JP4392087B2 - Surface treatment method of die casting mold and die - Google Patents
Surface treatment method of die casting mold and die Download PDFInfo
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- JP4392087B2 JP4392087B2 JP30247099A JP30247099A JP4392087B2 JP 4392087 B2 JP4392087 B2 JP 4392087B2 JP 30247099 A JP30247099 A JP 30247099A JP 30247099 A JP30247099 A JP 30247099A JP 4392087 B2 JP4392087 B2 JP 4392087B2
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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
- 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
- C23C28/044—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 coatings specially adapted for cutting tools or wear applications
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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
- 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
- C23C28/048—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 with layers graded in composition or physical properties
Description
【０００１】
【発明の属する技術分野】
本発明は、たとえばマグネシウム合金のダイカスト部品を製造する際に使用するダイカスト用金型の表面処理方法およびその金型に関するものである。
なお、本発明は、チクソモールド法に用いられる金型にも応用することができ、さらにはアルミニウムおよびその合金のダイカスト部品成形用金型としても適用が可能である。
【０００２】
【従来の技術】
一般に、マグネシウム (Mg) は、実用金属として最も比重(1.74)が軽いにもかかわらず、アルミニウム (Al) に匹敵する強度を有するとともに、放熱性、振動減衰性、電磁シールド性にも優れるという特徴がある。また、ダイカスト部材として薄肉化ができるという利点があるため、電子デバイスなどを保護する筐体材料として実用化が進んでいる。
【０００３】
従来、Mgの溶湯を鋳造するダイカスト成形用金型材料としては、高温強度に優れたＳＤＫ６１材が用いられていた。しかし、この材料を用いた金型は、高温のMg溶湯の注入により、急激な昇温と急冷とが繰り返し行われる結果、溶湯との接触面に熱疲労性の亀裂が発生しやすく、使用回数が増すに従って、その亀裂が次第に成長し、製品に有害な傷や欠陥を生じさせる原因となっていた。
【０００４】
この対策として従来、金型の表面に、TiＮやTiAlＮの薄膜を形成する方法 (例えば、特開平７−２０４８２２号公報) や、自溶合金溶射皮膜を施工する方法 (特開平８−２３２０５８号公報) 等の表面処理技術が提案されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、上掲の各従来技術が提案している表面処理技術のうち、TiＮ薄膜の成形による表面処理技術は、無処理の金型に比較すると、耐久性に優れた金型表面の形成には役立つものの、そのTiＮ自体は耐熱性に乏しく、一方、TiAlＮについてはMg合金溶湯の鋳造特性 (湯流れ) に問題があるほか、皮膜寿命そのものにも改善の余地があった。
