JP3226781B2 - Manufacturing method of non-tempered forged product excellent in fatigue strength - Google Patents
Manufacturing method of non-tempered forged product excellent in fatigue strengthInfo
- Publication number
- JP3226781B2 JP3226781B2 JP04556096A JP4556096A JP3226781B2 JP 3226781 B2 JP3226781 B2 JP 3226781B2 JP 04556096 A JP04556096 A JP 04556096A JP 4556096 A JP4556096 A JP 4556096A JP 3226781 B2 JP3226781 B2 JP 3226781B2
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- temperature
- steel
- forging
- less
- forged product
- Prior art date
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- Heat Treatment Of Steel (AREA)
Description
【０００１】[0001]
【発明の属する技術分野】本発明は疲労強度に優れた非
調質鍛造品の製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-heat treated forged product having excellent fatigue strength.
【０００２】[0002]
【従来の技術】鍛造品の製造方法の従来技術について、
自動車エンジンに使用される鋼系のコンロッドを例にと
って説明する。この鍛造品は、機械構造用炭素鋼である
S50C、S55Cなどを用い、熱間鍛造により所定の形状に成
形した後、高強度、高靱性を付与させるため、焼入焼も
どし等の熱処理（以下調質ともいう）が施されていた。2. Description of the Related Art Regarding the prior art of a forging product manufacturing method,
A steel connecting rod used for an automobile engine will be described as an example. This forged product is carbon steel for machine structure
After being formed into a predetermined shape by hot forging using S50C, S55C or the like, heat treatment such as quenching and tempering (hereinafter also referred to as tempering) has been performed to impart high strength and high toughness.
【０００３】しかし、熱間鍛造後の調質処理は莫大なエ
ネルギ−を必要とすることから、省エネルギ−の社会的
要請に応えるために、調質処理を廃止し、熱間鍛造した
後の自然空冷にて必要な性能を得られるように、C を
0.2〜0.5%程度含有する中炭素鋼に0.03〜0.20% のV を
添加した非調質鋼が提案され、昭和50年代後半から使用
されてきた。However, since the tempering after hot forging requires enormous energy, in order to meet social demands for energy saving, the tempering is abolished and after hot forging. C is selected so that the required performance can be obtained with natural air cooling.
A non-heat treated steel in which 0.03 to 0.20% V is added to medium carbon steel containing about 0.2 to 0.5% has been proposed, and has been used since the late 1975's.
【０００４】ところでこの鍛造品では、表面を黒皮鍛造
肌としたまま使用することが多いが、この場合には鍛造
品の疲労強度は鍛造品の表面性状に大きく影響される。
しかし鍛造品の表面は製造時に高温にさらされ、脱炭現
象、スケ−ル等が発生するため、表面性状が低下し易
く、切欠効果等の影響で、鍛造品の材料自体が本来持っ
ている強度特性を充分に発揮するのは非常に難しい。従
って、実際の鍛造品が持つ強度は、材料自体が本来持つ
強度に比べ著しく低くなってしまうのが通常であり、実
部品の疲労強度を上げることができず、高強度化は困難
であった。よって、表面が黒皮鍛造肌としたまま使用す
る鍛造品の場合には、鍛造品の材料自体の強度を上げる
だけでは不充分であり、表面性状を改善することが必要
となる。[0004] By the way, in this forged product, the surface is often used with the surface of black forged skin, but in this case, the fatigue strength of the forged product is greatly affected by the surface properties of the forged product.
However, the surface of the forged product is exposed to high temperatures during manufacturing, and the decarburization phenomenon, scale, etc. occur, so that the surface properties are apt to decrease, and the material itself of the forged product inherently has the effect of the notch effect etc. It is very difficult to fully exhibit strength properties. Therefore, the strength of an actual forged product is usually significantly lower than the original strength of the material itself, and the fatigue strength of an actual part cannot be increased, and it is difficult to increase the strength. . Therefore, in the case of a forged product which is used with the surface of which has a black forged skin, it is not sufficient to simply increase the strength of the material itself of the forged product, and it is necessary to improve the surface properties.
【０００５】本出願人は上記点に鑑み、特開平4-193931
号公報に記載の発明を既に開示している。この発明は、
100×V(%)× C(%)-Si(%)/3 >5の条件を満たす様に組成
を限定すると共に、鋼の加熱温度を900 ℃以上で10分間
以下し、これによりフェライト脱炭量の低減とフェライ
ト脱炭層の硬さ低下の抑制を図り、鍛造品の疲労強度の
向上を図るものである。In view of the above points, the present applicant has disclosed Japanese Patent Laid-Open No.
Has already disclosed the invention described in Japanese Patent Application Publication No. JP-A-2005-26095. The present invention
100 × V (%) × C (%)-Si (%) / 3 The composition is limited so as to satisfy the condition of> 5, and the heating temperature of the steel is reduced to 900 ° C or more and 10 minutes or less, thereby removing the ferrite. The purpose is to reduce the amount of coal and suppress the decrease in the hardness of the decarburized layer of ferrite, thereby improving the fatigue strength of the forged product.
【０００６】さらに、前記公報記載の鋼のドリル穴明け
加工等の被削性を改善するために、特開平6-212344号公
報記載の発明も本出願人は開示している。この発明は、
フェライト脱炭量とC 、Si、V 量との関係をさらに詳し
く検討し、 100×V(%)× C(%)-Si(%)/3 >3.5の条件を満
たす様に組成を限定すると共に、加熱温度を1050℃以下
として鍛造品の表面と内部の硬さの差を小さく抑えるこ
とにより、被削性の向上を図った鍛造用鋼である。Further, in order to improve the machinability such as the drilling of steel described in the above-mentioned publication, the present applicant also discloses the invention described in JP-A-6-212344. The present invention
Study the relationship between the amount of decarburized ferrite and the amounts of C, Si, and V in more detail, and limit the composition to satisfy the condition of 100 × V (%) × C (%)-Si (%) / 3> 3.5 At the same time, the forging steel is designed to improve the machinability by reducing the difference in hardness between the surface and the inside of the forged product by setting the heating temperature to 1050 ° C. or less.
【０００７】[0007]
【発明が解決しようとする課題】前記した２つの公報に
記載の発明により、フェライト脱炭量及び表面層の強度
向上が図られ、黒皮鍛造肌のままでも優れた疲労強度を
もつ鍛造品が得られるようになった。また前記した特開
平6-212344号公報記載の発明では、疲労強度に加え、被
削性についても改善することができた。According to the inventions described in the above two publications, the amount of decarburized ferrite and the strength of the surface layer are improved, and a forged product having excellent fatigue strength even with black scale forged skin can be obtained. Can now be obtained. In the invention described in JP-A-6-212344, machinability was improved in addition to fatigue strength.
【０００８】しかしながら、その後の調査により、前記
公報記載の発明には、以下に説明する問題点のあること
が、さらなる適用範囲の拡大に妨げとなることが明らか
となってきた。すなわち、特開平4-193931号公報記載の
発明は、熱間鍛造後の組織が粗大化する場合があり、粗
大化した場合には靱性が若干低下し、靱性に対する要求
水準の高い部品には靱性が若干不足する場合があること
がわかった。However, subsequent investigations have revealed that the problems described below in the invention described in the above publication hinder the further expansion of the applicable range. That is, the invention described in Japanese Patent Application Laid-Open No. 4-193931 discloses that the structure after hot forging may be coarsened, and when the structure is coarsened, the toughness is slightly reduced, and the toughness of a component having a high required level of toughness is reduced. Was found to be slightly short.
【０００９】また、前記した特開平6-212344号公報記載
の発明は、加熱温度を1050℃以下と低く抑えることによ
って、疲労強度、被削性の改善を図ることはできたが、
一方で鋼の加熱温度が低目のため、熱間鍛造の際におけ
る鋼の変形抵抗が大きく、鍛造型の寿命低下、鍛造品の
割れや欠肉等の問題が無視できなくなることがわかっ
た。しかしながら、鋼の加熱温度を1050℃以下と低くし
ないと、優れた特性を確保できない場合があるため、満
足する要求特性を得るためには、簡単に加熱温度を上げ
られないという事情があった。In the invention described in Japanese Patent Application Laid-Open No. Hei 6-212344, fatigue strength and machinability can be improved by suppressing the heating temperature to 1050 ° C. or less.
On the other hand, it was found that since the heating temperature of the steel was low, the deformation resistance of the steel during hot forging was large, and problems such as shortening of the life of the forging die, cracking and underfilling of the forged product could not be ignored. However, if the heating temperature of the steel is not lowered to 1050 ° C. or less, excellent characteristics may not be secured in some cases. Therefore, in order to obtain satisfactory required characteristics, the heating temperature cannot be easily increased.
