JP2831858B2 - Manufacturing method of high strength hot rolled steel sheet with excellent fatigue properties - Google Patents
Manufacturing method of high strength hot rolled steel sheet with excellent fatigue propertiesInfo
- Publication number
- JP2831858B2 JP2831858B2 JP6398091A JP6398091A JP2831858B2 JP 2831858 B2 JP2831858 B2 JP 2831858B2 JP 6398091 A JP6398091 A JP 6398091A JP 6398091 A JP6398091 A JP 6398091A JP 2831858 B2 JP2831858 B2 JP 2831858B2
- Authority
- JP
- Japan
- Prior art keywords
- strength
- steel sheet
- ferrite
- rolled steel
- fatigue
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
【０００１】[0001]
【産業上の利用分野】本発明は、疲労特性に優れた高強
度熱延鋼板の製造方法に係り、より詳しくは、高い疲労
特性と車体の軽量化のために軽量化が求められている自
動車用足回り部品用に適する、疲労特性に優れた５０〜
７０キロ級加工用熱延鋼板及びメッキ原板の製造方法に
関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength hot-rolled steel sheet having excellent fatigue properties, and more particularly, to an automobile which is required to have a high fatigue property and a lighter body for a lighter body. Suitable for undercarriage parts, excellent in fatigue characteristics
The present invention relates to a method for producing a hot-rolled steel sheet for 70-kilometer processing and a plated original sheet.
【０００２】[0002]
【従来の技術】自動車用足回り部品は、自動車の駆動部
に近い部分に用いられるため、高い疲労特性が要求され
る。また、車体の軽量化のため、足回り部品の軽量化が
求められている。このため、足回り部品として優れた高
強度の鋼板のニーズが高くなってきている。2. Description of the Related Art Undercarriage parts for automobiles are used in a portion close to a driving portion of an automobile, and therefore are required to have high fatigue characteristics. Further, in order to reduce the weight of the vehicle body, it is required to reduce the weight of the underbody parts. For this reason, the need for excellent high-strength steel sheets as underbody parts has been increasing.
【０００３】一般的に、引張強度（ＴＳ）を高めること
により疲労強度は向上する。しかし、必要以上にＴＳを
高めることは加工性の劣化を招く。特にＣの添加による
高強度化は鋼の延びフランジ性を著しく劣化させる。引
張強度が同じであっても炭化物を微細にすることにより
疲労強度を高めることができる。疲労は炭化物などの析
出物を起点にして進行するためである。In general, fatigue strength is improved by increasing tensile strength (TS). However, increasing the TS more than necessary causes deterioration in workability. In particular, the increase in strength due to the addition of C significantly deteriorates the stretch flangeability of steel. Even if the tensile strength is the same, the fineness of the carbide can increase the fatigue strength. This is because fatigue proceeds from precipitates such as carbides.
【０００４】従来、同一強度で疲労強度の高い高強度鋼
板は、Ｃの添加をできるだけ抑え、ＭｎやＮｂなどの他
の元素の添加により高強度化し、更に第２相組織をベイ
ナイトとし、セメンタイト（炭化鉄）を微細に分散させ
ることにより得られてきた。しかしながら、このような
方法だけでは、最近は部品の軽量化のために部品の薄肉
化も進んでいることもあり、不十分となりつつある。例
えば、特開昭５７−１０４６５０号公報ではＳｉ／Ｍｎ
比を規定して改善を図っているが、フェライト＋マルテ
ンサイト鋼は孔拡げ性に問題があり、充分ではない。ま
た特開昭５７−１５２４２号公報に見られるように製造
条件が複雑で製造コストが高くなる。Conventionally, a high-strength steel sheet having the same strength and high fatigue strength has been strengthened by suppressing the addition of C as much as possible, adding other elements such as Mn and Nb, and further forming bainite as a second phase structure. (Iron carbide) is finely dispersed. However, such a method alone is becoming inadequate in recent years due to the progress of thinning of parts for weight reduction of parts. For example, JP-A-57-104650 discloses that Si / Mn
Although the ratio is specified to improve, ferrite + martensitic steel has a problem in hole expandability and is not sufficient. Further, as seen in Japanese Patent Application Laid-Open No. 57-15242, the manufacturing conditions are complicated and the manufacturing cost increases.
