JP2018053337A - Carburized component excellent in wear resistance and fatigue characteristic, and process for producing the same - Google Patents
Carburized component excellent in wear resistance and fatigue characteristic, and process for producing the same Download PDFInfo
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Abstract
Description
本発明は自動車および各種産業機器に用いる高い耐摩耗性と高い疲労強度を有する浸炭部品およびその製造方法に関する。 The present invention relates to a carburized component having high wear resistance and high fatigue strength for use in automobiles and various industrial equipment and a method for manufacturing the same.
自動車等に用いられている軸類、歯車類は、近年、省エネルギーのための車体軽量化に伴って小型化が要求される。一方で、エンジンの高出力化により負荷が増大していることから、耐久性の向上が求められている。 In recent years, shafts and gears used in automobiles and the like are required to be reduced in size with a reduction in weight of the vehicle body for energy saving. On the other hand, since the load is increased due to the higher output of the engine, improvement in durability is required.
従来は、ＪＩＳ ＳＣＭ４２０Ｈ、ＳNＣＭ４２０Ｈ等の肌焼鋼を用いて部品を成形し、浸炭等の表面処理を行い自動車等に使用されてきた。しかし、高応力下での使用には耐えられないため、鋼材の変更、熱処理方法の変更、表面の加工硬化処理により耐摩耗性および疲労強度を向上させる研究開発が進められてきた。 Conventionally, parts have been formed using case-hardened steel such as JIS SCM420H, SNCM420H, etc., and surface treatment such as carburization has been performed and used for automobiles and the like. However, since it cannot withstand use under high stress, research and development has been advanced to improve wear resistance and fatigue strength by changing the steel material, changing the heat treatment method, and working hardening the surface.
たとえば、特許文献１には、特定の成分を有する鋼材で部品形状とした後に浸炭もしくは浸炭窒化処理および焼入れ・焼戻し処理を施し、表層部に平均粒径が５μｍ以下の炭化物または炭窒化物を析出させるいわゆる高濃度浸炭処理を用いることで耐摩耗性を向上させている。
また、特許文献２では耐摩耗性部品を表面硬さ、粗さで規定して、さらに素材としてはJIS G4053に規定されたクロム鋼またはクロムモリブデン鋼かさらにＭｎ、Ｍｏなどの合金を添加することが規定されている。
For example, in Patent Document 1, carburizing or carbonitriding treatment and quenching / tempering treatment are performed after forming a part shape with a steel material having a specific component, and carbide or carbonitride having an average particle size of 5 μm or less is deposited on the surface layer portion. Wear resistance is improved by using so-called high-concentration carburizing treatment.
In Patent Document 2, wear-resistant parts are defined by surface hardness and roughness, and as a material, chrome steel or chrome molybdenum steel specified in JIS G4053 or an alloy such as Mn or Mo is added. Is stipulated.
特許文献１では、成分としてＣｒが２〜８重量％含まれていて高合金であるために合金コストが高く、またこの熱処理は高温長時間での処理となる為に熱処理コストも嵩む。 In Patent Document 1, the alloy cost is high because Cr is contained as a component and is a high alloy, and this heat treatment is a treatment at a high temperature for a long time, so that the heat treatment cost is also increased.
特許文献２では表面硬さを高めることや粗さを規定することで摩耗性の向上を図るのは従来鋼でも可能な手法であるが、あまり効果は大きくない。さらにＭｎ、Ｍｏを高めるとコスト増となってしまう。 In Patent Document 2, it is possible to improve the wearability by increasing the surface hardness or regulating the roughness, but it is possible with conventional steel, but the effect is not so great. If Mn and Mo are further increased, the cost will increase.
本発明は、上述した問題を解決して、耐摩耗性および疲労特性に優れた浸炭部品およびその製造方法を提供することを目的とする。 An object of the present invention is to solve the above-described problems and provide a carburized component having excellent wear resistance and fatigue characteristics and a method for manufacturing the same.
本発明では、上記課題を解決するために、鋭意研究を行い、以下のことを見出した。
１．耐摩耗性に対して表面硬度を高める手段は一般的に使用されており、そのために表面硬化処理の一つである浸炭焼入れ焼戻しを行なっている。浸炭焼入れ焼戻しをして使用する場合には表面粗さを抑えて摩擦を抑えると共にその摩擦発熱による軟化の抑制が最も効果がある。
２．浸炭材の表面粗さをミクロ的に見ると浸炭時の表面の粒界酸化状況が表面粗さに影響を及ぼす。そのため、表面を研磨して使用する場合は必要ないが、浸炭焼入れ焼戻しままでの表面で使用する場合は、コストが嵩む為、粒界酸化を抑制する必要がある。
３．摩擦発熱による焼戻し軟化抑制については焼戻し軟化抵抗を有する合金添加が有効であり、その中でも代表的なものはＳｉである。
４．鋼材のＳｉ増量添加は、表面酸化は多くなるが、浸炭条件によっては表面の粒界・粒内の全域で酸化が進行するために深さ方向への酸化の進展が遅れる。結果、粒界優先で酸化した場合の表面の粗さよりも表面の粗さは小さくなる。さらに、ショットピーニングを行う事で表層の酸化層が層状に剥離するために粒界に沿った酸化だけが進行するような鋼よりも表面の欠陥が少なくなり、面粗さ向上に有利である。
５．Ｓｉを増量した鋼でショットピーニングを行なった場合、表層付近の圧縮残留応力は、実際の部品として使用する前は従来材と同様な傾向であるが、使用中は従来材よりも圧縮残留応力の減衰が小さく、そのために摩擦と同時に面圧が加わるような部品では疲労特性が向上する。
６．Ｓｉを添加すると鋼の変態点が上昇する。この点を利用して内部組織をコントロールし熱処理による歪みをコントロールすることで、歪み取り矯正の簡略化・簡素化を図れる。同時に、研磨の必要もなくなり、表面硬度を高めに維持することが可能となり、耐摩耗性が向上する。
In the present invention, in order to solve the above-mentioned problems, intensive research has been conducted and the following has been found.
1. A means for increasing the surface hardness with respect to the wear resistance is generally used, and therefore, carburizing, quenching and tempering, which is one of the surface hardening treatments, is performed. When carburizing, quenching and tempering are used, it is most effective to suppress the surface roughness to suppress friction and to suppress softening due to frictional heat generation.
2. When the surface roughness of the carburized material is viewed microscopically, the state of grain boundary oxidation at the time of carburizing affects the surface roughness. For this reason, it is not necessary when the surface is polished and used, but when used on the surface as it is carburized, quenched and tempered, the cost increases, so it is necessary to suppress grain boundary oxidation.
3. Addition of an alloy having temper softening resistance is effective for suppressing temper softening due to frictional heat generation, of which Si is representative.
4). The addition of Si to steel increases the surface oxidation, but depending on the carburizing conditions, the oxidation progresses in the depth direction due to the progress of oxidation at the surface grain boundaries and within the grains. As a result, the surface roughness is smaller than the surface roughness when oxidation is performed with priority given to grain boundaries. Further, by performing shot peening, the oxide layer on the surface layer is peeled off in a layered manner, so that there are fewer surface defects than steel in which only oxidation along the grain boundaries proceeds, and this is advantageous in improving surface roughness.
5. When shot peening is performed on steel with an increased amount of Si, the compressive residual stress near the surface layer tends to be the same as that of the conventional material before use as an actual part. Fatigue properties are improved in parts that have low damping and are therefore subjected to surface pressure simultaneously with friction.
6). When Si is added, the transformation point of steel increases. By taking advantage of this point to control the internal structure and to control distortion due to heat treatment, it is possible to simplify and simplify distortion correction. At the same time, there is no need for polishing, the surface hardness can be kept high, and wear resistance is improved.
