JP2019026881A - Steel member - Google Patents
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本発明は、焼き入れ・焼き戻し処理をして使用する、鋼部材に関するものである。 The present invention relates to a steel member that is used after being quenched and tempered.
機械、自動車等に使用される鋼部材のうち、軸受、歯車など、特に高い耐摩耗性を必要とされるものは、例えば、ＪＩＳ Ｇ４０５３規定のクロム鋼を素材として、浸炭処理を行ってから焼き入れ・焼き戻し処理をして使用されている。また、ＪＩＳ Ｇ４８０５規定の高炭素クロム鋼を素材として、焼き入れ・焼き戻し処理をして使用されているものもある。これらの鋼部材は、鋼材をオーステナイト単相域、あるいは、オーステナイトとセメンタイトの二相域となる高温に加熱した後に焼き入れ・低温焼き戻しを行い、表層を７５０ＨＶ以上の高硬度にすることで高い耐摩耗性を得ている。このような鋼部材は、高い面圧で他部材と接触・摺動することで起きる摩耗に強いだけでなく、例えば、歯車の歯元が受ける衝撃的な負荷や、曲げ応力に耐える強度も要求される。 Among steel members used in machinery, automobiles, etc., those that require particularly high wear resistance, such as bearings and gears, for example, are baked after carburizing treatment using chrome steel defined in JIS G4053. Used after tempering. In addition, some of the high-carbon chromium steel specified in JIS G4805 is used after being quenched and tempered. These steel members are high by heating the steel material to a high temperature that becomes an austenite single-phase region or a two-phase region of austenite and cementite, followed by quenching and low-temperature tempering to make the surface layer a high hardness of 750 HV or higher. Abrasion resistance is obtained. Such steel members are not only resistant to wear caused by contact and sliding with other members at high surface pressures, but also require, for example, the shock load received by the gear teeth and the strength to withstand bending stress. Is done.
鋼部材の耐摩耗性を向上させる手段として、浸炭処理により表層部のＣ濃度を上げたり、鋼素材として高炭素鋼を用いる方法がある。また、合金工具鋼、高速度工具鋼のように、鋼素材にＣｒ、Ｍｏ、Ｖ、Ｗを添加し、セメンタイトよりも硬い合金炭化物（Ｍｏ２Ｃ、ＷＣなど）を鋼中に分散させる方法が知られている。 As means for improving the wear resistance of the steel member, there are a method of increasing the C concentration in the surface layer portion by carburizing treatment or using high carbon steel as a steel material. In addition, there is a method in which Cr, Mo, V, W is added to a steel material and alloy carbides (Mo 2 C, WC, etc.) harder than cementite are dispersed in the steel, such as alloy tool steel and high-speed tool steel. Are known.
例えば、特許文献１には、Ｃ、Ｃｒ、Ｍｏ、Ｖ、Ｗを多量に添加した耐摩耗性に優れる鋼粉末に、Ｎｉ粉末を配合して成形焼結することで耐衝撃強度を与え、さらに前記焼結体に潤滑油を含浸させることで摺動特性を向上させる発明が記載されている。 For example, Patent Document 1 gives impact resistance strength by blending and sintering Ni powder into steel powder with excellent wear resistance added with a large amount of C, Cr, Mo, V, W, An invention is described in which sliding properties are improved by impregnating the sintered body with lubricating oil.
特許文献２には、Ｃ、Ｃｒ、Ｍｏ、Ｖ、Ｗ、Ｃｏを多量に添加した鋼に浸炭処理を施し、耐摩耗性、特に３００℃〜４００℃の高温における耐摩耗性を向上させる発明が記載されている。
特許文献３には、Ｃｒ、Ｍｏ、Ｖを多く添加した鋼に浸炭処理を施し、表面から深さ５０μｍ位置までの領域に存在する炭化物の面積率を６〜２５％とすることで、耐摩耗性を向上させる発明が記載されている。 In Patent Document 3, carburizing treatment is performed on steel to which a large amount of Cr, Mo, V is added, and the area ratio of carbide existing in the region from the surface to a depth of 50 μm is set to 6 to 25%. An invention for improving the performance is described.
しかしながら、特許文献１および特許文献２に記載された従来技術は、鋼の焼き入れ性が高いため内部まで焼きが入りやすく、さらに合金炭化物が多く存在するため、内部の靭性が低いという欠点があった。さらに、特許文献１は、鋼材成分が一様であるため、焼き入れ時、冷却速度の速い表面からマルテンサイト変態を起こし、その後、内部がマルテンサイト変態する。そのため、表面には高い引張残留応力が発生し、曲げ応力に対して著しく弱くなる。特許文献２および特許文献３に記載された従来技術には、耐摩耗性を向上させるためにＣｒ、Ｍｏ等の合金炭化物生成元素を多量に添加した場合、浸炭処理の際に、表面から侵入したＣが、過剰に存在する合金炭化物生成元素と反応して鋼内部への拡散が阻害され、硬化層深さを深くすることが困難という欠点があった。
However, the prior arts described in Patent Document 1 and
本発明は、上述の実情に鑑みてなされたものであり、耐摩耗性と靭性、曲げ疲労強度に優れた鋼部材を提供することを課題とする。 This invention is made | formed in view of the above-mentioned situation, and makes it a subject to provide the steel member excellent in abrasion resistance, toughness, and bending fatigue strength.
上記の欠点を解決するため、本発明では、以下の２点を解決手段として採用することとした。
（１）鋼部材の耐摩耗性を確保するために、耐摩耗性を必要とする表層部においては、Ｃ濃度を高めるとともに、Ｍｏ、Ｖ等の硬質な合金炭化物生成元素を含有させる成分設計とした。
（２）焼き入れ後に耐摩耗性を必要とする表層部に圧縮残留応力が発生するよう、また、表層部以外の基材部では靭性が損なわれないよう、基材部は表層部と比較してＣ濃度および合金元素濃度を低減する成分設計とした。
上記した設計思想により、本発明の鋼部材は、表層部のＣ濃度が高く、Ｍｏ、Ｖ等の硬質な合金炭化物生成元素を含有しているため、焼き入れ後に高い耐摩耗性が得られる。また、基材部はＣ濃度が低く、合金元素の濃度も低減されているため、焼き入れ後においても基材部は靭性に優れている。さらに、鋼成分が一様ではなく、表層部は基材部よりもＣ濃度および合金元素の濃度が高いため、Ｍｓ点が低い。そのため、焼き入れ時、最初にマルテンサイト変態を起こすのは表層部直下の基材部の低Ｃ低合金領域であり、その後、表層部が変態するため、表層部には圧縮残留応力が発生し、曲げ応力に対して強くなる。
上記した本発明の要旨は、以下の通りである。
In order to solve the above drawbacks, the present invention adopts the following two points as solving means.
(1) In order to ensure the wear resistance of the steel member, in the surface layer portion that requires wear resistance, while increasing the C concentration, the component design to contain a hard alloy carbide forming element such as Mo, V and the like did.
(2) Compare the base material with the surface layer so that compressive residual stress is generated in the surface layer that requires wear resistance after quenching, and the toughness is not impaired in the base material other than the surface layer. Therefore, the component design was made to reduce the C concentration and the alloy element concentration.
Due to the design concept described above, the steel member of the present invention has a high C concentration in the surface layer portion and contains a hard alloy carbide-forming element such as Mo and V, so that high wear resistance is obtained after quenching. Further, since the base material portion has a low C concentration and a reduced concentration of alloy elements, the base material portion is excellent in toughness even after quenching. Furthermore, the steel component is not uniform, and the surface layer portion has a higher C concentration and alloy element concentration than the base material portion, and thus the Ms point is low. Therefore, at the time of quenching, the first martensitic transformation occurs in the low C low-alloy region of the base material portion immediately below the surface layer portion, and then the surface layer portion is transformed, so that compressive residual stress is generated in the surface layer portion. It becomes strong against bending stress.
The gist of the present invention described above is as follows.