【００１０】本発明は上記した実情に鑑みなされたもの
であり、請求項１は、疲労強度について優れた特性を確
保できると共に、鍛造型の寿命の向上、鍛造割れや欠肉
等の欠陥の低減を図り得る非調質鍛造品の鍛造方法を提
供することを課題とする。請求項２は、疲労強度の他に
被削性についても優れた特性を確保できると共に、鍛造
型の寿命の向上、鍛造割れや欠肉等の欠陥の低減を図り
得る非調質鍛造品の鍛造方法を提供することを課題とす
る。[0010] The present invention has been made in view of the above-mentioned circumstances, and a first aspect of the present invention is to secure excellent characteristics regarding fatigue strength, to improve the life of a forging die, and to reduce defects such as forging cracks and underfilling. It is an object to provide a forging method for a non-heat-treated forged product which can achieve the following. The second aspect of the present invention provides forging of a non-finished forged product which can ensure excellent characteristics in machinability in addition to fatigue strength, improve the life of the forging die, and reduce defects such as forging cracks and underfill. It is an object to provide a method.
【００１１】[0011]
【課題を解決するための手段】本発明者等は疲労強度、
更には被削性が得られる条件について鋭意研究を重た結
果、以下の知見をなし本発明を得た。鍛造品におけるフ
ェライト脱炭量の低減とフェライト脱炭層の強化を図る
ため、Si量を低減し、V を適量添加するという考え方に
ついては、本発明も前記公報記載の発明と基本的には同
様である。SUMMARY OF THE INVENTION The present inventors have developed fatigue strength,
Furthermore, as a result of intensive studies on the conditions for obtaining machinability, the following findings were obtained and the present invention was obtained. In order to reduce the amount of decarburized ferrite in the forged product and strengthen the ferrite decarburized layer, the concept of reducing the amount of Si and adding an appropriate amount of V is basically the same as that of the invention described in the above publication. is there.
【００１２】ただし、C については、従来フェライト脱
炭量の低減に効果のある元素と考えられてきたが、今回
V 添加のフェライト・パーライト型非調質鋼に範囲を限
定し、詳細に調査、検討を行った結果、従来に比べC 量
を0.10〜0.25% と低めに設定した方が、かえってフェラ
イト脱炭量を低減できるという逆の傾向のあることを本
発明者は知見した。However, C has been conventionally considered to be an element effective in reducing the amount of decarburized ferrite.
As a result of a detailed investigation and examination of the range limited to the V-added ferrite / pearlite type non-heat treated steel, it was found that setting the C content to a low 0.10 to 0.25% compared to the conventional method The present inventor has found that there is an opposite tendency that can be reduced.
【００１３】また本発明者は、フェライト脱炭層の改善
に加え、さらに熱間鍛造後の金属組織と各種要求特性と
の関係に注目して調査を行い、熱間鍛造後の金属組織の
フェライト面積率を70% 以上に高めた組織とした場合に
は、鋼の加熱温度を高温にしても、鍛造品の疲労強度が
あまり低下しないことを見出したものである。そして、
さらに検討を進めた結果、70% 以上のフェライト面積率
を確保するためには、Ac3 変態点の温度に影響を与える
C 含有率を前記公報の鋼に比べ低めに抑えて、Ac3 変態
点を830 ℃以上とすることで達成できることを知見した
ものである。なお、本発明で言うAc3 変態点とは、成分
を変化させた多数の材料をフォーマスタ試験した結果得
られた以下に示す実験式で定義される温度のことであ
り、Ac3=910-203C0.5-15.2Ni+44.7Si+104V+31.5Mo （各
元素の単位は全て重量%)で規定される。203C0.5 とは 2
03と炭素量の平方根との積を意味する。In addition to the improvement of the decarburized layer of the ferrite, the present inventor has conducted an investigation focusing on the relationship between the metal structure after hot forging and various required characteristics, and has investigated the ferrite area of the metal structure after hot forging. It has been found that when the structure is increased to 70% or more, even if the heating temperature of the steel is increased, the fatigue strength of the forged product does not decrease so much. And
As a result of further study, it is necessary to influence the temperature of the Ac 3 transformation point in order to secure a ferrite area ratio of 70% or more.
It has been found that this can be achieved by keeping the C content lower than that of the steel disclosed in the above-mentioned publication and setting the Ac 3 transformation point to 830 ° C. or higher. Incidentally, the Ac 3 transformation point referred to in the present invention is a temperature defined by the following empirical formula obtained as a result of performing a Formaster test on a large number of materials having changed components, and Ac 3 = 910− 203C 0.5 -15.2Ni + 44.7Si + 104V + 31.5Mo (All the units of each element are specified by weight%). What is 203C 0.5 2
It means the product of 03 and the square root of the carbon content.
【００１４】ところで鍛造の際の鋼の変形抵抗を低減し
て鍛造品の割れや欠肉等の欠陥を低減するためには、ま
た、オーステナイトへの合金元素の溶け込み量を多くす
るためには、鋼の加熱温度を1050℃（＝特開平6-212344
号公報に係る加熱温度）を越える1200〜1300℃とすれば
良い。しかしこの場合には、通常の組成の鋼であれば、
金属組織の粗大化により強度が低下する。更に鋼の加熱
温度を1200〜1300℃に高めれば、前記公報に記載されて
いるように、フェライト脱炭量が増加して表面硬さが低
下すると共に、鋼表面のスケールの影響で表面性状が低
下し、切欠効果により、鋼自体が本来もつ疲労強度を充
分に発揮できなくなる問題が起きる。しかし上記した様
にAc3 変態点を830 ℃以上に規定してフェライト面積率
を70% 以上とすれば、鋼の加熱温度を、1050℃を越える
1200〜1300℃にしたとしても、優れた疲労強度を得るこ
とができることを本発明者は知見した。By the way, in order to reduce the deformation resistance of steel during forging to reduce defects such as cracks and underfill of the forged product, and to increase the amount of alloying elements dissolved in austenite, Heating temperature of steel at 1050 ° C (= JP-A-6-212344)
1200-1300 ° C., which is higher than the heating temperature according to the publication. However, in this case, if the steel of the normal composition,
The strength decreases due to the coarsening of the metal structure. If the heating temperature of the steel is further increased to 1200 to 1300 ° C., as described in the above publication, the amount of ferrite decarburization increases and the surface hardness decreases, and the surface texture is affected by the scale of the steel surface. This causes a problem that the fatigue strength of the steel itself cannot be sufficiently exhibited due to the notch effect. However, as described above, if the Ac 3 transformation point is specified to be 830 ° C or more and the ferrite area ratio is set to 70% or more, the heating temperature of the steel exceeds 1050 ° C.
The present inventors have found that excellent fatigue strength can be obtained even when the temperature is set to 1200 to 1300 ° C.
【００１５】本発明は上記した知見に基づいて完成され
たものである。なお熱間鍛造の場合には一般的には鍛造
型の温度は４００〜５００℃となるものであり、この温
度域では鍛造品のあばたが増加し、表面性状が低下する
傾向がある。即ち、請求項１は、重量％にして、Ｃ：
０．１０〜０．２５％、Ｓｉ：０．３５％以下、Ｍｎ：
０．５０〜１．２０％、Ｎｉ：０．１５％以下、Ｃｒ：
０．５０％以下、Ｍｏ：０．０６％以下、Ａｌ：０．０
０３〜０．０７０％、Ｖ：０．１５〜０．３５％を含有
し、残部がＦｅならびに不純物元素からなり、かつＡC3
変態温度（=９１０−２０３Ｃ0.5−１５．２Ｎｉ＋４
４．７Ｓｉ＋１０４Ｖ＋３１．５Ｍｏ）が８３０℃以上
である鋼を用い、前記鋼を１２００〜１３００℃に加熱
し、その直後に３００℃以下の鍛造型で鍛造温度１１５
０〜１３００℃において所定形状に熱間鍛造し、その
後、自然空冷して非調質とすると共に、熱間鍛造後のフ
ェライト面積率を７０％以上としたことを特徴とする疲
労強度に優れた非調質鍛造品の製造方法である。The present invention has been completed based on the above findings. In the case of hot forging, the temperature of the forging die is generally from 400 to 500 ° C., and in this temperature range, the forging of the forged product increases and the surface properties tend to decrease. That is, claim 1 is based on C:
0.10 to 0.25%, Si: 0.35% or less, Mn:
0.50 to 1.20%, Ni: 0.15% or less, Cr:
0.50% or less, Mo: 0.06% or less, Al: 0.0
03-0.070%, V: 0.15-0.35%, the balance being Fe and impurity elements, and A C3
Transformation temperature (= 910-203C 0.5 -15.2Ni + 4
(4.7Si + 104V + 31.5Mo) is a steel having a temperature of 830 ° C. or higher. The steel is heated to 1200 to 1300 ° C., and immediately thereafter, a forging temperature of 115 ° C. or lower is applied to a forging die having a temperature of 300 ° C. or lower.
Was hot forged into a predetermined shape at 0 to 1,300 ° C., then, with the natural cooling to non-heat treated, after hot forging off
This is a method for producing a non-heat treated forged product excellent in fatigue strength, characterized in that a ferrite area ratio is 70% or more .
