JP3327635B2 - Non-tempered steel for hot forging excellent in fatigue strength and method for producing non-heat-treated hot forged product using the steel - Google Patents
Non-tempered steel for hot forging excellent in fatigue strength and method for producing non-heat-treated hot forged product using the steelInfo
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- JP3327635B2 JP3327635B2 JP18423893A JP18423893A JP3327635B2 JP 3327635 B2 JP3327635 B2 JP 3327635B2 JP 18423893 A JP18423893 A JP 18423893A JP 18423893 A JP18423893 A JP 18423893A JP 3327635 B2 JP3327635 B2 JP 3327635B2
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- fatigue strength
- steel
- heat treated
- hot
- hot forging
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Description
【０００１】[0001]
【産業上の利用分野】本発明は疲労強度に優れた熱間鍛
造用非調質鋼材およびその鋼材を用いた非調質熱間鍛造
品の製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-heat treated steel material for hot forging having excellent fatigue strength and a method for producing a non-heat treated hot forged product using the steel material.
【０００２】[0002]
【従来の技術】一般的に、高強度高靭性を必要とする自
動車用部品、機械構造用部品等には、所定の形状に熱間
鍛造後、調質処理としてオフラインでの焼入れ・焼戻し
が施されている。しかしながら近年、製造コストの低
減、工程省略の観点から、自動車部品の製造には焼入れ
・焼戻しの調質処理を省略したいわゆる非調質鋼の使用
が広まっている。2. Description of the Related Art In general, automotive parts and mechanical structure parts that require high strength and high toughness are subjected to off-line quenching and tempering as a tempering treatment after hot forging into a predetermined shape. Have been. However, in recent years, the use of so-called non-heat treated steel in which the tempering treatment such as quenching and tempering is omitted has become widespread in the production of automobile parts from the viewpoint of reducing production costs and eliminating steps.
【０００３】現在広く使用されているフェライト・パー
ライト組織の非調質鋼では強度、特に低温靭性が不足す
るため、成分、冷却速度を調整してフェライト＋パーラ
イト＋ベイナイトの混合組織とした非調質鋼が開発され
ている（特開昭５８−１６７７５１号公報）。また、ベ
イナイト型熱間鍛造非調質鋼で、成分調整により変態温
度の下限を制限して、ベイナイト鋼の疲労特性を低下さ
せている島状マルテンサイトと残留オーステナイトを低
減することにより疲労特性を向上させようとするものも
ある（特開平４−１４１５４７号公報）。A non-heat treated steel having a ferrite / pearlite structure, which is currently widely used, lacks strength, particularly low temperature toughness. Therefore, the composition and cooling rate are adjusted to obtain a mixed structure of ferrite + pearlite + bainite. Steel has been developed (JP-A-58-167751). The bainite type hot-forged non-heat treated steel has its lower limit of transformation temperature by adjusting the composition to reduce island martensite and residual austenite, which are reducing the fatigue characteristics of bainite steel. There is also an attempt to improve it (JP-A-4-14147).
【０００４】[0004]
【発明が解決しようとする課題】従来のフェライト・パ
ーライト非調質鋼では強度、靭性が十分でなく、また上
記ベイナイトを混合させた組織では強度、靭性は満足で
きるが、機械構造用部品で最も重要視される性質の一つ
である疲労強度は逆に低下する恐れがあり、その使用範
囲は自ずと限定されてしまう。本発明の目的は、疲労強
度に優れた熱間鍛造用非調質鋼材およびその鋼材を用い
た非調質熱間鍛造品の製造方法を提供することである。The conventional ferritic / pearlite non-heat treated steel has insufficient strength and toughness, and the structure mixed with bainite can satisfy the strength and toughness. Conversely, fatigue strength, which is one of the important properties, may decrease, and the range of use is naturally limited. An object of the present invention is to provide a non-heat-treated non-heat treated steel material for hot forging having excellent fatigue strength and a method for producing a non-heat treated hot forged product using the steel material.
【０００５】[0005]
【課題を解決するための手段】本発明者らは、熱間鍛造
のままで従来の非調質鋼以上の疲労特性の保証を可能に
した熱間鍛造用高疲労強度非調質鋼および高疲労強度非
調質熱間鍛造品の製造方法を提供するために、鋭意検討
を行った。その結果、転位密度の高さ、マトリック
ス中に局部的に硬度の低い部分の存在、の２点が疲労亀
裂の早期発生につながり、疲労特性に悪影響を及ぼすこ
とが判明した。そのため鍛造後の冷却速度をある値以下
に規定することによって組織をフェライト・パーライト
とし、転位密度の高いベイナイトの生成を防止する。Means for Solving the Problems The present inventors have developed a high fatigue strength non-heat treated steel for hot forging, which has been able to assure the fatigue characteristics more than conventional non-heat treated steel while hot forging. In order to provide a method for producing a fatigue-strength non-refined hot forged product, intensive studies were conducted. As a result, it was found that the two points of the high dislocation density and the presence of a locally low hardness portion in the matrix lead to early generation of fatigue cracks, which adversely affects the fatigue properties. Therefore, by setting the cooling rate after forging to a certain value or less, the structure becomes ferrite / pearlite, and the formation of bainite having a high dislocation density is prevented.