本発明は以上の知見に基づいてなされたものであり、特徴は以下の通りである。
［１］成分組成が、Ｃ：０．１２〜０．３０ｍａｓｓ％、Ｓｉ：０．８０〜２．５０ｍａｓｓ％、Ｍｎ：０．４０〜０．８０ｍａｓｓ％、Ｃｒ：０．８０〜２．００ｍａｓｓ％、Ｍｏ：０．３ｍａｓｓ％以下（０ｍａｓｓ％を含む）、Ａｌ：０．０１０〜０．０８０ｍａｓｓ％、Ｎ：０．００４０〜０．０２００ｍａｓｓ％、Ｃｕ：０．５０ｍａｓｓ％以下（０ｍａｓｓ％を含む）、Ｎｉ：２．０ｍａｓｓ％以下（０ｍａｓｓ％を含む）、残部Ｆｅおよび不可避的不純物であり、かつ、下記（１）式を満足する非浸炭部と、該非浸炭部より表面側にあって、該非浸炭部に対してＣ含有量またはさらにＮ含有量が高い成分組成である浸炭部を有し、該浸炭部は、表面から３μｍ深さ位置までの酸化密度が４０％以上であり、表面から２５μｍ深さ位置までの圧縮残留応力の平均値が１０００ＭＰａ以上であり、前記非浸炭部の鋼組織はフェライト量が面積率で４０％以下であることを特徴とする耐摩耗性および疲労特性に優れた浸炭部品。
[Ｓｉ]＋３[Ｃｒ]−[Ｍｎ]≧４．０ ・・・（１）
但し、[Ｍ]はＭ元素の含有量（ｍａｓｓ％）を示す。
［２］成分組成として、更に、Ｎｂ：０．０６０ｍａｓｓ％以下、Ｖ：０．２０ｍａｓｓ％以下、Ｔｉ：０．２００ｍａｓｓ％以下の１種以上を含有することを特徴とする上記［１］に記載の耐摩耗性および疲労特性に優れた浸炭部品。
［３］成分組成として、更に、Ｂ：０．００５０ｍａｓｓ％以下を含有することを特徴とする上記［１］または［２］に記載の耐摩耗性および疲労特性に優れた浸炭部品。
［４］上記［１］乃至［３］のいずれか一つに記載の成分組成の鋼材を用いて機械加工、熱間鍛造、冷間鍛造、温間鍛造のいずれか一つ以上を行って部品形状とした後、浸炭焼入れあるいは浸炭浸窒焼入れの後、焼戻し処理を行い、次いで、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を用いてショットピーニングを行うことを特徴とする耐摩耗性および疲労特性に優れた浸炭部品の製造方法。
［５］上記［１］乃至［３］のいずれか一つに記載の成分組成の鋼材を用いて、機械加工、熱間鍛造、冷間鍛造、温間鍛造のいずれか一つ以上を行って部品形状とした後、浸炭焼入れあるいは浸炭浸窒焼入れの後、焼戻し処理を行い、次いで、粒径が０．４〜１．２ｍｍΦで硬さ７００ＨＶ以上の粒を用いてショットピーニングを行った後、さらに、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を用いて再度ショットピーニングを行うことを特徴とする耐摩耗性および疲労特性に優れた浸炭部品の製造方法。
［６］上記［１］乃至［３］のいずれか一つに記載の成分組成の鋼材を用いて、機械加工、熱間鍛造、冷間鍛造、温間鍛造のいずれか一つ以上を行って部品形状とした後、浸炭焼入れあるいは浸炭浸窒焼入れの後、焼戻し処理を行い、次いで、粒径が０．４〜１．２ｍｍΦで硬さ７００ＨＶ以上の粒と、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒とを混合してショットピーニングを行うことを特徴とする耐摩耗性および疲労特性に優れた浸炭部品の製造方法。
This invention is made | formed based on the above knowledge, and the characteristic is as follows.
[1] Component composition is C: 0.12-0.30 mass%, Si: 0.80-2.50 mass%, Mn: 0.40-0.80 mass%, Cr: 0.80-2.00 mass% , Mo: 0.3 mass% or less (including 0 mass%), Al: 0.010 to 0.080 mass%, N: 0.0040 to 0.0200 mass%, Cu: 0.50 mass% or less (including 0 mass%) Ni: 2.0 mass% or less (including 0 mass%), the remaining Fe and inevitable impurities, and a non-carburized portion satisfying the following formula (1), on the surface side from the non-carburized portion, The carburized part has a carburized part having a component composition having a high C content or even N content relative to the carburized part, and the carburized part has an oxidation density of 40% or more from the surface to a depth of 3 μm, and 25 μm from the surface. depth An average value of compressive residual stress up to a position is 1000 MPa or more, and the steel structure of the non-carburized portion has a ferrite content of 40% or less in terms of area ratio. .
[Si] +3 [Cr] − [Mn] ≧ 4.0 (1)
However, [M] indicates the content (mass%) of the M element.
[2] As described in [1] above, the composition further contains one or more of Nb: 0.060 mass% or less, V: 0.20 mass% or less, and Ti: 0.200 mass% or less. Carburized parts with excellent wear resistance and fatigue characteristics.
[3] The carburized part having excellent wear resistance and fatigue characteristics according to the above [1] or [2], further comprising B: 0.0050 mass% or less as a component composition.
[4] A part obtained by performing any one or more of machining, hot forging, cold forging, and warm forging using the steel material having the composition described in any one of [1] to [3] above. After making into a shape, after carburizing quenching or carburizing and nitriding quenching, tempering treatment is performed, and then shot peening is performed using particles having a particle size of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more. A method for manufacturing a carburized part having excellent wear resistance and fatigue characteristics.
[5] Performing any one or more of machining, hot forging, cold forging, and warm forging using the steel material having the composition described in any one of [1] to [3] above. After making the part shape, after carburizing quenching or carburizing and nitriding quenching, tempering is performed, and then shot peening is performed using grains having a particle size of 0.4 to 1.2 mmΦ and a hardness of 700 HV or more, Furthermore, a method for producing a carburized part excellent in wear resistance and fatigue characteristics, characterized in that shot peening is performed again using grains having a grain size of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more.
[6] Performing any one or more of machining, hot forging, cold forging, and warm forging using the steel material having the composition described in any one of [1] to [3] above. After making the part shape, after carburizing and quenching or carburizing and nitriding and quenching, a tempering treatment is performed, and then a grain size of 0.4 to 1.2 mmΦ and a hardness of 700 HV or more, and a grain size of 0.03 to 0 A method of manufacturing a carburized part excellent in wear resistance and fatigue characteristics, characterized in that shot peening is performed by mixing grains having a hardness of 700 HV or more at 1 mmΦ.
本発明によれば、耐摩耗性および疲労特性に優れた浸炭部品が得られる。本発明の浸炭部品は、自動車、産業機械の歯車等に好適に使用できる。また、本発明の製造方法によれば、本発明の浸炭部品を安価に量産可能に製造することができる。以上より、産業上極めて有用である。 According to the present invention, a carburized part having excellent wear resistance and fatigue characteristics can be obtained. The carburized parts of the present invention can be suitably used for automobiles, industrial machinery gears, and the like. Moreover, according to the manufacturing method of the present invention, the carburized component of the present invention can be manufactured at low cost so as to be mass-produced. From the above, it is extremely useful industrially.
本発明では素材となる鋼材の成分組成、浸炭焼入れ焼戻し・ショットピーニングを行った後の表面の酸化状態、表層から２５μｍ深さまでの圧縮残留応力の大きさ、および、非浸炭部の鋼組織を規定する。以下に各限定理由について述べる。
なお、以下の説明において、成分組成の各元素の含有量の単位はいずれも「ｍａｓｓ％」であり、特に断らない限り単に「％」で示す。
成分組成
In the present invention, the composition of the steel material used as a raw material, the oxidation state of the surface after carburizing, quenching, tempering and shot peening, the magnitude of the compressive residual stress from the surface layer to a depth of 25 μm, and the steel structure of the non-carburized part are specified. To do. Each limitation reason is described below.
In the following description, the unit of the content of each element of the component composition is “mass%”, and is simply “%” unless otherwise specified.
Ingredient composition
Ｃ：０．１２〜０．３０ｍａｓｓ％
Ｃは強度確保のために必要で、浸炭焼入れ焼戻しあるいは浸炭浸窒焼入れ焼戻し後の内部硬度を決定する。０．１２ｍａｓｓ％未満では非浸炭部硬度が低下し、耐曲げ応力が低下して強度を確保できない。一方、０．３０ｍａｓｓ％より多いと靭性が劣化し、疲労特性が悪くなる。よって、０．１２〜０．３０ｍａｓｓ％とする。
C: 0.12-0.30 mass%
C is necessary for ensuring the strength, and determines the internal hardness after carburizing, quenching, and tempering. If it is less than 0.12 mass%, the non-carburized part hardness decreases, the bending stress decreases, and the strength cannot be ensured. On the other hand, if it exceeds 0.30 mass%, the toughness deteriorates and the fatigue properties deteriorate. Therefore, it is set to 0.12 to 0.30 mass%.