一方、自溶合金溶射皮膜を形成して表面処理する技術の場合、皮膜形成後に1000℃以上の温度に加熱する必要があるため、金型に歪みが発生したり、材質劣化を招く等の問題点があった。
【０００６】
そこで、本発明の目的は、金型表面への皮膜の密着性に優れるほか、耐熱性、耐熱衝撃性、耐熱疲労性、耐摩耗性、断熱性に優れる皮膜を厚膜成形することができ、しかも、鋳造特性 (湯流れ) を阻害することのない金型表面処理技術の確立と、ダイカスト用金型として好適な、いわゆる金型の形状安定性に優れる金型を提案することにある。
【０００７】
【課題を解決するための手段】
上掲の目的実現に向けた研究の中で、発明者らは、窒化物層と微細な結晶質Cr２O３粒子からなるCr２O３積層薄膜とを複合化したものを、金型表面に形成することが有効であるとの知見を得て、本発明を開発するに到った。
【０００８】
即ち、本発明は、鋼製金型の表面処理に当たり、金型表面を窒化処理し、次いで窒化物層を形成した金型表面にクロム含有処理液を被成したのち乾燥すると共に、さらに 480℃〜600 ℃の温度域で加熱焼成することにより、前記窒化物層の表面にCr２O３薄膜層を生成させて、窒化物層とCr２O３薄膜層とからなる複合皮膜を形成することを特徴とするダイカスト用金型の表面処理方法を提案する。
【０００９】
また、本発明は、溶融金属と接触する鋼製金型の表面が、下層の窒化物層と、上層のクロム含有処理液を被成したのち、乾燥し、加熱焼成して得られるＣｒ２Ｏ３薄膜層とからなる複合皮膜にて覆われていることを特徴とするダイカスト用金型を提案する。
【００１０】
なお、本発明において、上記Cr２O３薄膜層の形成に当たり、クロム含有処理液を被成したのち、乾燥と加熱焼成する操作を複数回繰り返すことによって、Cr２O３薄膜層を積層皮膜化させること、および、
上記クロム含有処理液として、無水クロム酸、クロム酸アンモニウムあるいは重クロム酸アンモニウムを用いること、
上記Cr２O３薄膜層は、微細な結晶質Cr２O３粒子からなる薄膜が複数層にわたって設けられた積層皮膜にて構成したものであること、
が好ましい。
【００１１】
【発明の実施の形態】
本発明について、Mg合金鋳造のためのダイカスト用金型の、とくに鋳造金属Mgあるいはその合金の溶湯と接する側の表面に、本発明に適合する複合皮膜を形成したダイカスト用金型に適用した例で、実施の形態とその作用について説明する。
例えば、Mg合金のダイカスト鋳造用金型として、ＳＫＤ６１で代表される熱間工具鋼でつくられた金型の表面、とくにMg合金溶湯と接触する側の面を、あらかじめ窒化処理を行うことにより、金属の窒化物層 (例えば、FeＮx 、AlＮx 、CrＮx 、TiＮなどの層) を形成して、硬化表面とする。この処理において採用する窒化法としては、ガス窒化法、イオン窒化法あるいは塩浴窒化法のいずれを用いてもよいが、かかる窒化物層の厚さは少なくとも３μｍ以上が必要であり、これより薄い層では後述の化学的処理法によって形成するCr２O３皮膜の効果が十分に発揮できないおそれがある。
【００１２】
次に、金型の窒化物層のその表面に対し、クロム含有処理液を塗布して被成した後、大気中で乾燥し、さらに電気炉によって 480℃〜600 ℃の温度域に保持して加熱を行う。この操作により、クロム含有処理液は蒸発、分解、酸化されて最終的には結晶質のCr２O３微粒子の集合体からなるCr２O３薄膜が生成残留する。
【００１３】
以下、この処理工程につき、さらに詳しく説明する。
即ち、かかるCr２O３の生成工程を見ると、
▲１▼ 水分の蒸発によるクロム含有処理液の濃縮、
▲２▼ 軟質で非晶質なCr２O３粒子の析出、
▲３▼ 硬質で微細な結晶質Cr２O３粒子への変化、
が起こっていると考えられる。
【００１４】
