JP2019026874A - Raw material for high frequency induction hardening component - Google Patents
Raw material for high frequency induction hardening component Download PDFInfo
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この発明は、表面に高周波焼入れによる硬化層を備えた高周波焼入れ部品を得るのに好適な高周波焼入れ部品用素材に関する。 The present invention relates to a material for induction-quenched parts suitable for obtaining an induction-quenched part having a hardened layer by induction hardening on the surface.
例えば自動車用の各種部品においては、燃費削減を背景に、軽量化を目的とした部品の高強度化のニーズがますます高くなっている。このような高い強度が要求される部品については、浸炭や高周波焼入れ等の表面硬化処理が施される。高周波焼入れは、他の表面硬化処理と比較して素材の局部処理が容易で、かつ低コストである。加えて高周波焼入れによれば高硬度化や高圧縮残留応力の付与が可能であるため、多くの高強度部品に適用されている。高周波焼入れ部品は、熱間鍛造、さらには切削、冷間鍛造などを施して所定の形状に加工したのち、高周波焼入れ−焼戻しを行うことにより、所定の強度が確保される。 For example, in various parts for automobiles, there is a growing demand for higher strength of parts aimed at weight reduction against the background of reducing fuel consumption. For parts requiring such high strength, surface hardening treatment such as carburizing and induction hardening is performed. Induction hardening is easy in local treatment of the material and is low in cost as compared with other surface hardening treatments. In addition, since induction hardening can provide high hardness and high compressive residual stress, it is applied to many high-strength parts. The induction-hardened component is subjected to hot forging, further cutting, cold forging, and the like to be processed into a predetermined shape, and then subjected to induction hardening and tempering to ensure a predetermined strength.
しかしながら、高周波焼入れ部品では、部品の形状に起因して高周波加熱による渦電流が特定の部位に局所的に集中して過加熱が生じる問題がある。高周波加熱における過加熱は、結晶粒の粗粒化による強度低下の原因となり、さらに加熱された部位の一部が融点を超えれば、溶融割れが発生する。過加熱の防止は、高周波加熱の条件を変更して対応することも考えられるが、加熱条件の変更は高周波焼入れ工程での製造性を悪化させる場合もあり、被加熱材（高周波焼入れ部品用素材）側からの解決が望まれていた。 However, in the induction-hardened component, there is a problem that eddy current due to high-frequency heating is locally concentrated on a specific part due to the shape of the component and overheating occurs. Overheating in high-frequency heating causes a decrease in strength due to the coarsening of crystal grains, and if a part of the heated portion exceeds the melting point, melt cracking occurs. It is conceivable to prevent overheating by changing the conditions of induction heating, but changing the heating conditions may deteriorate the manufacturability in the induction hardening process. ) The solution from the side was desired.
尚、本発明に対する先行技術として、下記特許文献１には、所定の成分組成を満足するとともに〔80C2＋55C＋13Si＋4.8Mn＋30P＋30S＋1.5Cr〕が50以下、かつ〔C＋（Si／10）＋（Mn／5）−（5S／7）＋（5Cr／22）＋1.65V〕が0.80〜1.00の範囲である高周波焼入れ用非調質鋼が開示されている。しかしながら、この特許文献１に記載の鋼はＳｉ含有量が０．３超〜０．７％であり本発明と比べて多い。更に加熱時の鋼材の温度上昇を抑制する思想を有するものではなく、後述する本発明の式(１)，式(２)の両方を満たす合金組成は開示されていない。 As a prior art for the present invention, the following Patent Document 1 satisfies the predetermined component composition and [80C 2 + 55C + 13Si + 4.8Mn + 30P + 30S + 1.5Cr] is 50 or less and [C + (Si / 10) + (Mn / 5). )-(5S / 7) + (5Cr / 22) + 1.65V] is disclosed in the range of 0.80 to 1.00 for induction hardening non-heat treated steel. However, the steel described in Patent Document 1 has a Si content of more than 0.3 to 0.7%, which is larger than that of the present invention. Further, it does not have the idea of suppressing the temperature rise of the steel material during heating, and does not disclose an alloy composition that satisfies both formulas (1) and (2) of the present invention described later.
一方、下記特許文献２には、ＭｎＳ等の介在物の制御を行い、バーニング発生の原因となるＦｅＳの生成を抑制することで、熱間加工前や高周波を用いて加熱したときのバーニングの発生を防止した鋼材が開示されている。しかしながら特許文献２に記載の鋼材は、強度面からの考慮がなされておらず、後述する本発明の式(１)，式(２)の両方を満たす合金組成は開示されていない。 On the other hand, in Patent Document 2 below, by controlling inclusions such as MnS and suppressing the generation of FeS that causes burning, the occurrence of burning when heated before hot working or using high frequency The steel material which prevented this is disclosed. However, the steel material described in Patent Document 2 is not considered in terms of strength, and does not disclose an alloy composition that satisfies both formulas (1) and (2) of the present invention described later.
本発明は以上のような事情を背景とし、高周波焼入れ工程で過加熱が生じ難く製造性に優れ、高い強度の高周波焼入れ部品を製造可能な高周波焼入れ部品用素材を提供することを目的としてなされたものである。 The present invention has been made for the purpose of providing a material for induction-quenched parts that can produce high-strength induction-quenched parts that are less prone to overheating in the induction-quenching process and that are excellent in manufacturability. Is.
