JP5526689B2 - Carburizing steel - Google Patents
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- 229910000831 Steel Inorganic materials 0.000 title claims description 23
- 239000010959 steel Substances 0.000 title claims description 23
- 238000005255 carburizing Methods 0.000 title claims description 20
- 229910052710 silicon Inorganic materials 0.000 claims description 13
- 229910052804 chromium Inorganic materials 0.000 claims description 12
- 229910052759 nickel Inorganic materials 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 9
- 229910052802 copper Inorganic materials 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 12
- 238000010438 heat treatment Methods 0.000 description 9
- 238000009792 diffusion process Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 150000001247 metal acetylides Chemical class 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000007254 oxidation reaction Methods 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 239000011162 core material Substances 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 230000001629 suppression Effects 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910000746 Structural steel Inorganic materials 0.000 description 1
- 239000005539 carbonized material Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000009661 fatigue test Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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Description
本発明は、主に産業機器や自動車の分野にて機械構造用鋼として用いられる浸炭用鋼に関し、特に過剰の浸炭が回避される浸炭用鋼に関するものである。 The present invention relates to carburizing steel used as machine structural steel mainly in the fields of industrial equipment and automobiles, and more particularly to carburizing steel in which excessive carburization is avoided.
鋼の浸炭熱処理は、鋼材表面から炭素を侵入させて内部拡散させ、引き続いて焼入れる事によって、表層は硬く、かつ内部は元々の炭素含有量に従う、比較的軟らかい状態を得ることができる。よって、耐磨耗性や耐疲労特性が向上し、かつ内部靭性が良好といった優れた性質を素材に持たせることが出来、歯車やシャフトなどに幅広く利用されている。 In the carburizing heat treatment of steel, carbon is penetrated from the surface of the steel material to cause internal diffusion, followed by quenching, so that the surface layer is hard and the inside can be relatively soft according to the original carbon content. Therefore, the material can have excellent properties such as improved wear resistance and fatigue resistance and good internal toughness, and is widely used for gears and shafts.
しかしながら、浸炭熱処理では、表面の炭素濃度が被処理材の形状の影響を大きく受ける。すなわち、処理材の平坦部分では狙い通りの硬さや組織が得られても、角部分では浸炭が過剰となり、粗大炭化物の生成に伴う疲労強度の低下が懸念されている。特に、最近用いられるようになってきた真空浸炭では、この傾向がより顕著になっている。そこで、炭素の侵入拡散や炭化物の生成挙動に与える元素の影響を考慮した、成分組成の提案がなされている。 However, in the carburizing heat treatment, the carbon concentration on the surface is greatly affected by the shape of the material to be treated. That is, even if the intended hardness and structure are obtained in the flat portion of the treated material, carburization is excessive in the corner portion, and there is a concern that the fatigue strength is reduced due to the formation of coarse carbides. In particular, this tendency is more remarkable in vacuum carburizing that has recently been used. In view of this, a component composition has been proposed in consideration of the influence of elements on the intrusion diffusion of carbon and the generation behavior of carbides.
例えば、特許文献１には、炭化物の生成抑制効果のある、Si、CuおよびNiを増加させ、逆に炭化物を増大させやすいCr量を減らすことによって、過剰浸炭による疲労強度の低下を抑制することが提案されている。
For example, in
しかしながら、上述した特許文献１に記載された技術では、Ｓｉを多量に添加しているため、冷間鍛造性の低下が懸念され、またガス浸炭の場合には粒界酸化の問題が生じる。さらに、Ｃｒの低減に伴って強度を確保するためのCuおよびNiを添加せざるを得ず、合金コストが高くなることも問題である。
However, in the technique described in
本発明の目的は、上記の実情に鑑み開発されたものであり、浸炭の熱処理条件によることなく過剰な浸炭が抑制され、かつ優れた冷間鍛造性および疲労強度が得られる浸炭用鋼を提供することにある。 The object of the present invention was developed in view of the above circumstances, and provides a carburizing steel in which excessive carburization is suppressed and excellent cold forgeability and fatigue strength are obtained without depending on the heat treatment conditions of carburizing. There is to do.
