JP2917810B2 - Carbonitrided steel with excellent surface delamination resistance - Google Patents
Carbonitrided steel with excellent surface delamination resistanceInfo
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- JP2917810B2 JP2917810B2 JP9177094A JP9177094A JP2917810B2 JP 2917810 B2 JP2917810 B2 JP 2917810B2 JP 9177094 A JP9177094 A JP 9177094A JP 9177094 A JP9177094 A JP 9177094A JP 2917810 B2 JP2917810 B2 JP 2917810B2
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Description
【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION
【０００１】[0001]
【産業上の利用分野】本発明は、歯車、シャフト、構造
材等として用いられ、高い疲労強度が要求される表面処
理鋼に関し、特に処理組織が優れた耐剥離特性を示す炭
窒化物層を有する炭素鋼、低合金鋼等の表面改質鋼に関
する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel used for gears, shafts, structural materials and the like, which is required to have a high fatigue strength. The present invention relates to surface-modified steel such as carbon steel and low-alloy steel.
【０００２】[0002]
【従来の技術】従来、高い疲労強度を必要とする歯車材
等に対する表面改質法として、機械加工後の浸炭焼入れ
または素材調質後の機械加工などの方法が、要求特性に
応じて適用されてきた。しかし、浸炭焼入れでは熱処理
歪が大きく、この方法は高い寸法精度を要求する部品に
は不向きである。素材調質では疲労強度が一般に低くな
りすぎ、この方法も必ずしも満足できるものではない。
このため、近年、窒化処理による表面改質の手法が注目
されるようになった。2. Description of the Related Art Conventionally, methods such as carburizing and quenching after machining or machining after material refining are applied according to required characteristics as a surface modification method for gear materials and the like that require high fatigue strength. Have been. However, heat treatment distortion is large in carburizing and quenching, and this method is not suitable for parts requiring high dimensional accuracy. In the case of material refining, the fatigue strength is generally too low, and this method is not always satisfactory.
For this reason, in recent years, a technique of surface modification by nitriding has been attracting attention.
【０００３】窒化処理材では、浸炭焼入れ材に比べて処
理温度が低いため歪が小さく、寸法精度向上が期待でき
るという利点がある〔例えば、日本金属学会会報、第31
巻、第４号(1992)、p. 339〜341 参照〕。[0003] Nitrided materials have the advantage of lower distortion and lower dimensional accuracy due to lower processing temperatures than carburized and quenched materials.
Vol. 4, No. 4 (1992), pp. 339-341].
【０００４】窒化処理法としては、アンモニアガスを用
いる窒化法、タフトライド法に代表される塩浴窒化法、
アンモニアガスと吸熱性ガスの混合ガスを用いるガス軟
窒化法、減圧下でのイオン窒化法（プラズマ窒化法）等
があり、それぞれの方法によって、また処理条件によっ
て、鋼の表面層に生成する窒化物の組織（結晶相の種
類）が異なる。図２に基づいてこの例を説明する。As the nitriding method, a nitriding method using ammonia gas, a salt bath nitriding method represented by a tuftride method,
There are a gas soft nitriding method using a mixed gas of ammonia gas and an endothermic gas, an ion nitriding method under reduced pressure (plasma nitriding method), and the like. The structure of the product (type of crystal phase) is different. This example will be described with reference to FIG.
【０００５】図２は一般的な窒化処理鋼の表面組織を模
式的に示す断面図である。一般には図示するように、最
表層に化合物層１（深さ方向にポーラス層２と緻密層３
からなる）が存在し、その次の層がマトリックスに窒素
が固溶した拡散層４と呼ばれるものとなる。緻密層３と
拡散層４との境界の拡散層４側には、図示するようにマ
トリックスの結晶粒界部５が存在し、結晶粒界部５の組
織は緻密層３と同様である。FIG. 2 is a sectional view schematically showing a surface structure of a general nitriding steel. Generally, as shown in the figure, the compound layer 1 (the porous layer 2 and the dense layer 3 in the depth direction)
And the next layer is called a diffusion layer 4 in which nitrogen is dissolved in the matrix. On the diffusion layer 4 side of the boundary between the dense layer 3 and the diffusion layer 4, a crystal grain boundary part 5 of a matrix exists as shown in the figure, and the structure of the crystal grain boundary part 5 is the same as that of the dense layer 3.
【０００６】生成する化合物層の最表層であるポーラス
層２は、通常、酸化物を含有しているといわれている。
耐剥離特性を維持する観点から、ポーラス層２の厚さは
化合物層１の厚さの1/3 以下であることが望ましいとさ
れ、これが現場的な良品判定基準となっている。It is said that the porous layer 2, which is the outermost layer of the resulting compound layer, usually contains an oxide.
From the viewpoint of maintaining the peel resistance, it is considered that the thickness of the porous layer 2 is preferably 1/3 or less of the thickness of the compound layer 1, which is the on-site non-defective criterion.