［１］ 基材部と、前記基材部の少なくとも一部を覆う表層部とを備えた鋼部材であって、
前記基材部が、質量％で、
Ｃ：０．１０〜０．５０％、
Ｓｉ：０．０５〜０．５０％、
Ｍｎ：０．２０〜０．９０％、
Ａｌ：０．００５〜０．１００％、
Ｎ：０．００１０〜０．０２５０％、
Ｐ：０．００１〜０．０３０％、
Ｓ：０．００５〜０．０２５％および
Ｃｒ：０．１０〜１．５０％
を含有し、残部がＦｅおよび不純物からなり、
ビッカース硬さが３００〜６５０ＨＶであり、
前記表層部が、質量％で、
Ｃ：０．８０〜１．６０％、
Ｓｉ：０．０５〜２．００％、
Ｍｎ：０．２０〜１．５０％、
Ａｌ：０．００５〜０．１００％、
Ｎ：０．００１０〜０．０２５０％、
Ｐ：０．００１〜０．０３０％および
Ｓ：０．００５〜０．０２５％
を含有し、さらに、
Ｃｒ：０．６０〜４．００％、
Ｍｏ：０．２０〜３．００％、
Ｖ：０．４０〜２．００％および
Ｗ：０．３０〜２．５０％
からなる群から選択される１種または２種以上を含有し、残部がＦｅおよび不純物からなり、
ビッカース硬さが７５０ＨＶ以上であり、
前記表層部の表面の面内方向と平行な方向の圧縮残留応力が２００ＭＰａ以上であり、
厚さが０．３０〜２．００ｍｍである、鋼部材。
[1] A steel member comprising a base material portion and a surface layer portion covering at least a part of the base material portion,
The base material part is mass%,
C: 0.10 to 0.50%,
Si: 0.05 to 0.50%,
Mn: 0.20 to 0.90%,
Al: 0.005 to 0.100%,
N: 0.0010 to 0.0250%,
P: 0.001 to 0.030%,
S: 0.005 to 0.025% and Cr: 0.10 to 1.50%
And the balance consists of Fe and impurities,
Vickers hardness is 300-650HV,
The surface layer part is mass%,
C: 0.80 to 1.60%,
Si: 0.05 to 2.00%,
Mn: 0.20 to 1.50%,
Al: 0.005 to 0.100%,
N: 0.0010 to 0.0250%,
P: 0.001 to 0.030% and S: 0.005 to 0.025%
In addition,
Cr: 0.60 to 4.00%,
Mo: 0.20 to 3.00%
V: 0.40 to 2.00% and W: 0.30 to 2.50%
1 type or 2 types or more selected from the group which consists of, The remainder consists of Fe and an impurity,
Vickers hardness is 750HV or more,
The compressive residual stress in a direction parallel to the in-plane direction of the surface of the surface layer portion is 200 MPa or more,
A steel member having a thickness of 0.30 to 2.00 mm.
本発明の鋼部材は、硬く、圧縮残留応力を有する表層部と、靭性が高い基材部とを備えており、耐摩耗性と靭性に優れ、曲げ疲労強度にも優れたものとなる。 The steel member of the present invention is hard and has a surface layer portion having compressive residual stress and a base material portion having high toughness, and is excellent in wear resistance and toughness and in bending fatigue strength.
以下、本発明の実施の形態（以下、単に「実施形態」と称する場合がある）を詳細に説明する。これらの実施形態は、本発明を限定するものではない。また、下記実施形態の構成要素には、当業者が置換可能かつ容易なもの、或いは実質的に同一のものが含まれる。さらに、下記実施形態に含まれる各種形態は、当業者が自明の範囲内で任意に組み合わせることができる。 Hereinafter, embodiments of the present invention (hereinafter sometimes simply referred to as “embodiments”) will be described in detail. These embodiments do not limit the present invention. In addition, constituent elements of the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same. Furthermore, various forms included in the following embodiments can be arbitrarily combined within a range obvious to those skilled in the art.
本実施形態の鋼部材は、基材部と、基材部の少なくとも一部を覆う表層部とを備えた鋼部材である。この鋼部材は、表層部の化学成分を有する鋼と基材部の化学成分を有する鋼とを一体化させた鋼素材を製造した後、鋼素材に対して必要に応じて機械加工を施して部品形状とし、更に、焼き入れ、焼き戻しを施すことにより製造される。このような製造過程を経て得られる鋼部材は、硬く、圧縮残留応力を有する硬化層としての表層部と、靭性が高い基材部とを有するものとなる。このような本実施形態の鋼部材は、例えば、軸受、歯車といった部品に適用することができる。
以下、鋼部材について説明する。
The steel member of this embodiment is a steel member provided with a base material part and a surface layer part covering at least a part of the base material part. This steel member is manufactured by manufacturing a steel material in which steel having the chemical component of the surface layer part and steel having the chemical component of the base material part are integrated, and then machining the steel material as necessary. It is manufactured by making it into a part shape, and further quenching and tempering. The steel member obtained through such a manufacturing process is hard and has a surface layer portion as a hardened layer having compressive residual stress and a base material portion having high toughness. Such a steel member of this embodiment can be applied to components such as a bearing and a gear.
Hereinafter, the steel member will be described.
まず、鋼部材を構成する基材部と表層部との化学成分について説明する。以下に示す各元素の割合（％）は全て質量％を意味する。基材部と表層部との化学成分は、表層部と基材部とで同じ範囲の元素もあるし、異なる範囲の元素もある。以下の説明では、化学成分毎にその含有量の限定理由を説明する。
本実施形態に係る基材部は、質量％で、Ｃ：０．１０〜０．５０％、Ｓｉ：０．０５〜０．５０％、Ｍｎ：０．２０〜０．９０％、Ａｌ：０．００５〜０．１００％、Ｎ：０．００１０〜０．０２５０％、Ｐ：０．００１〜０．０３０％、Ｓ：０．００５〜０．０２５％およびＣｒ：０．１０〜１．５０％を含有し、残部がＦｅおよび不純物からなる。
また、表層部は、質量％で、Ｃ：０．８０〜１．６０％、Ｓｉ：０．０５〜２．００％、Ｍｎ：０．２０〜１．５０％、Ａｌ：０．００５〜０．１００％、Ｎ：０．００１０〜０．０２５０％、Ｐ：０．００１〜０．０３０％およびＳ：０．００５〜０．０２５％を含有し、さらに、Ｃｒ：０．６０〜４．００％、Ｍｏ：０．２０〜３．００％、Ｖ：０．４０〜２．００％およびＷ：０．３０〜２．５０％からなる群から選択される１種または２種以上を含有し、残部がＦｅおよび不純物からなる。
First, the chemical component of the base material part and surface layer part which comprise a steel member is demonstrated. The ratio (%) of each element shown below means mass%. The chemical components of the base material portion and the surface layer portion include elements in the same range in the surface layer portion and the base material portion, and there are also elements in different ranges. In the following description, the reason for limiting the content of each chemical component will be described.
The base material part which concerns on this embodiment is the mass%, C: 0.10-0.50%, Si: 0.05-0.50%, Mn: 0.20-0.90%, Al: 0 0.005 to 0.100%, N: 0.0010 to 0.0250%, P: 0.001 to 0.030%, S: 0.005 to 0.025% and Cr: 0.10 to 1.50 %, With the balance being Fe and impurities.
Moreover, a surface layer part is the mass%, C: 0.80-1.60%, Si: 0.05-2.00%, Mn: 0.20-1.50%, Al: 0.005-0 100%, N: 0.0010 to 0.0250%, P: 0.001 to 0.030% and S: 0.005 to 0.025%, and Cr: 0.60 to 4.25%. Contains one or more selected from the group consisting of 00%, Mo: 0.20 to 3.00%, V: 0.40 to 2.00% and W: 0.30 to 2.50% The balance consists of Fe and impurities.
Ｃ（表層部）：０．８０〜１．６０％
Ｃ（基材部）：０．１０〜０．５０％
炭素（Ｃ）は鋼部材の強度に大きく影響する重要な元素である。表層部は高い耐摩耗性を実現するため、硬さが７５０ＨＶ以上である必要がある。そのため、表層部のＣ含有量は０．８０〜１．６０％とする。表層部のＣ含有量が０．８０％未満では、焼き入れ・焼き戻し後でも７５０ＨＶ以上のビッカース硬さが得られず、一方、１．６０％を超えると鋳造・熱間圧延時の延性を劣化させると同時に、鋼素材の鍛造性および機械加工時の被削性を低下させる。そのため、表層部のＣ含有量を０．８０〜１．６０％とする。
鋼部材の基材部は硬さと靭性とのバランスが求められるため、硬さは３００〜６５０ＨＶである必要がある。そのため、基材部のＣ含有量は０．１０〜０．５０％とし、表層部よりも低くする。基材部のＣ含有量が０．１０％未満では、焼き入れ・焼き戻し後でも３００ＨＶ以上のビッカース硬さが得られず、一方、０．５０％を超えると、焼き入れ・焼き戻し後にビッカース硬さが６５０ＨＶ超となり十分な靭性が得られない。
C (surface layer part): 0.80 to 1.60%
C (base material part): 0.10 to 0.50%
Carbon (C) is an important element that greatly affects the strength of the steel member. The surface layer portion needs to have a hardness of 750 HV or higher in order to achieve high wear resistance. Therefore, the C content in the surface layer portion is set to 0.80 to 1.60%. If the C content of the surface layer is less than 0.80%, Vickers hardness of 750 HV or higher cannot be obtained even after quenching and tempering. On the other hand, if it exceeds 1.60%, the ductility during casting and hot rolling is reduced. At the same time, the forgeability of the steel material and the machinability during machining are reduced. Therefore, the C content in the surface layer portion is set to 0.80 to 1.60%.
