JP2020002447A - Carburization member - Google Patents
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- JP2020002447A JP2020002447A JP2018125395A JP2018125395A JP2020002447A JP 2020002447 A JP2020002447 A JP 2020002447A JP 2018125395 A JP2018125395 A JP 2018125395A JP 2018125395 A JP2018125395 A JP 2018125395A JP 2020002447 A JP2020002447 A JP 2020002447A
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- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 11
- 230000003647 oxidation Effects 0.000 claims abstract description 8
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 238000005255 carburizing Methods 0.000 claims description 16
- 238000000034 method Methods 0.000 abstract description 16
- 229910052748 manganese Inorganic materials 0.000 abstract description 8
- 229910052750 molybdenum Inorganic materials 0.000 abstract description 2
- 229910052698 phosphorus Inorganic materials 0.000 abstract description 2
- 239000002245 particle Substances 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 34
- 229910000831 Steel Inorganic materials 0.000 description 32
- 239000010959 steel Substances 0.000 description 32
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- 238000005480 shot peening Methods 0.000 description 8
- 239000002344 surface layer Substances 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 238000005452 bending Methods 0.000 description 5
- 229910052804 chromium Inorganic materials 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 238000005496 tempering Methods 0.000 description 5
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
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- KQFOGBLKSYORAM-UHFFFAOYSA-N CC1(C[IH]#C2)C2=C1 Chemical compound CC1(C[IH]#C2)C2=C1 KQFOGBLKSYORAM-UHFFFAOYSA-N 0.000 description 1
- 238000003723 Smelting Methods 0.000 description 1
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- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
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- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
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- 229910000859 α-Fe Inorganic materials 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
Description
本発明は、建産機や自動車の分野で用いられる、優れた回転曲げ疲労特性、ねじり疲労特性および衝撃疲労特性を有する浸炭部材に関するものである。 The present invention relates to a carburized member having excellent rotational bending fatigue characteristics, torsional fatigue characteristics, and impact fatigue characteristics used in the field of construction equipment and automobiles.
近年、自動車等に用いられる歯車やシャフト等は、省エネルギー化による車体重量の軽量化に伴って、サイズの小型化が要求される一方、エンジンの高出力化に伴って負荷は増大している。そこで、歯車やシャフトには、優れた耐疲労性を付与するための浸炭処理が施されている。 2. Description of the Related Art In recent years, gears and shafts used in automobiles and the like have been required to be reduced in size as the weight of a vehicle body is reduced due to energy saving, while the load is increasing as the output of an engine is increased. Therefore, the gears and shafts are subjected to carburizing treatment for imparting excellent fatigue resistance.
一般的に、歯車の耐久性は、歯の耐衝撃破壊、歯元の曲げ疲労破壊ならびに歯面の面圧疲労破壊によって決定される。衝撃的な応力がかかる部分、例えば自動車のデファレンシャル等で使用される歯車では、高い衝撃荷重により破壊が早期に起こる場合があるため、衝撃特性の向上が種々検討されている。 Generally, the durability of a gear is determined by impact fracture of a tooth, bending fatigue fracture of a tooth root, and surface pressure fatigue fracture of a tooth surface. In a part to which an impact stress is applied, for example, a gear used in a differential of an automobile or the like, a high impact load may cause early destruction.
例えば、特許文献１には、浸炭層の靭性を向上するためにＭｏを添加し、浸炭層の粒界強度を低下させるＭｎ、Ｃｒ、Ｐを少なくすること、Ｍｏ／（１０Ｓｉ＋１００Ｐ＋Ｍｎ＋Ｃｒ）により求まる値の下限を規定することおよび、浸炭硬化層深さの範囲を規定することにより、衝撃特性を向上させることが提案されている。
For example, in
特許文献２は、ミクロ組織を規定する技術である。すなわち、特許文献２には、ミクロ組織をマルテンサイトと内部の靭性を向上させるトルースタイトとの混合組織とし、ＭｎとＣｒの添加量の範囲を規定し、Ｍｏ添加量を規制してトルースタイトの量を制限することにより、内部硬度の低下を抑える方法が提案されている。
さらに、特許文献３には、特許文献２に記載の成分組成に、Ｍｏを添加した、鋼が提案されている。特許文献４には、成分組成においてＭｎ、ＣｒおよびＭｏの複合添加量を制限して鋼材の硬さを抑え、冷間鍛造性を損なうこと無く衝撃特性を向上させた傘歯車用鋼材が提案されている。
Further, Patent Document 3 proposes a steel in which Mo is added to the component composition described in
特許文献５には、歯車用鋼の衝撃疲労強度を向上させるために、低いＰ量の下でＢを添加することによって、粒界を強化し、粒界酸化層深さ、内部硬さおよび有効硬化層深さを適切にバランスさせることが提案されている。 Patent Document 5 discloses that in order to improve the impact fatigue strength of gear steel, B is added under a low P content to strengthen the grain boundaries, to improve the grain boundary oxide layer depth, internal hardness and effectiveness. It has been proposed to properly balance the depth of the hardened layer.
しかしながら、特許文献１に記載の方法では、衝撃特性を向上出来たとしても、高価な合金元素であるＭｏを多量に添加させるか、Ｍｏを多く入れない場合には浸炭時間を大幅に延長させることが必要であり、製品コストまたは製造コストの大幅な増加を招いてしまう。
However, in the method described in
特許文献２に記載の方法では、ＭｎとＣｒの複合添加量を指定し、Ｍｏ添加量を規制するのため、表層付近で発生する粒界酸化が多くなり、ＭｎおよびＣｒの酸化物が形成されて焼入れ性が低下し、表層に不完全焼入れ層が形成される。そのため、内部硬度が確保出来たとしても表層の硬さ低下による表層からの破壊が発生しやすくなり、結果的に衝撃疲労を含むすべての疲労強度が低下してしまう。
In the method described in
特許文献３に記載の方法では、Ｍｏを添加してもトルースタイトにより歯車内部の硬度低下が発生するため、衝撃特性が向上したとしても内部起因の曲げ疲労などの疲労強度が低下する。特許文献４に記載の方法は、歯車を熱間鍛造で整形する場合に硬度が低くなり、衝撃以外の疲労強度が低下してしまう。 In the method described in Patent Document 3, even when Mo is added, the hardness inside the gear decreases due to the troostite, so that even if the impact characteristics are improved, the fatigue strength such as bending fatigue caused by the inside decreases. In the method described in Patent Document 4, when the gear is shaped by hot forging, the hardness is reduced, and the fatigue strength other than the impact is reduced.
