JP2005076047A - Method for manufacturing hollow stabilizer superior in fatigue resistance - Google Patents
Method for manufacturing hollow stabilizer superior in fatigue resistance Download PDFInfo
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- 239000003381 stabilizer Substances 0.000 title claims abstract description 55
- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 23
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 76
- 239000010959 steel Substances 0.000 claims abstract description 76
- 238000005096 rolling process Methods 0.000 claims abstract description 31
- 238000005452 bending Methods 0.000 claims abstract description 26
- 238000010438 heat treatment Methods 0.000 claims abstract description 22
- 238000010791 quenching Methods 0.000 claims abstract description 14
- 230000000171 quenching effect Effects 0.000 claims abstract description 14
- 230000001186 cumulative effect Effects 0.000 claims abstract description 13
- 238000005496 tempering Methods 0.000 claims abstract description 8
- 239000000203 mixture Substances 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 239000000047 product Substances 0.000 description 9
- 230000007423 decrease Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
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- 239000013078 crystal Substances 0.000 description 4
- 238000010622 cold drawing Methods 0.000 description 3
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- 229910001566 austenite Inorganic materials 0.000 description 2
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- 238000009661 fatigue test Methods 0.000 description 2
- 239000003507 refrigerant Substances 0.000 description 2
- 238000005480 shot peening Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
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- 239000003638 chemical reducing agent Substances 0.000 description 1
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- 239000011159 matrix material Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
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Abstract
Description
本発明は、自動車等の車両に使用されるスタビライザの製造方法に係り、とくに中空スタビライザの耐疲労特性の向上に関する。 The present invention relates to a method of manufacturing a stabilizer used in a vehicle such as an automobile, and more particularly to improvement of fatigue resistance of a hollow stabilizer.
従来から、ほとんどの自動車には、コーナーリング時の車体のローリングを緩和したり、高速時の走行安定性を保持するために、スタビライザが装着されている。このスタビライザは、棒鋼を用いた中実のスタビライザが一般的に使用されてきた。しかし、最近では、地球環境保全の観点から自動車車体の軽量化を図ることが要求され、スタビライザにおいても、鋼管を用いた中空スタビライザの採用が検討されるようになっている。 Conventionally, most automobiles have been provided with a stabilizer in order to alleviate rolling of the vehicle body during cornering and maintain running stability at high speeds. As this stabilizer, a solid stabilizer using a steel bar has been generally used. However, recently, it has been required to reduce the weight of automobile bodies from the viewpoint of global environmental protection, and the adoption of hollow stabilizers using steel pipes has been considered for stabilizers.
中空スタビライザは車体の軽量化には大きく寄与するが、中実スタビライザに比べ断面積が大幅に減少するため、従来以上に強度靭性に優れた特性を有するとともに、複雑な形状に加工できるように曲げ加工性に優れること、高い疲労強度を確保するための十分な焼入れ性を有する素材を適用することが要求される。 The hollow stabilizer greatly contributes to the weight reduction of the vehicle body, but since the cross-sectional area is greatly reduced compared to the solid stabilizer, it has characteristics superior in strength and toughness than conventional ones and is bent so that it can be processed into a complicated shape It is required to apply a material having excellent workability and sufficient hardenability to ensure high fatigue strength.