Since the base material portion of the steel member is required to have a balance between hardness and toughness, the hardness needs to be 300 to 650 HV. Therefore, C content of a base material part shall be 0.10 to 0.50%, and is made lower than a surface layer part. When the C content of the base material is less than 0.10%, Vickers hardness of 300 HV or higher cannot be obtained even after quenching and tempering. On the other hand, when it exceeds 0.50%, Vickers after quenching and tempering is not obtained. The hardness exceeds 650 HV and sufficient toughness cannot be obtained.
Ｓｉ（表層部）：０．０５〜２．００％
Ｓｉ（基材部）：０．０５〜０．５０％
シリコン（Ｓｉ）は焼き戻し軟化抵抗を向上させ、温度上昇に伴う軟化を抑制する有用な元素である。表層部のＳｉ含有量が０．０５％未満では前記作用が発揮できず、一方、２．００％を超えると前記作用が飽和し始め、含有量に見合う効果が期待できない。そのため、表層部のＳｉ含有量を０．０５〜２．００％とする。
また、基材部には高い焼き戻し軟化抵抗は必要なく、鍛造性および機械加工時の被削性が優先される。そのため、基材部のＳｉ含有量を０．０５〜０．５０％とする。
Si (surface layer part): 0.05 to 2.00%
Si (base material part): 0.05 to 0.50%
Silicon (Si) is a useful element that improves the temper softening resistance and suppresses the softening associated with the temperature rise. If the Si content of the surface layer is less than 0.05%, the above-mentioned action cannot be exhibited. On the other hand, if it exceeds 2.00%, the action starts to saturate, and an effect commensurate with the content cannot be expected. Therefore, the Si content in the surface layer portion is set to 0.05 to 2.00%.
Further, the base material portion does not require high temper softening resistance, and forgeability and machinability during machining are given priority. Therefore, the Si content of the base material portion is set to 0.05 to 0.50%.
Ｍｎ（表層部）：０．２０〜１．５０％
Ｍｎ（基材部）：０．２０〜０．９０％
マンガン（Ｍｎ）は焼き入れ性を高めると同時に、赤熱脆性を抑制し、熱間延性を向上させる元素である。表層部のＭｎ含有量が０．２０％未満では前記作用が発揮できず、一方、１．５０％を超えると含有量に見合う効果が期待できない。そのため、表層部のＭｎ含有量を０．２０〜１．５０％とする。
また、基材部には高い焼き入れ性は必要なく、鋼素材の鍛造性および機械加工時の被削性が優先される。そのため、基材部のＭｎ含有量を０．２０〜０．９０％とする。
Mn (surface layer part): 0.20 to 1.50%
Mn (base material part): 0.20 to 0.90%
Manganese (Mn) is an element that improves hardenability and at the same time suppresses red heat embrittlement and improves hot ductility. If the Mn content in the surface layer is less than 0.20%, the above-described effect cannot be exhibited. On the other hand, if it exceeds 1.50%, an effect commensurate with the content cannot be expected. Therefore, the Mn content in the surface layer portion is set to 0.20 to 1.50%.
Further, the base material portion does not need high hardenability, and priority is given to the forgeability of the steel material and the machinability during machining. Therefore, the Mn content in the base material portion is set to 0.20 to 0.90%.
Ａｌ（表層部および基材部）：０．００５〜０．１００％
アルミニウム（Ａｌ）は脱酸作用を有するとともに、熱処理の際、Ｎと結合してＡｌＮを形成することによりオーステナイト粒の粗大化を防止し、靭性を高める効果を持つ。表層部および基材部のＡｌ含有量が０．００５％未満ではこれらの効果が発揮されず、一方、０．１００％を超えると上記効果が飽和する。そのため、表層部および基材部のＡｌ含有量をともに０．００５〜０．１００％とする。
Al (surface layer portion and base material portion): 0.005 to 0.100%
Aluminum (Al) has a deoxidizing action and also has the effect of preventing austenite grains from coarsening and increasing toughness by forming AlN by combining with N during heat treatment. If the Al content of the surface layer portion and the base material portion is less than 0.005%, these effects are not exhibited, while if it exceeds 0.100%, the above effects are saturated. Therefore, both Al content of a surface layer part and a base-material part shall be 0.005-0.100%.
Ｎ（表層部および基材部）：０．００１０〜０．０２５０％
窒素（Ｎ）はＡｌ、Ｖと結合して窒化物を形成することによりオーステナイト粒の粗大化を防止し、靭性を高める効果を有する。表層部および基材部のＮ含有量が０．００１０％未満ではその効果が小さく、一方、０．０２５０％を超えると上記効果が飽和する。そのため、表層部および基材部のＮ含有量をともに０．００１０〜０．０２５０％とする。好ましくは、０．００３０〜０．０１５０％とする。
N (surface layer part and base material part): 0.0010 to 0.0250%
Nitrogen (N) combines with Al and V to form nitrides, thereby preventing austenite grains from coarsening and increasing toughness. If the N content in the surface layer part and the base material part is less than 0.0010%, the effect is small, whereas if it exceeds 0.0250%, the effect is saturated. Therefore, both the N content in the surface layer portion and the base material portion are set to 0.0010 to 0.0250%. Preferably, the content is 0.0030 to 0.0150%.
Ｐ（表層部および基材部）：０．００１〜０．０３０％
リン（Ｐ）は不純物として含まれる元素である。Ｐは粒界に偏析して粒界強度を下げるため、Ｐ含有量はなるべく低い方が良い。そのため、表層部および基材部におけるＰ含有量の上限を０．０３０％以下とする。表層部および基材部におけるＰ含有量の好ましい上限は０．０２０％以下である。Ｐは製鋼工程において低減することができるものの、０．００１％未満とするには製造コストがかかり、また０．００１％未満としても粒界強度が顕著に向上することはないので、表層部および基材部におけるＰ含有量の下限を０．００１％以上とする。
P (surface layer part and base material part): 0.001 to 0.030%
Phosphorus (P) is an element contained as an impurity. Since P segregates at the grain boundaries to lower the grain boundary strength, the P content is preferably as low as possible. Therefore, the upper limit of the P content in the surface layer portion and the base material portion is set to 0.030% or less. The upper limit with preferable P content in a surface layer part and a base-material part is 0.020% or less. Although P can be reduced in the steelmaking process, it takes a manufacturing cost to make it less than 0.001%, and even if it is less than 0.001%, the grain boundary strength is not significantly improved. The lower limit of the P content in the base material portion is set to 0.001% or more.
Ｓ（表層部および基材部）：０．００５〜０．０２５％
硫黄（Ｓ）は鋼部材の被削性を向上させるため、０．００５％以上を含有させる。しかし、Ｓ含有量が多すぎると、Ｍｎによって固定されなかったＳがＦｅＳとして粒界に生成することで、熱間延性が低下する。また、大量に生成したＭｎＳによって、耐摩耗性が低下する。そのため、表層部および基材部におけるＳ含有量の上限を０．０２５％以下とする。したがって、表層部および基材部のＳ含有量をともに０．００５〜０．０２５％とする。
S (surface layer part and substrate part): 0.005 to 0.025%
Sulfur (S) is contained in an amount of 0.005% or more in order to improve the machinability of the steel member. However, when there is too much S content, hot ductility falls because S which was not fixed by Mn produces | generates in a grain boundary as FeS. Moreover, abrasion resistance falls by MnS produced | generated in large quantities. Therefore, the upper limit of the S content in the surface layer portion and the base material portion is set to 0.025% or less. Therefore, the S content in the surface layer portion and the base material portion is both 0.005 to 0.025%.
Ｃｒ（基材部）：０．１０〜１．５０％
基材部には高い焼き入れ性・耐摩耗性は必要なく、部品加工時の鍛造性および被削性が優先される。そのため、基材部のＣｒ含有量を０．１０〜１．５０％とする。
Cr (base material part): 0.10 to 1.50%
The base material portion does not need high hardenability and wear resistance, and priority is given to forgeability and machinability when processing parts. Therefore, the Cr content of the base material portion is set to 0.10 to 1.50%.