【０００７】結晶構造的には、化合物層１は、通常、
γ′相（Fez N 、ただし、z ≒４。以下、これをγ′−
Fez N 相と記す）とε相( Fen N 、n ＝２〜３）からな
る。このγ′−Fez N 相は、例えばイオン窒化反応にお
いて窒素ガスの混合比率が低いときに生成しやすいが、
炭素をほとんど固溶せず耐食性が悪い。これに対してε
相は炭素固溶型化合物であり、ε相に炭素を固溶させた
化合物相（以下、これを炭素固溶型ε相または炭素固溶
型ε−Fen (N,C) 相と記す。ただし、n はx 、mまたは
ｙ）にすると、γ′−Fez N 相に比べて耐食性が優れる
が、厚さが15〜20μｍ以上存在しないと耐食性改善の効
果はないとされる。[0007] In terms of crystal structure, the compound layer 1 usually comprises
γ ′ phase (Fe z N, where z ≒ 4. Hereinafter, this is referred to as γ′−
Fe z N phase) and ε phase (F n N, n = 2 to 3). This γ′-Fe z N phase is likely to be formed when the mixing ratio of nitrogen gas is low in, for example, an ion nitriding reaction,
It hardly dissolves carbon and has poor corrosion resistance. On the other hand, ε
The phase is a carbon solid solution type compound, and a compound phase in which carbon is dissolved in the ε phase (hereinafter, referred to as a carbon solid solution ε phase or a carbon solid solution ε-Fe n (N, C) phase). Here, n is x, when the m or y), but the corrosion resistance is excellent as compared with the γ'-Fe z n phase, the effect of improving the corrosion resistance when the thickness is not present or 15~20μm is not.
【０００８】γ′−Fez N 相は面心立方晶、ε相は稠密
六方晶であり、混相になると組織の境界において応力が
発生することからマイクロクラックが生じて脆化する。
このため、化合物層１がγ′−Fez N 相またはε相のい
ずれかの単相でなければ、機械的特性は良くならないと
いわれている〔鉄と鋼、第66年(1980)、第９号、p.1423
〜1434参照〕。[0008] γ'-Fe z N phase face centered cubic, the ε-phase is hexagonal close-packed crystal, microcracks embrittlement resulting from the stress is generated in the tissue boundary becomes mixed phase.
Therefore, if the compound layer 1 is not the one of single-phase γ'-Fe z N phase or ε phase, the mechanical properties are said not improved [Iron and Steel, 66 years (1980), the No. 9, p. 1423
To 1434].
【０００９】これらのことから、高い耐食性および機械
的特性を共に満足させるためには、炭素固溶型ε相が単
独で15μｍ以上の厚さの化合層１を形成していることが
望ましいと考えられる。From these facts, in order to satisfy both high corrosion resistance and mechanical properties, it is considered that it is desirable that the carbon solid solution type ε phase alone forms the compound layer 1 having a thickness of 15 μm or more. Can be
【００１０】しかし、炭素固溶型ε相中のFe成分も許容
範囲が広く、どの程度Fe成分を含む場合に上記の性能を
共に満足させ得るかに問題が残る。CrやAlを含む低合金
鋼などを対象とする炭窒化処理の場合には、それらの窒
化物や炭化物を含む化合物層も生成することになるが、
これらの許容度は不明である。さらに、ポーラス層２と
緻密層３の間で生じやすい剥離現象を低減させるのに必
要な化合物層１の形態に関しては、未だ明確になってい
ない。However, the Fe component in the carbon solid solution type ε phase also has a wide allowable range, and there remains a problem as to how much the Fe component is included to satisfy both of the above performances. In the case of carbonitriding for low alloy steel containing Cr or Al, a compound layer containing those nitrides or carbides will also be generated,
Their tolerance is unknown. Further, the form of the compound layer 1 necessary for reducing the peeling phenomenon that easily occurs between the porous layer 2 and the dense layer 3 has not yet been clarified.
【００１１】[0011]
【発明が解決しようとする課題】本発明の目的は、上記
の課題を解決し、高い機械的特性、特に耐剥離特性に優
れ、かつ高い耐食性を有する炭窒化物層で表面改質され
た鋼を提供することにある。SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a steel surface-modified with a carbonitride layer having high mechanical properties, particularly excellent exfoliation resistance, and high corrosion resistance. Is to provide.
【００１２】[0012]
【課題を解決するための手段】本発明は、次の表面の耐
剥離特性に優れた炭窒化処理鋼をその要旨とする。SUMMARY OF THE INVENTION The gist of the present invention is a carbonitrided steel having the following excellent surface peeling resistance.