本発明者らは、上記の課題を解決すべく鋭意研究を重ねた結果、以下に述べる知見を得た。
すなわち、Sbは、鋼材表面からの過剰な炭素の侵入そして拡散を抑制する作用を有するため、鋼中にSbを添加することによって、角部での過剰浸炭を防止し、平坦部と角部での炭素量の差を軽減することができるとの知見を得た。さらに、炭素の侵入そして拡散を抑制する作用を有するSi、さらにはCuおよびNiの含有量と、炭素の侵入そして拡散を助長する作用を有するCrの含有量と、前述のSbの含有量とを適正に調整することによって、角部での過剰浸炭を防止できるのではないかと考え、Sb，SiおよびCrを種々の量で含有させた鋼について、浸炭を行い、このときの過剰浸炭の有無を調査した。
As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
That is, Sb has an action of suppressing excessive carbon intrusion and diffusion from the steel surface, so by adding Sb into the steel, excessive carburization at the corners is prevented, and flat and corners are prevented. It was found that the difference in carbon content can be reduced. Further, the content of Si, further Cu and Ni, which suppresses the penetration and diffusion of carbon, the content of Cr that promotes the penetration and diffusion of carbon, and the content of Sb described above We think that it is possible to prevent excessive carburization at the corners by adjusting properly, and carburize steels containing various amounts of Sb, Si and Cr. investigated.
その調査結果について、浸炭に及ぼすSb量と、Sb，SiおよびCr量との関係を図１に示す。同図から、Sbを適正量で添加する事により、過剰浸炭になりやすい角部での炭素の侵入拡散を抑えられることがわかる。すなわち、Sbを用いることによって、Siの過剰添加に頼らない成分設計が可能となることを見出したのである。なお、過剰浸炭の有無の調査は、後述する実施例と同様の手法で行った。 Fig. 1 shows the relationship between the amount of Sb that affects carburization and the amount of Sb, Si, and Cr. From the figure, it can be seen that by adding an appropriate amount of Sb, it is possible to suppress the intrusion diffusion of carbon at corners that are prone to excessive carburization. That is, by using Sb, it has been found that a component design that does not rely on excessive addition of Si becomes possible. In addition, the investigation on the presence or absence of excessive carburization was performed by the same method as in Examples described later.
本願発明は、以上の知見に基づいて成されたものであり、その要旨構成は次のとおりである。
（１）質量％で、
Ｃ：0.10〜0.35％、
Si：0.01〜0.50％、
Mn：0.3〜1.5％、
Ｐ：0.02％以下、
Ｓ：0.03％以下、
Al：0.01〜0.05％、
Cr：1.52〜3.0％および
Sb：0.008〜0.035％
を、下記（１）式を満足する範囲で含有し、残部はFe及び不可避不純物の組成である浸炭用鋼。
記
150［％Sb］＋３［％Si］−［％Cr］≧ ０ --- （１）
但し、［ ］は各元素の質量％を示す
The present invention has been made on the basis of the above knowledge, and the gist of the present invention is as follows.
(1) In mass%,
C: 0.10 to 0.35%,
Si: 0.01 to 0.50%
Mn: 0.3-1.5%
P: 0.02% or less,
S: 0.03% or less,
Al: 0.01-0.05%
Cr: 1.52 to 3.0% and
Sb: 0.008 to 0.035%
In a range that satisfies the following formula (1), with the balance being the composition of Fe and inevitable impurities.
Record
150 [% Sb] + 3 [% Si]-[% Cr] ≥ 0 --- (1)
However, [] indicates mass% of each element.
（２）質量％で、
Ｃ：0.10〜0.35％、
Si：0.01〜0.50％、
Mn：0.3〜1.5％、
Ｐ：0.02％以下、
Ｓ：0.03％以下、
Al：0.01〜0.05％、
Cr：1.52〜3.0％および
Sb：0.008〜0.035％を含み、さらに
Cu：1.0％以下、
Ni：0.5％以下、
Mo：0.5％以下および
Ｖ：0.5％以下
のうちから選ばれる１種または２種以上を含有し、かつ下記（２）式を満足し、残部はFe及び不可避不純物の組成である浸炭用鋼。
記
150［％Sb］＋３［％Si］＋［％Cu］＋［％Ni］−［％Cr］≧０ --- （２）
但し、［ ］は各元素の質量％を示す
(2) In mass%,
C: 0.10 to 0.35%,
Si: 0.01 to 0.50%
Mn: 0.3-1.5%
P: 0.02% or less,
S: 0.03% or less,
Al: 0.01-0.05%
Cr: 1.52 to 3.0% and
Sb: 0.008-0.035% included, and
Cu: 1.0% or less,
Ni: 0.5% or less,
Mo: 0.5% or less and V: Carburizing steel containing one or more selected from 0.5% or less and satisfying the following formula (2), the balance being the composition of Fe and inevitable impurities.