一方、特許文献５に記載の手法によって、疲労強度、中でも衝撃疲労強度を高めることが可能になる。ここで、歯車以外の浸炭部材の典型であるシャフトについて、その耐久性は、主にねじりに起因する疲労破壊によって決まる。特に、シャフトには、一般に潤滑を目的とする、油が循環するための孔が設けられている。この油孔は空洞であることから応力が集中しやすく、この油孔からねじりに起因する疲労破壊が発生しやすいために、衝撃疲労強度以外に、ねじり疲労強度も高める必要がある。このねじり疲労強度については、特許文献６に何ら触れられていない。 On the other hand, the technique described in Patent Document 5 makes it possible to increase the fatigue strength, especially the impact fatigue strength. Here, the durability of a shaft that is a typical example of a carburized member other than a gear is mainly determined by fatigue fracture caused by torsion. In particular, the shaft is provided with a hole for oil circulation, generally for lubrication. Since the oil hole is hollow, stress tends to concentrate, and fatigue fracture due to torsion easily occurs from the oil hole. Therefore, it is necessary to increase torsional fatigue strength in addition to impact fatigue strength. Patent Document 6 does not mention this torsional fatigue strength at all.
そこで、本発明は、歯車やシャフトなどの浸炭部材に、優れた耐衝撃疲労特性に加えて優れた耐ねじり疲労特性を与えるための方途について提案することを目的とする。 Therefore, an object of the present invention is to propose a method for giving a carburized member such as a gear or a shaft with excellent torsional fatigue resistance in addition to excellent impact fatigue resistance.
本発明者等は上記課題を解決するため、従来用いられている生産コストの低い浸炭工法によっても、優れた耐衝撃疲労特性が得られる成分組成について鋭意検討を行った。
その結果、繰返される衝撃応力に対して衝撃力による変形を起こさないことが必要であり、そのためには適切な硬度分布と、それに影響を及ぼす、浸炭熱処理時に主に旧オ−ステナイト粒界に沿って生成する、Si、Mnなどを主体とした酸化物の表面からの深さ、すなわち粒界酸化層深さおよび内部硬さと、を適切な範囲に制御する必要のあることを知見し、この知見に基づいて以下の指針を得た。
In order to solve the above-mentioned problems, the present inventors have intensively studied a component composition which can provide excellent impact fatigue resistance even by a conventionally used carburizing method having a low production cost.
As a result, it is necessary not to cause deformation due to the impact force with respect to the repeated impact stress. For this purpose, an appropriate hardness distribution and its influence are mainly exerted along the former austenite grain boundaries during the carburizing heat treatment. It was found that it was necessary to control the depth from the surface of the oxide mainly composed of Si, Mn, etc., that is, the grain boundary oxide layer depth and the internal hardness, in an appropriate range. Based on the following guidelines were obtained.
ｉ）耐衝撃疲労特性の向上には旧オーステナイト粒界の強化が最も重要であり、Ｐを低減して旧オーステナイト粒界の脆化を抑制する。
ii）さらに、鋼中にＢを固溶させて旧オーステナイト粒界に優先的に偏析させ、Ｐの粒界偏析を抑制する。
iii）固溶Ｂを鋼中に存在させるには、Ｂとの結合力の強いＮをTiまたはAlで結合させるが、Tiを用いた場合に溶製時に析出するTiＮは比較的大きく、鋭利で硬質な介在物のため、疲労の起点となり易く、面疲労強度および曲げ疲労強度が低下する。
iv）Alを添加してＢ、Ｎとの平衡関係を利用してＮを固定した場合、ＢＮ、AlＮが鋼中に析出する。AlＮは微細なため、結晶粒は微細化し、衝撃疲労強度が向上する。また、AlＮは微細なために疲労の起点にはならず、Ti添加よりも疲労強度の向上が図られる。
ｖ）衝撃疲労強度には粒界酸化層深さと内部硬さおよび浸炭硬度分布（硬化層深さ）のバランスが大切であり、最適な範囲が存在する。
vi）また、シャフトを想定したときの、浸炭部材のねじり疲労強度の向上には、圧縮残留応力を付与することが有効であり、圧縮残留応力を粒界酸化層深さ、内部硬さおよび硬化層深さとバランスさせることが肝要になる。
i) Strengthening of the prior austenite grain boundaries is most important for improving the impact fatigue resistance. P is reduced to suppress embrittlement of the prior austenite grain boundaries.
ii) Further, B is dissolved in the steel to segregate preferentially at the prior austenite grain boundaries, thereby suppressing P grain boundary segregation.
iii) In order to make solid solution B exist in steel, N having a strong bonding force with B is bonded by Ti or Al. However, when Ti is used, TiN precipitated during melting is relatively large and sharp. Because of the hard inclusions, it tends to be a starting point of fatigue, and the surface fatigue strength and bending fatigue strength decrease.
iv) When N is fixed by adding Al and utilizing the equilibrium relationship with B and N, BN and AlN precipitate in the steel. Since AlN is fine, crystal grains are refined, and the impact fatigue strength is improved. Further, AlN is not a starting point of fatigue due to its fineness, so that the fatigue strength is improved as compared with the addition of Ti.
v) For impact fatigue strength, it is important to balance the depth of the grain boundary oxide layer with the internal hardness and the carburized hardness distribution (hardened layer depth), and there is an optimum range.
vi) In addition, to improve the torsional fatigue strength of the carburized member when a shaft is assumed, it is effective to apply a compressive residual stress, and the compressive residual stress is reduced to the grain boundary oxide layer depth, internal hardness and hardening. It is important to balance with layer depth.
すなわち、本発明の要旨構成は、以下のとおりである。
１．Ｃ：0.16質量％以上0.35質量％以下、
Si：0.01質量％以上0.20質量％以下、
Mn：0.50質量％以上1.5質量％以下、
Ｐ：0.015質量％以下、
Ｓ：0.03質量％以下、
Cu：0.30質量％以下（０質量％を含む）、
Cr：2.0質量％未満、
Mo：0.16質量％以上0.70質量％以下、
Al：0.055質量％以上0.100質量％以下、
Ｂ：0.0004質量％以上0.0030質量％以下および
Ｎ：0.0070質量％未満
を、次式（１）に従うＩ値が0.028 以上となる範囲にて含有し、残部はFe及び不可避不純物の成分組成と、浸炭層とを有する浸炭部材であって、
次式（２）に従うＡ値が120以上250以下かつ次式（３）に従うＢ値が900以上である部位を有する浸炭部材。
Ｉ＝14/27×Al＋14／10.8×Ｂ−Ｎ ・・・・ （１）
但し、上式（１）におけるAl、ＢおよびＮは各元素の含有量（質量％）
Ａ＝Ｅ／２×Ｈ−Ｄ／２ ・・・・ （２）
Ｂ＝４０Ｅ−１０Ｄ＋Ｒ ・・・・ （３）
但し、上式（２）および（３）において
Ｅ：有効硬化深さ（mm）
Ｈ：内部硬さ（HV）
Ｄ：粒界酸化深さ（μm）
Ｒ：圧縮残留応力（MPa）
That is, the gist configuration of the present invention is as follows.
