JP4506486B2 - ERW steel pipe for high-strength hollow stabilizer and method for producing high-strength hollow stabilizer - Google Patents
ERW steel pipe for high-strength hollow stabilizer and method for producing high-strength hollow stabilizer Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 106
- 239000010959 steel Substances 0.000 title claims description 106
- 239000003381 stabilizer Substances 0.000 title claims description 89
- 238000004519 manufacturing process Methods 0.000 title claims description 29
- 238000010791 quenching Methods 0.000 claims description 77
- 230000000171 quenching effect Effects 0.000 claims description 77
- 238000000034 method Methods 0.000 claims description 60
- 239000000203 mixture Substances 0.000 claims description 58
- 230000008569 process Effects 0.000 claims description 46
- 238000010438 heat treatment Methods 0.000 claims description 43
- 238000005496 tempering Methods 0.000 claims description 38
- 239000000463 material Substances 0.000 claims description 17
- 229910052757 nitrogen Inorganic materials 0.000 claims description 15
- 239000002994 raw material Substances 0.000 claims description 13
- 229910052719 titanium Inorganic materials 0.000 claims description 13
- 238000005096 rolling process Methods 0.000 claims description 11
- 239000012535 impurity Substances 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 claims description 10
- 229910052717 sulfur Inorganic materials 0.000 claims description 8
- 229910052782 aluminium Inorganic materials 0.000 claims description 7
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- 238000001816 cooling Methods 0.000 claims description 6
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- 229910052721 tungsten Inorganic materials 0.000 claims description 4
- 235000019589 hardness Nutrition 0.000 description 42
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- 238000005452 bending Methods 0.000 description 14
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- 230000007704 transition Effects 0.000 description 7
- 238000003466 welding Methods 0.000 description 7
- 229910052802 copper Inorganic materials 0.000 description 6
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- 150000001247 metal acetylides Chemical class 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 238000005422 blasting Methods 0.000 description 3
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- 239000007787 solid Substances 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
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Description
本発明は、自動車等の車両に使用されるスタビライザに係り、とくに高強度中空スタビライザ用として好適な電縫鋼管および高強度中空スタビライザの製造方法に関する。なお、本発明でいう「高強度」とは、焼入れ焼戻処理後の硬さが、肉厚方向平均でＨＶ400以上である場合をいうものとする。 The present invention relates to a stabilizer used for a vehicle such as an automobile, and more particularly, to an electric-resistance-welded steel pipe suitable for a high-strength hollow stabilizer and a method for manufacturing a high-strength hollow stabilizer. The “high strength” in the present invention refers to the case where the hardness after quenching and tempering is HV400 or more in the thickness direction average.
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、継目無鋼管や電縫鋼管等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. Recently, however, 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 seamless steel pipes, ERW steel pipes, etc. has also been considered for stabilizers. Yes.
中空スタビライザは、通常、素材である鋼管を冷間で所定の寸法形状に曲げ成形したのち、焼入れ処理あるいは焼入れ焼戻処理を施して製造されている。
このような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、素材として使用する鋼管には従来以上に優れた強度靭性を有すること、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できるための十分な焼入れ性を有すること、などが要求される。
The hollow stabilizer is usually manufactured by bending a steel pipe, which is a raw material, into a predetermined dimensional shape in a cold state and then performing a quenching process or a quenching and tempering process.
Such a hollow stabilizer greatly contributes to the weight reduction of the vehicle body, but since the cross-sectional area is greatly reduced compared to a solid stabilizer, the steel pipe used as a material has higher strength and toughness than before, complicated It is required to have excellent bending workability so that it can be processed into a simple shape, and to have 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、Ｐ、Ｓ、Alの適正量を含み、さらに、Ｎ＋Ｏ：200ppm以下、Ti：４〜10×（Ｎ＋Ｏ）％、Ｂ：0.0005〜0.009％を含み、さらに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。また、特許文献２には、Ｃ、Si、Mn、Cr、Ｐ、Ｓ、Alの適正量を含み、さらに、Ｎ＋Ｏ：200ppm以下、Ti：４〜12×（Ｎ＋Ｏ）％、Ｂ：0.0005〜0.009％を含み、さらに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中空スタビライザ用電縫鋼管用鋼が提案されている。これらの技術によれば、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。 In response to such a requirement, for example, Patent Document 1 includes appropriate amounts of C, Si, Mn, Cr, P, S, and Al, and further N + O: 200 ppm or less, Ti: 4 to 10 × (N + O) % B: comprises from 0.0005 to 0.009%, further C, Si, Mn, and Cr content, the ideal critical diameter D I at least 1.0in, using the adjusted slab so Ceq is 0.48% or less, heat There has been proposed a method for producing a steel for an electric-welded steel pipe for a hollow stabilizer, which is rolled by rolling and adjusted to a winding temperature of 570 to 690 ° C. Patent Document 2 includes appropriate amounts of C, Si, Mn, Cr, P, S, and Al, and further includes N + O: 200 ppm or less, Ti: 4 to 12 × (N + O)%, and B: 0.0005 to 0.009. % include further C, Si, Mn, and Cr content, the ideal critical diameter D I at least 1.0in, Ceq is steel for electric resistance welded steel pipe for a hollow stabilizer was adjusted to 0.48% or less has been proposed . According to these techniques, it is said that an electric resistance welded steel pipe having good mechanical properties and heat treatment characteristics can be manufactured, and a highly reliable hollow stabilizer can be manufactured.
また、特許文献３には、Ｃ、Si、Mn、Ｐ、Ｓの適正量と、Ti：0.020〜0.050％、Ｂ：0.0005〜0.0050％を含み、さらにCr：0.20〜0.50％、Mo：0.5％以下、Nb：0.015〜0.050％のうちの１種以上、あるいはさらにCa：0.0050％以下を含む鋼を素材として製造された電縫鋼管に850〜950℃でノルマライズ処理を施した後、焼入れする、ドアインパクトビーム、スタビライザ等に好適な高強度高延性電縫鋼管の製造方法が提案されている。 Patent Document 3 includes appropriate amounts of C, Si, Mn, P, and S, Ti: 0.020 to 0.050%, B: 0.0005 to 0.0050%, Cr: 0.20 to 0.50%, Mo: 0.5% Hereinafter, an ERW steel pipe manufactured using steel containing Nb: 0.015 to 0.050% or more and further containing Ca: 0.0050% or less is subjected to normalization treatment at 850 to 950 ° C and then quenched. A method of manufacturing a high-strength, high-ductility electric resistance welded steel pipe suitable for door impact beams, stabilizers, and the like has been proposed.
また、特許文献４には、Ｃ、Si、Mn、Alの適正量と、Cr：0.10〜1.00％、Mo：0.005〜1.00％、Ti：0.001〜0.02％、Ｂ：0.0005〜0.0050％、Ｎ：0.0010〜0.0100％を含み、さらにＮ／14＜Ti／47.9を満足し、あるいはさらに理想臨界直径Ｄi が1.0in以上となるように調整した組成を有する中空スタビライザ用電縫溶接鋼管が提案されている。この技術によれば、母材と電縫溶接部との硬度差が少ない電縫溶接鋼管が得られ、疲労耐久性が向上した中空スタビライザが製造できるとしている。
最近では自動車部品への要求性能がさらに高くなる傾向であり、中空スタビライザには耐久性を高めるため更なる高い疲労強度を具備することが熱望されている。しかし、特許文献１〜４に記載された従来組成の電縫鋼管を素材として用いた中空スタビライザでは、その要望に十分に対応できないという問題があった。というのは、疲労強度を高くするために、特許文献１〜４に記載された従来組成の範囲内でＣ含有量を増加したり、あるいは焼戻温度を低温としたりして焼入れ焼戻処理後の強度（硬さ）を高くすると、靭性が著しく劣化する。またとくに、鋼管に冷間で曲げ成形加工を施し所定の寸法形状に成形した中空スタビライザでは、焼入れ処理に際して通電加熱すると、曲げ部の偏肉部に電流が多く流れ高温に加熱されるという現象がある。このため、曲げ部では焼入れ処理後の強度（硬さ）が高くなるが、靭性が著しく劣化する。このようなことから、スタビライザ製造に際し、焼入れ焼戻処理後の強度（硬さ）が高くなっても優れた靭性が確保できる電縫鋼管、さらには焼入れ処理時に高温に加熱されても、優れた靭性が確保できる電縫鋼管が要望されている。 Recently, there is a tendency that required performance for automobile parts is further increased, and it is eagerly desired that hollow stabilizers have higher fatigue strength in order to enhance durability. However, the hollow stabilizer using the conventional electric resistance welded steel pipe described in Patent Documents 1 to 4 has a problem that it cannot sufficiently meet the demand. For increasing the fatigue strength, the C content is increased within the range of the conventional compositions described in Patent Documents 1 to 4, or the tempering temperature is lowered, and after quenching and tempering treatment. When the strength (hardness) is increased, the toughness is remarkably deteriorated. In particular, in hollow stabilizers that have been cold-formed into a steel pipe and formed into a predetermined size and shape, when energized and heated during the quenching process, there is a phenomenon in which a large amount of current flows in the uneven thickness portion of the bent portion and is heated to a high temperature. is there. For this reason, the strength (hardness) after the quenching treatment is increased in the bent portion, but the toughness is remarkably deteriorated. For this reason, when manufacturing stabilizers, even when the strength (hardness) after quenching and tempering is increased, an electric resistance steel pipe that can ensure excellent toughness, and even when heated to a high temperature during quenching, it is excellent. There is a demand for an ERW steel pipe that can ensure toughness.
