JP2001226744A - High tensile strength for rolled steel sheet excellent in backing hardenability and impact resistance and producing method therefor - Google Patents
High tensile strength for rolled steel sheet excellent in backing hardenability and impact resistance and producing method thereforInfo
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- JP2001226744A JP2001226744A JP2000036756A JP2000036756A JP2001226744A JP 2001226744 A JP2001226744 A JP 2001226744A JP 2000036756 A JP2000036756 A JP 2000036756A JP 2000036756 A JP2000036756 A JP 2000036756A JP 2001226744 A JP2001226744 A JP 2001226744A
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- rolled steel
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、自動車の構造部
材、足周り部材等の使途に供して好適な、歪時効強化能
すなわち焼付け硬化性（ＢＨ性）および耐衝撃性に優れ
た高張力熱延鋼板およびその製造方法に関する。本発明
において、歪時効強化能とは、２％の歪付与時の最高応
力と、該歪付与の後 170℃で20分保持した後、再度引張
変形を付与した時の上降伏点との差を意味する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-tensile heat-resistant heat-resistant steel which is suitable for use as a structural member of an automobile, a suspension member, and the like, and which has excellent strain aging enhancing ability, that is, baking hardenability (BH property) and impact resistance. The present invention relates to a rolled steel sheet and a method for manufacturing the same. In the present invention, the strain aging enhancing ability is defined as the difference between the maximum stress at the time of applying a strain of 2% and the upper yield point at the time of applying tensile deformation again after maintaining the material at 170 ° C. for 20 minutes after applying the strain. Means
【０００２】[0002]
【従来の技術】近年、自動車用鋼板には、軽量化による
燃費向上のため一層の高強度化が要求されている。しか
し、鋼板の高強度化は、プレス成形を困難にするという
問題がある。また、最近では乗員の安全確保という目的
から、衝突時におけるような高歪速度下での変形エネル
ギー量で評価される耐衝撃性の向上が望まれている。2. Description of the Related Art In recent years, steel sheets for automobiles have been required to have higher strength in order to improve fuel efficiency by reducing weight. However, increasing the strength of a steel sheet has a problem that press forming is difficult. Recently, for the purpose of ensuring the safety of occupants, it has been desired to improve the impact resistance, which is evaluated based on the amount of deformation energy under a high strain rate such as at the time of a collision.
【０００３】高強度化によるプレス成形性の劣化を防止
した高強度化技術としては、成形時には比較的低強度で
加工がしやすく、塗装時の焼付けによって強度を増加さ
せる、いわゆる焼付け硬化性（ＢＨ性）を利用した技術
が知られており、冷延鋼板については広く利用されてい
る（例えば、特開平６−73498 号公報、特開平７−2685
44号公報）。しかしながら、これらの技術で得られる焼
付け硬化性の向上により、降伏強さを増加させることが
可能であり、自動車外板における耐デント性の向上には
有効であるが、内装板に要求される耐衝撃性の向上を考
慮すると、増加量が小さく、十分な効果は得られない。[0003] As a high strength technology for preventing the deterioration of press formability due to the high strength, a so-called bake hardening property (BH), which is relatively low in strength during molding and easy to work and increases in strength by baking at the time of painting. Technology is known, and cold-rolled steel sheets are widely used (for example, JP-A-6-73498, JP-A-7-26885).
No. 44). However, by improving the bake hardenability obtained by these techniques, it is possible to increase the yield strength, which is effective for improving the dent resistance of an automobile outer panel, but is effective for improving the dent resistance required for an interior panel. In consideration of the improvement in impact properties, the increase is small and sufficient effects cannot be obtained.
【０００４】一方、特開平１−180917号公報には、Ｃ：
0.030 〜0.100 ％、Ｎ：0.0015〜0.0150％、Al：0.025
〜0.100 ％を含有する鋼を、1200℃以下に加熱し、（Ar
3 ＋30℃）〜950 ℃の温度で仕上圧延を行い、圧延後３
秒以内に30℃/s以上の冷却速度で500 ℃/s以下まで急冷
し、400 〜500 ℃で巻き取る、加工性、焼付け硬化性に
優れた熱延鋼板の製造方法が記載されている。そこで
は、圧延後急冷し、鋼板中のＣ，Ｎの固溶量を増加させ
ることによってＢＨ性の向上を図っている。On the other hand, JP-A-1-180917 discloses that C:
0.030 to 0.100%, N: 0.0015 to 0.0150%, Al: 0.025
A steel containing ~ 0.100% is heated to 1200 ° C or less,
3 + 30 ° C)-Finish rolling at a temperature of 950 ° C.
It describes a method of manufacturing a hot-rolled steel sheet which is rapidly cooled to 500 ° C./s or less within 30 seconds at a cooling rate of 30 ° C./s or more, and wound at 400 to 500 ° C., and has excellent workability and bake hardenability. In this case, BH property is improved by quenching after rolling and increasing the solid solution amount of C and N in the steel sheet.
【０００５】また、特開平４−74824 号公報には、Ｃ：
0.02〜0.13％、Ｎ：0.0080〜0.0250％、sol.Al：0.10％
以下を含有する鋼を、1100℃以上に再加熱し、850 〜95
0 ℃の温度で仕上圧延を終了する熱間圧延に供し、つい
で15℃/s以上の冷却速度で、一気にあるいは途中空冷を
挟んで、350 ℃以下まで冷却したのち巻き取る、焼付け
硬化性と加工性に優れた熱延鋼板の製造方法が記載され
ている。Japanese Patent Application Laid-Open No. 4-74824 discloses that C:
0.02-0.13%, N: 0.0080-0.0250%, sol.Al: 0.10%
Reheat steel containing 1850C or higher to 850-95
Finish rolling at a temperature of 0 ° C is performed, followed by hot rolling, then at a cooling rate of 15 ° C / s or more, at once, or with air cooling in between, cooling to 350 ° C or less, winding and winding, baking hardening and processing. A method for producing a hot-rolled steel sheet having excellent heat resistance is described.
【０００６】[0006]
【発明が解決しようとする課題】しかしながら、特開平
１−180917号公報に記載された技術で製造された熱延鋼
板では、耐常温時効性が劣化する、すなわち、常温で長
時間放置すると鋼の伸び特性が劣化するという問題を残
していた。また、特開平４−74824 号公報に記載された
技術で製造された熱延鋼板は、フェライトとマルテンサ
イトを主体とする複合組織を有するものであり、加工−
塗装焼付け処理後の引張強さは増加するが、耐常温時効
性については、配慮されておらず、劣化するという問題
を残していた。However, in the hot-rolled steel sheet manufactured by the technique described in Japanese Patent Application Laid-Open No. 1-180917, the aging resistance at room temperature is deteriorated. The problem that elongation characteristics deteriorate was left. A hot-rolled steel sheet manufactured by the technique described in Japanese Patent Application Laid-Open No. 4-74824 has a composite structure mainly composed of ferrite and martensite.
