JP4832790B2 - Steel member surface treatment method and steel member - Google Patents
Steel member surface treatment method and steel member Download PDFInfo
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本発明は鋼部材の表面処理方法並びに鋼部材および歯車に関し、特に、歯車等の動力伝達用転動部品、カムローラ、その他鋼部材に適用される鋼部材の表面処理方法並びに鋼部材および歯車に関する。 TECHNICAL FIELD The present invention relates to a steel member surface treatment method, a steel member, and a gear, and more particularly, to a steel member surface treatment method applied to a rolling member for power transmission such as a gear, a cam roller, and other steel members, and a steel member and a gear.
従来より、鋼部材（特に、歯車等の転動部品）においては、軟窒化／窒化処理（ガス軟窒化、イオン（プラズマ）軟窒化、ガス窒化、イオン（プラズマ）窒化を含む：以下、この明細書では「窒化処理」と総称する。）や浸炭処理が多用されている。このうち、窒化処理は、浸炭処理に比べ、処理温度が低く、焼き入れ処理がないため、熱処理変形が小さい等の特徴を有するので、高寸法精度を要求される用途に用いられている。窒化処理について、ガス軟窒化処理を例に説明すると、ガス軟窒化処理を鋼部材に施した場合、当該鋼部材の最表面に５〜３０μｍ程度の化合物層と呼ばれる窒化鉄層（Ｆｅ２−３Ｎ、Ｆｅ４Ｎ）と、その直下に窒素拡散層と呼ばれる窒素の拡散により硬さの高くなる層が形成される。 Conventionally, steel members (especially, rolling parts such as gears) include soft nitriding / nitriding (gas soft nitriding, ion (plasma) soft nitriding, gas nitriding, ion (plasma) nitriding: In the book, it is generally called “nitriding treatment”) and carburizing treatment is often used. Among these, the nitriding treatment has characteristics such as a low processing temperature and no quenching treatment compared to the carburizing treatment, and thus has a feature such as small heat treatment deformation, and is used for applications requiring high dimensional accuracy. As for nitriding treatment, gas soft nitriding treatment will be described as an example. When gas soft nitriding treatment is performed on a steel member, an iron nitride layer (Fe 2-3) called a compound layer of about 5 to 30 μm is formed on the outermost surface of the steel member. N, Fe 4 N), and a layer called “nitrogen diffusion layer” having a higher hardness due to diffusion of nitrogen is formed immediately below.
例えば、特許文献１に開示されている技術では、重量％でＣ；０．１８〜０．２３、Ｓｉ；０．１５〜０．３５、Ｍｎ；０．６０〜０．８５、Ｐ；０．０３以下、Ｓ；０．０３以下、Ｃｒ；０．９０〜１．２０、Ｍｏ；０．１５〜０．３０を含み、残余はＦｅ及び不純物からなる鋼に、ガス軟窒化処理を施すことにより、歯車の歯面に、厚さ２〜１２μｍのＮとＦｅの化合物を有する化合物層と、その下層に隣接して、前記鋼自体の硬度よりＨｖ５０以上の硬さを有する厚さ２００μｍ以上の窒素拡散層を形成している。 For example, in the technique disclosed in Patent Document 1, C: 0.18 to 0.23, Si; 0.15 to 0.35, Mn; 0.60 to 0.85, P; 03 or less, S; 0.03 or less, Cr; 0.90 to 1.20, Mo; 0.15 to 0.30, with the remainder being subjected to gas soft nitriding treatment on steel composed of Fe and impurities A compound layer having a compound of N and Fe having a thickness of 2 to 12 μm on the tooth surface of the gear, and a nitrogen having a thickness of 200 μm or more adjacent to the lower layer and having a hardness of Hv50 or more than the hardness of the steel itself A diffusion layer is formed.
このような窒化処理の施された鋼部材は、上述した窒素拡散層（化合物層直下の表面から深さ方向に形成される硬さの高い層）の硬さにより、繰り返し応力に対する疲労強度が確保される。
しかしながら、高負荷での使用環境では、鋼部材に次のような問題が生じる。 However, the following problems occur in the steel member in a use environment under a high load.
化合物層は窒素拡散層よりさらに硬さが高く、軽負荷の摺動部などでは耐摩耗性が向上するが、反面、脆いという性質を持つ。このため、例えば歯車のように転がり滑り運動をするような部品では、化合物層が剥離したり、摩耗したりするという問題が生じる。この化合物層の剥離や摩耗は、負荷が高くなるほどその程度は著しい。剥離や摩耗が生じると、本来高寸法精度であることが目的であるにも拘わらず、使用中に寸法精度の悪化を招いてしまう。例えば、歯車では、剥離や摩耗により本来の歯形形状が悪化（初期状態から噛み合い精度が悪化）してしまい、ギアノイズが大きくなり、ひいてはこの歯車を適用した車は、振動や騒音を招来することになる。このため、従来の窒化処理は、極軽負荷の鋼部材にしか使用できず、従来、浸炭部品が用いられているような高負荷の鋼部材には適用することができなかった。 The compound layer is even harder than the nitrogen diffusion layer, and wear resistance is improved in a lightly loaded sliding portion, but it is brittle. For this reason, for example, in a component that rolls and slides like a gear, there arises a problem that the compound layer peels off or wears. The degree of exfoliation and wear of the compound layer becomes more remarkable as the load increases. When peeling or wear occurs, the dimensional accuracy is deteriorated during use, although it is originally intended to have high dimensional accuracy. For example, with gears, the original tooth profile shape deteriorates due to peeling and wear (meshing accuracy deteriorates from the initial state), resulting in increased gear noise. As a result, a car using this gear causes vibration and noise. Become. For this reason, the conventional nitriding treatment can be used only for extremely light-load steel members, and cannot be applied to high-load steel members that conventionally use carburized parts.