このような要求に対し、例えば、特許文献1には、C、Si、Mn、Cr含有量を、理想臨界直径DI が1.0in以上、Ceqが0.48%以下となるように調整したスラブを用いて、熱間圧延し、巻取温度を570〜690℃に調整して巻取る中空スタビライザ用電縫鋼管用鋼の製造方法が提案されている。この技術によれば、機械的性質、熱処理特性のよい電縫鋼管が製造でき、信頼性が高い中空スタビライザを製造できるとしている。しかし、特許文献1に記載された技術で製造された電縫鋼管では、曲げ加工性が不足し、曲率半径が小さく複雑なスタビライザ形状への成形ができないという問題があった。このため、スタビライザ用鋼管に対する、更なる曲げ加工性の向上が要望されていた。 For such requirements, for example, Patent Document 1, using C, Si, Mn, and Cr content, the ideal critical diameter D I at least 1.0in, the adjusted slab so Ceq is 0.48% or less Thus, a method for producing a steel for an electric-welded steel pipe for a hollow stabilizer has been proposed which is hot-rolled and wound by adjusting the winding temperature to 570 to 690 ° C. According to this technique, it is said that an electric-welded steel pipe having good mechanical properties and heat treatment characteristics can be manufactured, and a highly reliable hollow stabilizer can be manufactured. However, the electric resistance welded steel pipe manufactured by the technique described in Patent Document 1 has a problem that bending workability is insufficient, and it is impossible to form a complicated stabilizer shape with a small curvature radius. For this reason, the further improvement of the bending workability with respect to the steel pipe for stabilizers was requested | required.
また、特許文献2には、中空スタビライザの製造方法が提案されている。特許文献2に記載された技術は、電縫管を熱間で連続的に縮管加工し素管を得る素管製造工程と、素管に減面率が30%以上となる冷間引抜加工を行い厚肉パイプ材とする冷間引抜工程と、厚肉パイプ材を冷間で所望のスタビライザ形状に曲げ加工する成形工程と、好ましくはさらに焼鈍工程およびショットピーニング工程と、を具備し、厚肉化を可能とした中空スタビライザの製造方法である。 Patent Document 2 proposes a method for manufacturing a hollow stabilizer. The technology described in Patent Document 2 includes a manufacturing process of obtaining a raw pipe by continuously shrinking an electric-welded pipe hot, and a cold drawing process in which the area reduction rate of the raw pipe is 30% or more. A cold drawing step to make a thick pipe material, a forming step for bending the thick pipe material into a desired stabilizer shape cold, and preferably an annealing step and a shot peening step, It is a manufacturing method of the hollow stabilizer which enabled the fleshing.
また、特許文献3には、中空スタビライザの製造方法が提案されている。特許文献3に記載された技術は、電縫管を熱間または温間で縮管して外径に対する肉厚の割合を18〜35%にする縮管工程と、縮管された電縫管をスタビライザ形状に冷間成形または熱間成形する成形工程と、成形されたスタビライザ半製品に熱処理工程を行い、ついで、ショットピーニングと、塗装とを行う方法である。
しかしながら、特許文献2、特許文献3に記載された技術では冷間引抜き加工により鋼管の曲げ加工性が著しく劣化するため適用できるスタビライザ形状に限界があった。また、特許文献2、特許文献3に記載された技術によってもなお、耐疲労特性が低下するという問題があり、更なる耐疲労特性の向上が要望されていた。 However, in the techniques described in Patent Document 2 and Patent Document 3, there is a limit to the shape of a stabilizer that can be applied because the bending workability of a steel pipe is significantly deteriorated by cold drawing. Further, the techniques described in Patent Document 2 and Patent Document 3 still have a problem that the fatigue resistance is lowered, and further improvement of the fatigue resistance has been demanded.
本発明は、上記した従来技術の問題を有利に解決し、耐疲労特性に優れた中空スタビライザの製造方法を提案することを目的とする。 An object of the present invention is to advantageously solve the above-described problems of the prior art and propose a method for manufacturing a hollow stabilizer having excellent fatigue resistance.
本発明者らは、上記した課題を達成するために、中空スタビライザの耐疲労特性に及ぼす各種要因について鋭意検討した。その結果、中空スタビライザの加工部での肉厚偏差が、耐疲労特性の劣化に大きく影響していることを突き止めた。そして、これは、素材鋼管の曲げ加工性の低下に起因していることに想到した。本発明は、上記した知見に基づき、さらに検討を加えて完成されたものである。 In order to achieve the above-described problems, the present inventors diligently studied various factors affecting the fatigue resistance characteristics of the hollow stabilizer. As a result, it was found that the thickness deviation in the processed portion of the hollow stabilizer greatly affects the deterioration of the fatigue resistance characteristics. And it came to mind that this originated in the fall of the bending workability of a raw material steel pipe. The present invention has been completed based on the above findings and further studies.