【００１６】請求項２は、重量％にして、Ｃ：０．１０
〜０．２５％、Ｓｉ：０．３５％以下、Ｍｎ：０．５０
〜１．２０％、Ｎｉ：０．１５％以下、Ｃｒ：０．５０
％以下、Ｍｏ：０．０６％以下、Ａｌ：０．００３〜
０．０７０％、Ｖ：０．１５〜０．３５％と、Ｓ：０．
０４〜０．１２％、Ｐｂ：０．０５〜０．３０％、Ｃ
ａ：０．０００５〜０．０１％のうち１種又は２種以上
を含有し、残部がＦｅならびに不純物元素からなり、か
つＡC3 変態温度（=９１０−２０３Ｃ0.5−１５．２Ｎ
ｉ＋４４．７Ｓｉ＋１０４Ｖ＋３１．５Ｍｏ）が８３０
℃以上である鋼を用い、前記鋼を１２００〜１３００℃
に加熱し、その直後に３００ ℃以下の鍛造型で鍛造温
度１１５０〜１３００℃において所定形状に熱間鍛造
し、その後、自然空冷して非調質とすると共に、熱間鍛
造後のフェライト面積率を７０％以上としたことを特徴
とする疲労強度に優れた非調質鍛造品の製造方法であ
る。According to a second aspect of the present invention, C: 0.10% by weight.
0.25%, Si: 0.35% or less, Mn: 0.50
１．２1.20%, Ni: 0.15% or less, Cr: 0.50
% Or less, Mo: 0.06% or less, Al: 0.003 to
0.070%, V: 0.15 to 0.35%, and S: 0.
04-0.12%, Pb: 0.05-0.30%, C
a: One or two or more of 0.0005 to 0.01% are contained, the balance is composed of Fe and impurity elements, and the AC 3 transformation temperature (= 910-203C 0.5 -15.2N)
i + 44.7Si + 104V + 31.5Mo) is 830
℃ 1300 ℃
It was heated to forging temperature at 300 ° C. or less of the forging die immediately thereafter
It was hot forged into a predetermined shape in degrees 1150 to 1300 ° C., then, with the natural cooling to non-heat treated, Netsukan鍛
This is a method for producing a non-heat treated forged product excellent in fatigue strength, characterized in that the ferrite area ratio after forming is 70% or more .
【００１７】[0017]
【発明の実施の形態】次に本発明方法で用いた鋼の成分
組成およびAc3 変態温度等の限定理由について以下に説
明する。 C:0.10〜0.25% C は強度を確保するための基本元素であり、0.10% 以
上、望ましくは0.15% 以上の含有が必要である。しかし
多量に含有させるとAc3 変態点が低下してAc3 変態が83
0 ℃未満となり易く、フェライト面積率が低下するとと
もに、フェライト脱炭量が増加して疲労強度、靱性が低
下するので、上限を0.25% とした。望ましくは上限を0.
23% とするのが良い。DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition of the steel used in the method of the present invention and the Ac 3 transformation temperature will be described below. C: 0.10 to 0.25% C is a basic element for securing the strength, and must be contained at 0.10% or more, preferably 0.15% or more. However, when it is contained in a large amount, the Ac 3 transformation point decreases and the Ac 3 transformation becomes 83
Since the temperature tends to be lower than 0 ° C., the area ratio of ferrite decreases, and the amount of decarburized ferrite increases, thereby reducing the fatigue strength and toughness. Therefore, the upper limit is set to 0.25%. Desirably the upper limit is 0.
A good value is 23%.
【００１８】Si:0.35%以下 Siはフェライト脱炭量低減のために含有量を極力減らす
ことが望ましいが、製鋼時の脱酸剤として不可欠である
ため、上限を0.35％とした。望ましくは0.30%以下とす
るのが良い。 Mn:0.50 〜1.20% Mnは製鋼時の脱酸ならびに鋼の強度、靱性バランスを調
整するため添加される元素であり、最低でも0.50％以
上、望ましくは0.60% 以上の含有が必要である。しかし
過剰に添加すると焼入性が向上し過ぎてベイナイト組織
が生成し、疲労強度、靱性が低下する。よって本発明に
おいては熱間鍛造後の空冷でベイナイト組織が生成しな
いようにするため、上限を1.20％とした。望ましくは1.
00% 以下とするのが良い。Si: 0.35% or less It is desirable to reduce the content of Si as much as possible in order to reduce the amount of decarburized ferrite. However, since Si is indispensable as a deoxidizing agent in steel making, the upper limit is set to 0.35%. Desirably, it is set to 0.30% or less. Mn: 0.50 to 1.20% Mn is an element added for deoxidation during steelmaking and for adjusting the strength and toughness balance of the steel. It must be contained at least 0.50% or more, preferably 0.60% or more. However, if added excessively, the hardenability is excessively improved, and a bainite structure is generated, and the fatigue strength and toughness are reduced. Therefore, in the present invention, the upper limit is set to 1.20% in order to prevent a bainite structure from being generated by air cooling after hot forging. Preferably 1.
It is better to be 00% or less.
【００１９】Ni:0.15%以下 Niはスクラップを電気炉にて溶解して製造する場合、積
極的に添加しなくても不純物として少量含有する元素で
ある。本発明においてもNiは積極的に添加するわけでは
ないが、NiはAc3 変態温度と密接な関係があり、多量に
存在するとAc3変態温度が低下して 830℃以上とするこ
とが困難となるので、上限を設定しておく必要があるた
め、0.15% 越えて含有しないこととした。Ni: 0.15% or less Ni is an element contained in a small amount as an impurity without being actively added when scrap is produced by melting it in an electric furnace. Although Ni is are not positively added in the present invention, Ni is Ac 3 is closely related to the transformation temperature, it is difficult to large amounts to the Ac 3 transformation temperature to 830 ° C. or higher reduction exist Therefore, it is necessary to set an upper limit, so it was decided not to contain more than 0.15%.
【００２０】Cr:0.50%以下 Crは鋼の強度、靱性バランスを調整するために有効な元
素であり、Mnと同様に焼入性を大きく向上させる効果の
ある元素である。従って、多量に含有させると、ベイナ
イト組織が生成して疲労強度、靱性が低下するので、上
限を0.50% とした。望ましくは0.30% 以下とするのが良
い。Cr: 0.50% or less Cr is an element effective for adjusting the balance between strength and toughness of steel, and is an element having an effect of greatly improving hardenability similarly to Mn. Therefore, if contained in a large amount, a bainite structure is formed and the fatigue strength and toughness are reduced, so the upper limit was made 0.50%. Desirably, it is set to 0.30% or less.
【００２１】Mo:0.06%以下 MoもNiと同様に不純物として少量含有する元素である
が、もし多量に含有すると焼入性が向上してベイナイト
が生成する可能性があるため、上限を決めておく必要が
あり、その範囲を0.06% 以下に限定した。 Al:0.003〜0.070% Alは脱酸効果を得るために不可欠な元素であるため、0.
003%以上の含有が必要である。しかしながら、多量に含
有させても前記脱酸効果が飽和するとともに、被削性が
低下するので、上限を0.070%とした。Mo: 0.06% or less Mo is an element contained in a small amount as an impurity like Ni, but if contained in a large amount, hardenability may be improved and bainite may be formed. And the range was limited to 0.06% or less. Al: 0.003 to 0.070% Al is an element indispensable for obtaining a deoxidizing effect.
003% or more is required. However, even if it is contained in a large amount, the deoxidizing effect is saturated and the machinability is reduced. Therefore, the upper limit is set to 0.070%.
【００２２】V:0.15〜0.35％ V は鋼中で炭窒化物となって鍛造後の冷却中に金属組織
において微細に析出することにより、フェライトを強化
するという非調質鋼にとっては必須の元素であり、通常
は0.10％程度添加されている。但し本発明の場合にはそ
れ以外の効果として、V がC と結合してトラップし、フ
ェライト脱炭量を低減させるとともに、フェライト脱炭
層の硬さ低下をV 炭窒化物による析出強化によって抑制
する効果もある。従って、それらの効果が十分に得られ
る最低量である0.15％を下限とした。望ましくは0.20%
以上含有させるのが良い。V: 0.15% to 0.35% V is an essential element for non-heat treated steel that strengthens ferrite by forming carbonitrides in the steel and precipitating finely in the metal structure during cooling after forging. Usually, about 0.10% is added. However, in the case of the present invention, as other effects, V bonds with C and traps, reducing the amount of decarburized ferrite and suppressing the decrease in hardness of the decarbonized ferrite layer by precipitation strengthening with V carbonitride. There is also an effect. Therefore, the lower limit was set to 0.15%, which is the minimum amount at which these effects can be sufficiently obtained. Desirably 0.20%
It is better to contain it.
【００２３】しかしながら多量に含有させても前記効果
が飽和するとともに、コスト高となるため、上限を0.35
% とした。望ましくは0.30% 以下とするのが良い。 S:0.04〜0.12% 、Pb:0.05 〜0.30% 、Ca:0.0005 〜0.01
% の１種又は２種以上 S 、Pb、Caは被削性の改善に有効な元素であり、熱間鍛
造後の切削の程度に応じて必要量添加されるものであ
る。前記効果を得るためにはS は0.04% 以上、Pbは0.05
% 以上、Caは0.0005% 以上の含有が必要である。しかし
多量に含有させてもその効果が飽和するとともに靱性を
低下させるので、上限をS は0.12% 、Pbは0.30% 、Caは
0.01% とした。However, even if it is contained in a large amount, the above effect is saturated and the cost becomes high.