表層部のＣｒは、Ｍｏ、ＶおよびＷとともに選択的に含有される元素であるため、基材部のＣｒとは別に説明する。なお、基材部の靭性を確保するため、表層部に選択的に含有させるＭｏ、ＶおよびＷは、基材部には含有させないこととする。Ｍｏ、ＶおよびＷは、表層部に対して基材部のＭｓ点を上げるためにも基材部には含有させない。 Since Cr in the surface layer is an element that is selectively contained together with Mo, V, and W, it will be described separately from Cr in the base material. In addition, in order to ensure the toughness of a base material part, suppose that Mo, V, and W which are selectively contained in a surface layer part are not contained in a base material part. Mo, V, and W are not contained in the base material part in order to raise the Ms point of the base material part relative to the surface layer part.
鋼材の表層部において、Ｃｒ、Ｍｏ、ＶおよびＷは、１種または２種以上を含有する。以下、各元素について説明する。 In the surface layer portion of the steel material, Cr, Mo, V and W contain one kind or two or more kinds. Hereinafter, each element will be described.
Ｃｒ（表層部）：０．６０〜４．００％
クロム（Ｃｒ）は鋼材の焼き入れ性を高めると同時に、硬い炭化物を形成し耐摩耗性を向上させる有用な元素である。表層部のＣｒ含有量が０．６０％未満では上記作用が発揮できず、一方、４．００％を超えると部品加工時の鍛造性および被削性を低下させる。そのため、表層部のＣｒ含有量を０．６０〜４．００％とする。
Cr (surface layer part): 0.60 to 4.00%
Chromium (Cr) is a useful element that improves the hardenability of the steel material and at the same time forms hard carbides and improves wear resistance. If the Cr content of the surface layer is less than 0.60%, the above-mentioned effect cannot be exhibited. Therefore, the Cr content in the surface layer portion is set to 0.60 to 4.00%.
Ｍｏ（表層部）：０．２０〜３．００％
モリブデン（Ｍｏ）は鋼材の焼き入れ性を高めると同時に、硬い炭化物を形成して耐摩耗性を向上させる有用な元素である。表層部のＭｏ含有量が０．２０％未満では上記作用が発揮できず、一方、３．００％を超えると部品加工時の鍛造性および被削性を低下させる。そのため、表層部のＭｏ含有量を０．２０〜３．００％とする。
Mo (surface layer part): 0.20 to 3.00%
Molybdenum (Mo) is a useful element that improves the hardenability of the steel material and at the same time forms hard carbides to improve wear resistance. If the Mo content in the surface layer is less than 0.20%, the above effect cannot be exhibited. On the other hand, if the Mo content exceeds 3.00%, the forgeability and machinability at the time of part processing are lowered. Therefore, the Mo content in the surface layer portion is set to 0.20 to 3.00%.
Ｖ（表層部）：０．４０〜２．００％
バナジウム（Ｖ）は硬い炭化物を形成して耐摩耗性を向上させるとともに、結晶粒を微細化して靭性を向上させる有用な元素である。表層部のＶ含有量が０．４０％未満では耐摩耗性向上効果が発揮できず、一方、２．００％を超えると部品加工時の鍛造性および被削性を低下させる。そのため、表層部のＶ含有量を０．４０〜２．００％とする。
V (surface layer part): 0.40 to 2.00%
Vanadium (V) is a useful element that forms hard carbides to improve wear resistance and refines crystal grains to improve toughness. When the V content in the surface layer is less than 0.40%, the effect of improving the wear resistance cannot be exhibited. On the other hand, when the V content exceeds 2.00%, the forgeability and machinability at the time of processing the parts are lowered. Therefore, the V content in the surface layer portion is set to 0.40 to 2.00%.
Ｗ（表層部）：０．３０〜２．５０％
タングステン（Ｗ）は鋼材の焼き戻し軟化抵抗を高めると同時に、硬い炭化物を形成して耐摩耗性を向上させる有用な元素である。表層部のＷ含有量が０．３０％未満では上記作用が発揮できず、一方、２．５０％を超えると部品加工時の鍛造性および被削性を低下させる。そのため、表層部のＷ含有量を０．３０〜２．５０％とする。
W (surface layer part): 0.30 to 2.50%
Tungsten (W) is a useful element that improves the temper softening resistance of the steel material and at the same time forms hard carbides to improve wear resistance. If the W content in the surface layer portion is less than 0.30%, the above-mentioned effect cannot be exhibited. On the other hand, if it exceeds 2.50%, the forgeability and machinability at the time of part processing are lowered. Therefore, the W content in the surface layer portion is set to 0.30 to 2.50%.
上記鋼材の表層部および基材部における化学組成の残部は鉄（Ｆｅ）及び不純物である。不純物とは、鋼の原料として利用される鉱石やスクラップ、又は、製造工程の環境等から混入する成分であって、鋼材に意図的に含有させた成分ではない成分を意味する。 The balance of the chemical composition in the surface layer portion and the base material portion of the steel material is iron (Fe) and impurities. Impurities mean components that are mixed in from the ore and scrap used as a raw material for steel, or the environment of the manufacturing process, and are not intentionally contained in steel materials.
次に、表層部及び基材部の化学成分以外の構成について説明する。 Next, configurations other than the chemical components of the surface layer portion and the base material portion will be described.
（表層部）
本実施形態の鋼部材における表層部は、他の鋼部材と接触して摺動する部位となる。よって、本実施形態に係る表層部は、鋼部材の表面のうち、摺動を受ける部分を覆ったものでなければならない。表層部には高い耐摩耗性が必要となる。そのため、表層部は、前述のようにＭｏ、Ｖ等の硬質な合金炭化物生成元素と、高濃度のＣとを含有させ、ビッカース硬さを７５０ＨＶ以上とする。鋼部材の表層部におけるビッカース硬さが７５０ＨＶ未満であると、表層部の耐摩耗性を確保できなくなる。
なお、表層部のビッカース硬さは、表層部の表面から５０μｍ深さの位置におけるビッカース硬さを測定するとよい。
(Surface part)
The surface layer part in the steel member of this embodiment serves as a part which contacts and slides with other steel members. Therefore, the surface layer part which concerns on this embodiment must cover the part which receives sliding among the surfaces of a steel member. The surface layer portion needs to have high wear resistance. Therefore, the surface layer portion contains a hard alloy carbide forming element such as Mo or V and a high concentration of C as described above, and has a Vickers hardness of 750 HV or more. When the Vickers hardness in the surface layer portion of the steel member is less than 750 HV, the wear resistance of the surface layer portion cannot be ensured.
In addition, the Vickers hardness of the surface layer part is good to measure the Vickers hardness at a position of 50 μm depth from the surface of the surface layer part.
また、表層部は、曲げ応力に対して強いことも必要不可欠である。従って、表層部の表面の面内方向と平行な方向の圧縮残留応力を２００ＭＰａ以上とする。鋼部材における表層部の面内方向と平行な方向の圧縮残留応力が２００ＭＰａ未満であると、曲げ応力に対して弱くなり、曲げ疲労強度が劣化する。本実施形態に係る表層部は、基材部と比較してＣ濃度および合金元素濃度を高めており、Ｍｓ点が基材部よりも低くなっている。これにより、焼き入れの際に表層部は基材部よりも遅れてマルテンサイト変態するため、表層部の表面の面内方向と平行な方向に２００ＭＰａ以上の圧縮残留応力が付与されることになる。
なお、表層部の表面の面内方向と平行な方向の圧縮残留応力は、Ｘ線回折結果を解析することによって求めるとよい。具体的には、表層部の表面にＸ線を種々の入射角で照射し、回折角の変化から、表層部の面内方向と平行な方向の表面の圧縮残留応力を求めるとよい。
Further, it is indispensable that the surface layer portion is strong against bending stress. Therefore, the compressive residual stress in the direction parallel to the in-plane direction of the surface of the surface layer portion is set to 200 MPa or more. When the compressive residual stress in the direction parallel to the in-plane direction of the surface layer portion of the steel member is less than 200 MPa, the bending fatigue strength is degraded due to weakening against bending stress. The surface layer part which concerns on this embodiment has raised C density | concentration and alloy element density | concentration compared with a base material part, and Ms point is lower than a base material part. As a result, the surface layer part undergoes martensite transformation later than the base material part during quenching, and therefore a compressive residual stress of 200 MPa or more is applied in a direction parallel to the in-plane direction of the surface of the surface layer part. .