【０００５】[0005]
【発明が解決しようとする課題】一方、フェライト＋ベ
イナイト鋼は、特開昭５７−１０１６４９号公報に見ら
れるように、孔拡げ性と疲労特性が良好なため足回り用
鋼板として広く使用されているが、最近では、更なる薄
肉化のため、疲労強度の向上が強く求められている。On the other hand, ferrite + bainite steel has been widely used as a steel plate for undercarriage due to its good hole-expanding properties and fatigue properties, as disclosed in Japanese Patent Application Laid-Open No. 57-101649. However, recently, there is a strong demand for improvement in fatigue strength for further thinning.
【０００６】ところで、最近の研究により、極低炭素鋼
においてＰ、Ｃｕを複合添加することにより、疲労強度
の向上が図れることが明らかになってきた。しかしなが
ら、極低炭素鋼では十分な強度が得られない上、単に従
来の高強度鋼にＰ、Ｃｕを添加しただけでは良好な疲労
特性は得られない。[0006] Recent research has revealed that the addition of P and Cu to ultra-low carbon steel can improve fatigue strength. However, sufficient strength cannot be obtained with ultra-low carbon steel, and good fatigue properties cannot be obtained simply by adding P and Cu to conventional high-strength steel.
【０００７】このように、従来の方法のみでは疲労強度
が不十分である。勿論、引張強度を上げて疲労強度を高
めれば、加工性が劣化し、部品に加工できないことは云
うまでもない。As described above, the conventional method alone is insufficient in fatigue strength. Of course, if the fatigue strength is increased by increasing the tensile strength, it goes without saying that the workability is deteriorated and it is not possible to process the component.
【０００８】本発明は、上記従来技術の欠点を解消し
て、高い引張強度を維持しつつ優れた疲労特性を備えた
高強度熱延鋼板を製造し得る方法を提供することを目的
とするものである。An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method for producing a high-strength hot-rolled steel sheet having excellent fatigue characteristics while maintaining high tensile strength. It is.
【０００９】[0009]
【課題を解決するための手段】前記課題を解決するた
め、本発明者らは、従来の方法において良好な疲労特性
が得られない原因並びに疲労強度の向上策について検討
した結果、単に従来の高強度鋼にＰ、Ｃｕを添加しただ
けでは良好な疲労特性は得られないことが明らかになっ
た。In order to solve the above-mentioned problems, the present inventors have studied the causes of failure to obtain good fatigue characteristics in the conventional method and measures for improving the fatigue strength. It became clear that good fatigue characteristics could not be obtained only by adding P and Cu to the strength steel.
【００１０】図１に鋼の疲労強度に及ぼす、熱間圧延終
了から冷却開始までの時間の影響を示す。この図から、
圧延後３秒以上空冷してから水冷しなければ、ＰとＣｕ
の添加の効果が少ないことがわかる。この理由は明らか
ではないが、圧延後直ちに冷却した場合、未再結晶オー
ステナイトの部分から優先的にフェライトが析出し、他
の部分に比べてＣｕの析出挙動に変化が生じるためと考
えられる。FIG. 1 shows the effect of the time from the end of hot rolling to the start of cooling on the fatigue strength of steel. From this figure,
P and Cu must be air-cooled for at least 3 seconds after rolling and then water-cooled.
It can be seen that the effect of the addition of is small. The reason for this is not clear, but it is considered that when cooled immediately after rolling, ferrite is preferentially precipitated from the unrecrystallized austenite portion, and the precipitation behavior of Cu is changed as compared with other portions.
【００１１】図２は疲労強度度に及ぼすＰ、Ｃｕ添加の
影響を示している。Ｐを単独で添加しても疲労強度はそ
れほど向上しないが、Ｃｕと複合して添加することによ
り疲労強度が向上することがわかる。FIG. 2 shows the effect of the addition of P and Cu on the fatigue strength. It can be seen that the fatigue strength is not significantly improved by adding P alone, but the fatigue strength is improved by adding in combination with Cu.