%. Desirably, it is set to 0.30% or less. S: 0.04-0.12%, Pb: 0.05-0.30%, Ca: 0.0005-0.01
One or more of S, Pb, and Ca are effective elements for improving machinability, and are added in necessary amounts according to the degree of cutting after hot forging. To obtain the above effect, S is 0.04% or more, and Pb is 0.05
% And Ca must be contained at 0.0005% or more. However, even if it is contained in a large amount, its effect is saturated and the toughness is reduced, so the upper limits are 0.12% for S, 0.30% for Pb, and
It was set to 0.01%.
【００２４】鋼の Ac3変態温度 本発明では鋼の加熱温度を高温としても、優れた疲労強
度、靱性を確保するために、鋼がもつAc3 変態温度を 8
30℃以上に規定することによって、鍛造後の組織のフェ
ライト面積率の増加を図っている。もし、鋼がもつ Ac3
変態温度が低くなると、フェライト面積率が低下して、
加熱温度を低くしないと優れた特性を確保出来なくなる
ため、その下限値を830 ℃とした。[0024] Also as a high-temperature heating temperature of the steel in the Ac 3 transformation temperature present invention steel, excellent fatigue strength, in order to secure the toughness, the Ac 3 transformation temperature with the steel 8
By specifying the temperature at 30 ° C. or higher, the ferrite area ratio of the structure after forging is increased. If steel has Ac 3
When the transformation temperature decreases, the ferrite area ratio decreases,
Unless the heating temperature is lowered, excellent characteristics cannot be secured, so the lower limit was set to 830 ° C.
【００２５】鋼の加熱温度 鋼の加熱温度は1200〜1300℃である。鋼の加熱温度と
は、鋼の表面を測定した温度を意味する。鋼の伝熱性を
考慮すれば、鋼の内部も実質的に同温と考えられる。鋼
の加熱温度が1200℃未満であると変形抵抗の増大により
鍛造品の形状の制約が生じる。更に鍛造型への負荷が増
し、鍛造型の寿命低下、鍛造品の割れや欠肉等の欠陥が
発生し易くなる。更に、V が十分に固溶しないため析出
強化が不充分、脱炭抑制効果が不充分となり易く、疲労
強度が低下する。Heating temperature of steel The heating temperature of steel is 1200 to 1300 ° C. The heating temperature of the steel means a temperature at which the surface of the steel is measured. Considering the heat conductivity of the steel, the inside of the steel is considered to be substantially at the same temperature. If the heating temperature of the steel is lower than 1200 ° C., the shape of the forged product is restricted due to an increase in deformation resistance. Further, the load on the forging die is increased, and the life of the forging die is shortened, and defects such as cracks and underfilling of the forged product are likely to occur. Further, since V does not form a solid solution, precipitation strengthening is insufficient, the effect of suppressing decarburization tends to be insufficient, and fatigue strength is reduced.
【００２６】逆に1300℃を超えると、鋼表面のスケール
増加を招き、鍛造品の表面にあばたが多くなり、表面性
状が低下し、鍛造品の疲労強度が低下する。更に、金属
組織の粗大化、脱炭量の増加等の不具合を来たし、この
意味においても疲労強度が低下する。このように鋼の加
熱温度が1200〜1300℃であれば、鋼の変形抵抗が低減
し、鍛造の際の材料歩留りが向上する。加熱手段として
は高周波誘導加熱が好ましい。急速加熱に有利であり、
鋼のスケールを抑え得るからである。鋼の加熱温度の測
定手段としては、非接触で測温する方式、例えば放射温
度計を採用できる。On the other hand, when the temperature exceeds 1300 ° C., the scale of the steel surface is increased, and the surface of the forged product is pocked, the surface properties are reduced, and the fatigue strength of the forged product is reduced. In addition, problems such as coarsening of the metal structure and an increase in the amount of decarburization occur, and in this sense, the fatigue strength is reduced. If the heating temperature of the steel is 1200 to 1300 ° C., the deformation resistance of the steel is reduced, and the material yield during forging is improved. As the heating means, high-frequency induction heating is preferable. Advantageous for rapid heating,
This is because the steel scale can be suppressed. As a means for measuring the heating temperature of the steel, a method of measuring the temperature in a non-contact manner, for example, a radiation thermometer can be adopted.
【００２７】鋼の加熱温度が1200〜1300℃であり、加熱
終了直後にすみやかに熱間鍛造するため、鋼の鍛造温度
は一般的には1150〜1200〜1300℃である。なお鍛造温度
は鍛造開始温度を意味する。鍛造工程が荒地鍛造、仕上
鍛造と続けば、後の鍛造ほど鍛造温度は低くなるのが一
般的である。 鍛造型の型温度 鍛造型の温度は300 ℃以下である。本発明方法に係る鍛
造型の温度は鍛造型の成形キャビティ型面から３〜５ｍ
ｍ程度の深さの温度をいう。鍛造品の割れの防止性を考
慮すると、好ましくは、鍛造型の温度は100 〜300 ℃が
良い。鍛造型の型温度を300 ℃以下とするため、鍛造型
を冷却水等で適宜冷却することが好ましい。なお熱間鍛
造した後では、鍛造品は自然空冷すなわち非調質とされ
る。The heating temperature of the steel is 1200 to 1300 ° C., and hot forging is performed immediately after the heating is completed. Therefore, the forging temperature of the steel is generally 1150 to 1200 to 1300 ° C. The forging temperature means a forging start temperature. If the forging process continues with wasteland forging and finish forging, it is common that the later forging, the lower the forging temperature. Mold temperature of forging die The temperature of the forging die is 300 ° C or less. The temperature of the forging die according to the method of the present invention is 3 to 5 m from the molding cavity surface of the forging die.
It means a temperature at a depth of about m. Considering the prevention of cracking of the forged product, the temperature of the forging die is preferably 100 to 300 ° C. In order to reduce the temperature of the forging die to 300 ° C. or less, it is preferable to appropriately cool the forging die with cooling water or the like. After hot forging, the forged product is subjected to natural air cooling, that is, non-refined.
【００２８】鍛造型の型温度は300 ℃以下であるため、
高温領域に加熱された鋼の表面が鍛造型の成形キャビテ
ィ型面に触れると、伝熱で鋼の表面は即座に冷却され
る。従って荒地鍛造後に仕上鍛造を行う場合、荒地鍛造
を複数行う場合等の様に鍛造回数が複数の場合には、第
１回目の鍛造で鋼の最表面の温度が低目にされ、それ以
後のスケール抑止に有利である。Since the temperature of the forging die is 300 ° C. or less,
When the surface of the steel heated to the high temperature region touches the surface of the mold cavity of the forging die, the surface of the steel is immediately cooled by heat transfer. Therefore, when performing finish forging after rough land forging, or when performing multiple forging such as performing multiple rough land forgings, the temperature of the outermost surface of the steel is lowered in the first forging, and thereafter, This is advantageous for scale suppression.
【００２９】[0029]
【実施例】以下に本発明方法で製造した本発明鋼の特徴
を比較鋼、従来鋼と比較し、実施例でもって明らかにす
る。表１は実施例に用いた供試鋼の化学成分を示したも
のである。EXAMPLES The characteristics of the steel of the present invention produced by the method of the present invention will be clarified in the following examples in comparison with comparative steels and conventional steels. Table 1 shows the chemical components of the test steels used in the examples.
【００３０】[0030]
【表１】 [Table 1]
【００３１】（１）表１において１〜８鋼は本発明鋼で
あり、１〜４鋼は請求項１に係る第１発明鋼、５〜８鋼
は請求項２に係る第２発明鋼である。また９〜14鋼はい
ずれかの成分又はAc3 変態温度が本発明の条件を満足し
ない比較鋼である。15鋼は従来鋼であるS50Cである。比
較鋼のうち11、14鋼は前記した特開平6-212344号公報に
記載の範囲内の鋼であって、 Ac3変態温度が830 ℃以下
であり、本発明によるAc3 変態温度の下限値の設定によ
る効果を明確にするために選択したものである。(1) In Table 1, steels 1 to 8 are steels of the invention, steels 1 to 4 are steels of the first invention according to claim 1, and steels 5 to 8 are steels of the second invention according to claim 2. is there. 9 to 14 steels are comparative steels in which any component or Ac 3 transformation temperature does not satisfy the conditions of the present invention. Fifteen steel is S50C, a conventional steel. Among the comparative steels, steels 11 and 14 are steels within the range described in JP-A-6-212344, in which the Ac 3 transformation temperature is 830 ° C. or lower, and the lower limit of the Ac 3 transformation temperature according to the present invention. This was selected to clarify the effect of the setting.