而して請求項１に記載のものは、質量％で、Ｃ：０．３５〜０．４５％，Ｓｉ：０．３０％以下，Ｍｎ：０．８０〜１．３０％，Ｐ：０．０３０％以下，Ｓ：０．０１０〜０．０７０％，Ｃｒ：０．３０％以下，を含有し、更に、Ｃｕ：０．２０％以下，Ｎｉ：０．１５％以下，Ｍｏ：０．１０％以下，Ｖ：０．３０％以下，Ａｌ：０．０３％以下，Ｔｉ：０．０５％以下，Ｎｂ：０．１０％以下，の何れか１種若しくは２種以上を含有し、残部がＦｅ及び不可避的不純物であり、且つ下記式（１），式（２）を満足する組成の鋼から成ることを特徴とする。
ｆｎ１＜１．４８・・式(１)、０．７６＜ｆｎ２＜０．９０・・式(２)
但しｆｎ１＝[C]＋1.2[Si]＋0.5[Mn]＋0.3[Cr]＋0.45([Cu]＋[Ni]＋[Mo])
ｆｎ２＝[C]＋[Si]／13＋[Mn]／6＋3[P]／5＋2[Cu]／5＋[Ni]／5＋[Cr]／6＋[V]
（ｆｎ１，ｆｎ２の式中[ ]は、[ ]内元素の含有質量％を表す）
Thus, in the first aspect, the mass% is C: 0.35 to 0.45%, Si: 0.30% or less, Mn: 0.80 to 1.30%, P: 0.00. 030% or less, S: 0.010 to 0.070%, Cr: 0.30% or less, and Cu: 0.20% or less, Ni: 0.15% or less, Mo: 0.10 % Or less, V: 0.30% or less, Al: 0.03% or less, Ti: 0.05% or less, Nb: 0.10% or less. It is characterized by being made of steel having a composition which is Fe and inevitable impurities and satisfies the following formulas (1) and (2).
fn1 <1.48 .. Formula (1), 0.76 <fn2 <0.90 .. Formula (2)
However, fn1 = [C] +1.2 [Si] +0.5 [Mn] +0.3 [Cr] +0.45 ([Cu] + [Ni] + [Mo])
fn2 = [C] + [Si] / 13 + [Mn] / 6 + 3 [P] / 5 + 2 [Cu] / 5 + [Ni] / 5 + [Cr] / 6 + [V]
(In the formula of fn1 and fn2, [] represents the content mass% of the element in [])
請求項２のものは、請求項１において、質量％で、Ｂ：０．００１０〜０．０１００％，Ｐｂ：０．３００％以下，Ｂｉ：０．３００％以下，Ｃａ：０．０００５〜０．００５０％，の何れか１種若しくは２種以上を更に含有することを特徴とする。 A second aspect of the present invention is the same as in the first aspect, wherein B: 0.0010 to 0.0100%, Pb: 0.300% or less, Bi: 0.300% or less, Ca: 0.0005-0. Any one or more of .0050% is further contained.
高周波加熱の際に温度の上がり易い素材は、過加熱の問題も生じ易い。本発明者らは、高周波加熱時の素材温度の上がり易さが何と関連しているかを調査したところ、素材の電気抵抗率との間に一定の相関があることを見出した。図１は、高周波加熱時の最高到達温度と、素材の電気抵抗率との関係を示している。詳しくは、電気抵抗率の異なる鋼から作成された複数の試験片（Φ２０ｍｍ×長さ５０ｍｍ）に対し、同一条件下で高周波加熱を行い、その際に得られた最高到達温度と試験片の電気抵抗率（常温）との関係を示している。 A material whose temperature easily rises during high-frequency heating is likely to cause overheating. The present inventors have investigated what is related to the ease of increasing the material temperature during high-frequency heating, and found that there is a certain correlation with the electrical resistivity of the material. FIG. 1 shows the relationship between the maximum temperature achieved during high-frequency heating and the electrical resistivity of the material. Specifically, a plurality of test pieces (Φ20 mm × length 50 mm) made from steels having different electrical resistivity are subjected to high-frequency heating under the same conditions, and the maximum temperature obtained at that time and the electrical properties of the test pieces are measured. The relationship with resistivity (room temperature) is shown.
この図１から明らかなように、試験片の電気抵抗率が低い場合、素材の最高到達温度は低くなる。即ち、高周波焼入れ部品用素材の電気抵抗率を低くして、加熱された際の温度の上がり方（単位時間当たりの温度上昇勾配）を緩やかにすることで、特定の部位に渦電流が集中した場合の過加熱を緩和することができる。
本発明はこのような知見に基づくものであり、素材の電気抵抗率に及ぼす合金成分の影響を定式化し、素材の電気抵抗率を表す指数ｆｎ１を設け、指数ｆｎ１の値が所定の値よりも低くなるように、各合金元素の含有量を規定したことを１つの特徴とするものである。
As is clear from FIG. 1, when the electrical resistivity of the test piece is low, the maximum temperature reached by the material is low. That is, by reducing the electrical resistivity of the material for induction-hardened parts and making the temperature rise when heated (gradient of temperature rise per unit time) gentle, eddy currents are concentrated on specific parts. In some cases, overheating can be mitigated.