【００１３】表面層がその深さ方向に化合物層（ポーラ
ス層及び緻密層）と拡散層とからなる炭窒化処理表面改
質鋼であって、化合物層の最表層部は下記の炭素固溶
型ε相を、化合物層の残部は下記の炭素固溶型ε相
を、化合物層と拡散層との境界部は下記の相を、それ
ぞれ主体とするものからなり、炭素固溶型ε相の格子定
数が深さ方向で連続的に減少していることを特徴とする
表面の耐剥離特性に優れた炭窒化処理鋼。The surface layer is a carbonitrided surface-modified steel comprising a compound layer (porous layer and dense layer) and a diffusion layer in the depth direction, and the outermost layer of the compound layer is a carbon solid solution type as described below. The ε phase, the remainder of the compound layer is composed of the following carbon solid solution type ε phase, and the boundary between the compound layer and the diffusion layer is composed mainly of the following phase, respectively. Carbonitrided steel with excellent surface delamination resistance, characterized in that the constant decreases continuously in the depth direction.
【００１４】Fex (N,C) 、ただし、x ＝ 2.1〜2.7 Fem (N,C) 、ただし、x ≦m ≦ y γ′相（Fez N 、ただし、z ≒４）を体積率で20％以
下で含む炭素固溶型ε相〔Fey (N,C) 、ただし、y ＝
2.8〜3.0 〕、またはこの炭素固溶型ε相とマトリック
ス相 ここでいう「主体とする」とは、他元素の窒化物および
炭化物の合計が体積率で10％以下で存在してもよいこ
と、またポーラス層中には従来の場合と同程度の酸化物
が存在してもよいこと、を意味する。Fe x (N, C), where x = 2.1 to 2.7 Fe m (N, C), where x ≦ m ≦ y γ ′ phase (Fe z N, zz4) Ε phase [Fe y (N, C), where y = 20% or less, where y =
2.8-3.0], or the carbon solid solution type ε phase and the matrix phase. The term “mainly included” as used herein means that the total of nitrides and carbides of other elements may be present in a volume fraction of 10% or less. This means that the same level of oxides as in the conventional case may be present in the porous layer.
【００１５】同じく「境界部」とは、層境界±５μｍの
範囲を意味する。「連続的」とは、Ｘ線回折による結晶
相同定の際の回折Ｘ線強度ピークが、表面層の深さ方向
で回折角２θの高角度側に連続的にシフトして行く状態
を基準とする連続である。Similarly, "boundary portion" means a range of a layer boundary ± 5 μm. “Continuous” refers to a state where the diffraction X-ray intensity peak at the time of identifying the crystal phase by X-ray diffraction continuously shifts toward the high angle side of the diffraction angle 2θ in the depth direction of the surface layer. It is continuous.
【００１６】[0016]
【作用】本発明の炭窒化処理鋼の表面構造を前記のよう
に定めた理由を説明する。The reason why the surface structure of the carbonitrided steel of the present invention is determined as described above will be described.
【００１７】1. 化合物層の最表層部 化合物層の最表層部、すなわち、ポーラス層の表面層
は、炭素固溶型ε−Fex(N,C) 相を主体とするものから
なる層であり、x の範囲は 2.1〜2.7 でなければならな
い。1. The outermost layer of the compound layer The outermost layer of the compound layer, that is, the surface layer of the porous layer is a layer mainly composed of a carbon solid solution type ε-Fe x (N, C) phase. And the range of x must be between 2.1 and 2.7.
【００１８】ε相に炭素を積極的に固溶させた炭素固溶
型ε相は高い耐食性を有する。炭窒化処理鋼の表面層の
耐食性を向上させるため、ポーラス層は炭素固溶型ε相
主体のものとした。The carbon-dissolved ε-phase in which carbon is positively dissolved in the ε-phase has high corrosion resistance. In order to improve the corrosion resistance of the surface layer of the carbonitrided steel, the porous layer was mainly made of a carbon solid solution ε phase.
【００１９】しかし、炭素固溶型ε相のFe含有比率の範
囲は広く、すべての場合に良好な耐食性および耐剥離特
性を示すものではない。耐食性および耐剥離特性をさら
に向上させるには、Fe成分比率、すなわちε−Fex (N,
C) 相中のx の範囲を明確に定める必要がある。However, the range of the Fe content ratio of the carbon solid solution type ε phase is wide, and does not show good corrosion resistance and peeling resistance in all cases. In order to further improve the corrosion resistance and peeling resistance, the Fe component ratio, that is, ε-Fe x (N,
C) The range of x in a phase needs to be clearly defined.
【００２０】高耐食性および高耐剥離特性を得る観点か
らは、ポーラス層でのFe成分比率は低いことが必要であ
る。x が2.1 未満ではこれらの特性の向上効果が少な
い。一方、x が2.7 を超えると耐食性が劣化する。x の
範囲 2.1〜2.7 は、炭素固溶型ε相中において、Feが原
子比率で67.7％から73.0％の範囲で存在することを意味
する。From the viewpoint of obtaining high corrosion resistance and high peeling resistance, it is necessary that the Fe component ratio in the porous layer is low. When x is less than 2.1, the effect of improving these characteristics is small. On the other hand, when x exceeds 2.7, the corrosion resistance deteriorates. The range of 2.1 to 2.7 of x means that Fe is present in the carbon solid solution type ε phase in an atomic ratio of 67.7% to 73.0%.