【０００６】更にマトリックス中の局部的に硬度の低い
部分を減少するため、高Ｓｉ化による固溶体強化の活用
とＶの多量添加によるＶ炭化物の析出強化によりフェラ
イト地の強化を図り、フェライトとパーライトの硬度差
を小さくする。また鍛造肌のままで使用される部分で
は、表面脱炭による疲労強度低下が問題となるため、加
熱温度を低く設定するが、析出強化に使用するＶは窒化
物を形成すると、その小さい溶解度積のため該加熱温度
では固溶しきれない。そのため溶解度積の大きなＶ炭化
物を形成すべくＮを大幅に低減し、更にＮをＴｉＮとし
て固定するためにＴｉを添加する。Further, in order to reduce locally low hardness portions in the matrix, the use of solid solution strengthening by increasing the Si content and the strengthening of ferrite ground by the precipitation strengthening of V carbide by adding a large amount of V are attempted to strengthen the ferrite ground. Reduce the hardness difference. In addition, in the part where the forged skin is used as it is, the heating temperature is set low because the fatigue strength decreases due to surface decarburization. However, when V used for precipitation strengthening forms nitride, its small solubility product Therefore, solid solution cannot be obtained at the heating temperature. Therefore, N is significantly reduced to form V carbide having a large solubility product, and Ti is added to fix N as TiN.
【０００７】すなわち本発明は以上の知見に基づき、従
来の非調質鋼にはなかった高い疲労強度の保証が可能で
あるとされたものであって、その要旨とするところは下
記の通りである。 （１）重量比として、 Ｃ ：０.１０〜０.６０％， Ｓｉ：０.００５〜２.００％， Ｍｎ：０.５５〜２.００％， Ｓ ：０.０１〜０.１０％， Ａｌ：０.０００５〜０.０５％， Ｖ ：０.３０％超０.７０％以下， Ｔｉ：０.０２０超〜０.０５０％， を含有し、更にＮ：０.００８％未満、Ｐ：０.０３５％
以下に制限し、残部が鉄および不可避的不純物からな
り、熱間鍛造後の引張強度が７０kgf/mm 2 以上であるこ
とを特徴とする疲労強度に優れた熱間鍛造用非調質鋼
材。That is, based on the above findings, the present invention has been described as being able to guarantee a high fatigue strength that was not available in conventional non-heat-treated steel. The gist of the present invention is as follows. is there. (1) As a weight ratio, C: 0.10 to 0.60%, Si: 0.005 to 2.00%, Mn: 0.55 to 2.00%, S: 0.01 to 0.10% , Al: 0.0005 to 0.05%, V: more than 0.30% to 0.70% or less, Ti: more than 0.020 to 0.050%, and N: less than 0.008%; P: 0.035%
Limited to the following, is it from the iron and unavoidable impurities balance
Ri, hot forging after the tensile strength of 70 kgf / mm 2 or more at which this <br/> and excellent fatigue strength, wherein the hot forging non-heat treated steels.
【０００８】（２）成分が更に、 Ｎｂ：０.００５〜０.１０％， を含有する請求項１記載の疲労強度に優れた熱間鍛造用
非調質鋼材。2. The non-heat treated steel material for hot forging having excellent fatigue strength according to claim 1, wherein the component (2) further contains Nb: 0.005 to 0.10%.
【０００９】（３）成分が更に、 Ｃｒ：０.１０〜１.５０％， Ｍｏ：０.０５〜１.００％， のうち一種または二種を含有する請求項１または２記載
の疲労強度に優れた熱間鍛造用非調質鋼材。The fatigue strength according to claim 1, wherein the component (3) further comprises one or two of Cr: 0.10 to 1.50%, Mo: 0.05 to 1.00%. Excellent non-heat treated steel for hot forging.
【００１０】（４）成分が更に Ｃａ：０.０００５〜０.００５％， Ｐｂ：０.０４〜０.３０％， のうち一種または二種を含有する請求項１または２また
は３記載の疲労強度に優れた熱間鍛造用非調質鋼材。The fatigue according to claim 1, wherein the component (4) further contains one or two of Ca: 0.0005 to 0.005% and Pb: 0.04 to 0.30%. Non-heat treated steel for hot forging with excellent strength.
【００１１】（５）成分が更に、 Ｔｅ：０.０１〜０.１５％， Ｓｅ：０.０１〜０.１５％， Ｂｉ：０.０４〜０.３％ のうち一種または二種以上を含有する請求項１または２
または３または４記載の疲労強度に優れた熱間鍛造用非
調質鋼材。The component (5) further comprises one or more of Te: 0.01 to 0.15%, Se: 0.01 to 0.15%, Bi: 0.04 to 0.3%. Claim 1 or 2 containing
Or a non-heat treated steel material for hot forging having excellent fatigue strength according to 3 or 4.