すなわち、本発明の要旨は、つぎのとおりである。
(1)素材鋼管に、冷間曲げ加工によりスタビライザー形状に成形する成形工程と、該成形された鋼管に焼入れ処理および焼戻し処理を行う熱処理工程とを順次施す中空スタビライザーの製造方法において、前記素材鋼管が、母鋼管に、加熱処理を施したのち、圧延温度:600〜850℃で累積縮径率:40%以上の絞り圧延を施してなる鋼管であることを特徴とする耐疲労特性に優れた中空スタビライザの製造方法。
(2)(1)において、前記冷間曲げ加工の曲げ半径Rが素材鋼管外径Dに対して2D以下である部分を有することを特徴とする中空スタビライザの製造方法。
(3)(1)または(2)において、前記母鋼管が、質量%で、C:0.2〜0.38%、Si:0.35%以下、Mn:0.3〜1.5%、P:0.025%以下、S:0.005%以下、Al:0.1%以下、Ti:0.005 〜0.1%、B:0.0005〜0.005%を含み、残部Feおよび不可避的不純物からなる組成を有する溶接鋼管であることを特徴とする中空スタビライザの製造方法。
(4)(1)ないし(3)のいずれかにおいて、前記加熱処理の温度を、800〜1000℃の範囲の温度とすることを特徴とする中空スタビライザの製造方法。
That is, the gist of the present invention is as follows.
(1) In the method of manufacturing a hollow stabilizer, in which a raw steel pipe is sequentially subjected to a forming step of forming into a stabilizer shape by cold bending and a heat treatment step of quenching and tempering the formed steel pipe. However, the steel tube is excellent in fatigue resistance, characterized by being subjected to heat treatment, and then subjected to drawing rolling at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more. Manufacturing method of hollow stabilizer.
(2) The method for manufacturing a hollow stabilizer according to (1), wherein a bending radius R of the cold bending process has a portion that is 2D or less with respect to the raw steel pipe outer diameter D.
(3) In (1) or (2), the base steel pipe is, by mass%, C: 0.2 to 0.38%, Si: 0.35% or less, Mn: 0.3 to 1.5%, P: 0.025% or less, S: 0.005 %, Al: 0.1% or less, Ti: 0.005 to 0.1%, B: 0.0005 to 0.005%, a welded steel pipe having a composition consisting of the remaining Fe and inevitable impurities .
(4) The method for manufacturing a hollow stabilizer according to any one of (1) to (3), wherein the temperature of the heat treatment is a temperature in a range of 800 to 1000 ° C.
本発明によれば、安価な方法で、耐疲労特性に優れた中空スタビライザが製造でき、スタビライザの耐久性を顕著に向上させることができ、自動車車体の軽量化が可能となり、産業上格段の効果を奏する。 According to the present invention, a hollow stabilizer having excellent fatigue resistance can be manufactured by an inexpensive method, the durability of the stabilizer can be remarkably improved, the weight of the automobile body can be reduced, and the industrial effect is remarkable. Play.
中空スタビライザの一例を図1に示す。図1に示す例では、中空スタビライザ1は、車体の幅方向に延びるトーション部11と、トーション部11の両端に連なる一対のアーム部12,12とを有している。トーション部11はブッシュ類11aを介して車体に取り付けられる。アーム部12の端部12a,12aはスタビライザリンク等(図示せず)を介してサスペンション機構等に連結される。なお、トーション部11とアーム部12の一部には、曲げ半径Rで加工された曲げ加工部13を有する。
An example of a hollow stabilizer is shown in FIG. In the example shown in FIG. 1, the hollow stabilizer 1 includes a
本発明の中空スタビライザの製造方法では、素材鋼管に、冷間曲げ加工によりスタビライザ形状に成形する成形工程と、該成形された鋼管に焼入れ処理および焼戻処理を行う熱処理工程とを順次施す。 In the method for manufacturing a hollow stabilizer of the present invention, a raw steel pipe is sequentially subjected to a forming process for forming into a stabilizer shape by cold bending, and a heat treatment process for quenching and tempering the formed steel pipe.