【００２１】この場合の炭素固溶型ε相中の炭素濃度
は、鋼の成分や処理時の汚染などによって不可避的に含
有される場合も含め、この結晶相の安定性の面から、原
子比率でＣ／（Ｃ＋Ｎ）が0.5 以下であることが望まし
い。なお、ポーラス層中には従来の窒化処理鋼の場合と
同程度の酸化物は存在してもよい。In this case, the carbon concentration in the carbon-dissolved ε phase is determined from the viewpoint of the stability of the crystal phase, including the case where it is inevitably contained due to the composition of steel and contamination during processing. And C / (C + N) is desirably 0.5 or less. In the porous layer, an oxide of the same degree as that of the conventional nitrided steel may be present.
【００２２】2. 化合物層の残部およびポーラス層と緻
密層との境界部 表面層の剥離はポーラス層と緻密層との境界部で最も発
生しやすい。ここで急激にFe成分比率が増加方向に変化
すると、境界部でマイクロクラックの発生が助長される
ため、耐剥離特性が劣化する。このため、化合物層の残
部およびポーラス層と緻密層との境界部（層境界±５μ
ｍの範囲）におけるFe成分比率の増加（炭素固溶型ε相
の格子定数の減少）変化は、ポーラス層の表層部から緻
密層へと連続的に続くものでなければならない。さら
に、緻密層中のFe成分比率は、緻密層と拡散層との境界
部に向かって深さ方向に増加させ、高い耐剥離特性を維
持させる必要がある。2. The remainder of the compound layer and the boundary between the porous layer and the dense layer The separation of the surface layer is most likely to occur at the boundary between the porous layer and the dense layer. Here, if the Fe component ratio suddenly changes in the increasing direction, the generation of microcracks at the boundary portion is promoted, so that the peeling resistance is deteriorated. Therefore, the remainder of the compound layer and the boundary between the porous layer and the dense layer (layer boundary ± 5 μm)
The change in the Fe component ratio (decrease in the lattice constant of the carbon-dissolved ε phase) within the range of m) must be continuous from the surface layer of the porous layer to the dense layer. Further, it is necessary to increase the Fe component ratio in the dense layer in the depth direction toward the boundary between the dense layer and the diffusion layer, and to maintain high peel resistance.
【００２３】この理由で、化合物層の残部は炭素固溶型
ε相〔Fem (N,C) 、ただし、x ≦m≦ y〕を主体とする
ものからなるとした。x は前述の数値であり、y は後述
する化合物層と拡散層との境界部の場合の数値である。For this reason, the remainder of the compound layer is assumed to consist mainly of a carbon solid solution type ε phase [Fe m (N, C), where x ≦ m ≦ y]. x is the numerical value described above, and y is a numerical value in the case of a boundary portion between a compound layer and a diffusion layer described later.
【００２４】この結果、ポーラス層と緻密層とからなる
化合物層中のFe成分比率が連続的に増加し、化合物層中
の炭素固溶型ε相の格子定数は、連続的に減少したもの
となる。このため、化合物層全体の耐剥離特性が向上す
る。As a result, the Fe component ratio in the compound layer composed of the porous layer and the dense layer continuously increased, and the lattice constant of the carbon solid solution type ε phase in the compound layer decreased continuously. Become. For this reason, the peel resistance of the entire compound layer is improved.
【００２５】3. 化合物層と拡散層との境界部 この境界部（層境界±５μｍの範囲）の組織相は、炭素
固溶型ε−Fey (N,C)相（ただし、y ＝ 2.8〜3.0 ）、
またはこの炭素固溶型ε−Fey (N,C) 相とマトリックス
相とを主体とするものからなる。すなわち、層境界から
５μｍ拡散層側に入った範囲（層境界＋５μｍ）では、
図２に示すようにマトリックス相の結晶粒界が存在し、
上記の境界部の定義ではマトリックス相の結晶粒部を一
部含む場合もあり得る。ただし、この炭素固溶型ε相
は、γ′−Fez N 相（ただし、z ≒４）を、このε相お
よびマトリックス相の総和に対する体積率で20％以下で
含むものである。3. Boundary between Compound Layer and Diffusion Layer The texture phase at this boundary (layer boundary ± 5 μm) is a carbon solid solution ε-Fe y (N, C) phase (where y = 2.8 ~ 3.0),
Alternatively, it is composed mainly of the carbon solid solution type ε-Fe y (N, C) phase and the matrix phase. That is, in the range (layer boundary +5 μm) within the diffusion layer side of 5 μm from the layer boundary,
As shown in FIG. 2, there are crystal grain boundaries of the matrix phase,
The above definition of the boundary portion may include a part of the crystal grains of the matrix phase. However, the carbon solid solution type ε phase, γ'-Fe z N phase (where z ≒ 4), and those containing 20% or less by volume to the total of the ε-phase and the matrix phase.