Although the tensile strength after the paint baking treatment increases, the aging resistance at room temperature is not taken into consideration, leaving a problem of deterioration.
【０００７】本発明の目的は、上記従来技術の問題を有
利に解決し、引張強さ440 MPa 以上の高強度熱延鋼板に
おいて、焼付け硬化性、耐衝撃性をともに向上させた、
自動車の内装材として好適な熱延鋼板およびその製造方
法を提供することにある。An object of the present invention is to advantageously solve the above-mentioned problems of the prior art, and to improve both bake hardenability and impact resistance in a high-strength hot-rolled steel sheet having a tensile strength of 440 MPa or more.
An object of the present invention is to provide a hot-rolled steel sheet suitable as an interior material of an automobile and a method for manufacturing the same.
【０００８】[0008]
【課題を解決するための手段】本発明者らは、前記目的
を達成すべく鋭意考究・実験した結果、440 MPa 以上の
引張強さを有する鋼について加工−塗装焼付け処理によ
り降伏強さを80MPa 以上上昇させれば低歪速度での変形
時の吸収エネルギーが高まり、耐衝撃性が向上し、加工
−塗装焼付け処理による降伏強さの上昇を、耐時効性を
劣化させずに達成するには、鋼板中に固溶状態で存在す
るＮすなわち固溶Ｎの量ならびにフェライト粒径を適正
範囲内に制御することが有効であり、固溶Ｎの量および
フェライト粒径は、仕上圧延条件および仕上圧延後の冷
却条件を適正化することにより制御可能であることを知
見するに至った。Means for Solving the Problems As a result of intensive studies and experiments to achieve the above object, the present inventors have found that a steel having a tensile strength of 440 MPa or more has a yield strength of 80 MPa by processing-paint baking. By increasing the above, the absorbed energy at the time of deformation at a low strain rate is increased, the impact resistance is improved, and the increase in yield strength due to processing-paint baking treatment can be achieved without deteriorating the aging resistance It is effective to control the amount of N present in the solid solution in the steel sheet, that is, the amount of the solute N and the ferrite particle size within an appropriate range. They have found that control is possible by optimizing the cooling conditions after rolling.
【０００９】例えば図１は、前記実験結果の一例を示す
もので、表１の鋼Ｃ相当組成を有する鋼素材を種々の条
件で熱間圧延し、得られた熱延鋼板について調査した曲
げ圧壊試験の吸収エネルギー上昇率ηとＢＨ量の関係を
示すグラフである。ここに、曲げ圧壊試験は、図３に示
す形状の試験片、すなわち、曲げ加工により成形したハ
ット成形部品１と平板２とをスポット溶接により接合し
た試験片３を、図４に示すように、間隔 500mmの２点で
支持しておき、これに先端が曲率半径Ｒ＝ 150mmの曲面
形状をした50kgのポンチ４を55km/hの速度で衝突させて
３点曲げ変形を生じさせ、その時の吸収エネルギーを求
めることにより行った。For example, FIG. 1 shows an example of the above experimental results. A steel material having a composition equivalent to steel C shown in Table 1 was hot-rolled under various conditions, and bending crushing was performed on the obtained hot-rolled steel sheet. It is a graph which shows the relationship between the absorption energy increase rate (eta) of a test, and BH amount. Here, in the bending crush test, as shown in FIG. 4, a test piece having a shape shown in FIG. 3, that is, a test piece 3 in which a hat-formed part 1 formed by bending and a flat plate 2 were joined by spot welding was used. It is supported at two points with an interval of 500 mm, and a 50 kg punch 4 whose tip has a curved surface shape with a radius of curvature R = 150 mm collides with it at a speed of 55 km / h to cause three-point bending deformation and absorption at that time. This was done by seeking energy.
【００１０】前記吸収エネルギー上昇率ηは、前記曲げ
圧壊試験において、試験片として曲げ加工およびスポッ
ト溶接したままのものと、該曲げ加工およびスポット溶
接ののち170 ℃×20分の塗装焼付け相当の熱処理を施し
たものとを用いて、それぞれ圧壊して吸収エネルギーＥ
（曲げ加工スポット溶接まま）、ＥBH（熱処理後）を測
定し、η＝｛（ＥBH−Ｅ）／Ｅ｝×100 （％）なる式に
より算出した。In the bending crushing test, the absorbed energy increase rate η is determined by assuming that a test piece is subjected to bending and spot welding, and a heat treatment equivalent to baking at 170 ° C. × 20 minutes after the bending and spot welding. , And crush each to absorb energy E
(Bending spot welding) and E BH (after heat treatment) were measured and calculated by the formula of η = {(E BH −E) / E} × 100 (%).
【００１１】また、ＢＨ量（MPa ）は、JIS 13 B号引張
試験片に、２％引張予歪付与→除荷→170 ℃×20分保持
（塗装焼付け処理相当の熱処理）を順次行う歪時効処理
を施し、次いで歪速度10-3/sの引張試験を行い、２％引
張予歪付与時の最高応力と、前記引張試験により求めら
れる上降伏点の差を求めることにより得られる。なお、
ＢＨ量（MPa ）を歪時効強化能と称する。The BH amount (MPa) is obtained by applying a 2% tensile pre-strain to a JIS 13B tensile test specimen, unloading it, and holding it at 170 ° C. for 20 minutes (heat treatment equivalent to paint baking treatment). After the treatment, a tensile test is performed at a strain rate of 10 −3 / s, and the difference between the maximum stress at the time of applying a 2% tensile prestrain and the upper yield point obtained by the tensile test is obtained. In addition,
The BH amount (MPa) is referred to as strain aging enhancing ability.
【００１２】図１に示すようにＢＨ量が80MPa を超える
とηが急増し、高い耐衝撃性向上能が発現する。なお、
得られた熱延鋼板について、固溶Ｎ量およびフェライト
粒径を測定したところ、このＢＨ量＞80MPa の範囲（良
好範囲と称する）となるものでは固溶Ｎ：0.0030％以上
でかつフェライト粒径：7.0 μｍ以下であった。すなわ
ち、固溶Ｎを0.0030％以上、フェライト粒径を7.0 μｍ
以下に制御することにより、80MPa を超えるＢＨ量が得
られ、同時に耐衝撃性を顕著に向上させることができ
る。As shown in FIG. 1, when the amount of BH exceeds 80 MPa, η rapidly increases, and a high impact resistance improving ability is exhibited. In addition,
The obtained hot-rolled steel sheet was measured for the amount of solid solution N and the particle size of ferrite. When the BH amount was within the range of 80 MPa (referred to as a good range), the solid solution N: 0.0030% or more and the ferrite particle size : 7.0 μm or less. That is, the solid solution N is 0.0030% or more, and the ferrite particle size is 7.0 μm.
