JP2002161339A - High tensile-strength hot-rolled steel sheet superior in formability and manufacturing method therefor - Google Patents
High tensile-strength hot-rolled steel sheet superior in formability and manufacturing method thereforInfo
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- JP2002161339A JP2002161339A JP2000356929A JP2000356929A JP2002161339A JP 2002161339 A JP2002161339 A JP 2002161339A JP 2000356929 A JP2000356929 A JP 2000356929A JP 2000356929 A JP2000356929 A JP 2000356929A JP 2002161339 A JP2002161339 A JP 2002161339A
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、プレス成形加工を
施して用いられる熱延鋼板に関し、とくに自動車ボディ
ーのメンバー、フレーム、サスペンションなど、自動車
用の構造部材や足まわり部品などの使途に好適な高張力
熱延鋼板およびそ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 hot-rolled steel sheet which is used after being subjected to press forming, and is particularly suitable for use in structural members and undercarriage parts for automobiles, such as members of automobile bodies, frames and suspensions. The present invention relates to a high-strength hot-rolled steel sheet and a method for producing the same.
【０００２】[0002]
【従来の技術】自動車車体の軽量化を図るためには、高
張力鋼板の適用が最も有効な方法の一つである。なかで
も、ボディーの強度部材あるいはサスペンションなど、
さほど優れた表面品質が要求されない部位には、冷延鋼
板よりも安価な熱延鋼板が用いられるようになってき
た。このような状況から、熱延高張力鋼板の使途もます
ます拡大されつつある。従来から、引張強さが 490〜 7
80 MPa程度の高張力熱延鋼板の材質強化方法としては、
1)マルテンサイト相、パーライト相あるいはベイナイト
相などによる変態組織強化法と、2)Ti、Nb、Ｖなどの炭
窒化物による析出強化法が利用されてきており、これら
の強化方法は、鋼板の成形性あるいは部品として要求さ
れる特性に応じて選択されてきた。例えば、安価な汎用
の高張力熱延鋼板では析出強化されたフェライト相と、
パーライト相あるいはベイナイト相組織の鋼板（ＨＳＬ
Ａ：High Strength Low Alloy)が、また延性が要求され
る場合には、フェライト相とマルテンサイ相のDualPhas
e（ＤＰ）鋼が、また伸びフランジ成形性が要求される
場合には、析出強化されたDual Phase鋼が選択されると
いったものである。また、ＤＰ鋼と同様な特性を有して
いるものとして、ＴＲＩＰ鋼（transformation induced
plasticitysteel)も挙げられる。2. Description of the Related Art One of the most effective methods for reducing the weight of an automobile body is to use a high-tensile steel sheet. Above all, such as body strength members or suspension
Hot-rolled steel sheets, which are less expensive than cold-rolled steel sheets, have come to be used for parts that do not require very good surface quality. Under such circumstances, the use of hot-rolled high-tensile steel sheets is being expanded more and more. Conventionally, tensile strength is 490-7
As a method of strengthening the material of hot-rolled steel sheets with a high tensile strength of about 80 MPa,
1) A transformation structure strengthening method using a martensite phase, a pearlite phase, a bainite phase, etc., and 2) a precipitation strengthening method using a carbonitride such as Ti, Nb, V, etc., have been used. It has been selected according to the moldability or the properties required for the part. For example, inexpensive general-purpose high-strength hot-rolled steel sheets have a precipitation-strengthened ferrite phase,
Steel plate with pearlite phase or bainite phase structure (HSL
A: High Strength Low Alloy), and when ductility is required, the dual phase of ferrite phase and martensite phase
If e (DP) steel and stretch flange formability are required, precipitation strengthened Dual Phase steel is selected. In addition, TRIP steel (transformation induced) is considered to have the same properties as DP steel.
plasticitysteel).