いま、クロム含有処理液を、無水クロム酸の水溶液とすると、上記▲１▼および▲２▼の段階で非常に強い酸化力を発揮して、金属窒化物の一部を酸化, 分解するため、窒化物はＮＯx となって揮散する。このため、上記窒化物層の表面は微細な凹凸を形造り、その凹部へ上記▲１▼または▲２▼の状態の処理液や軟質のCr２O３粒子が入り込み、両者は物理的に強固な結びつきとなるとともに、窒化処理を施さない金型表面に対する同じ処理工程と比較すると、はるかに厚膜のCr２O３層を形成することができるようになる。
例えば、ＳＫＤ６１の試験片を用い、一方をイオン窒化処理して窒化物層を形成し、その後、ボーメ比重1.6 のCrO３水溶液を用いて塗布と加熱・分解の操作を１２回繰り返すと、３〜７μｍ厚のCr２O３積層薄膜層を生成するが、窒化処理をしないＳＫＤ６１試験片の場合、このCr２O３薄膜層は僅かに0.7 〜0.8 μｍの厚みにしかすぎなかった。
【００１５】
図１は、このような方法で形成した本発明方法に適合するCr２O３薄膜層と比較例となるCr２O３薄膜層との断面を模式的に示したものである。ここで、１はＳＫＤ６１基材、２は窒素の拡散部 (固溶体) 、３は窒化物層 (FeＮx)、４はCr２O３薄膜層である。
本発明に適合する方法で形成したCr２O３薄膜は、外側から硬質で緻密なCr２O３薄膜−金属窒化物層−基質 (含窒素の固溶体) の順となっており、一種の複合皮膜となっていることがわかる。
【００１６】
なお、本発明方法において用いるクロム含有処理液としては、上記の無水クロム酸〔CrO３〕の他に、クロム酸アンモニウム〔(NH４)２CrO４〕、重クロム酸アンモニウム〔(NH４)２Cr２O７〕などを使用することができる。また、本発明においては、薬液の塗布に代えて、浸漬やスプレー処理によって被成する方法を適用することができる。
【００１７】
さて、このようにして形成したCr２O３薄膜層を形成してなる金型を、Mg合金溶湯をダイカスト鋳造金型に用いた場合、次に示すような利点がある。
▲１▼ 金型の溶湯と接する面に形成されたCr２O３薄膜層は、金属質に比較すると熱伝導性が低いため、金型に注入されたMg合金溶湯の冷却速度が遅くなり、良好な流動性を維持できることから、金型への馴染みがよく生産性の向上に寄与する。
▲２▼ また、かかるCr２O３薄膜層は、クロム含有処理液を加熱し分解させることによって生成させたものであるから、微細な結晶質Cr２O３粒子の集合体からなるものであり、その表面は非常に平滑であり、ダイカスト部材の表面が美麗に仕上がるという利点がある。
このような知見は、実際のダイカスト用金型に本発明方法を適用して形成したCr２O３薄膜層を実用に供した結果、判明したものである。
【００１８】
かかるCr２O３薄膜層に関しては、この薄膜が溶融Mg合金溶湯と接触した場合、熱力学的にはMgの方がCrより酸素との化学的親和力が大きいため、Cr２O３の皮膜はMgによって還元され、皮膜破壊が起こる筈である。ところが、本発明者らの研究によれば、平衡論的には一見成立しないように見えるCr２O３薄膜の有効性 (耐溶融金属性) も、速度論的に考察すると、場合によっては十分に耐えるものになることが判明した。即ち、かかるCr２O３薄膜を、480 ℃〜600 ℃の高温に加熱して十分に結晶化させておくと、ダイカスト成型時というのは鋳造すべき溶融Mg合金と金型との接触時間が短いため、反応速度論的には還元反応が起こりにくい条件下になるためと考えられる。
【００１９】
なお、本発明において、上記のCr２O３薄膜層は、窒化物層への上記クロム酸水溶液の塗布、乾燥、加熱焼成という一連の操作を複数回、好ましくは２〜１０回程度繰り返すことによって、薄膜を何層にもわたって積層し肥厚させた積層皮膜とすることが好ましく、かつこのようなCr２O３薄膜積層皮膜を上層とし、その下層に上記金属窒化物層が介在する複合皮膜になっていることが望ましい実施形態である。
【００２０】
また、上記窒化物層は、窒化処理によって金属窒化物の粒子が基材表面に拡散浸透した窒化物拡散部とその表面を覆う窒化物層とから形成されていることが望ましい。
【００２１】
【実施例】
実施例１