By controlling as follows, a BH amount exceeding 80 MPa can be obtained, and at the same time, the impact resistance can be significantly improved.
【００１３】また、図２は、前記実験結果を一部整理し
て得られた、フェライト粒径と仕上圧延の最終３パス合
計圧下率ＲFL3P、仕上圧延終了温度ＦＤＴの関係を示す
グラフである。図示のように、ＦＤＴが（Ar3 ＋10℃）
程度〜（Ar3 ＋100 ℃）程度の温度域にあり、かつＲ
FL3Pが15％程度以上の場合に、フェライト粒径が7.0 μ
ｍ以下となる。FIG. 2 is a graph showing the relationship between the ferrite grain size, the final three-pass total rolling reduction R FL3P , and the finish rolling end temperature FDT obtained by partially organizing the experimental results. . As shown, FDT is (Ar 3 + 10 ° C)
In the temperature range of about to (Ar 3 + 100 ° C.)
When FL3P is about 15% or more, ferrite grain size is 7.0 μ
m or less.
【００１４】本発明は、これらの知見に基づきさらに検
討を重ねてなされたものであって、その要旨とするとこ
ろは、Ｃ：0.01〜0.16％、Si：2.0 ％以下、Mn：3.0 ％
以下、Ｐ：0.005 〜0.2 ％、Al：0.001 〜0.1 ％、Ｎ：
0.0060超〜0.0200％うち固溶Ｎ：0.0030〜0.0100％、残
部Feおよび不可避的不純物からなる組成および平均結晶
粒径7.0 μｍ以下のフェライトを主相とする組織を有
し、引張強さ440 〜840MPa、歪時効強化能80MPa 超を有
する焼付け硬化性および耐衝撃性に優れた高張力熱延鋼
板にある。The present invention has been further studied on the basis of these findings, and the gist thereof is as follows: C: 0.01 to 0.16%, Si: 2.0% or less, Mn: 3.0%
Hereinafter, P: 0.005 to 0.2%, Al: 0.001 to 0.1%, N:
More than 0.0060% to 0.0200% of which solid solution N: 0.0030% to 0.0100%, with the composition consisting of the main phase of ferrite with the composition consisting of the balance Fe and unavoidable impurities and the average crystal grain size of 7.0 μm or less, and the tensile strength of 440 to 840MPa High tensile strength hot rolled steel sheet with excellent bake hardenability and impact resistance that has a strain aging strengthening capacity of over 80 MPa.
【００１５】本発明では、前記組成にさらに、Ti：0.00
1 〜0.1 ％、Nb：0.001 〜0.1 ％のうちの１種または２
種および／またはNi：0.1 〜1.5 ％、Cr：0.1 〜1.5
％、Mo：0.1 〜1.5 ％のうちの１種または２種以上が付
加されたものが好ましい。また、前記組織のフェライト
体積率が65％以上であることが好ましい。また、前記組
織がパーライト、ベイナイト、マルテンサイト、残留オ
ーステナイトの１種または２種以上からなる第２相を有
するものが好ましい。また、本発明の高張力熱延鋼板
は、鋼板表面にめっき層を有するものであってもよい。In the present invention, the composition further contains Ti: 0.00
One or two of 1 to 0.1%, Nb: 0.001 to 0.1%
Species and / or Ni: 0.1-1.5%, Cr: 0.1-1.5
%, Mo: 0.1 to 1.5%, to which one or more kinds are added. Further, the ferrite volume ratio of the structure is preferably 65% or more. Further, it is preferable that the structure has a second phase composed of one or more of pearlite, bainite, martensite, and retained austenite. Further, the high-tensile hot-rolled steel sheet of the present invention may have a plating layer on the surface of the steel sheet.
【００１６】また、本発明は、Ｃ：0.01〜0.16％、Si：
2.0 ％以下、Mn：3.0 ％以下、Ｐ：0.005 〜0.2 ％、A
l：0.001 〜0.1 ％、Ｎ：0.0060超〜0.0200％を含む組
成になる鋼素材を950 〜1250℃に加熱後、粗圧延し、次
いで最終３パス合計圧下率：15〜65％、圧延終了温度Ｆ
ＤＴ：（Ar3 ＋10℃）〜（Ar3 ＋100 ℃）になる仕上圧
延に供し、該仕上圧延の終了後0.5 秒以内に冷却速度20
℃/s以上で冷却し、600〜300 ℃で巻き取ることを特徴
とする焼付け硬化性および耐衝撃性に優れた高張力熱延
鋼板の製造方法である。Further, the present invention relates to a method for producing C: 0.01 to 0.16%, Si:
2.0% or less, Mn: 3.0% or less, P: 0.005 to 0.2%, A
l: A steel material having a composition containing 0.001 to 0.1% and N: more than 0.0060 to 0.0200% is heated to 950 to 1250 ° C, then rough-rolled, and then the final three-pass total rolling reduction: 15 to 65%, the rolling end temperature F
DT: subjected to finish rolling at (Ar 3 + 10 ° C.) to (Ar 3 + 100 ° C.), and cooled within 0.5 seconds after completion of the finish rolling to a cooling rate of 20
This is a method for producing a high-strength hot-rolled steel sheet excellent in bake hardenability and impact resistance, characterized in that the steel sheet is cooled at a temperature of at least 600 ° C / s and wound up at 600 to 300 ° C.
【００１７】[0017]
【発明の実施の形態】本発明における組成の限定理由は
以下の通りである。なお、化学成分含有量（濃度）に係
る％は質量パーセントを意味する。 Ｃ：0.01〜0.16％ Ｃは、鋼の強度を増加させる元素であり、強度確保の観
点から0.01％以上を必要とするが、一方、0.16％を超え
て含有すると溶接性が劣化するので、0.01〜0.16％とす
る。就中 0.01 〜0.12％が好ましい。DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition in the present invention are as follows. In addition,% concerning the chemical component content (concentration) means percent by mass. C: 0.01 to 0.16% C is an element that increases the strength of steel, and requires 0.01% or more from the viewpoint of securing the strength. On the other hand, if it exceeds 0.16%, the weldability deteriorates. To 0.16%. Especially, 0.01 to 0.12% is preferable.