【００３２】試験材は、熱間圧延にて製造した直径50mm
の丸棒を高周波誘導加熱炉により1300℃に数１０秒で加
熱し、数秒〜数１０秒放置した後、鍛造型の成形キャビ
ティ型面（型温度：200 ℃）により1250〜1300℃で荒地
鍛造工程を実施し、更に、仕上鍛造工程、バリ取り工程
を順に実施し、その後、室温まで自然空冷して、図１に
示すようなコンロッド形状にしたものである。なお荒地
鍛造工程は、第１荒地鍛造と第２荒地鍛造とを行った。
荒地鍛造で用いた鍛造型、仕上鍛造で用いた鍛造型の型
温度はいずれも300 ℃以下である。この鍛造品は非調質
であるため、焼入焼もどしはしていない。The test material was 50 mm in diameter manufactured by hot rolling.
Is heated in a high frequency induction heating furnace at 1300 ° C for several tens of seconds, left for several seconds to several tens of seconds, and then forged at 1250 to 1300 ° C using the mold cavity surface of the forging die (mold temperature: 200 ° C). The process is performed, a finish forging process and a deburring process are sequentially performed, and thereafter, the device is naturally cooled to room temperature to form a connecting rod as shown in FIG. In the wasteland forging process, a first wasteland forging and a second wasteland forging were performed.
The die temperature of the forging die used for rough land forging and the forging die used for finish forging are both 300 ° C. or less. Since this forged product is not tempered, it is not quenched and tempered.
【００３３】鋼の加熱温度は放射温度計で測定した。鍛
造型の型温度は成形キャビティ型面の深さ３ｍｍの位置
に熱電対等の温度センサを取付けて測定した。鍛造型は
冷却水が流れる通水路を備えており、設定温度になる様
に冷却制御されている。なお従来鋼である15鋼のみ、空
冷後通常行われている調質処理を行った。上記したコン
ロッド鍛造品を試験材として用い、電気油圧式疲労試験
機を採用し、図２に示す様に大径端側にキャップ１０を
取付けた状態で固定軸１２に固定すると共に小径端側に
駆動軸１４を取付け、駆動軸１４に矢印方向の荷重を繰
り返して作用させることにより、引張・圧縮荷重負荷方
式の実体疲労試験を行い、１０7 回にて、疲労強度を意
味する耐久限と判断した。The heating temperature of the steel was measured with a radiation thermometer. The die temperature of the forging die was measured by mounting a temperature sensor such as a thermocouple at a position of a depth of 3 mm on the mold cavity die surface. The forging die has a water passage through which cooling water flows, and is controlled to be cooled to a set temperature. In addition, only the 15 conventional steels were subjected to the air-cooling treatment which is usually performed after air cooling. Using the above forged connecting rod as a test material, an electro-hydraulic fatigue tester was used, and as shown in FIG. 2, the cap 10 was fixed to the fixed shaft 12 with the cap 10 attached to the large-diameter end and the small-diameter end was used. mounting a drive shaft 14, by acting repeatedly load the arrow direction to the drive shaft 14, performs real fatigue test of the tensile-compressive load application system, at 10 7 times, determines that the endurance limit to mean fatigue strength did.
【００３４】また、前記コンロッド鍛造品から試験片を
採取し、以下に説明する方法で、硬さ測定、顕微鏡組織
の観察、被削性の評価を行った。硬さは、前記コンロッ
ド鍛造品を切断して切断面を研摩した後、表面から0.1m
m の位置と、中心部について、ビッカース硬度計（荷重
500gf)によりそれぞれ測定した。顕微鏡組織は、前記鍛
造品のフェライト脱炭の深さと中心部の組織とを、ナイ
タール腐食した後、倍率400 倍で観察した。フェライト
脱炭の深さは、パーライト量が０であるときの表面から
の深さを意味する。フェライト面積率の測定は、50視野
のポイントカウンティング法により行った。図３に本発
明鋼である７鋼の顕微鏡組織（観察位置：深さ3mm 、ナ
イタール腐食、倍率：４００倍）を示す。図３において
黒色の粒状領域がパーライト、白色の領域がフェライト
である。Further, test specimens were collected from the forged connecting rod, and the hardness was measured, the microstructure was observed, and the machinability was evaluated by the methods described below. Hardness is 0.1 m from the surface after cutting the forged connecting rod and polishing the cut surface.
The Vickers hardness tester (load
500 gf). As for the microstructure, the depth of ferrite decarburization of the forged product and the structure of the central part were observed at 400 times magnification after nital corrosion. The ferrite decarburization depth means the depth from the surface when the pearlite amount is zero. The measurement of the ferrite area ratio was performed by a point counting method in 50 visual fields. FIG. 3 shows the microstructure of the steel 7 of the present invention (observation position: depth 3 mm, nital corrosion, magnification: 400 times). In FIG. 3, the black granular region is pearlite, and the white region is ferrite.
【００３５】図３から理解できる様に本発明鋼（＝７
鋼）によれば、フェライトリッチ（フェライト面積率：
70％以上）なフェライト・パーライト混合組織であり、
鋼の加熱温度が1300℃と高温であるにもかかわらず、パ
ーライト、フェライトの粒子が共に細かい。組織を観察
した限りではベイナイトは生成していない。図４は従来
鋼である15鋼の顕微鏡組織（ナイタール腐食、４００
倍）を示す。図４から理解できる様にＣが0.49％と高い
従来鋼によれば、加熱温度が1300℃と高温であるため、
かなり粗大化した黒色領域であるパーライトが生成して
おり、パーライトの周囲に白いフェライトが網状に析出
しているのがわかる。As can be understood from FIG. 3, the steel of the present invention (= 7)
According to steel, ferrite rich (ferrite area ratio:
(70% or more)
Despite the high heating temperature of 1300 ° C, both pearlite and ferrite particles are fine. No bainite was formed as far as the structure was observed. FIG. 4 shows the microstructure of a conventional steel, 15 steel (nital corrosion, 400 steel).
Times). As can be understood from FIG. 4, according to the conventional steel having a high C of 0.49%, since the heating temperature is as high as 1300 ° C.,
It can be seen that pearlite, which is a considerably coarsened black region, is generated, and that white ferrite is precipitated in a network around the pearlite.
【００３６】被削性の評価は、鋼種がSKH51 のφ5mm ス
トレートドリルを用い、試験片について深さ15mmの穴明
けを連続的に行い、ドリル寿命を測定することにより行
った。なお、結果は従来鋼である15鋼の寿命を100 とし
た指数で示した。以上の試験結果を表２に示す。なお表
２に示す鍛造温度は、荒地鍛造の開始直前に測定した鍛
造開始温度を意味する。The machinability was evaluated by using a 155 mm straight drill having a steel type of SKH51, continuously drilling a 15 mm depth test piece, and measuring the drill life. In addition, the result was shown by the index which set the life of 15 steel which is a conventional steel to 100. Table 2 shows the test results. In addition, the forging temperature shown in Table 2 means the forging start temperature measured just before the start of wasteland forging.
【００３７】[0037]
【表２】 比較鋼、従来鋼を使用して製造した鍛造品を、本発明鋼
による鍛造品と比較すると、比較鋼である11鋼はC 含有
率が0.34％と高いため、変態温度が822 ℃と低目であ
り、表２に示す様にフェライト面積率が64％と低下して
おり、疲労強度を意味する耐久限が266MPaと低く、更に
衝撃値も劣るものである。[Table 2] When a forged product manufactured using the comparative steel and the conventional steel is compared with a forged product using the steel of the present invention, the comparative steel 11 steel has a high C content of 0.34% and thus has a low transformation temperature of 822 ° C. As shown in Table 2, the area ratio of ferrite is as low as 64%, the durability limit meaning fatigue strength is as low as 266 MPa, and the impact value is also inferior.
【００３８】比較鋼である12鋼は、Mn含有率が1.69％と
高いため、組織の一部にベイナイトが生成しており、フ
ェライト面積率が40％と低下し、疲労強度、衝撃値が低
下したものである。比較鋼である13鋼は、V 含有率が0.
10％と低いため、フェライト脱炭の深さが0.6mm と大き
くなるとともに、Ｖ炭窒化物による析出強化が充分に期
待できず、耐久限が256MPaと著しく低下したものであ
る。Since the comparative steel No. 12 has a high Mn content of 1.69%, bainite is formed in a part of the structure, the ferrite area ratio is reduced to 40%, and the fatigue strength and impact value are reduced. It was done. Comparative steel 13 has a V content of 0.
Since it is as low as 10%, the depth of ferrite decarburization is as large as 0.6 mm, and precipitation strengthening by V carbonitride cannot be expected sufficiently, and the durability limit is significantly reduced to 256 MPa.