The present invention is based on such knowledge, formulates the influence of the alloy component on the electrical resistivity of the material, provides an index fn1 representing the electrical resistivity of the material, and the value of the index fn1 is higher than a predetermined value. One feature is that the content of each alloy element is defined so as to be low.
一方で、これら合金元素の含有量を過度に少なくすれば、高周波焼入れ部品用素材の内部硬さが不足して、十分な部品強度を得ることができなくなることから、本発明では、更に高周波焼入れ部品用素材の内部硬さの指数であるｆｎ２を設け、ｆｎ２の値が上記式（２）を満たすようにすることで最適なバランスの合金組成を規定している。 On the other hand, if the content of these alloy elements is excessively reduced, the internal hardness of the induction-hardened component material becomes insufficient, and sufficient component strength cannot be obtained. By providing fn2 which is an index of the internal hardness of the component material, and the value of fn2 satisfies the above formula (2), an alloy composition with an optimal balance is defined.
このような本発明の高周波焼入れ部品用素材によれば、所定の内部硬さを確保しつつ、高周波加熱時の温度上昇勾配を緩やかにすることができるため、加熱されやすい部位での過度な温度上昇、更には過加熱による溶融割れが良好に防止され、高周波焼入れによる高強度な部品を得ることができる。
また温度上昇勾配を緩やかした本発明の高周波焼入れ部品用素材を用いることで、許容される加熱処理の範囲が拡大するため、高周波焼入れ工程における加熱制御が容易となり製造性を高めることが可能である。
According to such a material for induction-quenched parts of the present invention, it is possible to moderate a temperature rise gradient during induction heating while ensuring a predetermined internal hardness, and thus an excessive temperature at a part that is easily heated. The melt cracking due to the rise and further overheating is prevented well, and a high-strength part can be obtained by induction hardening.
Moreover, since the range of allowable heat treatment is expanded by using the material for induction-quenched parts of the present invention having a gentle temperature rise gradient, it is easy to control heating in the induction hardening process, and it is possible to improve productivity. .
次に本発明における各化学成分の限定理由を以下に詳述する。尚、以降の説明では、特にことわりがない限り「％」は「質量％」を意味するものとする。
Ｃ：０．３５〜０．４５％
Ｃは、高周波焼入れ性、硬さおよび強度を高めるのに有効な元素である。必要な高周波焼入れ性、硬さおよび強度を得るには０．３５％以上の添加を必要とする。但し、過剰な添加は靭性の低下を引き起こす為、その含有量を０．３５〜０．４５％とする。
Next, the reasons for limiting each chemical component in the present invention will be described in detail below. In the following description, “%” means “mass%” unless otherwise specified.
C: 0.35-0.45%
C is an element effective for increasing induction hardenability, hardness and strength. Addition of 0.35% or more is required to obtain the necessary induction hardenability, hardness and strength. However, excessive addition causes a decrease in toughness, so the content is made 0.35 to 0.45%.
Ｓｉ：０．３０％以下
Ｓｉは、脱酸および焼入れ性を高めるのに有効な元素である。但し、０．３０％より多く添加されると靭性が低下するため、その上限を０．３０％とする。
Si: 0.30% or less Si is an element effective for improving deoxidation and hardenability. However, if added more than 0.30%, the toughness decreases, so the upper limit is made 0.30%.
Ｍｎ：０．８０〜１．３０％
Ｍｎは、硬さおよび強度を高めるのに有効な元素である。０．８０％より少ないと必要な硬さおよび強度が得られず、また１．３０％より多いと靭性が低下するので、その含有量を０．８０〜１．３０％とする。
Mn: 0.80 to 1.30%
Mn is an element effective for increasing hardness and strength. If it is less than 0.80%, the required hardness and strength cannot be obtained, and if it exceeds 1.30%, the toughness decreases, so the content is made 0.80 to 1.30%.
Ｐ：０．０３０％以下
Ｐは、不純物であり少ないほうが好ましいが、０．０３０％以下であれば特性にそれ程の影響がなく、その上限を０．３０％とする。
P: 0.030% or less P is an impurity and preferably less, but if it is 0.030% or less, there is no significant influence on the characteristics, and the upper limit is set to 0.30%.
Ｓ：０．０１０〜０．０７０％
Ｓは、被削性を高めるのに有効な元素である。その効果を得るため０．０１０％以上添加する。但し、過剰な添加は粗大なＭｎＳを生成し、高周波焼入れ時の焼割れの原因となることがあるため、その含有量を０．０１０〜０．０７０％とする。
S: 0.010 to 0.070%
S is an element effective for improving the machinability. In order to obtain the effect, 0.010% or more is added. However, excessive addition generates coarse MnS and may cause quenching cracks during induction hardening, so the content is made 0.010 to 0.070%.