【００２６】すなわち、この炭素固溶型ε相のy の範囲
2.8〜3.0 は、Feが原子比率で73.7％から75.0％の範囲
で存在することを意味する。y が2.8 未満では、耐剥離
特性の向上効果が少ない。一方、y が3.0 を超えると、
耐剥離特性の向上効果が飽和する。That is, the range of y of the carbon solid solution type ε phase
2.8 to 3.0 means that Fe is present in an atomic ratio of 73.7% to 75.0%. When y is less than 2.8, the effect of improving the peel resistance is small. On the other hand, if y exceeds 3.0,
The effect of improving the peel resistance is saturated.
【００２７】化合物層と拡散層では完全に結晶系が異な
るため、通常、γ′−Fez N 相( z≒４) の析出を伴
う。しかし、これが析出した場合でも、化合物層と拡散
層の境界部において、上記の炭素固溶型ε相とマトリッ
クス相の総和に対して体積率で20％以下であれば、耐剥
離特性の悪化に影響しない。[0027] Since the fully crystal system with a compound layer and the diffusion layer are different, usually accompanied by precipitation of γ'-Fe z N phase (z ≒ 4). However, even when this is precipitated, if the volume ratio is 20% or less with respect to the total amount of the carbon-dissolved ε phase and the matrix phase at the boundary between the compound layer and the diffusion layer, the peeling resistance is deteriorated. It does not affect.
【００２８】化合物層の残部および化合物層と拡散層と
の境界部における前記のいずれの炭素固溶型ε相の場合
も、炭素濃度は前述のポーラス層表層部の場合と同様に
限定するのが望ましい。In any case of the above-mentioned carbon solid solution type ε phase at the remaining portion of the compound layer and at the boundary portion between the compound layer and the diffusion layer, the carbon concentration is limited in the same manner as in the case of the above-mentioned surface layer portion of the porous layer. desirable.
【００２９】低合金鋼等の場合は、処理過程で添加合金
元素 (Cr、Ｖ、Mo、Ti、Alなど) も窒化または炭化さ
れ、微細な窒化物または炭化物となる。これらの窒化物
または炭化物の生成元素は、化合物層生成時の反応速度
に影響を与えるだけでなく、疲労強度にも影響を与え
る。しかし、耐食性および耐剥離特性の観点からする
と、化合物層中に添加元素による窒化物または炭化物が
体積率で全体の10％以下で存在する場合においても、化
合物層の形態が上記の各条件を満足していれば問題にな
らない。In the case of a low alloy steel or the like, additional alloying elements (Cr, V, Mo, Ti, Al, etc.) are also nitrided or carbonized during the processing, and become fine nitrides or carbides. These nitride or carbide forming elements affect not only the reaction rate at the time of forming the compound layer but also the fatigue strength. However, from the viewpoint of corrosion resistance and peeling resistance, even when nitride or carbide due to an additive element is present in the compound layer at a volume ratio of 10% or less, the morphology of the compound layer satisfies the above conditions. It does not matter if you do.
【００３０】本発明の表面改質鋼における化合物層の厚
さは、高耐食性および高耐剥離特性を達成する観点か
ら、10μｍ以上30μｍ以下とするのが望ましい。The thickness of the compound layer in the surface-modified steel of the present invention is desirably 10 μm or more and 30 μm or less from the viewpoint of achieving high corrosion resistance and high peeling resistance.
【００３１】[0031]
【実施例】炭窒化処理は、炭素鋼もしくは低合金鋼を対
象として、タフトライド法、ガス軟窒化法、イオン窒化
法のいずれかを適宜使用し、場合によっては再熱処理を
施すことにより実施した。これらの処理条件は次のとお
りである。EXAMPLE The carbonitriding treatment was performed on carbon steel or low alloy steel by appropriately using any of the tuftride method, gas soft nitriding method, and ion nitriding method, and in some cases, performing reheat treatment. These processing conditions are as follows.
【００３２】本発明例 ガス軟窒化法：体積比率で、CO：H2：CH4:N2：NH3 ＝1
0.4：20.4：0.2:19.0：50.0の混合ガス中で、570 ℃×
４〜８時間処理した後、油急冷。Example of the present invention Gas nitrocarburizing method: CO: H 2 : CH 4 : N 2 : NH 3 = 1 by volume ratio
570 ℃ in a mixed gas of 0.4: 20.4: 0.2: 19.0: 50.0
After 4 to 8 hours treatment, oil quenching.
【００３３】イオン窒化法：体積比率で、N2：H2＝90：
10の混合ガス中、５Torrの減圧下で、400 Ｖの直流電圧
を印加し、570 ℃×５時間処理した後、炉内放冷。Ion nitriding method: N 2 : H 2 = 90 by volume ratio:
After applying a DC voltage of 400 V under a reduced pressure of 5 Torr in the mixed gas of No. 10 and treating at 570 ° C. for 5 hours, the furnace was allowed to cool.
【００３４】比較例 タフトライド法：KCNOを主成分とするシアン酸塩中で、
580 ℃×３〜６時間処理した後、水急冷。ただし、比較
例７では、さらにN2雰囲気下で580 ℃×10分間再加熱し
た後、放冷。Comparative Example Tuftride method: In a cyanate containing KCNO as a main component,
After processing at 580 ° C for 3 to 6 hours, water is rapidly cooled. However, in Comparative Example 7, it was further heated under a N 2 atmosphere at 580 ° C. for 10 minutes and then allowed to cool.