本発明では、素材鋼管として、母鋼管に加熱処理を施したのち、圧延温度:600〜850℃で累積縮径率:40%以上の絞り圧延を施してなる鋼管を使用する。 In the present invention, a steel pipe obtained by subjecting the base steel pipe to a heat treatment and then subjecting the base steel pipe to drawing rolling at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more is used.
母鋼管としては、質量%で、C:0.2〜0.38%、Si:0.35%以下、Mn:0.3〜1.5%、P:0.025%以下、S:0.005%以下、Al:0.1%以下、Ti:0.005〜0.1%、B:0.0005〜0.005%を含み、残部Feおよび不可避的不純物からなる組成を有する溶接鋼管を用いることが好ましい。 As a base steel pipe, it is mass%, C: 0.2-0.38%, Si: 0.35% or less, Mn: 0.3-1.5%, P: 0.025% or less, S: 0.005% or less, Al: 0.1% or less, Ti: 0.005 It is preferable to use a welded steel pipe having a composition comprising -0.1%, B: 0.0005-0.005%, and remaining Fe and inevitable impurities.
母鋼管の組成を上記した範囲に限定した理由は、つぎのとおりである。以下、質量%は単に%で記す。 The reason why the composition of the mother pipe is limited to the above range is as follows. Hereinafter, mass% is simply expressed as%.
C:0.2〜0.38%
Cは、鋼の焼入れ性を向上させ、鋼管の強度を増加させる元素であり、所望のスタビライザ強度を確保するために、0.2%以上含有することが好ましい。一方、0.38%を超える含有は、強度が高くなりすぎて延性が低下するとともに溶接硬化性が増加し溶接鋼管性状に悪影響を及ぼす。このようなことから、Cは0.2〜0.38%の範囲に限定することが好ましい。
C: 0.2-0.38%
C is an element that improves the hardenability of the steel and increases the strength of the steel pipe, and is preferably contained in an amount of 0.2% or more in order to ensure a desired stabilizer strength. On the other hand, if the content exceeds 0.38%, the strength becomes too high, the ductility is lowered, the weld hardenability is increased, and the weld steel pipe properties are adversely affected. Therefore, C is preferably limited to a range of 0.2 to 0.38%.
Si:0.35%以下
Siは、脱酸剤として作用するとともに、基地中に固溶して鋼の焼入れ性を向上させ鋼管の強度を増加させる。このような効果は0.01%以上、より好ましくは0.10%以上で認められるが、0.35%を超えて含有すると、延性低下が顕著となる。このようなことから、Siは
0.35%以下に限定することが好ましい。
Si: 0.35% or less
Si acts as a deoxidizer and dissolves in the matrix to improve the hardenability of the steel and increase the strength of the steel pipe. Such an effect is recognized at 0.01% or more, and more preferably at 0.10% or more. However, when the content exceeds 0.35%, the ductility is remarkably reduced. Because of this, Si
It is preferable to limit it to 0.35% or less.
Mn:0.3〜1.5%
Mnは、鋼の焼入れ性を向上させ、鋼管の強度を増加させる元素であり、所望のスタビライザ強度を確保するために、0.3%以上含有することが好ましい。一方、1.5%を超えて含有すると、延性低下とともに溶接硬化性が顕著に増加し、溶接部の健全性が低下する。このため、Mnは0.3〜1.5%とすることが好ましい。
Mn: 0.3-1.5%
Mn is an element that improves the hardenability of the steel and increases the strength of the steel pipe, and is preferably contained in an amount of 0.3% or more in order to ensure a desired stabilizer strength. On the other hand, if the content exceeds 1.5%, the weld hardenability increases remarkably with the decrease in ductility, and the soundness of the welded portion decreases. For this reason, Mn is preferably 0.3 to 1.5%.