1. C: 0.16% by mass or more and 0.35% by mass or less,
Si: 0.01% by mass to 0.20% by mass,
Mn: 0.50 mass% to 1.5 mass%,
P: 0.015% by mass or less,
S: 0.03% by mass or less,
Cu: 0.30% by mass or less (including 0% by mass),
Cr: less than 2.0% by mass,
Mo: 0.16% by mass or more and 0.70% by mass or less,
Al: 0.055% by mass or more and 0.100% by mass or less,
B: 0.0004% by mass or more and 0.0030% by mass or less and N: 0.0070% by mass or less in the range where the I value according to the following formula (1) is 0.028 or more, and the balance is the composition of Fe and unavoidable impurities, A carburized member having a layer and
A carburized member having a portion where the A value according to the following formula (2) is 120 or more and 250 or less and the B value according to the following formula (3) is 900 or more.
I = 14/27 x Al + 14 / 10.8 x BN (1)
Here, Al, B and N in the above formula (1) are the contents (% by mass) of each element.
A = E / 2 × H−D / 2 (2)
B = 40E-10D + R (3)
However, in the above equations (2) and (3), E: Effective curing depth (mm)
H: Internal hardness (HV)
D: Grain boundary oxidation depth (μm)
R: Residual compressive stress (MPa)
２．前記成分組成は、更に、
Ni：2.0質量％以下、
Ti：0.050質量％未満、
Nb：0.050質量％以下および
Ｖ：0.200質量％以下
のうちから選ばれる１種または２種以上を含有する前記１に記載の浸炭部材。
2. The component composition further comprises:
Ni: 2.0 mass% or less,
Ti: less than 0.050% by mass,
2. The carburized member according to the above 1, containing one or more selected from Nb: 0.050 mass% or less and V: 0.200 mass% or less.
３．前記成分組成は、更に、
Ca：0.0050質量％以下および
Mg：0.0020質量％以下
の１種または２種を含有する前記１または２に記載の浸炭部材。
3. The component composition further comprises:
Ca: 0.0050 mass% or less and
3. The carburized member according to the
４．前記成分組成は、更に、
Sb：0.030質量％以下
を含有する前記１から３のいずれかに記載の浸炭部材。
4. The component composition further comprises:
4. The carburized member according to any one of the
本発明によれば、耐衝撃疲労特性および耐ねじり疲労特性に共に優れる浸炭部材を提供することができる。従って、自動車や建機に用いられる部材の耐火性を高めることができ、産業上極めて有用である。 ADVANTAGE OF THE INVENTION According to this invention, the carburizing member which is excellent in both impact fatigue resistance and torsional fatigue resistance can be provided. Therefore, the fire resistance of the members used for automobiles and construction machines can be enhanced, which is extremely useful in industry.
以下に、本発明の成分組成における各元素量の限定理由について述べる。以下の説明において、成分組成に関する％表示は、特に断らない限り質量％を意味する。
Ｃ：0.16％以上0.35％以下
Ｃは、浸炭処理後の焼入れにより浸炭材中心部の硬度を高めるのに有効であり、そのためには、0.16％以上のＣを必要とする。一方、含有量が0.35％を超えると、前記中心部の靭性が低下するため、Ｃ量は0.35％以下とする。好ましくは、0.16％以上0.3％以下の範囲である。
Hereinafter, the reasons for limiting the amounts of the respective elements in the composition of the present invention will be described. In the following description, the percentage display relating to the component composition means mass% unless otherwise specified.
C: 0.16% or more and 0.35% or less C is effective for increasing the hardness of the central portion of the carburized material by quenching after carburizing treatment, and therefore requires 0.16% or more of C. On the other hand, if the content exceeds 0.35%, the toughness of the central portion is reduced, so the C content is set to 0.35% or less. Preferably, it is in the range of 0.16% or more and 0.3% or less.
Si：0.01％以上0.20％以下
Siは、脱酸剤として、少なくとも0.01％の添加が必要である。しかしながら、Siは浸炭層の表面側で優先的に酸化し、粒界酸化を促進する元素である。さらに、フェライトを固溶強化し加工性を劣化させる。ため、上限を0.20％とする。好ましくは0.02〜0.18％である。更に好ましくは0.02〜0.15％である。
Si: 0.01% or more and 0.20% or less
Si needs to be added at least 0.01% as a deoxidizing agent. However, Si is an element that preferentially oxidizes on the surface side of the carburized layer and promotes grain boundary oxidation. Further, ferrite is solid-solution strengthened to deteriorate workability. Therefore, the upper limit is set to 0.20%. Preferably it is 0.02-0.18%. More preferably, it is 0.02 to 0.15%.
Mn：0.50％以上1.5％以下
Mnは、焼入れ性を高める元素であり、焼入れ性を確保するためには0.50％以上の含有量とする。なお、1.5％を超えると、ミクロ偏析の悪化、MnS生成増による疲労特性低下が起きるため1.5％を上限とする。
Mn: 0.50% or more and 1.5% or less
Mn is an element that enhances the hardenability, and in order to ensure the hardenability, the content is set to 0.50% or more. If it exceeds 1.5%, deterioration of microsegregation and deterioration of fatigue characteristics due to increased MnS generation occur, so the upper limit is 1.5%.
Ｐ：0.015％以下
Ｐは、結晶粒界に偏析し、靭性を低下させるため、0.015％以下に抑制する。その混入は低いほど望ましいが、必要以上に低減することは、製造コストの上昇につながるため、0.002％以上とすることが好ましい。
P: 0.015% or less P segregates at crystal grain boundaries and lowers toughness, so P is suppressed to 0.015% or less. It is desirable that the contamination be as low as possible. However, since an excessive reduction leads to an increase in the production cost, it is preferably set to 0.002% or more.
Ｓ：0.03％以下
Ｓは、硫化物系介在物として存在し、被削性の向上に有効な元素であり、そのためには0.003％以上で含有させることが好ましい。しかしながら、過剰な添加は疲労強度の低下を招くため、上限を0.03％とした。
S: 0.03% or less S is an element that exists as a sulfide-based inclusion and is effective in improving machinability. For that purpose, it is preferable to contain S in an amount of 0.003% or more. However, excessive addition causes a decrease in fatigue strength, so the upper limit was made 0.03%.