また、一般的に疲労強度を高めるための手段として表面に圧縮残留応力を付加するためショットピーニングが用いられる。しかし、窒化処理の施された鋼部材では、最表面に脆い化合物層が存在するため、ショットピーニングが施されると、この化合物層にクラックや欠けが生じたり、化合物層が剥離したりする恐れがあった。そのため、窒素拡散層には有効なショットピーニングについても、従来の窒化処理が施された鋼部材には適用できないという問題があった。 In general, shot peening is used to add compressive residual stress to the surface as a means for increasing fatigue strength. However, a steel member subjected to nitriding treatment has a brittle compound layer on the outermost surface, and therefore, when shot peening is applied, there is a risk that the compound layer may be cracked or chipped or the compound layer may be peeled off. was there. For this reason, there is a problem that shot peening effective for the nitrogen diffusion layer cannot be applied to a steel member subjected to conventional nitriding treatment.
本発明は上記不具合に鑑みてなされたものであり、高負荷環境で使用される鋼部材の耐摩耗性、耐剥離性を高めることのできる鋼部材の表面処理方法並びに鋼部材および歯車を提供することを課題としている。 The present invention has been made in view of the above problems, and provides a steel member surface treatment method, a steel member, and a gear capable of improving the wear resistance and peel resistance of a steel member used in a high load environment. It is an issue.
上記課題を解決するために本発明は、ＣｒおよびＶを含有する合金鋼からなる鋼部材の表面処理方法において、当該鋼部材の最表面にＮとＦｅの化合物層を形成するとともに、該化合物層の下側にＣｒＮおよびＶＮが析出した窒素拡散層を形成する窒化処理と、濃度が５０容量％から１００容量％の範囲に設定された水素ガスと濃度が１０容量％から２０容量％までの範囲に設定された酸素とを択一的に含む脱窒ガス雰囲気中で、５００℃から６５０℃までの範囲の処理温度で前記化合物層の脱窒反応を生成することにより脱窒層を形成する脱窒処理とを鋼部材に施すことを特徴とする鋼部材の表面処理方法である。この態様では、窒化処理によって、製造過程にある鋼部材の最表面に化合物層が形成され、その下側には、ＣｒＮおよびＶＮが析出した窒素拡散層が形成される。この鋼部材に脱窒処理を施すことにより、化合物層に脱窒反応（窒化処理で生成したε−Ｆｅ2-3Ｎまたはγ’−Ｆｅ4Ｎよりなる化合物層からＮを奪う反応）が生成される。これにより、化合物層からＮが奪われるので、鋼部材の最表面は、硬さが高く、しかも、耐摩耗性、耐剥離性の高い脱窒層で構成されることになる。 In order to solve the above problems, the present invention provides a surface treatment method for a steel member made of alloy steel containing Cr and V , wherein a compound layer of N and Fe is formed on the outermost surface of the steel member, and the compound layer A nitriding treatment for forming a nitrogen diffusion layer in which CrN and VN are deposited on the lower side, a hydrogen gas whose concentration is set in the range of 50% to 100% by volume, and a concentration in the range of 10% to 20% by volume A denitrification layer is formed by generating a denitrification reaction of the compound layer at a treatment temperature in the range of 500 ° C. to 650 ° C. in a denitrification gas atmosphere that alternatively contains oxygen set to oxygen. A surface treatment method for a steel member, wherein the steel member is subjected to a nitriding treatment. In this embodiment, a compound layer is formed on the outermost surface of the steel member in the manufacturing process by nitriding, and a nitrogen diffusion layer in which CrN and VN are deposited is formed below the compound layer. By denitrifying this steel member, a denitrification reaction (reaction of depriving N from a compound layer made of ε-Fe 2-3 N or γ′-Fe 4 N generated by nitriding) is generated in the compound layer. Is done. Thereby, N is deprived from the compound layer, so that the outermost surface of the steel member is composed of a denitrification layer having high hardness and high wear resistance and peeling resistance.
また、脱窒ガスの処理温度を５００℃から６５０℃までの範囲とすることで、処理時間が長くなることなく、脱窒処理による表面部の強度低下を防止することができる。 Further, by setting the treatment temperature of the denitrification gas in the range from 500 ° C. to 650 ° C., it is possible to prevent the strength of the surface portion from being reduced by the denitrification treatment without increasing the treatment time.
好ましい態様において、前記窒化処理と前記脱窒処理とは、同一の炉内にて連続的に実行される。この態様では、窒化処理の後、直ちに脱窒処理に移行することができるので、効率的な処理を施すことが可能になる。 In a preferred embodiment, the nitriding treatment and the denitrifying treatment are continuously performed in the same furnace. In this aspect, since the denitrification process can be immediately performed after the nitriding process, an efficient process can be performed.
好ましい態様において、前記脱窒処理の後、ショットピーニングがさらに施される。この態様では、脱窒処理によって鋼部材の最表面に露出している脱窒層にショットピーニングが施されることになるので、剥離を来すことなく当該鋼部材表面部の脱窒層および窒素拡散層に圧縮残留応力が付加され、鋼部材の疲労強度を高めることが可能になる。 In a preferred embodiment, shot peening is further performed after the denitrification treatment. In this aspect, since the denitrification layer exposed on the outermost surface of the steel member is subjected to shot peening by the denitrification treatment, the denitrification layer and nitrogen on the surface of the steel member are not peeled off. Compressive residual stress is added to the diffusion layer, and the fatigue strength of the steel member can be increased.
好ましい態様において、前記脱窒処理の処理時間は、１時間から２時間である。
好ましい態様において、前記脱窒処理後の前記化合物層の厚さは０μｍである。
別の好ましい態様において、前記脱窒処理の温度は、５４０℃から６００℃までの範囲である。
本発明の別の態様は、上述した鋼部材の表面処理方法によって処理されたものであることを特徴とする鋼部材である。
かかる態様において、前記鋼部材は、動力伝達用の歯車である。
In a preferred embodiment, the treatment time for the denitrification treatment is 1 hour to 2 hours.
