AP (a parameter composed of an austenite-forming element) satisfies the requirement of [Mn] + 3 × ([Cu] + [Ni]) ≦ 2.5.
However, in the above formula, [] indicates the content (% by mass) of each element. 更に、Ｖ：０．５％以下（０％を含む）を含有する請求項１記載の冷間金型用鋼。   Furthermore, the steel for cold molds of Claim 1 containing V: 0.5% or less (0% is included). 更に、Ｔｉ、Ｚｒ、Ｈｆ、Ｔａ、Ｎｂからなる群から選択される少なくとも１種の元素を、合計０．５％以下含有する請求項１または２記載の冷間金型用鋼。   The cold mold steel according to claim 1 or 2, further comprising a total of 0.5% or less of at least one element selected from the group consisting of Ti, Zr, Hf, Ta, and Nb. 更に、Ｃｏを１０％以下含有する請求項１乃至３のいずれかに記載の冷間金型用鋼。   The steel for cold mold according to any one of claims 1 to 3, further comprising 10% or less of Co. 請求項１乃至４のいずれかに記載の冷間金型用鋼を用いて得られる冷間プレス用金型。   A cold press die obtained by using the cold die steel according to any one of claims 1 to 4.
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