本発明は、このような従来技術の問題を有利に解決し、焼入れ焼戻処理後に、肉厚方向の平均硬さＨＶがＨＶ400以上の高強度で、かつシャルピー衝撃試験の破面遷移温度vTrs(℃)が次式vTrs＜20／67×（ＨＶ−400）−120を満足する高靭性を有し、強度−靭性バランスに優れた、高強度中空スタビライザ用として好適な電縫鋼管および高強度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。 The present invention advantageously solves such problems of the prior art, and after quenching and tempering treatment, the average hardness HV in the thickness direction is high strength of HV400 or more, and the fracture surface transition temperature vTrs ( ° C) has high toughness satisfying the following formula vTrs <20/67 × (HV-400) -120 and has excellent strength-toughness balance, suitable for high-strength hollow stabilizer and high-strength hollow It aims at proposing the manufacturing method of a stabilizer.
なお、{20／67×（ＨＶ−400）−120}は肉厚方向平均硬さＨＶがＨＶ400以上である従来技術相当材のvTrs（℃）の最低値を意味する。 In addition, {20/67 × (HV−400) −120} means the minimum value of vTrs (° C.) of the prior art equivalent material whose thickness direction average hardness HV is HV400 or more.
本発明者らは、上記した課題を達成するため、焼入れ焼戻処理後の強度（硬さ）と靭性に及ぼす各種要因の影響について鋭意検討した。その結果、Ｗを適正量含有させた鋼管組成とすることにより、焼入れ処理時に加熱温度を1000℃という高温に加熱したのち急冷しても、焼入れ焼戻処理後の硬さがＨＶ400以上の高強度でかつvTrsが従来技術相当材のvTrsの；最低値{20／67×（ＨＶ−400）−120}より低温の優れた靭性を確保でき、強度−靭性バランスを顕著に改善できることを見出した。 In order to achieve the above-described problems, the present inventors diligently studied the influence of various factors on strength (hardness) and toughness after quenching and tempering. As a result, by adopting a steel pipe composition containing an appropriate amount of W, the hardness after quenching and tempering treatment is high strength of HV400 or higher even if it is rapidly cooled after being heated to a high temperature of 1000 ° C during quenching treatment. And vTrs was found to be able to secure excellent toughness at a lower temperature than the lowest value {20/67 × (HV-400) -120} of vTrs of the prior art equivalent material, and to significantly improve the strength-toughness balance.
まず、本発明の基礎になった実験結果について説明する。
質量％で、0.25％Ｃ−0.2％Si−0.5％Mn−0.024％Ti−0.002％Ｂを基本組成とし、あるいはさらに、Cu、Ni、Cr、Mo、Ｗ等の合金元素の含有量を種々変化させて含む各種熱延鋼板(板厚：5mm)を素材として、冷間で管状に成形したのち、突合せ部分を高周波電気抵抗溶接して各種電縫鋼管（25.4mmφ×肉厚5mm）とした。これら電縫鋼管に、通電加熱により外表面の温度が1000℃となるように加熱したのち水槽に浸漬する焼入れ処理を施し、ついで種々の温度で20min間加熱する焼戻処理を施した。焼戻処理済み電縫鋼管から試験片を採取し、断面硬さの測定および鋼管長さ方向を試験片長さ方向とする２mmＶノッチ試験片（試験片厚さ2.5mm）を用いたシャルピー衝撃試験を実施し、硬さＨＶ（肉厚方向平均値）および破面遷移温度vTrsを求め、強度、靭性を評価した。得られた結果をＨＶ−vTrsの関係として図１に示す。
First, the experimental results on which the present invention is based will be described.
Based on mass%, 0.25% C-0.2% Si-0.5% Mn-0.024% Ti-0.002% B is used as the basic composition, or the content of alloying elements such as Cu, Ni, Cr, Mo, W, etc. is varied. The various hot-rolled steel sheets (thickness: 5 mm) included were formed into cold tubular shapes, and then the butt portions were subjected to high-frequency electric resistance welding to form various ERW steel pipes (25.4 mmφ × wall thickness 5 mm). These electric resistance welded steel pipes were subjected to a quenching treatment in which the outer surface was heated to 1000 ° C. by energization heating and then immersed in a water tank, and then tempered by heating at various temperatures for 20 minutes. Specimens were taken from tempered ERW steel pipes, cross-sectional hardness measurements, and Charpy impact tests using 2 mm V notch specimens (test specimen thickness 2.5 mm) with the steel pipe length direction as the specimen length direction. The hardness HV (average value in the thickness direction) and the fracture surface transition temperature vTrs were determined, and the strength and toughness were evaluated. The obtained results are shown in FIG. 1 as the relationship of HV-vTrs.
図１から、基本組成、および基本組成にCu、Ni、Cr、Moをそれぞれ添加した電縫鋼管のvTrsはいずれもＨＶ400以上では従来技術相当材のvTrsの最低値：{20／67×（ＨＶ−400）−120}より高温であるのに対し、基本組成にＷを含む電縫鋼管のvTrsは{20／67×（ＨＶ−400）−120}よりすべての硬さＨＶにわたって低温側となっており、Ｗを適正量含有することにより、肉厚方向平均硬さＨＶがＨＶ400以上の高強度においても、強度−靭性バランスが顕著に改善されることがわかる。例えば、同一硬さ（ＨＶ450）で比較すると、従来技術相当材のvTrsの最低値は−105℃であるのに対し、基本組成にＷ（：0.3質量％）含む電縫鋼管のvTrsは−118℃である。 From FIG. 1, the vTrs of the ERW steel pipe with the basic composition and Cu, Ni, Cr, and Mo added to the basic composition are all HV400 or more, and the minimum value of vTrs of the conventional equivalent material: {20/67 × (HV -400) -120}, whereas the vTrs of ERW steel pipes containing W in the basic composition is on the low temperature side for all hardnesses HV than {20/67 × (HV-400) -120}. It can be seen that, by containing an appropriate amount of W, the strength-toughness balance is remarkably improved even at high strength where the thickness direction average hardness HV is HV400 or more. For example, when the same hardness (HV450) is compared, the lowest value of vTrs of the equivalent material of the prior art is −105 ° C., whereas the vTrs of the ERW steel pipe containing W (: 0.3 mass%) in the basic composition is −118. ° C.
また、質量％で、0.25％Ｃ−0.2％Si−0.5％Mn−0.024％Ti−0.002％Ｂを基本組成とし、さらに、Ｗを無添加、又はＷを0.001〜1.5％の範囲で含む各熱延鋼板(板厚：5mm)を素材として、冷間で管状に成形したのち、突合せ部分を高周波電気抵抗溶接して電縫鋼管（25.4mmφ×肉厚5mm）とした。通電加熱により外表面をＴ：800〜1050℃の各温度に加熱したのち水槽に浸漬する焼入れ処理を施し、ついで種々の温度で20min間加熱する焼戻処理を施した。焼戻処理済み電縫鋼管から試験片を採取し、断面硬さの測定および鋼管長さ方向を試験片長さ方向とする２mmＶノッチ試験片（厚さ：2.5mm）を用いたシャルピー衝撃試験を実施し、硬さＨＶ（肉厚方向平均値）および破面遷移温度vTrsを求めた。得られた値から強度（硬さ）と靭性の関係を求め、各電縫鋼管の硬さがＨＶ450となる場合の靭性vTrsを推定した。得られた結果を、焼入れ処理時の加熱温度Ｔと破面遷移温度vTrsの関係で図２に示す。 In addition, each heat containing, in mass%, 0.25% C-0.2% Si-0.5% Mn-0.024% Ti-0.002% B and further containing no W or 0.001 to 1.5% of W. Using a rolled steel sheet (thickness: 5 mm) as a raw material, it was cold-formed into a tubular shape, and then the butt portion was subjected to high-frequency electrical resistance welding to form an electric resistance welded steel pipe (25.4 mmφ × wall thickness 5 mm). The outer surface was heated to each temperature of T: 800 to 1050 ° C. by energization heating, and then subjected to a quenching treatment in which it was immersed in a water tank, followed by a tempering treatment in which heating was performed at various temperatures for 20 minutes. Specimens were taken from tempered ERW steel pipes, cross-sectional hardness measurements, and Charpy impact tests using 2 mm V notch specimens (thickness: 2.5 mm) with the steel pipe length direction as the specimen length direction. The hardness HV (average value in the thickness direction) and the fracture surface transition temperature vTrs were determined. The relationship between strength (hardness) and toughness was obtained from the obtained values, and toughness vTrs was estimated when the hardness of each ERW steel pipe was HV450. The obtained results are shown in FIG. 2 in relation to the heating temperature T during the quenching process and the fracture surface transition temperature vTrs.