【００１２】図３はＰ、Ｃｕを添加した鋼（フェライト
＋ベイナイト組織）のフェライトの硬さと疲労強度の関
係を示している。フェライトの硬さが１２０Ｈｖ未満で
は疲労強度の向上は少ない。Ｐは固溶強化能の大きな元
素であり、またＣｕは析出によリフェライトを強度化す
るが、これらの襖合添加により疲労強度の向上が大きく
なる理由は明らかではないが、Ｃｕの析出強化にＰが効
果的に作用するものと考えられる。Ｐ、Ｃｕはフェライ
トの硬さが１２０Ｈｖ以上になるのに十分な量だけ添加
すればよいことも判明した。必要以上のＰの添加は鋼の
脆化を引き起こし、またＣｕは多量に添加すると高価と
なる上、鋼板の表面品質が劣化するためである。図４は
引張強度（ＴＳ）と疲労強度の関係を示したものであ
り、後述の本発明法によれば、同一強度の従来鋼よりも
高い疲労強度が得られている。FIG. 3 shows the relationship between the hardness of ferrite and the fatigue strength of steel (ferrite + bainite structure) to which P and Cu are added. If the hardness of the ferrite is less than 120 Hv, the improvement in fatigue strength is small. P is an element having a large solid solution strengthening ability, and Cu strengthens the ferrite by precipitation. It is not clear why the addition of these fusuma increases the fatigue strength, but the precipitation strengthening of Cu is not clear. It is considered that P acts effectively on. It has also been found that P and Cu need only be added in amounts sufficient for the hardness of the ferrite to be 120 Hv or more. This is because excessive addition of P causes embrittlement of the steel, and addition of a large amount of Cu increases the cost and deteriorates the surface quality of the steel sheet. FIG. 4 shows the relationship between the tensile strength (TS) and the fatigue strength. According to the method of the present invention described later, a higher fatigue strength than that of the conventional steel having the same strength is obtained.
【００１３】本発明は、以上の知見に基づき、更に詳細
に実験研究を重ねて、ここに本発明を完成したものであ
る。Based on the above findings, the present invention has been made through further experimental studies, and the present invention has been completed.
【００１４】すなわち、本発明は、Ｃ：０．０１〜０．
１０％、Ｓｉ≦０．４％、Ｍｎ≦２．００％、Ｓ≦０．
００４０％、Ａｌ：０．０１０〜０．０６％、Ｎｂ：
０．０１５〜０．１０％、Ｎ≦０．００４０％、Ｐ：
０．０５〜０．１２％及びＣｕ：０．２〜０．５％を含
有し、必要に応じて更にＴｉ≦０．０６％、Ｎｉ≦０．
５％及びＣｒ≦０．５％の少なくとも１種を含有し、残
部が鉄及び不可避的不純物からなる鋼を、熱延仕上げ温
度８８０〜９５０℃で熱間圧延し、圧延後３秒以上空冷
した後、冷却速度５０〜１００℃／ｓｅｃで冷却し、４
００〜５００℃で巻き取ることにより、フェライト部の
硬さが１２０Ｈｖ以上で、ベイナイト及びフェライトか
らなる組織とすることを特徴とする疲労特性に優れた高
強度熱延鋼板の製造方法を要旨とするものである。That is, in the present invention, C: 0.01-0.
10%, Si ≦ 0.4%, Mn ≦ 2.00%, S ≦ 0.
0040%, Al: 0.010 to 0.06%, Nb:
0.015 to 0.10%, N ≦ 0.0040%, P:
It contains 0.05 to 0.12% and Cu: 0.2 to 0.5%, and further contains Ti ≦ 0.06% and Ni ≦ 0.
A steel containing at least one of 5% and Cr ≦ 0.5%, the balance being iron and unavoidable impurities, was hot-rolled at a hot-rolling finishing temperature of 880 to 950 ° C., and air-cooled for 3 seconds or more after rolling. Then, it is cooled at a cooling rate of 50 to 100 ° C./sec.
A method for producing a high-strength hot-rolled steel sheet excellent in fatigue characteristics, characterized in that the ferrite portion has a hardness of 120 Hv or more by winding at 00 to 500 ° C. and has a structure composed of bainite and ferrite. Things.