この実施例では、ＳＫＤ６１試験片 (寸法 幅５０ｍｍ×長１００ｍｍ×厚５ｍｍ) の表層部をイオン窒化し、３０μｍ厚の窒素拡散層と５μｍ厚の窒化物層を設けた基材を用い、その基材の５μｍ厚の窒化物層の表面にCr２O３薄膜を５μｍ厚に形成し、その後、大気中で７２０℃×１５分間の加熱を行って複合皮膜を形成した。その後、皮膜形成後の試験片を20℃の水中に投入し冷却した。そして、上記皮膜の加熱−冷却のサイクルを、１５回繰り返す熱衝撃試験を行った。その結果、外観的には全く異常は認められなかった。また、試験片を切断して、その断面を光学顕微鏡で観察しても皮膜は健全な状態を維持していた。
これに対し、Cr２O３皮膜を窒化処理をしないＳＫＤ６１試験片表面に形成したケース (比較例) では、局部的な剥離が発生した。また、特公昭55−14833 号公報で提案されている珪素粒子を含むCr２O３皮膜では、５０〜７０μｍの厚膜は形成できたものの、熱衝撃試験後には微細な割れの発生が認められた。
【００２２】
実施例２
実施例１の熱衝撃試験用の供試皮膜を用いて６３０℃に加熱したJIS H 5303規定のマグネシウム合金 (ＭＤＩＡ）浴中に１０秒間浸漬した後、これを引き上げて送風機によって１分間冷却する操作を１サイクルとし、１０サイクル繰返した。この結果、本発明法に従ってイオン窒化を施したＳＫＤ５１試験片上にCr２O３皮膜を形成したものは、１０サイクル後も健全な状態を示し、加熱−冷却の繰返しによる熱衝撃抵抗に対して優れた効果を示すとともに、マグネシウム合金による侵食に対しても優れた耐食性を示すことが認められた。
これに対し、窒化処理をしないＳＫＤ５１試験片上にCr２O３皮膜を形成した比較例の皮膜は、６サイクル後に微細な割れが発生するとともに、割れ部からマグネシウム合金が皮膜内部へ侵入し、ＳＫＤ５１基材と冶金反応を起こして固着成長して皮膜を底部から破損させる現象が認められた。
【００２３】
実施例３
本実施例は、ホットチャンバ方式によるパソコンボディの本体を、Mg合金 (JIS H 5303規定のＭＤＩＡ）を用いて製造する際、イオン窒化したＳＫＤ６１金型の表面に本発明法に従って形成した、窒化物層−Cr２O３薄膜層からなる複合皮膜を５μｍ厚に形成したものを供試した。その結果、従来品のイオン窒化処理のみのＳＫＤ６１金型では、Mg合金の冷却速度が速いため、金属溶湯の流れが不十分となり、生産性が低く、その上品質上でも板厚が不揃いになりやすいなどの問題があったのに対し、本発明に適合する表面処理金型は、保温効果に優れているため、溶湯の流れがよく、良好な品質を有する製品を効率よく生産することができた。
【００２４】
【発明の効果】
以上説明したように本発明によれば、鋼製金型基材の表面を窒化処理した後、その上に化学的な方法によってCr２O３薄膜を形成して複合皮膜としたものは、皮膜どうしの密着性が強固で厚く成膜することができる。その結果、窒化物層とCr２O３薄膜層との複合皮膜化によって、ダイカスト用金型の耐熱性、耐熱衝撃性、耐熱疲労性、耐摩耗性、断熱性を向上させることができると共に、たとえばマグネシウム合金の溶湯をダイカスト鋳造する場合にもその湯流れを良好に維持することができ、ひいては製品の品質および生産性の向上をはじめ生産コストの低減にも大きく貢献することができる。
【図面の簡単な説明】
【図１】本発明の方法によって鋼製基材の表面に形成した本発明に適合する窒化物層とCr２O３薄膜層とからなる複合皮膜の例と、比較例の皮膜とを模式的に示す断面図である。
【符号の説明】
１ 基材
２ 窒化物拡散部
３ 窒化物層
４ Cr２O３薄膜層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface treatment method of a die casting mold used when, for example, a magnesium alloy die casting part is manufactured, and the mold.
The present invention can also be applied to a mold used in the thixomold method, and can also be applied as a mold for die-casting parts of aluminum and its alloys.