Cu：0.30％以下（０質量％を含む）
Cuは、原料としてスクラップを使用した場合に混入する元素であるが、熱間圧延や熱間鍛造等の熱間加工性を低下させ、歯車やシャフト等の形状に加工する場合に疵などの欠陥の生成を助長する元素である。そのため、その含有量は0.30％以下とする。なお、Ｃｕは０％であってもよい。
Cu: 0.30% or less (including 0% by mass)
Cu is an element that is mixed in when scrap is used as a raw material.However, it reduces the hot workability such as hot rolling and hot forging, and defects such as flaws when processing into shapes such as gears and shafts. Is an element that promotes the formation of Therefore, the content is set to 0.30% or less. Note that Cu may be 0%.
Cr：2.0％未満
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り、そのためには0.1％以上で含有させることが好ましい。しかし、Crの含有量が2.0％以上になると、軟化抵抗を高める効果は飽和する一方で、焼入れ性が高くなりすぎて浸炭部材内部の靭性が劣化し、衝撃疲労強度が低くなるばかりでなく曲げ疲労強度も低下する。よって、Crの含有量は2.0％未満にする。
Cr: less than 2.0%
Cr is an element that enhances the temper softening resistance as well as the quenching property improving element, and for that purpose, it is preferable to contain Cr at 0.1% or more. However, when the Cr content is 2.0% or more, the effect of increasing the softening resistance is saturated, but the quenchability becomes too high, and the toughness inside the carburized member is deteriorated. Fatigue strength also decreases. Therefore, the content of Cr is set to less than 2.0%.
Mo：0.16％以上0.70％以下
Moは、焼入れ性を向上させるのに有効な元素であり、焼入れ性を確保するために0.16％以上の含有とする。一方、Moは高価な元素である上に、0.70％を超えて含有させても前記効果は飽和するため、上限を0.70％とする。好ましくは、0.18〜0.65％である。
Mo: 0.16% or more and 0.70% or less
Mo is an element effective for improving the hardenability, and is contained at 0.16% or more in order to secure the hardenability. On the other hand, Mo is an expensive element and the effect is saturated even if it is contained in excess of 0.70%, so the upper limit is made 0.70%. Preferably, it is 0.18 to 0.65%.
Al：0.055％以上0.100％以下
Alは、ＮとＢとの平衡において固溶Ｂを確保するために必要な元素である。その添加量が0.055％未満ではその効果が得られず、0.100％を超えて添加すると溶製時において鋳造異常等の虞があるため、0.055〜0.100％とする。好ましくは、0.055〜0.090％である。
Al: 0.055% or more and 0.100% or less
Al is an element necessary for securing solid solution B in the equilibrium between N and B. If the addition amount is less than 0.055%, the effect cannot be obtained. If the addition amount exceeds 0.100%, there is a possibility of casting abnormality at the time of smelting, so the content is set to 0.055 to 0.100%. Preferably, it is 0.055 to 0.090%.
Ｂ：0.0004％以上0.0030％以下
Ｂは、鋼中に固溶して粒界偏析し焼入れ性を向上させ、低Si化による焼入れ性の低下を補う。また、Ｐの粒界偏析を妨げ、粒界強度を向上させて疲労特性を改善する効果を有する。そのために、Ｂ量は0.0004％以上とする。なお、0.0030％を超えると、その効果が飽和するため、0.0030％以下とする。
B: 0.0004% or more and 0.0030% or less B forms a solid solution in steel, segregates at grain boundaries, improves quenching properties, and compensates for a decrease in quenching properties due to low Si. Further, it has the effect of preventing segregation of P at the grain boundary, improving the grain boundary strength, and improving the fatigue properties. Therefore, the B content is set to 0.0004% or more. If the content exceeds 0.0030%, the effect saturates.
Ｎ：0.0070％未満
Ｎは、Ｂと結合してＢＮを生成することから、上記した固溶Ｂを確保するためにはＮは少ないほど良いが、次に示すAl、ＮおよびＢの平衡関係において、Ｎが0.0070％未満であれば固溶Ｂの確保は可能となるため、0.0070％未満とする。好ましくは、0.0065％以下である。
N: less than 0.0070% N bonds with B to form BN. Therefore, in order to secure the above-mentioned solid solution B, the smaller the N, the better. However, in the equilibrium relationship of Al, N and B shown below, , N is less than 0.0070%, so that solid solution B can be secured. Preferably, it is 0.0065% or less.
さらに、上記した成分のうち、Al、ＮおよびＢは、次式（１）に従うＩ値が0.028以上となる範囲で含有する必要がある。
Ｉ＝14/27×Al＋14／10.8×Ｂ−Ｎ ・・・・ （１）
但し、上式（１）におけるAl、ＢおよびＮは各元素の含有量（質量％）
このＩ値は、衝撃疲労強度やねじり疲労強度を向上させる固溶Ｂの確保のためにAl、ＢおよびＮのバランスを決める指標である。Ｉ値が0.028未満の場合は、鋼中に固溶するＢの確保が出来なくなるため、Ｉは0.028以上とする。
Further, among the above components, Al, N and B need to be contained in a range where the I value according to the following formula (1) is 0.028 or more.
I = 14/27 x Al + 14 / 10.8 x BN (1)
Here, Al, B and N in the above formula (1) are the contents (% by mass) of each element.
The I value is an index for determining the balance between Al, B and N to secure solid solution B for improving the impact fatigue strength and the torsional fatigue strength. If the I value is less than 0.028, it is not possible to secure B that forms a solid solution in steel, so I is set to 0.028 or more.
上記した成分以外の残部は、Feおよび不可避不純物である。ここで、不可避不純物としての酸素含有量は、コストが許す範囲内で出来るだけ低いほうが望ましい。 The balance other than the above components is Fe and inevitable impurities. Here, the oxygen content as an unavoidable impurity is desirably as low as possible within the range permitted by the cost.
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、Ni、Ti、NbおよびＶのいずれか１種または２種以上を、以下に説明する含有量の範囲内で含有することができる。
Ni：2.0％以下
Niは、靭性を劣化させずに、強度を高められる元素として非常に有用であり、そのためには0.1％以上添加することが好ましい。しかし、高価であり2.0％を超えると前記効果は飽和することから、上限を2.0％とする。
The above is the basic component composition of the present invention. In the case of further improving the characteristics, one or more of Ni, Ti, Nb and V should be contained within the content range described below. Can be.
Ni: 2.0% or less
Ni is very useful as an element that can increase the strength without deteriorating the toughness, and therefore, it is preferable to add 0.1% or more. However, since the effect is saturated when it is expensive and exceeds 2.0%, the upper limit is made 2.0%.