Record
150 [% Sb] +3 [% Si] + [% Cu] + [% Ni] − [% Cr] ≧ 0 --- (2)
However, [] indicates mass% of each element.
（３）前記（１）または（２）において、前記組成は、更に、質量％で
Ca：0.0005〜0.005％および
Mg：0.0002〜0.002％
のうちから選ばれる１種または２種を含有する浸炭用鋼。
(3) In the above (1) or (2), the composition is further in mass%.
Ca: 0.0005 to 0.005% and
Mg: 0.0002 to 0.002%
Carburizing steel containing one or two selected from among them.
本発明によれば、浸炭熱処理条件や部品形状によらずに、角部での過剰浸炭は抑制され、優れた冷間鍛造性および疲労強度を得ることができるため、工業上非常に有用である。 According to the present invention, regardless of carburizing heat treatment conditions and part shapes, excessive carburization at corners is suppressed, and excellent cold forgeability and fatigue strength can be obtained, which is very useful industrially. .
以下、本発明の浸炭用鋼を具体的に説明する。
まず、本発明において、鋼の成分組成を上記の範囲に限定した理由について、成分元素毎に詳しく説明する。なお、各元素の含有量に関する「％」表示は、特に断らない限り「質量％」を意味するものとする。
Hereinafter, the carburizing steel of the present invention will be specifically described.
First, the reason why the component composition of steel is limited to the above range in the present invention will be described in detail for each component element. In addition, unless otherwise indicated, the "%" display regarding content of each element shall mean "mass%".
Ｃ：0.10〜0.35％
Ｃは、浸炭熱処理後の焼入れにより被処理材芯部の硬度を高めるために、0.10％以上の含有量が必要になるが、含有量が0.35％を超えると芯部の靭性が低下するため、Ｃ量は0.10〜0.35％の範囲に限定した。好ましくは、0.30％以下の範囲である。
C: 0.10 to 0.35%
C, in order to increase the hardness of the core material to be treated by quenching after carburizing heat treatment, a content of 0.10% or more is required, but if the content exceeds 0.35%, the toughness of the core portion decreases. The amount of C was limited to the range of 0.10 to 0.35%. Preferably, it is 0.30% or less of range.
Si：0.01〜0.50％
Siは、脱酸剤として必要であり、少なくとも0.01％の添加が必要である。しかしながら、Siは浸炭表層で優先的に酸化し、粒界酸化を促進する元素である。また、フェライトを固溶強化して変形抵抗を高める結果、冷間鍛造性を劣化させるため、上限を0.50％とする。好ましくは、0.03〜0.35％である。
Si: 0.01-0.50%
Si is necessary as a deoxidizing agent, and it is necessary to add at least 0.01%. However, Si is an element that preferentially oxidizes in the carburized surface layer and promotes grain boundary oxidation. In addition, the upper limit is set to 0.50% in order to deteriorate the cold forgeability as a result of enhancing the deformation resistance by solid solution strengthening of ferrite. Preferably, it is 0.03 to 0.35%.
Mn：0.30〜1.50％
Mnは、焼入性に有効な元素であり、少なくとも0.30％の添加を必要とする。しかし、Mnは粒界酸化を引き起こしやすく、また過剰な添加は残留オーステナイトを増加させ、表面硬度の低下を招くことから、上限を1.50％とする。好ましくは、0.60〜1.40％の範囲である。
Mn: 0.30 to 1.50%
Mn is an element effective for hardenability, and requires addition of at least 0.30%. However, Mn tends to cause grain boundary oxidation, and excessive addition increases residual austenite, leading to a decrease in surface hardness, so the upper limit is made 1.50%. Preferably, it is 0.60 to 1.40% of range.
Ｐ：0.02％以下
Ｐは、結晶粒界に偏析し、靱性を低下させるため、その混入は低いほど望ましいが、0.02％までは許容される。好ましくは、0.018％以下である。
P: 0.02% or less P is segregated at the grain boundaries and lowers the toughness. Therefore, the lower the content, the better, but 0.02% is acceptable. Preferably, it is 0.018% or less.
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る。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 sulfide inclusions and is effective in improving machinability. However, excessive addition causes a decrease in fatigue strength, so the upper limit was made 0.03%.