図２から、破面遷移温度vTrs：−110℃が得られる、焼入れ処理の加熱温度ＴとＷ含有量との関係を求め、図３に示す。
図３から、下記（２）式
（Ｔ／140）−7.84 ≦ log（Ｗ） …………（２）
ここで、Ｔ：焼入れ処理時の加熱温度(℃)、
Ｗ：Ｗ含有量（質量％）
を満足するように、Ｗ含有量に応じて焼入れ処理時の加熱温度（均一に加熱されない場合には、最も高温に加熱される個所の温度）を調整するか、あるいは焼入れ処理時の加熱温度（均一に加熱されない場合には、最も高温に加熱される個所の温度）に応じてＷ含有量を調整することにより、ＨＶ450という高硬度にもかかわらず、vTrs：−110℃以下の高靭性が得られ、Ｗ無添加材に比較して靭性が顕著に改善されることがわかる。
From FIG. 2, the relationship between the heating temperature T and the W content in the quenching treatment at which the fracture surface transition temperature vTrs: −110 ° C. is obtained is shown in FIG. 3.
From Fig. 3, the following equation (2)
(T / 140) -7.84 ≤ log (W) (2)
Here, T: heating temperature (° C) during quenching,
W: W content (% by mass)
In order to satisfy the above, the heating temperature at the time of quenching treatment is adjusted according to the W content (the temperature at the highest temperature if not uniformly heated), or the heating temperature at the time of quenching treatment ( If it is not uniformly heated, the toughness of vTrs: -110 ° C or less can be obtained by adjusting the W content according to the temperature of the portion heated to the highest temperature) despite the high hardness of HV450. It can be seen that the toughness is remarkably improved as compared with the W-free material.
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。すなわち、本発明の要旨はつぎのとおりである。
（１）質量％で、Ｃ：0.20〜0.38％、Si：0.10〜0.50％、Mn：0.30〜2.00％、Al：0.01〜0.10％、Ｗ：0.01〜1.50％、Ｂ：0.0005〜0.0050％、を含みさらにTi、ＮをTi：0.001〜0.04％、N：0.0010〜0.0100％の範囲でかつ次（１）式
Ｎ／14 ＜ Ti／47.9 …………（１）
（ここで、Ｎ，Ti：各元素の含有量（質量％））
を満足するように含有し、残部Feおよび不可避的不純物からなる組成を有し、焼入れ焼戻処理後の強度−靭性バランスに優れることを特徴とする高強度中空スタビライザー用電縫鋼管。
（２）（１）において、前記組成に加えてさらに、質量％で、Cr：1.0％以下、Mo：1.0％以下のうちから選ばれた１種又は２種を含有する組成とすることを特徴とする高強度中空スタビライザー用電縫鋼管。
（３）（１）または（２）において、前記組成に加えてさらに、質量％で、Nb：0.2％以下、Ｖ：0.2％以下のうちから選ばれた１種又は２種を含有する組成とすることを特徴とする高強度中空スタビライザー用電縫鋼管。
（４）（１）ないし（３）のいずれかにおいて、前記組成に加えてさらに、質量％で、Ni：1.0％以下、Cu：1.0％以下のうちから選ばれた１種又は２種を含有する組成とすることを特徴とする高強度中空スタビライザー用電縫鋼管。
（５）（１）ないし（４）のいずれかにおいて、前記組成が、不可避的不純物として、質量％で、Ｐ：0.020％以下、Ｓ：0.010％以下、Ｏ：0.005％以下を含む組成であることを特徴とする高強度中空スタビライザー用電縫鋼管。
（６）（１）ないし（５）のいずれかに記載の電縫鋼管を素材とし、該素材に成形加工と、焼入れ焼戻処理を施してなる高強度中空スタビライザー。
（７）電縫鋼管を素材とし、該素材に所定のスタビライザー形状に成形する成形加工を施す成形工程と、該成形された素材に、焼入れ処理あるいはさらに焼戻処理を施す熱処理工程を順次施す中空スタビライザーの製造方法において、前記電縫鋼管を、質量％で、Ｃ：0.20〜0.38％、Si：0.05〜0.50％、Mn：0.30〜2.00％、Al：0.01〜0.10％、Ｗ：0.01〜1.50％、Ｂ：0.0005〜0.0050％、を含みさらにTi、ＮをTi：0.001〜0.04％、N：0.0010〜0.0100％の範囲でかつ次（１）式
Ｎ／14 ＜ Ti／47.9 …………（１）
（ここで、Ｎ，Ti：各元素の含有量（質量％））
を満足するように含有し、残部Feおよび不可避的不純物からなる組成を有する鋼管とし、前記焼入れ処理を、Ａc３変態点以上でかつ中空スタビライザー全体で最も高い温度に加熱される個所の温度Ｔが次（２）式
（Ｔ／140）−7.84 ≦ log（Ｗ） …………（２）
（ここで、Ｔ：焼入れ処理時の加熱に際し、中空スタビライザー全体で最も高い温度に加
熱される個所の温度(℃)、Ｗ：Ｗの含有量（質量％））
を満足するように加熱したのち急冷する処理とし、前記焼戻処理を、350℃以下の温度に加熱し冷却する処理として、前記中空スタビライザーの硬さを所望の硬さに調整することを特徴とする高強度中空スタビライザーの製造方法。
（８）（７）において、前記組成に加えてさらに、質量％で、Cr：1.0％以下、Mo：1.0％以下のうちから選ばれた１種又は２種を含有する組成とすることを特徴とする高強度中空スタビライザーの製造方法。
（９）（７）又は（８）において、前記組成に加えてさらに、質量％で、Nb：1.0％以下、Ｖ：1.0％以下のうちから選ばれた１種又は２種を含有する組成とすることを特徴とする高強度中空スタビライザーの製造方法。
（１０）（７）ないし（９）のいずれかにおいて、前記組成に加えてさらに、質量％で、Ni：1.0％以下、Cu：1.0％以下のうちから選ばれた１種又は２種を含有する組成とすることを特徴とする高強度中空スタビライザーの製造方法。
（１１）（７）ないし（１０）のいずれかにおいて、前記組成が、不可避的不純物として、質量％で、Ｐ：0.020％以下、Ｓ：0.010％以下、Ｏ：0.005％以下を含む組成であることを特徴とする高強度中空スタビライザーの製造方法。
（１２）（７）ないし（１１）のいずれかにおいて、前記素材が、縮径圧延を施された電縫鋼管であることを特徴とする高強度中空スタビライザーの製造方法。
（１３）（７）ないし（１２）のいずれかにおいて、前記焼入れ処理における加熱が、通電加熱であることを特徴とする高強度中空スタビライザーの製造方法。
（１４）（７）ないし（１３）のいずれかにおいて、前記焼入れ処理後に、または前記焼戻処理後に、ショットブラスト処理を施すことを特徴とする高強度中空スタビライザーの製造方法。
The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: 0.20 to 0.38%, Si: 0.10 to 0.50%, Mn: 0.30 to 2.00%, Al: 0.01 to 0.10%, W: 0.01 to 1.50%, B: 0.0005 to 0.0050% In addition, Ti and N are within the range of Ti: 0.001 to 0.04%, N: 0.0010 to 0.0100%, and the following formula (1)
N / 14 <Ti / 47.9 (1)
(N, Ti: content of each element (mass%))
An electric resistance steel pipe for a high-strength hollow stabilizer having a composition composed of the balance Fe and inevitable impurities and having an excellent strength-toughness balance after quenching and tempering.
(2) In (1), in addition to the above composition, the composition further contains, by mass%, one or two selected from Cr: 1.0% or less and Mo: 1.0% or less. ERW steel pipe for high-strength hollow stabilizer.
