JP3757537B2 - Manufacturing method of connecting rod - Google Patents

Description

【００２３】
通常の場合、準安定（５００℃以上）オーステナイトを含め、加工硬化された未再結晶オーステナイトから焼入れを行う場合、拡散変態であるフェライト、パーライト、ベイナイトの生成が著しく促進されるため、焼入れ性は大幅に低下する。従って、本発明で意図したような低い温度からの鍛造焼き入れを行なうためには、十分な焼入れ性が確保されていなければならない。逆に、十分な焼入れ性が確保されれば、加工硬化オーステナイトから焼入れることによって、かなり高い強度を得ることができるようになる。
【００２４】
準安定オーステナイトを鍛造加工する場合には、主に、Ｃ含有量に比例して変形抵抗は大きくなる。これは、オーステナイト中にＣが固溶するためである。このときの変形抵抗は、同じ温度でありながら、直接鍛造温度に加熱した直後に加工を加えるような場合(通常の方法の場合)よりもかなり大きい値となる。なぜなら、通常の方法では、柔らかいフェライトの状態で鍛造されるからである。
【００２５】
本発明が適用される上記の合金組成を有する鋼は、焼鈍し等により軟化させにくい成分系でありながら、Ｃ含有量を低く抑えることによって、逆に変形抵抗を小さくすることができた。これは、Ｃの固溶量が少ないオーステナイト域で鍛造できるためである。
【００２６】
コネクティングロッドの精度を高めるためには、事前に行なうプリフォーム加工において、アイセクション部（桿部）を細く加工することが必要である。この場合のプリフォーム加工としては、鍛造加工、ロール加工、スピニング加工などの塑性加工や、切削加工等が考えられるが、実際の製造を考慮した場合には、切削加工よりも塑性加工の方が、より好ましいといえる。そして、より高精度に加工するためには、冷間加工とすることが望ましい。
【００２７】
したがって、プリフォーム加工前の段階では、硬さが低く、また、変形能が十分に高いことが要求される。この要求を満たすためには、圧延後の組織を、フェライト主体またはベイナイト主体の組織にすることが望ましいが、上記した焼入れ性の問題があるため、ベイナイト主体の組織となるようにすることが好ましい。そして、マンガン当量の上限を６．０とすることによって、極低Ｃベイナイト主体の組織を得ることができ、良好な冷間鍛造性を実現することができる。極低Ｃベイナイトが非常に延性に富んだ組織であることは、よく知られている。
【００２８】
次に、鍛造後の焼入れ性について述べる。本発明のように、いったんＡｃ_３変態点以上の温度（たとえば、８５０℃以上）に加熱した後、準安定オーステナイト領域付近である５５０〜９５０℃の範囲の温度で鍛造など塑性加工をしたのち、連続して焼入れを行なう場合（図１（Ａ）に示すプロセス１の場合）には、図２に示すように、拡散的に析出変態するフェライトのノーズが、大きく左側に寄ってくる。
【００２９】
そこで、安定した焼入れ性を実現させるには、フェライト変態、あるいはパーライトやベイナイト変態を遅らせるよう、焼入れ性向上元素であるＭｎ、Ｃｒ等を多量に含有させなければならない。そこで、これらの総重をマンガン当量Ｍｎeqで表わして、本発明ではその値が３．４以上となるよう規定した。
【００３０】
図３は、マンガン当量と鍛造焼入れ後の硬さ（ＨＶ）との関係を示し、図４は、鍛造温度と引張り強さとの関係を示す。基本的に、温間鍛造（γ領域での鍛造）に適した材料は、本発明で使用する鋼のような、低Ｃ含有鋼であることが望ましい。
【００３１】
図５は、鍛造焼入れ後に１００〜７００℃の温度範囲で時効処理を行なったときの、時効温度と強度との関係を示す。鍛造焼入れ後にこの温度範囲、より好ましくは、２００〜６００℃の温度範囲で１分間以上の時効処理を行なうことによって、強度、とりわけ降伏強度が、鍛造を行わずに焼入れ・時効処理したものよりも高くなり、有利になる。
【００３２】
さらに、鍛造性について述べる。図１の（Ａ）および（Ｂ）にそれぞれ示したプロセス１とプロセス２における、鍛造時の変形抵抗を図６に示す。図６から明らかなように、プロセス１における変形抵抗は、プロセス２における変形抵抗よりも低いものとなっている。そして、極低Ｃで、しかもマンガン当量が３．４以上であるような材料では、焼鈍し後の組織である［フェライト＋ベイナイト＋微細なセメンタイト］よりも、Ｃ固溶量の少ないオーステナイトの方が軟らかいため、プロセス１の鍛造時の変形抵抗の方が低いものとなる。また、焼鈍しのような、軟化熱処理によって硬さが低下しにくいことも大きく関係している。
【００３３】
図７は、Ｃ含有量と変形抵抗との関係を調べた結果を示すものであって、低温γの変形抵抗はＣ含有量の影響が最も大きく、Ｃ量の増大につれて変形抵抗も増加する。図７はその結果をよく反映している。ここでも、基本的に温間鍛造（γ領域）に適した材料は、本発明で使用する鋼のような、低Ｃ含有鋼である。
【００３４】