【００１２】（６）重量比として、 Ｃ ：０.１０〜０.６０％， Ｓｉ：０.００５〜２.００％， Ｍｎ：０.５５〜２.００％， Ｓ ：０.０１〜０.１０％， Ａｌ：０.０００５〜０.０５％， Ｖ ：０.３０％超０.７０％以下， Ｔｉ：０.０２０超〜０.０５０％， を含有し、更にＮ：０.００８％未満、Ｐ：０.０３５％
以下に制限し、残部が鉄および不可避的不純物からなる
鋼を、Ａc3点以上１２５０℃以下のオーステナイト化温
度において鍛造を行い、その後３００℃まで０.０５℃
／秒以上２℃／秒未満の平均冷却速度で冷却することを
特徴とするフェライト・パーライト組織からなり、引張
強度が７０kgf/mm 2 以上である、疲労強度に優れた非調
質熱間鍛造品の製造方法。(6) As weight ratios, C: 0.10 to 0.60%, Si: 0.005 to 2.00%, Mn: 0.55 to 2.00%, S: 0.01 to 0. .10%, Al: 0.0005 to 0.05%, V: more than 0.30% to 0.70% or less, Ti: more than 0.020 to 0.050%, and N: 0.008 %, P: 0.035%
The forging is performed at an austenitizing temperature of 3 points or more and 1250 ° C. or less, and then 0.05 ° C. to 300 ° C., with the balance being iron and unavoidable impurities.
/ Sec cooling at an average cooling rate of less than or 2 ° C. / sec consist ferrite-pearlite structure, wherein the tensile
A method for producing a non-refined hot forged product excellent in fatigue strength, having a strength of 70 kgf / mm 2 or more .
【００１３】（７）成分が更に、 Ｎｂ：０.００５〜０.１０％， を含有する請求項６記載の疲労強度に優れた非調質熱間
鍛造品の製造方法。7. The method of claim 6, wherein the component (7) further contains Nb: 0.005 to 0.10%.
【００１４】（８）成分が更に、 Ｃｒ：０.１０〜１.５０％， Ｍｏ：０.０５〜１.００％， のうち一種または二種を含有する請求項６または７記載
の疲労強度に優れた非調質熱間鍛造品の製造方法。The fatigue strength according to claim 6, wherein the component (8) further contains one or two of Cr: 0.10 to 1.50% and Mo: 0.05 to 1.00%. Method for manufacturing non-refined hot forged products excellent in quality.
【００１５】（９）成分が更に、 Ｃａ：０.０００５〜０.００５％， Ｐｂ：０.０４〜０.３０％ のうち一種または二種を含有する請求項６または７また
は８記載の疲労強度に優れた非調質熱間鍛造品の製造方
法。The fatigue according to claim 6, wherein the component (9) further comprises one or two of Ca: 0.0005 to 0.005% and Pb: 0.04 to 0.30%. Manufacturing method of non-refined hot forged product with excellent strength.
【００１６】（１０）成分が更に、 Ｔｅ：０.０１〜０.１５％， Ｓｅ：０.０１〜０.１５％， Ｂｉ：０.０４〜０.３％ のうち一種または二種以上を含有する請求項６または７
または８または９記載の疲労強度に優れた非調質熱間鍛
造品の製造方法。The component (10) further contains one or more of Te: 0.01 to 0.15%, Se: 0.01 to 0.15%, Bi: 0.04 to 0.3%. Claim 6 or 7 containing
Or a method for producing a non-heat treated hot forged product excellent in fatigue strength according to 8 or 9.
【００１７】以下に、本発明を詳細に説明する。まず、
Ｃは機械部品としての最終製品の強度を増加させ、パー
ライトを増加させるのに有効な元素であるが、０.１０
％未満ではその効果は不十分で、また０.６０％を超え
るとむしろ最終製品の靭性の劣化を招くので、含有量を
０.１０〜０.６０％とした。Hereinafter, the present invention will be described in detail. First,
C is an element effective for increasing the strength of the final product as a mechanical part and increasing pearlite, but 0.10.
%, The effect is insufficient, and if it exceeds 0.60%, the toughness of the final product is rather deteriorated. Therefore, the content is set to 0.10 to 0.60%.
【００１８】次に、Ｓｉは脱酸元素として、またフェラ
イト中に固溶し、固溶体硬化によりフェライトを強化
し、疲労特性を向上させる目的で添加するが、０.００
５％未満ではこれらの効果は不十分であり、一方、２.
００％を超えるとこれらの効果は飽和しむしろ最終製品
の靭性の劣化を招くので、その含有量を０.００５〜２.
００％とした。Next, Si is added as a deoxidizing element and is added as a solid solution in the ferrite for the purpose of strengthening the ferrite by solid solution hardening and improving the fatigue properties.
Below 5%, these effects are insufficient, while 2.
If the content exceeds 0.00%, these effects are not saturated but rather deteriorate the toughness of the final product.
00%.
【００１９】Ｍｎはパーライト量を増加させ、ラメラー
間隔を狭くすることにより最終製品の強度を増加させる
のに有効な元素であるが、０.５５％未満ではこの効果
は不十分であり、一方、２.００％を超えるとこの効果
は飽和しむしろ最終製品の靭性の劣化を招くので、その
含有量を０.５５〜２.００％とした。Mn is an element effective for increasing the amount of pearlite and increasing the strength of the final product by narrowing the lamellar interval, but if it is less than 0.55%, this effect is insufficient. If the content exceeds 2.00%, the effect is not saturated but rather deteriorates the toughness of the final product. Therefore, the content is set to 0.55 to 2.00%.