(3) In (1) or (2), in addition to the above composition, the composition further contains, by mass%, Nb: 0.2% or less, V: 0.2% or less, one or two selected from An electric-welded steel pipe for a high-strength hollow stabilizer.
(4) In any one of (1) to (3), in addition to the above composition, the composition further contains one or two kinds selected from Ni: 1.0% or less and Cu: 1.0% or less by mass%. An electric resistance steel pipe for a high-strength hollow stabilizer, characterized by comprising
(5) In any one of (1) to (4), the composition is a composition containing, as inevitable impurities, mass%, P: 0.020% or less, S: 0.010% or less, and O: 0.005% or less. ERW steel pipe for high-strength hollow stabilizer.
(6) A high-strength hollow stabilizer obtained by using the ERW steel pipe according to any one of (1) to (5) as a raw material, and subjecting the raw material to a forming process and a quenching and tempering process.
(7) A hollow in which an electric-welded steel pipe is used as a raw material, and a molding process is performed in which the raw material is molded into a predetermined stabilizer shape, and a heat treatment process in which the molded material is subjected to quenching or further tempering. In the manufacturing method of a stabilizer, the said ERW steel pipe is mass: C: 0.20 to 0.38%, Si: 0.05 to 0.50%, Mn: 0.30 to 2.00%, Al: 0.01 to 0.10%, W: 0.01 to 1.50% , B: 0.0005 to 0.0050%, and Ti and N in the range of Ti: 0.001 to 0.04%, N: 0.0010 to 0.0100%, and the following formula (1)
N / 14 <Ti / 47.9 (1)
(N, Ti: content of each element (mass%))
And a steel pipe having a composition comprising the balance Fe and inevitable impurities, and the quenching treatment is performed at a temperature T at a location where the temperature is higher than the Ac 3 transformation point and the highest temperature in the entire hollow stabilizer. Next formula (2)
(T / 140) -7.84 ≤ log (W) (2)
(Here, T: the temperature at which the hollow stabilizer is heated to the highest temperature (° C.) and W: W content (mass%) during heating during quenching)
It is characterized by adjusting the hardness of the hollow stabilizer to a desired hardness as a process of heating and cooling so as to satisfy the above, and as a process of heating and cooling the tempering process to a temperature of 350 ° C. or lower. To manufacture a high-strength hollow stabilizer.
(8) In (7), in addition to the above composition, the composition further contains, by mass%, one or two selected from Cr: 1.0% or less and Mo: 1.0% or less. A method for producing a high-strength hollow stabilizer.
(9) In (7) or (8), in addition to the above composition, the composition further contains, in mass%, one or two selected from Nb: 1.0% or less and V: 1.0% or less A method for producing a high-strength hollow stabilizer characterized by comprising:
(10) In any one of (7) to (9), in addition to the above-described composition, the composition further contains one or two kinds selected from Ni: 1.0% or less and Cu: 1.0% or less by mass%. The manufacturing method of the high intensity | strength hollow stabilizer characterized by the above-mentioned.
(11) In any one of (7) to (10), the composition is a composition containing, as inevitable impurities, mass%, P: 0.020% or less, S: 0.010% or less, and O: 0.005% or less. A method for producing a high-strength hollow stabilizer characterized by the above.
(12) The method for producing a high-strength hollow stabilizer according to any one of (7) to (11), wherein the material is an ERW steel pipe subjected to reduced diameter rolling.
(13) The method for producing a high-strength hollow stabilizer according to any one of (7) to (12), wherein the heating in the quenching process is electric heating.
(14) The method for producing a high-strength hollow stabilizer according to any one of (7) to (13), wherein shot blasting is performed after the quenching process or after the tempering process.
本発明によれば、従来では得られなかったような、高強度（高硬度）でかつ高靭性を有し、強度（硬さ）−靭性バランスに優れた中空スタビライザを容易にしかも安定して製造でき、産業上格段の効果を奏する。また、本発明にしたがって製造された中空スタビライザは、各部における機械的特性のばらつきが少なく、しかも高い疲労強度を有し、自動車部品の耐久性向上に寄与するという効果もある。 According to the present invention, a hollow stabilizer having high strength (high hardness) and high toughness, and having an excellent strength (hardness) -toughness balance, which has not been obtained in the past, can be easily and stably produced. Yes, and it has a remarkable industrial effect. In addition, the hollow stabilizer manufactured according to the present invention has an effect that there is little variation in mechanical properties in each part, high fatigue strength, and contribution to improving the durability of automobile parts.
まず、本発明電縫鋼管の組成限定理由について説明する。なお、以下、質量％は単に％で記す。
Ｃ：0.20〜0.38％
Ｃは、固溶して、あるいは炭化物、炭窒化物として析出して鋼材の強度を増加させる元素であり、本発明では素材である鋼管の強度や、製品である中空スタビライザの焼入れ処理後硬さを所定値以上とするために、0.20％以上の含有を必要とする。一方、0.38％を超える含有は、焼入れ処理後の靭性が低下する。このため、Ｃは、0.20〜0.38％の範囲に限定した。なお、好ましくは強度−靭性バランスの観点から0.24〜0.35％である。
First, the reasons for limiting the composition of the ERW steel pipe of the present invention will be described. Hereinafter, the mass% is simply expressed as%.
C: 0.20 ~ 0.38%
C is an element that increases the strength of the steel material by solid solution or precipitates as a carbide or carbonitride. In the present invention, the strength of the steel pipe as the material and the hardness after quenching of the hollow stabilizer as the product In order to make the content more than the predetermined value, the content of 0.20% or more is required. On the other hand, if the content exceeds 0.38%, the toughness after the quenching treatment decreases. For this reason, C was limited to the range of 0.20 to 0.38%. In addition, Preferably it is 0.24 to 0.35% from a viewpoint of strength-toughness balance.
Si：0.05〜0.50％
Siは、脱酸剤として作用するとともに、固溶して鋼の強度を増加させる元素であり、本発明では0.05％以上の含有を必要とするが、0.50％を超えて含有しても、脱酸剤としての効果が飽和するうえ、電縫溶接時に介在物を生じやすく、かえって電縫溶接部の健全性に悪影響を及ぼす。このため、Siは0.05〜0.50％の範囲に限定した。なお、好ましくは0.10〜0.30％である。
Si: 0.05-0.50%
Si is an element that acts as a deoxidizer and increases the strength of the steel by solid solution. In the present invention, it needs to be contained in an amount of 0.05% or more. The effect as an acid agent is saturated, and inclusions are easily generated during ERW welding, which adversely affects the soundness of ERW welds. For this reason, Si was limited to the range of 0.05 to 0.50%. In addition, Preferably it is 0.10 to 0.30%.
Mn：0.30〜2.00％
Mnは、固溶して、あるいは焼入れ性の増加を介して、鋼材の強度を増加させる元素であり、本発明では素材である鋼管の強度や、製品である中空スタビライザの焼入れ処理後硬さを所定値以上とするために、0.30％以上の含有を必要とする。一方、2.00％を超えて含有すると、残留オーステナイト（以下、残留γともいう）が生じやすくなり焼戻後の靭性が低下する。このため、Mnは0.30〜2.00％の範囲に限定した。なお、好ましくは、0.3〜1.0％である。
Mn: 0.30 to 2.00%
Mn is an element that increases the strength of the steel material through solid solution or through an increase in hardenability.In the present invention, the strength of the steel pipe that is the material and the hardness after quenching of the hollow stabilizer that is the product are determined. In order to make it a predetermined value or more, it is necessary to contain 0.30% or more. On the other hand, if the content exceeds 2.00%, retained austenite (hereinafter also referred to as residual γ) is likely to occur, and the toughness after tempering decreases. For this reason, Mn was limited to the range of 0.30 to 2.00%. In addition, Preferably, it is 0.3 to 1.0%.
Al：0.01〜0.10％
Alは、脱酸剤として作用するとともに、AlNとしてＮを固定し、焼入れ性向上に有効な固溶Ｂを所定量以上確保することに有効に作用する。このような効果を得るためには、0.01％以上の含有を必要とするが、0.10％を超えて含有すると、介在物量が増加し、疲労寿命を低下させる場合がある。このため、Alは0.01〜0.10％の範囲に限定した。なお、好ましくは0.02〜0.04％である。
Al: 0.01-0.10%
Al acts as a deoxidizing agent and also fixes N as AlN and effectively acts to secure a predetermined amount or more of solid solution B effective for improving hardenability. In order to obtain such an effect, the content of 0.01% or more is required. However, if the content exceeds 0.10%, the amount of inclusions may increase and the fatigue life may be reduced. For this reason, Al was limited to the range of 0.01 to 0.10%. In addition, Preferably it is 0.02 to 0.04%.