Al：0.01〜0.05％
Alは、脱酸剤として必要であり、少なくとも0.01％以上の添加が必要である。また、AlはＮと結合してAlＮを形成し、オーステナイトの結晶粒の微細化に寄与する元素である。しかしながら、含有量が0.05％を超えると疲労強度に対して有害なAl２Ｏ３介在物の生成を助長するため、0.01〜0.05％の範囲に限定した。
Al: 0.01-0.05%
Al is necessary as a deoxidizer, and at least 0.01% or more must be added. Al is an element that combines with N to form AlN and contributes to the refinement of austenite crystal grains. However, if the content exceeds 0.05%, the formation of Al 2 O 3 inclusions harmful to fatigue strength is promoted, so the content is limited to 0.01 to 0.05%.
Cr：1.0〜3.0％
Crは、焼入性のみならず、焼戻し軟化抵抗の向上に寄与し、さらには炭化物の球状化促進にも有用な元素であるが、含有量が1.52％に満たないとその添加効果に乏しく、一方、3.0％を超えると浸炭部での炭化物生成を促進し、疲労強度に悪影響を与える場合がある。よってCr量は1.52〜3.0％の範囲に限定した。好ましくは、1.52〜2.6％の範囲である。
Cr: 1.0-3.0%
Cr is an element that contributes not only to hardenability but also to the improvement of temper softening resistance, and also useful for promoting the spheroidization of carbides, but if the content is less than 1.52 %, its addition effect is poor, On the other hand, if it exceeds 3.0%, the formation of carbides in the carburized part is promoted, which may adversely affect the fatigue strength. Therefore, the Cr content is limited to the range of 1.52 to 3.0%. Preferably, it is 1.52 to 2.6%.
Sb：0.008〜0.035％
Sbは、本発明において、最も重要な元素である。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％以上の添加が必要である。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0.035％とした。さらに、好ましくは、0.013〜0.035％である。
Sb: 0.008 to 0.035%
Sb is the most important element in the present invention. Sb can suppress excessive carbon intrusion and diffusion from the surface of the steel material, and can reduce the difference in carbon content between the flat portion and the corner portion. In order to exhibit this effect, addition of 0.008% or more is necessary. On the other hand, excessive addition causes a decrease in forgeability and the like, so the upper limit was made 0.035%. Furthermore, it is preferably 0.013 to 0.035%.
前述したように、Sbの過剰浸炭の抑制効果は、鋼中のSiやCrの含有量に影響を受ける。図１に示したように、Sb、SiおよびCr量の関係が下記（１）式を満足する範囲にすることにより、過剰浸炭を抑制できる。なお、CuおよびNiも同様に炭化物生成の抑制効果を示すことから、後述するようにCuおよびNiを添加した場合は、下記（２）式の条件を満たすことにより過剰浸炭の抑制が可能となる。
記
150［％Sb］＋３［％Si］−［％Cr］≧０ --- （１）
150［％Sb］＋３［％Si］＋［％Cu］＋［％Ni］−［％Cr］≧０ --- （２）
As described above, the suppression effect of excessive carburization of Sb is affected by the contents of Si and Cr in the steel. As shown in FIG. 1, excessive carburization can be suppressed by setting the relationship among the amounts of Sb, Si and Cr to satisfy the following formula (1). In addition, since Cu and Ni show the inhibitory effect of carbide | carbonized_material production | generation similarly, when Cu and Ni are added so that it may mention later, suppression of excessive carburization is attained by satisfy | filling the following (2) Formula. .
Record
150 [% Sb] + 3 [% Si]-[% Cr] ≥ 0 --- (1)
150 [% Sb] +3 [% Si] + [% Cu] + [% Ni] − [% Cr] ≧ 0 --- (2)
さらに、本発明では、焼入性を高めるために上記の基本成分に、更にCu：1.0％以下、Ni：0.5％以下、Mo：0.5％以下およびＶ：0.5％以下から選ばれる１種または２種以上を含有することができる。
Cuは、焼入性の向上に有効な元素であり、0.1％以上で添加することが好ましいが、多量の添加は鋼材の表面性状の劣化や合金コストの増加を招くため、上限を1.0％とした。
Ni、MoおよびＶは、焼入性や靭性の向上に有効な元素であり、0.05％以上で添加することが好ましいが、高価であるため、上限をそれぞれ0.5％とした。
Further, in the present invention, in order to improve hardenability, one or two selected from the above basic components are further selected from Cu: 1.0% or less, Ni: 0.5% or less, Mo: 0.5% or less, and V: 0.5% or less. More than seeds can be contained.