【００３５】ガス軟窒化法：体積比率で、CO：CH4:N2：
NH3 ＝15.3：12.0：54.7:18.0 の混合ガス中で、570 ℃
×８〜９時間処理した後、油急冷。Gas nitrocarburizing method: by volume ratio, CO: CH 4 : N 2 :
570 ° C in a mixed gas of NH 3 = 15.3: 12.0: 54.7: 18.0
× 8-9 hours after treatment, oil quenching.
【００３６】イオン窒化法：体積比率で、N2：H2＝40：
60の混合ガス中、５Torrの減圧下で、400 Ｖの直流電圧
を印加し、570 ℃×５時間処理した後、炉内放冷。Ion nitriding method: N 2 : H 2 = 40 by volume ratio:
After applying a DC voltage of 400 V under a reduced pressure of 5 Torr in a mixed gas of 60 and treating at 570 ° C. for 5 hours, the furnace was allowed to cool.
【００３７】このような処理によって作製した試料の化
合物層、ポーラス層の各厚さを表１に示す。厚さは、試
料断面を研磨した後、Ｘ線マイクロアナライザー（ＥＰ
ＭＡ）によって求めた。いずれもポーラス層の厚さが化
合物層の厚さの1/3 以下になっている。Table 1 shows the respective thicknesses of the compound layer and the porous layer of the sample prepared by such a treatment. After polishing the sample cross section, the thickness was measured using an X-ray microanalyzer (EP
MA). In each case, the thickness of the porous layer is 1/3 or less of the thickness of the compound layer.
【００３８】[0038]
【表１】 [Table 1]
【００３９】これらの試料について、次の方法で評価し
た。These samples were evaluated by the following methods.
【００４０】（１）化合物層におけるFe成分比率：試料
断面を研磨した後、ＥＰＭＡによって、ポーラス層の最
表層部、化合物層の中央部および緻密層と拡散層との境
界部（化合物層と拡散層との境界部）のFe、Ｃ、Ｎ濃度
を求めた。このようにして得られたFe、Ｃ、Ｎ濃度の原
子比の和を100 として、新たに炭素固溶型ε相の原子比
率に換算し直した。(1) Fe component ratio in the compound layer: After polishing the sample cross section, the outermost layer portion of the porous layer, the center portion of the compound layer, and the boundary portion between the dense layer and the diffusion layer (the compound layer and the diffusion layer) were polished by EPMA. Fe, C, and N concentrations at the boundary with the layer) were determined. With the sum of the atomic ratios of the Fe, C, and N concentrations thus obtained as 100, the atomic ratio of the carbon solid solution type ε phase was newly converted again.
【００４１】（２）深さ方向での炭素固溶型ε相の結晶
構造変化：試料の深さ方向での結晶構造変化は、処理表
面から1200番のエメリーペーパーで徐々に研磨しては研
磨深さを測定し、その後、Ｘ線回折測定を実施するとい
う一連の操作を繰り返すことによって行った。この方法
を図１で説明する。(2) Crystal structure change of carbon solid solution type ε phase in the depth direction: The crystal structure change in the depth direction of the sample is gradually polished from the treated surface with # 1200 emery paper. The measurement was performed by repeating a series of operations of measuring the depth and then performing X-ray diffraction measurement. This method will be described with reference to FIG.
【００４２】図１は、本発明例の試料No.4の場合の、炭
素固溶型ε相に対する回折Ｘ線強度と回折角との関係が
表面層の深さに従って変化する状態を示す図である。FIG. 1 is a view showing a state where the relationship between the diffraction X-ray intensity and the diffraction angle with respect to the carbon solid solution type ε phase in the case of Sample No. 4 of the present invention changes according to the depth of the surface layer. is there.
【００４３】図１では、炭素固溶型ε相の回折Ｘ線ピー
クが研磨深さに伴って連続的に回折角２θの高角度側に
シフトしており、これは深さ方向で上記ε相の格子定数
（ａεおよびｃε）が連続的に減少（すなわち、Fe成分
比率が連続的に増加）していることを意味している。こ
れに対して、急激な格子定数変化が観察される場合、あ
るいは格子定数の異なる複数の上記ε相が存在している
（回折線ピークに重複が観察される）場合もある。格子
定数が深さ方向で連続的に変化している前者の場合が
「連続」、そうではない後者の場合が「不連続」であ
る。In FIG. 1, the diffraction X-ray peak of the carbon solid solution type ε phase continuously shifts to the higher angle side of the diffraction angle 2θ with the polishing depth. Means that the lattice constants (aε and cε) are continuously reduced (ie, the Fe component ratio is continuously increased). On the other hand, a rapid change in the lattice constant may be observed, or a plurality of ε-phases having different lattice constants may be present (duplication line peaks may be observed). The former case in which the lattice constant changes continuously in the depth direction is "continuous", and the latter case in which the lattice constant is not continuous is "discontinuous".