【００１８】Si：2.0 ％以下 Siは、固溶強化により鋼の強度増加に寄与する元素であ
り、所望の強度に応じて含有量を調整する。しかし、2.
0 ％を超えると加工性を劣化させるため2.0 ％以下とす
る。なお、強度の確保の観点からは、Siは0.003 ％以上
含有させるのが望ましい。Si: 2.0% or less Si is an element that contributes to the increase in the strength of steel by solid solution strengthening, and its content is adjusted according to the desired strength. But 2.
If it exceeds 0%, the workability is deteriorated, so the content is made 2.0% or less. From the viewpoint of securing the strength, it is desirable that Si is contained at 0.003% or more.
【００１９】Mn：3.0 ％以下 Mnは、鋼の強度を増加させるとともに、Ｓによる熱間脆
性を防止する元素であり、積極的に含有させる。しか
し、3.0 ％を超えて含有させると加工性が低下する。こ
のため、Mnは3.0 ％以下に限定した。なお、所望の強度
を確保し、熱間脆性を防止するためには0.01％以上含有
させることが望ましい。Mn: 3.0% or less Mn is an element that increases the strength of steel and prevents hot brittleness due to S, and is positively contained. However, if the content exceeds 3.0%, the processability decreases. For this reason, Mn was limited to 3.0% or less. In addition, in order to secure desired strength and prevent hot brittleness, it is desirable to contain 0.01% or more.
【００２０】Ｐ：0.005 〜0.2 ％ Ｐは、鋼の強度を増加させる元素であり、引張強さ440
MPa 以上を確保するには0.005 ％以上を必要とするが、
一方、0.2 ％を超えると溶接性が劣化し、またＰが粒界
に偏析して粒界割れを発生させる虞があるため、0.005
〜0.2 ％とする。就中 0.005〜0.15％が好ましい。P: 0.005 to 0.2% P is an element that increases the strength of steel and has a tensile strength of 440%.
To secure more than MPa, you need 0.005% or more,
On the other hand, if it exceeds 0.2%, the weldability deteriorates, and P may segregate at the grain boundaries to cause grain boundary cracking.
To 0.2%. In particular, 0.005 to 0.15% is preferable.
【００２１】Al：0.001 〜0.1 ％ Alは、脱酸剤として作用し、鋼の脱酸のためには0.001
％以上含有する必要があるが、一方、0.1 ％を超えると
表面性状を劣化させるため、0.001 〜0.1 ％とする。就
中 0.005〜0.07％が好ましい。 Ｎ：0.0060超〜0.0200％うち固溶Ｎ：0.0030〜0.0100％ Ｎは、本発明ではとくに重要な元素であり、鋼中に固溶
して加工−塗装焼付け処理後に降伏強さを顕著に増加さ
せる、すなわち歪時効強化能を著しく向上させる働きを
もつ。この働きは固溶Ｎが0.0030％以上で発現するが、
一方、固溶Ｎが0.0100％超では成形性が劣化するため、
固溶Ｎは0.0030〜0.0100％の範囲に限定される。また、
全Ｎが0.0060％以下では固溶Ｎが0.0030％に届かず、一
方、全Ｎが0.0200％を超えると固溶Ｎが0.0100％を超え
てしまうため、全Ｎは0.0060超〜0.0200％とする。就中
好ましくは、固溶Ｎ：0.0050〜0.0100％である。Al: 0.001 to 0.1% Al acts as a deoxidizing agent, and 0.001 to 0.1% for deoxidizing steel.
%, On the other hand, if it exceeds 0.1%, the surface properties deteriorate, so the content is made 0.001 to 0.1%. In particular, 0.005 to 0.07% is preferable. N: more than 0.0060 to 0.0200%, of which solid solution is N: 0.0030 to 0.0100% N is a particularly important element in the present invention, and forms a solid solution in steel to significantly increase the yield strength after processing-paint baking. That is, it has a function of remarkably improving the ability to enhance strain aging. This function is manifested when the solute N is 0.0030% or more,
On the other hand, if the solute N exceeds 0.0100%, the formability deteriorates.
The solute N is limited to the range of 0.0030 to 0.0100%. Also,
If the total N is 0.0060% or less, the solid solution N does not reach 0.0030%, while if the total N exceeds 0.0200%, the solid solution N exceeds 0.0100%. Therefore, the total N is set to more than 0.0060 to 0.0200%. Particularly preferably, the solid solution N is 0.0050 to 0.0100%.
【００２２】なお、Ｎ（全Ｎ）は湿式分析により定量さ
れ、固溶Ｎは、抽出分離法による窒化物中のＮ定量値を
前記全Ｎの定量値から差し引くことにより定量される。 Ti：0.001 〜0.1 ％、Nb：0.001 〜0.1 ％のうちの１種
または２種 Ti、Nbはいずれも炭化物、窒化物、硫化物を形成し強度
および靱性の向上に寄与する。これらの効果は、0.001
％以上で認められるが、0.1 ％を超えると焼付け硬化性
に寄与するＣ、Ｎが減少し、所望の焼付け硬化性を確保
しにくくなる。よって、Ti、Nbはいずれも0.001 〜0.1
％が好ましい。Incidentally, N (total N) is determined by wet analysis, and solute N is determined by subtracting the quantitative value of N in the nitride by the extraction separation method from the quantitative value of the total N. One or two of Ti: 0.001 to 0.1% and Nb: 0.001 to 0.1% Ti and Nb both form carbides, nitrides, and sulfides and contribute to improvement in strength and toughness. These effects are 0.001
%, But if it exceeds 0.1%, C and N contributing to bake hardenability decrease, making it difficult to secure desired bake hardenability. Therefore, both Ti and Nb are 0.001 to 0.1
% Is preferred.
【００２３】Ni：0.1 〜1.5 ％、Cr：0.1 〜1.5 ％、M
o：0.1 〜1.5 ％のうちの１種または２種以上 Ni、Cr、Moは、いずれも固溶強化により鋼の強度を増加
させる元素であるとともに、熱延後の冷却過程でオース
テナイト（γ）を安定化し二相組織を形成しやすくする
効果もある。かかる効果は0.1 ％以上で認められる。一
方、1.5 ％を超えると成形性、めっき性、スポット溶接
性を劣化させる。よって、Ni、Cr、Moは、いずれも0.1
〜1.5 ％が好ましい。Ni: 0.1-1.5%, Cr: 0.1-1.5%, M
o: One or more of 0.1 to 1.5% Ni, Cr and Mo are elements that increase the strength of steel by solid solution strengthening, and austenite (γ) during the cooling process after hot rolling. And has the effect of facilitating the formation of a two-phase structure. Such effects are observed at 0.1% or more. On the other hand, if it exceeds 1.5%, the formability, the plating property, and the spot weldability deteriorate. Therefore, Ni, Cr and Mo are all 0.1
~ 1.5% is preferred.