【００３９】比較鋼である14鋼は各化学成分の範囲は本
発明の条件を満足しているが、Ａc3変態温度が824 ℃と
低いためにフェライト面積率が64％と低下しており、耐
久限が286MPaと低下したものであり、衝撃値も劣るもの
である。また従来鋼であるS50Cを調質処理した15鋼は、
バナジウム（V ）を全く含有していないために、表２に
示す様にフェライト脱炭深さが1.0mm と非常に大きく、
しかもフェライト面積率も2 ％と極めて小さく、耐久限
が187MPaと著しく劣るものである。Although the range of each chemical component of the comparative steel 14 satisfies the conditions of the present invention, the Ac 3 transformation temperature was as low as 824 ° C., so that the ferrite area ratio was reduced to 64%. The durability limit is reduced to 286 MPa, and the impact value is also inferior. In addition, the 15 steel that has been tempered from the conventional steel, S50C,
Since it contains no vanadium (V), the ferrite decarburization depth is as large as 1.0 mm as shown in Table 2,
In addition, the ferrite area ratio is extremely small at 2%, and the durability limit is 187 MPa, which is extremely poor.
【００４０】これに対して、本発明鋼により製造した鍛
造品である１〜８鋼は、表１に示す様にV を適量含有
し、C 、Siの含有量を抑えており、Ａｃ3 変態点温度は
いずれも830 ℃以上であり、表２に示す様にフェライト
脱炭の深さもせいぜい0.1mm 程度と小さく、フェライト
面積率も70％以上とかなり大きいことがわかる。この様
に本発明鋼によれば、フェライト脱炭を抑えていること
がわかる。On the other hand, as shown in Table 1, the forged products 1 to 8 produced from the steel of the present invention contain an appropriate amount of V, suppress the contents of C and Si, and exhibit the Ac 3 transformation. The spot temperatures are all 830 ° C. or higher, and as shown in Table 2, the depth of ferrite decarburization is as small as 0.1 mm at most, and the ferrite area ratio is as large as 70% or more. Thus, according to the steel of the present invention, it can be seen that ferrite decarburization is suppressed.
【００４１】即ち第１発明鋼により製造した鍛造品であ
る１〜４鋼は、表１に示す様にいずれもAc3 変態温度を
830 ℃以上とし、表２に示す様にフェライト面積率を70
% 以上としている。したがって鋼の加熱温度を1300℃と
高めても、耐久限が320MPa以上確保されており、優れた
疲労強度特性の得られることが確認できた。また表２に
示す様に被削性についても、第１発明鋼である１〜４鋼
は、115 〜132 であり、従来鋼である15鋼（＝100 ）に
比べ優れている。特に第２発明鋼つまり被削性改善元素
であるＳ、Ｐｂ、Ｃａを添加した５〜８鋼は、ドリル寿
命が189 〜223 であり、従来鋼である15鋼（＝100 ）に
比べ著しく向上することが確認できた。 （２）鍛造型の型温度の影響 第１発明鋼の組成をもつ３鋼について、鋼の加熱温度を
1300℃とし、鍛造温度を1250〜1300℃（比較鋼に係る３
鋼Ｅのみ鍛造温度：1150〜1200℃）とし、鍛造型の型温
度を 100℃、200 ℃、300 ℃、400 ℃と種々変えた状態
で、熱間鍛造し、これについて前述した様にフェライト
脱炭の深さ、鍛造品の表面粗さ、鍛造品の表面における
あばた発生の個数（肉眼検査：試験片100 個あたり）、
変形抵抗、絞り、鍛造の割れの個数、疲労強度を意味す
る耐久限について試験した。その試験結果を表３に示
す。That is, as shown in Table 1, the forged products 1 to 4 produced from the first invention steel all have the Ac 3 transformation temperature.
830 ° C or higher, and the ferrite area ratio was 70% as shown in Table 2.
% Or more. Therefore, even if the heating temperature of the steel was increased to 1300 ° C., the durability limit was secured at 320 MPa or more, and it was confirmed that excellent fatigue strength characteristics could be obtained. Also, as shown in Table 2, the machinability of the first invention steels 1 to 4 is 115 to 132, which is superior to the conventional steel 15 (= 100). In particular, the second invention steel, that is, 5 to 8 steel to which S, Pb, and Ca, which are the machinability improving elements, are added, has a drill life of 189 to 223, which is remarkably improved as compared with the conventional 15 steel (= 100). I was able to confirm. (2) Influence of die temperature of forging die For three steels having the composition of the first invention steel, the heating temperature of the steel
1300 ° C and forging temperature 1250-1300 ° C (3 for comparative steel)
Forging temperature of steel E only: 1150-1200 ° C), hot forging was performed with the forging die temperature varied to 100 ° C, 200 ° C, 300 ° C, and 400 ° C, and ferrite removal was performed as described above. Depth of charcoal, surface roughness of the forged product, number of pock formations on the surface of the forged product (visual inspection: per 100 test pieces),
Tests were conducted on deformation resistance, drawing, the number of cracks in forging, and the durability limit meaning fatigue strength. Table 3 shows the test results.
【００４２】[0042]
【表３】 [Table 3]
【００４３】前記した表３から理解できる様に、第１発
明鋼の組成を備えた３鋼Ｅの場合、加熱温度が1200℃で
鍛造型の型温度が400 ℃であっても、フェライト脱炭の
深さが0.2mm と抑えることができ、あばた発生の個数は
１個で済み、耐久限も329MPaと比較的高いが、変形抵抗
が93MPa とかなり大きくなり、鍛造型の寿命低下、鍛造
品の欠肉等の欠陥が誘発され易い。As can be understood from Table 3 above, in the case of 3 steel E having the composition of the first invention steel, even if the heating temperature is 1200 ° C. and the die temperature of the forging die is 400 ° C., ferrite decarburization is performed. The depth of the forging can be suppressed to 0.2mm, the number of occurrences of pocking is only one, and the durability limit is relatively high at 329MPa. However, the deformation resistance is considerably large at 93MPa, the life of the forging die is shortened, Defects such as underfill are easily induced.
【００４４】しかし表３の３鋼Ａに示す様に、加熱温度
を1300℃とし、鍛造温度を1250〜1300℃と高温とした場
合であっても、鍛造型の型温度が100 ℃であれば、フェ
ライト脱炭の深さが0.0mm であり、表面粗さは33μｍと
良好であり、あばた発生の個数も０個と少なくて済み、
耐久限も349 MPa と大きい。表３の３鋼Ｂに示す様に、
加熱温度を1300℃とし、鍛造温度を1250〜1300℃と高温
とした場合であっても、鍛造型の型温度が200 ℃であれ
ば、フェライト脱炭の深さが0.0mm であり、表面粗さは
36μｍと良好であり、あばた発生の個数も１個と少なく
て済み、耐久限も345 MPa と大きい。However, even if the heating temperature is 1300 ° C. and the forging temperature is as high as 1250 to 1300 ° C. as shown in 3 Steel A in Table 3, if the die temperature of the forging die is 100 ° C. The ferrite decarburization depth is 0.0mm, the surface roughness is good at 33μm, and the number of pock generations is as small as 0,
The durability limit is as large as 349 MPa. As shown in 3 Steel B in Table 3,
Even when the heating temperature is 1300 ° C and the forging temperature is as high as 1250 to 1300 ° C, if the forging die temperature is 200 ° C, the ferrite decarburization depth is 0.0mm and the surface roughness is low. Saha
It is as good as 36 μm, the number of occurrences of pocking is as small as one, and the durability limit is as large as 345 MPa.
【００４５】また表３の３鋼Ｃに示す様に、鍛造型の型
温度が300 ℃であれば、フェライト脱炭の深さが0.1mm
と小さく、表面粗さは39μｍも良好であり、あばた発生
数も２個で済み、しかも耐久限も340 MPa と高かった。
また比較鋼である３鋼Ｄに示す様に、鍛造型の型温度が
400 ℃と高温であれば、フェライト脱炭の深さが0.3mm
と大きく、表面粗さは80μｍと悪くなり、あばた発生数
も５個と悪く、耐久限も287MPaとかなり低かった。この
様に鍛造型の型温度が鍛造品の耐久限に大きな影響を与
えることがわかる。耐久限が低いのは、スケールの巻き
込みの影響と考えられる。Further, as shown in Table 3, 3 steel C, when the forging die temperature is 300 ° C., the ferrite decarburization depth is 0.1 mm.
The surface roughness was as good as 39 μm, the number of pock generations was only two, and the durability limit was as high as 340 MPa.
Also, as shown in the comparative steel 3 steel D, the die temperature of the forging die
At a high temperature of 400 ° C, the ferrite decarburization depth is 0.3mm
The surface roughness was as bad as 80 μm, the number of pock generation was as bad as 5, and the durability was as low as 287 MPa. Thus, it can be seen that the mold temperature of the forging die has a great influence on the durability limit of the forged product. The low durability is considered to be due to the influence of scale entrainment.