In a preferred embodiment, the thickness of the compound layer after the denitrification treatment is 0 μm.
In another preferred embodiment, the temperature of the denitrification treatment ranges from 540 ° C to 600 ° C.
Another aspect of the present invention is a steel member characterized by being processed by the above-described surface treatment method for a steel member.
In this aspect, the steel member is a power transmission gear .
また、さらに具体的には、上述した鋼部材の表面処理方法によって処理されたものであることを特徴とする動力伝達用の歯車である。 More specifically, the power transmission gear is characterized by being processed by the above-described surface treatment method for a steel member.
以上説明したように本発明によれば、脱窒処理によって生成された脱窒層で鋼部材の最表面が構成されるので、高負荷環境で使用される鋼部材の耐摩耗性、耐剥離性を高めることができるという顕著な効果を奏する。 As described above, according to the present invention, since the outermost surface of the steel member is constituted by the denitrification layer generated by the denitrification treatment, the wear resistance and the peel resistance of the steel member used in a high load environment. There is a remarkable effect that can be increased.
以下、添付図面を参照しながら、本発明の好ましい実施の形態について、説明する。 Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
図１は本発明の鋼部材の表面処理方法によって製造された歯車１の正面図であり、図２は同歯車表面の金属組織を示す模式図である。 FIG. 1 is a front view of a gear 1 manufactured by the surface treatment method for a steel member of the present invention, and FIG. 2 is a schematic view showing a metal structure on the surface of the gear.
図１および図２を参照して、歯車１は、本実施形態における鋼部材の一例であり、外周に歯１ａを有するはすば歯車である。この歯車１は、比較的負荷の高いトランスミッションで動力を伝達するためのものであり、その最表面には、脱窒層１１が形成され、脱窒層１１の下側（図２の右側）には、窒素拡散層１２が形成されている。 With reference to FIG. 1 and FIG. 2, the gear 1 is an example of the steel member in this embodiment, and is a helical gear which has the tooth | gear 1a on the outer periphery. The gear 1 is for transmitting power with a transmission having a relatively high load. A denitrification layer 11 is formed on the outermost surface of the gear 1 and is located below the denitrification layer 11 (on the right side in FIG. 2). The nitrogen diffusion layer 12 is formed.
次に、この歯車１の加工方法について説明する。 Next, a method for processing the gear 1 will be described.
まず、合金鋼、例えばＪＩＳ−ＳＣＭ４２０からなる材料を熱間鍛造、素材焼準、焼鈍、ブランク機械加工、歯切り／シェービングの順で加工し、図１で示す形状に仕上げた後、ガス軟窒化処理および脱窒処理を施すことにより、図２で示す金属組織を有する歯車１を製造することが可能になる。 First, alloy steel such as JIS-SCM420 is processed in the order of hot forging, material normalization, annealing, blank machining, gear cutting / shaving, and finished into the shape shown in FIG. By performing the treatment and the denitrification treatment, the gear 1 having the metal structure shown in FIG. 2 can be manufactured.
図３は本実施形態に係る処理温度と処理時間の関係を示すグラフである。 FIG. 3 is a graph showing the relationship between the processing temperature and the processing time according to the present embodiment.
図３を参照して、ガス軟窒化処理としては、図略の炉に、歯切り／シェービングまでが施された鋼部材を載置し、所定の処理温度を有する窒化処理ガス雰囲気中におくことにより行われる。 Referring to FIG. 3, as the gas soft nitriding treatment, a steel member subjected to gear cutting / shaving is placed in a furnace (not shown) and placed in a nitriding treatment gas atmosphere having a predetermined treatment temperature. Is done.
窒化処理ガスとしては、ＲＸガスまたはＮ2ガス中にＮＨ３ガスを１０容量％から９０容量％の範囲で添加したものが好適である。 As the nitriding gas, a gas obtained by adding NH 3 gas in RX gas or N 2 gas in a range of 10 volume% to 90 volume% is preferable.
窒化処理ガスの処理温度としては、５００℃から６５０℃までの範囲（図３の例では５８０℃）が好適である。 The processing temperature of the nitriding gas is preferably in the range from 500 ° C. to 650 ° C. (580 ° C. in the example of FIG. 3).
また、窒化処理の処理時間としては、２時間が好適である。 In addition, the processing time for the nitriding treatment is preferably 2 hours.
この窒化処理は、周知の方法と同様であり、歯車１に要求される強度特性を持たせるために必要な窒素拡散層深さが得られる条件で行われる。このガス軟窒化処理により、鋼部材の最表面には、化合物層が生成される。図の例では、トランスミッション用の歯車１であるから、窒素拡散層の深さは、１００μｍから３００μｍまでの範囲となるように、処理条件が設定される。 This nitriding treatment is the same as a known method, and is performed under the condition that a nitrogen diffusion layer depth necessary for giving the gear 1 the required strength characteristics can be obtained. By this gas soft nitriding treatment, a compound layer is formed on the outermost surface of the steel member. In the example of the figure, since the gear 1 is for transmission, the processing conditions are set so that the depth of the nitrogen diffusion layer is in the range from 100 μm to 300 μm.
化合物層は、窒化鉄Ｆｅ２−３Ｎ（ε相）やＦｅ４Ｎ（γ’−相）からなる。化合物層から内部の深さ方向へは、Ｎが拡散し、窒化物形成元素であるＣｒやＶと結びつき、窒化物（ＣｒＮやＶＮ）が析出する。化合物層より内部深さ方向で硬さが高くなるのは、この窒化物が基地に析出するためと考えられており、この硬さの高くなる層が、窒素拡散層と呼ばれている。 The compound layer is made of iron nitride Fe 2-3 N (ε phase) or Fe 4 N (γ′-phase). From the compound layer, N diffuses in the depth direction, and is combined with the nitride-forming elements Cr and V to precipitate nitrides (CrN and VN). The reason why the hardness is higher in the inner depth direction than the compound layer is thought to be because this nitride precipitates on the matrix, and the layer having the higher hardness is called a nitrogen diffusion layer.