Note that the compressive residual stress in the direction parallel to the in-plane direction of the surface of the surface layer portion may be obtained by analyzing the X-ray diffraction result. Specifically, the surface of the surface layer portion is irradiated with X-rays at various incident angles, and the compressive residual stress on the surface in a direction parallel to the in-plane direction of the surface layer portion is obtained from the change in the diffraction angle.
さらに、表層部の厚さ（表面に垂直な方向）も重要である。表層部の厚さが０．３０ｍｍより薄いと、接触応力によるピッチングなど、摩耗以外の破損形態で表層部が破壊されてしまう。一方、表層部の厚さが２．００ｍｍを越えると、焼き入れによって生じる圧縮残留応力が弱まる。これにより、表層部の表面の面内方向と平行な方向の圧縮残留応力を２００ＭＰａ以上とすることができなくなり、曲げ応力に対して弱くなり、曲げ疲労強度が劣化する。よって、表層部の厚さは、０．３０〜２．００ｍｍとする。
なお、表層部の厚さは、試料断面にナイタール腐食を行った後、光学顕微鏡観察により断面を観察し、金属組織あるいは腐食度合いが基材部と異なる部分を表層部と判断して、表層部の厚さを測定するとよい。
Furthermore, the thickness of the surface layer portion (direction perpendicular to the surface) is also important. If the thickness of the surface layer portion is less than 0.30 mm, the surface layer portion is destroyed in a damaged form other than wear, such as pitching due to contact stress. On the other hand, when the thickness of the surface layer portion exceeds 2.00 mm, the compressive residual stress generated by quenching is weakened. As a result, the compressive residual stress in the direction parallel to the in-plane direction of the surface of the surface layer portion cannot be made 200 MPa or more, becomes weak against bending stress, and the bending fatigue strength deteriorates. Therefore, the thickness of the surface layer portion is set to 0.30 to 2.00 mm.
The thickness of the surface layer portion is determined by observing the cross section by optical microscope observation after performing the nital corrosion on the sample cross section, and determining the portion having a metal structure or corrosion degree different from the base portion as the surface layer portion. It is good to measure the thickness.
（基材部）
本実施形態の鋼部材における基材部は、必ずしもその全面が表層部に覆われた領域を指すものではなく、他の部品と接触しない表面や、高い曲げ応力が付与されない表面に基材部が露出していてもよい。例えば、本実施形態の鋼部材なるギヤ付シャフトにおける中心軸方向と垂直な断面上には基材部が露出する場合があるが、この部分には耐摩耗性が要求されないので、基材部が露出していてもよい。
基材部は、鋼部材に加えられる衝撃的な力に耐える必要がある。また、表層部に高い圧縮残留応力を付与するため、基材部は表層部よりもＭｓ点を高くする必要がある。そのため、基材部は、前述のように表層部と比較してＣ量を下げるとともに、焼き入れ性を高める合金元素も表層部より低減させる。
また、基材部は、靭性を確保するために、ビッカース硬さを３００〜６５０ＨＶとする。なお、基材部のビッカース硬さは、表層部と基材部との境界から、基材部方向に５０μｍ深さの位置におけるビッカース硬さを測定するとよい。
(Base material part)
The base material part in the steel member of this embodiment does not necessarily indicate a region whose entire surface is covered with the surface layer part, and the base material part is on a surface that does not come into contact with other parts or a surface that is not given high bending stress. It may be exposed. For example, the base material portion may be exposed on the cross section perpendicular to the central axis direction of the geared shaft of the steel member of the present embodiment, but the wear resistance is not required for this portion, so the base material portion is It may be exposed.
The base material portion needs to withstand an impact force applied to the steel member. Moreover, in order to give a high compressive residual stress to a surface layer part, it is necessary for a base material part to make Ms point higher than a surface layer part. Therefore, as described above, the base material portion reduces the amount of C as compared with the surface layer portion, and also reduces the alloy elements that improve the hardenability from the surface layer portion.
The base material portion has a Vickers hardness of 300 to 650 HV in order to ensure toughness. In addition, the Vickers hardness of a base material part is good to measure the Vickers hardness in the position of 50 micrometers depth in a base material part direction from the boundary of a surface layer part and a base material part.
（製造方法）
以下、本実施形態の鋼部材の製造方法を説明する。上述したように、本実施形態の鋼部材は、表層部の化学成分を有する鋼と基材部の化学成分を有する鋼とを一体化させた鋼素材を製造した後、必要に応じて機械加工することで部品形状とし、焼き入れ、焼き戻しを施して製造される。
(Production method)
Hereinafter, the manufacturing method of the steel member of this embodiment is demonstrated. As described above, the steel member of the present embodiment is manufactured by manufacturing a steel material in which steel having a chemical component of the surface layer part and steel having a chemical component of the base part are integrated, and then machined as necessary. By doing so, it is made into a part shape, and it is manufactured by quenching and tempering.
まず、鋼部材の素材となる鋼素材の製造方法の一例を説明する。
上記表層部の化学成分を有する鋼と、上記基材部の化学成分を有する鋼とを用意する。例えば、基材部の化学成分を有する鋼を棒状に成形し、表層部の化学成分を有する鋼を中空筒状に成形する。そして、中空筒状に成形した鋼の中空部に、棒状に成形した基材部の化学成分を有する鋼を挿入して一体化させる。一体化は、中空筒状の鋼と棒状の鋼とを一体化させた状態での熱間鍛造、熱間押出や、電磁圧接などの手段により一体化する。
また、別の方法として、上記表層部の化学成分を有する鋼板と、上記基材部の化学成分を有する鋼板とを用意し、基材部となる鋼板の表面に、表層部となる鋼板を配置し、熱間圧延や電磁圧接することにより一体化する。
First, an example of the manufacturing method of the steel raw material used as the raw material of a steel member is demonstrated.
A steel having a chemical component of the surface layer part and a steel having a chemical component of the base material part are prepared. For example, steel having the chemical component of the base part is formed into a rod shape, and steel having the chemical component of the surface layer part is formed into a hollow cylindrical shape. And the steel which has the chemical component of the base-material part shape | molded in the rod shape is inserted and integrated in the hollow part of the steel shape | molded in the hollow cylinder shape. The integration is performed by means such as hot forging, hot extrusion, and electromagnetic pressure welding in a state where the hollow cylindrical steel and the rod-shaped steel are integrated.
As another method, a steel plate having the chemical component of the surface layer part and a steel plate having the chemical component of the base material part are prepared, and the steel plate to be the surface layer part is disposed on the surface of the steel plate to be the base material part. And integrated by hot rolling or electromagnetic pressure welding.
更に、別の方法として、上記表層部の化学成分を有する鋼と、上記基材部の化学成分を有する鋼とを用意し、基材部の化学成分を有する鋼は所定の形状とし、表層部の化学成分を有する鋼は粉末とする。そして、基材部の化学成分を有する鋼の表面に、表層部の化学成分を有する鋼粉末を配置し、鋼粉末を焼結することで一体化する。
更にまた、別の方法として、上記表層部の化学成分を有する鋼と、上記基材部の化学成分を有する鋼とを用意し、これらの鋼を粉末とする。そして、基材部の化学成分を有する鋼の粉末を仮成形して所定の形状とし、その周囲に表層部の化学成分を有する鋼粉末を配置し、これら鋼粉末を焼結することで一体化する。
また、上記表層部の化学成分を有する鋼と、上記基材部の化学成分を有する鋼とを用意し、基材部の化学成分を有する鋼は所定の形状とし、表層部の化学成分を有する鋼を溶射や金属３Ｄプリンターなどで一体化してもよい。
Furthermore, as another method, a steel having a chemical component of the surface layer part and a steel having a chemical component of the base material part are prepared, and the steel having the chemical component of the base material part has a predetermined shape, and the surface layer part The steel having the chemical composition is powdered. And the steel powder which has the chemical component of a surface layer part is arrange | positioned on the surface of steel which has the chemical component of a base material part, and it integrates by sintering a steel powder.
Furthermore, as another method, steel having the chemical component of the surface layer portion and steel having the chemical component of the base material portion are prepared, and these steels are used as powder. Then, the steel powder having the chemical component of the base material portion is temporarily formed into a predetermined shape, and the steel powder having the chemical component of the surface layer portion is arranged around the steel powder, and the steel powder is integrated by sintering. To do.
Moreover, the steel which has the chemical component of the said surface layer part and the steel which has the chemical component of the said base material part are prepared, the steel which has the chemical component of a base material part is made into a defined shape, and has the chemical component of a surface layer part. Steel may be integrated by thermal spraying or a metal 3D printer.