Ｓｉ：０．８０〜２．５０ｍａｓｓ％
Ｓｉは焼戻し軟化抵抗を高めるのに有効な元素である。軟化抵抗が低いと、摩擦熱による軟化が発生してしまい摩耗を早めてしまう。この抑制効果は０．８０ｍａｓｓ％以上で有効である。また、Ｓｉは変態点を上げる作用がある。浸炭焼入れ焼戻しあるいは浸炭浸窒焼入れ焼戻し後に、非浸炭部にフェライトを好適に１５％以上存在させるためにはＳｉは０．８０ｍａｓｓ％以上必要である。一方、２．５０ｍａｓｓ％以上含有した場合は、フェライトが４０％を超えてしまう。よって０．８０〜２．５０ｍａｓｓ％とする。
Si: 0.80 to 2.50 mass%
Si is an element effective for increasing the temper softening resistance. When the softening resistance is low, softening due to frictional heat occurs and wear is accelerated. This suppression effect is effective at 0.80 mass% or more. Si also has the effect of raising the transformation point. After carburizing and tempering or carburizing and nitrocarburizing and quenching and tempering, Si is required to be 0.80 mass% or more so that ferrite is preferably present in 15% or more in the non-carburized part. On the other hand, when it contains 2.50 mass% or more, ferrite will exceed 40%. Therefore, it is set to 0.80 to 2.50 mass%.
Ｍｎ：０．４０〜０．８０ｍａｓｓ％
Ｍｎは焼入れ性を高める元素である。焼入れ性を確保するため０．４０ｍａｓｓ％以上とする。一方、０．８０ｍａｓｓ％を超えて含有すると浸炭部品非浸炭部の靭性が下がりすぎて疲労特性が劣る。よって、０．４０〜０．８０ｍａｓｓ％とする。
Mn: 0.40 to 0.80 mass%
Mn is an element that enhances hardenability. In order to ensure hardenability, the content is set to 0.40 mass% or more. On the other hand, if the content exceeds 0.80 mass%, the toughness of the non-carburized part of the carburized part is excessively lowered and the fatigue characteristics are inferior. Therefore, it is set to 0.40 to 0.80 mass%.
Ｃｒ：０．８０〜２．００ｍａｓｓ％
Ｃｒは焼入れ性向上元素であるとともに、焼戻し軟化抵抗を高める元素である。両方の性能を発揮させるには０．８０ｍａｓｓ％以上の含有が必要である。一方、２．００ｍａｓｓ％を超えると軟化抵抗を高める効果は飽和する。また、焼入れ性が高くなりすぎるため歯車内部の靭性が劣化し、疲労亀裂の進展が早くなって曲げ疲労強度が低下するようになる。よって、０．８０〜２．００ｍａｓｓ％とする。
Cr: 0.80 to 2.00 mass%
Cr is an element improving the temper softening resistance as well as a hardenability improving element. In order to exhibit both performances, it is necessary to contain 0.80 mass% or more. On the other hand, if it exceeds 2.00 mass%, the effect of increasing the softening resistance is saturated. Further, since the hardenability becomes too high, the toughness inside the gear is deteriorated, the fatigue crack progresses quickly, and the bending fatigue strength decreases. Therefore, it is set to 0.80-2.00 mass%.
Ｍｏ：０．３ｍａｓｓ％以下（０ｍａｓｓ％を含む）
Ｍｏ含有は必須ではないが、焼入れ性向上元素であるため、０．３ｍａｓｓ％を上限として含有することができる。０．３ｍａｓｓ％を超えると焼入れ性が高すぎて焼割れが起こりやすくなり、また高価なため経済性も悪くなるので、０．３ｍａｓｓ％以下とする。
Mo: 0.3 mass% or less (including 0 mass%)
Although containing Mo is not essential, since it is a hardenability improving element, it can be contained up to 0.3 mass%. If it exceeds 0.3 mass%, the hardenability is too high and cracking easily occurs, and since it is expensive, the economic efficiency is also deteriorated.
Ａｌ：０．０１０〜０．０８０ｍａｓｓ％
Ａｌは脱酸に有効な元素であり、その効果は０．０１０ｍａｓｓ％以上の含有で発揮される。また、０．０８０ｍａｓｓ％までの含有でＮと結合してＡｌＮを生成し、結晶粒の粗大化を抑える働きがある。０．０８０ｍａｓｓ％を超えると粗大粒が発生して疲労亀裂が進展し易くなって曲げ疲労強度が低下する。よって、０．０１０〜０．０８０ｍａｓｓ％とする。
Al: 0.010-0.080 mass%
Al is an element effective for deoxidation, and the effect is exhibited when the content is 0.010 mass% or more. Further, when it is contained up to 0.080 mass%, it combines with N to produce AlN, and has the function of suppressing the coarsening of crystal grains. If it exceeds 0.080 mass%, coarse grains are generated and fatigue cracks are easily developed, and the bending fatigue strength is lowered. Therefore, it is set to 0.010 to 0.080 mass%.
Ｎ：０．００４０〜０．０２００ｍａｓｓ％
ＮはＡｌと結合してＡｌＮを生成し、結晶粒の粗大化を抑えて疲労強度を向上させる。その効果を得るには０．００４０ｍａｓｓ％以上必要である。一方、０．０２００ｍａｓｓ％を超えるとその効果は飽和するだけでなく、内部にブローホール等の欠陥を発生させ、曲げ疲労強度の低下を招く。よって、０．００４０〜０．０２００ｍａｓｓ％とする。
N: 0.0040-0.0200 mass%
N combines with Al to produce AlN, which suppresses coarsening of crystal grains and improves fatigue strength. To obtain the effect, 0.0040 mass% or more is necessary. On the other hand, if it exceeds 0.0200 mass%, the effect is not only saturated, but also defects such as blow holes are generated inside, leading to a decrease in bending fatigue strength. Therefore, it is set as 0.0040-0.0200 mass%.
Ｃｕ：０．５０ｍａｓｓ％以下（０ｍａｓｓ％を含む）
Ｃｕは必ずしもその含有を必須とするものではないが、鋼中に固溶して、鋼材の強度を高める元素であるため０．５０ｍａｓｓ％を上限として含有してもよい。しかし、０．５０ｍａｓｓ％を超えると鋼材製造時に表面疵が発生して部品製造の際に表面欠陥が発生しやすくなり、また表面研削等を行なった後に部品製造をするとコスト増となる等、不利益となる。よって、Ｃｕは０．５０ｍａｓｓ％以下で使用する。なお、Ｃｕによる固溶強化を有効に発現させるためには、０．０２ｍａｓｓ％以上で含有させることが好ましい。さらにＣｕを含有する場合は表面疵の発生を抑制する効果の高いＮｉを同時に含有することが好ましい。
Cu: 0.50 mass% or less (including 0 mass%)
The content of Cu is not necessarily essential, but may be contained up to 0.50 mass% because it is an element that dissolves in steel and increases the strength of the steel material. However, if it exceeds 0.50 mass%, surface flaws occur during steel production, and surface defects are likely to occur during parts production. If parts are produced after surface grinding, etc., the cost increases. Profit. Therefore, Cu is used at 0.50 mass% or less. In order to effectively develop the solid solution strengthening by Cu, it is preferable to contain 0.02 mass% or more. Furthermore, when it contains Cu, it is preferable to contain Ni with the high effect which suppresses generation | occurrence | production of surface flaws simultaneously.
Ｎｉ：２．０ｍａｓｓ％以下（０ｍａｓｓ％を含む）
Ｎｉは必ずしもその含有を必須とするものではない。しかし、鋼中に固溶して強度を高めると共に、焼入れ性を高くして表面の硬化層深さを深くする働きがあるため含有することができる。含有する場合は、Ｎｉは合金としては高価であるため２．０ｍａｓｓ％を上限とする。なお、Ｎｉによる固溶強化や焼入れ性を高める効果を有効に発現させるためには、０．０２ｍａｓｓ％以上含有されることが好ましい。
Ni: 2.0 mass% or less (including 0 mass%)
Ni is not necessarily required to contain Ni. However, it can be contained because it has a function of increasing the strength by solid solution in steel and increasing the hardenability of the surface by increasing the hardenability. When Ni is contained, the upper limit is set to 2.0 mass% because Ni is expensive as an alloy. In addition, in order to effectively express the effect of enhancing solid solution strengthening and hardenability by Ni, it is preferable to contain 0.02 mass% or more.
以上が本発明の基本成分組成であるが、更に特性を向上させる場合、Ｎｂ、Ｖ、Ｔｉ、Ｂの一種または二種以上を含有することができる。 The above is the basic component composition of the present invention, but in the case of further improving the characteristics, one or more of Nb, V, Ti and B can be contained.