【００１５】以下に本発明を更に詳述する。Hereinafter, the present invention will be described in more detail.
【００１６】[0016]
【作用】まず、本発明における鋼の化学成分の限定理由
を示す。Ｃは強化元素として添加するが、０．０１％未
満では強度が不十分であり、また０．１０％を超えると
加工性、特に延びフランジ性が劣化するので、Ｃ量は
０．０１〜０．１０％の範囲とする。First, the reasons for limiting the chemical components of steel in the present invention will be described. C is added as a strengthening element, but if it is less than 0.01%, the strength is insufficient, and if it exceeds 0.10%, the workability, especially the stretch flangeability is deteriorated. .10%.
【００１７】Ｓｉは強化元素として添加するが、０．４
％を超えると表面品質が劣化し、また溶融亜鉛メッキの
付着性も劣化するので、０．４％以下に規定する。Si is added as a strengthening element.
%, The surface quality deteriorates and the adhesion of hot-dip galvanized coating also deteriorates.
【００１８】Ｍｎは強化元素として添加するが、２．０
０％を超えると強度が高くなりすぎて加工性が劣化する
ので、２．００％以下に規定する。Mn is added as a strengthening element.
If it exceeds 0%, the strength becomes too high and the workability deteriorates.
【００１９】Ｓは介在物を形成するため少ないほど良
い。その含有量が０．００４０％を超えるとＭｎＳ等の
介在物のため、延びフランジ性が劣化するので、０．０
０４０％以下に抑制する。S is preferably as small as possible to form inclusions. If the content exceeds 0.0040%, the extension flangeability is deteriorated due to inclusions such as MnS.
040% or less.
【００２０】Ａｌは脱酸剤として添加する。しかし、
０．０１０％未満では酸化物系介在物のために加工性が
劣化する。一方、０．０６％より多いと脱酸の効果が飽
和する上、高価となる。したがって、Ａｌ量は０．０１
０〜０．０６％の範囲とする。Al is added as a deoxidizing agent. But,
If it is less than 0.010%, workability is deteriorated due to oxide-based inclusions. On the other hand, if it is more than 0.06%, the deoxidizing effect is saturated and the cost is high. Therefore, the amount of Al is 0.01
The range is 0 to 0.06%.
【００２１】Ｎｂは強化元素として添加するが、組織を
ベイナイト化し炭化物を微細化する効果も期待できる。
しかし、０．０１５％未満では強度が不十分であり、ま
た０．１０％を超えると強度向上効果が飽和する上、鋼
板の板表面性状が劣化するので、Ｎｂ量は０．０１５〜
０．１０％の範囲とする。Although Nb is added as a strengthening element, an effect of bainizing the structure and refining carbide can be expected.
However, if it is less than 0.015%, the strength is insufficient, and if it exceeds 0.10%, the strength improvement effect is saturated, and the sheet surface properties of the steel sheet are deteriorated.
The range is 0.10%.
【００２２】ＮはＡｌＮなどの窒化物を生成し、これが
鋼の加工性を劣化させるので少ないほど良い。０．００
４０％より多いと加工性が劣化するので、０．００４０
％以下に抑制する。N produces nitrides such as AlN, which deteriorates the workability of steel. 0.00
If it is more than 40%, the workability deteriorates.
% Or less.
【００２３】Ｐは固溶強化能の大きな元素であるが、Ｃ
ｕと共に複合添加することにより疲労強度を著しく向上
させる効果がある。しかし、０．０５％未満ではそのよ
うな効果が得られず、０．１２％を超えると鋼の脆化を
招く。したがって、Ｐ量は、フェライトの硬さをＨｖ１
２０以上になるのに充分な量を考慮し、０．０５〜０．
１２％の範囲とする。P is an element having a large solid solution strengthening ability.
The combined addition with u has the effect of significantly improving fatigue strength. However, if it is less than 0.05%, such an effect cannot be obtained, and if it exceeds 0.12%, the steel becomes brittle. Therefore, the amount of P determines the hardness of the ferrite as Hv1.
Considering an amount sufficient to be 20 or more, 0.05 to 0.