【００２０】また、Ｓは鋼中でＭｎＳとして存在し、被
削性の向上および組織の微細化に寄与する。更に切削抵
抗低減により部品の被削性を向上させる。０.０１％未
満ではその効果は不十分である。一方、０.１０％を超
えるとその効果は飽和し、むしろ靭性の劣化および異方
性の増加を招く。以上の理由から、Ｓの含有量を０.０
１〜０.１０％とした。S is present as MnS in steel, and contributes to improvement of machinability and miniaturization of structure. Further, the machinability of the part is improved by reducing the cutting resistance. If it is less than 0.01%, the effect is insufficient. On the other hand, when the content exceeds 0.10%, the effect is saturated, and rather, the toughness is deteriorated and the anisotropy is increased. For the above reasons, the content of S is set to 0.0.
1 to 0.10%.
【００２１】次に、Ａｌは脱酸元素および結晶粒微細化
元素として添加するが、０.０００５％未満ではその効
果は不十分であり、一方、０.０５％を超えるとその効
果は飽和し、むしろ靭性を劣化させるので、その含有量
を０.０００５〜０.０５％とした。Next, Al is added as a deoxidizing element and a grain refining element, but if its content is less than 0.0005%, its effect is insufficient, while if it exceeds 0.05%, its effect is saturated. However, since the toughness is rather deteriorated, the content is set to 0.0005 to 0.05%.
【００２２】さらに本発明においては、炭化物として析
出させ、フェライト地を強化し、疲労特性を向上させる
目的で、Ｖを必須元素として含有させる。しかしなが
ら、Ｖ含有量が０.３０％以下ではその効果は不十分で
あり、一方Ｖ含有量０.７０％超ではその効果は飽和
し、むしろ靭性を劣化させるので、この含有量をＶ：
０.３０〜０.７０％とした。Further, in the present invention, V is contained as an essential element for the purpose of precipitating as carbide, strengthening the ferrite ground, and improving the fatigue properties. However, if the V content is less than 0.30%, the effect is insufficient, while if the V content is more than 0.70%, the effect is saturated and the toughness is rather deteriorated.
0.30 to 0.70%.
【００２３】また、本発明の方法において、オーステナ
イト中でＴｉＮを形成しＮを固定し更に加熱中のオース
テナイト粒粗大化防止のためと炭化物として析出させる
目的で特定量のＴｉを必須元素として添加するが、Ｔｉ
含有量０.０２０％以下ではＮ固定のＴｉが不足するた
めＶＮ形成を防止することはできず、またＴｉ含有量
０.０５０％超では粗大ＴｉＮが形成され靭性が大きく
低下するので、Ｔｉ含有量を０.０２０超〜０.０５０％
とした。Further, in the method of the present invention, a specific amount of Ti is added as an essential element for the purpose of forming TiN in austenite, fixing N, preventing coarsening of austenite grains during heating, and precipitating as carbide. Is Ti
If the content is 0.020% or less , VN formation cannot be prevented because of insufficient N-fixed Ti, and if the Ti content is more than 0.050%, coarse TiN is formed and toughness is greatly reduced. The amount is more than 0.020 to 0.050%
And
【００２４】更に本発明では、Ｎを０.００８％以下に
制限することを特徴とする。ＮはＶと窒化物を形成しや
すい元素であるが、鋼中溶解度の小さいＶＮを形成して
しまうと、加熱時に鋼中に固溶させることができず、フ
ェライト変態時に析出強化を図ることができない。鋼中
溶解度積の小さいＶの炭化物の析出強化を有効に活用す
るために、Ｎを０.００８％未満に制限する。Further, the present invention is characterized in that N is limited to 0.008% or less. N is an element that easily forms nitrides with V. However, if VN having low solubility in steel is formed, it cannot be dissolved in steel at the time of heating, and precipitation strengthening can be achieved during ferrite transformation. Can not. In order to effectively utilize the precipitation strengthening of V carbide having a small solubility product in steel, N is limited to less than 0.008%.
【００２５】一方、Ｐは鋼中で粒界偏析や中心偏析を起
こし、靭性劣化の原因となる。特にＰが０.０３５％を
超えると靭性の劣化が顕著となるため、０.０３５％以
下とした。On the other hand, P causes grain boundary segregation and central segregation in steel, which causes deterioration of toughness. In particular, when P exceeds 0.035%, the deterioration of toughness becomes remarkable, so that the content is made 0.035% or less.
【００２６】請求項(２)は更に析出強化を活用すること
により、耐久比向上を図ったものである。そのためＮｂ
を添加するが、０.００５％未満では析出強化は期待で
きず、また０.１０％超ではこの効果は飽和し、コスト
高になるばかりでなく、靭性の低下にもつながるので、
Ｎｂ添加量は０.００５〜０.１０％とした。Claim (2) is intended to improve the durability ratio by further utilizing precipitation strengthening. Therefore Nb
If less than 0.005%, precipitation strengthening cannot be expected, and if more than 0.10%, this effect saturates and not only increases the cost but also lowers the toughness.
The amount of Nb added was 0.005 to 0.10%.