ついで、窒化処理を行った炉の中で、引き続き、脱窒処理が施される。窒化処理を施した鋼部材の最表面には、窒化鉄ε−Ｆｅ２−３Ｎや、γ’−Ｆｅ４Ｎを成分とする化合物層が生成されている。この化合物層を除去するために、本実施形態では、ＲＸガスまたはＮ2ガス中にＨ2ガス（或いは、Ｈ2ガスに代えて、空気）を５０容量％から１００容量％までの範囲で添加した雰囲気を５００℃から６５０℃までの範囲（図３の例では同じく５８０℃）に制御して、約２時間脱窒処理を施すこととしている。 Next, denitrification treatment is subsequently performed in the furnace in which nitriding treatment has been performed. A compound layer containing iron nitride ε-Fe 2-3 N or γ′-Fe 4 N as a component is formed on the outermost surface of the steel member subjected to nitriding treatment. In order to remove this compound layer, in this embodiment, H 2 gas (or air instead of H 2 gas) is added in the range of 50% to 100% by volume in RX gas or N 2 gas. The controlled atmosphere is controlled to a range from 500 ° C. to 650 ° C. (same as 580 ° C. in the example of FIG. 3), and denitrification is performed for about 2 hours.
この脱窒処理は、鋼部材に要求される耐久性等に応じて、次のような条件範囲で行うことが望ましい。 This denitrification treatment is desirably performed in the following condition range according to the durability required for the steel member.
まず、処理温度としては、５００℃から６５０℃までの範囲が望ましい。特に、５４０℃から６００℃までの範囲が好適である。５００℃未満では、いわゆる脱窒反応（窒化処理で生成したε−Ｆｅ２−３Ｎまたはγ’−Ｆｅ４Ｎよりなる化合物層からＮを奪う反応）が遅くなり、長時間処理が必要となるため経済的ではないからである。他方、６５０℃を越えると、表面の窒素拡散層硬さの低下が著しくなり、また、素材の鋼の種類によっては、オーステナイト組織が生成されるため強度的な低下を招くからである。 First, the processing temperature is preferably in the range of 500 ° C. to 650 ° C. The range from 540 ° C. to 600 ° C. is particularly suitable. When the temperature is lower than 500 ° C., a so-called denitrification reaction (reaction of depriving N from a compound layer made of ε-Fe 2-3 N or γ′-Fe 4 N generated by nitriding treatment) becomes slow, and a long-time treatment is required. Because it is not economical. On the other hand, when the temperature exceeds 650 ° C., the hardness of the nitrogen diffusion layer on the surface is remarkably reduced, and depending on the type of steel as the material, an austenite structure is generated, resulting in a reduction in strength.
次に、脱窒ガスの成分としてＨ2ガスを使用する場合、Ｈ2ガス濃度を５０容量％から１００容量％の範囲に設定することが望ましい。Ｈ2ガス濃度が高いほど、上記脱窒反応は促進され、５０容量％未満では、脱窒反応が遅くなるため経済的ではないからである。Ｈ2ガスによる脱窒反応は次のように進行すると考えられる。 Next, when H 2 gas is used as a component of the denitrification gas, it is desirable to set the H 2 gas concentration in the range of 50% to 100% by volume. This is because the higher the H 2 gas concentration, the more the denitrification reaction is promoted. If the H 2 gas concentration is less than 50% by volume, the denitrification reaction becomes slow, which is not economical. It is considered that the denitrification reaction with H 2 gas proceeds as follows.
２ε−Ｆｅ３Ｎ＋３Ｈ2→６α−Ｆｅ＋２ＮＨ３または
２ε−Ｆｅ２Ｎ＋３Ｈ2→４α−Ｆｅ＋２ＮＨ３
２γ’−Ｆｅ４Ｎ＋３Ｈ2→８α−Ｆｅ＋２ＮＨ３
次に、脱窒ガスの成分として空気を使用する場合、空気の濃度を５０容量％から１００容量％の範囲に設定することが望ましい（空気中のＯ2濃度が１／５として、Ｏ2濃度：１０容量％から２０容量％までの範囲）。
2ε-Fe 3 N + 3H 2 → 6α-Fe + 2NH 3 or 2ε-Fe 2 N + 3H 2 → 4α-Fe + 2NH 3
2γ′-Fe 4 N + 3H 2 → 8α-Fe + 2NH 3
Next, when air is used as a component of the denitrification gas, it is desirable to set the air concentration in the range of 50% to 100% by volume (O 2 concentration in the air is 1/5, O 2 concentration : 10 volume% to 20 volume%).
空気濃度が高いほど、脱窒反応は促進され、５０容量％未満では、脱窒反応が遅くなるため経済的ではないからである。空気（Ｏ2ガス）による脱窒反応は次のように進行すると考えられる。 This is because the higher the air concentration is, the more the denitrification reaction is promoted. If the concentration is less than 50% by volume, the denitrification reaction is delayed, which is not economical. The denitrification reaction with air (O 2 gas) is considered to proceed as follows.
３ε−Ｆｅ３Ｎ＋３Ｏ2→９α−Ｆｅ＋３ＮＯ2または
２ε−Ｆｅ２Ｎ＋２Ｏ2→４α−Ｆｅ＋２ＮＯ2
４γ’−Ｆｅ４Ｎ＋４Ｏ2→１６α−Ｆｅ＋４ＮＯ2
空気を添加する場合には、火災の危険性を回避するために雰囲気は、ＲＸガスではなく、Ｎ2ガスを使用することが望ましい。また、脱窒反応をさらに促進させる目的で空気の代わりにＯ2ガスを添加してもよい。但し、Ｏ2ガスの濃度が２０容量％を越えると、鉄の酸化反応が進み、表面に鉄酸化物が増加する。その場合には、鋼部材の表面が脆化するため望ましくない。
3ε-Fe 3 N + 3O 2 → 9α-Fe + 3NO 2 or 2ε-Fe 2 N + 2O 2 → 4α-Fe + 2NO 2
4γ′-Fe 4 N + 4O 2 → 16α-Fe + 4NO 2
When adding air, it is desirable to use N 2 gas instead of RX gas as an atmosphere in order to avoid fire hazard. Further, O 2 gas may be added instead of air for the purpose of further promoting the denitrification reaction. However, if the concentration of O 2 gas exceeds 20% by volume, the iron oxidation reaction proceeds and iron oxide increases on the surface. In that case, the surface of the steel member becomes brittle, which is not desirable.