[0002]
[Prior art]
In general, magnesium (Mg) has the strength equivalent to aluminum (Al), although it has the lightest specific gravity (1.74) as a practical metal, and has excellent heat dissipation, vibration damping, and electromagnetic shielding properties. There is. Moreover, since it has the advantage that it can be thinned as a die-cast member, it has been put into practical use as a housing material for protecting electronic devices and the like.
[0003]
Conventionally, as a die casting mold material for casting a molten Mg, an SDK61 material excellent in high-temperature strength has been used. However, molds using this material are subject to repeated rapid heating and quenching due to the injection of high-temperature molten Mg, and as a result, thermal fatigue cracks are likely to occur on the contact surface with the molten metal. As it increased, the cracks gradually grew, causing harmful scratches and defects in the product.
[0004]
Conventionally, as a countermeasure, a method of forming a thin film of TiN or TiAlN on the surface of a mold (for example, JP-A-7-204822) or a method of applying a self-fluxing alloy spray coating (JP-A-8-232058) ) And other surface treatment techniques have been proposed.
[0005]
[Problems to be solved by the invention]
However, among the surface treatment technologies proposed by the above-mentioned conventional technologies, the surface treatment technology by forming a TiN thin film is more suitable for forming a mold surface having superior durability compared to an untreated mold. Although useful, TiN itself has poor heat resistance. On the other hand, TiAlN has problems in casting characteristics (molten metal flow) of Mg alloy molten metal, and there is room for improvement in film life itself.
On the other hand, in the case of surface treatment by forming a self-fluxing alloy sprayed coating, it is necessary to heat it to a temperature of 1000 ° C or higher after forming the coating, which causes problems such as distortion in the mold and deterioration of the material. There was a point.
[0006]
Therefore, the object of the present invention is to form a film having excellent heat resistance, thermal shock resistance, heat fatigue resistance, wear resistance, and heat insulation, in addition to excellent adhesion of the film to the mold surface, In addition, the present invention is to establish a mold surface treatment technique that does not hinder casting characteristics (molten metal flow) and to propose a mold that is suitable as a die casting mold and that is excellent in so-called mold shape stability.
[0007]
[Means for Solving the Problems]
In the research for realizing the above-mentioned purpose, the inventors obtained a composite of a nitride layer and a Cr 2 O 3 laminated thin film composed of fine crystalline Cr 2 O 3 particles on the mold surface. The present invention has been developed with the knowledge that it is effective to form the film.
[0008]
That is, according to the present invention, the surface treatment of the steel mold is performed by nitriding the mold surface, and then applying a chromium-containing treatment solution on the mold surface on which the nitride layer is formed, followed by drying, and further at 480 ° C. Forming a composite film composed of a nitride layer and a Cr 2 O 3 thin film layer by forming a Cr 2 O 3 thin film layer on the surface of the nitride layer by heating and firing in a temperature range of ˜600 ° C. We propose a surface treatment method for die casting molds characterized by the following.
[0009]
Further, the present invention provides a Cr 2 O obtained by drying, heating and firing after forming the lower nitride layer and the upper chromium-containing treatment liquid on the surface of the steel mold in contact with the molten metal. A die casting mold characterized by being covered with a composite coating composed of three thin film layers is proposed.
[0010]
In the present invention, the Cr 2 O 3 thin film layer is formed into a laminated film by repeating the operations of drying and heating and firing a plurality of times after forming the chromium-containing treatment liquid in forming the Cr 2 O 3 thin film layer. Letting and
As the chromium-containing treatment liquid, using anhydrous chromic acid, ammonium chromate or ammonium dichromate,
The Cr 2 O 3 thin film layer is constituted by a laminated film in which a thin film composed of fine crystalline Cr 2 O 3 particles is provided over a plurality of layers,
Is preferred.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Example of the present invention applied to a die casting mold for casting a Mg alloy, particularly a die casting mold in which a composite film conforming to the present invention is formed on the surface in contact with the molten metal of the cast metal Mg or its alloy. The embodiment and its operation will now be described.