図８は、低温焼き鈍し（６８０℃×２ｈ／ＡＣ）後のマンガン当量と、冷間における変形抵抗、および限界圧縮率との関係を調べた結果を示す。このとき、圧延後の組織が、フェライト主体、またはベイナイト主体となる条件、すなわち、マンガン当量が６．０以下であれば、すぐれた鍛造性、とりわけ、高い変形能を示す。したがって、マンガン当量の上限を６．０とすることによって、すぐれた冷間プリフォーム性を得ることができる。マンガン当量が６．０を超える場合、かなり長い軟化処理を行なうことによって、鋼製品の冷間プリフォーム性を改善することはできるが、コスト的な面からは好ましくない。
【００３５】
図９は、快削成分を添加した鋼について、鍛造温度と引張り強さとの関係を調べた結果を示し、図１０は、快削成分を添加した鋼について、限界圧縮率を調べた結果を示す。快削成分を添加した場合であっても、良好なる鍛造・焼入れ後の強度と、すぐれた冷間鍛造性とが確保されていることがわかる。
【００３６】
【実施例】
表１に示した合金組成の鋼のうち、Ｂ鋼およびＦ鋼を素材として使用し、コネクティングロッドを製作した。ここでも、圧延ままの素材を切断して図１１（Ａ）に示すような棒材（１１）を用意し、塑性加工としてスエージング加工（冷間プリフォーム加工）を行なって、図１１（Ｂ）に示すような、大端部対応部（１２ａ）、桿部対応部（１２ｂ）および小端部対応部（１２ｃ）を有する、冷間プリフォーム加工成形体（１２）を得た。
【００３７】
この冷間プリフォーム加工成形体（１２）を鍛造用ブランクとして、いったんＡｃ_３点以上の温度である８２０℃に加熱したのち、温度８００℃で温間（閉塞）鍛造を行なって、図１１（Ｃ）に示すような、大端部（１３ａ）、桿部(アイセクション部)（１３ｂ）および小端部（１３ｃ）を有するコネクティングロッド成形体（１３）の形状に塑性加工し、その後、油冷による焼き入れ（鍛造直後から焼き入れまでの経過時間は約２０秒）を行なって、図１１（Ｄ）に示すような、大端部（１４ａ）、桿部（アイセクション部）（１４ｂ）および小端部（１４ｃ）を有するコネクティングロッド（１４）を得た。鍛造加工後の成形体の形状は、Ｂ鋼を素材とするものも、Ｆ鋼を素材とするものも、著しく良好であった。
【００３８】
各コネクティングロッドにおいて、図１２に示す部位(Ａ−Ａ’，Ｂ−Ｂ’，Ｃ−Ｃ’)において硬さを測定したところ、あわせて図１２に示した結果であった。図１２のデータから明らかなように、鋼種Ｆと鋼種Ｂとでは焼入れ後の硬さが大きく異なっており、後者はマンガン当量が不足しているため、焼入れ後の組織はほとんどすべてベイナイトとなっていて、硬さが低いものであった。これに対して、鋼種Ｆでは安定した硬さ分布を示しており、組織的にもすべてマルテンサイトとなっており、高強度でかつ高精度のコネクティングロッドを製造することができた。
【００３９】
【発明の効果】
本発明のコネクティングロッドの製造方法によれば、冷間プリフォーム性（冷間塑性加工性）が良好で、閉塞鍛造時の温間鍛造性にすぐれ、しかも、温間鍛造後の比較的低い温度から焼入れを行なうことができる鋼を素材とするので、高強度で、かつ高精度のコネクティングロッドを製造することが可能である。
【００４０】
実施に当たり、窒化物形成元素として特定量のＴｉを含有する鋼を素材とすることによって、結晶粒が微細化され、靭性もいっそうすぐれた、高強度で、かつ高精度のコネクティングロッドを得ることができる。素材とする鋼に、被削性向上元素として、特定量のＳ，Ｐｂ，Ｂｉ，ＴｅおよびＣａの１種または２種以上を添加したものを使用することによって、鍛造時における素材の切削加工性を高く保って、コネクティングロッドを製造することができる。
【００４１】
焼入れを行った後に、２００〜６００℃の温度範囲で１分間以上の時効処理を行なう態様を選ぶことによって、強度、とりわけ降伏強度がさらに向上したコネクティングロッドを製造することができる。焼入れの後に、ショットピーニング処理を行なうことによっても、強度、とりわけ疲労強度がいっそうすぐれたコネクティングロッドとすることができる。
【図面の簡単な説明】
【図１】コネクティングロッドの製造方法における基本プロセス示す説明図であって、Ａは本発明によるもの（プロセス１）、Ｂは既知の一般的な製造方法によるもの（プロセス２）。
【図２】いったん８５０℃以上に加熱した後、準安定オーステナイト領域付近である５５０〜９５０℃の範囲で鍛造し、連続して焼入れを行なった場合に、拡散的に析出変態するフェライトのノーズが大きく左側に寄ってくる様子を示す説明図。
【図３】マンガン当量（Mneq）と鍛造焼入れ後の硬さとの関係を例示するグラフ。
【図４】鍛造温度と引張り強さとの関係を調べた結果を例示するグラフ。
【図５】鍛造焼入れ後に１００〜７００℃の温度範囲で時効処理したときの、時効温度と強度との関係を例示するグラフ。
【図６】鍛造温度と変形抵抗との関係を調べた結果を例示するグラフ。
【図７】Ｃ含有量と変形抵抗との関係を調べた結果を例示するグラフ。