P:0.025%以下
Pは、固溶して鋼の強度を増加させるが、延性を低下させるとともに、粒界に偏析し、熱処理後の低温焼戻し脆性を助長する傾向が強いため、できるだけ低減することが望ましく、本発明では0.025%以下に限定することが好ましい。
P: 0.025% or less P increases the strength of the steel by solid solution, but reduces ductility, segregates at the grain boundaries, and tends to promote low temperature temper embrittlement after heat treatment. In the present invention, it is preferably limited to 0.025% or less.
S:0.005%以下
Sは、鋼中では硫化物として存在し、清浄度を劣化させ、延性を低下させる。素材鋼管の加工性を向上させるために、母鋼管のSは0.005%以下でできるだけ低減することが望ましい。
S: 0.005% or less S exists as a sulfide in steel, and deteriorates cleanliness and lowers ductility. In order to improve the workability of the raw steel pipe, it is desirable to reduce S of the base steel pipe as much as possible at 0.005% or less.
Al:0.1%以下
Alは、脱酸剤として作用するとともに、結晶粒を微細化する作用を有している。結晶粒微細化のために、Alは0.001%以上含有することが好ましい。しかし、0.1%を超えて含有すると、酸素系介在物量が多くなり、清浄度が低下する。このため、Alは0.1%以下に限定することが好ましい。
Al: 0.1% or less
Al acts as a deoxidizer and has the effect of refining crystal grains. In order to refine crystal grains, Al is preferably contained in an amount of 0.001% or more. However, if the content exceeds 0.1%, the amount of oxygen-based inclusions increases and the cleanliness decreases. For this reason, it is preferable to limit Al to 0.1% or less.
Ti:0.005〜0.1%
Tiは、Nと結合しTiNを形成し、結晶粒の微細化に寄与するとともに、窒素を固定しBの焼入れ性向上効果を有効に作用させる。このような効果を得るためには、0.005%以上含有することが好ましい。一方、0.1%を超えて含有すると延性が低下し、鋼管の加工性が劣化する。このため、Tiは0.005〜0.1%に限定することが好ましい。なお、より好ましくは0.01〜0.05%である。
Ti: 0.005-0.1%
Ti combines with N to form TiN, contributes to refinement of crystal grains, and fixes nitrogen to effectively improve the hardenability of B. In order to acquire such an effect, it is preferable to contain 0.005% or more. On the other hand, if the content exceeds 0.1%, the ductility decreases and the workability of the steel pipe deteriorates. For this reason, it is preferable to limit Ti to 0.005 to 0.1%. In addition, More preferably, it is 0.01 to 0.05%.
B:0.0005〜0.005%
Bは、微量の含有で鋼の焼入れ性を大幅に向上させる元素であり、このような効果を得るためには、0.0005%以上含有することが好ましい。一方、0.005%を超える含有は却って焼入れ性が低下する。このため、Bは0.0005〜0.005%に限定することが好ましい。
B: 0.0005-0.005%
B is an element that greatly improves the hardenability of the steel by containing a small amount. In order to obtain such an effect, B is preferably contained in an amount of 0.0005% or more. On the other hand, if the content exceeds 0.005%, the hardenability decreases. For this reason, it is preferable to limit B to 0.0005 to 0.005%.
なお、上記した成分以外の残部は、Feおよび不可避的不純物であり、不可避的不純物としては、N:0.005%以下、O:0.005%以下が許容できる。 The balance other than the above components is Fe and inevitable impurities, and N: 0.005% or less and O: 0.005% or less are acceptable as the inevitable impurities.