次に、脱窒処理の処理時間としては、窒化処理で生成された化合物層の厚さに応じて調整することが好ましい。上述したように窒化処理は、製造される鋼部材（本実施形態では歯車１）に要請される強度特性に応じて、必要な窒素拡散層深さが得られる条件で行われることから、窒化処理によって生成される化合物層についても、設定された窒化処理の処理条件に基づいて変化する。このため、脱窒処理の処理時間は、設定された窒化処理の処理条件に応じて、化合物層がほぼ完全に除去されるために必要充分な長さに設定される。尤も、化合物層がほぼ完全に除去される条件は、当該脱窒処理における処理温度やＨ2ガス濃度、Ｏ2ガス濃度にも左右されるので、これらの要因をも考慮して設定される。脱窒反応は、処理温度が高いほど、また、Ｈ2ガス濃度、Ｏ2ガス濃度が高いほど促進させるので、必要とされる処理時間は短くなる。 Next, it is preferable to adjust the treatment time of the denitrification treatment according to the thickness of the compound layer generated by the nitriding treatment. As described above, the nitriding treatment is performed under the condition that the necessary nitrogen diffusion layer depth is obtained according to the strength characteristics required for the steel member to be manufactured (the gear 1 in the present embodiment). The compound layer generated by the above also changes based on the set nitriding treatment conditions. For this reason, the treatment time of the denitrification treatment is set to a length that is necessary and sufficient for the compound layer to be almost completely removed according to the set treatment conditions of the nitriding treatment. However, the conditions under which the compound layer is almost completely removed depend on the processing temperature, H 2 gas concentration, and O 2 gas concentration in the denitrification process, and are set in consideration of these factors. Since the denitrification reaction is promoted as the treatment temperature is higher and the H 2 gas concentration and O 2 gas concentration are higher, the required treatment time is shortened.
さらに、本実施形態においては、定法により、脱窒処理後の鋼部材にショットピーニングが施される。 Furthermore, in this embodiment, shot peening is performed on the steel member after the denitrification treatment by a conventional method.
この処理によって、図１で示す歯車１が完成される。 By this process, the gear 1 shown in FIG. 1 is completed.
以上説明したように、本実施形態では、鋼部材の表面処理方法において、当該鋼部材の最表面にＮとＦｅの化合物層を形成するとともに、該化合物層の下側に窒素拡散層を形成する窒化処理と、所定の処理温度の脱窒ガス雰囲気中で、前記化合物層の脱窒反応を生成することにより脱窒層を形成する脱窒処理とを鋼部材に施すことを特徴とする鋼部材の表面処理方法である。このため本実施形態では、窒化処理によって、製造過程にある鋼部材の最表面に化合物層が形成され、その下側には、窒素拡散層が形成される。この鋼部材に脱窒処理を施すことにより、化合物層に脱窒反応が生成され、化合物層が除去されるので、鋼部材の最表面は、硬さが高く、しかも、耐摩耗性、耐剥離性の高い脱窒層１１で構成されることになる。 As described above, according to the present embodiment, in the surface treatment method for a steel member, a compound layer of N and Fe is formed on the outermost surface of the steel member, and a nitrogen diffusion layer is formed below the compound layer. A steel member characterized by performing a nitriding treatment and a denitrifying treatment for forming a denitrification layer by generating a denitrification reaction of the compound layer in a denitrification gas atmosphere at a predetermined treatment temperature. This is a surface treatment method. For this reason, in this embodiment, a compound layer is formed on the outermost surface of the steel member in the manufacturing process by nitriding, and a nitrogen diffusion layer is formed below the compound layer. By performing denitrification treatment on this steel member, a denitrification reaction is generated in the compound layer and the compound layer is removed. Therefore, the outermost surface of the steel member is high in hardness and wear resistance and delamination resistance. It is composed of a highly denitrifying layer 11.
本実施形態では、前記窒化処理と前記脱窒処理とは、同一の炉内にて連続的に実行される。このため本実施形態では、窒化処理の後、直ちに脱窒処理に移行することができるので、効率的な処理を施すことが可能になる。 In the present embodiment, the nitriding treatment and the denitrifying treatment are continuously performed in the same furnace. For this reason, in this embodiment, since it can transfer to a denitrification process immediately after a nitridation process, it becomes possible to perform an efficient process.
本実施形態では、前記脱窒処理の後、ショットピーニングがさらに施される。このため本実施形態では、脱窒処理によって鋼部材の最表面に露出している脱窒層にショットピーニングが施されることになるので、剥離を来すことなく当該鋼部材表面部の脱窒層および窒素拡散層に圧縮残留応力が付加され、鋼部材の疲労強度を高めることが可能になる。 In the present embodiment, shot peening is further performed after the denitrification treatment. For this reason, in this embodiment, shot peening is performed on the denitrification layer exposed on the outermost surface of the steel member by the denitrification treatment. A compressive residual stress is added to the layer and the nitrogen diffusion layer, and the fatigue strength of the steel member can be increased.
なお、上述した実施形態とは別に、窒化処理を施した鋼部材を一旦冷却した後、再度加熱して脱窒処理を施すようにしてもよい。 In addition to the above-described embodiment, the steel member subjected to nitriding treatment may be once cooled and then heated again to perform denitrification treatment.
以下に、図１の歯車１の具体的な実施例について説明する。 Below, the specific Example of the gearwheel 1 of FIG. 1 is described.