次いで、得られた鋼素材に対し、機械加工することで部品形状とし、焼き入れ・焼き戻しを施す。このようにして、本実施形態の鋼部材を製造する。本実施形態に係る表層部は、基材部と比較してＣ濃度および合金元素濃度を高めており、Ｍｓ点が基材部よりも低くなっている。このため、焼き入れの際に表層部は基材部よりも遅れてマルテンサイト変態するため、表層部の表面の面内方向と平行な方向に２００ＭＰａ以上の圧縮残留応力が付与されることになる。 Next, the obtained steel material is machined into a part shape, which is quenched and tempered. Thus, the steel member of this embodiment is manufactured. The surface layer part which concerns on this embodiment has raised C density | concentration and alloy element density | concentration compared with a base material part, and Ms point is lower than a base material part. For this reason, the surface layer part undergoes martensite transformation later than the base material part during quenching, and therefore a compressive residual stress of 200 MPa or more is applied in a direction parallel to the in-plane direction of the surface of the surface layer part. .
なお、表層部の厚みは、鋼素材の一体化の際に調整してもよく、鋼素材を機械加工する際に鋼素材の表面を切削等することで、表層部の厚みを調整してもよい。 The thickness of the surface layer portion may be adjusted when the steel material is integrated, or the surface layer portion may be adjusted by cutting the surface of the steel material when machining the steel material. Good.
以上、製造方法の一例について説明したが、本実施形態の鋼部材は上記以外の方法によって製造してもよいのはもちろんである。 As mentioned above, although an example of the manufacturing method was demonstrated, of course, you may manufacture the steel member of this embodiment by methods other than the above.
なお、本実施形態の鋼部材は、表層部と基材部との境界で成分、硬さが急激に変化するため、表層部の厚さや使用条件によっては、当該境界が破壊起点となることが考えられる。そのような場合、鋼部材において、表層部と基材部との中間の成分を有する層を間に挟んで成分を段階的に変化させる、あるいは、高温で拡散処理を行って成分を連続的に変化させるなどの対策を講じることができる。 In addition, the steel member of the present embodiment has a component and hardness abruptly changed at the boundary between the surface layer portion and the base material portion, and therefore, depending on the thickness of the surface layer portion and usage conditions, the boundary may be a starting point for fracture. Conceivable. In such a case, in the steel member, the component is changed stepwise with a layer having an intermediate component between the surface layer portion and the base material portion interposed therebetween, or the component is continuously processed by performing diffusion treatment at a high temperature. Measures such as changing can be taken.
表１の「表層部」に示す化学成分を有する鋼を溶製し、連続鋳造により鋼片を製造した。この鋼片を外径５４ｍｍ、内径３６ｍｍの中空筒状に加工した。また、表１の「基材部」に示す化学成分を有する鋼を溶製し、連続鋳造により鋼片を製造した。この鋼片を外径３６ｍｍの棒状に加工した。次に、それらを嵌め合わせてＡｒガス雰囲気中で１１５０℃に加熱し、熱間押出加工で外径３６ｍｍの棒状に成形して圧着させた後、室温まで徐冷した。得られた棒状素材から、図１に示すローラーピッチング試験片を機械加工にて作製し、焼き入れ温度８５０℃で油焼き入れを行った後、１２０℃で焼き戻しを行った。
ただし、表１および表２の比較例Ｋは、熱間押出後の外径を３８．３ｍｍとすることで、ローラーピッチング試験片における表層部の厚さを薄くした。また、表１および表２の比較例Ｌは、熱間押出後の外径を３１ｍｍとすることで、ローラーピッチング試験片における表層部の厚さを厚くした。
Steel having chemical components shown in “Surface Layer” in Table 1 was melted, and a steel slab was produced by continuous casting. This steel piece was processed into a hollow cylinder having an outer diameter of 54 mm and an inner diameter of 36 mm. Moreover, the steel which has a chemical component shown in the "base material part" of Table 1 was melted, and the steel piece was manufactured by continuous casting. This steel piece was processed into a rod shape having an outer diameter of 36 mm. Next, they were fitted together, heated to 1150 ° C. in an Ar gas atmosphere, formed into a rod shape having an outer diameter of 36 mm by hot extrusion and pressed, and then gradually cooled to room temperature. A roller pitching test piece shown in FIG. 1 was prepared from the obtained rod-shaped material by machining, and after oil quenching at a quenching temperature of 850 ° C., tempering was performed at 120 ° C.
However, in Comparative Example K in Tables 1 and 2, the thickness of the surface layer portion of the roller pitching test piece was reduced by setting the outer diameter after hot extrusion to 38.3 mm. Moreover, the comparative example L of Table 1 and Table 2 made the thickness of the surface layer part in a roller pitching test piece thick by setting the outer diameter after hot extrusion to 31 mm.
次に、焼き入れ・焼き戻し後の上記ローラーピッチング試験片を用いて、すべり率１０％、面圧１．５ＧＰａ、回転数１０００ｒｐｍ、油温８０℃、相手ローラーＪＩＳ Ｇ４８０５ ＳＵＪ２の条件で、繰り返し数１００万回のローラーピッチング試験を行った。その後、相手ローラーと接触していた直径２６ｍｍの試験部（表層部）について、試験片長手方向の表面プロファイルを、周囲９０°ごとに４回、粗さ計で測定し、最大摩耗深さの平均値を求めた。最大摩耗深さの平均値が５．０μｍ以下の場合を、耐摩耗性に優れるとして合格と判定した。また、最大摩耗深さの平均値が５．０μｍ超の場合を、耐摩耗性に劣るとして不合格と判定した。
Next, using the roller pitching test piece after quenching and tempering, the number of repetitions is as follows: slip
また、ローラーピッチング試験に供さなかった試験片を、直径２６ｍｍの試験部を通り、試験片長手方向に対して垂直な面で切断し、ナイタール腐食を行った後、光学顕微鏡観察により表層部の厚さを測定した。なお、基材部と比較してより黒く腐食された部分を表層部と判断した。表層部の厚さが０．３０〜２．００ｍｍの場合を、本発明の範囲内であるとして合格と判定した。また、表層部の厚さが０．３０ｍｍ未満および、２．００ｍｍ超の場合を、本発明の範囲外であるとして不合格と判定した。 In addition, a test piece that was not subjected to the roller pitching test was cut through a test portion having a diameter of 26 mm and perpendicular to the longitudinal direction of the test piece and subjected to nital corrosion, and then the surface layer portion was observed by optical microscope observation. The thickness was measured. In addition, the part corroded more black compared with the base-material part was judged as the surface layer part. The case where the thickness of the surface layer portion was 0.30 to 2.00 mm was determined to be acceptable as being within the scope of the present invention. Moreover, the case where the thickness of the surface layer part was less than 0.30 mm and more than 2.00 mm was determined to be unacceptable as being outside the scope of the present invention.
さらに、表層部の硬さとして、上記試験片長手方向に対して垂直な面において、半径方向外側の表面から５０μｍ深さの位置で、ＪＩＳ Ｚ ２２４４に準拠して、ビッカース硬さを測定した。表層部のビッカース硬さが７５０ＨＶ以上の場合を、本発明の範囲内であるとして合格と判定した。 Furthermore, as the hardness of the surface layer portion, the Vickers hardness was measured in accordance with JIS Z 2244 at a position 50 μm deep from the radially outer surface in a plane perpendicular to the longitudinal direction of the test piece. A case where the surface layer portion had a Vickers hardness of 750 HV or higher was determined to be acceptable as being within the scope of the present invention.
次に、基材部焼入前硬さとして、表１の「基材部」に示す化学成分を有する外径３６ｍｍの棒状素材の、素材長手方向に対して垂直な面において、半径方向外側の表面から９ｍｍ深さの位置で、ＪＩＳ Ｚ ２２４４に準拠して、ビッカース硬さを測定した。基材部焼入前硬さが２２０ＨＶ未満の場合を、基材部の加工性に優れるとして合格と判定した。一方、基材部焼入前硬さが２２０ＨＶ以上の場合を、基材部の加工性に劣るとして不合格と判定した。 Next, as the hardness before quenching of the base material portion, the surface of the rod-shaped material having an outer diameter of 36 mm having the chemical component shown in “Base material portion” in Table 1 is radially outer on the surface perpendicular to the material longitudinal direction. Vickers hardness was measured according to JIS Z 2244 at a position 9 mm deep from the surface. The case where the hardness before quenching of the base material portion was less than 220 HV was determined to be acceptable as being excellent in workability of the base material portion. On the other hand, the case where the hardness before quenching of the base material portion was 220 HV or higher was determined to be unacceptable as being inferior in workability of the base material portion.