【０００３】[0003]
【発明が解決しようとする課題】しかしながら、上述し
た従来の強化方法を適用した鋼板は、いずれも、延性ま
たは伸びフランジ成形性のいずれか一方の特性は良好で
あっても、他方の特性が劣っていた。しかも、従来良好
であるとされてきた伸びフランジ成形性のレベルでは、
今日の厳しい加工に十分に耐えられない場合がしばしば
生じていた。そこで、本発明の目的は、特に伸びフラン
ジ成形性（穴拡がり性）が従来レベルよりはるかに優
れ、しかも延性も良好な、成形加工性に優れる高張力熱
延鋼板を提供することにある。なお、本発明鋼板が目標
とする具体的材質特性は、引張強さ：５４０ＭＰａ以
上、伸び：３０％以上であって、穴拡がり率：１４０％
以上である。However, any steel sheet to which the above-mentioned conventional strengthening method is applied has good one property of ductility or stretch flangeability, but the other property is inferior. I was In addition, at the level of stretch flangeability, which has been regarded as good in the past,
Frequently, they have not been able to withstand today's demanding operations. Therefore, an object of the present invention is to provide a high-tensile hot-rolled steel sheet having excellent stretch formability (hole-expandability), which is far superior to conventional levels, and excellent ductility. The specific material properties targeted by the steel sheet of the present invention are as follows: tensile strength: 540 MPa or more, elongation: 30% or more, and hole expansion rate: 140%.
That is all.
【０００４】[0004]
【課題を解決するための手段】発明者らは、Si、Mnを含
有する低炭素鋼を基本として、成分組成、熱間圧延方法
を適正化することにより、固溶強化をはかりながらアシ
キュラーフェライト単相の金属組織とし、かつ鋼中の硫
化物を調整すれば、高穴拡がり率を具えた高張力熱延鋼
板が得られることを知見し、本発明を完成するにいたっ
た。Means for Solving the Problems The inventors of the present invention, based on a low-carbon steel containing Si and Mn, optimize the composition of the components and the hot rolling method to achieve solid solution strengthening while achieving acicular ferrite. The inventors have found that a high-strength hot-rolled steel sheet having a high hole expansion ratio can be obtained by forming a single-phase metal structure and adjusting the sulfide in the steel, and have completed the present invention.
【０００５】こうして完成した本発明は、質量％で、
Ｃ：0.06〜0.15％、Si：0.50〜1.50％、Mn：1.0 〜2.0
％、Ｓ：0.002 ％未満を含み、かつTi、Nb、Ｖ、Zrから
選ばれる１種または２種以上を合計で0.005 〜0.020 ％
を含有して、さらにＢ、Caから選ばれる１種または２種
を合計で0.0010〜0.0060％を含有し、残部はFeおよび不
可避的不純物からなり、アシキュラーフェライト単相の
組織からなることを特徴とする加工性に優れる高張力熱
延鋼板である。また、上記高張力熱延鋼板は、質量％
で、Ｃ：0.06〜0.15％、Si：0.50〜1.50％、Mn：1.0 〜
2.0 ％、Ｓ：0.002 ％未満を含み、かつTi、Nb、Ｖ、Zr
から選ばれる１種または２種以上を合計で0.005 〜0.02
0 ％を含有して、さらにＢ、Caから選ばれる１種または
２種を合計で0.0010〜0.0060％を含有し、残部はFeおよ
び不可避的不純物からなる鋼素材を、加熱後、仕上げ温
度：Ａr３変態点以上として熱間圧延し、400 〜600 ℃
の温度範囲でコイルに巻き取ることにより有利に製造す
ることができる。[0005] The present invention completed in this way, by mass%,
C: 0.06 to 0.15%, Si: 0.50 to 1.50%, Mn: 1.0 to 2.0
%, S: less than 0.002%, and one or more selected from Ti, Nb, V, and Zr in a total amount of 0.005 to 0.020%
And further contains one or two selected from B and Ca in a total content of 0.0010 to 0.0060%, with the balance being Fe and unavoidable impurities, and a structure of an acicular ferrite single phase. It is a high-tensile hot-rolled steel sheet with excellent workability. The high-tensile hot-rolled steel sheet is
And C: 0.06-0.15%, Si: 0.50-1.50%, Mn: 1.0-
2.0%, S: contains less than 0.002%, and Ti, Nb, V, Zr