Cu is an element effective for improving hardenability, and is preferably added at 0.1% or more. However, addition of a large amount causes deterioration of the surface properties of the steel material and increase of the alloy cost, so the upper limit is set to 1.0%. did.
Ni, Mo and V are effective elements for improving hardenability and toughness, and are preferably added at 0.05% or more. However, since they are expensive, the upper limit is set to 0.5%.
また、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：0.0005〜0.005％およびMg：0.0005〜0.002％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0.005％および0.002％とした。 In addition, the present invention controls the form of the sulfide, and in order to improve the machinability and cold forgeability, the above component is further added to Ca: 0.0005 to 0.005% and Mg: 0.0005 to 0.002%. Two types can be added. In order to obtain the above effect 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 0.005% and 0.002%, respectively.
次に、本発明の実施例について説明する。
まず、供試鋼として表１に示す成分組成の鋼を溶製し、熱間圧延により直径60mmの丸棒を製造した。得られた丸棒について、図２に示す角部（角度：60°）を持つ試験片を採取し、図３に示す熱履歴に従って平坦部における有効硬化深さ（Hv≧550となる表面からの深さ）が1.2mm狙いとした浸炭熱処理を施し、該浸炭熱処理を施した後の試験片の角部１および平坦部２の炭素濃度を調査した。
また、角部１については、表面硬度、残留オーステナイト量、粒界酸化深さをそれぞれ測定した。
Next, examples of the present invention will be described.
First, steel having the composition shown in Table 1 was melted as test steel, and a round bar having a diameter of 60 mm was manufactured by hot rolling. With respect to the obtained round bar, a test piece having a corner (angle: 60 °) shown in FIG. 2 was collected, and the effective hardening depth in the flat portion (Hv ≧ 550 from the surface where Hv ≧ 550) was obtained according to the thermal history shown in FIG. Carburizing heat treatment with a target depth of 1.2 mm was performed, and the carbon concentration in the
Further, for the
ここで、表面硬度がHv700以下、残留オーステナイト量が40％以上、粒界酸化深さが20μm以上のいずれかを満たす場合は過剰浸炭である。 Here, when the surface hardness satisfies Hv 700 or less, the retained austenite amount is 40% or more, and the grain boundary oxidation depth is 20 μm or more, it is excessive carburization.
また、上記の丸棒より試験歯車を作製し、上記と同様の浸炭熱処理を施し、同一素材の２枚の歯車をかみ合わせて、疲労試験を行い、107回強度を測定した。疲労強度が665MPa以上であれば、疲労強度は良好であるといえる。 Further, a test gear was produced from the above round bar, subjected to the same carburizing heat treatment as described above, two gears of the same material were engaged, a fatigue test was performed, and the strength was measured 10 7 times. If the fatigue strength is 665 MPa or more, it can be said that the fatigue strength is good.
さらに、冷間加工性は、限界据え込み率および変形抵抗の２項目で評価した。
すなわち、変形抵抗は、圧延ままの棒鋼の直径の1/4深さ位置から、直径10mmおよび高さ15mmの試験片を採取し、300ｔプレス機を用いて、60％据え込み時の圧縮荷重を測定し、日本塑性加工学会が提唱している端面拘束圧縮により、変形抵抗測定方法を用いて求めた。また、限界据え込み率は、変形抵抗を測定した方法で圧縮加工を行い、端部に割れが入ったときの据え込み率を限界据え込み率とした。
なお、変形抵抗値が899MPa以下および限界割れ率が74％以上であれば、冷間鍛造性は良好であるといえる。
得られた結果を表２に示す。
Furthermore, the cold workability was evaluated by two items, the limit upsetting rate and the deformation resistance.
In other words, the deformation resistance was measured by taking a test piece with a diameter of 10 mm and a height of 15 mm from a 1/4 depth position of the diameter of the rolled steel bar, and using a 300-ton press to apply a compression load at 60% upsetting. It measured and calculated | required using the deformation resistance measuring method by the end surface restraint compression which the Japan Society for Technology of Plasticity advocated. Further, the limit upsetting rate was defined as the upsetting rate when the end portion was cracked by compressing by a method of measuring deformation resistance.
If the deformation resistance value is 899 MPa or less and the critical crack rate is 74% or more, it can be said that the cold forgeability is good.