Ｗ：0.01〜1.50％
Ｗは、鋼の焼入れ性を高めるとともに、焼入れ焼戻処理後の靭性を向上させ、強度（硬さ）−靭性バランスを向上させる本発明で最も重要な元素である。このような効果を得るためには0.01％以上の含有を必要とする。一方、1.50％を超えて含有しても、効果が飽和し含有量に見合う効果を期待できず経済的に不利となる。このため、Ｗは0.01〜1.50％の範囲に限定した。なお、中空スタビライザの焼入れ処理時の加熱温度Ｔが限定される場合には、次（２）式
（Ｔ／140）−7.84 ≦ log（Ｗ） …………（２）
（ここで、Ｔ：焼入れ処理時の加熱に際し、中空スタビライザー全体で最も高い温度に加熱される個所の温度(℃)、Ｗ：Ｗの含有量（質量％））
を満足する下限のＷ含有量とすることが好ましい。
W: 0.01 to 1.50%
W is the most important element in the present invention that enhances the hardenability of steel, improves the toughness after quenching and tempering treatment, and improves the strength (hardness) -toughness balance. In order to acquire such an effect, 0.01% or more of content is required. On the other hand, if the content exceeds 1.50%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, W was limited to the range of 0.01 to 1.50%. In addition, when the heating temperature T at the time of quenching treatment of the hollow stabilizer is limited, the following equation (2)
(T / 140) -7.84 ≤ log (W) (2)
(Here, T: the temperature at which the hollow stabilizer is heated to the highest temperature (° C.) and W: W content (mass%) during heating during quenching)
Preferably, the lower limit of the W content is satisfied.
Ｂ：0.0005〜0.0050％
Ｂは、鋼の焼入れ性を向上させ、中空スタビライザの焼入れ処理後の硬さを所望の硬さにするとともに、粒界を強化して焼割れの発生を防止する有効な元素である。このような効果を得るために0.0005％以上の含有を必要とする。一方、0.0050％を超えて含有しても、効果が飽和し含有量に見合う効果が期待できず経済的に不利となるとともに、粗大なＢ含有析出物が生成し靭性が低下する場合がある。このため、Ｂは0.0005〜0.0050％の範囲に限定した。さらに好ましくは0.0010〜0.0030％である。
B: 0.0005-0.0050%
B is an effective element that improves the hardenability of the steel, makes the hardness of the hollow stabilizer after the quenching treatment a desired hardness, and strengthens the grain boundary to prevent the occurrence of quenching cracks. In order to acquire such an effect, 0.0005% or more needs to be contained. On the other hand, even if the content exceeds 0.0050%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous, and coarse B-containing precipitates are formed and the toughness may be lowered. For this reason, B was limited to the range of 0.0005 to 0.0050%. More preferably, it is 0.0010 to 0.0030%.
Ti：0.001〜0.04％
Tiは、Ｎと結合し、焼入れ性向上に有効な固溶Ｂを所定量以上確保することに有効に作用するとともに、微細な炭化物を生成して溶接時、熱処理時の結晶粒粗大化を抑制し、靭性を向上させる作用を有する元素である。このような効果を得るためには0.001％以上の含有を必要とする。一方、0.04％を超える含有は、介在物量が増加して靭性が低下する場合がある。このため、Tiは0.001〜0.04％の範囲に限定した。
Ti: 0.001 to 0.04%
Ti combines with N and works effectively to secure a predetermined amount or more of solid solution B effective in improving hardenability, and generates fine carbides to suppress grain coarsening during welding and heat treatment. It is an element that has the effect of improving toughness. In order to obtain such an effect, a content of 0.001% or more is required. On the other hand, if the content exceeds 0.04%, the amount of inclusions may increase and the toughness may decrease. For this reason, Ti was limited to the range of 0.001 to 0.04%.
N：0.0010〜0.0100％
Ｎは、焼戻時に窒化物、炭窒化物として析出し、焼戻処理後に所望の強度（硬さ）を確保するために有効に作用する。このような効果を得るためには0.0010％以上の含有を必要とするが、0.0100％を超える含有は窒化物、炭窒化物の粗大化を促進して、靭性、疲労寿命を低下させる場合がある。このため、Ｎは0.0010〜0.0100％の範囲に限定した。
N: 0.0010 to 0.0100%
N precipitates as nitrides and carbonitrides during tempering, and effectively acts to ensure a desired strength (hardness) after tempering. In order to obtain such an effect, the content of 0.0010% or more is required. However, if the content exceeds 0.0100%, the coarsening of nitrides and carbonitrides is promoted, and the toughness and fatigue life may be reduced. . For this reason, N was limited to the range of 0.0010 to 0.0100%.
本発明では、Ti、Ｎは、上記した含有量範囲を満足しかつ次（１）式
Ｎ／14 ＜ Ti／47.9…………（１）
（ここで、Ｎ、Ti：各元素の含有量（質量％））
を満足する範囲に限定する。Ti、Ｎ含有量が、（１）式を満足しない場合には、固溶Ｂが減少して焼入性が低下する。
In the present invention, Ti and N satisfy the above-described content range and the following formula (1) N / 14 <Ti / 47.9 (1)
(N, Ti: content of each element (mass%))
Is limited to a range satisfying. If the Ti and N contents do not satisfy the formula (1), the solid solution B is reduced and the hardenability is lowered.
本発明では、上記した基本成分に加えて、必要に応じて、Cr：1.0％以下、Mo：1.0％以下のうちから選ばれた１種又は２種、および／または、Nb：1.0％以下、Ｖ：1.0％以下のうちから選ばれた１種又は２種、および／または、Ni：1.0％以下、Cu：1.0％以下のうちから選ばれた１種又は２種を、選択して含有できる。
Cr：1.0％以下、Mo：1.0％以下のうちから選ばれた１種又は２種
Cr、Moはいずれも、鋼の焼入れ性を向上させるとともに、微細な炭化物を生成して強度を向上させる元素であり、必要に応じ選択して含有できる。このような効果はそれぞれCr：0.1％以上、Mo：0.1％以上の含有で顕著となる。一方、Cr：1.0％を超えて含有しても効果が飽和して含有量に見合う効果が期待できなくなり経済的に不利となることに加えて、電縫溶接時に介在物を生じやすくなり電縫溶接部の健全性が低下する。また、Mo：1.0％を超えて含有しても効果が飽和して含有量に見合う効果が期待できなくなり経済的に不利となることに加えて、粗大な炭化物を生成して靭性が低下する。このため、Cr：1.0％以下、Mo：1.0％以下にそれぞれ限定することが好ましい。なお、好ましくはCr：0.10〜0.50%、Mo：0.10〜0.50%である。
In the present invention, in addition to the above basic components, if necessary, one or two selected from Cr: 1.0% or less, Mo: 1.0% or less, and / or Nb: 1.0% or less, V: 1 or 2 types selected from 1.0% or less and / or 1 or 2 types selected from Ni: 1.0% or less and Cu: 1.0% or less can be selected and contained .
One or two selected from Cr: 1.0% or less, Mo: 1.0% or less
Both Cr and Mo are elements that improve the hardenability of the steel and generate fine carbides to improve the strength, and can be selected and contained as necessary. Such effects become remarkable when Cr: 0.1% or more and Mo: 0.1% or more are contained. On the other hand, even if Cr exceeds 1.0%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. In addition, inclusions are likely to occur during ERW welding, and ERW The soundness of the weld is reduced. Moreover, even if it contains more than 1.0% of Mo, the effect is saturated and an effect commensurate with the content cannot be expected and it becomes economically disadvantageous. In addition, coarse carbides are generated and toughness is lowered. For this reason, it is preferable to limit to Cr: 1.0% or less and Mo: 1.0% or less, respectively. Preferably, Cr: 0.10 to 0.50%, Mo: 0.10 to 0.50%.
Nb：1.0％以下、Ｖ：1.0％以下のうちから選ばれた１種又は２種
Nb、Ｖはいずれも、焼戻時に微細な炭化物を生成し強度増加に寄与する元素であり、必要に応じ選択して含有できる。このような効果はそれぞれNb：0.01％以上、Ｖ：0.01％以上の含有で顕著となる。一方、Nb：1.0％、Ｖ：1.0％をそれぞれ超えて含有しても、効果が飽和して含有量に見合う効果が期待できなくなり経済的に不利となる。このため、Nb：1.0％以下、Ｖ：1.0％以下にそれぞれ限定することが好ましい。なお、より好ましくはNb：0.012〜0.020%、Ｖ：0.012〜0.020%である。
One or two selected from Nb: 1.0% or less, V: 1.0% or less
Both Nb and V are elements that generate fine carbides during tempering and contribute to an increase in strength, and can be selected and contained as necessary. Such an effect becomes remarkable when Nb is 0.01% or more and V is 0.01% or more. On the other hand, even if it contains exceeding Nb: 1.0% and V: 1.0% respectively, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, it is preferable to limit to Nb: 1.0% or less and V: 1.0% or less, respectively. More preferably, Nb is 0.012 to 0.020% and V is 0.012 to 0.020%.