【００２７】請求項(３)は強度の向上、特に重要保安部
品等を使用することができるように、強度、靭性両方の
向上を図ったものである。そのためＣｒ、Ｍｏを添加す
る。Ｃｒは、フェライト地を強化し最終製品の強度を増
加させるのに有効な元素である。含有量０.１０％未満
ではその効果はなく、また１.５０％超では硬度が高く
なりすぎ、靭性の低下を招き、また経済性の点で好まし
くないためその含有量を０.１０〜１.５０％とした。ま
たＭｏも最終製品の強度を増加させるのに有効な元素で
あるが、含有量０.０５％未満ではその効果はなく、ま
た１.００％超では硬さの増加を招き、また経済性の点
で好ましくないためその含有量を０.０５〜１.００％と
した。Claim (3) is intended to improve both the strength and the toughness so that the strength can be improved, and particularly the important security parts can be used. Therefore, Cr and Mo are added. Cr is an element effective in strengthening the ferrite ground and increasing the strength of the final product. If the content is less than 0.10%, the effect is not obtained. If the content exceeds 1.50%, the hardness becomes too high, and the toughness is lowered. .50%. Mo is also an effective element for increasing the strength of the final product. However, if its content is less than 0.05%, it has no effect, and if it exceeds 1.00%, it causes an increase in hardness and economical efficiency. Therefore, the content is set to 0.05% to 1.00%.
【００２８】請求項(４)は、鍛造後の部品の被削性向上
を図ったものである。そのためＣａ，Ｐｂを添加する。
Ｐｂは鋼中で低融点の金属介在物として存在し、部品の
被削性を向上させる元素である。含有量０.０４％未満
ではその効果はなく、また０.３％超では、熱間、温間
での加工性を損なうため、その含有量を０.０４〜０.３
％とした。またＣａも軟質介在物を形成し、被削性の向
上に寄与する元素である。０.０００５％未満ではその
効果はなく、０.００５％超ではむしろ介在物は硬質化
してしまうため、その含有量を０.０００５〜０.００５
％とした。Ｃａ添加の場合、望ましくはＡｌ添加量を
０.００２％以下とする。Claim (4) aims to improve the machinability of the forged part. Therefore, Ca and Pb are added.
Pb is an element that exists as low-melting metal inclusions in steel and improves the machinability of components. If the content is less than 0.04%, the effect is not obtained. If the content is more than 0.3%, hot or warm workability is impaired, so that the content is 0.04 to 0.3.
%. Ca is also an element that forms soft inclusions and contributes to improving machinability. If the content is less than 0.0005%, the effect is not obtained. If the content is more than 0.005%, the inclusions are rather hardened, so that the content is 0.0005 to 0.005.
%. In the case of adding Ca, the added amount of Al is desirably 0.002% or less.
【００２９】請求項(５)も、鍛造後の部品の被削性向上
を図ったものである。そのためＴｅ，Ｓｅ，Ｂｉを添加
する。Ｔｅ，Ｓｅは切削抵抗低減させ、被削性の向上に
寄与する元素である。０.０１％未満ではその効果はほ
とんどなく、０.１５％超では機械的性質を劣化させ、
特に異方性が顕著となるため、その含有量を０.０１〜
０.１５％とした。Ｂｉは鋼中で低融点の金属介在物と
して存在し、部品の被削性を向上させる元素である。含
有量０.０４％未満ではその効果はなく、また０.３％超
では熱間、温間での加工性を損なうため、その含有量を
０.０４〜０.３％とした。Claim (5) also improves the machinability of the forged part. Therefore, Te, Se, and Bi are added. Te and Se are elements that reduce cutting resistance and contribute to improving machinability. If it is less than 0.01%, there is almost no effect, and if it exceeds 0.15%, the mechanical properties deteriorate,
In particular, since the anisotropy becomes remarkable, the content is 0.01 to
0.15%. Bi is an element that exists as low-melting metal inclusions in steel and improves the machinability of components. If the content is less than 0.04%, there is no effect, and if it exceeds 0.3%, the workability in hot and warm is impaired, so the content is made 0.04 to 0.3%.
【００３０】次に、本発明において、加熱温度、冷却速
度を限定した理由について述べる。まず、加熱温度の下
限をＡｃ3変態点としたのは、Ａｃ3変態点未満の加熱温
度では、組織はフェライトとオーステナイトの混合であ
り、Ｖ炭化物を十分にオーステナイト中に固溶させるこ
とができず、冷却時にフェライト中へのＶ炭化物の析出
を有効に使えないためである。また加熱温度の上限を１
２５０℃以下としたのは、１２５０℃超の加熱温度では
オーステナイト結晶粒が粗大化し始め、更に鋼材表面の
脱炭も激しくなり、鍛造後の機械部品の疲労強度が大幅
に低下するためである。Next, the reason why the heating temperature and the cooling rate are limited in the present invention will be described. First, the lower limit of the heating temperature was set to the Ac 3 transformation point. At a heating temperature lower than the Ac 3 transformation point, the structure is a mixture of ferrite and austenite, and the V carbide can be sufficiently dissolved in austenite. This is because precipitation of V carbide in ferrite during cooling cannot be used effectively. The upper limit of the heating temperature is 1
The reason why the temperature is set to 250 ° C. or less is that at a heating temperature exceeding 1250 ° C., austenite crystal grains start to coarsen, and decarburization of the steel material surface also becomes severe, so that the fatigue strength of a mechanical part after forging is greatly reduced.