Ｃｒ：０．３０％以下
Ｃｒは、高周波焼入れ性、硬さおよび強度を高めるために有効な元素である。但し０．３０％を超えて含有させようとすれば、安価な屑鉄を使用することができなくなり原料価格が高くなるため、その上限を０．３０％とする。
Cr: 0.30% or less Cr is an effective element for enhancing induction hardenability, hardness and strength. However, if the content exceeds 0.30%, inexpensive scrap iron cannot be used and the raw material price increases, so the upper limit is made 0.30%.
Ｃｕ：０．２０％以下
Ｎｉ：０．１５％以下
Ｃｕ及びＮｉは、鍛造後の硬さ、強度および高周波焼入性を高めるために有効な元素である。Ｃｕ及びＮｉは電炉原料のスクラップに不可避的に含まれる元素であるが、Ｃｕを０．２０％，Ｎｉを０．１５％を超えて含有しようとすると、原料にスクラップだけでなく高価な合金の添加が必要となり、配合コストがかさむため、その上限をＣｕで０．２０％，Ｎｉで０．１５％とする。
Cu: 0.20% or less Ni: 0.15% or less Cu and Ni are effective elements for increasing the hardness, strength, and induction hardenability after forging. Cu and Ni are elements inevitably contained in scrap of raw materials for electric furnaces. However, if Cu is contained in an amount exceeding 0.20% and Ni exceeds 0.15%, not only scrap but also an expensive alloy is included in the raw material. Since addition is required and the blending cost is increased, the upper limit is made 0.20% for Cu and 0.15% for Ni.
Ｍｏ：０．１０％以下
Ｍｏは、焼入れ性を高めるとともに、高周波焼入れ部の強度を向上させるのに有効な元素である。但し、多量に添加しようとすれば原料価格が高くなるため、その上限を０．１０％とする。
Mo: 0.10% or less Mo is an element effective for enhancing the hardenability and improving the strength of the induction-quenched portion. However, since the raw material price will increase if a large amount is added, the upper limit is made 0.10%.
Ｖ：０．３０％以下
Ｖは、鍛造後の硬さを向上させ、高周波焼入れを施さない部分の強度を確保するのに有効な元素である。但し、過剰に添加しても効果が飽和する上に、原料価格が高くなるため、その上限を０．３０％とする。
V: 0.30% or less V is an element effective in improving the hardness after forging and ensuring the strength of a portion not subjected to induction hardening. However, even if added excessively, the effect is saturated and the raw material price increases, so the upper limit is made 0.30%.
Ａｌ：０．０３％以下
Ａｌは、脱酸および鍛造加熱時の結晶粒粗大化を抑制するのに有効な元素である。但し、過剰に添加すると粗大なＡｌ2Ｏ3を生成し、被削性が悪化するため、その上限を０．０３％とする。
Al: 0.03% or less Al is an element effective for suppressing coarsening of crystal grains during deoxidation and forging heating. However, if added excessively, coarse Al 2 O 3 is generated and machinability deteriorates, so the upper limit is made 0.03%.
Ｔｉ：０．０５％以下
Ｔｉは、鍛造加熱時の結晶粒粗大化を抑制する効果を有する元素である。但し、過剰に添加すると粗大な窒化物や硫化物を生成し、被削性が悪化するので、その上限を０．０５０％とする。
Ti: 0.05% or less Ti is an element having an effect of suppressing grain coarsening during forging heating. However, if added excessively, coarse nitrides and sulfides are formed and the machinability deteriorates, so the upper limit is made 0.050%.
Ｎｂ：０．１０％以下
Ｎｂは、鍛造加熱時の結晶粒粗大化を抑制する効果を有する元素である。但し、過剰に添加してもその効果が飽和する上に、原料価格が高くなるため、上限を０．１０％とする。
Nb: 0.10% or less Nb is an element having an effect of suppressing coarsening of crystal grains during forging heating. However, even if added excessively, the effect is saturated and the raw material price becomes high, so the upper limit is made 0.10%.
ｆｎ1＜１．４８・・式(１)、但しｆｎ1＝[C]＋1.2[Si]＋0.5[Mn]＋0.3[Cr]＋0.45([Cu]＋[Ni]＋[Mo])
ｆｎ１は、高周波焼入れ部品用素材の電気抵抗率を表す指数である。Ｃ，Ｓｉ，Ｍｎ，Ｃｒ，Ｃｕ，Ｎｉ，Ｍｏは、高周波焼入れ部品用素材の電気抵抗率を変動させる元素であり、Ｃ，Ｓｉ，Ｍｎ，Ｃｒ，Ｃｕ，Ｎｉ，Ｍｏの係数は、それぞれ素材の電気抵抗率に対する寄与度を表している。ｆｎ１の値が小さいほど素材の電気抵抗率は低くなり、高周波加熱時の温度上昇は抑制される。このため特定の部位に渦電流が集中した場合（過加熱が生じた場合）の温度上昇を抑制することができる。
本発明では、本発明者らが定めた過加熱による溶融割れが発生し易い加熱条件（後述の実施例参照）の下、高周波加熱を行ったとき、素材に溶融割れの発生が無ければ、実際の高周波焼入れ工程でも過加熱を防止する効果が発揮できるとの知見の下、指数ｆｎ１の値を１．４８未満と規定している。なお、ｆｎ１の式にて無添加の元素に対応する項は、ゼロとして計算する。
fn1 <1.48 .. Formula (1), where fn1 = [C] +1.2 [Si] +0.5 [Mn] +0.3 [Cr] +0.45 ([Cu] + [Ni] + [Mo ])
fn1 is an index representing the electrical resistivity of the material for induction-hardened parts. C, Si, Mn, Cr, Cu, Ni, and Mo are elements that fluctuate the electrical resistivity of the material for induction-hardened parts, and the coefficients of C, Si, Mn, Cr, Cu, Ni, and Mo are the respective materials. Represents the degree of contribution to the electrical resistivity. The smaller the value of fn1, the lower the electrical resistivity of the material, and the temperature rise during high-frequency heating is suppressed. For this reason, the temperature rise when eddy current concentrates on a specific part (when overheating arises) can be suppressed.