Ti：0.050％未満
Tiは、Ｎと最も結合しやすいことから、固溶Ｂを確保するには有効な元素であり、そのためには0.003％以上添加することが好ましい。しかし、Tiは過剰に添加されると硬くて鋭利な形状の粗大なTiＮが多く形成され、曲げ疲労や衝撃疲労の破壊の起点となり、強度を低下させる。その影響は0.050％以上の添加で顕著になる。よって、Tiを添加する場合は、0.050％未満とする。好ましくは、0.035％未満である。
Ti: less than 0.050%
Ti is an element effective for securing solid solution B since it is most easily bonded to N, and therefore it is preferable to add 0.003% or more. However, if Ti is added excessively, a large amount of coarse TiN having a hard and sharp shape is formed, which becomes a starting point of bending fatigue and impact fatigue, and lowers the strength. The effect becomes remarkable at the addition of 0.050% or more. Therefore, when Ti is added, the content is less than 0.050%. Preferably, it is less than 0.035%.
Nb：0.050％以下
Nbは、結晶粒を微細化させて粒界を強化して疲労強度を向上させる効果を有する。そのためには0.003％以上添加することが好ましい。この効果は0.050％で飽和することから、Ｎｂを添加する場合は0.050％以下とする。好ましくは、0.035％未満である。
Nb: 0.050% or less
Nb has the effect of refining crystal grains, strengthening grain boundaries and improving fatigue strength. Therefore, it is preferable to add 0.003% or more. Since this effect is saturated at 0.050%, when Nb is added, the content is set to 0.050% or less. Preferably, it is less than 0.035%.
Ｖ：0.200％以下
Ｖは、浸炭後の内部強度を上昇させて全体の疲労強度を向上させる効果を有し、そのためには0.030％以上添加することが好ましい。一方、0.200％を超えると前記効果は飽和する。従って、Ｖを添加する場合は、0.200％以下とする。
V: 0.200% or less V has the effect of increasing the internal strength after carburization and improving the overall fatigue strength. For that purpose, it is preferable to add 0.030% or more. On the other hand, when the content exceeds 0.200%, the effect is saturated. Therefore, when V is added, the content is set to 0.200% or less.
さらに、本発明は、硫化物の形態を制御し、被削性や冷間鍛造性を高めるために上記成分に、更にCa： 0.0050％以下およびMg： 0.0020％以下から選ばれる１種または２種を添加することができる。CaおよびMgによる上記効果を得るには、少なくとも0.0005％以上の添加を行うことが好ましい。一方、過剰に添加した場合には、粗大な介在物を形成し、疲労強度に悪影響を与えるため、CaおよびMgについてそれぞれ上限を0.0050％および0.0020％とした。 Further, the present invention further comprises one or more kinds selected from the group consisting of Ca: 0.0050% or less and Mg: 0.0020% or less in order to control the form of sulfide and enhance machinability and cold forgeability. Can be added. In order to obtain the above effects by Ca and Mg, it is preferable to add at least 0.0005% or more. On the other hand, when excessively added, coarse inclusions are formed and the fatigue strength is adversely affected. Therefore, the upper limits of Ca and Mg are set to 0.0050% and 0.0020%, respectively.
さらにまた、本発明では、Sb：0.008〜0.030％以下で添加することができる。すなわち、Sbは、鋼材表面から過剰な炭素の侵入並びに拡散を抑制し、平坦部と角部での炭素量の差を軽減することが可能である。この効果を発揮するためには、0.008％以上で添加することが好ましい。一方、過剰な添加は、鍛造性などの低下を招くことから上限を0.030％とすることが好ましい。さらに、好ましくは、0.013〜0.025％である。 Furthermore, in the present invention, Sb: 0.008 to 0.030% or less can be added. That is, Sb can suppress excessive intrusion and diffusion of carbon from the steel material surface, and can reduce the difference in carbon amount between the flat portion and the corner portion. In order to exhibit this effect, it is preferable to add 0.008% or more. On the other hand, an excessive addition causes a decrease in forgeability and the like, so the upper limit is preferably made 0.030%. More preferably, it is 0.013 to 0.025%.
以上の成分組成を有する鋼素材（例えばビレット）に熱間圧延を施した後、予備成形、次いで機械加工を行って歯車やシャフトの形状とした後、浸炭焼入れ処理を施し、更にショットピーニングあるいは、さらに研磨加工を施して浸炭部材とする。この浸炭部材は、次式（２）に従うＡ値が120以上250以下かつ次式（３）に従うＢ値が900以上であることが肝要である。
Ａ＝Ｅ／２×Ｈ−Ｄ／２ ・・・・ （２）
Ｂ＝４０Ｅ−１０Ｄ＋Ｒ ・・・・ （３）
但し、上式（２）および（３）において
Ｅ：有効硬化深さ（mm）
Ｈ：内部硬さ（HV）
Ｄ：粒界酸化深さ（μm）
Ｒ：圧縮残留応力（MPa）
After hot rolling a steel material (for example, a billet) having the above-mentioned component composition, preforming, then performing machining to form gears and shafts, performing carburizing and quenching, and further performing shot peening or Further polishing is performed to obtain a carburized member. It is important that this carburized member has an A value according to the following equation (2) of 120 or more and 250 or less and a B value according to the following equation (3) of 900 or more.
A = E / 2 × H−D / 2 (2)
B = 40E-10D + R (3)
However, in the above equations (2) and (3), E: Effective curing depth (mm)
H: Internal hardness (HV)
D: Grain boundary oxidation depth (μm)
R: Residual compressive stress (MPa)
まず、Ａ値は、とりわけ歯車に要求される、優れた耐衝撃疲労特性を付与するための指標になり、120以上250以下とする。また、Ｂ値は、とりわけシャフトに要求される、高い耐ねじり疲労特性を付与するための指標になり、900以上とする。以下に、これら指標において適切な範囲を導くに到った実験結果について、詳しく説明する。 First, the A value is an index for imparting excellent impact fatigue resistance particularly required for gears, and is set to 120 or more and 250 or less. In addition, the B value is an index for imparting high torsional fatigue resistance particularly required for a shaft, and is set to 900 or more. Hereinafter, the experimental results that led to an appropriate range for these indices will be described in detail.