Ｎｂ：０．０６０ｍａｓｓ％以下
Ｎｂは炭窒化物形成により結晶粒を微細化し、疲労特性を向上させる。結晶粒の微細化効果は０．０１０ｍａｓｓ％以上で増大するので、０．０１０ｍａｓｓ％以上含有させることが好ましい。一方、０．０６０ｍａｓｓ％を超えて含有してもその効果は飽和するようになるので、０．０６０ｍａｓｓ％を上限とする。
Nb: 0.060 mass% or less Nb refines crystal grains by forming carbonitride and improves fatigue characteristics. Since the effect of refining crystal grains increases at 0.010 mass% or more, it is preferable to contain 0.010 mass% or more. On the other hand, even if the content exceeds 0.060 mass%, the effect is saturated, so 0.060 mass% is made the upper limit.
Ｖ：０．２０ｍａｓｓ％以下
Ｖは焼入性を向上させるとともにＳｉ、Ｃｒと同じく焼戻し軟化抵抗を高める。また、炭窒化物を形成して結晶粒の粗大化を抑制する。このような効果を発揮させるためには、０．０３０ｍａｓｓ％以上の含有が好ましい。一方、０．２０ｍａｓｓ％を超えて含有しても飽和してしまい、十分な効果は得られず、製造コストが上がるだけとなるので、含有する場合は０．２０ｍａｓｓ％を上限とする。
V: 0.20 mass% or less V improves the hardenability and increases the temper softening resistance like Si and Cr. In addition, carbonitride is formed to suppress coarsening of crystal grains. In order to exert such an effect, the content is preferably 0.030 mass% or more. On the other hand, even if it contains exceeding 0.20 mass%, it will saturate and sufficient effect will not be acquired, but only a manufacturing cost will rise, Therefore When it contains, 0.20 mass% is made an upper limit.
Ｔｉ：０．２００ｍａｓｓ％以下
Ｔｉは微細Ｔｉ化合物を生成して鍛造後の結晶粒を小さくして強度を高める。その効果は０．００５ｍａｓｓ％以上で増大するので、０．００５ｍａｓｓ％以上含有させることが好ましい。一方、０．２００ｍａｓｓ％を超えて含有するとＴｉ析出物が粗大化し、疲労破壊の起点となって寿命が低下するようになるので、含有する場合は、０．２００ｍａｓｓ％を上限とする。
Ti: 0.200 mass% or less Ti generates a fine Ti compound to reduce crystal grains after forging and increase the strength. Since the effect increases at 0.005 mass% or more, it is preferable to contain 0.005 mass% or more. On the other hand, if the content exceeds 0.200 mass%, the Ti precipitate becomes coarse, and the life becomes a starting point of fatigue fracture, so that the life is reduced. Therefore, if contained, the upper limit is 0.200 mass%.
Ｂ：０．００５０ｍａｓｓ％以下
Ｂは焼入れ性を上げるのに有効である。その効果は０．０００５ｍａｓｓ％以上で得られるため、０．０００５ｍａｓｓ％以上で含有させることが好ましい。一方、０．００５０ｍａｓｓ％を超えると上記の効果が飽和するようになるので、含有する場合は０．００５０ｍａｓｓ％を上限とする。
B: 0.0050 mass% or less B is effective in increasing the hardenability. Since the effect is obtained at 0.0005 mass% or more, it is preferably contained at 0.0005 mass% or more. On the other hand, if it exceeds 0.0050 mass%, the above-mentioned effect becomes saturated. Therefore, when it is contained, the upper limit is set to 0.0050 mass%.
以上に説明した元素以外の残部はＦｅおよび不可避的不純物である。不可避的不純物としては、Ｐ、Ｓが挙げられ、Ｐについては０．０３０ｍａｓｓ％まで、Ｓについては０．０３０ｍａｓｓ％までは含有を許容できる。 The balance other than the elements described above is Fe and inevitable impurities. Inevitable impurities include P and S. P can be contained up to 0.030 mass%, and S can be contained up to 0.030 mass%.
さらに、耐摩耗性を向上させるパラメータとして以下の（１）式を満足させる必要がある。
[Ｓｉ]＋３[Ｃｒ]−[Ｍｎ]≧４．０・・・（１）
但し、[Ｍ]はＭ元素の含有量（ｍａｓｓ％）を示す。
上記（１）式は焼戻し軟化抑制および粒界酸化状況改善、さらに非浸炭部フェライト量確保の３つの要素をコントロールするのに必要である、この値が４．０よりも小さい場合、焼戻し軟化抵抗、表層酸化状況、非浸炭部フェライト量不足による変形量のいずれかが満たされなくなり耐摩耗性が改善されない。
Furthermore, it is necessary to satisfy the following expression (1) as a parameter for improving wear resistance.
[Si] +3 [Cr] − [Mn] ≧ 4.0 (1)
However, [M] indicates the content (mass%) of the M element.
The above equation (1) is necessary to control the three factors of suppressing temper softening, improving the grain boundary oxidation state, and ensuring the amount of ferrite in the non-carburized part. When this value is smaller than 4.0, temper softening resistance Either the surface oxidation state or the deformation amount due to the insufficient amount of ferrite in the non-carburized part is not satisfied, and the wear resistance is not improved.
浸炭部表層酸化密度
本発明は、浸炭処理が施されて表面から所定深さまでに浸炭部を有する浸炭部品に関するものである。浸炭処理は、上述した成分組成からなる鋼を部品形状としたものに対して行うが、浸炭領域（浸炭部）は表層に形成し、それよりも深い部分は上述した成分組成からなる非浸炭部となる。つまり浸炭部が非浸炭部の表面側に形成される。当然、浸炭部のＣ含有量は非浸炭部のＣ含有量に対して高くなる。また、浸炭処理と同時あるいは浸炭処理の後に、浸窒処理が施されていてもよく、この場合、浸炭部のＮ含有量が非浸炭部のＮ含有量よりも高くなる。このような、浸炭あるいは浸炭浸窒した場合、表層付近は酸化されるが、本発明ではその酸化密度が重要な要件となる。ショットピーニング後に表面から３μｍ深さ位置までの表層酸化密度が４０％未満の場合は表面の酸化が粒界を主体に内部へ伸展しており、部品として使用し、摩擦が発生した場合に表面が荒れ易く、局部摩耗が伸展しやすくなり疲労特性が落ちる。よって、４０％以上必要である。尚、表層酸化密度については、表面から３μｍ深さ位置までについてＥＰＭＡを使用して酸素との結合力の強いＳｉのマッピングを行い、素材（＝内部：浸炭されてない非浸炭部）のＳｉ量と比較して濃度が４倍以上の部分の面積を観察面積全体で除して求めた。観察面積は３０００倍で２００視野を観察した。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburized part that is carburized and has a carburized portion from a surface to a predetermined depth. Carburizing treatment is performed on steel having the above component composition in the shape of a part, but the carburized region (carburized portion) is formed on the surface layer, and the deeper part is the non-carburized portion consisting of the above-described component composition. It becomes. That is, the carburized portion is formed on the surface side of the non-carburized portion. Naturally, the C content of the carburized portion is higher than the C content of the non-carburized portion. Further, a nitriding treatment may be performed simultaneously with the carburizing treatment or after the carburizing treatment. In this case, the N content of the carburized portion is higher than the N content of the non-carburized portion. When carburizing or carburizing and nitriding is performed, the vicinity of the surface layer is oxidized, but the oxidation density is an important requirement in the present invention. When the surface layer oxidation density from the surface to the depth of 3 μm after shot peening is less than 40%, the surface oxidation extends mainly inside the grain boundary and is used as a part. Fatigue easily, local wear tends to extend, and fatigue characteristics decrease. Therefore, 40% or more is necessary. As for the surface layer oxidation density, from the surface to the depth of 3 μm, mapping of Si with strong binding force with oxygen using EPMA is performed, and the amount of Si in the material (= inside: non-carburized non-carburized part) The area of the portion where the concentration is 4 times or more compared with the total observation area was obtained by dividing the area. The observation area was 3000 times and 200 fields were observed.
表面から２５μｍ深さ位置までの圧縮残留応力の平均値
表面から２５μｍ深さ位置までの圧縮残留応力の平均値を１０００ＭＰａ以上とすることで、疲労強度および耐摩耗性が向上する。なお、圧縮残留応力の平均値は後述する実施例の方法にて測定することができる。
Average value of compressive residual stress from surface to 25 μm depth position By setting the average value of compressive residual stress from surface to 25 μm depth position to 1000 MPa or more, fatigue strength and wear resistance are improved. In addition, the average value of a compressive residual stress can be measured by the method of the Example mentioned later.