母鋼管の製造方法については、とくに限定されないが、製造コストの観点からは溶接鋼管とすることが好ましい。溶接鋼管の製造方法は、鋼帯を成形加工により造管し、シーム部を電縫溶接して製造される公知の方法がいずれも適用できる。継目無鋼管を用いても何ら問題はない。 The manufacturing method of the mother steel pipe is not particularly limited, but it is preferable to use a welded steel pipe from the viewpoint of manufacturing cost. As a method for manufacturing a welded steel pipe, any known method can be applied, in which a steel strip is formed by forming and a seam portion is manufactured by electro-welding. There is no problem even if seamless steel pipes are used.
本発明では、上記した組成の母鋼管に、加熱処理を施し、圧延温度:600〜850℃で累積縮径率:40%以上の絞り圧延を施してなる鋼管を、素材鋼管として使用する。 In the present invention, a steel pipe formed by subjecting the base steel pipe having the above composition to heat treatment and drawing at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more is used as the raw steel pipe.
母鋼管を加熱する温度は、800〜1000℃とすることが好ましい。加熱する温度が800℃未満では適正な絞り圧延の圧延温度を確保できない。一方、加熱する温度が1000℃を超えて高くなると、表面性状が劣化するとともに、オーステナイト粒が粗大化して、素材鋼管の延性が低下する。なお母鋼管の加熱方法はとくに限定されないが、誘導加熱による加熱とすることが好ましい。 The temperature at which the mother steel pipe is heated is preferably 800 to 1000 ° C. If the heating temperature is less than 800 ° C, it is not possible to ensure an appropriate rolling temperature for drawing. On the other hand, when the heating temperature exceeds 1000 ° C., the surface properties deteriorate, austenite grains become coarse, and the ductility of the material steel pipe decreases. The method for heating the mother steel pipe is not particularly limited, but it is preferable to use induction heating.
加熱された母鋼管は、ついで絞り圧延を施される。絞り圧延は、レデューサと呼ばれる連続して配設された複数基(複数スタンド)の孔型圧延機による圧延とすることが好ましい。 The heated mother pipe is then subjected to drawing rolling. The drawing rolling is preferably rolling by a plurality of (a plurality of stands) continuous rolling mills called reducers.
絞り圧延は、600〜850℃のオーステナイト温度域以下とする。この温度域で絞り圧延を行うことにより圧延集合組織が発達して結果としてr値が高くなり、鋼管の加工性が顕著に向上することになる。絞り圧延の圧延温度が600℃未満では、変形抵抗が高く、圧延が困難となるか、あるいは再結晶が不十分となり加工歪が残存し延性が低下して、曲げ加工性が劣化する。一方、絞り圧延の圧延温度が850℃を超えて高くなると、結晶粒の成長が著しくなり、また圧延集合組織の形成が不十分となり延性、曲げ加工性が低下する。このため、絞り圧延の圧延温度は600〜850℃の温度域に限定した。なお、好ましくは700〜800℃である。 Drawing rolling is performed at 600 to 850 ° C. or less in the austenite temperature range. By carrying out drawing rolling in this temperature range, the rolling texture develops and as a result, the r value increases and the workability of the steel pipe is significantly improved. When the rolling temperature of drawing rolling is less than 600 ° C., deformation resistance is high and rolling becomes difficult, or recrystallization becomes insufficient, so that processing strain remains, ductility decreases, and bending workability deteriorates. On the other hand, when the rolling temperature of the drawing rolling is higher than 850 ° C., the growth of crystal grains becomes remarkable, the formation of the rolling texture becomes insufficient, and the ductility and bending workability are lowered. For this reason, the rolling temperature of drawing rolling was limited to the temperature range of 600-850 degreeC. In addition, Preferably it is 700-800 degreeC.