表１のNo.１〜３に示す成分組成を有する丸棒鋼（32ｍｍφ）から衝撃疲労試験用の試験片を、後述の実施例と同様に作製し、種々の条件での浸炭焼入れ・焼戻しを行うことによって、粒界酸化層深さ、内部硬さおよび有効硬化層深さの異なる、種々の衝撃疲労試験片を作製し、試験片毎に、後述の実施例における測定方法に従って衝撃エネルギーを測定し、該衝撃エネルギーにて衝撃疲労強度を評価した。この衝撃疲労強度の評価結果を、表２に示す。 Test specimens for impact fatigue tests were prepared from round bar steel (32 mmφ) having the component compositions shown in Nos. 1 to 3 in Table 1 in the same manner as in the examples described later, and carburized and tempered under various conditions. By doing so, various impact fatigue test specimens having different grain boundary oxide layer depth, internal hardness and effective hardened layer depth were prepared, and for each test specimen, the impact energy was measured in accordance with the measurement method in Examples described later. The impact energy was used to evaluate the impact fatigue strength. Table 2 shows the evaluation results of the impact fatigue strength.
ここで、粒界酸化層深さとは、浸炭熱処理時に主に旧オ−ステナイト粒界に沿って生成する、Si、Mnなどを主体とした酸化物の表面からの深さであり、８μm以下とすることが好ましい。内部硬さとは、浸炭層の表面から５mmの位置の硬さであり、438HV以上を確保することが好ましい。有効硬化層深さとは、ビッカース硬さHV550以上となる部位の部材表面からの深さであり、0.61mm 以上を確保することが好ましい。
なお、粒界酸化層深さ、内部硬さおよび有効硬化層深さは、後述の実施例における測定方法に従って測定することができる。
Here, the grain boundary oxide layer depth is a depth from the surface of the oxide mainly composed of Si, Mn, etc., which is mainly formed along the prior austenite grain boundary during the carburizing heat treatment, and is 8 μm or less. Is preferred. The internal hardness is a hardness at a position 5 mm from the surface of the carburized layer, and it is preferable to secure 438 HV or more. The effective hardened layer depth is a depth from a member surface at a portion where the Vickers hardness is HV550 or more, and it is preferable to secure 0.61 mm or more.
The depth of the grain boundary oxide layer, the internal hardness, and the effective hardened layer depth can be measured according to the measuring method in the examples described later.
表２に示す衝撃疲労強度の評価結果において、衝撃疲労強度（衝撃エネルギー）が2.5Ｎ・ｍ以上となる、優れた耐衝撃疲労特性を示す試験片について解析したところ、衝撃疲労試験結果は、有効硬化層深さＥ（ｍｍ）、内部硬さＨ（ＨＶ）および粒界酸化層深さＤ（μｍ）に関する関係式（Ｅ／２×Ｈ−Ｄ／２）にて整理できることを見出すに到った。さらに、この関係式で求められるＡ値と衝撃疲労強度との関係を整理して図１に示すように、Ａ値が１３０以上２５０以下であれば、衝撃疲労強度が2.5Ｎ・ｍ以上の優れた耐衝撃疲労特性が得られることが判明した。尚、Ａ値を算出する際のＥ、ＨおよびＤには、上記したそれぞれの単位系における数値自体を用いる。 In the evaluation results of the impact fatigue strength shown in Table 2, analysis was performed on a test piece having excellent impact fatigue properties in which the impact fatigue strength (impact energy) was 2.5 N · m or more. It has been found that the relational expression (E / 2 × HD / 2) relating to the depth E (mm) of the hardened layer, the internal hardness H (HV), and the depth D (μm) of the grain boundary oxide layer can be obtained. Was. Further, the relationship between the A value and the impact fatigue strength obtained by this relational expression is arranged and as shown in FIG. 1, when the A value is 130 or more and 250 or less, the excellent impact fatigue strength is 2.5 N · m or more. It was found that high impact fatigue resistance was obtained. It should be noted that the numerical values in the respective unit systems described above are used as E, H and D when calculating the A value.
同様に、No.１〜３に示す成分組成を有する丸棒鋼（32ｍｍφ）からねじり疲労試験用の試験片を、後述の実施例と同様に作製し、種々の条件での浸炭焼入れ、焼戻しを行ったのち、種々の条件でのショットピーニング処理を行うことによって、粒界酸化層深さ、有効硬化層深さおよび残留圧縮応力の異なる、種々のねじり疲労試験片を作製し、試験片毎に、表面の残留圧縮応力をＸ線にて測定するとともに、後述の実施例における測定方法に従って105回の時間強度（トルク）を測定し、該時間強度にてねじり疲労強度を評価した。このねじり疲労強度の評価結果を、表２に併記する。 Similarly, test pieces for torsional fatigue tests were prepared from round bar steel (32 mmφ) having the component compositions shown in Nos. 1 to 3 in the same manner as in Examples described later, and carburized and quenched and tempered under various conditions. After that, by performing shot peening treatment under various conditions, various torsional fatigue test specimens having different grain boundary oxide layer depth, effective hardened layer depth and residual compressive stress were prepared, and for each test specimen, the residual compressive stress on the surface as well as measured by X-ray, 10 five times the strength (torque) was measured according to the measurement method in the examples below were evaluated fatigue strength twisting at said time strength. Table 2 also shows the evaluation results of the torsional fatigue strength.
ここで、残留圧縮応力とは、外力を除去したあとでも物体内に残る応力のことである。なお、残留圧縮応力は、後述の実施例における測定方法に従って測定することができる。 Here, the residual compressive stress is a stress that remains in an object even after external force is removed. In addition, the residual compressive stress can be measured according to a measuring method in Examples described later.
表２に示すねじり疲労強度の評価結果において、ねじり疲労強度が735Ｎ・ｍ以上となる、優れたねじり疲労特性を示す試験片について解析したところ、有効硬化層深さＥ（ｍｍ）、粒界酸化層深さＤ（μｍ）および残留圧縮応力Ｒ（MPa）に関する関係式（４０Ｅ−１０Ｄ＋Ｒ）にて整理できることを見出すに到った。さらに、この関係式で求められるＢ値とねじり疲労強度との関係を整理して図２に示すように、Ｂ値が900以上であれば、ねじり疲労強度が735Ｎ・ｍ以上の優れた耐ねじり疲労特性が得られることが判明した。一方、Ｂ値の上限は特に限定する必要はない。
尚、Ｂ値を算出する際のＥ、ＤおよびＲには、上記したそれぞれの単位系における数値自体を用いる。
According to the evaluation results of the torsional fatigue strength shown in Table 2, when a torsional fatigue strength of 735 N · m or more was analyzed for a test piece exhibiting excellent torsional fatigue properties, the effective hardened layer depth E (mm), the grain boundary oxidation It has been found that the relationship can be organized by a relational expression (40E-10D + R) relating to the layer depth D (μm) and the residual compressive stress R (MPa). Further, the relationship between the B value and the torsional fatigue strength obtained by this relational expression is arranged, and as shown in FIG. 2, when the B value is 900 or more, an excellent torsional fatigue strength with a torsional fatigue strength of 735 N · m or more is obtained. It has been found that fatigue properties can be obtained. On the other hand, the upper limit of the B value does not need to be particularly limited.