非浸炭部のフェライト量
浸炭焼入れ焼戻しあるいは浸炭浸窒焼入れ焼戻し後の非浸炭部の組織中にフェライトを一定量存在させると部品の変形を少なくする事が可能である。そのため、フェライト量は面積率で１５％以上が好ましい。一方、４０％を超えて存在させると、非浸炭部の硬度が下がりすぎて疲労強度が低下してしまう。よって、非浸炭部のフェライト量は面積率で４０％以下に限定する。なお、フェライト量の測定にはナイタールでエッチングした浸炭部品の切断・研磨品を光学顕微鏡で４００倍の倍率で１００視野観察し、それらを画像処理にて二値化し、白い部分の面積を求め、全体の面積に対する割合とする。
The amount of ferrite in the non-carburized part When a certain amount of ferrite is present in the structure of the non-carburized part after carburizing and quenching tempering or carburizing and nitriding quenching and tempering, it is possible to reduce the deformation of parts. Therefore, the ferrite content is preferably 15% or more in terms of area ratio. On the other hand, if it exceeds 40%, the hardness of the non-carburized portion will be too low and the fatigue strength will be reduced. Therefore, the amount of ferrite in the non-carburized portion is limited to 40% or less in terms of area ratio. In addition, in the measurement of the ferrite amount, the cut and polished product of the carburized parts etched with nital is observed with 100 optical fields at a magnification of 400 times with an optical microscope, binarized with image processing, and the area of the white part is obtained, It is a ratio to the total area.
浸炭部品の製造方法
本発明に係る浸炭部品は以下のように製造する。上記成分組成の鋼材を機械加工、熱間鍛造、温間鍛造、冷間鍛造のいずれか一つ以上の加工により、歯車等の所望の部品形状とする。または、熱間鍛造、冷間鍛造または温間鍛造のいずれかの後に機械加工で歯車等の所望の部品形状としてもよい。また、これらの加工を如何様に組み合わせてもよい。熱間鍛造や温間鍛造の温度条件は従来実施されている方法で良く、例えば、熱間鍛造は１０００〜１３００℃で行い、温間鍛造は４００〜９５０℃で行う。
Manufacturing method of carburized part The carburized part which concerns on this invention is manufactured as follows. The steel material having the above component composition is formed into a desired part shape such as a gear by one or more of machining, hot forging, warm forging, and cold forging. Alternatively, a desired part shape such as a gear may be formed by machining after hot forging, cold forging, or warm forging. These processes may be combined in any way. The temperature conditions for hot forging and warm forging may be the conventional methods. For example, hot forging is performed at 1000 to 1300 ° C, and warm forging is performed at 400 to 950 ° C.
歯車等の部品形状に加工された部材に対して、浸炭焼入れあるいは浸炭浸窒焼入れを行い、その後、焼戻し処理を行う。浸炭焼入れ、浸炭浸窒焼入れ、焼戻し処理については、従来法に従えばよく、特に条件は設けないが、例えば、９００〜１０５０℃で、浸炭処理を行い、その後、７８０〜８８０℃まで炉冷した後、０〜３時間保持し、その後６０〜１３０℃の油へ投入、または、窒素ガスあるいはヘリウムガス等の不活性ガスを用いて冷却して焼入れ後、１５０〜２２０℃に再加熱して焼戻しを行う処理を行えばよい。なお、浸炭処理には拡散処理を伴う場合も含まれる。また、上記の浸炭処理、炉冷および保持のいずれか一つ以上と同時に浸窒処理を行ってもよい。
浸炭処理時の雰囲気制御についてはカーボンポテンシャル制御を行うが、その鋼の成分組成により平衡炭素濃度ならびに酸化状態が異なるため、事前に同一鋼材にてある条件で浸炭して、その結果により適宜調整する必要がある。また、この雰囲気制御の調整により最終的な鋼材表層の酸化状態が決定するが、必要な浸炭硬化層深さを得ると同時に規定する鋼材表層の酸化状態のコントロールには、成分組成の限定並びに雰囲気制御の両方が必要となる。
Carburizing quenching or carburizing and nitriding quenching is performed on a member processed into a part shape such as a gear, and then tempering is performed. About carburizing quenching, carburizing nitrocarburizing quenching, and tempering treatment, what is necessary is just to follow a conventional method, and there is no particular condition. For example, carburizing treatment is performed at 900 to 1050 ° C, and then furnace cooling is performed to 780 to 880 ° C. After that, hold for 0 to 3 hours, then put into oil at 60 to 130 ° C, or cool and quench with inert gas such as nitrogen gas or helium gas, then reheat to 150 to 220 ° C and temper The process of performing The carburizing process includes a case involving a diffusion process. Moreover, you may perform a nitriding process simultaneously with any one or more of said carburizing process, furnace cooling, and holding | maintenance.
The carbon potential is controlled for the atmosphere control during the carburizing treatment, but the equilibrium carbon concentration and oxidation state differ depending on the component composition of the steel, so carburize under the same steel material in advance, and adjust accordingly depending on the result There is a need. In addition, the final oxidation state of the steel surface layer is determined by adjusting the atmosphere control. In order to control the oxidation state of the steel surface layer as well as obtaining the required carburized hardened layer depth, the component composition is limited and the atmosphere is controlled. Both controls are required.
なお、このような浸炭処理あるいは浸炭浸窒処理、焼き入れ、焼戻しの処理を施すことにより、上述した本発明の成分組成の範囲であれば、非浸炭部のフェライト量は４０％以下となる。また、後述するショットピーニングを行って表面から２５μｍまでの深さで１０００ＭＰａ以上の圧縮残留応力を付与した後には、表面から３μｍ深さ位置までの表層酸化密度が４０％以上となる。 In addition, by performing such carburizing treatment or carburizing and nitriding treatment, quenching, and tempering treatment, the ferrite content in the non-carburized portion is 40% or less within the range of the component composition of the present invention described above. In addition, after performing shot peening described later and applying a compressive residual stress of 1000 MPa or more at a depth of 25 μm from the surface, the surface layer oxidation density from the surface to a depth of 3 μm becomes 40% or more.
部品形状とした後にショットピーニングを行う。ショットピーニングは、（１）粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を用いたショットピーニング、（２）粒径が０．４〜１．２ｍｍΦで硬さ７００ＨＶ以上の粒を用いて行った後、粒径が０．０３〜０．１ｍｍΦの硬さ７００ＨＶ以上の粒を用いて再度行う、（３）粒径が０．４〜１．２ｍｍΦで硬さ７００ＨＶ以上の粒と、０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を混合して行う、のいずれで行うことができる。ショットピーニングとして（１）〜（３）の順で疲労特性は良好となるが、製造コストを考慮して適宜選定する。 Shot peening is performed after making the part shape. Shot peening is (1) shot peening using grains having a particle size of 0.03 to 0.1 mmΦ and hardness of 700 HV or more, and (2) grains having a particle size of 0.4 to 1.2 mmΦ and hardness of 700 HV or more. And then again using particles having a particle size of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more. (3) Particles having a particle size of 0.4 to 1.2 mmΦ and a hardness of 700 HV or more And mixing with particles having a hardness of 700 HV or more at 0.03 to 0.1 mmΦ. As the shot peening, the fatigue characteristics are improved in the order of (1) to (3), but the proper selection is made in consideration of the manufacturing cost.
なお、（１）〜（３）のいずれにおいても、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を用いたショットピーニングを行うが、ショットピーニングに用いる粒の粒径が０．１ｍｍφを超えたり、０．０３ｍｍφ未満であったり、粒の硬さが７００ＨＶ未満であると、表面から２５μｍ深さ位置までの圧縮残留応力の平均値を１０００ＭＰａ以上とすることができない。なお、粒の投射圧、投射量、投射時間によっても、付与できる圧縮残留応力は変化する、すなわち、これらの値があまりに小さいと所期した圧縮残留応力を付与できなくなるので、これらの値を、表面から２５μｍ深さ位置までで１０００ＭＰａ以上の圧縮残留応力を付与できる程度の値に調整する必要がある。
以下、本発明の作用効果を実施例で具体的に示す。
In any of (1) to (3), shot peening is performed using particles having a particle size of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more, but the particle size of the particles used for shot peening is 0. When the thickness exceeds 0.1 mmφ, less than 0.03 mmφ, or the hardness of the grains is less than 700 HV, the average value of the compressive residual stress from the surface to the 25 μm depth position cannot be 1000 MPa or more. It should be noted that the compressive residual stress that can be applied also changes depending on the projection pressure, the projection amount, and the projection time of the grains, that is, if these values are too small, the desired compressive residual stress cannot be applied. It is necessary to adjust to a value that can give a compressive residual stress of 1000 MPa or more from the surface to a depth of 25 μm.