【００４４】なお、図１で拡散層部でも上記ε相が検出
されているのは、拡散層粒界部に生成したものによる。In FIG. 1, the reason why the ε phase is also detected in the diffusion layer portion is that generated in the diffusion layer grain boundary portion.
【００４５】（３）化合物層と拡散層との境界部のγ′
−Fez N 相の体積率：上記境界部におけるγ′−Fez N
相の炭素固溶型ε相とマトリックス相とに対する存在率
（体積率）は、上記（２）で得られたＸ線回折図形にお
ける回折Ｘ線ピーク強度比から算出できる。しかし、
γ′−Fez N 相の存在率は深さ方向で変化しているた
め、研磨深さが化合物層と拡散層との境界部（層境界±
５μｍの領域）に達したときに得られたＸ線回折図形か
ら体積率を求め、このときの最大値をγ′−Fez N 相の
存在率とした。(3) γ 'at the boundary between the compound layer and the diffusion layer
The volume ratio of -fe z N phase: at the boundary portion γ'-Fe z N
The abundance (volume ratio) of the phase with respect to the carbon solid solution type ε phase and the matrix phase can be calculated from the diffraction X-ray peak intensity ratio in the X-ray diffraction pattern obtained in the above (2). But,
gamma prime-Fe z for the presence of N-phase is changing in the depth direction, the boundary portion between the polishing depth compound layer and the diffusion layer (layer boundary ±
Calculated volume fraction from the obtained X-ray diffraction pattern when it reaches the area) of 5 [mu] m, and the maximum value of this time and the presence ratio of γ'-Fe z N phase.
【００４６】なお、他の窒化物相等の存在比率も確認す
るため、透過電子顕微鏡（ＴＥＭ）を用いる断面観察も
付加的に実施した。In order to confirm the abundance ratio of other nitride phases and the like, cross-sectional observation using a transmission electron microscope (TEM) was additionally performed.
【００４７】（４）表面層の耐剥離特性の評価：耐剥離
特性は、ローラーピッチング試験機によって、面圧250k
gf/mm2、回転数50000 回の試験を実施したときの、ピッ
チングが生じた部分の総面積Ａt を接触部総面積Ａ0 で
割った値、すなわちＡt ／Ａ0 （剥離面積比率）を用い
て評価し、このＡt ／Ａ0 が 2.5×10-3以下のとき耐剥
離特性に優れる (表３中で○と表示) とした。(4) Evaluation of peeling resistance of the surface layer: The peeling resistance was measured by a roller pitting tester at a surface pressure of 250 k.
gf / mm 2, when the test was carried out with a rotational speed of 50000, pitting divided by the contact portion the total area A 0 of the total area A t of the portion resulting value, i.e. A t / A 0 (peeling area ratio) assessed using, and this a t / a 0 has excellent anti-peeling properties when 2.5 × 10 -3 or less (shown as ○ in Table 3).
【００４８】表２および表３に、上記の方法によって評
価した結果をまとめて示す。Tables 2 and 3 collectively show the results evaluated by the above method.
【００４９】[0049]
【表２】 [Table 2]
【００５０】[0050]
【表３】 [Table 3]
【００５１】これらの表から明らかなように、化合物層
の最表層部は炭化物固溶型ε−Fex(N,C) 相 (ただし、x
＝ 2.1〜2.7)主体のものからなり、化合物層と拡散層
との境界部はγ′−Fez N 相の体積率が20％以下で、炭
化物固溶型ε−Fey (N,C) 相(ただし、y ＝ 2.8〜3.0)
主体のものからなり、かつ深さ方向で化合物層中のε相
の格子定数が連続的に減少（すなわち、Fe成分比率が連
続的に増加）している場合に表面層の耐剥離特性が優れ
ていることがわかる。As is clear from these tables, the outermost layer of the compound layer is a carbide solid solution type ε-Fe x (N, C) phase (where x
= 2.1 to 2.7) consists mainly of one, the boundary portion between the compound layer and the diffusion layer γ'-Fe z N phase volume ratio of 20% or less, carbide solid solution type ε-Fe y (N, C ) Phase (However, y = 2.8 to 3.0)
When the lattice constant of the ε phase in the compound layer is continuously reduced in the depth direction (that is, the Fe component ratio is continuously increased), the surface layer has excellent exfoliation resistance. You can see that it is.
【００５２】[0052]
【発明の効果】本発明の表面改質鋼は、化合物層中のε
相が炭素固溶型であるとともに、この相中のFe成分比率
とその表面層の深さ方向での増加の度合いが適正である
ため、高い耐食性と高い耐剥離特性とを有するものであ
る。As described above, the surface-modified steel of the present invention is characterized in that ε in the compound layer
Since the phase is a carbon solid solution type and the ratio of the Fe component in the phase and the degree of increase in the depth direction of the surface layer are appropriate, the phase has high corrosion resistance and high peeling resistance.