In addition, the numerical values themselves in the respective unit systems described above are used for E, D, and R when calculating the B value.
本発明に係る鋼部材（たとえば、歯車またはシャフト）を作製するには、常法により溶解鋳造して、上記した成分組成のビレットとし、このビレットに熱間圧延を施した後、歯車およびシャフト等の形状とするための予備成形を行う。予備成形としては、熱間鍛造が挙げられる。この予備成形後に機械加工、あるいは予備成形後に鍛造してから機械加工を行って、歯車およびシャフト等の形状とした後、浸炭焼入れ、焼戻し処理を施す。ここでの浸炭焼入れ、焼戻し処理の条件を適宜選択することによって、有効硬化層深さＥ、内部硬さＨおよび粒界酸化層深さＤを上記したＡ値を満足する範囲に調整する。なお、浸炭焼入れ、焼戻し処理は、浸炭温度９００〜１０５０℃、焼入れ温度８００〜９００℃とし、焼戻し温度は１２０〜２５０℃の範囲とすることが好ましく、これらの範囲内で処理条件を適宜選択する。 In order to manufacture the steel member (for example, a gear or a shaft) according to the present invention, a billet having the above-described composition is formed by melting and casting according to a conventional method. Preforming is performed to obtain a shape. Preforming includes hot forging. Machine processing is performed after the preforming, or forging is performed after the preforming to form a gear and a shaft, and then carburizing and tempering are performed. The depth of the effective hardened layer E, the internal hardness H, and the depth of the grain boundary oxide layer D are adjusted to a range that satisfies the above-mentioned A value by appropriately selecting the conditions of the carburizing, quenching and tempering treatments. The carburizing and quenching and tempering treatments are preferably performed at a carburizing temperature of 900 to 1050 ° C and a quenching temperature of 800 to 900 ° C, and the tempering temperature is preferably in a range of 120 to 250 ° C, and the processing conditions are appropriately selected within these ranges. .
さらに、鋼部材の疲労強度を向上させるべき部位、例えば、鋼部材が歯車の場合は少なくとも歯面およびシャフトの場合は少なくとも油孔近傍にショットピーニング処理を施す。ここでのショットピーニング処理の条件を適宜選択することによって、上記部位の残留圧縮応力Ｒを上記したＢ値を満足する範囲に調整する。さらに（必要に応じて）研磨加工を施して最終製品とする。 Furthermore, shot peening is applied to a portion of the steel member at which the fatigue strength is to be improved, for example, at least a tooth surface when the steel member is a gear and at least a vicinity of an oil hole when the steel member is a shaft. By appropriately selecting the conditions of the shot peening process here, the residual compressive stress R at the above-mentioned portion is adjusted to a range satisfying the above-mentioned B value. Further, if necessary, polishing is performed to obtain a final product.
ここで、ショットピーニング処理は、各種手法があるが、鋼部材の表層に大きな圧縮残留応力を導入でき、かつ表面粗さを極力大きくしない方法を用いることが好ましい。たとえば、２段ショットピーニング法を用いる場合は、１段目にショット粒硬さ約650〜800HVで0.5〜1.0mmφをカバレージ200％以上で主として残留応力を与え、続く２段目をシ
ョット粒硬さ約650〜800HVで0.1mmφ未満をカバレージ200％以上で行い、表面粗さを
整えることが好ましく、これらの範囲内で処理条件を適宜選択する。
Here, there are various methods for the shot peening treatment, but it is preferable to use a method that can introduce a large compressive residual stress into the surface layer of the steel member and does not increase the surface roughness as much as possible. For example, when the two-stage shot peening method is used, the residual stress is mainly applied to the first stage at a shot grain hardness of about 650 to 800 HV and 0.5 to 1.0 mmφ at a coverage of 200% or more, and the second stage is shot grain hardness. It is preferable that the surface roughness is adjusted to about 650 to 800 HV with less than 0.1 mmφ at a coverage of 200% or more, and the processing conditions are appropriately selected within these ranges.
表３に示す化学成分を有する鋼を溶製し供試鋼とした。表中、No.Ａ〜Ｌは、本発明範囲内の成分組成の適合鋼であり、No.Ｍ〜ＡＥは本発明範囲外の比較鋼である。
溶製された上記の適合鋼および比較鋼のインゴットを熱間圧延により直径32mm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。
焼準処理後の丸棒鋼から直径20mmの丸棒、衝撃疲労試験片、孔付ねじり疲労試験片を採取した。丸棒および各疲労試験片に対して、図３に示す条件に従って浸炭焼入れ、焼戻し処理を施し、次いでショットピーニング処理を前述の条件に従って施した後、表面硬さ、内部硬さ、有効硬化層深さ、圧縮残留応力を調査した。その後、後述する衝撃疲労試験およびねじり疲労試験を実施した。以下に、それぞれの調査内容について詳細に説明する。
Steels having the chemical components shown in Table 3 were melted and used as test steels. In the table, No. A to L are compatible steels having a component composition within the range of the present invention, and No. M to AE are comparative steels outside the range of the present invention.
The ingots of the above-mentioned compatible steel and comparative steel that had been melted were prepared into round bars having a diameter of 32 mm by hot rolling, and the obtained round bars were subjected to normalizing treatment.
A round bar having a diameter of 20 mm, an impact fatigue test piece, and a torsion fatigue test piece with a hole were collected from the round bar steel after the normalizing treatment. The round bar and each fatigue test piece were subjected to carburizing and quenching according to the conditions shown in FIG. 3, and then subjected to shot peening according to the above-described conditions, followed by surface hardness, internal hardness, and effective hardened layer depth. Now, the compressive residual stress was investigated. Thereafter, an impact fatigue test and a torsional fatigue test described below were performed. The details of each survey are described below.
［粒界酸化層深さ、有効硬化層深さ、内部硬さ、圧縮残留応力］
上記した直径20mmの丸棒（適合鋼および比較鋼）において、ショットピーニング処理後に、Ｘ線にて圧縮残留応力を測定した。また、該丸棒を切断し、浸炭表層を1000倍で５視野観察し、酸化物の深さが最大となる粒界酸化層深さを光学顕微鏡にて測定した。さらに、断面の硬度分布を測定し、ビッカース硬さで550HVの得られる深さを調査し「有効硬化層深さ」とした。さらにまた、丸棒の表面より５mm深さ位置の硬さをビッカース硬度計にて測定し、この値を「内部硬さ」とした。
[Grain boundary oxide layer depth, effective hardened layer depth, internal hardness, compressive residual stress]
In the above-mentioned round bar having a diameter of 20 mm (conforming steel and comparative steel), the compressive residual stress was measured by X-ray after the shot peening treatment. In addition, the round bar was cut, and the carburized surface layer was observed at 5 times at a magnification of 1000 times, and the depth of the grain boundary oxide layer at which the oxide depth was maximum was measured with an optical microscope. Further, the hardness distribution of the cross section was measured, and the depth at which 550 HV was obtained in terms of Vickers hardness was investigated and defined as "effective hardened layer depth". Furthermore, the hardness at a position 5 mm deep from the surface of the round bar was measured with a Vickers hardness meter, and this value was defined as “internal hardness”.