One or two or more selected from the group consisting of 0.005 to 0.02 in total
0%, further contains one or two selected from the group consisting of B and Ca in a total content of 0.0010 to 0.0060%, with the balance being Fe and unavoidable impurities. Hot-rolled at three or more transformation points, 400-600 ° C
It can be advantageously produced by winding a coil in a temperature range of
【０００６】[0006]
【発明の実施の形態】以下、成分組成および製造条件の
限定理由について説明する。なお、本発明に用いる％
は、とくにことわらない限り、質量％を意味するものと
する。 Ｃ：0.06〜0.15％ Ｃは、その含有量が0.06％未満では、アシキュラーフェ
ライト組織が形成されなくなり、良好な伸びフランジ成
形性が得られなくなる。また、Ｃ含有量が0.15％を超え
ると、溶接熱影響部の硬さ上昇のために疲労特性が劣化
する。よって、Ｃ含有量は、0.06〜0.15％の範囲とす
る。DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition of components and the production conditions will be described below. In addition,% used in the present invention
Means mass% unless otherwise specified. C: 0.06 to 0.15% If the content of C is less than 0.06%, no acicular ferrite structure is formed, and good stretch flange formability cannot be obtained. On the other hand, if the C content exceeds 0.15%, the fatigue properties deteriorate due to an increase in the hardness of the heat affected zone. Therefore, the C content is in the range of 0.06 to 0.15%.
【０００７】Si：0.50〜1.50％ Siは、固溶強化による強度向上に有効な元素である。そ
の含有量が0.50％未満ではその効果が十分にあらわれ
ず、1.50％を超えると、溶接性の劣化、とくに溶接熱影
響部の硬度上昇による疲労特性の低下を招くほか、鋼板
表面にファイアライトを形成して脱スケール性を低下さ
せて表面性状を悪化させる。このため、Si含有量は、0.
50〜1.50％の範囲とする。Si: 0.50-1.50% Si is an element effective for improving strength by solid solution strengthening. If the content is less than 0.50%, the effect will not be sufficiently exhibited, and if it exceeds 1.50%, the weldability will deteriorate, especially the fatigue properties will decrease due to the increase in the hardness of the welding heat affected zone, and firelite will be added to the steel sheet surface. It forms to lower the descalability and deteriorate the surface properties. Therefore, the Si content is 0.
The range is 50 to 1.50%.
【０００８】Mn：1.0 〜2.0 ％ Mnは、Siと同様に、固溶強化による強度向上に有効な元
素である。その含有量が1.0 ％未満ではその効果が十分
にあらわれず、一方2.0 ％を超えると、溶接性の劣化、
とくに溶接熱影響部の硬度上昇による疲労特性の低下を
招くので、1.0〜2.0 ％の含有範囲とする。Mn: 1.0 to 2.0% Mn, like Si, is an element effective for improving strength by solid solution strengthening. If the content is less than 1.0%, the effect is not sufficiently exhibited, while if it exceeds 2.0%, the weldability deteriorates,
In particular, since the fatigue properties decrease due to an increase in the hardness of the weld heat affected zone, the content is set to 1.0 to 2.0%.
【０００９】Ｓ：0.002 ％未満 Ｓは、延伸性の硫化物を生成するために、伸びフランジ
成形性に有害な元素である。Ｓ量が0.002 ％以上になる
と、本発明で目標とする穴広がり率が達成できなくな
る。このため、Ｓ量は0.002 ％未満に制限する。S: less than 0.002% S is an element that is harmful to stretch flange formability because it produces extensible sulfides. If the S content is 0.002% or more, the hole expansion rate targeted by the present invention cannot be achieved. For this reason, the S content is limited to less than 0.002%.