【図８】低温焼鈍し後のマンガン当量と変形抵抗および限界圧縮率との関係を例示するグラフ。
【図９】快削成分を含有する鋼について、鍛造温度と引張り強さとの関係を例示するグラフ。
【図１０】快削成分を含有する鋼について、限界圧縮率を調べた結果を例示するグラフ。
【図１１】本発明の実施例におけるコネクティングロッドの製造工程を示す説明図。
【図１２】本発明の実施例および比較例で得たコネクティングロッドの、硬さの測定部位および測定結果を示す説明図。
【符号の説明】
１１ 素材(棒材)
１２ 冷間プリフォーム加工成形体
１３ コネクティングロッド成形体
１４ コネクティングロッド
１４ａ 大端部
１４ｂ 桿部（アイセクション部）
１４ｃ 小端部BACKGROUND OF THE INVENTION
[0001]
The present invention relates to a connecting rod manufacturing method capable of manufacturing a connecting rod used to connect a piston and a crankshaft in a reciprocating engine with high strength and high accuracy.
[0002]
[Prior art]
Conventionally, when manufacturing a connecting rod, hot forging by a deburring method is generally employed. However, hot forging by the deburring method has the disadvantages that it is difficult to ensure sufficient accuracy and that the material yield is considerably poor.
[0003]
In recent years, in order to improve the accuracy of connecting rods, a closed forging method that does not generate burrs has been devised and put into practical use, but with this closed forging method, the load during forging becomes considerably large. This is a difficult point.
[0004]
In addition, in order to increase the accuracy, attempts have been made to perform a cold preform before forging so as to obtain a highly accurate blank, or to lower the forging temperature.
[0005]
For high-accuracy connecting rods, in order to reduce the weight, it is not possible to adequately cope with conventional ferrite + pearlite structure steel when considering strength enhancement exceeding 1100 MPa, In addition, the tough steel that is quenched and tempered has a problem that it is difficult to ensure high accuracy due to warpage, distortion, cracking, and the like during heat treatment.
[0006]
Therefore, in order to enable the production of a high-strength and high-precision connecting rod, the cold preformability (cold plastic workability such as cold forgeability) is good and the temperature during closed forging is good. There is a need for a material that is excellent in hot forgeability and that can be quenched from a relatively low temperature after warm forging.