［耐衝撃疲労特性］
直径32mmの丸棒鋼から、図４に示す試験片を作製し、図３に示す条件の浸炭焼入れ、焼き戻し処理を施した後、落錘型衝撃疲労試験機により、繰返し数２００回で破壊する衝撃エネルギーを調査した。
[Impact fatigue resistance]
A test piece shown in FIG. 4 was prepared from a round steel bar having a diameter of 32 mm, and after carburizing and quenching under the conditions shown in FIG. 3, it was broken at a repetition number of 200 times by a falling weight impact fatigue tester. The impact energy was investigated.
［耐ねじり疲労特性］
直径32mm径の丸棒鋼から、図５に示す試験片を作製し、得られた試験片の全数（適合鋼、比較鋼）に図３に示す条件の浸炭焼入れ、焼戻し処理および上記した条件のショットピーニング処理を行い、その後、ねじり疲労試験機を使用して２Hzおよびsin波の条件にて負荷トルクを変化させて３本以上実施し、トルク寿命線図から105回の時間強度（トルク）を求めた。
[Torsional fatigue resistance]
A test piece shown in FIG. 5 was prepared from a round bar steel having a diameter of 32 mm, and all of the obtained test pieces (conforming steel, comparative steel) were carburized and tempered under the conditions shown in FIG. 3 and shots under the conditions described above. performs peening process, then changing the load torque at the conditions of 2Hz and sin wave using a torsion fatigue test machine was performed three or more, the time-intensity of 10 5 times the torque life diagram (torque) I asked.
表４に上記の各調査の結果を示す。本発明に従う鋼部材は有効硬化層深さが0.61mm以上、粒界酸化深さが８μm以下、内部硬さは438HV以上であり、衝撃疲労強度は2.7Ｎ・ｍ以上、ねじり疲労強度741N・m以上が得られ、No.13〜29の比較例より優れていた。 Table 4 shows the results of each of the above surveys. The steel member according to the present invention has an effective hardened layer depth of 0.61 mm or more, a grain boundary oxidation depth of 8 μm or less, an internal hardness of 438 HV or more, an impact fatigue strength of 2.7 Nm or more, and a torsional fatigue strength of 741 Nm. The above results were obtained and were superior to the comparative examples of Nos. 13 to 29.
Claims (4)
Si：0.01質量％以上0.20質量％以下、
Mn：0.50質量％以上1.5質量％以下、
Ｐ：0.015質量％以下、
Ｓ：0.03質量％以下、
Cu：0.30質量％以下（０質量％を含む）、
Cr：2.0質量％未満、
Mo：0.16質量％以上0.70質量％以下、
Al：0.055質量％以上0.100質量％以下、
Ｂ：0.0004質量％以上0.0030質量％以下および
Ｎ：0.0070質量％未満
を、次式（１）に従うＩ値が0.028 以上となる範囲にて含有し、残部はFe及び不可避不純物の成分組成と、浸炭層とを有する浸炭部材であって、
次式（２）に従うＡ値が120以上250以下かつ次式（３）に従うＢ値が900以上である部位を有する浸炭部材。
Ｉ＝14/27×Al＋14／10.8×Ｂ−Ｎ ・・・・ （１）
但し、上式（１）におけるAl、ＢおよびＮは各元素の含有量（質量％）
Ａ＝Ｅ／２×Ｈ−Ｄ／２ ・・・・ （２）
Ｂ＝４０Ｅ−１０Ｄ＋Ｒ ・・・・ （３）
但し、上式（２）および（３）において
Ｅ：有効硬化深さ（mm）
Ｈ：内部硬さ（HV）
Ｄ：粒界酸化深さ（μm）
Ｒ：圧縮残留応力（MPa） C: 0.16% by mass or more and 0.35% by mass or less,
Si: 0.01% by mass to 0.20% by mass,
Mn: 0.50 mass% to 1.5 mass%,
P: 0.015% by mass or less,
S: 0.03% by mass or less,
Cu: 0.30% by mass or less (including 0% by mass),
Cr: less than 2.0% by mass,
Mo: 0.16% by mass or more and 0.70% by mass or less,
Al: 0.055% by mass or more and 0.100% by mass or less,
B: 0.0004% by mass or less and 0.0030% by mass or less and N: 0.0070% by mass or less in a range where the I value according to the following formula (1) is 0.028 or more, and the balance is Fe and the unavoidable impurity component composition and carburizing. A carburized member having a layer and
A carburized member having a portion where the A value according to the following formula (2) is 120 or more and 250 or less and the B value according to the following formula (3) is 900 or more.
I = 14/27 x Al + 14 / 10.8 x BN (1)
Here, Al, B and N in the above formula (1) are the contents (% by mass) of each element.
A = E / 2 × H−D / 2 (2)
B = 40E-10D + R (3)
However, in the above equations (2) and (3), E: Effective curing depth (mm)
H: Internal hardness (HV)
D: Grain boundary oxidation depth (μm)
R: Residual compressive stress (MPa)
Ni：2.0質量％以下、
Ti：0.050質量％未満、
Nb：0.050質量％以下および
Ｖ：0.200質量％以下
のうちから選ばれる１種または２種以上を含有する請求項１に記載の浸炭部材。 The component composition further comprises:
Ni: 2.0 mass% or less,
Ti: less than 0.050% by mass,
2. The carburized member according to claim 1, comprising one or more members selected from Nb: 0.050 mass% or less and V: 0.200 mass% or less. 3.
Ca：0.0050質量％以下および
Mg：0.0020質量％以下
の１種または２種を含有する請求項１または２に記載の浸炭部材。 The component composition further comprises:
Ca: 0.0050 mass% or less and
The carburized member according to claim 1, comprising one or two kinds of Mg: 0.0020% by mass or less.
Sb：0.030質量％以下
を含有する請求項１から３のいずれかに記載の浸炭部材。 The component composition further comprises:
The carburized member according to any one of claims 1 to 3, containing Sb: 0.030% by mass or less.
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