【００３１】鍛造後の冷却速度の上限を２℃／秒とする
のは、これ以上の冷却速度では組織に転位密度の高いベ
イナイトが混入し疲労強度が低下し、また疲労特性向上
のためのフェライト中へのＶ炭化物の析出が十分に行わ
れないためである。冷却速度の下限を０.０５℃／秒と
するのは、これ未満の冷却速度では粗大フェライト粒が
形成され靭性の大幅な低下が生じたり、オーステナイト
中でＶ、Ｔｉの炭化物が析出し始めるので、フェライト
中で析出するＶ、Ｔｉの炭化物量が減少することにな
り、十分な疲労強度が得られないためである。また冷却
速度を規定する範囲を鍛造温度〜３００℃としたのは、
３００℃以下で冷却速度を制御しても、組織、機械的性
質に実質的な変化は生じないためである。以下に、本発
明の効果を実施例により、さらに具体的に示す。The upper limit of the cooling rate after forging is set to 2 ° C./sec. If the cooling rate is higher than that, bainite having a high dislocation density is mixed into the structure, thereby lowering the fatigue strength. This is because V carbide is not sufficiently precipitated therein. The reason for setting the lower limit of the cooling rate to 0.05 ° C./sec is that if the cooling rate is lower than this, coarse ferrite grains are formed and the toughness is greatly reduced, and carbides of V and Ti begin to precipitate in austenite. This is because the amount of carbides of V and Ti precipitated in ferrite decreases, and sufficient fatigue strength cannot be obtained. The reason for setting the cooling rate range to the forging temperature to 300 ° C. is as follows.
This is because even if the cooling rate is controlled at 300 ° C. or less, no substantial change occurs in the structure and mechanical properties. Hereinafter, the effects of the present invention will be more specifically described with reference to examples.
【００３２】[0032]
【実施例】表１〜３に示す化学成分の鋼を高周波炉にて
溶製し、１５０ｋｇのインゴットに鋳造した。これから
試験片を切り出し、表４〜６に示す条件で鍛造を行っ
た。それらの材料の中央部よりＪＩＳ１４号引張試験
片、ＪＩＳ３号衝撃試験片、ＪＩＳ１号回転曲げ試験
片、およびドリル穴あけ試験片を採取し、引張強度、−
５０℃シャルピー衝撃値、疲労強度、および被削性を求
めた。EXAMPLES Steels having the chemical components shown in Tables 1 to 3 were melted in a high-frequency furnace and cast into 150 kg ingots. From this, a test piece was cut out and forged under the conditions shown in Tables 4 to 6. JIS No. 14 tensile test pieces, JIS No. 3 impact test pieces, JIS No. 1 rotary bending test pieces, and drilling test pieces were collected from the center of these materials, and tensile strength,-
The Charpy impact value at 50 ° C., fatigue strength, and machinability were determined.
【００３３】被削性の評価にはＶL1000という指標を使
用した。送り速度０.３３ｍｍ／ｓのドリル(材質：ＳＫ
Ｈ５１−φ３ｍｍ)の周速を種々変化させ、各速度にお
いてドリルが切削不能になる総穴深さを求め、周速−ド
リル寿命曲線を作成し、ドリル寿命が１０００ｍｍとな
る最大速度をＶL1000と規定し、被削性の評価基準とし
た。表４〜６に各鋼材の材質特性の本発明と比較例を対
比して示す。An index of VL 1000 was used for the evaluation of the machinability. Drill with a feed rate of 0.33 mm / s (Material: SK
H51-.phi.3 mm) while varying the peripheral speed of the drill is determined the total hole depth becomes impossible cutting at each speed, the peripheral speed - to create a drill life curve, the maximum speed at which the drill life is 1000mm and VL 1000 It was stipulated and used as an evaluation standard for machinability. Tables 4 to 6 show the material properties of each steel material in comparison with the present invention and comparative examples.
【００３４】表４に示すように、比較例において本発明
の成分、鍛造方法から外れた鋼Ｎｏ．１〜７で降伏比で
最高値０.７０、耐久比で最高値０.４５と低く、共に本
発明の下限値に達しなかった。これに比べ、鋼Ｎｏ.１
１〜３７で本発明の第６〜第８発明法による鍛造では、
例えば第７発明法の鋼Ｎｏ.２７の降伏比０.７６、耐久
比０.５６や、第８発明法の鋼Ｎｏ.３１の降伏比０.８
６、耐久比０.５６や、鋼Ｎｏ.３６の降伏比０.７９、
耐久比０.５９のように降伏比、耐久比共に比較法を大
きく上回っている。As shown in Table 4, in Comparative Examples, the components of the present invention, steel No. In the case of 1 to 7, the maximum yield ratio was 0.70 and the maximum durability ratio was 0.45, which was lower than the lower limit of the present invention. In comparison, steel No. 1
In the forging according to the sixth to eighth invention methods of the present invention in 1 to 37,
Seventh aspect methods yield ratio 0.76 Steel No.27 For example, and durability ratio 0.56, the yield ratio of the eighth invention method Steel No.31 0.8
6, endurance ratio 0.56, yield ratio of steel No. 36 0.79,
As shown in the durability ratio of 0.59, both the yield ratio and the durability ratio greatly exceed the comparison method.