For example, by performing nitriding treatment in advance on the surface of a mold made of hot tool steel represented by SKD61, in particular, the surface in contact with the molten Mg alloy as a die for die casting of Mg alloy, A metal nitride layer (for example, a layer of FeNx, AlNx, CrNx, TiN, etc.) is formed to provide a hardened surface. As a nitriding method employed in this treatment, any of a gas nitriding method, an ion nitriding method, and a salt bath nitriding method may be used, but the thickness of the nitride layer is required to be at least 3 μm or thinner. In the layer, there is a possibility that the effect of the Cr 2 O 3 film formed by the chemical treatment method described later cannot be sufficiently exhibited.
[0012]
Next, a chromium-containing treatment solution is applied to the surface of the nitride layer of the mold and formed, then dried in the atmosphere, and further maintained in a temperature range of 480 ° C. to 600 ° C. by an electric furnace. Heat. By this operation, the chromium-containing treatment liquid is evaporated, decomposed, and oxidized, and finally a Cr 2 O 3 thin film composed of an aggregate of crystalline Cr 2 O 3 fine particles remains.
[0013]
Hereinafter, this processing step will be described in more detail.
That is, when looking at the production process of such Cr 2 O 3 ,
(1) Concentration of chromium-containing treatment liquid by evaporation of water,
(2) Precipitation of soft and amorphous Cr 2 O 3 particles,
(3) Changes to hard and fine crystalline Cr 2 O 3 particles
Seems to be happening.
[0014]
Now, if the chromium-containing treatment solution is an aqueous solution of chromic anhydride, it exerts a very strong oxidizing power in the above steps (1) and (2) to oxidize and decompose part of the metal nitride. The nitride is volatilized as NOx. For this reason, the surface of the nitride layer forms fine irregularities, and the treatment liquid in the state of (1) or (2) and soft Cr 2 O 3 particles enter the concave portions, and both are physically strong. As a result, a much thicker Cr 2 O 3 layer can be formed as compared with the same treatment process for the mold surface not subjected to nitriding.
For example, when a test piece of SKD61 is used, one of which is ion-nitrided to form a nitride layer, and then the coating, heating and decomposition operations are repeated 12 times using a CrO 3 aqueous solution having a Baume specific gravity of 1.6. In the case of the SKD61 test piece that produced a 7 μm thick Cr 2 O 3 laminated thin film layer but was not nitrided, this Cr 2 O 3 thin film layer was only 0.7 to 0.8 μm thick.
[0015]
Figure 1 is a cross section of such a as a comparative example with the present invention a method in a compatible Cr 2 O 3 thin film layer formed by the method Cr 2 O 3 thin film layer shows schematically. Here, 1 is an SKD61 base material, 2 is a nitrogen diffusion part (solid solution), 3 is a nitride layer (FeNx), and 4 is a Cr 2 O 3 thin film layer.
The Cr 2 O 3 thin film formed by the method suitable for the present invention is in the order of hard and dense Cr 2 O 3 thin film-metal nitride layer-substrate (solid solution containing nitrogen) from the outside. It turns out that it is a film.
[0016]
As the chromium-containing treatment solution used in the process of the present invention, in addition to the above chromic acid anhydride [CrO 3], ammonium chromic acid [(NH 4) 2 CrO 4], ammonium dichromate [(NH 4) 2 Cr 2 O 7 ] can be used. Moreover, in this invention, it can replace with application | coating of a chemical | medical solution, and can apply the method formed by immersion or a spray process.
[0017]
Now, when the mold formed by forming the Cr 2 O 3 thin film layer as described above is used in a die-casting mold with a molten Mg alloy, there are the following advantages.
(1) Since the Cr 2 O 3 thin film layer formed on the surface in contact with the molten metal of the mold has a lower thermal conductivity than the metal, the cooling rate of the molten Mg alloy injected into the mold is slow, Because it can maintain good fluidity, it is well-familiar with the mold and contributes to the improvement of productivity.