In the present invention, when high-frequency heating is performed under the heating conditions (see Examples described later) in which melt cracking is likely to occur due to overheating determined by the present inventors, Under the knowledge that the effect of preventing overheating can be exhibited even in the induction hardening process, the value of the index fn1 is defined as less than 1.48. The term corresponding to the non-added element in the fn1 equation is calculated as zero.
０．７６＜ｆｎ２＜０．９０・・式(２)、但しｆｎ２＝[C]＋[Si]／13＋[Mn]／6＋3[P]／5＋2[Cu]／5＋[Ni]／5＋[Cr]／6＋[V]
ｆｎ２は、高周波焼入れ部品用素材の内部硬さを表す指数である。Ｃ，Ｓｉ，Ｍｎ，Ｐ，Ｃｕ，Ｎｉ，Ｃｒ，Ｖは、高周波焼入れ部品用素材の内部硬さを高める効果がある。ｆｎ２中のＣ，Ｓｉ，Ｍｎ，Ｐ，Ｃｕ，Ｎｉ，Ｃｒ，Ｖの係数は、それぞれ内部硬さ上昇に対する寄与度を表している。内部硬さは強度や加工性（切削される場合は被削性）に影響を及ぼす因子であり、内部硬さが低すぎると目的の部品強度を得ることができず、逆に硬さが高すぎると加工性の劣化を招き好ましくない。このようなことが生じないようにするため適切な硬さ範囲に調整することが必要である。このため本発明では、ｆｎ２の範囲を０．７６超〜０．９０未満とした。なお、ｆｎ２の式にて無添加の元素に対応する項は、ゼロとして計算する。
0.76 <fn2 <0.90 .. Formula (2), where fn2 = [C] + [Si] / 13 + [Mn] / 6 + 3 [P] / 5 + 2 [Cu] / 5 + [Ni] / 5 + [Cr ] / 6 + [V]
fn2 is an index representing the internal hardness of the material for induction-hardened parts. C, Si, Mn, P, Cu, Ni, Cr, and V have an effect of increasing the internal hardness of the material for induction-hardened parts. The coefficients of C, Si, Mn, P, Cu, Ni, Cr, and V in fn2 represent the degree of contribution to the increase in internal hardness. Internal hardness is a factor that affects strength and workability (machinability when machined). If the internal hardness is too low, the desired component strength cannot be obtained. Too much is not preferable because it causes deterioration of workability. In order to prevent this from occurring, it is necessary to adjust to an appropriate hardness range. Therefore, in the present invention, the range of fn2 is set to be more than 0.76 and less than 0.90. Note that the term corresponding to the non-added element in the fn2 equation is calculated as zero.
Ｂ：０．００１０〜０．０１００％
Ｂは、焼入れ性を高めるとともに、高周波焼入れ部の強度を高める効果を有する元素である。十分な効果を得るためには０．００１０％以上添加する必要がある。但し、Ｂを過剰に添加しても効果が飽和する上に、ホウ化物を形成して靭性を低下させるため、その上限を０．０１００％とする。
B: 0.0010 to 0.0100%
B is an element that has the effect of increasing the hardenability and increasing the strength of the induction-hardened portion. In order to obtain a sufficient effect, it is necessary to add 0.0010% or more. However, even if B is added excessively, the effect is saturated, and a boride is formed to reduce toughness. Therefore, the upper limit is made 0.0100%.
Ｐｂ：０．３００％以下
Ｂｉ：０．３００％以下
Ｐｂ及びＢｉは、高周波焼入れ部品用素材の被削性を向上させる効果を有する元素である。但し、０．３００％より多く添加してもその効果が飽和するため、これら元素の上限を０．３００％とする。
Pb: 0.300% or less Bi: 0.300% or less Pb and Bi are elements having an effect of improving the machinability of the material for induction-hardened parts. However, since the effect is saturated even if adding more than 0.300%, the upper limit of these elements is made 0.300%.
Ｃａ：０．０００５〜０．００５０％
Ｃａは、高周波焼入れ部品用素材の被削性を向上させる効果を有する元素である。その効果を得るためには０．０００５％以上添加する必要がある。但し、過剰に添加してもその効果が飽和するため、上限を０．００５０％とする。
Ca: 0.0005 to 0.0050%
Ca is an element having an effect of improving the machinability of the material for induction-hardened parts. In order to acquire the effect, it is necessary to add 0.0005% or more. However, the effect is saturated even if added excessively, so the upper limit is made 0.0050%.