【００３５】更に被削性を向上させた鋼Ｎｏ.４１〜６
７での本発明の第６〜第８発明法では、例えば第９発明
法の鋼Ｎｏ.４３の引張強度９３.８kgf/mm2で降伏比０.
８１、耐久比０.５８に達しながらＶL1000２４.８ｍ／m
inを有し、第１０発明法の鋼Ｎｏ.５６の引張強度９７.
７kgf/mm2で降伏比０.７５、耐久比０.６０に達しなが
ら、ＶL1000４６.１ｍ／minを有し、比較例に比べて降
伏比、耐久比、被削性共に上回っている。Steel Nos. 41 to 6 with further improved machinability
In the sixth to eighth invention methods of the present invention at No. 7 , for example, the steel No. 43 of the ninth invention method has a tensile strength of 93.8 kgf / mm 2 and a yield ratio of 0.
81, VL 1000 24.8m / m while reaching a durability ratio of 0.58
and the tensile strength of steel No. 56 of the 10th invention method 97.
It has a VL 1000 of 46.1 m / min while reaching a yield ratio of 0.75 and a durability ratio of 0.60 at 7 kgf / mm 2 , and exceeds the yield ratio, the durability ratio and the machinability as compared with the comparative example.
【００３６】このように本発明法によると引張強度７
０.８〜９７.７ｋｇｆ／ｍｍ2で、降伏比０.７５〜０.
８９、耐久比０.５１〜０.６０を得ることができ、比較
法より高い降伏比、耐久比を有し、更に比較鋼と同等以
上の被削性を有することがわかる。As described above, according to the method of the present invention, the tensile strength of 7
0.8 to 97.7 kgf / mm 2 , yield ratio 0.75 to 0.7
89, a durability ratio of 0.51 to 0.60 can be obtained, and it can be seen that it has a higher yield ratio and durability ratio than the comparative method, and has machinability equal to or higher than that of the comparative steel.
【００３７】[0037]
【発明の効果】以上述べたごとく、本発明法を用いれ
ば、高降伏強度、高疲労強度を有する非調質熱間鍛造品
の製造が可能であり、機械構造部品の軽量化が可能とな
り、産業上の効果は極めて顕著なるものがある。As described above, by using the method of the present invention, it is possible to produce a non-heat treated hot forged product having a high yield strength and a high fatigue strength, and it is possible to reduce the weight of mechanical structural parts. The industrial effects are very significant.
【００３８】[0038]
【表１】 [Table 1]
【００３９】[0039]
【表２】 [Table 2]
【００４０】[0040]
【表３】 [Table 3]
【００４１】[0041]
【表４】 [Table 4]
【００４２】[0042]
【表５】 [Table 5]
【００４３】[0043]
【表６】 [Table 6]
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 平１−176031（ＪＰ，Ａ) 特開 平１−176055（ＪＰ，Ａ) 特開 昭62−96653（ＪＰ，Ａ) 特開 平５−195140（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 C21D 8/00 - 8/10 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 1-176031 (JP, A) JP-A 1-176055 (JP, A) JP-A 62-96653 (JP, A) JP-A 5- 195140 (JP, A) (58) Field surveyed (Int. Cl. 7 , DB name) C22C 38/00-38/60 C21D 8/00-8/10
Claims (10)
以下に制限し、残部が鉄および不可避的不純物からな
り、熱間鍛造後の引張強度が７０kgf/mm 2 以上であるこ
とを特徴とする疲労強度に優れた熱間鍛造用非調質鋼
材。1. The weight ratio of C: 0.10 to 0.60%, Si: 0.005 to 2.00%, Mn: 0.55 to 2.00%, S: 0.01 to 0.1%. 10%, Al: 0.0005 to 0.05%, V: more than 0.30% to 0.70% or less, Ti: more than 0.020 to 0.050%, and N: 0.008% , P: 0.035%
Limited to the following, is it from the iron and unavoidable impurities balance
Ri, hot forging after the tensile strength of 70 kgf / mm 2 or more at which this <br/> and excellent fatigue strength, wherein the hot forging non-heat treated steels.
非調質鋼材。2. The non-heat treated steel material for hot forging having excellent fatigue strength according to claim 1, wherein the component further contains Nb: 0.005 to 0.10%.
の疲労強度に優れた熱間鍛造用非調質鋼材。3. The fatigue strength according to claim 1, wherein the component further comprises one or two of Cr: 0.10 to 1.50%, Mo: 0.05 to 1.00%. Excellent non-heat treated steel for hot forging.
は３記載の疲労強度に優れた熱間鍛造用非調質鋼材。4. The fatigue according to claim 1, wherein the component further contains one or two of Ca: 0.0005 to 0.005% and Pb: 0.04 to 0.30%. Non-heat treated steel for hot forging with excellent strength.
または３または４記載の疲労強度に優れた熱間鍛造用非
調質鋼材。5. The composition further comprises one or more of Te: 0.01 to 0.15%, Se: 0.01 to 0.15%, Bi: 0.04 to 0.3%. Claim 1 or 2
Or a non-heat treated steel material for hot forging having excellent fatigue strength according to 3 or 4.