Ni：1.0％以下、Cu：1.0％以下のうちから選ばれた１種又は２種
Ni、Cuはいずれも、鋼の焼入れ性を向上させ、スタビライザの強度を増加させる元素であり、必要に応じ選択して含有できる。このような効果はそれぞれNi：0.1％以上、Cu：0.1％以上の含有で顕著となる。一方、Ni：1.0％、Cu：1.0％をそれぞれ超えて含有しても効果が飽和し、含有量に見合う効果が期待できなくなり経済的に不利となるとともに、加工性が低下する。このため、Ni：1.0％以下、Cu：1.0％以下にそれぞれ限定することが好ましい。なお、より好ましくはNi：0.25〜0.50%、Cu：0.25〜0.50%である。
One or two selected from Ni: 1.0% or less and Cu: 1.0% or less
Both Ni and Cu are elements that improve the hardenability of the steel and increase the strength of the stabilizer, and can be selected and contained as necessary. Such an effect becomes remarkable when Ni: 0.1% or more and Cu: 0.1% or more are contained. On the other hand, if the content exceeds Ni: 1.0% and Cu: 1.0%, the effect is saturated, an effect commensurate with the content cannot be expected, and it becomes economically disadvantageous, and the workability decreases. For this reason, it is preferable to limit to Ni: 1.0% or less and Cu: 1.0% or less, respectively. More preferably, Ni: 0.25 to 0.50%, Cu: 0.25 to 0.50%.
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る。不可避的不純物としては、Ｐ：0.020％以下、Ｓ：0.010％以下、Ｏ：0.005％以下に制限することが好ましい。
Ｐは、溶接割れ性、靭性に悪影響を及ぼす元素であり0.020％以下に低減することが好ましい。
Ｓは、鋼中では介在物（硫化物）として存在し、鋼管の加工性、靭性、疲労寿命等を低下させるとともに、再熱割れ感受性をも増大させるため、0.010％以下に低減することが好ましい。なお、より好ましくは0.005％以下である。
The balance other than the above components is Fe and inevitable impurities. Inevitable impurities are preferably limited to P: 0.020% or less, S: 0.010% or less, and O: 0.005% or less.
P is an element that adversely affects weld cracking and toughness, and is preferably reduced to 0.020% or less.
S is present as an inclusion (sulfide) in steel and decreases the workability, toughness, fatigue life, etc. of the steel pipe and also increases the reheat cracking susceptibility, so it is preferable to reduce it to 0.010% or less. . More preferably, it is 0.005% or less.
Ｏは、鋼中では介在物（酸化物）として存在し、鋼管の加工性、靭性、疲労寿命等を低下させるため、0.005％以下に低減することが好ましい。なお、より好ましくは0.002％以下である。
本発明電縫鋼管の製造方法は、上記した組成を有する鋼板を使用すること以外はとくに限定する必要はないが、鋼管長手方向のｒ値が大きく、スタビライザ形状に曲げ成形加工するに際し発生する減肉、増肉量が小さい鋼管が得られる製造方法を採用することが望ましい。減肉、増肉量が小さくなることにより、スタビライザの焼入れ処理時の加熱に際し、温度むらが小さくなり、スタビライザの強度（硬さ）−靭性バランスをより一層向上させることができる。
O is present as inclusions (oxides) in steel and reduces the workability, toughness, fatigue life, etc. of the steel pipe, so it is preferably reduced to 0.005% or less. More preferably, it is 0.002% or less.
The method for producing the electric resistance welded steel pipe of the present invention is not particularly limited except that the steel plate having the above composition is used, but the r value in the longitudinal direction of the steel pipe is large, and the reduction generated when bending to the stabilizer shape is generated. It is desirable to adopt a manufacturing method that can obtain a steel pipe with a small amount of meat and increased thickness. By reducing the amount of thinning and increasing the thickness, unevenness in temperature is reduced during heating during the quenching treatment of the stabilizer, and the strength (hardness) -toughness balance of the stabilizer can be further improved.
なお、鋼管長手方向のｒ値が大きく、曲げ成形加工時の減肉、増肉量が小さい鋼管を得る方法としては、上記した組成を有する鋼管に、さらに縮径圧延を施す方法がある。好ましい縮径圧延としては、例えば、鋼管を、Ａc３変態点以上に加熱し、引き続き、縮径圧延し、650〜850℃の範囲の温度で縮径率：20％以上の縮径圧延を行って仕上げる方法が例示できる。このような縮径圧延を施された電縫鋼管は、素材として、とくに細径厚肉の中空スタビライザを製造するうえで有利である。 In addition, as a method of obtaining a steel pipe having a large r value in the longitudinal direction of the steel pipe and a small thickness reduction and a small increase in thickness at the time of bending forming, there is a method of further reducing the diameter of the steel pipe having the above composition. As a preferred diameter reduction rolling, for example, a steel pipe is heated to the Ac 3 transformation point or higher, followed by diameter reduction rolling, and a diameter reduction ratio of 20% or more is performed at a temperature in the range of 650 to 850 ° C. The method of finishing can be illustrated. The electric resistance welded steel pipe subjected to such reduced diameter rolling is advantageous as a raw material particularly for producing a thin and thick hollow stabilizer.
つぎに、本発明の中空スタビライザの製造方法について説明する。
本発明では、上記した組成を有し、好ましくは上記した縮径圧延を含む製造方法で製造された電縫鋼管を素材として、該素材に成形工程と熱処理工程を順次施して中空スタビライザとする。
成形工程では、素材である鋼管に、通常の成形方法でスタビライザ形状に成形する。通常の成形方法としては、冷間曲げ加工がある。冷間曲げ加工では、回転引き曲げ、プレス曲げとしてもよい。なお、冷間曲げ加工では、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。
Below, the manufacturing method of the hollow stabilizer of this invention is demonstrated.
In the present invention, an electric-welded steel pipe having the above-described composition and preferably manufactured by the above-described manufacturing method including diameter reduction rolling is used as a raw material, and a forming process and a heat treatment process are sequentially performed on the raw material to obtain a hollow stabilizer.
In the forming step, a steel pipe as a material is formed into a stabilizer shape by a normal forming method. As a normal molding method, there is a cold bending process. In the cold bending process, it may be a rotary pulling bending or a press bending. In the cold bending process, it is preferable to use an NC bender that can be formed into an almost arbitrary shape.
スタビライザ形状に成形された成形品は、ついで熱処理工程を施される。熱処理工程は、焼入れ処理または、焼入れ処理および焼戻処理からなる。焼入れ処理は、所定の温度（焼入れ温度）に加熱されたのち、焼入れ槽に投入され急冷される処理とすることが好ましい。加熱は、生産性の観点から通電加熱とすることが好ましい。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。 The molded product formed into the stabilizer shape is then subjected to a heat treatment step. The heat treatment step includes a quenching process or a quenching process and a tempering process. It is preferable that the quenching process is a process in which after heating to a predetermined temperature (quenching temperature), it is put into a quenching tank and rapidly cooled. The heating is preferably energization heating from the viewpoint of productivity. 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.
焼入れ処理は、Ａc３変態点以上でかつ中空スタビライザー全体で最も高い温度に加熱される個所の温度Ｔが次（２）式
（Ｔ／140）−7.84 ≦ log（Ｗ） …………（２）
（ここで、Ｔ：焼入れ処理時の加熱に際し、中空スタビライザー全体で最も高い温度に加
熱される個所の温度(℃)、Ｗ：Ｗの含有量（質量％））
を満足するように加熱したのち急冷する処理とすることが好ましい。これにより、焼入れ処理後に、または焼入れ焼戻処理後に、高強度でかつ高靭性を具備する中空スタビライザとすることができる。焼入れ処理の通電加熱時に際し、（２）式が満足されない場合には、焼入れ処理後または焼入れ焼戻処理後の靭性が劣化する。
In the quenching process, the temperature T at which the temperature is higher than the Ac 3 transformation point and is heated to the highest temperature in the entire hollow stabilizer is expressed by the following equation (2).