【００４６】更に表３に示す様に第２発明鋼に係る７鋼
についても、加熱温度を1300℃とし、鍛造温度を1250〜
1300℃とし、型温度を200 ℃、300 ℃、400 ℃と変えた
状態で、熱間鍛造し、同様に試験した。その試験結果を
表３に示す。表３に示す比較鋼である７鋼Ｃによれば、
加熱温度が1300℃、鍛造温度が1250〜1300℃であり、鍛
造型の型温度が400 ℃であるため、フェライト脱炭の深
さが0.3mm と大きくなり、表面粗さは82μｍと悪くな
り、あばた発生の個数は５個と多く、耐久限も276MPaと
かなり低い。Further, as shown in Table 3, the heating temperature of 1300 ° C. and the forging temperature of 1250 ° C.
Hot forging was performed at 1300 ° C. and the mold temperature was changed to 200 ° C., 300 ° C., and 400 ° C., and the same test was performed. Table 3 shows the test results. According to 7 steel C which is a comparative steel shown in Table 3,
Since the heating temperature is 1300 ℃, the forging temperature is 1250-1300 ℃, and the die temperature of the forging die is 400 ℃, the depth of ferrite decarburization is as large as 0.3mm, and the surface roughness is as bad as 82μm. The number of occurrences of pocking is as many as 5 and the durability limit is 276 MPa, which is quite low.
【００４７】しかし表３に示す第２発明鋼である７鋼Ａ
によれば、加熱温度が1300℃、鍛造温度が1250〜1300℃
であっても、鍛造型の型温度が200 ℃であれば、フェラ
イト脱炭の深さが0.0mm であり、表面粗さは35μｍと良
好であり、あばた発生の個数も１個と少なくて済み、耐
久限も338 MPa と大きい。このことからも鍛造型の型温
度を低温に維持することが、鍛造品の耐久限の向上に貢
献できることがわかる。However, 7 steel A, which is the second invention steel shown in Table 3,
According to the heating temperature is 1300 ℃, forging temperature is 1250-1300 ℃
However, if the forging die temperature is 200 ° C, the ferrite decarburization depth is 0.0mm, the surface roughness is good at 35μm, and the number of pock generation is as small as one. , Its durability is as large as 338 MPa. This also indicates that maintaining the mold temperature of the forging die at a low temperature can contribute to the improvement of the durability limit of the forged product.
【００４８】第２発明鋼である７鋼Ｂに示す様に、加熱
温度を1300℃とし、鍛造温度を1250〜1300℃と高温とし
た場合であっても、鍛造型の型温度が300 ℃であれば、
フェライト脱炭の深さが0.0mm であり、表面粗さも38μ
ｍと良好であり、あばた発生の個数も３個と比較的少な
くて済み、耐久限も345 MPa と大きい。同様に更に、Ｃ
量が0.28％と高目の比較鋼である９鋼についても、同様
に鍛造型の型温度を200 ℃、300 ℃、400 ℃と変えて試
験を行い、その結果を表３に示す。この比較鋼の場合に
は、加熱温度を1300℃とし鍛造温度を1250〜1300℃とし
ているため、型温度を200 ℃、300 ℃と低めにした場合
であっても、耐久限は９鋼Ａでは293 MPa 、９鋼Ｂでは
284MPaといずれも小さい。Ｃ量が多いためとと考えられ
る。As shown in the second invention steel 7 steel B, even if the heating temperature is 1300 ° C. and the forging temperature is as high as 1250 to 1300 ° C., the forging die temperature is 300 ° C. if there is,
Ferrite decarburization depth is 0.0mm and surface roughness is 38μ
m, and the number of occurrences of pocking was relatively small at three, and the durability was as large as 345 MPa. Similarly, C
The test was also performed on 9 steels, which are comparative steels having a higher amount of 0.28%, with the forging die temperature being changed to 200 ° C., 300 ° C., and 400 ° C., and the results are shown in Table 3. In the case of this comparative steel, since the heating temperature is 1300 ° C and the forging temperature is 1250 to 1300 ° C, even if the mold temperature is as low as 200 ° C and 300 ° C, the durability limit is 9 A for steel. 293 MPa, 9 steel B
Both are small at 284MPa. This is probably because the amount of C is large.
【００４９】（試験例） 型温度 加熱温度を1300℃にした鋼を用い、鍛造型で熱間鍛造し
てコンロッド鍛造品を成形し、このときの鍛造型の型温
度とコンロッド鍛造品の表面粗さとの関係、鍛造型の型
温度とコンロッド鍛造品の疲労強度との関係を試験し
た。前者を図５の特性線Ａに示し、後者を図５の特性線
Ｂに示す。特性線Ａに示す様に、鍛造型の型温度が300
℃を越えると、鍛造品の表面粗さが大きくなることがわ
かる。また図５の特性線Ｂに示す様に、鍛造型の型温度
が300 ℃を越えると、コンロッド鍛造品の疲労強度が低
下することがわかる。この結果から鍛造型の温度を300
℃以下とすることが好ましいことがわかる。 鍛造温度 丸棒状の引張試験片を用い、引張試験機により、鍛造温
度とその温度における絞りとの関係、鍛造温度と変形抵
抗との関係を試験した。前者を図６の特性線Ｃに示し、
後者を図６の特性線Ｄに示す。特性線Ｃ及び特性線Ｄに
示す様に、鍛造温度が1200℃未満であれば、絞りは低下
し、変形抵抗も高い。よって欠肉や鍛造割れが誘発され
易い。この結果から鍛造温度を1200〜1300℃とすること
が好ましいことがわかる。(Test Example) Mold Temperature Using a steel heated at 1300 ° C., hot forging was performed with a forging die to form a forged connecting rod, and the die temperature of the forging die and the surface roughness of the forged connecting rod were measured. And the relationship between the die temperature of the forging die and the fatigue strength of the forged connecting rod were tested. The former is shown by a characteristic line A in FIG. 5, and the latter is shown by a characteristic line B in FIG. As shown by the characteristic line A, the die temperature of the forging die is 300
It is found that when the temperature exceeds ℃, the surface roughness of the forged product becomes large. Further, as shown by the characteristic line B in FIG. 5, when the die temperature of the forging die exceeds 300 ° C., it is understood that the fatigue strength of the forged connecting rod decreases. From this result, the temperature of the forging die was set to 300
It is understood that the temperature is preferably set to not more than ° C. Forging temperature Using a round bar-shaped tensile test piece, the relationship between the forging temperature and the drawing at that temperature and the relationship between the forging temperature and the deformation resistance were tested by a tensile tester. The former is shown by the characteristic line C in FIG.
The latter is shown by the characteristic line D in FIG. As shown by the characteristic lines C and D, when the forging temperature is lower than 1200 ° C., the drawing is reduced and the deformation resistance is high. Therefore, underfill or forging crack is easily induced. From this result, it is understood that the forging temperature is preferably set to 1200 to 1300 ° C.
【００５０】なおこの試験では、丸棒とその両端に径大
な掴み部とを一体的にもつ試験片（試験片の軸長140mm
、丸棒の軸長120mm 、 丸棒の直径8mm 、 掴み部の直径1
4mm）を形成し、その試験片を常温域から鍛造温度まで
１００秒で加熱し、引張速度50mm/sの引張速度で引張っ
て行った。 鍛造型の型温度 コンロッド鍛造品を成形するに際して、鍛造型の型温度
と鍛造品のあばた発生率との関係を試験した。試験片の
数は１００個とした。試験結果を図７の特性線Ｅに示
す。特性線Ｅに示す様に、鍛造型の型温度が300 ℃以下
であれば、あばた発生率は３％未満であるが、型温度が
300 ℃を越えると、あばた発生率が増大する。型温度が
400 ℃であれば、あばた発生率は５％程度と高くなる。
この結果から鍛造型の型温度を300 ℃以下とすることが
好ましいことがわかる。In this test, a test piece (140 mm in axial length of a test piece) having a round bar and a large-diameter grip portion at both ends thereof was integrally formed.
, Shaft length of round bar 120mm, diameter of round bar 8mm, diameter of gripper 1
4 mm), and the test piece was heated from a normal temperature range to a forging temperature in 100 seconds and pulled at a pulling speed of 50 mm / s. Mold Temperature of Forging Die When forming a connecting rod forged product, the relationship between the mold temperature of the forging die and the incidence of pocking of the forged product was tested. The number of test pieces was 100. The test result is shown by a characteristic line E in FIG. As shown by the characteristic line E, if the die temperature of the forging die is 300 ° C. or less, the pock generation rate is less than 3%, but the die temperature is lower.
Above 300 ° C, the incidence of pock increases. Mold temperature
At 400 ° C., the rate of pock generation is as high as about 5%.
From these results, it can be seen that it is preferable to set the die temperature of the forging die to 300 ° C. or less.