【００２４】本発明に係る熱延鋼板では、上記成分以外
の残部はFeおよび不可避的不純物である。不可避的不純
物に属するＳ、Ｏは、非金属介在物を形成し品質に悪影
響を及ぼすため、それぞれ0.05％以下、0.01％以下に低
減するのが好ましい。本発明の熱延鋼板の組成は上記の
通りであるが、所望の焼付け硬化性を得るには組成の限
定のみでは不十分であり、その組織が平均結晶粒径7.0
μｍ以下のフェライトを主相とする組織であることを要
する。ここに、主相とは体積率50〜100 ％を占める相を
意味し、この相が平均結晶粒径7.0 μｍ以下のフェライ
トからなる。主相がフェライト以外のものでは加工性に
乏しく、また、主相がフェライトであってもその平均粒
径が7.0 μｍ超では図１の良好範囲を逸脱して焼付け硬
化性およびこれによる耐衝撃性の同時向上は望みえな
い。この組織要件を付加することで、組織が微細化する
とともに、固溶Ｎの偏在箇所になる結晶粒界が増大し、
そのことによって初めて、引張強さ：440 〜840MPa、歪
時効強化能：80MPa超を確保することができ、なおか
つ、常温時効性をも向上させることができる。In the hot-rolled steel sheet according to the present invention, the balance other than the above components is Fe and inevitable impurities. Since S and O belonging to unavoidable impurities form nonmetallic inclusions and adversely affect the quality, it is preferable to reduce the content to 0.05% or less and 0.01% or less, respectively. Although the composition of the hot-rolled steel sheet of the present invention is as described above, it is not enough to limit the composition only to obtain the desired bake hardenability, and the structure has an average crystal grain size of 7.0.
It is necessary that the structure has a main phase of ferrite of μm or less. Here, the main phase means a phase occupying 50 to 100% by volume, and this phase is made of ferrite having an average crystal grain size of 7.0 μm or less. If the main phase is other than ferrite, the workability is poor. Even if the main phase is ferrite, if the average particle size exceeds 7.0 μm, the baking hardenability and the impact resistance due to the deviation from the good range of FIG. Is not expected to improve at the same time. By adding this structure requirement, the structure becomes finer, and the crystal grain boundaries that become the unevenly distributed portions of solid solution N increase,
For the first time, a tensile strength of 440 to 840 MPa and a strain aging strengthening ability of more than 80 MPa can be ensured, and the aging property at ordinary temperature can be improved.
【００２５】なお、フェライト体積率65％以上のものと
これ未満のものとを比べると、前者のほうが一段と焼付
け硬化性、耐衝撃性に優れる。よって、主相であるフェ
ライトの体積率は65％以上が好ましい。また、前記組織
がパーライト、ベイナイト、マルテンサイト、残留オー
ステナイトの１種または２種以上からなる第２相を有す
るものが好ましい。第２相を存在させると、高価な合金
元素の多量添加を要さずに高強度化することができるか
らである。なお、第２相の体積率は加工性の観点から３
〜30％が好ましい。When the ferrite having a volume fraction of 65% or more is compared with a ferrite having a volume fraction of less than 65%, the former is more excellent in bake hardenability and impact resistance. Therefore, the volume fraction of ferrite as the main phase is preferably 65% or more. Further, it is preferable that the structure has a second phase composed of one or more of pearlite, bainite, martensite, and retained austenite. This is because the presence of the second phase can increase the strength without requiring the addition of a large amount of expensive alloying elements. The volume ratio of the second phase is 3 from the viewpoint of workability.
~ 30% is preferred.
【００２６】また、本発明に係る高張力熱延鋼板は、鋼
板表面に、亜鉛、錫、クロム、ニッケル等のめっき層を
有するものであってもよい。次に、本発明に係る高張力
熱延鋼板の好ましい製造方法について説明する。これ
は、Ｃ：0.01〜0.16％、Si：2.0 ％以下、Mn：3.0 ％以
下、Ｐ：0.005 〜0.2 ％、Al：0.001 〜0.1 ％、Ｎ：0.
0060超〜0.0200％を含む組成になる鋼素材を950 〜1250
℃に加熱後、粗圧延し、次いで最終３パス合計圧下率：
15〜65％、圧延終了温度ＦＤＴ：（Ar3 ＋10℃）〜（Ar
3 ＋100 ℃）になる仕上圧延に供し、該仕上圧延の終了
後0.5 秒以内に冷却速度20℃/s以上で冷却し、600 〜30
0 ℃で巻き取るという方法である。The high-tensile hot-rolled steel sheet according to the present invention may have a plating layer of zinc, tin, chromium, nickel or the like on the surface of the steel sheet. Next, a preferred method for producing a high-tensile hot-rolled steel sheet according to the present invention will be described. These are: C: 0.01 to 0.16%, Si: 2.0% or less, Mn: 3.0% or less, P: 0.005 to 0.2%, Al: 0.001 to 0.1%, N: 0.
A steel material having a composition containing more than 0.0200%
℃, rough rolling, then the final three-pass total rolling reduction:
15-65%, rolling end temperature FDT: (Ar 3 + 10 ° C.)-(Ar
3 + 100 ° C), and at a cooling rate of 20 ° C / s or more within 0.5 seconds after the finish rolling,
This is a method of winding at 0 ° C.
【００２７】前記鋼素材は、公知の溶製方法により溶製
された溶鋼を公知の連続鋳造法もしくは造塊法により鋳
造してスラブ等の形状に凝固させたものが好ましい。凝
固後の鋼素材は、加熱炉等通常公知の装置で950 〜1250
℃に加熱される。この加熱温度が950 ℃未満では窒化物
が溶解しにくくなって、熱延板の固溶Ｎが不足し、一
方、1250℃超ではオーステナイト粒が粗大化して、熱延
板のフェライト粒径が7.0 μｍ以下にならない。よっ
て、加熱温度は950 〜1250℃とする。就中1000〜1100℃
がより好ましい。It is preferable that the steel material is obtained by casting molten steel produced by a known smelting method by a known continuous casting method or ingot casting method and solidifying it into a slab or the like. The steel material after solidification is 950 to 1250 by a generally known device such as a heating furnace.