Hereafter, the effect of this invention is shown concretely by an Example.
表１に示す化学成分を有する鋼を溶解した。表中に示す鋼Ｎｏ．１〜２６は本発明の成分組成を満足する適合鋼であり、鋼Ｎｏ．４０〜５７は本発明の成分範囲外になる比較鋼である。鋼Ｎｏ．５６、５７は従来鋼で、Ｎｏ．５６はＪＩＳ ＳＣＭ４２０Ｈ、Ｎｏ．５７はＳＣＭ８２２Ｈ規格材である。なお、表１中、Ｐ、Ｓについては不可避的不純物として混入した含有量である。また、Ｃｕ、Ｎｉについては、０．０２ｍａｓｓ％未満の場合は、積極的に添加は行っていないが不可避的に混入しているＣｕ、Ｎｉの含有量として記載したものである。 Steels having chemical components shown in Table 1 were melted. Steel No. shown in the table. Nos. 1-26 are compatible steels satisfying the composition of the present invention. Reference numerals 40 to 57 are comparative steels that are outside the component range of the present invention. Steel No. Nos. 56 and 57 are conventional steels. 56 is JIS SCM420H, No. 56. 57 is an SCM822H standard material. In Table 1, P and S are contents mixed as inevitable impurities. Moreover, about Cu and Ni, when it is less than 0.02 mass%, it is described as content of Cu and Ni which are not added positively but are inevitably mixed.
溶製された上記、適合鋼、比較鋼、従来鋼のインゴットを熱間圧延により直径７０ｍｍの丸棒鋼に調製し、得られた丸棒鋼に対し焼準処理を実施した。 The ingots of the above-described compatible steel, comparative steel, and conventional steel were prepared into a round bar steel having a diameter of 70 mm by hot rolling, and the obtained round bar steel was subjected to normalization treatment.
それらの丸棒鋼よりローラーピッチング疲労試験片を作製した。ローラーピッチング試験片は、図１に示すように、９５０℃に加熱して浸炭・拡散処理をした後、炉内で冷却し、８５０℃で３０分均熱を行なった後、７０℃の油にて焼入れを実施した。その後１８０℃に再加熱し２時間均熱したのち空冷した。また、鋼Ｎｏ２６およびＮｏ５５（表２中Ｎｏ７およびＮｏ５６）については浸炭処理後の冷却過程でアンモニアガスを炉内に導入することにより浸炭浸窒焼入れ、焼戻し処理を行い試験片を作成した。 Roller pitting fatigue test pieces were produced from these round steel bars. As shown in FIG. 1, the roller pitching test piece was heated to 950 ° C. and subjected to carburizing / diffusion treatment, then cooled in a furnace, soaked at 850 ° C. for 30 minutes, and then heated to 70 ° C. oil. And quenching. Thereafter, it was reheated to 180 ° C., soaked for 2 hours, and then air-cooled. For steel No. 26 and No. 55 (No. 7 and No. 56 in Table 2), ammonia gas was introduced into the furnace during the cooling process after carburizing treatment, and carburizing nitrocarburizing and tempering treatments were performed to prepare test pieces.
さらに直径０．０３ｍｍで硬さ７５０ＨＶの鋼製ショット粒を用いてエアノズル式のショットピーニング装置を用いて圧力０．２ＭＰａ、投射量４ｋｇ/ｍｉｎで処理を実施した。尚、鋼Ｎｏ．２５鋼については別途、直径０．７ｍｍで硬さ７５０ＨＶの鋼製ショット粒を用いてエアノズル式のショットピーニング装置を用いて圧力０．４ＭＰａ、投射量１０ｋｇ/ｍｉｎでショットピーニングを行ったもの（表２のＮｏ.５９）と、ショット粒が直径０．０３ｍｍで硬さ７５０ＨＶの鋼製ショット粒を用いて圧力０．０５ＭＰａ、投射量１ｋｇ/ｍｉｎで実施したもの（表２のＮｏ.６０）と、直径０．０３ｍｍで硬さ６５０ＨＶの鋼製ショット粒を用いてエアノズル式のショットピーニング装置を用いて圧力０．２ＭＰａ、投射量４ｋｇ/ｍｉｎでショットピーニングを行ったもの（表２のＮｏ.６１）についても用意した。 Further, using steel shot grains having a diameter of 0.03 mm and a hardness of 750 HV, treatment was performed at a pressure of 0.2 MPa and a projection amount of 4 kg / min using an air nozzle type shot peening apparatus. Steel No. For 25 steel, shot peening was performed using a steel shot grain having a diameter of 0.7 mm and a hardness of 750 HV using an air nozzle type shot peening apparatus at a pressure of 0.4 MPa and a projection amount of 10 kg / min (Table No. 59 of No. 2) and a shot grain having a diameter of 0.03 mm and a steel shot grain having a hardness of 750 HV and a pressure of 0.05 MPa and a projection amount of 1 kg / min (No. 60 in Table 2) The shot peening was performed using a steel shot grain having a diameter of 0.03 mm and a hardness of 650 HV using an air nozzle type shot peening apparatus at a pressure of 0.2 MPa and a projection amount of 4 kg / min (No. 61 in Table 2). ) Was also prepared.
[有効硬化層深さ、組織観察、表層硬度、内部硬度、残留オーステナイト量]
浸炭焼入焼戻しを実施したローラーピッチング試験片の試験前材について転送面を切断し、断面の硬度分布を測定して有効硬化層深さを求めた。
また内部の非浸炭部において硬度測定と組織観察を行ない、フェライトの面積率を測定した。フェライトの面積率の測定は、試験片の芯部（径方向中心）よりサンプルを採取し、研磨後にナイタールでエッチングした面を光学顕微鏡を用いて４００倍の倍率で１００視野観察し、それらを画像処理にて二値化し、白い部分の面積を求め、全体の面積に対する割合求めることで行った。内部硬度については、試験片の芯部（径方向中心）よりサンプルを採取しビッカース硬さ（マイクロビッカース2.94Ｎ）を５点測定し、これらの平均値を求めた。
[Effective hardened layer depth, structure observation, surface hardness, internal hardness, retained austenite amount]
For the pre-test material of the roller pitching specimen subjected to carburizing, quenching and tempering, the transfer surface was cut, and the hardness distribution of the cross section was measured to determine the effective hardened layer depth.
Moreover, hardness measurement and structure observation were performed in the internal non-carburized part, and the area ratio of ferrite was measured. The area ratio of ferrite is measured by taking a sample from the core (diameter center) of the test piece, observing 100 views of the surface etched with nital after polishing with an optical microscope at a magnification of 400 times, and imaging them. It binarized by processing, and the area of the white portion was obtained, and the ratio to the total area was obtained. Regarding the internal hardness, a sample was taken from the core part (diameter center) of the test piece, and the Vickers hardness (micro Vickers 2.94N) was measured at five points, and the average value thereof was obtained.
また、浸炭焼入焼戻しを実施したローラーピッチング試験片の試験前材について、表層硬度、浸炭部の旧オーステナイト粒度（旧γ粒度）、表層の残留オーステナイト量（残留γ量）についても調査した。表層硬度は、表面より深さ0.03ｍｍの位置について、ビッカース硬さ（マイクロビッカース2.94Ｎ）を５点測定し、これらの平均値を求めた。旧オーステナイト粒度は、表層硬度を測定したものと同一箇所について、光学顕微鏡で100倍で観察してオーステナイト結晶粒度番号を求めた。残留オーステナイト量は、Ｘ線回折により表層部の残留オーステナイト量を調査した。 Further, the surface hardness, the prior austenite grain size (old γ grain size) of the carburized portion, and the residual austenite amount (residual γ amount) of the surface layer were also investigated for the pre-test material of the roller pitching test piece subjected to carburizing, quenching and tempering. For the surface hardness, five points of Vickers hardness (micro Vickers 2.94N) were measured at a position 0.03 mm deep from the surface, and the average value thereof was determined. The prior austenite grain size was obtained by observing the same spot with the surface hardness measured at 100 times with an optical microscope to obtain the austenite grain size number. Regarding the amount of retained austenite, the amount of retained austenite in the surface layer portion was examined by X-ray diffraction.