【００１０】Ti、Nb、Ｖ、Zr：合計で0.005 〜0.020 ％ Ti、Nb、Ｖ、Zrは、いずれも炭窒化物を形成して、スラ
ブ加熱時のオーステナイト粒の粗大化を抑制し、微細な
アシキュラーフェライトを形成するのに有用な元素であ
る。これら元素の合計量が0.005 ％に満たないと前記の
効果が十分には現れず、一方0.020 ％を超えて含有する
と、炭窒化物の析出量が過多となり、かえって伸びフラ
ンジ成形性が低下する。このため、Ti、Nb、Ｖ、Zrの含
有量は、合計で0.005 〜0.020 ％の範囲とする。Ti, Nb, V, Zr: 0.005 to 0.020% in total Ti, Nb, V, and Zr all form carbonitrides to suppress coarsening of austenite grains during slab heating. It is an element useful for forming a suitable acicular ferrite. If the total amount of these elements is less than 0.005%, the above effect will not be sufficiently exhibited, while if it exceeds 0.020%, the precipitation amount of carbonitride will be excessive, and the stretch flangeability will be rather deteriorated. For this reason, the contents of Ti, Nb, V, and Zr are in the range of 0.005 to 0.020% in total.
【００１１】Ｂ、Ca：合計で0.0010〜0.0060％ Ｂ、Caは、硫化物を難延伸性のものに変化させ、伸びフ
ランジ成形性を向上させる元素である。伸びフランジ成
形性を大幅に向上させるためには、Ｓ量の制限ととも
に、これらの元素を所定の範囲で含有させることが必要
である。Ｂ、Caの含有量が合計で0.0010％に満たないと
前記効果に乏しく、一方0.0060％を超えて含有すると熱
延鋼板の耐食性が低下する。よって、Ｂ、Caの含有量は
合計で0.0010〜0.0060％の範囲とする。B and Ca: 0.0010 to 0.0060% in total B and Ca are elements that change sulfides into those that are difficult to stretch and improve stretch flange formability. In order to greatly improve the stretch flange formability, it is necessary to limit the amount of S and to include these elements in a predetermined range. If the total content of B and Ca is less than 0.0010%, the above effect is poor, while if the content exceeds 0.0060%, the corrosion resistance of the hot-rolled steel sheet decreases. Therefore, the contents of B and Ca are in the range of 0.0010 to 0.0060% in total.
【００１２】金属組織 本発明の目指す特性を達成するには、硫化物の調整とと
もに、熱間圧延後の金属組織をアシキュラーフェライト
単相の組織とすることが必要である。とくに、軟質なフ
ェライトと硬質な第２相からなる、硬度差の大きい組織
では、伸びフランジ成形性の低下が避けられなくなる。
そこで、本発明においては、熱延鋼板の金属組織をアシ
キュラーフェライト単相にすることによって、極めて良
好な伸びフランジ成形性が得られるようにする。Metallographic Structure In order to achieve the characteristics aimed at by the present invention, it is necessary to adjust the sulfide and make the metallic structure after hot rolling into a single phase of acicular ferrite. In particular, in a structure composed of soft ferrite and a hard second phase and having a large difference in hardness, a reduction in stretch flange formability cannot be avoided.
Therefore, in the present invention, by setting the metal structure of the hot-rolled steel sheet to a single phase of acicular ferrite, it is possible to obtain extremely good stretch flange formability.