Heat to ° C. If the heating temperature is lower than 950 ° C., the nitride is difficult to dissolve, and the solid solution N of the hot-rolled sheet becomes insufficient. μm or less. Therefore, the heating temperature is 950 to 1250 ° C. 1000-1100 ℃
Is more preferred.
【００２８】加熱された鋼素材は、公知の粗圧延機によ
る粗圧延、公知の仕上圧延機による仕上圧延に順次供せ
られる。なお、加熱後粗圧延前に公知の幅プレス装置に
よる幅調整を行ってもよい。仕上圧延は、その最終３パ
ス合計圧下率ＲFL3P（３スタンド以上のタンデムミルに
よる通常公知の連続圧延では、後段３スタンドの合計圧
下率に該当する）が15〜65％に収まり、かつ圧延終了温
度ＦＤＴが（Ar3 ＋10℃）〜（Ar3 ＋100 ℃）に収まる
ように行う必要がある。ＲFL3Pが15％未満であるかまた
はＦＤＴが（Ar3 ＋100 ℃）超であると、フェライト変
態前の歪エネルギーの蓄積が不十分となり、フェライト
粒径を 7.0μm 以下に微細化することができなくなる。
また、ＦＤＴが（Ar3 ＋10℃）未満であると変態前の板
厚方向歪分布が不均一となって、フェライト粒径の微細
化が図れなくなる。また、ＲFL3Pが65％超では圧延形状
の乱れが発生しやすくなる。The heated steel material is sequentially subjected to rough rolling by a known rough rolling machine and finish rolling by a known finishing rolling machine. The width may be adjusted by a known width press after heating and before rough rolling. In the finish rolling, the final three-pass total rolling reduction R FL3P (corresponding to the total rolling reduction of the latter three stands in the case of a generally known continuous rolling by a tandem mill having three or more stands) falls within 15 to 65%, and the rolling is completed. It is necessary to adjust the temperature so that the temperature FDT falls within the range of (Ar 3 + 10 ° C.) to (Ar 3 + 100 ° C.). If R FL3P is less than 15% or FDT exceeds (Ar 3 + 100 ° C.), the accumulation of strain energy before ferrite transformation becomes insufficient, and the ferrite grain size can be reduced to 7.0 μm or less. Disappears.
On the other hand, if the FDT is less than (Ar 3 + 10 ° C.), the strain distribution in the thickness direction before the transformation becomes non-uniform, and it becomes impossible to reduce the ferrite grain size. On the other hand, if R FL3P exceeds 65%, the rolling shape is likely to be disordered.
【００２９】仕上圧延終了後は、該終了時点から0.5 秒
以内に20℃/s以上の冷却速度で冷却し、巻取温度ＣＴ：
600 〜300 ℃で巻き取る必要がある。仕上圧延終了から
巻取りまでに係る限定要件は、歪エネルギーを十分に蓄
積した状態で過冷度を大きくし、より多くのフェライト
核を生成させるために設けられる。仕上圧延終了から冷
却開始までの時間が0.5 秒を超え、もしくは巻取りまで
の冷却速度が20℃/sを下回ると、フェライト核生成が不
十分となり、また、フェライト粒成長も促進されて、フ
ェライトを微細化することができない。After the finish rolling is completed, the roll is cooled at a cooling rate of 20 ° C./s or more within 0.5 seconds from the end of the finish rolling.
It must be wound at 600-300 ° C. The limited requirements from the finish rolling to the winding are provided to increase the degree of supercooling in a state where the strain energy is sufficiently accumulated and to generate more ferrite nuclei. If the time from the end of finish rolling to the start of cooling exceeds 0.5 seconds, or the cooling rate before winding is less than 20 ° C / s, ferrite nucleation will be insufficient and ferrite grain growth will be accelerated, and ferrite grain growth will be accelerated. Cannot be miniaturized.
【００３０】巻取温度ＣＴに係る限定要件は、固溶Ｎの
析出抑制と操業上の問題回避のために設けられる。ＣＴ
が600 ℃超では固溶Ｎが過剰に析出してしまい、焼付け
硬化に必要な固溶Ｎ量を確保できなくなる。一方、ＣＴ
が300 ℃未満では板形状が悪化したり通板性が悪化する
など操業上の問題が発生する。上記の製造方法によって
得られた本発明の熱延鋼板は、各種めっき用原板として
好適であり、必要に応じてその表面に各種めっき層を形
成し、各種めっき鋼板として使用することもできる。め
っきの種類としては、電気亜鉛めっき、溶融亜鉛めっ
き、電気錫めっき、電気クロムめっき、電気ニッケルめ
っき等が挙げられ、いずれも本発明の熱延鋼板の表面に
形成されるめっき層として好適である。The limitation on the winding temperature CT is provided to suppress the precipitation of solute N and to avoid operational problems. CT
However, if the temperature exceeds 600 ° C., excessive amount of solid solution N precipitates, and the amount of solid solution N required for baking hardening cannot be secured. On the other hand, CT
However, if the temperature is lower than 300 ° C., operational problems such as deterioration of the shape of the sheet and deterioration of the sheet passing property occur. The hot-rolled steel sheet of the present invention obtained by the above-described production method is suitable as an original sheet for various platings, and can be used as various plated steel sheets by forming various plating layers on its surface as needed. Examples of the type of plating include electrogalvanizing, hot-dip galvanizing, electrotin plating, electrochromic plating, and electronickel plating, all of which are suitable as a plating layer formed on the surface of the hot-rolled steel sheet of the present invention. .
【００３１】[0031]
【実施例】表１に示す組成になる溶鋼を転炉で溶製し、
連続鋳造法でスラブとなし、これらスラブを表２に示す
加熱温度に加熱後、粗圧延してシートバーとなし、これ
らシートバーを表２に示す最終３パス合計圧下率
ＲFL3P、仕上圧延終了温度ＦＤＴになる仕上圧延に供
し、該仕上圧延の終了時点から表２に示す時間τ秒以内
に表２に示す冷却速度ＣＲ（℃/s）で表２に示す巻取温
度ＣＴ（℃）まで冷却し、コイル状に巻き取って熱延鋼
板（板厚 1.6mm）となした。これら熱延鋼板について、
組織試験、固溶Ｎ測定、引張試験、穴拡げ試験、歪時効
試験、常温時効試験、曲げ圧壊試験を行った。なお、表
２中No.19 の熱延鋼板については、鋼板表面に溶融亜鉛
めっきを施した後に、各種試験に供した。EXAMPLE Molten steel having the composition shown in Table 1 was melted in a converter.