[表層酸化密度、粒界酸化層深さ]
上記の浸炭焼入焼戻しを実施したローラーピッチング試験片について表面下３μｍ位置までのＳｉの濃化をＥＰＭＡにより調査した。非浸炭部（浸炭焼入焼戻しを実施したローラーピッチング試験片の断面中心位置）の濃度に対して４倍以上濃化した部分について全体の面積との比である面積率を測定した。尚、分析前には表層の粒界酸化状況をすべての視野で観察してもっとも深くまで酸化が進行していた部分を粒界酸化層深さとした。
[Surface layer oxidation density, grain boundary oxide layer depth]
Regarding the roller pitching test piece subjected to the above carburizing quenching and tempering, the concentration of Si up to a position of 3 μm below the surface was investigated by EPMA. The area ratio which is a ratio with the whole area was measured about the part concentrated 4 times or more with respect to the density | concentration of the non-carburizing part (cross-sectional center position of the roller pitching test piece which performed carburizing quenching tempering). Before the analysis, the state of grain boundary oxidation on the surface layer was observed in all fields of view, and the portion where oxidation proceeded to the deepest was defined as the grain boundary oxide layer depth.
[圧縮残留応力]
ローラーピッチング試験片の転送面について表面から２５μｍ深さ位置での圧縮残留応力を測定した。尚、測定面の研磨には電解研磨を使用し、測定にはＸ線回折装置を使用した。圧縮残留応力の測定は、同一条件でショットピーニングした中の１本の試験片を用いて、転送面の円周上で９０度間隔で４位置について、円周方向、軸方向についてそれぞれ行った。各位置において、表層から深さ方向へ５μｍ間隔で２５μｍ深さまで測定し、そのすべての平均値を求めた。
[Compressive residual stress]
On the transfer surface of the roller pitching test piece, a compressive residual stress at a depth position of 25 μm from the surface was measured. Electrolytic polishing was used for polishing the measurement surface, and an X-ray diffractometer was used for measurement. The measurement of the compressive residual stress was performed in the circumferential direction and the axial direction at four positions at intervals of 90 degrees on the circumference of the transfer surface using one test piece that was shot peened under the same conditions. At each position, the surface layer was measured from the surface layer to the depth direction at a depth of 25 μm at intervals of 5 μm, and the average value of all of them was obtained.
[摩耗量測定]
摩耗量はローラーピッチング試験により調査した。大ローラー側のクラウニング量を１５０ｍｍＲとし、面圧３５００ＭＰａで１０万回まで回転させ、その試験片の接触面の横断面の摩耗曲線を採取して、試験前表面に対する摩耗最大深さを求めた。
[Abrasion measurement]
The amount of wear was investigated by a roller pitching test. The crowning amount on the large roller side was 150 mmR, the surface pressure was rotated to 100,000 times at 3500 MPa, and the wear curve of the cross section of the contact surface of the test piece was collected to determine the maximum wear depth with respect to the pre-test surface.
[歯車疲労試験]
さらに溶製された上記、適合鋼、比較鋼、従来鋼のインゴットより熱間圧延により直径１００ｍｍの丸棒鋼に調製し、得られた丸棒鋼に対し焼準処理を実施した。歯幅１０ｍｍ、モジュール２．５、ピッチ円１００ｍｍの歯車にて回転数３０００ｒｐｍ、潤滑油はトランスミッション用オイルを８０℃として、トルクを変化させて破損までの繰り返し数を調べ、繰り返し数１０００万回で破損しない最大トルクを疲労強度として評価した。
[Gear fatigue test]
Further, a round bar steel having a diameter of 100 mm was prepared by hot rolling from the ingots of the above-described compatible steel, comparative steel, and conventional steel, and the obtained round bar steel was subjected to normalization treatment. Gears with tooth width 10mm, module 2.5, pitch circle 100mm, rotating speed 3000rpm, lubricating oil with transmission oil at 80 ° C, changing torque and examining the number of repetition until breakage, with 10 million repetitions The maximum torque that did not break was evaluated as fatigue strength.
表２に上記試験結果を示す。
発明鋼であるＮｏ．１〜２７については、対摩耗性が良好であり、高い疲労強度が得られた。それに対して、Ｎｏ．４０はＣ量が発明範囲より低い。そのため浸炭焼入れ焼戻し後の内部硬度が低く、さらに表層硬度も発明例よりも低くなった。その結果、耐摩耗性が低くなり、歯元の折損および歯面でのピッチングが起こりやすくなり、歯車疲労強度が低下した。 Invented steel No. About 1-27, abrasion resistance was favorable and high fatigue strength was obtained. In contrast, no. 40 has a C content lower than the scope of the invention. Therefore, the internal hardness after carburizing, quenching and tempering was low, and the surface layer hardness was lower than that of the inventive examples. As a result, wear resistance was reduced, tooth root breakage and tooth surface pitching were likely to occur, and the gear fatigue strength was reduced.
Ｎｏ．４１はＣ量が発明範囲より高い。そのため、浸炭後の残留γ量が多くなりすぎており、高い表面硬度が得られていない、その結果、耐摩耗性が低下した。また、非浸炭部の靭性が足りず歯元部での破壊も起こりやすくなった。よって歯車疲労強度が低下した。 No. No. 41 has a higher C content than the scope of the invention. For this reason, the amount of residual γ after carburization is too large, and high surface hardness is not obtained. As a result, the wear resistance is lowered. Further, the toughness of the non-carburized portion was insufficient and the tooth root portion was easily broken. Therefore, the gear fatigue strength decreased.
Ｎｏ．４２はＳｉ量が本発明範囲よりも少なく、そのために粒界酸化層が深めになっている。焼戻し軟化抵抗が低くなりすぎたために、耐摩耗性が低下した。またピッチングが起こりやすくなり、歯車疲労強度が低下した。 No. No. 42 has a Si content less than the range of the present invention, and therefore the grain boundary oxide layer is deeper. Since the temper softening resistance was too low, the wear resistance decreased. Also, pitching was likely to occur, and the gear fatigue strength was reduced.
Ｎｏ．４３はＳｉ量が本発明範囲よりも多い。その結果、内部に軟質なフェライトが発生しすぎて、歯元での曲げ疲労破壊が起こりやすくなり、歯車疲労強度が低下した。
Ｎｏ．４４はＭｎ量が本発明範囲よりも低い。そのため、焼入れ性が低下しすぎており、有効硬化層深さが浅すぎるために、歯元での曲げ疲労破壊が起こりやすくなり歯車疲労強度が低下した。
No. No. 43 has more Si than the scope of the present invention. As a result, too much soft ferrite was generated inside, and bending fatigue failure at the tooth root was likely to occur, and the gear fatigue strength was reduced.
No. No. 44 has a Mn content lower than the range of the present invention. For this reason, the hardenability is too low, and the effective hardened layer depth is too shallow, so that bending fatigue failure at the root tends to occur, and the gear fatigue strength is reduced.
Ｎｏ．４５はＭｎ量が本発明範囲より高い。そのために浸炭後の内部硬度が高くなりすぎたために、曲げ疲労特性が低下した。また、（１）式も満足できず、摩耗量が大きくなりピッチングが起こりやすくなった。 No. No. 45 has a Mn content higher than the range of the present invention. Therefore, since the internal hardness after carburizing became too high, the bending fatigue characteristics deteriorated. In addition, the formula (1) was not satisfied, and the amount of wear increased and pitching was likely to occur.
Ｎｏ．４６はＣｒ量が少なく、焼入れ性が低下しすぎている。そのため、硬化層深さが浅くなりすぎて歯元での折損が起こりやすくなり、またピッチングも起こりやすくなって、歯車疲労強度が低下した。 No. No. 46 has a small amount of Cr, and the hardenability is too low. For this reason, the hardened layer depth becomes too shallow and breakage at the tooth base is likely to occur, and pitching is also likely to occur, resulting in a reduction in gear fatigue strength.
Ｎｏ．４７はＣｒ量が高すぎるために、内部硬度が高くなりすぎている。そのため、歯元の靭性が劣化して曲げ折損しやすくなり、疲労強度が低下した。 No. 47 has an excessively high internal hardness because the amount of Cr is too high. As a result, the toughness of the tooth root deteriorates and the bending breakage easily occurs, and the fatigue strength decreases.