まず、歯車１の素材としては、表１に示すものを使用した。 First, as the material of the gear 1, those shown in Table 1 were used.
この表１の素材を熱間鍛造、素材焼準、焼鈍、ブランク機械加工、歯切り／シェービングの順で加工し、図１で示す形状に仕上げた。歯車１の諸元は、表２の通りとした。 The materials shown in Table 1 were processed in the order of hot forging, material normalization, annealing, blank machining, and gear cutting / shaving, and finished in the shape shown in FIG. The specifications of the gear 1 are as shown in Table 2.
次に、歯切り／シェービングが終了した鋼素材に窒化処理を施した。窒化処理の条件としては、窒素拡散層の深さが２００μｍとなるように、ＲＸガスとＮＨ３ガスとが５０容量％：５０容量％の雰囲気を５８０℃に昇温し、処理時間を２時間とした。この処理時間は、図３に示すように、処理温度が５８０℃に達してからカウントを開始した。 Next, nitriding treatment was applied to the steel material that had been subjected to gear cutting / shaving. As conditions for the nitriding treatment, an atmosphere of 50% by volume: 50% by volume of RX gas and NH 3 gas is heated to 580 ° C. so that the depth of the nitrogen diffusion layer is 200 μm, and the treatment time is 2 hours. It was. As shown in FIG. 3, the processing time was counted after the processing temperature reached 580 ° C.
図４はガス軟窒化処理を施した鋼素材の金属組織の顕微鏡写真である。 FIG. 4 is a photomicrograph of the metal structure of a steel material that has been subjected to gas soft nitriding.
図４を参照して、上述した条件でガス軟窒化処理を施した鋼素材の最表面（図の左側）には、白色で観察される１２μｍの化合物層が生成された。 Referring to FIG. 4, a 12 μm compound layer observed in white was formed on the outermost surface (left side of the figure) of the steel material subjected to the gas soft nitriding treatment under the above-described conditions.
次に、同一条件で窒化処理を行い、処理時間が２時間経過後に炉内への脱窒ガスを変更し、脱窒処理を引き続き行った。 Next, nitriding treatment was performed under the same conditions, and after the treatment time of 2 hours, the denitrification gas into the furnace was changed and the denitrification treatment was continued.
表３は、脱窒ガスとして、Ｈ2ガスを採用した場合の実施例１〜５と調査例１〜４の処理条件と処理後の化合物層の厚さを示すものである。 Table 3 shows the treatment conditions of Examples 1 to 5 and Investigation Examples 1 to 4 and the thickness of the compound layer after treatment when H 2 gas is used as the denitrification gas.
脱窒処理を施した結果、図５〜図８に示す金属組織が鋼部材の表面に生成された。各図において、図の左側が鋼部材の最表面である。 As a result of the denitrification treatment, a metal structure shown in FIGS. 5 to 8 was generated on the surface of the steel member. In each figure, the left side of the figure is the outermost surface of the steel member.
図５は、実施例１によって得られた金属組織の顕微鏡写真である。同図から明らかなように、処理温度が５８０℃の脱窒ガス（Ｈ2ガス濃度＝１００容量％）で処理時間を１時間とした場合、鋼部材の最表面に生成されていた化合物層は、黒色の脱窒層のみとなり、顕微鏡で確認する限り、化合物層は、認められなかった。実施例４、５に示すように、脱窒ガスのＨ2ガス濃度を減らした場合であっても、処理時間をそれに対応して長く設定することで同様の結果を得ることができた。 FIG. 5 is a photomicrograph of the metal structure obtained in Example 1. As is apparent from the figure, when the treatment temperature is 580 ° C. and the treatment time is 1 hour with a denitrification gas (H 2 gas concentration = 100% by volume), the compound layer produced on the outermost surface of the steel member is As a result, only a black denitrification layer was obtained, and no compound layer was observed as long as it was confirmed with a microscope. As shown in Examples 4 and 5, even when the H 2 gas concentration of the denitrification gas was reduced, the same result could be obtained by setting the treatment time to be longer correspondingly.
但し、調査例１〜４から明らかなように、処理時間が不十分な場合には、図６から図８に示すように、最表面に白色の化合物層が観察された。 However, as is clear from Investigation Examples 1 to 4, when the treatment time was insufficient, a white compound layer was observed on the outermost surface as shown in FIGS.
次に、表４は、脱窒ガスとして、空気を採用した場合の実施例６、７と調査例５、６である。 Next, Table 4 shows Examples 6 and 7 and Investigation Examples 5 and 6 when air is used as the denitrification gas.
この結果、図９、図１０に示す金属組織が鋼素材の表面に生成された。 As a result, the metal structures shown in FIGS. 9 and 10 were generated on the surface of the steel material.
図９は、実施例６によって得られた金属組織の顕微鏡写真である。同図から明らかなように、処理温度が５８０℃の脱窒ガス（空気濃度＝１００容量％）で処理時間を２時間とした場合においても、鋼部材の最表面に生成されていた化合物層は、黒色の脱窒層のみとなり、顕微鏡で確認する限り、化合物層は、認められなかった。実施例７に示すように、脱窒ガスの空気濃度を減らした場合であっても、処理時間が２時間の場合には同様の結果を得ることができた。 FIG. 9 is a photomicrograph of the metal structure obtained in Example 6. As is clear from the figure, even when the treatment temperature is 580 ° C. and the treatment time is 2 hours with a denitrification gas (air concentration = 100% by volume), the compound layer produced on the outermost surface of the steel member is As a result, only a black denitrification layer was obtained, and no compound layer was observed as long as it was confirmed with a microscope. As shown in Example 7, even when the air concentration of the denitrification gas was reduced, similar results could be obtained when the treatment time was 2 hours.
但し、調査例５、６から明らかなように、処理時間が不十分な場合には、図１０に示すように、最表面に白色の化合物層が観察された。 However, as apparent from Investigation Examples 5 and 6, when the treatment time was insufficient, a white compound layer was observed on the outermost surface as shown in FIG.