[0007]
OBJECT OF THE INVENTION
The object of the present invention is to address the above-mentioned problems, and has good cold preformability, excellent warm forgeability during closed forging, and a relatively low temperature after warm forging. An object of the present invention is to provide a method for manufacturing a high-strength and high-accuracy connecting rod using steel that can be hardened as a raw material.
[0008]
[Means for Solving the Problems]
The method for producing a high-strength and high-precision connecting rod according to the present invention is as follows: wt.%, C: 0.04 to 0.15%, Si: 0.08 to 0.50%, Mn: 3.0% or less , Cr: 3.0% or less, B: 0.01% or less, and Ti: 0.1% or less, and further represented by the following formula (1), a manganese equivalent Mneq exhibiting hardenability
Mneq = Mn (%) + Cr (%) + XB (1)
(However, when the B content is 0.0005 to 0.01%, XB = 1.0, and when it is less than 0.0005%, XB = 0. Round off to the second decimal place. )
Is made of steel having an alloy composition composed of the remaining Fe and impurities, satisfying the condition of 3.4 to 6.0, and used in a rolled state or subjected to softening heat treatment Then, forging blank is obtained by cold plastic working or cutting to obtain a forging blank, and once heated to a temperature of ₃ or more points of Ac, forging is performed at a temperature in the range of 550 to 950 ° C. to form a connecting rod shape. It is characterized in that a martensite structure is formed by quenching.
[0009]
The steel used as a raw material in the manufacturing method of the connecting rod according to the present invention can have an alloy composition containing one or both of the following optional additive components .
1) One or two elements of Ni: 4.0% or less and Mo: 3.0% or less, which are elements for improving hardenability
In this case, the manganese equivalent Mn eq showing the hardenability is expressed by the following formula (2).
Mn eq = Mn ( % ) + Cr ( % ) + Ni ( % ) / 2 + Mo ( % ) + XB (2)
2) From machinability improving elements, S: 0.3% or less, Pb: 0.3% or less, Bi: 0.15% or less, Te: 0.1% or less, and Ca: 0.05% or less 1 type or 2 types or more selected
In carrying out the manufacturing method of the connecting rod of the present invention, one or both of the following modes can be taken after quenching by water cooling or oil cooling.
1) Perform an aging treatment for 1 minute or more at a temperature in the range of 200 to 600 ° C. 2) Perform a shot peening treatment.
[Operation]
The reason why the alloy composition of steel used as a raw material for manufacturing a connecting rod in the present invention is limited as described above will be described below.
[0012]
C: 0.04 to 0.15%
C determines the hardness of martensite depending on its content, and has the effect of increasing the deformation resistance during metastable austenite. By setting the C content in the range of 0.04 to 0.15%, the deformation resistance during metastable austenite is low, and it is possible to ensure a strength of about 1100 to 1600 MPa.
[0013]
Si: 0.08 to 0.50%
Si is an element that enhances the hardenability of steel, but at the same time, it increases deformation resistance, especially deformation resistance in the cold, so its content is set in the range of 0.08 to 0.50%.
[0014]
Ti: 0.1% or less Ti has a function of ensuring good toughness by forming a stable nitride and preventing coarsening of crystal grains. Moreover, there exists an effect | action which prevents that it becomes BN when B is added. However, since the forgeability is lowered when the content increases, an addition amount of 0.1% or less is selected.
[0015]
Mn: 3.0% or less Mn is an element that enhances the hardenability of steel, but it is also an element that increases deformation resistance like Si. Therefore, the upper limit of the content is determined and is set to 3.0% or less.
[0016]
Cr: 3.0% or less Cr is an element that enhances the hardenability of the steel, and also an element that precipitates carbides during tempering to increase tempering and softening resistance. However, Cr tends to produce primary carbides, which lowers the deformability at the time of forging, so 3.0% was made the content limit.
[0017]
Ni: 4.0% or less Ni is an element that improves the hardenability of the steel without increasing the deformation resistance. However, since the action is saturated even if it is contained in a large amount, an addition amount of 4.0% or less is selected.
[0018]
Mo: 3.0% or less Mo is an element that increases the hardenability of steel, and also an element that increases tempering and softening resistance. However, like Cr, since the effect | action which reduces the deformability at the time of forging acts, it stops at addition of 3.0% or less.