The slabs were formed by continuous casting, and these slabs were heated to the heating temperature shown in Table 2 and then rough-rolled to form sheet bars. These sheet bars were subjected to final three-pass total rolling reduction R FL3P shown in Table 2, and finish rolling was completed. It is subjected to finish rolling at a temperature FDT, and within a time τ seconds shown in Table 2 from the end of the finish rolling to a winding rate CT (° C.) shown in Table 2 at a cooling rate CR (° C./s) shown in Table 2. It was cooled and wound into a coil to form a hot-rolled steel sheet (sheet thickness 1.6 mm). About these hot rolled steel sheets,
A texture test, a solid solution N measurement, a tensile test, a hole expansion test, a strain aging test, a normal temperature aging test, and a bending crush test were performed. The hot-rolled steel sheet No. 19 in Table 2 was subjected to various tests after hot-dip galvanizing on the steel sheet surface.
【００３２】(i) 組織試験 前記熱延鋼板から該鋼板の圧延方向に垂直な断面を有す
る試片を採取し、該断面を適宜の腐食液で処理し現出さ
せた組織を光学顕微鏡にて観察して同定した。また、画
像解析によりフェライト体積率およびフェライト粒径
（平均結晶粒径）を測定した。(I) Microstructure Test A specimen having a cross section perpendicular to the rolling direction of the hot-rolled steel sheet was sampled from the hot-rolled steel sheet, and the cross-section was treated with an appropriate corrosive liquid to reveal a microstructure by an optical microscope. Observed and identified. The ferrite volume fraction and ferrite grain size (average crystal grain size) were measured by image analysis.
【００３３】(ii)固溶Ｎ測定 電解抽出法により熱延鋼板中に窒化物として存在するＮ
を定量し、その結果を表１のＮ量から差し引くことによ
り測定した。 (iii) 引張試験 前記熱延鋼板から採取したJIS 13 B号引張試験片に歪速
度10-3/sの引張試験を行って降伏強さＹＳ（MPa ）、引
張強さＴＳ（MPa ）、伸びＥＬ（％）を測定した。(Ii) Measurement of solid solution N N present in the hot-rolled steel sheet as nitride by electrolytic extraction method
Was quantified, and the result was measured by subtracting the result from the N amount in Table 1. (iii) Tensile test A tensile test at a strain rate of 10 -3 / s was performed on a JIS 13B tensile test specimen collected from the hot-rolled steel sheet, yield strength YS (MPa), tensile strength TS (MPa), elongation EL (%) was measured.
【００３４】(iv)穴拡げ試験 前記熱延鋼板に初期直径d0=10mm の穴を打ち抜き、頂角
60°の円錐ポンチを上昇させ穴を拡げた際に、亀裂が板
厚貫通したところでポンチ上昇を止め、亀裂貫通後の打
ち抜き穴径d を測定し、穴拡げ率λ=((d-d0)/d0)×100
（％）を算出して伸びフランジ性の指標とした。(Iv) Hole expansion test A hole having an initial diameter d 0 = 10 mm was punched out from the hot-rolled steel sheet, and a vertex angle was obtained.
When raising the 60 ° conical punch and expanding the hole, stop the punch rise when the crack penetrates the plate thickness, measure the punched hole diameter d after the crack penetrating, the hole expansion rate λ = ((dd 0 ) / d 0 ) × 100
(%) Was calculated and used as an index of stretch flangeability.
【００３５】(v) 歪時効試験 前記熱延鋼板から採取したJIS 13 B号引張試験片に前述
の、２％引張予歪付与→除荷→ 170℃×20分保持という
歪時効処理を施した後歪速度10-3/sの引張試験を行って
ＢＨ量を求めた。また、JIS13B号引張試験片に５％の引
張歪を付与した後、一旦除荷し、 170℃×20分の塗装焼
付処理相当の熱処理を施し、次いで引張試験により引張
強さＴＳBH（MPa ）を求め、ΔTS＝ＴＳBH−ＴＳを求め
た。(V) Strain aging test A JIS 13B tensile test specimen collected from the hot-rolled steel sheet was subjected to the above-described strain aging treatment of imparting 2% tensile prestrain → unloading → holding at 170 ° C. × 20 minutes. A BH amount was determined by performing a tensile test at a post-strain rate of 10 −3 / s. Also, after imparting 5% tensile strain to the JIS13B tensile test specimen, the specimen is once unloaded, subjected to a heat treatment equivalent to a paint baking treatment at 170 ° C. for 20 minutes, and then subjected to a tensile test to obtain a tensile strength TS BH (MPa). Was determined, and ΔTS = TS BH −TS was determined.
【００３６】(vi)常温時効試験 前記熱延鋼板から採取して50℃×400 ｈの時効処理を施
した試料から採取したJIS 13 B号引張試験片に歪速度10
-3/sの引張試験を行って伸びＥＬA （％）を測定し、伸
び減分ΔEL＝ＥＬ−ＥＬA で耐常温時効性を評価した。 (vii) 曲げ圧壊試験 前記熱延鋼板について前述の曲げ圧壊試験を行い、その
吸収エネルギー上昇率ηで耐衝撃性向上能を評価した。(Vi) Aging test at room temperature A JIS 13B tensile test piece taken from the hot-rolled steel sheet and subjected to aging treatment at 50 ° C. × 400 h was subjected to a strain rate of 10
A tensile test of −3 / s was performed to measure the elongation EL A (%), and the room temperature aging resistance was evaluated by elongation loss ΔEL = EL−EL A. (vii) Bending crush test The above-mentioned bending crush test was performed on the hot-rolled steel sheet, and the ability to improve impact resistance was evaluated based on the absorbed energy increase rate η.
【００３７】これら試験の結果を表３に示す。表３よ
り、実施例はいずれも本発明要件を満足し、高い耐常温
時効性、耐衝撃性向上能を示すのに対し、比較例は本発
明要件の少なくともいずれかを満たしておらず、耐常温
時効性、耐衝撃性向上能の少なくとも一つが実施例より
も大きく劣っている。Table 3 shows the results of these tests. From Table 3, all the examples satisfy the requirements of the present invention, and exhibit high aging resistance at normal temperature and high ability to improve impact resistance. On the other hand, Comparative Examples do not satisfy at least one of the requirements of the present invention. At least one of the room-temperature aging property and the impact resistance improving ability is significantly inferior to the examples.
【００３８】[0038]
【表１】 [Table 1]
【００３９】[0039]
【表２】 [Table 2]
【００４０】[0040]
【表３】 [Table 3]
【００４１】[0041]
【発明の効果】かくして本発明によれば、引張り強さ44
0 MPa 以上の高強度熱延鋼板において、焼付け硬化性、
耐衝撃性をともに向上させた、自動車の内装材として好
適な熱延鋼板を安定して供給することができるようにな
るという、産業上寄与するところ大なる格段の効果を奏
する。Thus, according to the present invention, the tensile strength 44
For high strength hot rolled steel sheets of 0 MPa or more, bake hardenability,
It is possible to stably supply a hot-rolled steel sheet having improved impact resistance and suitable as an interior material of an automobile.