【図１】本発明例の試料No.4の場合の、ε相に対する回
折Ｘ線強度と回折角との関係が表面層の深さに従って変
化する状態を示す図である。FIG. 1 is a diagram showing a state in which the relationship between the diffraction X-ray intensity and the diffraction angle with respect to the ε phase changes according to the depth of the surface layer in the case of Sample No. 4 of the present invention.
【図２】一般的な炭窒化処理鋼の表面組織を模式的に示
す断面図である。FIG. 2 is a cross-sectional view schematically showing a surface structure of a general carbonitrided steel.
１：化合物層、 ２：ポーラス層、 ３：緻密層、
４：拡散層、５：拡散層中の結晶粒界部1: compound layer, 2: porous layer, 3: dense layer,
4: diffusion layer, 5: grain boundary in diffusion layer
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 昭61−69957（ＪＰ，Ａ) 実開 平４−106354（ＪＰ，Ｕ) (58)調査した分野(Int.Cl.6，ＤＢ名) C23C 8/20 - 8/32 C23C 8/50,8/56,8/76 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-69957 (JP, A) JP-A-4-106354 (JP, U) (58) Fields investigated (Int. Cl. 6 , DB name) C23C 8/20-8/32 C23C 8 / 50,8 / 56,8 / 76
Claims (1)
ス層及び緻密層）と拡散層とからなる炭窒化処理表面改
質鋼であって、化合物層の最表層部は炭素固溶型ε相
〔Fex(N,C) 、ただし、x ＝ 2.1〜2.7 〕を主体とする
ものからなり、化合物層の残部は炭素固溶型ε相〔Fem
(N,C) 、ただし、x ≦m ≦ y〕を主体とするものからな
り、化合物層と拡散層との境界部はγ′相（Fez N 、た
だし、z ≒４）を体積率で20％以下で含む炭素固溶型ε
相〔Fey (N,C) 、ただし、y ＝ 2.8〜3.0 〕、またはこ
の炭素固溶型ε相とマトリックス相とを主体とするもの
からなり、炭素固溶型ε相の格子定数が深さ方向で連続
的に減少していることを特徴とする表面の耐剥離特性に
優れた炭窒化処理鋼。1. A carbonitrided surface-modified steel in which a surface layer comprises a compound layer (porous layer and dense layer) and a diffusion layer in the depth direction, and the outermost layer of the compound layer is a carbon solid solution type steel. ε phase [Fe x (N, C), where x = 2.1 to 2.7], and the remainder of the compound layer is a carbon solid solution ε phase [Fe m
(N, C), however, consists mainly formed of x ≦ m ≦ y], the boundary portion between the compound layer and the diffusion layer is gamma 'phase (Fe z N, where z ≒ 4) at a volume ratio 20% or less carbon solid solution type ε
Phase [Fe y (N, C), where y = 2.8 to 3.0], or a phase mainly composed of the carbon-dissolved ε phase and the matrix phase, and the lattice constant of the carbon-dissolved ε phase is deep. Carbonitrided steel with excellent surface delamination resistance, characterized by a continuous decrease in the vertical direction.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9177094A JP2917810B2 (en) | 1994-04-28 | 1994-04-28 | Carbonitrided steel with excellent surface delamination resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9177094A JP2917810B2 (en) | 1994-04-28 | 1994-04-28 | Carbonitrided steel with excellent surface delamination resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07300662A JPH07300662A (en) | 1995-11-14 |
| JP2917810B2 true JP2917810B2 (en) | 1999-07-12 |
Family
ID=14035815
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP9177094A Expired - Fee Related JP2917810B2 (en) | 1994-04-28 | 1994-04-28 | Carbonitrided steel with excellent surface delamination resistance |
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| Country | Link |
|---|---|
| JP (1) | JP2917810B2 (en) |
Cited By (1)
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|---|---|---|---|---|
| CN102925853A (en) * | 2012-11-21 | 2013-02-13 | 大连理工大学 | Ultrahigh nitrogen austenite phase diffusion hardening covering layer for pump shafts of nuclear grade pumps |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2747398B1 (en) * | 1996-04-12 | 1998-05-15 | Nitruvid | METHOD FOR THE SURFACE TREATMENT OF A METAL PART |
| JP4998654B2 (en) * | 2001-01-31 | 2012-08-15 | 日立オートモティブシステムズ株式会社 | Method of gas soft nitriding treatment of steel members |
| JP4531448B2 (en) * | 2004-06-07 | 2010-08-25 | 山陽特殊製鋼株式会社 | Mold nitriding method |
| CN110408885B (en) * | 2019-08-27 | 2021-06-11 | 南京工程学院 | Light gear for vehicle and manufacturing process thereof |
-
1994
- 1994-04-28 JP JP9177094A patent/JP2917810B2/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102925853A (en) * | 2012-11-21 | 2013-02-13 | 大连理工大学 | Ultrahigh nitrogen austenite phase diffusion hardening covering layer for pump shafts of nuclear grade pumps |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH07300662A (en) | 1995-11-14 |
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