[0019]
B: 0.01% or less B is contained in a very small amount and has the effect of remarkably enhancing the hardenability of the steel, but preferably 0.0005% or more is added. However, if the content is too large, the hardenability is rather lowered, so the content was made 0.01% or less.
[0020]
S: 0.3% or less, Pb: 0.3% or less, Bi: 0.15% or less, Te: 0.1% or less,
Ca: 0.05% or less These all have the effect of enhancing the machinability of the steel, but are also components that inhibit the forgeability, so even if included, about 0.3% or less for S and about Pb It was 0.3% or less, Bi was 0.15% or less, Te was 0.1% or less, and Ca was 0.05% or less.
[0021]
The manufacturing method of the connecting rod of this invention is demonstrated in detail. Hereinafter, the results of examining the various characteristics shown in FIGS. 3 to 10 using the steel having the alloy composition and manganese equivalent shown in Table 1 will be described.
[0022]
[Table 1]

[0023]
Normally, when quenching from work-hardened non-recrystallized austenite, including metastable (500 ° C or higher) austenite, the formation of ferrite, pearlite, and bainite, which are diffusion transformations, is remarkably accelerated. Decrease significantly. Therefore, in order to perform forging and quenching from a low temperature as intended in the present invention, sufficient hardenability must be ensured. On the contrary, if sufficient hardenability is ensured, considerably high strength can be obtained by quenching from work-hardened austenite.
[0024]
When forging metastable austenite, the deformation resistance increases mainly in proportion to the C content. This is because C dissolves in austenite. The deformation resistance at this time is a value that is considerably larger than the case where processing is performed immediately after heating to the forging temperature directly (in the case of a normal method), although the temperature is the same. This is because the normal method forges in a soft ferrite state.
[0025]
Although the steel having the above alloy composition to which the present invention is applied is a component system that is difficult to be softened by annealing or the like, the deformation resistance can be reduced conversely by suppressing the C content low. This is because forging can be performed in an austenite region with a small amount of C dissolved.
[0026]
In order to increase the accuracy of the connecting rod, it is necessary to thin the eye section (saddle) in the preform processing performed in advance. As the preform processing in this case, plastic processing such as forging processing, roll processing, and spinning processing, cutting processing, and the like can be considered. However, in consideration of actual manufacturing, plastic processing is more preferable than cutting processing. It is more preferable. And in order to process with higher precision, it is desirable to use cold working.
[0027]
Therefore, it is required that the hardness is low and the deformability is sufficiently high before the preform processing. In order to satisfy this requirement, the structure after rolling is preferably a ferrite-based structure or a bainite-based structure. However, because of the above-described problem of hardenability, it is preferable to have a bainite-based structure. . And by setting the upper limit of the manganese equivalent to 6.0, it is possible to obtain an ultra-low C bainite-based structure and realize good cold forgeability. It is well known that extremely low C bainite is a very ductile structure.
[0028]
Next, hardenability after forging will be described. As in the present invention, after heating to a temperature not lower than the Ac ₃ transformation point (for example, 850 ° C. or higher), after plastic processing such as forging at a temperature in the range of 550 to 950 ° C. near the metastable austenite region, In the case of continuous quenching (in the case of process 1 shown in FIG. 1A), as shown in FIG. 2, the nose of ferrite that undergoes diffusive precipitation transformation largely approaches the left side.
[0029]
Therefore, in order to realize stable hardenability, it is necessary to contain a large amount of Mn, Cr, and the like, which are hardenability improving elements, so as to delay ferrite transformation or pearlite or bainite transformation. Therefore, the total weight of these is expressed as manganese equivalent Mneq, and in the present invention, the value is specified to be 3.4 or more.
[0030]
FIG. 3 shows the relationship between manganese equivalent and hardness after forging and quenching (HV), and FIG. 4 shows the relationship between forging temperature and tensile strength. Basically, a material suitable for warm forging (forging in the γ region) is desirably a low C content steel such as the steel used in the present invention.
[0031]
FIG. 5 shows the relationship between aging temperature and strength when aging treatment is performed in the temperature range of 100 to 700 ° C. after forging and quenching. By performing aging treatment for 1 minute or more in this temperature range, more preferably 200 to 600 ° C. after forging and quenching, the strength, particularly the yield strength, is higher than that obtained by quenching and aging treatment without forging. It becomes higher and more advantageous.