(T / 140) -7.84 ≤ log (W) (2)
(Here, T: the temperature at which the hollow stabilizer is heated to the highest temperature (° C.) and W: W content (mass%) during heating during quenching)
It is preferable to carry out the process of rapid cooling after heating to satisfy the above. Thereby, it can be set as the hollow stabilizer which has high intensity | strength and toughness after a quenching process or a quenching and tempering process. If the formula (2) is not satisfied during the energization heating in the quenching process, the toughness after the quenching process or after the quenching and tempering process is deteriorated.
また、焼戻処理は、350℃以下の温度に加熱し冷却する処理とすることが好ましい。より好ましくは200〜300℃である。焼戻処理を施すことにより靭性が顕著に向上する。焼戻温度が350℃を超えて高くなると、強度(硬さ)が低下し、所望の強度（硬さ）範囲（HV400〜530）を確保できなくなる。硬さがＨＶ530を超えて高くなると遅れ破壊の問題が生じるため実用的ではない。 The tempering process is preferably a process of heating to 350 ° C. or lower and cooling. More preferably, it is 200-300 degreeC. The toughness is remarkably improved by performing the tempering treatment. When the tempering temperature is higher than 350 ° C., the strength (hardness) is lowered and the desired strength (hardness) range (HV400 to 530) cannot be secured. If the hardness exceeds HV530, a problem of delayed fracture occurs, which is not practical.
また、焼入れ処理、あるいは焼入れ処理または焼戻処理後に、ショットブラスト処理を施すことが疲労強度向上の観点から好ましい。なお、ショットブラスト処理は通常の方法を用いればよい。 In addition, it is preferable to perform shot blasting after quenching, or quenching or tempering from the viewpoint of improving fatigue strength. Note that a normal method may be used for shot blasting.
(実施例１)
表１に示す組成の熱延鋼板（鋼板No.Ａ〜No.Ｗ）を、冷間で管状に成形したのち、突き合わせ部を高周波電気抵抗溶接法を用いて溶接して電縫鋼管（外径25.4mmφ×肉厚5mm）とした。ついで、これら電縫鋼管に表２に示す条件で焼入れ処理および焼戻処理を施した。なお、焼入れ処理は、鋼管外表面が表２に示す加熱温度Ｔとなるように通電加熱した後、水槽に浸漬し急冷する処理とした。
(Example 1)
Hot-rolled steel sheets (steel plates No. A to No. W) having the composition shown in Table 1 were formed into a tubular shape in the cold, and then the butt portion was welded using a high-frequency electric resistance welding method to form an electric resistance welded steel pipe (outer diameter) 25.4 mmφ x 5 mm thickness). Next, these electric resistance welded steel pipes were subjected to quenching treatment and tempering treatment under the conditions shown in Table 2. In addition, the quenching process was set as the process of carrying out the electrical heating so that the outer surface of a steel pipe may become the heating temperature T shown in Table 2, and then immersing in a water tank and quenching rapidly.
焼入れ処理あるいは焼入れ処理および焼戻処理を施された鋼管から試験片を採取し、硬さ測定、シャルピー衝撃試験を実施した。
硬さ測定は鋼管のＣ断面について行い、鋼管の外表面を起点として肉厚方向に内表面まで、0.4mmピッチで測定し、その平均値を該鋼管の焼入れ焼戻後の硬さとした。硬さはビッカース硬さ計を用いて荷重500gf（4.9Ｎ）で行った。
Test specimens were collected from the steel pipe that had been subjected to quenching treatment or quenching treatment and tempering treatment, and subjected to hardness measurement and Charpy impact test.
The hardness was measured on the C cross section of the steel pipe, measured from the outer surface of the steel pipe to the inner surface in the thickness direction at a pitch of 0.4 mm, and the average value was the hardness after quenching and tempering of the steel pipe. Hardness was measured with a load of 500 gf (4.9 N) using a Vickers hardness tester.
また、試験片の長さ方向を鋼管の管軸方向（長手方向）に一致させて鋼管から、JIS Z 2202の規定に準拠して削り出し採取した特殊サイズの２mmＶノッチシャルピー衝撃試験片（55mmL×10mmW×2.5mmT）を用い、JIS Z 2242の規定に準拠してシャルピー衝撃試験を行い、破面遷移温度vＴrsを求め、靭性を評価した。
得られた結果を表２に示す。
In addition, a special-sized 2mm V-notch Charpy impact test piece (55mmL ×) was taken from a steel pipe in accordance with JIS Z 2202 with the length direction of the test piece aligned with the pipe axis direction (longitudinal direction) of the steel pipe. 10 mmW × 2.5 mmT), Charpy impact test was conducted in accordance with the provisions of JIS Z 2242 to determine the fracture surface transition temperature vTrs and toughness was evaluated.
The obtained results are shown in Table 2.
鋼管No.1〜No.36の比較から、Ｗを本発明範囲内含有することにより、Cr、Mo、Ni、Cu単独含有の場合に比べて、強度(硬さ)−靭性バランスが向上することがわかる。また、（２）式を満足する加熱温度で焼入れ処理を施すことにより、同じ硬さに調整した場合，比較例であるＷ無添加材(鋼板No.Ａ)やＷ少量添加材（鋼板No.Ｇ）に比べて靭性が良好になっていることがわかる。なお、（２）式を満足しない加熱温度で焼入れ処理を施した場合には、化学組成が本発明範囲でも靭性が低下している。また、電縫鋼管の化学組成を本発明範囲内の化学組成とすることにより、高い焼入れ加熱温度で焼入れ処理しても焼戻後に安定して高靭性を確保できることがわかる。 From the comparison of steel pipes No. 1 to No. 36, the inclusion of W within the scope of the present invention improves the strength (hardness) -toughness balance as compared with the case of containing Cr, Mo, Ni, Cu alone. I understand. Moreover, when it adjusts to the same hardness by performing the quenching process at the heating temperature which satisfies Formula (2), it is a W additive-free material (steel plate No. A) and a small amount of W additive (steel plate No. It can be seen that the toughness is better than G). In addition, when quenching is performed at a heating temperature that does not satisfy the formula (2), the toughness is lowered even if the chemical composition is within the range of the present invention. It can also be seen that by setting the chemical composition of the ERW steel pipe to a chemical composition within the range of the present invention, high toughness can be secured stably after tempering even if quenching is performed at a high quenching heating temperature.
本発明例は、焼入れ処理または焼入れ焼戻処理後に、ＨＶ400以上の高強度と、vＴrs−110℃以下の高靭性を安定して得られる製造条件の範囲が広く、強度(硬さ)−靭性バランスに優れたスタビライザを安定して製造できる電縫鋼管であることがわかる。一方、本発明の範囲を外れる比較例は、とくに高い焼入れ加熱温度で焼入れ処理を施すと、焼入れ焼戻後の靭性の低下が著しい。
(実施例２)
表１に示す組成の熱延鋼板（鋼板No.Ａ、No.Ｆ）を、冷間で管状に成形したのち、突き合わせ部を高周波電気抵抗溶接方法を用いて溶接して電縫鋼管No.ＡＡ、No.ＦＡ（外径30.5mmφ×肉厚7mm）および電縫鋼管（外径89mmφ×肉厚7mm）とした。電縫鋼管（外径89mmφ×肉厚7mm）については、さらに加熱温度：920℃、仕上げ温度：790℃とする縮径圧延（縮径率：66％）を施して、外径30.5mmφ×肉厚7mm の電縫鋼管No. ＡＢ、No.ＦＢとした。
The examples of the present invention have a wide range of manufacturing conditions in which high strength of HV400 or higher and high toughness of vTrs−110 ° C. or lower can be stably obtained after quenching or quenching and tempering, and a balance of strength (hardness) and toughness. It can be seen that this is an ERW steel pipe that can stably produce an excellent stabilizer. On the other hand, in the comparative example that is out of the scope of the present invention, the toughness after quenching and tempering is markedly lowered particularly when the quenching treatment is performed at a high quenching heating temperature.
(Example 2)
After hot-rolled steel sheets (steel plates No. A and No. F) having the composition shown in Table 1 are formed into a cold tube, the butt portion is welded using a high-frequency electric resistance welding method, and an ERW steel pipe No. AA. No. FA (outer diameter 30.5 mmφ x thickness 7 mm) and ERW steel pipe (outer diameter 89 mmφ x thickness 7 mm). For ERW steel pipe (outer diameter 89mmφ x wall thickness 7mm), it is further subjected to reduction rolling (reduction ratio: 66%) with heating temperature: 920 ° C and finishing temperature: 790 ° C, outer diameter 30.5mmφ x meat 7mm thick ERW steel pipe No. AB and No. FB.