また、絞り圧延における累積縮径率は、40%以上とする。なお、累積縮径率は、
累積縮径率(%)={(母鋼管外径−圧延後鋼管外径)/母鋼管外径}×100%
で定義される。
Further, the cumulative diameter reduction ratio in the drawing rolling is 40% or more. The cumulative diameter reduction rate is
Cumulative diameter reduction rate (%) = {(base pipe outer diameter-steel pipe outer diameter after rolling) / base pipe outer diameter} x 100%
Defined by
累積縮径率が40%未満では縮径率が少なすぎて、上記した絞り圧延の効果が期待できない。また、累積縮径率が40%未満では生産性が低いという問題もある。なお、累積縮径率を40%以上とすることにより、組織の微細化、集合組織の形成が顕著となり、著しく曲げ加工性が向上する。このため、母鋼管絞り圧延の累積縮径率は40%以上とすることが好ましい。なお、累積縮径率は50%以上とすることがより好ましい。 If the cumulative diameter reduction ratio is less than 40%, the diameter reduction ratio is too small, and the effect of the above-described drawing rolling cannot be expected. There is also a problem that productivity is low when the cumulative diameter reduction is less than 40%. By setting the cumulative diameter reduction ratio to 40% or more, the refinement of the structure and the formation of the texture become remarkable, and the bending workability is remarkably improved. For this reason, it is preferable that the cumulative diameter reduction ratio of the base steel pipe drawing rolling is 40% or more. The cumulative diameter reduction rate is more preferably 50% or more.
本発明では、上記した条件で得られた素材鋼管に、成形工程と熱処理工程とを施し中空スタビライザとする。 In the present invention, the raw steel pipe obtained under the above-described conditions is subjected to a forming process and a heat treatment process to obtain a hollow stabilizer.
成形工程では、素材鋼管に冷間曲げ加工を加えてスタビライザ形状に成形する。成形には、略任意の形状に成形可能なNCベンダーを用いることが好ましい。なお、曲げ型を用いて成形してもよい。本発明では、加工性に富む素材鋼管を用いるため、加工部、とくに曲げ部外側の肉厚の減少が抑えられる。本発明では、冷間曲げ加工の曲げ半径Rが素材鋼管外径Dに対し2D以下である部分を有していても、肉厚の減少は少ない。 In the forming process, cold bending is applied to the raw steel pipe to form a stabilizer shape. For molding, it is preferable to use an NC bender that can be molded into a substantially arbitrary shape. In addition, you may shape | mold using a bending die. In the present invention, since a material steel pipe having a high workability is used, a reduction in the thickness of the outside of the processed part, particularly the bent part can be suppressed. In this invention, even if it has the part whose bending radius R of a cold bending process is 2D or less with respect to the raw steel pipe outer diameter D, thickness reduction is small.
スタビライザ形状に成形された成形品は、ついで、所定の温度(焼入れ温度)に通電加熱されたのち、焼入れ槽に投入され急冷される焼入れ処理を施される。通電加熱は、成形品の両端部を電極でクランプし通電することにより行う方法が、成形品の変形も少なく廉価であることから好ましい。焼入れ槽の冷媒は、水または焼入れ油とすることが好ましい。なお、所定の焼入れ温度は、鋼管の組成に依存して決定される。 The molded product formed in the stabilizer shape is then heated to a predetermined temperature (quenching temperature), and then subjected to a quenching process in which it is put into a quenching tank and rapidly cooled. The method of conducting heating by clamping both ends of the molded product with electrodes and energizing is preferable because the molded product is less deformed and inexpensive. The refrigerant in the quenching tank is preferably water or quenching oil. The predetermined quenching temperature is determined depending on the composition of the steel pipe.
焼入れされた成形品は、ついで焼戻し処理を施される。焼戻し処理により、不安定な粒界炭化物が粒内に析出し靭性が顕著に向上する。なお、焼戻し温度は、180〜400℃とすることが好ましい。 The quenched molded product is then tempered. By tempering, unstable grain boundary carbides precipitate in the grains, and the toughness is remarkably improved. The tempering temperature is preferably 180 to 400 ° C.