[0032]
Furthermore, forgeability will be described. FIG. 6 shows the deformation resistance during forging in Process 1 and Process 2 shown in FIGS. 1A and 1B, respectively. As is apparent from FIG. 6, the deformation resistance in the process 1 is lower than the deformation resistance in the process 2. For materials with extremely low C and a manganese equivalent of 3.4 or more, austenite with a lower C solid solution amount than [ferrite + bainite + fine cementite], which is the structure after annealing, Is soft, the deformation resistance during forging in Process 1 is lower. In addition, it is greatly related to the fact that the hardness is not easily lowered by a softening heat treatment such as annealing.
[0033]
FIG. 7 shows the result of investigating the relationship between the C content and the deformation resistance. The deformation resistance at the low temperature γ is most affected by the C content, and the deformation resistance increases as the C content increases. FIG. 7 well reflects the result. Again, a material that is basically suitable for warm forging (γ region) is a low C content steel, such as the steel used in the present invention.
[0034]
FIG. 8 shows the results of examining the relationship between the manganese equivalent after low-temperature annealing (680 ° C. × 2 h / AC), the deformation resistance in the cold, and the critical compressibility. At this time, if the structure after rolling is mainly ferrite or bainite, that is, if the manganese equivalent is 6.0 or less, excellent forgeability, particularly high deformability is exhibited. Therefore, by setting the upper limit of manganese equivalent to 6.0, excellent cold preformability can be obtained. When the manganese equivalent exceeds 6.0, it is possible to improve the cold preformability of the steel product by performing a considerably long softening treatment, but this is not preferable from the viewpoint of cost.
[0035]
FIG. 9 shows the results of investigating the relationship between forging temperature and tensile strength for the steel with the free cutting component added, and FIG. 10 shows the results of examining the critical compressibility of the steel with the free cutting component added. . Even when the free-cutting component is added, it can be seen that good strength after forging and quenching and excellent cold forgeability are ensured.
[0036]
【Example】
Among the steels having the alloy compositions shown in Table 1, B steel and F steel were used as raw materials to produce connecting rods. Again, the raw material is cut to prepare a bar (11) as shown in FIG. 11 (A), swaging (cold preform processing) is performed as plastic processing, and FIG. A cold preform processed molded body (12) having a large end corresponding part (12a), a flange corresponding part (12b) and a small end corresponding part (12c) as shown in FIG.
[0037]
This cold preform processed body (12) was used as a forging blank, and once heated to 820 ° C., which is a temperature of Ac ₃ or higher, warm (closed) forging was performed at a temperature of 800 ° C., and FIG. C), and plastically processed into the shape of a connecting rod molded body (13) having a large end (13a), a collar (eye section) (13b), and a small end (13c) as shown in FIG. Perform quenching by cooling (elapsed time from immediately after forging to quenching is about 20 seconds), as shown in FIG. 11 (D), large end (14a), collar (eye section) (14b) And a connecting rod (14) having a small end (14c) was obtained. The shape of the molded body after forging was remarkably good both for the material using B steel and the material using F steel.
[0038]
In each connecting rod, the hardness was measured at the site (AA ′, BB ′, CC ′) shown in FIG. 12, and the result was shown in FIG. As is clear from the data in FIG. 12, the hardness after quenching differs greatly between steel type F and steel type B, and the latter is deficient in manganese equivalent, so that the microstructure after quenching is almost all bainite. The hardness was low. On the other hand, steel type F shows a stable hardness distribution and is all martensite structurally, and a high-strength and high-accuracy connecting rod could be manufactured.
[0039]
【The invention's effect】
According to the manufacturing method of the connecting rod of the present invention, the cold preformability (cold plastic workability) is good, the warm forgeability at the time of closed forging is excellent, and a relatively low temperature after the warm forging. Therefore, it is possible to manufacture a high-strength and high-accuracy connecting rod.
[0040]
In practice, by using a steel containing a specific amount of Ti as a nitride-forming element as a raw material, it is possible to obtain a high-strength and high-accuracy connecting rod with finer crystal grains and better toughness. it can. By using a steel with a specific amount of one or more of S, Pb, Bi, Te and Ca added as a machinability improving element, the machinability of the material at the time of forging The connecting rod can be manufactured while keeping the height high.