以上のような本発明によれば、高周波焼入れ工程で過加熱が生じ難く製造性に優れ、高い強度の高周波焼入れ部品を製造可能な高周波焼入れ部品用素材を提供することができる。 According to the present invention as described above, it is possible to provide an induction-quenched component material that is less prone to overheating in the induction hardening step, is excellent in manufacturability, and can produce a high-strength induction-quenched component.
次に本発明の実施例を以下に説明する。
［最高到達温度測定および溶融割れ評価］
先ず表１に示す化学成分の合金材料を高周波誘導炉にて溶製し、得られたインゴットを熱間鍛造加工しその後大気中で放冷して４２ｍｍ角の棒鋼とした。そして、その中心部からΦ２０ｍｍ×長さ５０ｍｍの丸棒の試験片を作製した。
Next, examples of the present invention will be described below.
[Maximum temperature measurement and melt crack evaluation]
First, alloy materials having chemical components shown in Table 1 were melted in a high-frequency induction furnace, and the obtained ingot was hot forged and then allowed to cool in the atmosphere to obtain a 42 mm square steel bar. And the test piece of the round bar of (PHI) 20mm x length 50mm was produced from the center part.
このようにして得られた試験片の表面に熱電対を溶接し、試験片を高周波加熱した。高周波加熱は、１ターンコイルを用いて、出力３６ｋＷで１０秒行った。その際の最高到達温度を記録するとともに、加熱後の試験片内部を観察し、溶融割れ発生の有無を調査した。 A thermocouple was welded to the surface of the test piece thus obtained, and the test piece was heated at high frequency. High frequency heating was performed for 10 seconds at an output of 36 kW using a one-turn coil. The maximum temperature reached at that time was recorded, and the inside of the test piece after heating was observed to investigate the occurrence of melt cracking.
溶融割れの調査は、加熱処理後の試験片の横断面を、ピクラール試薬にて腐食し、光学顕微鏡で観察し、以下のように評価した。
例えば図２に示すように、粒界部分に数μｍの幅で明瞭に腐食された組織が認められた場合、溶融割れありと判断し結果「×」とした。
一方、溶融割れの発生が認められなかった場合（例えば図３参照）、溶融割れ無しと判断し結果「○」とした。
For the investigation of the melt cracking, the cross section of the test piece after the heat treatment was corroded with a Picral reagent, observed with an optical microscope, and evaluated as follows.
For example, as shown in FIG. 2, when a clearly corroded structure having a width of several μm is observed at the grain boundary portion, it is determined that there is a melt crack, and the result is “x”.
On the other hand, when the occurrence of melt cracking was not observed (see, for example, FIG. 3), it was determined that there was no melt cracking and the result was “◯”.
［内部硬さ評価］
また、上記高周波加熱用の試験片作製の際に得られた４２ｍｍ角の棒鋼を用い、棒鋼の横断面での中心軸と外表面との間の径方向の中間位置（Ｒ／２位置）におけるロックウェル硬さを４点測定し、その平均値を内部硬さとした。尚、内部硬さの目標値は２１〜２７ＨＲＣとした。内部硬さが２１ＨＲＣ未満では十分な部品強度が確保できず、他方、２７ＨＲＣ超では加工性が確保できないからである。
これらの結果が表２に示してある。
[Internal hardness evaluation]
In addition, using a 42 mm square steel bar obtained at the time of producing the test piece for high-frequency heating, at a radial intermediate position (R / 2 position) between the central axis and the outer surface in the cross section of the steel bar The Rockwell hardness was measured at four points, and the average value was defined as the internal hardness. The target value of internal hardness was 21 to 27 HRC. This is because if the internal hardness is less than 21 HRC, sufficient component strength cannot be ensured, and if it exceeds 27 HRC, workability cannot be ensured.
These results are shown in Table 2.
比較例１は、電気抵抗率を表す指数ｆｎ１の値が本発明の上限値（１．４８）を上回っており、後述する実施例と比べて電気抵抗率が高い。このため高周波加熱時の最高到達温度が１４３０℃を超えており、試験片の一部において溶融割れの発生が認められた。この比較例１の組成から成る高周波焼入れ部品用素材を用いた場合には、形状に起因した過加熱による温度上昇が生じやすくなる。このような場合、溶融割れが懸念され、溶融割れを防止しようとすれば高周波焼入れ工程における加熱制御が難しくなり製造性が悪化する。 In Comparative Example 1, the value of the index fn1 representing the electrical resistivity is higher than the upper limit (1.48) of the present invention, and the electrical resistivity is higher than that in Examples described later. For this reason, the highest temperature reached during high-frequency heating exceeded 1430 ° C., and the occurrence of melt cracking was observed in a part of the test piece. When an induction-hardened component material having the composition of Comparative Example 1 is used, a temperature increase due to overheating due to the shape tends to occur. In such a case, there is a concern about melt cracking, and if it is attempted to prevent melt cracking, the heating control in the induction hardening process becomes difficult and the productivity deteriorates.