Ｎｏ．４８はＭｏ量が高い。そのため焼入れ性が高すぎて、靭性が低すぎるために曲げ折損により疲労強度が低下した。 No. 48 has a high Mo content. Therefore, the hardenability was too high and the toughness was too low, so that the fatigue strength was lowered due to bending breakage.
Ｎｏ．４９はＡｌ量が低くすぎるために介在物起点による歯元および歯面での破壊が起こりやすくなり、歯車疲労強度が低下した。 No. In No. 49, since the Al amount was too low, destruction at the root and tooth surface due to inclusion starting points was likely to occur, and the gear fatigue strength was reduced.
Ｎｏ．５０はＡｌ量が高すぎるため、浸炭部のオーステナイト粒が粗大化してしまい、歯元および歯面での破壊が起こりやすくなり、歯車疲労強度が低下した。 No. In No. 50, since the amount of Al was too high, the austenite grains in the carburized portion were coarsened, and the fracture at the tooth root and the tooth surface was likely to occur, and the gear fatigue strength was reduced.
Ｎｏ．５１はＴｉ量が多すぎる。そのためＴｉ系介在物起点での破壊が多発した。そのために歯元での曲げ折損および歯面でのピッチングが起こりやすくなり、歯車疲労強度が低下した。 No. 51 has too much Ti amount. Therefore, destruction at the Ti-based inclusion starting point occurred frequently. For this reason, bending breakage at the tooth root and pitching at the tooth surface are likely to occur, and the gear fatigue strength is reduced.
Ｎｏ．５２はＮ量が低すぎる。そのために結晶粒の粗大化が起こり、歯元での曲げ折損が起こりやすくなり、歯車疲労強度が低下した。 No. 52 is too low in N content. As a result, coarsening of the crystal grains occurred, bending breakage at the tooth roots easily occurred, and the gear fatigue strength decreased.
Ｎｏ．５３はＮ量が高すぎる。そのため、内部割れ起点での破壊が多く発生し、歯車疲労強度が低下した。 No. 53 has too much N content. Therefore, many fractures occurred at the starting point of internal cracks, and the gear fatigue strength decreased.
Ｎｏ．５４、５５、５６は（１）式を満足していない。そのために摩耗量が大きくなっており、そのため疲労強度も低下した。 No. 54, 55 and 56 do not satisfy the expression (1). For this reason, the amount of wear has increased, and the fatigue strength has also decreased.
Ｎｏ．５７、５８はＳｉ量が本発明範囲よりも低いために３００℃焼戻し硬度と残留応力が低くなっている。また、（１）式を満足しておらず、ピッチングが発生しやすくなった。また、表面酸化が粒界に沿って深く進行したため、歯元曲げ応力による折損がしやすくなり、歯車疲労強度が低下した。 No. Nos. 57 and 58 are low in 300 ° C. tempering hardness and residual stress because the Si amount is lower than the range of the present invention. Further, the formula (1) was not satisfied, and pitching was likely to occur. Further, since the surface oxidation proceeded deeply along the grain boundary, it was easy to break due to the root bending stress, and the gear fatigue strength decreased.
Ｎｏ．５９はショット粒の大きいものを用いたために、最表面の残留応力も低くなり、摩耗量が大きくなり、疲労強度が低下した。 No. Since No. 59 used had large shot grains, the residual stress on the outermost surface was reduced, the amount of wear was increased, and the fatigue strength was reduced.
Ｎｏ．６０、６１は最表面の残留応力が低くなり、摩耗量が大きくなり、疲労強度が低下した。 No. In Nos. 60 and 61, the residual stress on the outermost surface was lowered, the wear amount was increased, and the fatigue strength was lowered.
本発明によれば、耐摩耗性および耐久性に優れた浸炭部品、および、量産可能なその製造方法を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the carburized component excellent in abrasion resistance and durability, and its manufacturing method which can be mass-produced can be provided.
Claims (6)
かつ、下記（１）式を満足する非浸炭部と、該非浸炭部より表面側にあって、該非浸炭部に対してＣ含有量またはさらにＮ含有量が高い成分組成である浸炭部を有し、
該浸炭部は、表面から３μｍ深さ位置までの酸化密度が４０％以上であり、表面から２５μｍ深さ位置までの圧縮残留応力の平均値が１０００ＭＰａ以上であり、
前記非浸炭部の鋼組織はフェライト量が面積率で４０％以下であることを特徴とする耐摩耗性および疲労特性に優れた浸炭部品。
[Ｓｉ]＋３[Ｃｒ]−[Ｍｎ]≧４．０ ・・・（１）
但し、[Ｍ]はＭ元素の含有量（ｍａｓｓ％）を示す。 Component composition is C: 0.12-0.30 mass%, Si: 0.80-2.50 mass%, Mn: 0.40-0.80 mass%, Cr: 0.80-2.00 mass%, Mo: 0.3 mass% or less (including 0 mass%), Al: 0.010 to 0.080 mass%, N: 0.0040 to 0.0200 mass%, Cu: 0.50 mass% or less (including 0 mass%), Ni: 2.0 mass% or less (including 0 mass%), the balance Fe and inevitable impurities,
And a non-carburized portion that satisfies the following formula (1), and a carburized portion that is on the surface side of the non-carburized portion and has a component composition having a higher C content or higher N content than the non-carburized portion. ,
The carburized portion has an oxidation density of 40% or more from the surface to a depth of 3 μm, an average value of compressive residual stress from the surface to a depth of 25 μm is 1000 MPa or more,
A carburized part excellent in wear resistance and fatigue characteristics, wherein the steel structure of the non-carburized part has an ferrite content of 40% or less in terms of area ratio.
[Si] +3 [Cr] − [Mn] ≧ 4.0 (1)
However, [M] indicates the content (mass%) of the M element.
浸炭焼入れあるいは浸炭浸窒焼入れの後、焼戻し処理を行い、
次いで、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を用いてショットピーニングを行うことを特徴とする耐摩耗性および疲労特性に優れた浸炭部品の製造方法。 After performing any one or more of machining, hot forging, cold forging, and warm forging using the steel material having the component composition according to any one of claims 1 to 3,
After carburizing quenching or carburizing and nitrocarburizing quenching,
Next, a method for producing a carburized part excellent in wear resistance and fatigue characteristics, characterized by performing shot peening using grains having a grain size of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more.
浸炭焼入れあるいは浸炭浸窒焼入れの後、焼戻し処理を行い、
次いで、粒径が０．４〜１．２ｍｍΦで硬さ７００ＨＶ以上の粒を用いてショットピーニングを行った後、
さらに、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒を用いて再度ショットピーニングを行うことを特徴とする耐摩耗性および疲労特性に優れた浸炭部品の製造方法。 Using the steel material having the component composition according to any one of claims 1 to 3, after performing any one or more of machining, hot forging, cold forging, and warm forging into a part shape,
After carburizing quenching or carburizing and nitrocarburizing quenching,
Next, after performing shot peening using particles having a particle size of 0.4 to 1.2 mmΦ and a hardness of 700 HV or more,
Furthermore, a method for producing a carburized part excellent in wear resistance and fatigue characteristics, characterized in that shot peening is performed again using grains having a grain size of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more.
浸炭焼入れあるいは浸炭浸窒焼入れの後、焼戻し処理を行い、
次いで、粒径が０．４〜１．２ｍｍΦで硬さ７００ＨＶ以上の粒と、粒径が０．０３〜０．１ｍｍΦで硬さ７００ＨＶ以上の粒とを混合してショットピーニングを行うことを特徴とする耐摩耗性および疲労特性に優れた浸炭部品の製造方法。 Using the steel material having the component composition according to any one of claims 1 to 3, after performing any one or more of machining, hot forging, cold forging, and warm forging into a part shape,
After carburizing quenching or carburizing and nitrocarburizing quenching,
Next, shot peening is performed by mixing grains having a particle diameter of 0.4 to 1.2 mmΦ and a hardness of 700 HV or more with grains having a particle diameter of 0.03 to 0.1 mmΦ and a hardness of 700 HV or more. A method for producing a carburized part having excellent wear resistance and fatigue characteristics.
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| JP2020164900A (en) * | 2019-03-28 | 2020-10-08 | Ｊｆｅスチール株式会社 | Carburized member |
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| KR102274744B1 (en) * | 2020-02-07 | 2021-07-08 | 이래에이엠에스 주식회사 | Heat treatment method for tubular shaft for drive shaft having ball spline structure and tubular shaft manufactured by the same |
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