[0041]
By selecting an embodiment in which aging treatment is performed for 1 minute or more in a temperature range of 200 to 600 ° C. after quenching, a connecting rod having further improved strength, particularly yield strength, can be produced. By performing a shot peening treatment after quenching, it is possible to obtain a connecting rod having further improved strength, particularly fatigue strength.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a basic process in a manufacturing method of a connecting rod, wherein A is according to the present invention (process 1) and B is according to a known general manufacturing method (process 2).
FIG. 2 shows that the ferrite nose that undergoes diffusive precipitation transformation when heated to 850 ° C. or higher, forged in the range of 550 to 950 ° C. near the metastable austenite region, and continuously quenched. Explanatory drawing which shows a mode that it approaches a large left side.
FIG. 3 is a graph illustrating the relationship between manganese equivalent (Mneq) and hardness after forging and quenching.
FIG. 4 is a graph illustrating the result of examining the relationship between forging temperature and tensile strength.
FIG. 5 is a graph illustrating the relationship between aging temperature and strength when aging treatment is performed in a temperature range of 100 to 700 ° C. after forging and quenching.
FIG. 6 is a graph illustrating the result of examining the relationship between forging temperature and deformation resistance.
FIG. 7 is a graph illustrating the result of examining the relationship between C content and deformation resistance.
FIG. 8 is a graph illustrating the relationship between manganese equivalent after low-temperature annealing, deformation resistance, and critical compressibility.
FIG. 9 is a graph illustrating the relationship between forging temperature and tensile strength for steel containing a free-cutting component.
FIG. 10 is a graph illustrating the result of examining the critical compressibility of steel containing a free-cutting component.
FIG. 11 is an explanatory view showing a manufacturing process of the connecting rod in the embodiment of the present invention.
FIG. 12 is an explanatory diagram showing hardness measurement sites and measurement results of the connecting rods obtained in Examples and Comparative Examples of the present invention.
[Explanation of symbols]
11 Material (bar material)
12 Cold preform processed molded body 13 Connecting rod molded body 14 Connecting rod 14a Large end portion 14b Hook (eye section portion)
14c Small end

Claims (5)

A method for producing a high-strength and high-precision connecting rod, in terms of weight percent, C: 0.04 to 0.15%, Si: 0.08 to 0.50%, Mn: 3.0% or less, Containing Cr: 3.0% or less, B: 0.01% or less, and Ti: 0.1% or less, and further represented by the following formula (1), a manganese equivalent Mneq exhibiting hardenability
Mneq = Mn (%) + Cr (%) + XB (1)
(However, when the B content is 0.0005 to 0.01%, XB = 1.0, and when it is less than 0.0005%, XB = 0. Round off to the second decimal place. )
Is made of steel having an alloy composition composed of the remaining Fe and impurities, satisfying the condition of 3.4 to 6.0, and used in a rolled state or subjected to softening heat treatment Then, forging blanks are obtained by cold plastic working or cutting to obtain forging blanks, and once heated to a temperature of ₃ or more points of Ac, forged at a temperature in the range of 550 to 950 ° C. to form a connecting rod shape. A method for producing a connecting rod, characterized in that a martensite structure is obtained by quenching. As a raw material, in addition to the alloy components according to claim 1, as a hardenability improving element, Ni: 4.0% or less and Mo: 3.0% or less of one or two kinds are contained. Manganese equivalent Mneq which shows hardenability represented by the formula (2)
Mneq = Mn (%) + Cr (%) + Ni (%) / 2 + Mo (%) + XB (2)
(However, when the B content is 0.0005 to 0.01%, XB = 1.0, and when it is less than 0.0005%, XB = 0. Round off to the second decimal place. )
The manufacturing method of the connecting rod of Claim 1 implemented using the steel which satisfies the conditions which become the range of 3.4-6.0, and has the alloy composition which consists of remainder Fe and an impurity. As materials, machinability improving elements, S: 0.3% or less, Pb: 0.3% or less, Bi: 0.15% or less, Te: 0.1% or less, and Ca: 0.05% or less The manufacturing method of the connecting rod of Claim 1 or 2 implemented using the steel which has the alloy composition containing 1 type, or 2 or more types selected from. The method of manufacturing a connecting rod according to any one of claims 1 to 3, wherein after tempering, an aging treatment is performed at a temperature in the range of 200 to 600 ° C for 1 minute or more. The method of manufacturing a connecting rod according to claim 1, wherein shot peening is performed after quenching.

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