比較例２は、Ｍｎ量が本発明の上限値を上回っているのに加え、電気抵抗率を表す指数ｆｎ１の値が本発明の上限値を上回っている。この比較例２においても高周波加熱時の最高到達温度が１４３０℃を超えており、試験片の一部において溶融割れの発生が認められた。
また比較例３は、Ｃ量が本発明の上限値を上回っているのに加え、電気抵抗率を表す指数ｆｎ１の値が本発明の上限値を上回っている。この比較例３においても高周波加熱時の最高到達温度が１４３０℃を超えており、試験片の一部において溶融割れの発生が認められた。
これら比較例２，３の組成から成る高周波焼入れ部品用素材を用いた場合にも、形状に起因した過加熱による温度上昇が生じやすく、溶融割れ等の問題が懸念される。
In Comparative Example 2, in addition to the Mn amount exceeding the upper limit value of the present invention, the value of the index fn1 representing the electrical resistivity exceeds the upper limit value of the present invention. Also in Comparative Example 2, the maximum temperature reached during high-frequency heating exceeded 1430 ° C., and the occurrence of melt cracking was observed in a part of the test piece.
In Comparative Example 3, in addition to the amount of C exceeding the upper limit of the present invention, the value of the index fn1 representing the electrical resistivity exceeds the upper limit of the present invention. Also in Comparative Example 3, the maximum temperature reached during high-frequency heating exceeded 1430 ° C., and the occurrence of melt cracking was observed in a part of the test piece.
Even when the materials for induction-hardened parts having the compositions of Comparative Examples 2 and 3 are used, a temperature increase due to overheating due to the shape tends to occur, and there is a concern about problems such as melt cracking.
比較例４，５は、電気抵抗率を表す指数ｆｎ１の値が本発明の規定範囲内であり、高周波加熱時の最高到達温度は比較例１〜３に比べて低く、溶融割れの発生も認められなかった。しかしながら素材の内部硬さを表す指数ｆｎ２の値が本発明の上限値（０．９０）を超えており、内部硬さは目標とする範囲２１〜２７ＨＲＣより高くなった。このため、比較例４，５の組成から成る高周波焼入れ部品用素材では加工性の悪化が懸念される。 In Comparative Examples 4 and 5, the value of the index fn1 representing the electrical resistivity is within the specified range of the present invention, the highest temperature reached during high-frequency heating is lower than those in Comparative Examples 1 to 3, and the occurrence of melt cracking is also recognized. I couldn't. However, the value of the index fn2 representing the internal hardness of the material exceeded the upper limit (0.90) of the present invention, and the internal hardness was higher than the target range of 21 to 27 HRC. For this reason, in the induction-hardened component material having the composition of Comparative Examples 4 and 5, there is a concern about deterioration of workability.
次に比較例６は、電気抵抗率を表す指数ｆｎ１の値が本発明の規定範囲内であり、高周波加熱時の最高到達温度は比較例１〜３に比べて低く、溶融割れの発生も認められなかった。しかしながら素材の内部硬さを表す指数ｆｎ２の値が本発明の下限値（０．７６）を下回っており、内部硬さが目標とする範囲２１〜２７ＨＲＣより低くなった。このため、比較例６の組成から成る高周波焼入れ部品用素材では、高周波焼入れ部品に要求される強度が確保できない虞がある。 Next, in Comparative Example 6, the value of the index fn1 representing the electrical resistivity is within the specified range of the present invention, the maximum temperature reached during high-frequency heating is lower than those of Comparative Examples 1 to 3, and the occurrence of melt cracking is also recognized. I couldn't. However, the value of the index fn2 representing the internal hardness of the material is below the lower limit (0.76) of the present invention, and the internal hardness is lower than the target range of 21 to 27 HRC. For this reason, in the material for induction-hardened components having the composition of Comparative Example 6, there is a possibility that the strength required for the induction-hardened components cannot be ensured.
これに対し、指数ｆｎ１，ｆｎ２を含めて各元素が本発明の成分範囲を満たす実施例１〜１１は、何れも最高到達温度が１４３０℃以下で、比較例１〜３と比べて最高到達温度が低い。電気抵抗率を低くして高周波加熱時の温度の上がり方を緩やかした効果が認められた。また、何れの実施例においても溶融割れは認められなかった。尚、各実施例を比較すると、ｆｎ１の値が最も小さい実施例３において最高到達温度は１３２４℃と最も低く、ｆｎ１の値が最も大きい実施例１１において最高到達温度は１４２９℃と最も高く、ｆｎ１の値と最高到達温度の間には一定の相関が認められた。 On the other hand, Examples 1-11 which each element satisfy | fills the component range of this invention including the index | exponent fn1, fn2 are all the highest ultimate temperature 1430 degrees C or less, and are the highest ultimate temperature compared with Comparative Examples 1-3. Is low. An effect was observed in which the electrical resistivity was lowered to moderately increase the temperature during high-frequency heating. Also, no melt cracking was observed in any of the examples. In addition, when each example is compared, in Example 3 where the value of fn1 is the smallest, the highest attained temperature is the lowest at 1324 ° C., and in Example 11 where the value of fn1 is the largest, the highest attained temperature is the highest as 1429 ° C., and fn1 There was a certain correlation between the value of and the maximum temperature reached.