The range is 12%.
【００２４】Ｃｕは析出によリフェライトを強化する元
素であるが、Ｐとの複合添加により疲労強度を著しく向
上させる効果がある。しかし、０．２％未満ではそのよ
うな効果が得られず、０．５％より多く添加すると鋼板
の表面品質が劣化すると共に高価となる。したがって、
Ｃｕ量は、フェライトの硬さをＨｖ１２０以上になるの
に充分な量を考慮し、０．２〜０．５％の範囲とする。Cu is an element that strengthens the ferrite by precipitation, but has an effect of significantly improving the fatigue strength when added in combination with P. However, if it is less than 0.2%, such an effect cannot be obtained, and if it is added more than 0.5%, the surface quality of the steel sheet deteriorates and the steel plate becomes expensive. Therefore,
The amount of Cu is in the range of 0.2 to 0.5% in consideration of an amount sufficient to make the hardness of the ferrite Hv 120 or more.
【００２５】なお、本発明では、必要に応じてＴｉ、Ｎ
ｉ、Ｃｒの少なくとも１種を適量にて添加することがで
きる。Ｔｉは０．０６％より多いと効果が飽和するうえ
高価となり、Ｎｉは０．５％より多いと効果が飽和する
うえ高価となり、Ｃｒは０．５％より多いと効果が飽和
するうえ高価となるので、Ｔｉ量は０．０６％以下、Ｎ
ｉ量及びＣｒ量はそれぞれ０．５％以下とする。In the present invention, Ti, N
At least one of i and Cr can be added in an appropriate amount. If Ti is more than 0.06%, the effect is saturated and expensive, and if Ni is more than 0.5%, the effect is saturated and expensive. If Cr is more than 0.5%, the effect is saturated and expensive. Therefore, the Ti content is 0.06% or less,
The amount of i and the amount of Cr are each set to 0.5% or less.
【００２６】次に、本発明の製造条件を説明する。上記
化学成分を有する鋼の熱間圧延は、熱延仕上温度（ＦＤ
Ｔ）、圧延後の冷却開始時間、冷却速度（ＣＲ）、巻取
温度（ＣＴ）を規制する必要がある。Next, the manufacturing conditions of the present invention will be described. The hot rolling of steel having the above chemical composition is performed at a hot rolling finish temperature (FD).
T), cooling start time after rolling, cooling rate (CR), and winding temperature (CT) need to be regulated.
【００２７】ＦＤＴが８８０℃未満では２相域圧延とな
り、加工性が劣化することとなり、また９５０℃を超え
ると操業が困難なうえスケールキズが多発することとな
るので、ＦＤＴは８８０〜９５０℃の範囲とする。圧延
終了後３秒以内に冷却を開始すると、図１に示すように
ＰとＣｕの複合添加効果が少ないので、冷却は圧延終了
後３秒以上空冷してから開始する。冷却速度は、５０℃
／ｓｅｃ未満では十分な鋼の強度が得られず、また１０
０℃／ｓｅｃを超えると板の形状不良が多発し生産性を
阻害することとなるので、５０〜１００℃／ｓｅｃの範
囲とする。If the FDT is less than 880 ° C., two-phase rolling occurs and the workability is deteriorated. If the FDT exceeds 950 ° C., the operation becomes difficult and scale flaws occur frequently. Range. If the cooling is started within 3 seconds after the end of the rolling, the effect of the composite addition of P and Cu is small as shown in FIG. 1, so the cooling is started after air cooling for at least 3 seconds after the end of the rolling. Cooling rate is 50 ° C
/ Sec, sufficient steel strength cannot be obtained and 10
If the temperature exceeds 0 ° C./sec, the shape of the plate is often defective and the productivity is impaired, so the range is 50 to 100 ° C./sec.
【００２８】巻取温度は、４００℃未満では板の平坦度
が劣化することとなり、また５００℃を超えると縦割遷
移温度が上昇し脆化することとなるので、４００〜５０
０℃の範囲とする。If the winding temperature is lower than 400 ° C., the flatness of the plate is deteriorated. If the winding temperature is higher than 500 ° C., the vertical transition temperature increases and the material becomes brittle.