(2) Since the Cr 2 O 3 thin film layer is formed by heating and decomposing a chromium-containing treatment solution, it is composed of an aggregate of fine crystalline Cr 2 O 3 particles. The surface of the die casting member is very smooth and has an advantage that the surface of the die cast member is finished beautifully.
Such knowledge has been clarified as a result of practical use of a Cr 2 O 3 thin film layer formed by applying the method of the present invention to an actual die casting mold.
[0018]
With respect to such a Cr 2 O 3 thin film layer, if the thin film is in contact with molten Mg alloy melt, because who Mg is thermodynamically greater chemical affinity for oxygen than Cr, coating of Cr 2 O 3 is It should be reduced by Mg and film destruction should occur. However, according to the study by the present inventors, the effectiveness of the Cr 2 O 3 thin film that does not seem to hold at first glance in terms of equilibrium (molten metal resistance) is also sufficient depending on the case. It turned out to be able to withstand. That is, when such a Cr 2 O 3 thin film is heated to a high temperature of 480 ° C. to 600 ° C. and sufficiently crystallized, the contact time between the molten Mg alloy to be cast and the mold is the time of die casting. This is considered to be due to the fact that the reduction reaction is less likely to occur in terms of reaction kinetics.
[0019]
In the present invention, the Cr 2 O 3 thin film layer is formed by repeating a series of operations of applying the chromic acid aqueous solution to the nitride layer, drying, and heating and firing a plurality of times, preferably about 2 to 10 times. It is preferable to form a laminated film in which a thin film is laminated and thickened over several layers, and such a Cr 2 O 3 thin film laminated film is used as an upper layer and the metal nitride layer is interposed in the lower layer. It is a desirable embodiment to be.
[0020]
The nitride layer is preferably formed of a nitride diffusion portion in which metal nitride particles are diffused and permeated into the substrate surface by nitriding treatment, and a nitride layer covering the surface.
[0021]
【Example】
Example 1
In this example, a surface layer portion of an SKD61 test piece (dimensions 50 mm × length 100 mm × thickness 5 mm) is ion-nitrided, and a substrate provided with a 30 μm-thick nitrogen diffusion layer and a 5 μm-thick nitride layer is used. A Cr 2 O 3 thin film was formed to a thickness of 5 μm on the surface of the 5 μm thick nitride layer of the material, and then heated in the atmosphere at 720 ° C. for 15 minutes to form a composite film. Thereafter, the test piece after film formation was poured into water at 20 ° C. and cooled. And the thermal shock test which repeats the heating-cooling cycle of the said film | membrane 15 times was done. As a result, no abnormality was observed in appearance. Moreover, even if it cut | disconnected the test piece and observed the cross section with an optical microscope, the film | membrane was maintaining the healthy state.
On the other hand, in the case (comparative example) in which the Cr 2 O 3 film was formed on the surface of the SKD61 test piece that was not nitrided, local peeling occurred. In addition, in the Cr 2 O 3 coating containing silicon particles proposed in Japanese Patent Publication No. 55-14833, although a thick film of 50 to 70 μm could be formed, fine cracks were observed after the thermal shock test. It was.
[0022]
Example 2
The sample was immersed in a magnesium alloy (MDIA) bath specified in JIS H 5303 heated to 630 ° C. for 10 seconds using the test film for thermal shock test of Example 1, and then pulled up and cooled by a blower for 1 minute. Was 1 cycle and repeated 10 cycles. As a result, those formed with Cr 2 O 3 coating on a piece SKD51 test which has been subjected to ion nitriding in accordance with the present invention method, after 10 cycles showed even healthy state, heating - superior to thermal shock resistance due to cooling of repeated In addition to the above-mentioned effects, it was confirmed that the alloy exhibited excellent corrosion resistance against erosion by the magnesium alloy.