これら電縫鋼管No.ＡＡ〜No.ＦＢをそれぞれ所定長さに切断し、冷間の回転引き曲げ加工による成形工程を施し、所定のスタビライザ形状に成形した。なお、曲げ加工は、内側の曲げ半径が鋼管直径の２倍とする90°曲げとした。ついで、スタビライザ形状の両端部をクランプして通電により曲げ部の外側外表面温度が900℃となるように加熱したのち、水槽に浸漬して急冷する焼入れ処理を施した。焼入れ処理後、300℃で20min間保持する焼戻処理を施した。 These electric resistance welded steel pipes No. AA to No. FB were cut into predetermined lengths, respectively, subjected to a forming process by cold rotary drawing and formed into a predetermined stabilizer shape. The bending process was 90 ° bending in which the inner bending radius was twice the diameter of the steel pipe. Next, both ends of the stabilizer shape were clamped and heated by energization so that the outer outer surface temperature of the bent portion became 900 ° C., and then subjected to a quenching process of immersing in a water bath and rapidly cooling. After the quenching treatment, a tempering treatment was performed at 300 ° C. for 20 minutes.
得られた中空スタビライザについて、曲げ部の内側の硬さを実施例１と同様な測定方法で測定した。また、中空スタビライザの曲げ部の内側に隣接する直管部から実施例１と同様にシャルピー試験片を採取してシャルピー衝撃試験を実施し、破面遷移温度vＴrsを求め、靭性を評価した。
得られた結果を表３に示す。
About the obtained hollow stabilizer, the hardness inside a bending part was measured with the measuring method similar to Example 1. FIG. Moreover, the Charpy test piece was extract | collected from the straight pipe | tube part adjacent to the inner side of the bending part of a hollow stabilizer similarly to Example 1, the Charpy impact test was implemented, the fracture surface transition temperature vTrs was calculated | required, and toughness was evaluated.
The obtained results are shown in Table 3.
縮径圧延を施された電縫鋼管No.Ｂを用いた中空スタビライザでは、縮径圧延を施さない電縫鋼管を用いた中空スタビライザに比べて、曲げ部内側に隣接する直管部の靭性が向上していることがわかる。 In the hollow stabilizer using the ERW steel pipe No. B subjected to reduced diameter rolling, compared to the hollow stabilizer using the ERW steel pipe not subjected to reduced diameter rolling, the toughness of the straight pipe portion adjacent to the inside of the bent portion is higher. It can be seen that it has improved.
Claims (14)
Ｃ：0.20〜0.38％、 Si：0.10〜0.50％、
Mn：0.30〜2.00％、 Al：0.01〜0.10％、
Ｗ：0.01〜1.50％、 Ｂ：0.0005〜0.0050％、
を含みさらにTi、Ｎを
Ti：0.001〜0.04％、 N：0.0010〜0.0100％
の範囲で、かつ下記（１）式を満足するように含有し、残部Feおよび不可避的不純物からなる組成を有し、焼入れ処理後あるいは焼入れ焼戻処理後の強度−靭性バランスに優れることを特徴とする高強度中空スタビライザー用電縫鋼管。
記
Ｎ／14 ＜ Ti／47.9 …………（１）
ここで、Ｎ，Ti：各元素の含有量（質量％） % By mass
C: 0.20 to 0.38%, Si: 0.10 to 0.50%,
Mn: 0.30 to 2.00%, Al: 0.01 to 0.10%,
W: 0.01 to 1.50%, B: 0.0005 to 0.0050%,
Including Ti and N
Ti: 0.001 to 0.04%, N: 0.0010 to 0.0100%
The composition is contained so as to satisfy the following formula (1), has a composition composed of the remaining Fe and inevitable impurities, and has an excellent strength-toughness balance after quenching or quenching and tempering. ERW steel pipe for high-strength hollow stabilizer.
Record
N / 14 <Ti / 47.9 (1)
Here, N, Ti: Content of each element (mass%)
前記電縫鋼管を、質量％で、
Ｃ：0.20〜0.38％、 Si：0.10〜0.50％、
Mn：0.30〜2.00％、 Al：0.01〜0.10％、
Ｗ：0.01〜1.50％、 Ｂ：0.0005〜0.0050％、
を含みさらにTi、Ｎを
Ti：0.001〜0.04％、 N：0.0010〜0.0100％
の範囲でかつ下記（１）式を満足するように含有し、残部Feおよび不可避的不純物からなる組成を有する鋼管とし、
前記焼入れ処理を、Ａc３変態点以上でかつ中空スタビライザー全体で最も高い温度に加熱される個所の温度Ｔが下記（２）式を満足するように加熱したのち急冷する処理とし、前記焼戻処理を、350℃以下の温度に加熱し冷却する処理として、
前記中空スタビライザーの硬さを所望の硬さに調整することを特徴とする高強度中空スタビライザーの製造方法。
記
Ｎ／14 ＜ Ti／47.9 …………（１）
（Ｔ／140）−7.84 ≦ log（Ｗ） …………（２）
ここで、Ｔ：焼入れ処理時の加熱に際し、中空スタビライザー全体で最も高い温度に加熱される個所の温度(℃)、Ｎ，Ti、Ｗ：各元素の含有量（質量％） Manufacturing of a hollow stabilizer in which an electric-welded steel pipe is used as a raw material, a forming process for forming the raw material into a predetermined stabilizer shape, and a heat treatment process for subjecting the formed material to quenching or further tempering In the method
The electric resistance welded steel pipe in mass%,
C: 0.20 to 0.38%, Si: 0.10 to 0.50%,
Mn: 0.30 to 2.00%, Al: 0.01 to 0.10%,
W: 0.01 to 1.50%, B: 0.0005 to 0.0050%,
Including Ti and N
Ti: 0.001 to 0.04%, N: 0.0010 to 0.0100%
And a steel pipe having a composition consisting of the remaining Fe and inevitable impurities, so as to satisfy the following formula (1):
The tempering treatment is a quenching treatment in which the temperature T of the portion heated to the highest temperature in the entire hollow stabilizer is equal to or higher than the Ac 3 transformation point and then rapidly cooled so as to satisfy the following formula (2). As a process of heating and cooling to a temperature of 350 ° C. or less,
A method for producing a high-strength hollow stabilizer, comprising adjusting the hardness of the hollow stabilizer to a desired hardness.
Record
N / 14 <Ti / 47.9 (1)
(T / 140) -7.84 ≤ log (W) (2)
Here, T: the temperature at which the entire hollow stabilizer is heated to the highest temperature during the quenching process (° C.), N, Ti, W: content of each element (mass%)
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| JP4859618B2 (en) * | 2006-10-13 | 2012-01-25 | 日新製鋼株式会社 | Manufacturing method of hollow stabilizer with excellent delayed fracture resistance |
| JP5303842B2 (en) | 2007-02-26 | 2013-10-02 | Ｊｆｅスチール株式会社 | Manufacturing method of ERW welded steel pipe for heat treatment with excellent flatness |
| JP4859240B2 (en) * | 2007-04-03 | 2012-01-25 | 日新製鋼株式会社 | Manufacturing method of ERW steel pipe for hollow stabilizer |
| JP5353256B2 (en) * | 2008-01-21 | 2013-11-27 | Ｊｆｅスチール株式会社 | Hollow member and manufacturing method thereof |
| JP5306845B2 (en) | 2009-02-12 | 2013-10-02 | Ｊｆｅ条鋼株式会社 | Steel for vehicle high strength stabilizer excellent in corrosion resistance and low temperature toughness, its manufacturing method and stabilizer |
| JP5511451B2 (en) | 2010-03-16 | 2014-06-04 | 中央発條株式会社 | Manufacturing method of automotive stabilizer |
| KR101180561B1 (en) | 2010-10-18 | 2012-09-06 | 현대하이스코 주식회사 | The method for multi-step heat treatment of electric resistance welded pipe with a function of improved impact toughness and reduced hardness deviation and the manufacturing method of the pipe |
| JP5736929B2 (en) * | 2011-04-19 | 2015-06-17 | Ｊｆｅスチール株式会社 | Ultra-high-strength ERW steel pipe with excellent workability and low-temperature toughness and method for producing the same |
| KR101706839B1 (en) * | 2012-05-25 | 2017-02-14 | 신닛테츠스미킨 카부시키카이샤 | Hollow stabilizer, and steel pipe for hollow stabilizers and method for production thereof |
| MX2018003854A (en) | 2015-09-29 | 2018-06-15 | Jfe Steel Corp | Electric res. |
| MX2019002073A (en) | 2016-10-24 | 2019-07-01 | Jfe Steel Corp | Electric resistance welded steel pipe for high-strength thin hollow stabilizer and manufacturing method therefor. |
| JP6885472B2 (en) * | 2018-06-27 | 2021-06-16 | Ｊｆｅスチール株式会社 | Electric pipe for manufacturing hollow stabilizers and its manufacturing method |
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