【００１３】製造方法 上述した熱延鋼板の製造方法について説明する。鋼素材
の加熱はとくに定めないが、1100〜1280℃の温度範囲で
行うのが好適である。余りに高温で加熱することは、炭
窒化物の溶解、オーステナイト粒の粗大化を招くので好
ましくはない。加熱後の熱間圧延においては、アシキュ
ラーフェライト単相の金属組織を形成して、目標とする
強度、伸び、穴広がり率（伸びフランジ成形性）を達成
するために、仕上げ温度をＡr３変態点以上とし、400
〜600 ℃の温度範囲でコイルに巻き取る。Ａr３変態点
以上で圧延を終了するのは、フェライトの生成を防止す
るためである。なお、熱間圧延終了から巻き取るまでの
冷却はとくに条件を定めないが、Ａr３変態点の上か
ら、30〜80℃／ｓの範囲で行うのが好ましい。図１は、
本発明範囲にある成分組成の鋼スラブを熱間圧延したと
きの巻取温度（ＣＴ）が、引張強さ（ＴＳ）、伸び（Ｅ
ｌ）、穴広がり率（λ）に及ぼす影響を示したものであ
る。図１から、400 〜600 ℃の温度範囲で巻き取ること
により、これら全ての特性が目標値を満足することがわ
かる。Manufacturing Method A method for manufacturing the above-described hot-rolled steel sheet will be described. The heating of the steel material is not particularly limited, but is preferably performed in a temperature range of 1100 to 1280 ° C. Heating at an excessively high temperature is not preferable because it causes dissolution of carbonitrides and coarsening of austenite grains. In the hot rolling after the heating, the finishing temperature is changed to the Ar 3 transformation in order to form the metallic structure of acicular ferrite single phase and to achieve the target strength, elongation, and hole expansion rate (stretch flange formability). Points and above, 400
It is wound around a coil in the temperature range of ~ 600 ° C. The reason for terminating the rolling at the Ar 3 transformation point or more is to prevent the formation of ferrite. The cooling from the end of the hot rolling to the winding is not particularly limited, but is preferably performed in the range of 30 to 80 ° C./s from above the Ar 3 transformation point. FIG.
The coiling temperature (CT) at the time of hot rolling a steel slab having a component composition falling within the range of the present invention is determined by the tensile strength (TS) and the elongation (E).
1) shows the effect on the hole spreading rate (λ). From FIG. 1, it can be seen that all of these characteristics satisfy the target values by winding in the temperature range of 400 to 600 ° C.
【００１４】[0014]
【実施例】表１に示す種々の化学組成の鋼を溶製し、連
続鋳造スラブとした。このスラブを表２に示す各製造条
件で、加熱、熱間圧延し、冷却した後、コイルに巻取
り、板厚2.9ｍｍの熱延鋼板を製造した。得られた、熱
延鋼板のコイルの１／４Ｗ (幅方向エッジとセンターの
中間) 位置で、金属組織観察、引張試験、伸びフランジ
試験を行った。ここに、引張試験には、ＪＩＳ５号試験
片を用いた。また、伸びフランジ試験は、一辺100 ｍｍ
の正方形試験片の中央に10ｍｍ（ｄ0)の穴をあけ、先端
角度60°の円錐ポンチでこの穴を拡げ、穴の縁にクラッ
クが発生する限界の穴径（ｄ）から次式： λ＝（ｄ−ｄ0)×100 ／ｄ0 により、穴広がり率λを求めて評価した。その結果を表
２に併せて示す。これらの結果から、発明例は、良好な
伸びフランジ成形性と伸び−強度特性を具えており、加
工性に優れていることがわかる。EXAMPLES Steels having various chemical compositions shown in Table 1 were melted to form continuous cast slabs. The slab was heated, hot-rolled and cooled under the respective manufacturing conditions shown in Table 2, and then wound around a coil to produce a hot-rolled steel sheet having a thickness of 2.9 mm. At a position of 1/4 W (middle of the width direction edge and the center) of the obtained coil of the hot rolled steel sheet, a metal structure observation, a tensile test, and a stretch flange test were performed. Here, a JIS No. 5 test piece was used for the tensile test. The stretch flange test is 100 mm on each side.
A hole of 10 mm (d0) is made in the center of the square test piece, and this hole is expanded with a conical punch having a tip angle of 60 °. From the limit hole diameter (d) at which a crack occurs at the edge of the hole, the following formula: λ = The hole spreading ratio λ was obtained from (d−d0) × 100 / d0 and evaluated. The results are also shown in Table 2. From these results, it can be seen that the inventive examples have good stretch flange formability and elongation-strength characteristics and are excellent in workability.
【００１５】[0015]
【表１】 [Table 1]
【００１６】[0016]
【表２】 [Table 2]
【００１７】[0017]
【発明の効果】以上説明したように、本発明によれば、
鋼板の化学組成、熱間圧延および巻き取りの条件を適正
化することによって、格段に優れた伸びフランジ成形性
を具えた、高張力熱延鋼板を提供することができる。As described above, according to the present invention,
By optimizing the chemical composition of the steel sheet and the conditions of hot rolling and winding, a high-tensile hot-rolled steel sheet having remarkably excellent stretch flange formability can be provided.