【００５１】[0051]
【発明の効果】請求項１及び請求項２に係る製造方法に
よれば、C 、Si、V 量を最適化して表面のフェライト脱
炭量を低減することに加え、Ac3 変態温度を830 ℃以上
としてフェライト面積率を70% 以上とした鋼を用いるの
で、鋼の加熱温度を1200〜1300℃としても、金属組織の
粗大化を防止できると共に、優れた疲労強度が得られ
る。更に加熱温度が高温であるため、鍛造の際における
鋼の変形抵抗の低減を図り得、鍛造品の割れや欠肉等の
欠陥を抑制することができ、鍛造型の型寿命も改善する
ことができる。According to the first and second aspects of the present invention, the amount of decarbonized ferrite on the surface is reduced by optimizing the amounts of C, Si, and V, and the Ac 3 transformation temperature is increased to 830 ° C. As described above, since the steel having a ferrite area ratio of 70% or more is used, even if the heating temperature of the steel is set to 1200 to 1300 ° C., the coarsening of the metal structure can be prevented, and excellent fatigue strength can be obtained. Further, since the heating temperature is high, it is possible to reduce the deformation resistance of the steel during forging, to suppress cracks and underfilling of the forged product, and to improve the life of the forging die. it can.
【００５２】更に鍛造型の型温度を300 ℃以下に規定す
るので、鍛造品のあばたの低減も図ることができ、鍛造
品の疲労強度を一層向上できる。従って、この技術は例
えばコンロッド等の機械部品に適用でき、自動車の軽量
化、低燃費化等産業上寄与するところは極めて大であ
る。更に請求項２に係る製造方法によれば、被削性改善
元素であるS 、 Pb、 Caが適量含有されているため、鍛造
品の被削性を改善できる。Further, since the temperature of the forging die is set at 300 ° C. or less, it is possible to reduce the pock of the forged product, and it is possible to further improve the fatigue strength of the forged product. Therefore, this technology can be applied to, for example, mechanical parts such as connecting rods, and greatly contributes to the industry such as reducing the weight of vehicles and reducing fuel consumption. Furthermore, according to the manufacturing method of the second aspect, since the machinability improving elements S, Pb, and Ca are contained in appropriate amounts, the machinability of the forged product can be improved.
【図１】製造したコンロッドの形状を示す平面図であ
る。FIG. 1 is a plan view showing the shape of a manufactured connecting rod.
【図２】疲労試験を行う形態を模式的に示す構成図であ
る。FIG. 2 is a configuration diagram schematically showing a form in which a fatigue test is performed.
【図３】第１発明鋼の金属組織を示す顕微鏡写真であ
る。FIG. 3 is a micrograph showing a metal structure of a first invention steel.
【図４】従来鋼の金属組織を示す顕微鏡写真である。FIG. 4 is a micrograph showing a metal structure of a conventional steel.
【図５】鍛造型の型温度と鍛造品の表面粗さとの関係、
鍛造型の型温度と鍛造品の疲労強度との関係を示すグラ
フである。FIG. 5 shows a relationship between a mold temperature of a forging die and a surface roughness of a forged product;
It is a graph which shows the relationship between the mold temperature of a forging die, and the fatigue strength of a forged product.
【図６】鍛造温度と絞りとの関係、鍛造温度と変形抵抗
との関係を示すグラフである。FIG. 6 is a graph showing a relationship between forging temperature and drawing, and a relationship between forging temperature and deformation resistance.
【図７】鍛造型の型温度と鍛造品におけるあばた発生率
との関係を示すグラフである。FIG. 7 is a graph showing a relationship between a mold temperature of a forging die and a popping rate in a forged product.
図中、１２は固定軸、１４は駆動軸を示す。 In the figure, reference numeral 12 denotes a fixed shaft, and 14 denotes a drive shaft.
フロントページの続き (72)発明者 岩間 直樹 愛知県東海市荒尾町ワノ割１番地 愛知 製鋼株式会社内 (56)参考文献 特開 平７−233435（ＪＰ，Ａ) 特開 平４−118135（ＪＰ，Ａ) 特開 昭57−70202（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C21D 8/00 - 8/10 C22C 38/00 - 38/60 B21J 5/00 Continuation of front page (72) Inventor Naoki Iwama 1 Wanowari, Arao-cho, Tokai City, Aichi Prefecture Inside Aichi Steel Works, Ltd. (56) References JP-A-7-233435 (JP, A) JP-A-4-118135 (JP) , A) JP-A-57-70202 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) C21D 8/00-8/10 C22C 38/00-38/60 B21J 5/00
Claims (2)
％、Ｓｉ：０．３５％以下、Ｍｎ：０．５０〜１．２０
％、Ｎｉ：０．１５％以下、Ｃｒ：０．５０％以下、Ｍ
ｏ：０．０６％以下、Ａｌ：０．００３〜０．０７０
％、Ｖ：０．１５〜０．３５％を含有し、残部がＦｅな
らびに不純物元素からなり、かつＡC3 変態温度(=９１
０−２０３Ｃ0.5−１５．２Ｎｉ＋４４．７Ｓｉ＋１０
４Ｖ＋３１．５Ｍｏ)が８３０℃以上である鋼を用い、 前記鋼を１２００〜１３００℃に加熱し、 その直後に３００℃以下の鍛造型で鍛造温度１１５０〜
１３００℃において所定形状に熱間鍛造し、 その後、自然空冷して非調質とすると共に、熱間鍛造後
のフェライト面積率を７０％以上としたことを特徴とす
る疲労強度に優れた非調質鍛造品の製造方法。C: 0.10 to 0.25% by weight
%, Si: 0.35% or less, Mn: 0.50 to 1.20
%, Ni: 0.15% or less, Cr: 0.50% or less, M
o: 0.06% or less, Al: 0.003 to 0.070
%, V: 0.15 to 0.35%, the balance consists of Fe and impurity elements, and the A C3 transformation temperature (= 91
0-203C 0.5 -15.2Ni + 44.7Si + 10
4V + 31.5Mo) using steel having a temperature of 830 ° C or higher, the steel is heated to 1200 to 1300 ° C, and immediately thereafter, a forging temperature of 1150 to 1300 ° C is used.
Hot forging into a predetermined shape at 1300 ° C, and then natural air cooling to make it non-tempered and after hot forging
The method for producing a non-heat treated forged product excellent in fatigue strength, characterized in that the ferrite area ratio is 70% or more .
％、Ｓｉ：０．３５％以下、Ｍｎ：０．５０〜１．２０
％、Ｎｉ：０．１５％以下、Ｃｒ：０．５０％以下、Ｍ
ｏ：０．０６％以下、Ａｌ：０．００３〜０．０７０
％、Ｖ：０．１５〜０．３５％と、Ｓ：０．０４〜０．
１２％、Ｐｂ：０．０５〜０．３０％、Ｃａ：０．００
０５〜０．０１％のうち１種又は２種以上を含有し、残
部がFeならびに不純物元素からなり、かつＡC3 変態温
度（=９１０−２０３Ｃ0.5−１５．２Ｎｉ＋４４．７Ｓ
ｉ＋１０４Ｖ＋３１．５Ｍｏ）が８３０℃以上である鋼
を用い、 前記鋼を１２００〜１３００℃に加熱し、 その直後に３００℃以下の鍛造型で鍛造温度１１５０〜
１３００℃において所定形状に熱間鍛造し、 その後、自然空冷して非調質とすると共に、熱間鍛造後
のフェライト面積率を７０％以上としたことを特徴とす
る疲労強度に優れた非調質鍛造品の製造方法。2. C: 0.10 to 0.25% by weight
%, Si: 0.35% or less, Mn: 0.50 to 1.20
%, Ni: 0.15% or less, Cr: 0.50% or less, M
o: 0.06% or less, Al: 0.003 to 0.070
%, V: 0.15 to 0.35%, and S: 0.04 to 0.
12%, Pb: 0.05 to 0.30%, Ca: 0.00
Containing one or more of 05 to 0.01%, the balance being Fe and impurity elements, and A C3 transformation temperature (= 910-203C 0.5 -15.2Ni + 44.7S
i + 104V + 31.5Mo) using steel is the 830 ° C. or higher, heating the steel to 1200 to 1300 ° C., forging temperature 1150～ forging type 300 ° C. or less immediately after its
Hot forging into a predetermined shape at 1300 ° C, and then natural air cooling to make it non-tempered and after hot forging
The method for producing a non-heat treated forged product excellent in fatigue strength, characterized in that the ferrite area ratio is 70% or more .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP04556096A JP3226781B2 (en) | 1996-01-12 | 1996-01-12 | Manufacturing method of non-tempered forged product excellent in fatigue strength |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP04556096A JP3226781B2 (en) | 1996-01-12 | 1996-01-12 | Manufacturing method of non-tempered forged product excellent in fatigue strength |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09194933A JPH09194933A (en) | 1997-07-29 |
| JP3226781B2 true JP3226781B2 (en) | 2001-11-05 |
Family
ID=12722749
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP04556096A Expired - Fee Related JP3226781B2 (en) | 1996-01-12 | 1996-01-12 | Manufacturing method of non-tempered forged product excellent in fatigue strength |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3226781B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4497842B2 (en) * | 2003-05-26 | 2010-07-07 | 新日本製鐵株式会社 | Method for manufacturing ultra-high temperature hot forged non-tempered parts |
| JP2010172947A (en) * | 2009-01-30 | 2010-08-12 | Toyota Motor Corp | Method of super-high temperature hot forging |
-
1996
- 1996-01-12 JP JP04556096A patent/JP3226781B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH09194933A (en) | 1997-07-29 |
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