【図１】曲げ圧壊試験の吸収エネルギー上昇率ηとＢＨ
量の関係を示すグラフである。FIG. 1: Absorption energy increase rate η and BH in bending crush test
It is a graph which shows the relationship of quantity.
【図２】フェライト粒径と仕上圧延の最終３パス合計圧
下率ＲFL3P、仕上圧延終了温度ＦＤＴの関係を示すグラ
フである。FIG. 2 is a graph showing a relationship between a ferrite grain size, a final three-pass rolling reduction R FL3P of finish rolling, and a finish rolling end temperature FDT.
【図３】曲げ圧壊試験の試験片形状を示す斜視図であ
る。FIG. 3 is a perspective view showing a test piece shape in a bending crush test.
【図４】曲げ圧壊試験要領を示す説明図である。FIG. 4 is an explanatory view showing a procedure of a bending crush test.
１ ハット成形部品 ２ 平板 ３ 試験片 ４ ポンチ Reference Signs List 1 hat-formed part 2 flat plate 3 test piece 4 punch
───────────────────────────────────────────────────── フロントページの続き (72)発明者 金子 真次郎 千葉県千葉市中央区川崎町１番地 川崎製 鉄株式会社技術研究所内 (72)発明者 登坂 章男 千葉県千葉市中央区川崎町１番地 川崎製 鉄株式会社技術研究所内 Ｆターム(参考） 4K037 EA01 EA05 EA06 EA11 EA15 EA16 EA17 EA18 EA19 EA20 EA23 EA25 EA27 EA28 EA31 EB06 EB08 EB09 EB11 FA01 FA02 FA03 FB08 FC04 FC07 FD03 FD04 FE01 FE02 FE06 GA05 HA01 JA06 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinjiro Kaneko 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel (72) Inventor Akio Tosaka 1-Kawasaki-cho, Chuo-ku Chiba City, Chiba Prefecture 4K037 EA01 EA05 EA06 EA11 EA15 EA16 EA17 EA18 EA19 EA20 EA23 EA25 EA27 EA28 EA31 EB06 EB08 EB09 EB11 FA01 FA02 FA03 FB08 FC04 FE03 FE03 FE04
Claims (6)
n：3.0 ％以下、Ｐ：0.005 〜0.2 ％、Al：0.001 〜0.1
％、Ｎ：0.0060超〜0.0200％うち固溶Ｎ：0.0030〜0.0
100％、残部Feおよび不可避的不純物からなる組成およ
び平均結晶粒径7.0 μｍ以下のフェライトを主相とする
組織を有し、引張強さ440 〜840MPa、歪時効強化能80MP
a 超を有する焼付け硬化性および耐衝撃性に優れた高張
力熱延鋼板。1. C: 0.01 to 0.16%, Si: 2.0% or less, M
n: 3.0% or less, P: 0.005 to 0.2%, Al: 0.001 to 0.1
%, N: 0.0060 to 0.0200% of which solid solution N: 0.0030 to 0.0
It has a composition consisting of 100%, the balance of Fe and the unavoidable impurities, and a structure mainly composed of ferrite having an average crystal grain size of 7.0 μm or less.
a High tensile strength hot rolled steel sheet with excellent bake hardenability and impact resistance.
％、Nb：0.001 〜0.1％のうちの１種または２種および
／またはNi：0.1 〜1.5 ％、Cr：0.1 〜1.5 ％、Mo：0.
1 〜1.5 ％のうちの１種または２種以上が付加された請
求項１記載の高張力熱延鋼板。2. The composition further comprises Ti: 0.001 to 0.1.
%, Nb: one or two of 0.001 to 0.1% and / or Ni: 0.1 to 1.5%, Cr: 0.1 to 1.5%, Mo: 0.
The high-tensile hot-rolled steel sheet according to claim 1, wherein one or more of 1% to 1.5% are added.
である請求項１または２に記載の高張力熱延鋼板。3. The high-tensile hot-rolled steel sheet according to claim 1, wherein the ferrite volume ratio of the structure is 65% or more.
ルテンサイト、残留オーステナイトのうちの１種または
２種以上からなる第２相を有する請求項１〜３のいずれ
かに記載の高張力熱延鋼板。4. The high-tensile hot-rolled steel sheet according to claim 1, wherein the structure has a second phase composed of one or more of pearlite, bainite, martensite, and retained austenite.
熱延鋼板の表面にめっき層を形成してなる焼付け硬化性
および耐衝撃性に優れた高張力熱延鋼板。5. A high-tensile hot-rolled steel sheet having excellent bake hardenability and impact resistance, comprising a plating layer formed on the surface of the high-tensile hot-rolled steel sheet according to claim 1.
n：3.0 ％以下、Ｐ：0.005 〜0.2 ％、Al：0.001 〜0.1
％、Ｎ：0.0060超〜0.0200％を含む組成になる鋼素材
を950 〜1250℃に加熱後、粗圧延し、次いで最終３パス
合計圧下率：15〜65％、圧延終了温度ＦＤＴ：（Ar3 ＋
10℃）〜（Ar3 ＋100 ℃）になる仕上圧延に供し、該仕
上圧延の終了後0.5 秒以内に冷却速度20℃/s以上で冷却
し、600〜300 ℃で巻き取ることを特徴とする焼付け硬
化性および耐衝撃性に優れた高張力熱延鋼板の製造方
法。6. C: 0.01 to 0.16%, Si: 2.0% or less, M
n: 3.0% or less, P: 0.005 to 0.2%, Al: 0.001 to 0.1
%, N: a steel material having a composition containing more than 0.0060 to 0.0200% is heated to 950 to 1250 ° C., rough-rolled, and then a final three-pass total rolling reduction: 15 to 65%, a rolling end temperature FDT: (Ar 3 +
It is characterized in that it is subjected to finish rolling at a temperature of 10 ° C.) to (Ar 3 + 100 ° C.), cooled at a cooling rate of 20 ° C./s or more within 0.5 seconds after completion of the finish rolling, and wound up at 600 to 300 ° C. A method for producing a high-strength hot-rolled steel sheet with excellent bake hardenability and impact resistance.
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| JP2000036756A JP4306078B2 (en) | 2000-02-15 | 2000-02-15 | High tensile hot-rolled steel sheet excellent in bake hardenability and impact resistance and method for producing the same |
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