The range is 0 ° C.
【００２９】かくして、フェライト部の硬さがＨｖ１２
０以上で、ベイナイト及びフェライトからなる組織の熱
延鋼板を得る。この熱延鋼板は高強度で優れた疲労特性
を兼ね備えているものである。フェライトの硬さがＨｖ
１２０より低いと、前述したように疲労特性が劣化する
こととなり好ましくない。またべイナイト＋フェライト
の組織以外の組織では穴拡げ性を損うこととなり好まし
くない。Thus, the hardness of the ferrite portion is Hv12
When it is 0 or more, a hot-rolled steel sheet having a structure composed of bainite and ferrite is obtained. This hot-rolled steel sheet has both high strength and excellent fatigue characteristics. Ferrite hardness is Hv
If it is lower than 120, the fatigue characteristics deteriorate as described above, which is not preferable. Further, a structure other than the structure of bainite + ferrite undesirably deteriorates hole expandability.
【００３０】次に本発明の実施例を示す。Next, examples of the present invention will be described.
【００３１】[0031]
【実施例】表１に示す化学成分を有する供試材を、表２
及び表３に示す種々の条件で、熱間圧延し、圧延後所定
の冷却開始時間まで空冷した後、所定の冷却速度で冷却
し、所定の巻取温度で巻き取って熱延鋼板を製造した。
その機械的性質、穴拡げ率［穴拡げ試験（直径１０ｍｍ
打抜穴）による延びフランジ性評価］、フェライトの硬
さ（Ｈｖ）、縦割遷移温度及び疲労強度を調べた結果を
表２及び表３に併記する。EXAMPLE A test material having the chemical components shown in Table 1 was used in Table 2
And, under various conditions shown in Table 3, after hot rolling, air-cooled to a predetermined cooling start time after rolling, cooled at a predetermined cooling rate, and wound at a predetermined winding temperature to produce a hot-rolled steel sheet. .
Its mechanical properties, hole expansion rate [hole expansion test (diameter 10 mm
Evaluation of Stretch Flangeability by Punching Hole), Hardness (Hv) of Ferrite, Transition Temperature and Fatigue Strength are also shown in Tables 2 and 3.
【００３２】[0032]
【表１】 [Table 1]
【００３３】[0033]
【表２】 [Table 2]
【００３４】[0034]
【表３】 [Table 3]
【００３５】表２及び表３より、本発明範囲の化学成分
及び条件で製造した熱延鋼板（本発明例）は、強度が５
０キロ級以上で高い疲労強度と高い延びフランジ性を兼
ね備えている。一方、本発明範囲外の化学成分又は製造
条件で製造した熱延鋼板（比較例）は、強度に対応し
て、高い疲労強度或いは高い延びフランジ性の一方又は
双方が欠如している。From Tables 2 and 3, it can be seen that the hot-rolled steel sheet (Example of the present invention) manufactured under the chemical components and conditions within the range of the present invention has a strength of 5
It has both high fatigue strength and high stretch flangeability in the 0 kg class or higher. On the other hand, a hot-rolled steel sheet (comparative example) manufactured under a chemical composition or manufacturing conditions outside the scope of the present invention lacks one or both of high fatigue strength and high stretch flangeability in accordance with the strength.
【００３６】[0036]
【発明の効果】以上詳述したように、本発明によれば、
高強度で優れた疲労特性、更には優れた加工性を有する
熱延鋼板が得られる。したがって、自動車の足回り用部
品に用いることにより部品の軽量化を図ることが可能で
ある。また、本発明により得られる熱延鋼板はＰ、Ｃｕ
を添加しているため耐候性にも優れ、錆易い足回り部品
に最適である。As described in detail above, according to the present invention,
A hot-rolled steel sheet having high strength, excellent fatigue properties, and excellent workability can be obtained. Therefore, it is possible to reduce the weight of parts by using them for underbody parts of automobiles. The hot-rolled steel sheet obtained by the present invention is P, Cu
It has excellent weather resistance due to the addition of, and is most suitable for undercarriage parts that are easily rusted.