次に、ビッカース硬さを測定した上記棒状素材から、図２に示すＶノッチシャルピー試験片を機械加工（切削）にて作製し、焼き入れ温度８５０℃で油焼き入れを行った後、１２０℃で焼き戻しを行った。 Next, the V-notch Charpy test piece shown in FIG. 2 was produced by machining (cutting) from the rod-shaped material whose Vickers hardness was measured, and after oil quenching at a quenching temperature of 850 ° C., 120 ° C. And tempered.
焼き入れ・焼き戻し後の上記Ｖノッチシャルピー試験片を用いて、ＪＩＳ Ｚ ２２４２に準拠して、室温（２３℃）でシャルピー衝撃試験を行い、基材部のシャルピー衝撃値を測定した。基材部のシャルピー衝撃値が３０Ｊ／ｃｍ２以上の場合を、靭性に優れるとして合格と判定した。また、基材部のシャルピー衝撃値が３０Ｊ／ｃｍ２未満の場合を、靭性に劣るとして不合格と判定した。 Using the V-notched Charpy test piece after quenching and tempering, a Charpy impact test was performed at room temperature (23 ° C.) in accordance with JIS Z 2242 to measure the Charpy impact value of the base material. The case where the Charpy impact value of the base material portion was 30 J / cm 2 or more was determined to be acceptable as being excellent in toughness. Moreover, it determined with the case where the Charpy impact value of a base-material part was less than 30 J / cm < 2 > being inferior as toughness.
また、シャルピー衝撃試験に供さなかった試験片を、Ｖノッチ底を通り、試験片長手方向に対して垂直な面で切断した後、基材部の硬さとして、ノッチ底から５０μｍ深さの位置でビッカース硬さを測定した。基材部のビッカース硬さが３００〜６５０ＨＶの場合を、本発明の範囲内であるとして、合格と判定した。一方、基材部のビッカース硬さが３００ＨＶ未満および、６５０ＨＶ超の場合を、本発明の範囲外であるとして、不合格と判定した。 In addition, the test piece that was not subjected to the Charpy impact test was cut along a plane perpendicular to the longitudinal direction of the test piece through the V-notch bottom, and then the hardness of the base material was 50 μm deep from the notch bottom. Vickers hardness was measured at the position. The case where the Vickers hardness of the base material portion was 300 to 650 HV was determined to be acceptable as being within the scope of the present invention. On the other hand, the case where the Vickers hardness of the base material portion was less than 300 HV and more than 650 HV was determined to be unacceptable as being outside the scope of the present invention.
次に、四点曲げ疲労試験片を作製して、曲げ応力に対する疲労寿命を測定し、曲げ疲労強度を評価した。 Next, a four-point bending fatigue test piece was prepared, the fatigue life against bending stress was measured, and the bending fatigue strength was evaluated.
表１の「表層部」に示す化学成分を有する厚さ１０ｍｍの鋼板二枚の間に、表１の「基材部」に示す化学成分を有する厚さ１４ｍｍの鋼板を重ね合わせてＡｒガス雰囲気中で１１５０℃に加熱し、熱間圧延で厚さ１７ｍｍの鋼板にして圧着させた後、室温まで徐冷した。得られた板状素材から、図３に示すノッチ付き角状試験片を機械加工にて作製した。なお、図３の面Ａと、表層部と基材部の境界面が平行になるように、面Ａの表面から深さ３．００ｍｍまでが表層部となるように試験片を作製した。つまり、破壊起点となるノッチ底では、表層部の厚さは１．００ｍｍとなる。その後、焼き入れ温度８５０℃で油焼き入れを行った後、１２０℃で焼き戻しを行った。
ただし、表１および表２の比較例Ｋは、面Ａの表面から深さ２．２３ｍｍまでが表層部となるように試験片を作製して、ノッチ底における表層部の厚さを０．２３ｍｍとした。また、表１および表２の比較例Ｌは、面Ａの表面から深さ４．６７ｍｍまでが表層部となるように試験片を作製して、ノッチ底における表層部の厚さを２．６７ｍｍとした。
An Ar gas atmosphere is formed by superposing a 14 mm-thick steel plate having a chemical component shown in “Base Material” of Table 1 between two 10 mm-thick steel plates having a chemical component shown in “Surface Layer” in Table 1. The steel plate was heated to 1150 ° C., hot rolled into a steel plate having a thickness of 17 mm, and then pressure-bonded, and then gradually cooled to room temperature. From the obtained plate-like material, a square test piece with a notch shown in FIG. 3 was produced by machining. In addition, the test piece was produced so that the surface A of FIG. 3 may be a surface layer part from the surface A to a depth of 3.00 mm so that the boundary surface of a surface layer part and a base-material part may become parallel. That is, the thickness of the surface layer portion is 1.00 mm at the notch bottom that is the starting point of fracture. Thereafter, oil quenching was performed at a quenching temperature of 850 ° C., followed by tempering at 120 ° C.
However, in Comparative Example K in Table 1 and Table 2, a test piece was prepared so that the surface portion from the surface A to a depth of 2.23 mm was the surface layer portion, and the thickness of the surface layer portion at the notch bottom was 0.23 mm. It was. Further, in Comparative Example L in Table 1 and Table 2, a test piece was prepared so that the surface layer portion from the surface A to a depth of 4.67 mm was the surface layer portion, and the thickness of the surface layer portion at the notch bottom was 2.67 mm. It was.
次に、図４に示すように、焼き入れ・焼き戻し後の上記四点曲げ疲労試験片を用いて、試験片長手方向に８０ｍｍ離れた２つの下側支点と、試験片長手方向に２０ｍｍ離れた２つの上側支点とを配置して、上側支点に、矢印方向ａに繰り返し荷重を負荷する四点曲げ疲労試験を行った。試験速度は１０Ｈｚ、切り欠き底に発生する最大応力は５００ＭＰａ、応力比は０．０５として、疲労寿命（試験片の破断に要した繰り返し数）を調べた。ただし、繰り返し数は１００万回を上限とした。１００万回の繰り返し荷重を負荷しても破断しなかった場合を、曲げ疲労強度に優れるとして合格と判定した。一方、１００万回未満の繰り返し荷重によって破断した場合を、曲げ疲労強度に劣るとして不合格と判定した。 Next, as shown in FIG. 4, using the above-mentioned four-point bending fatigue test piece after quenching and tempering, two lower fulcrums 80 mm apart in the test piece longitudinal direction and 20 mm apart in the test piece longitudinal direction Further, a four-point bending fatigue test was performed in which two upper fulcrums were arranged and a load was repeatedly applied to the upper fulcrum in the arrow direction a. The fatigue life (the number of repetitions required for fracture of the test piece) was examined with a test speed of 10 Hz, a maximum stress generated at the notch bottom of 500 MPa, and a stress ratio of 0.05. However, the upper limit of the number of repetitions was 1,000,000. The case where it did not break even when a load of 1,000,000 cycles was applied was judged as passing because it was excellent in bending fatigue strength. On the other hand, the case where the fracture was caused by a repeated load of less than 1 million times was determined to be unacceptable as being inferior in bending fatigue strength.
表層部の表面の面内方向と平行な方向の圧縮残留応力は、Ｘ線回折結果を解析することによって求めた。具体的には、焼き入れ・焼き戻し後の上記四点曲げ疲労試験片について、図３におけるノッチ付き角状試験片の奥行き方向中央で、ノッチ底表面にビーム径φ０．５ｍｍのＸ線を種々の入射角で照射し、回折角の変化から試験片長手方向の圧縮残留応力を求めた。表層部の表面の面内方向と平行な方向の圧縮残留応力が２００ＭＰａ以上の場合を、本発明の範囲内であるとして合格と判定した。一方、表層部の表面の面内方向と平行な圧縮残留応力が２００ＭＰａ未満の場合を、本発明の範囲外であるとして不合格と判定した。 The compressive residual stress in the direction parallel to the in-plane direction of the surface of the surface layer portion was determined by analyzing the X-ray diffraction result. Specifically, with respect to the above four-point bending fatigue test piece after quenching and tempering, various X-rays with a beam diameter of φ0.5 mm are applied to the notch bottom surface at the center in the depth direction of the notched square test piece in FIG. The compression residual stress in the longitudinal direction of the test piece was determined from the change in the diffraction angle. The case where the compressive residual stress in the direction parallel to the in-plane direction of the surface of the surface layer portion was 200 MPa or more was determined to be acceptable as being within the scope of the present invention. On the other hand, the case where the compressive residual stress parallel to the in-plane direction of the surface of the surface layer portion was less than 200 MPa was determined to be unacceptable as being outside the scope of the present invention.