On the other hand, in the comparative example film in which the Cr 2 O 3 film was formed on the SKD51 test piece not subjected to nitriding treatment, fine cracks occurred after 6 cycles, and the magnesium alloy penetrated into the film from the cracked part, and SKD51 A phenomenon was observed in which the metallurgical reaction with the base material caused adhesion and growth to break the film from the bottom.
[0023]
Example 3
This example is a nitride formed on the surface of an ion nitrided SKD61 mold in accordance with the method of the present invention when the body of a personal computer body using a hot chamber method is manufactured using Mg alloy (MDIA defined in JIS H 5303). Layer-Cr 2 O 3 A thin film layer composed of a composite film having a thickness of 5 μm was used. As a result, in the conventional SKD61 mold only for ion nitriding treatment, the Mg alloy has a high cooling rate, so the flow of the molten metal is insufficient, the productivity is low, and the plate thickness is not uniform in terms of quality. While the surface treatment mold suitable for the present invention has an excellent heat retention effect, the molten metal flow is good and products with good quality can be produced efficiently. It was.
[0024]
【The invention's effect】
As described above, according to the present invention, after nitriding the surface of a steel mold base material, a Cr 2 O 3 thin film is formed thereon by a chemical method to form a composite film. The adhesion between each other is strong and the film can be formed thick. As a result, the composite film of the nitride layer and the Cr 2 O 3 thin film layer can improve the heat resistance, thermal shock resistance, thermal fatigue resistance, wear resistance, and heat insulation of the die casting mold, For example, even when a molten magnesium alloy is die-cast, the flow of the molten metal can be maintained well, and as a result, the quality and productivity of the product can be improved and the production cost can be greatly reduced.
[Brief description of the drawings]
FIG. 1 schematically shows an example of a composite film composed of a nitride layer conforming to the present invention formed on the surface of a steel substrate by the method of the present invention and a Cr 2 O 3 thin film layer, and a film of a comparative example. FIG.
[Explanation of symbols]
DESCRIPTION OF
Claims (5)
℃の温度域で加熱焼成することにより、前記窒化物層の表面にＣｒ２Ｏ３薄膜層を生成させて、窒化物層とＣｒ２Ｏ３薄膜層とからなる複合皮膜を形成することを特徴とするダイカスト用金型の表面処理方法。In the surface treatment of the steel mold, the mold surface is nitrided, and then the chromium-containing treatment liquid is formed on the mold surface on which the nitride layer is formed, and then dried, and further, 480 ° C. to 600 ° C.
A composite film composed of a nitride layer and a Cr 2 O 3 thin film layer is formed by heating and firing in a temperature range of ° C. to form a Cr 2 O 3 thin film layer on the surface of the nitride layer. A surface treatment method for a die casting mold.
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| JP30247099A JP4392087B2 (en) | 1999-10-25 | 1999-10-25 | Surface treatment method of die casting mold and die |
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| JP30247099A JP4392087B2 (en) | 1999-10-25 | 1999-10-25 | Surface treatment method of die casting mold and die |
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| CN109266998A (en) * | 2018-11-13 | 2019-01-25 | 河源佳祺金属塑胶科技有限公司 | A kind of metal die high temperature resistant processing method |
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| JP2008188608A (en) * | 2007-02-02 | 2008-08-21 | Daido Steel Co Ltd | Die for die-casting and its surface treating method |
| JP2009101385A (en) * | 2007-10-23 | 2009-05-14 | Daido Steel Co Ltd | Die casting die and its manufacturing method |
| JP6236031B2 (en) * | 2015-05-29 | 2017-11-22 | パーカー熱処理工業株式会社 | Die casting mold |
| CN108115109B (en) * | 2017-12-22 | 2021-09-07 | 西安交通大学 | Die-casting die for plastic metal ceramic laminated coating and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109266998A (en) * | 2018-11-13 | 2019-01-25 | 河源佳祺金属塑胶科技有限公司 | A kind of metal die high temperature resistant processing method |
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