【図１】疲労強度に及ぼす水冷開始までの時間の影響を
示す図である。FIG. 1 is a diagram showing the effect of the time until the start of water cooling on fatigue strength.
【図２】疲労強度に及ぼすＰ、Ｃｕ添加の影響を示す図
である。FIG. 2 is a diagram showing the effect of addition of P and Cu on fatigue strength.
【図３】疲労強度に及ぼすフェライトの硬さの影響を示
す図である。FIG. 3 is a graph showing the effect of ferrite hardness on fatigue strength.
【図４】引張強度（ＴＳ）と疲労強度の関係を示す図で
ある。FIG. 4 is a diagram showing a relationship between tensile strength (TS) and fatigue strength.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 平４−276024（ＪＰ，Ａ) 特開 昭55−31123（ＪＰ，Ａ) 特開 昭57−104650（ＪＰ，Ａ) 特開 昭56−133418（ＪＰ，Ａ) (58)調査した分野(Int.Cl.6，ＤＢ名) C21D 9/46 - 9/48 C21D 8/02 - 8/04──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-276024 (JP, A) JP-A-55-31123 (JP, A) JP-A-57-104650 (JP, A) 133418 (JP, A) (58) Field surveyed (Int. Cl. 6 , DB name) C21D 9/46-9/48 C21D 8/02-8/04
Claims (2)
〜０．１０％、Ｓｉ≦０．４％、Ｍｎ≦２．００％、Ｓ
≦０．００４０％、Ａｌ：０．０１０〜０．０６％、Ｎ
ｂ：０．０１５〜０．１０％、Ｎ≦０．００４０％、
Ｐ：０．０５〜０．１２％及びＣｕ：０．２〜０．５％
を含有し、残部が鉄及び不可避的不純物からなる鋼を、
熱延仕上げ温度８８０〜９５０℃で熱間圧延し、圧延後
３秒以上空冷した後、冷却速度５０〜１００℃／ｓｅｃ
で冷却し、４００〜５００℃で巻き取ることにより、フ
ェライト部の硬さが１２０Ｈｖ以上で、ベイナイト及び
フェライトからなる組織とすることを特徴とする疲労特
性に優れた高強度熱延鋼板の製造方法。C: 0.01% by weight (hereinafter the same)
~ 0.10%, Si ≦ 0.4%, Mn ≦ 2.00%, S
≦ 0.0040%, Al: 0.010-0.06%, N
b: 0.015 to 0.10%, N ≦ 0.0040%,
P: 0.05 to 0.12% and Cu: 0.2 to 0.5%
Containing steel, the balance consisting of iron and unavoidable impurities,
After hot rolling at a hot rolling finish temperature of 880 to 950 ° C. and air cooling for 3 seconds or more after rolling, a cooling rate of 50 to 100 ° C./sec.
The method for producing a high-strength hot-rolled steel sheet excellent in fatigue characteristics, characterized in that the ferrite portion has a hardness of 120 Hv or more and has a structure composed of bainite and ferrite by cooling at 400 to 500 ° C. .
≦０．５％及びＣｒ≦０．５％の少なくとも１種を含有
する請求項１に記載の方法。2. The steel according to claim 1, further comprising Ti ≦ 0.06%, Ni
2. The method according to claim 1, comprising at least one of ≤0.5% and Cr ≤0.5%.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6398091A JP2831858B2 (en) | 1991-03-04 | 1991-03-04 | Manufacturing method of high strength hot rolled steel sheet with excellent fatigue properties |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6398091A JP2831858B2 (en) | 1991-03-04 | 1991-03-04 | Manufacturing method of high strength hot rolled steel sheet with excellent fatigue properties |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04276016A JPH04276016A (en) | 1992-10-01 |
| JP2831858B2 true JP2831858B2 (en) | 1998-12-02 |
Family
ID=13244942
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6398091A Expired - Lifetime JP2831858B2 (en) | 1991-03-04 | 1991-03-04 | Manufacturing method of high strength hot rolled steel sheet with excellent fatigue properties |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2831858B2 (en) |
-
1991
- 1991-03-04 JP JP6398091A patent/JP2831858B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH04276016A (en) | 1992-10-01 |
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