The obtained results are shown in Table 2.
表２に示したとおり、本発明により得られた発明例はいずれも、冷間加工性に優れかつ疲労強度にも優れていることが分かる。
一方、No．11は、Si含有量が高い鋼を用いているため、変形抵抗が高く、また、限界据え込み率が低い。No．12はＳｂ含有量が低い鋼を用いているため、角部に過剰浸炭が生じていた。また、疲労強度も低い値を示した。No．13は、Sb、SiおよびCrの含有量が上記した（１）式を満足しないため、角部に過剰浸炭が生じており、また、疲労強度も低い値を示した。No．14は、Sb、SiおよびCrの含有量が上記した（２）式を満足しないため、角部に過剰浸炭が生じており、また疲労強度も低い値を示した。
As shown in Table 2, it can be seen that all of the inventive examples obtained by the present invention are excellent in cold workability and fatigue strength.
On the other hand, No. No. 11 uses steel with a high Si content, so it has high deformation resistance and a low limit upsetting rate. No. Since No. 12 uses steel having a low Sb content, excessive carburization occurred at the corners. Moreover, the fatigue strength also showed a low value. No. In No. 13, since the contents of Sb, Si and Cr do not satisfy the above formula (1), excessive carburization occurs at the corners, and the fatigue strength is low. No. In No. 14, since the contents of Sb, Si and Cr do not satisfy the above-mentioned formula (2), excessive carburization occurs at the corners and the fatigue strength is low.
Claims (3)
Ｃ：0.10〜0.35％、
Si：0.01〜0.50％、
Mn：0.3〜1.5％、
Ｐ：0.02％以下、
Ｓ：0.03％以下、
Al：0.01〜0.05％、
Cr：1.52〜3.0％および
Sb：0.008〜0.035％
を、下記（１）式を満足する範囲で含有し、残部はFe及び不可避的不純物の組成である浸炭用鋼。
記
150［％Sb］＋３［％Si］−［％Cr］≧０ ---（１）
但し、［ ］は各元素の質量％を示す % By mass
C: 0.10 to 0.35%,
Si: 0.01 to 0.50%
Mn: 0.3-1.5%
P: 0.02% or less,
S: 0.03% or less,
Al: 0.01-0.05%
Cr: 1.52 to 3.0% and
Sb: 0.008 to 0.035%
In a range that satisfies the following formula (1), with the balance being the composition of Fe and unavoidable impurities.
Record
150 [% Sb] +3 [% Si]-[% Cr] ≧ 0 --- (1)
However, [] indicates mass% of each element.
Ｃ：0.10〜0.35％、
Si：0.01〜0.50％、
Mn：0.3〜1.5％、
Ｐ：0.02％以下、
Ｓ：0.03％以下、
Al：0.01〜0.05％、
Cr：1.52〜3.0％および
Sb：0.008〜0.035％を含み、さらに
Cu：1.0％以下、
Ni：0.5％以下、
Mo：0.5％以下および
Ｖ：0.5％以下
のうちから選ばれる１種または２種以上を含有し、かつ下記（２）式を満足し、残部はFe及び不可避的不純物の組成である浸炭用鋼。
記
150［％Sb］＋３［％Si］＋［％Cu］＋［％Ni］−［％Cr］≧０ --- （２）
但し、［ ］は各元素の質量％を示す % By mass
C: 0.10 to 0.35%,
Si: 0.01 to 0.50%
Mn: 0.3-1.5%
P: 0.02% or less,
S: 0.03% or less,
Al: 0.01-0.05%
Cr: 1.52 to 3.0% and
Sb: 0.008-0.035% included, and
Cu: 1.0% or less,
Ni: 0.5% or less,
Mo: 0.5% or less and V: Carburizing steel containing one or more selected from 0.5% or less, satisfying the following formula (2), the balance being the composition of Fe and inevitable impurities .
Record
150 [% Sb] +3 [% Si] + [% Cu] + [% Ni] − [% Cr] ≧ 0 --- (2)
However, [] indicates mass% of each element.
Ca：0.0005〜0.005％および
Mg：0.0002〜0.002％
のうちから選ばれる１種または２種を含有する浸炭用鋼。 The composition according to claim 1 or 2, further comprising:
Ca: 0.0005 to 0.005% and
Mg: 0.0002 to 0.002%
Carburizing steel containing one or two selected from among them.
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