表1に示す組成の電縫鋼管(88mmφ×肉厚7.5mm)を母鋼管として、該母鋼管に、表2に示す条件で絞り圧延を施して、素材鋼管(25.4mmφ×肉厚7mm)とした。母鋼管は熱延鋼板を冷間成形してオープン管とし端部を電縫溶接し、電縫鋼管としたものを用いた。 ERW steel pipe (88mmφ x thickness 7.5mm) with the composition shown in Table 1 is used as the base steel pipe, and the base steel pipe is subjected to drawing rolling under the conditions shown in Table 2 to obtain a raw steel pipe (25.4mmφ x thickness 7mm). did. The base steel pipe used was a hot-rolled steel sheet that was cold-formed to form an open pipe, and the end was electro-welded and made into an electric-welded steel pipe.
得られた素材鋼管を所定の長さに切断し、冷間の回転引き曲げ加工による成形工程を施し図1に示すような所定のスタビライザ形状に成形し、成形品(最小曲げ半径R:40 mm)とした。なお、アーム部端部は潰した状態に成形した。ついで、成形品の両端部をクランプして通電により950℃に加熱したのち、焼入れ槽(冷媒:水)に投入する焼入れ処理を施した。焼入れ処理後、350℃で焼戻する焼戻し処理を施して製品(中空スタビライザ)を得た。 The obtained material steel pipe is cut into a predetermined length, subjected to a forming process by cold rotary drawing bending, and formed into a predetermined stabilizer shape as shown in FIG. 1, and a molded product (minimum bending radius R: 40 mm) ). In addition, the arm part edge part was shape | molded in the crushed state. Subsequently, both ends of the molded product were clamped and heated to 950 ° C. by energization, and then subjected to a quenching treatment to be put into a quenching tank (refrigerant: water). After the quenching treatment, a tempering treatment was performed by tempering at 350 ° C. to obtain a product (hollow stabilizer).
得られた製品について、ブッシュを固定しアーム部両先端を反対方向に上下する疲労試験を実施し、割れ発生までの繰り返し数を求め、耐疲労特性を評価した。 The obtained product was subjected to a fatigue test in which the bush was fixed and both ends of the arm portion were moved up and down in the opposite direction, the number of repetitions until the occurrence of cracking was determined, and the fatigue resistance was evaluated.
疲労試験の他の条件は、次のとおりとした。 Other conditions of the fatigue test were as follows.
・負荷応力:曲げ部分の表面応力で700MPa
・繰り返し速度:2Hz
また、得られた製品の曲げ加工部から試験片を採取し、管断面外側肉厚の減少率(%)を調査した。肉厚減少率は、次式で定義される。
・ Load stress: 700MPa as the surface stress of the bent part
・ Repetition rate: 2Hz
In addition, a test piece was collected from the bending portion of the obtained product, and the reduction rate (%) of the tube section outer wall thickness was investigated. The thickness reduction rate is defined by the following equation.
肉厚減少率={{(素材鋼管の肉厚)−(曲げ加工後の鋼管外側肉厚)}/(素材鋼管の肉厚)}×100%
得られた結果を表2に示す。
Thickness reduction rate = {{(Raw steel pipe wall thickness)-(Bend outer steel pipe wall thickness)} / (Raw steel pipe wall thickness)} x 100%
The obtained results are shown in Table 2.
本発明例はいずれも、加工部の肉厚減少率も少なく、また耐疲労特性が顕著に向上している。一方、本発明範囲を外れる素材鋼管を用いた比較例では、加工部の肉厚減少率が大きくなり、耐疲労特性も劣化している。 In all of the examples of the present invention, the thickness reduction rate of the processed part is small, and the fatigue resistance is remarkably improved. On the other hand, in the comparative example using the raw steel pipe outside the scope of the present invention, the thickness reduction rate of the processed part is increased, and the fatigue resistance is also deteriorated.
1 中空スタビライザ
11 トーション部
11a ブッシュ類
12 アーム部
12a アーム部端
13 曲げ加工部
1 Hollow stabilizer
11 Torsion club
11a Bush
12 Arm
12a Arm end
13 Bending part
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