図１１は化合物層厚さと脱窒処理の処理条件との関係を示すグラフである。 FIG. 11 is a graph showing the relationship between the compound layer thickness and the denitrification treatment conditions.
図１１並びに各実施例１〜７、調査例１〜６から明らかなように、化合物層厚さは、脱窒ガス（処理中の雰囲気）の成分としてＨ2ガス、空気を採用した場合の何れであってもゼロにすることが可能であり、その効果は、Ｈ2ガスまたは空気の濃度が高いほど促進される。 As is clear from FIG. 11 and each of Examples 1 to 7 and Investigation Examples 1 to 6, the compound layer thickness is any when H 2 gas or air is used as a component of denitrification gas (atmosphere during treatment). However, it can be made zero, and the effect is promoted as the concentration of H 2 gas or air increases.
次に、実施例１、３、６並びに調査例１について行ったＸ線回析試験結果について説明する。 Next, the results of X-ray diffraction test performed on Examples 1, 3, 6 and Investigation Example 1 will be described.
図１２は、実施例１のＸ線回析結果を示すグラフ、図１３は、実施例３、６のＸ線回析結果を示すグラフ、図１４は調査例１について、駆動側歯面と非駆動側歯面におけるＸ線回析結果を示すグラフである。 FIG. 12 is a graph showing the X-ray diffraction results of Example 1, FIG. 13 is a graph showing the X-ray diffraction results of Examples 3 and 6, and FIG. It is a graph which shows the X-ray diffraction result in a drive side tooth surface.
図１２〜図１４を参照して、各実施例１、３、６並びに調査例１によって得られた鋼部材の表面をＸ線解析し、窒化鉄からなる化合物層が残存しているかどうかを調査した。 With reference to FIGS. 12-14, the surface of the steel member obtained by each of Examples 1, 3, 6 and Investigation Example 1 is subjected to X-ray analysis to investigate whether a compound layer made of iron nitride remains. did.
図１２を参照して、実施例１の場合、窒化鉄は検出されず、鉄が主成分の層であることが確認された。 Referring to FIG. 12, in the case of Example 1, iron nitride was not detected, and it was confirmed that iron was a main component layer.
また、図１３を参照して、実施例３においても、窒化鉄は殆ど検出されず、鉄が主成分の良好な層であることが確認された。 Referring to FIG. 13, in Example 3, iron nitride was hardly detected, and it was confirmed that iron was a good layer composed mainly of iron.
図１４を参照して、調査例１の場合には、僅かながら、窒化鉄が残存していることが確認され、脱窒反応が不十分であったことが確認された。 Referring to FIG. 14, in the case of Investigation Example 1, it was confirmed that iron nitride remained slightly, and it was confirmed that the denitrification reaction was insufficient.
次に、表５を参照して、ガス軟窒化処理の後に脱窒処理を施した歯車（実施例２）と、脱窒処理を施していないガス軟窒化処理のみの歯車（比較例１、２）とを比較した耐久テストの結果を示す。 Next, referring to Table 5, a gear that was subjected to denitrification after gas soft nitriding (Example 2) and a gear that was only subjected to gas soft nitriding that was not subjected to denitrification (Comparative Examples 1 and 2) The result of the endurance test comparing with) is shown.
表５に示すように、ガス軟窒化処理としては、何れもＲＸガス中にＮＨ３ガスを５０容量％添加した雰囲気中で、処理温度を５８０℃とし、処理時間を２時間として行った。 As shown in Table 5, the gas soft nitriding treatment was performed in an atmosphere in which 50% by volume of NH 3 gas was added to RX gas at a treatment temperature of 580 ° C. and a treatment time of 2 hours.
耐久テスト条件としては、エンジントルクを２１３Ｎ・ｍとし、エンジン回転数を３０００ｒｐｍとして、比較例１の駆動時間を１００時間、比較例２、実施例２の駆動時間を１８０時間とした。 As the durability test conditions, the engine torque was 213 N · m, the engine speed was 3000 rpm, the driving time of Comparative Example 1 was 100 hours, and the driving time of Comparative Example 2 and Example 2 was 180 hours.
図１５は表５の試験を行った試験材料の状態を示す斜視図であり、（Ａ）が比較例１、（Ｂ）が比較例２、（Ｃ）が実施例２の結果をそれぞれ示している。 FIG. 15 is a perspective view showing the state of the test material subjected to the test of Table 5, where (A) shows the results of Comparative Example 1, (B) shows the results of Comparative Example 2, and (C) shows the results of Example 2. Yes.
図１５（Ａ）を参照して、比較例１では、歯１ａの表面の一部で、化合物層が剥離し、白色状の傷２が生じる現象が見られた。化合物層の剥離は、テスト後の歯車の断面組織観察および歯形測定からも確認された。 Referring to FIG. 15A, in Comparative Example 1, a phenomenon was observed in which the compound layer was peeled off and a white scratch 2 was generated on a part of the surface of the tooth 1a. The peeling of the compound layer was also confirmed by observation of the cross-sectional structure of the gear after the test and measurement of the tooth profile.
また、図１５（Ｂ）を参照して、比較例２では、歯１ａの歯面３の外観が白色に変色していた。テスト後の歯車の断面組織観察から、表面の化合物層が歯面３全体にわたって剥離していることが確認された。また歯形測定から、歯元部に大きなへこみがあり、摩耗が進展していることが確認された。 15B, in Comparative Example 2, the appearance of the tooth surface 3 of the tooth 1a was changed to white. From the observation of the cross-sectional structure of the gear after the test, it was confirmed that the surface compound layer was peeled over the entire tooth surface 3. From the measurement of the tooth profile, it was confirmed that there was a large dent at the root of the tooth and that the wear was progressing.