以下に制限し、残部が鉄および不可避的不純物からなる
鋼を、Ａc3点以上１２５０℃以下のオーステナイト化温
度において鍛造を行い、その後３００℃まで０.０５℃
／秒以上２℃／秒未満の平均冷却速度で冷却することを
特徴とするフェライト・パーライト組織からなり、引張
強度が７０kgf/mm 2 以上である、疲労強度に優れた非調
質熱間鍛造品の製造方法。6. As a weight ratio, C: 0.10 to 0.60%, Si: 0.005 to 2.00%, Mn: 0.55 to 2.00%, S: 0.01 to 0.1%. 10%, Al: 0.0005 to 0.05%, V: more than 0.30% to 0.70% or less, Ti: more than 0.020 to 0.050%, and N: 0.008% , P: 0.035%
The forging is performed at an austenitizing temperature of 3 points or more and 1250 ° C. or less, and then 0.05 ° C. to 300 ° C., with the balance being iron and unavoidable impurities.
/ Sec cooling at an average cooling rate of less than or 2 ° C. / sec consist ferrite-pearlite structure, wherein the tensile
A method for producing a non-refined hot forged product excellent in fatigue strength, having a strength of 70 kgf / mm 2 or more .
鍛造品の製造方法。7. The method for producing a non-heat treated hot forged product excellent in fatigue strength according to claim 6, wherein the component further contains Nb: 0.005 to 0.10%.
の疲労強度に優れた非調質熱間鍛造品の製造方法。8. The fatigue strength according to claim 6, wherein the component further contains one or two of Cr: 0.10 to 1.50%, Mo: 0.05 to 1.00%. Excellent non-refined hot forging product manufacturing method.
は８記載の疲労強度に優れた非調質熱間鍛造品の製造方
法。9. The fatigue according to claim 6, wherein the component further contains one or two of Ca: 0.0005 to 0.005% and Pb: 0.04 to 0.30%. Manufacturing method of non-refined hot forged product with excellent strength.
または８または９記載の疲労強度に優れた非調質熱間鍛
造品の製造方法。10. The composition further comprises one or more of Te: 0.01 to 0.15%, Se: 0.01 to 0.15%, Bi: 0.04 to 0.3%. Claim 6 or 7
Or a method for producing a non-heat treated hot forged product excellent in fatigue strength according to 8 or 9.
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|---|---|---|---|
| JP18423893A JP3327635B2 (en) | 1993-04-23 | 1993-07-26 | Non-tempered steel for hot forging excellent in fatigue strength and method for producing non-heat-treated hot forged product using the steel |
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|---|---|---|---|
| JP9756793 | 1993-04-23 | ||
| JP5-97567 | 1993-04-23 | ||
| JP18423893A JP3327635B2 (en) | 1993-04-23 | 1993-07-26 | Non-tempered steel for hot forging excellent in fatigue strength and method for producing non-heat-treated hot forged product using the steel |
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| Publication Number | Publication Date |
|---|---|
| JPH073386A JPH073386A (en) | 1995-01-06 |
| JP3327635B2 true JP3327635B2 (en) | 2002-09-24 |
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| JP3715744B2 (en) * | 1997-05-26 | 2005-11-16 | 新日本製鐵株式会社 | Non-tempered steel for hot forging used by fracture cutting |
| JP3954751B2 (en) * | 1999-04-02 | 2007-08-08 | 新日本製鐵株式会社 | Steel with excellent forgeability and machinability |
| KR20010059686A (en) * | 1999-12-30 | 2001-07-06 | 이계안 | Bainite steel composition which could be produced by press quenching |
| JP4957325B2 (en) * | 2007-03-29 | 2012-06-20 | 住友金属工業株式会社 | Non-tempered steel |
| JP5482342B2 (en) * | 2010-03-18 | 2014-05-07 | 新日鐵住金株式会社 | Hot rolled steel for direct cutting and method for producing the same |
| US10266908B2 (en) | 2014-07-03 | 2019-04-23 | Nippon Steel & Sumitomo Metal Corporation | Rolled steel bar for machine structural use and method of producing the same |
| JP6249100B2 (en) | 2014-07-03 | 2017-12-20 | 新日鐵住金株式会社 | Rolled steel bar for machine structure and manufacturing method thereof |
| JP7270420B2 (en) * | 2019-03-13 | 2023-05-10 | 株式会社神戸製鋼所 | Hot forged non-heat treated parts, manufacturing method thereof, and steel materials for hot forged non-heat treated parts |
| JP7189053B2 (en) * | 2019-03-14 | 2022-12-13 | 株式会社神戸製鋼所 | Non-tempered forging steel and non-tempered forged parts |
| CN114959500B (en) * | 2022-06-29 | 2023-05-09 | 马鞍山钢铁股份有限公司 | Non-quenched and tempered steel for Nb-Ti composite reinforced medium-carbon expansion-break connecting rod, expansion-break connecting rod produced by non-quenched and tempered steel, and forging and cooling control process |
| CN115261734B (en) * | 2022-08-19 | 2023-05-23 | 中天钢铁集团有限公司 | High-homogeneity non-quenched and tempered steel for engineering machinery and production method thereof |
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