以上により得られた結果を表２に示す。なお、表２の「−」は、ローラーピッチング試験において、繰り返し数１００万回までにピッチングが発生して、試験が途中で終了したことを示す。また、表２の「表層部圧縮残留応力」は、表層部の表面の面内方向と平行な圧縮残留応力を示す。 The results obtained as described above are shown in Table 2. In addition, “-” in Table 2 indicates that in the roller pitching test, pitching occurred up to 1 million repetitions, and the test was completed in the middle. Further, “surface layer compressive residual stress” in Table 2 indicates compressive residual stress parallel to the in-plane direction of the surface of the surface layer portion.
表１および表２のＡ〜Ｈが本発明例で、その他（Ｉ〜Ｑ）は比較例である。
比較例Ｉは、表層部のＣ量が低いため、表層部のビッカース硬さが低くなり、耐摩耗性が低下した例である。
比較例Ｊは、基材部のＣ量が高いため、焼き入れ前の基材部のビッカース硬さが高くなり、部品加工時の鍛造性および被削性が低下するとともに、焼き入れ・焼き戻し後の基材部のビッカース硬さが高くなり、靭性が低下した例である。
In Tables 1 and 2, A to H are examples of the present invention, and the others (I to Q) are comparative examples.
Comparative Example I is an example in which the Vickers hardness of the surface layer portion is low and the wear resistance is low because the amount of C in the surface layer portion is low.
In Comparative Example J, since the C content of the base material portion is high, the Vickers hardness of the base material portion before quenching is increased, and the forgeability and machinability at the time of part processing are reduced, and quenching and tempering are performed. This is an example in which the Vickers hardness of the subsequent base material portion is increased and the toughness is decreased.
比較例Ｋは、表層部が薄いため、ローラーピッチング試験において繰り返し数１００万回までにピッチングが発生して試験が途中で終了するとともに、曲げ疲労試験において基材部起点で破壊が起こり、曲げ疲労強度が劣化した例である。
比較例Ｌは、表層部が厚いため、焼き入れ後、表層部に高い圧縮残留応力が発生せず、曲げ疲労強度が劣化した例である。
In Comparative Example K, since the surface layer portion is thin, pitching occurs in the roller pitching test up to several million times and the test is terminated halfway, and in the bending fatigue test, fracture occurs at the base material portion starting point, and bending fatigue occurs. This is an example in which the strength has deteriorated.
Comparative Example L is an example in which since the surface layer portion is thick, a high compressive residual stress does not occur in the surface layer portion after quenching, and the bending fatigue strength deteriorates.
比較例Ｍは、表層部が硬質な合金炭化物生成元素であるＣｒ、Ｍｏ、Ｖ、Ｗのいずれも含有していなかったため、表層部の耐摩耗性が低下した例である。
比較例Ｎは、表層部のＣｒ量が低いため、表層部のビッカース硬さおよび耐摩耗性が低下した例である。
Comparative Example M is an example in which the wear resistance of the surface layer portion was lowered because none of Cr, Mo, V, and W, which are hard alloy carbide forming elements in the surface layer portion, was contained.
Comparative Example N is an example in which the Vickers hardness and wear resistance of the surface layer portion are reduced because the Cr amount of the surface layer portion is low.
比較例Ｏは、表層部のＭｏ量が低いため表層部の耐摩耗性が低下したことに加えて、基材部のＳｉ量が高いため焼き入れ前の基材部のビッカース硬さが高くなりＶノッチシャルピー試験片作製時の被削性が低下した例である。
比較例Ｐは、表層部のＶ量が低いため表層部の耐摩耗性が低下したことに加えて、基材部のＭｎ量が高いため焼き入れ前の基材部のビッカース硬さが高くなりＶノッチシャルピー試験片作製時の被削性が低下した例である。
比較例Ｑは、表層部のＷ量が低いため表層部のビッカース硬さおよび耐摩耗性が低下したことに加えて、基材部のＣｒ量が高いため焼き入れ前の基材部のビッカース硬さが高くなりＶノッチシャルピー試験片作製時の被削性が低下した例である。
In Comparative Example O, the surface layer portion has a low amount of Mo, so that the wear resistance of the surface layer portion is reduced. In addition, since the Si amount of the base material portion is high, the Vickers hardness of the base material portion before quenching is increased. This is an example in which the machinability at the time of preparing a V-notch Charpy test piece was lowered.
In Comparative Example P, since the V amount of the surface layer portion is low, the wear resistance of the surface layer portion is lowered, and since the Mn amount of the base material portion is high, the Vickers hardness of the base material portion before quenching is increased. This is an example in which the machinability at the time of preparing a V-notch Charpy test piece was lowered.
In Comparative Example Q, the Vickers hardness and wear resistance of the surface layer portion decreased because the W amount of the surface layer portion was low, and the Vickers hardness of the base material portion before quenching was high because the Cr amount of the base material portion was high. This is an example in which the machinability at the time of preparation of a V-notch Charpy test piece was lowered.
本発明によれば、硬く、圧縮残留応力を有する表層部と、靭性が高い基材部とを備えており、耐摩耗性と靭性に優れ、曲げ疲労強度にも優れた鋼部材を得ることができ、産業上の利用価値は大である。 According to the present invention, it is possible to obtain a steel member having a hard surface layer portion having a compressive residual stress and a base portion having high toughness, excellent wear resistance and toughness, and excellent bending fatigue strength. Yes, the industrial utility value is great.
Claims (1)
前記基材部が、質量％で、
Ｃ：０．１０〜０．５０％、
Ｓｉ：０．０５〜０．５０％、
Ｍｎ：０．２０〜０．９０％、
Ａｌ：０．００５〜０．１００％、
Ｎ：０．００１０〜０．０２５０％、
Ｐ：０．００１〜０．０３０％、
Ｓ：０．００５〜０．０２５％および
Ｃｒ：０．１０〜１．５０％
を含有し、残部がＦｅおよび不純物からなり、
ビッカース硬さが３００〜６５０ＨＶであり、
前記表層部が、質量％で、
Ｃ：０．８０〜１．６０％、
Ｓｉ：０．０５〜２．００％、
Ｍｎ：０．２０〜１．５０％、
Ａｌ：０．００５〜０．１００％、
Ｎ：０．００１０〜０．０２５０％、
Ｐ：０．００１〜０．０３０％および
Ｓ：０．００５〜０．０２５％
を含有し、さらに、
Ｃｒ：０．６０〜４．００％、
Ｍｏ：０．２０〜３．００％、
Ｖ：０．４０〜２．００％および
Ｗ：０．３０〜２．５０％
からなる群から選択される１種または２種以上を含有し、残部がＦｅおよび不純物からなり、
ビッカース硬さが７５０ＨＶ以上であり、
前記表層部の表面の面内方向と平行な方向の圧縮残留応力が２００ＭＰａ以上であり、
厚さが０．３０〜２．００ｍｍである、鋼部材。 A steel member comprising a base material part and a surface layer part covering at least a part of the base material part,
The base material part is mass%,
C: 0.10 to 0.50%,
Si: 0.05 to 0.50%,
Mn: 0.20 to 0.90%,
Al: 0.005 to 0.100%,
N: 0.0010 to 0.0250%,
P: 0.001 to 0.030%,
S: 0.005 to 0.025% and Cr: 0.10 to 1.50%
And the balance consists of Fe and impurities,
Vickers hardness is 300-650HV,
The surface layer part is mass%,
C: 0.80 to 1.60%,
Si: 0.05 to 2.00%,
Mn: 0.20 to 1.50%,
Al: 0.005 to 0.100%,
N: 0.0010 to 0.0250%,
P: 0.001 to 0.030% and S: 0.005 to 0.025%
In addition,
Cr: 0.60 to 4.00%,
Mo: 0.20 to 3.00%
V: 0.40 to 2.00% and W: 0.30 to 2.50%
1 type or 2 types or more selected from the group which consists of, The remainder consists of Fe and an impurity,
Vickers hardness is 750HV or more,
The compressive residual stress in a direction parallel to the in-plane direction of the surface of the surface layer portion is 200 MPa or more,
A steel member having a thickness of 0.30 to 2.00 mm.
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| JP7453524B2 (en) | 2020-03-19 | 2024-03-21 | 日本製鉄株式会社 | steel parts |
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