これに対して実施例２の場合は、図１５（Ｃ）に示すように、外観からも損傷は全く見られず、断面組織観察や歯形測定からも、脱窒層の剥離や摩耗は皆無であった。 On the other hand, in the case of Example 2, as shown in FIG. 15C, no damage was observed from the appearance, and the denitrification layer was not peeled off or worn from the cross-sectional structure observation and the tooth profile measurement. there were.
次に、ショットピーニングを施した実施例の試験結果について説明する。 Next, the test result of the Example which performed shot peening is demonstrated.
実施例２の歯車と、脱窒処理を施していないガス軟窒化処理のみの歯車とに対し、それぞれ表６の条件でショットピーニングを施して、厚さの変化を調べた結果、表７並びに図１６で示す結果を得た。図１６はショットピーニング処理による表面層厚さの変化を示すグラフである。 Shot peening was performed on the gear of Example 2 and the gear of only gas soft nitriding treatment that was not subjected to denitrification treatment under the conditions of Table 6, and the change in thickness was examined. The result shown in 16 was obtained. FIG. 16 is a graph showing changes in surface layer thickness due to shot peening.
表７および図１６を参照して、比較例の場合、ショットピーニングの強さを高くするほど、化合物層の厚さが減少してくるのに対し、実施例の場合には、ショットピーニングの強さを高くしても、表面の脱窒層の厚さは、殆ど変化しなかった。この結果から、窒化処理のみの場合では、ショットピーニングにより化合物層にクラックや欠け、剥離が発生しており、非常に最表面が脆い性質を持つことがわかる。これに対して、実施例の場合には、剥離はもちろん、クラックや欠けも全く見られず、非常に靱性の高い特性を持つことがわかる。 Referring to Table 7 and FIG. 16, in the case of the comparative example, the thickness of the compound layer decreases as the shot peening strength increases, whereas in the example, the shot peening strength increases. Even when the thickness was increased, the thickness of the denitrification layer on the surface hardly changed. From this result, it can be seen that in the case of only the nitriding treatment, the compound layer is cracked, chipped or peeled off by shot peening, and the outermost surface has a brittle property. On the other hand, in the case of the example, it can be seen that not only peeling but also cracks and chips are not seen at all, and the characteristics are extremely tough.
図１７は、窒化処理後に脱窒処理を施した実施例２の歯車について、ショットピーニング（表６におけるＨＳＰ処理条件）前後の硬さ分布を示すグラフであり、図１８は、窒化処理後に脱窒処理を施した実施例２の歯車について、ショットピーニング前後の圧縮残留応力の分布を示すグラフである。 FIG. 17 is a graph showing the hardness distribution before and after shot peening (HSP treatment conditions in Table 6) for the gear of Example 2 subjected to denitrification after nitriding, and FIG. 18 shows denitrification after nitriding. It is a graph which shows distribution of the compression residual stress before and behind shot peening about the gear of Example 2 which performed processing.
図１７および図１８を参照して、ショットピーニングにより、歯車の表面部の硬さは向上し、圧縮残留応力も表面部で大幅に増大していることがわかる。 Referring to FIGS. 17 and 18, it is understood that the hardness of the surface portion of the gear is improved by shot peening, and the compressive residual stress is also greatly increased in the surface portion.
１ 歯車
１１ 脱窒層
１２ 窒素拡散層
1 Gear 11 Denitrification layer 12 Nitrogen diffusion layer
Claims (8)
当該鋼部材の最表面にＮとＦｅの化合物層を形成するとともに、該化合物層の下側にＣｒＮおよびＶＮが析出した窒素拡散層を形成する窒化処理と、
濃度が５０容量％から１００容量％の範囲に設定された水素ガスと濃度が１０容量％から２０容量％までの範囲に設定された酸素とを択一的に含む脱窒ガス雰囲気中で、５００℃から６５０℃までの範囲の処理温度で前記化合物層の脱窒反応を生成することにより脱窒層を形成する脱窒処理と
を鋼部材に施すことを特徴とする鋼部材の表面処理方法。 In the surface treatment method of a steel member made of an alloy steel containing Cr and V ,
A nitriding treatment in which a compound layer of N and Fe is formed on the outermost surface of the steel member, and a nitrogen diffusion layer in which CrN and VN are deposited is formed below the compound layer;
In a denitrification gas atmosphere that selectively contains hydrogen gas whose concentration is set in the range of 50% to 100% by volume and oxygen whose concentration is set in the range of 10% to 20% by volume. A surface treatment method for a steel member, comprising: subjecting the steel member to a denitrification treatment for forming a denitrification layer by generating a denitrification reaction of the compound layer at a treatment temperature in a range of from 650C to 650C.
前記窒化処理と前記脱窒処理とは、同一の炉内にて連続的に実行されることを特徴とする鋼部材の表面処理方法。 In the surface treatment method of the steel member according to claim 1,
The surface treatment method for a steel member, wherein the nitriding treatment and the denitrifying treatment are continuously performed in the same furnace.
前記脱窒処理の後、ショットピーニングがさらに施されることを特徴とする鋼部材の表面処理方法。 In the surface treatment method of the steel member according to claim 1 or 2 ,
A steel member surface treatment method, wherein shot peening is further performed after the denitrification treatment.
前記脱窒処理後の前記化合物層の厚さが０μｍであることを特徴とする鋼部材の表面処理方法。 In the surface treatment method of the steel member according to any one of claims 1 to 3,
A method for surface treatment of a steel member , wherein the thickness of the compound layer after the denitrification treatment is 0 μm .
前記脱窒処理の温度が５４０℃から６００℃までの範囲であることを特徴とする鋼部材の表面処理方法。 In the surface treatment method of the steel member according to any one of claims 1 to 4 ,
The method for surface treatment of a steel member, wherein a temperature of the denitrification treatment is in a range from 540 ° C to 600 ° C.
前記脱窒処理の処理時間は、１時間から２時間であるThe treatment time for the denitrification treatment is 1 to 2 hours.
ことを特徴とする鋼部材の表面処理方法。A method for surface treatment of a steel member.
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