また実施例１〜１１は、何れも内部硬さが目標とする２１〜２７ＨＲＣの範囲内に収まっており、良好な加工性及び部品強度を得るための内部硬さを有している。
このように各実施例は、良好な加工性及び部品強度を得るために必要な内部硬さを確保した上で、電気抵抗率の低減が図られているため、かかる実施例の組成から成る高周波焼入れ部品用素材を用いれば、仮に高周波焼入れ部品の形状が、過加熱を起こしやすい形状であったとしても、過加熱による温度上昇は抑制されるため、溶融割れを起こすことなく高周波焼入れによる高強度を得ることができる。
Moreover, all Examples 1-11 are settled in the range of 21-27HRC which internal hardness aims at, and have internal hardness for obtaining favorable workability and component strength.
As described above, each example is intended to reduce the electrical resistivity after securing the internal hardness necessary for obtaining good workability and component strength. If a material for hardened parts is used, even if the shape of the induction-hardened part is prone to overheating, the temperature rise due to overheating is suppressed, so high strength by induction hardening without causing melt cracking Can be obtained.
Claims (2)
Ｃ：０．３５〜０．４５％
Ｓｉ：０．３０％以下
Ｍｎ：０．８０〜１．３０％
Ｐ：０．０３０％以下
Ｓ：０．０１０〜０．０７０％
Ｃｒ：０．３０％以下
を含有し、更に
Ｃｕ：０．２０％以下
Ｎｉ：０．１５％以下
Ｍｏ：０．１０％以下
Ｖ：０．３０％以下
Ａｌ：０．０３％以下
Ｔｉ：０．０５％以下
Ｎｂ：０．１０％以下
の何れか１種若しくは２種以上を含有し、
残部がＦｅ及び不可避的不純物であり、且つ下記式（１），式（２）を満足する組成の鋼から成ることを特徴とする高周波焼入れ部品用素材。
ｆｎ１＜１．４８・・式(１)
０．７６＜ｆｎ２＜０．９０・・式(２)
但しｆｎ１＝[C]＋1.2[Si]＋0.5[Mn]＋0.3[Cr]＋0.45([Cu]＋[Ni]＋[Mo])
ｆｎ２＝[C]＋[Si]／13＋[Mn]／6＋3[P]／5＋2[Cu]／5＋[Ni]／5＋[Cr]／6＋[V]
（ｆｎ１，ｆｎ２の式中[ ]は、[ ]内元素の含有質量％を表す） By mass% C: 0.35 to 0.45%
Si: 0.30% or less Mn: 0.80 to 1.30%
P: 0.030% or less S: 0.010-0.070%
Cr: 0.30% or less Cu: 0.20% or less Ni: 0.15% or less Mo: 0.10% or less V: 0.30% or less Al: 0.03% or less Ti: 0 .05% or less, Nb: 0.10% or less
A material for induction-hardened parts, characterized in that the balance is Fe and inevitable impurities and is made of steel having a composition satisfying the following formulas (1) and (2).
fn1 <1.48 .. Formula (1)
0.76 <fn2 <0.90 .. Formula (2)
However, fn1 = [C] +1.2 [Si] +0.5 [Mn] +0.3 [Cr] +0.45 ([Cu] + [Ni] + [Mo])
fn2 = [C] + [Si] / 13 + [Mn] / 6 + 3 [P] / 5 + 2 [Cu] / 5 + [Ni] / 5 + [Cr] / 6 + [V]
(In the formula of fn1 and fn2, [] represents the content mass% of the element in [])
Ｂ：０．００１０〜０．０１００％
Ｐｂ：０．３００％以下
Ｂｉ：０．３００％以下
Ｃａ：０．０００５〜０．００５０％
の何れか１種若しくは２種以上を更に含有することを特徴とする高周波焼入れ部品用素材。 In Claim 1, In mass% B: 0.0010-0.0100%
Pb: 0.300% or less Bi: 0.300% or less Ca: 0.0005 to 0.0050%
A material for induction-hardened parts, which further contains one or more of any of the above.
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| JPH09111401A (en) * | 1995-10-17 | 1997-04-28 | Kawasaki Steel Corp | Steel for machine structural use, excellent in machinability and quenching crack resistance, and its production |
| JP2005133155A (en) * | 2003-10-30 | 2005-05-26 | Kobe Steel Ltd | High strength and high toughness non-heat-treated bar steel, and its production method |
| JP2007182606A (en) * | 2006-01-06 | 2007-07-19 | Ntn Corp | Power transfer shaft and its production method |
| JP2015124406A (en) * | 2013-12-26 | 2015-07-06 | 株式会社神戸製鋼所 | Steel material and method of producing the same |
| WO2017188284A1 (en) * | 2016-04-26 | 2017-11-02 | 新日鐵住金株式会社 | Untempered steel for induction hardening |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP7417091B2 (en) | 2020-03-27 | 2024-01-18 | 日本製鉄株式会社 | steel material |
| WO2023017829A1 (en) * | 2021-08-10 | 2023-02-16 | 日本製鉄株式会社 | Steel material |
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