【図面の簡単な説明】[Brief description of the drawings]
【図１】巻取温度（ＣＴ）と引張強さ、伸びおよび穴広
がり性との関係を示すグラフである。FIG. 1 is a graph showing a relationship between a winding temperature (CT) and tensile strength, elongation and hole spreadability.
Claims (2)
1.50％、Mn：1.0 〜2.0 ％、Ｓ：0.002 ％未満を含み、
かつTi、Nb、Ｖ、Zrから選ばれる１種または２種以上を
合計で0.005 〜0.020 ％を含有して、さらにＢ、Caから
選ばれる１種または２種を合計で0.0010〜0.0060％を含
有し、残部はFeおよび不可避的不純物からなり、アシキ
ュラーフェライト単相の組織からなることを特徴とする
加工性に優れる高張力熱延鋼板。(1) In mass%, C: 0.06 to 0.15%, Si: 0.50 to
1.50%, Mn: 1.0-2.0%, S: less than 0.002%,
In addition, one or more selected from Ti, Nb, V, and Zr is contained in a total of 0.005 to 0.020%, and one or two selected from B and Ca is further contained in a total of 0.0010 to 0.0060%. A high tensile strength hot-rolled steel sheet with excellent workability, characterized in that the balance consists of Fe and unavoidable impurities and has a structure of acicular ferrite single phase.
1.50％、Mn：1.0 〜2.0 ％、Ｓ：0.002 ％未満を含み、
かつTi、Nb、Ｖ、Zrから選ばれる１種または２種以上を
合計で0.005 〜0.020 ％を含有して、さらにＢ、Caから
選ばれる１種または２種を合計で0.0010〜0.0060％を含
有し、残部はFeおよび不可避的不純物からなる鋼素材
を、加熱後、仕上げ温度：Ａr３変態点以上として熱間
圧延し、400 〜600 ℃の温度範囲でコイルに巻き取るこ
とを特徴とする加工性に優れる高張力熱延鋼板の製造方
法。2. A mass%, C: 0.06 to 0.15%, Si: 0.50 to
1.50%, Mn: 1.0-2.0%, S: less than 0.002%,
In addition, one or more selected from Ti, Nb, V, and Zr is contained in a total of 0.005 to 0.020%, and one or two selected from B and Ca is further contained in a total of 0.0010 to 0.0060%. The remaining process is characterized in that a steel material consisting of Fe and unavoidable impurities is heated, then hot-rolled at a finishing temperature of at least the Ar 3 transformation point, and wound around a coil in a temperature range of 400 to 600 ° C. For producing high-strength hot-rolled steel sheets with excellent heat resistance.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2604716A4 (en) * | 2010-08-10 | 2015-09-02 | Jfe Steel Corp | High-strength hot-rolled steel sheet having excellent workability, and a method for producing same |
| JP2016211047A (en) * | 2015-05-11 | 2016-12-15 | 新日鐵住金株式会社 | Hot rolled steel sheet and production method therefor |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1036917A (en) * | 1996-07-25 | 1998-02-10 | Nippon Steel Corp | Production of high strength hot-rolled steel plate excellent in stretch-flanging property |
-
2000
- 2000-11-24 JP JP2000356929A patent/JP4639464B2/en not_active Expired - Fee Related
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1036917A (en) * | 1996-07-25 | 1998-02-10 | Nippon Steel Corp | Production of high strength hot-rolled steel plate excellent in stretch-flanging property |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2604716A4 (en) * | 2010-08-10 | 2015-09-02 | Jfe Steel Corp | High-strength hot-rolled steel sheet having excellent workability, and a method for producing same |
| JP2016211047A (en) * | 2015-05-11 | 2016-12-15 | 新日鐵住金株式会社 | Hot rolled steel sheet and production method therefor |
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| JP4639464B2 (en) | 2011-02-23 |
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