JP2001335891A - High tensile steel sheet excellent in ductility and impact resistance, and its production method - Google Patents
High tensile steel sheet excellent in ductility and impact resistance, and its production methodInfo
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- JP2001335891A JP2001335891A JP2000160296A JP2000160296A JP2001335891A JP 2001335891 A JP2001335891 A JP 2001335891A JP 2000160296 A JP2000160296 A JP 2000160296A JP 2000160296 A JP2000160296 A JP 2000160296A JP 2001335891 A JP2001335891 A JP 2001335891A
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、プレス加工や曲げ
加工などによって成形される高強度構造部材の素材とし
て好適な、延性と耐衝撃特性に優れた高張力鋼板および
その製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength steel sheet excellent in ductility and impact resistance, which is suitable as a material for high-strength structural members formed by press working or bending work, and a method for producing the same.
【0002】[0002]
【従来の技術】自動車における衝突安全性の向上と軽量
化に対応して、構造部材の高張力化が進められている。
その際、高強度鋼板を自動車の構造部材に適用するにあ
たっていくつかの課題が指摘されている。2. Description of the Related Art In order to improve the collision safety and reduce the weight of automobiles, the tension of structural members has been increased.
At that time, some problems have been pointed out when applying high-strength steel sheets to structural members of automobiles.
【0003】一般的に鋼板の強度と成形性は相反する関
係にあり、鋼板の強度が高くなるにつれてプレス成形が
困難になり、高強度鋼板の適用が可能な部材が制限され
るという問題がある。この課題に対しては、残留オース
テナイトのTRIP(Transformaion Induced Plastici
ty)効果を利用した、強度−延性バランスに優れた鋼板
が開発されている。[0003] Generally, the strength and formability of a steel sheet are in a contradictory relationship, and the higher the strength of the steel sheet, the more difficult it is to press-form, and there is a problem that members to which the high-strength steel sheet can be applied are limited. . To solve this problem, TRIP (Transformaion Induced Plastici)
ty) A steel sheet excellent in strength-ductility balance utilizing the effect has been developed.
【0004】例えば、特開平5−117761号公報に
は、化学組成が質量%で(以下、化学組成の%表示は質
量%を意味する)、C:0.08〜0.30%、Mn:
1.0〜2.0%、Si:0.5〜2.5%、Al:
0.5〜1.5%を含有する熱間圧延鋼板または冷間圧
延鋼板を特定条件で焼鈍することにより、残留オーステ
ナイト相を有する結晶組織を備えて、強度と加工成形性
を兼備した高強度薄鋼板の製造方法が開示されている。[0004] For example, Japanese Patent Application Laid-Open No. HEI 5-117761 discloses that a chemical composition is expressed in mass% (hereinafter, the expression of% in chemical composition means mass%), C: 0.08 to 0.30%, Mn:
1.0-2.0%, Si: 0.5-2.5%, Al:
By annealing a hot-rolled steel sheet or a cold-rolled steel sheet containing 0.5 to 1.5% under specific conditions, a high-strength steel having a crystal structure having a retained austenite phase and having both strength and workability. A method for manufacturing a thin steel sheet is disclosed.
【0005】また、鋼板の強度を高めるにつれて静動比
が小さくなり、高強度鋼板を使用した割には耐衝突特性
が向上しない、という問題がある。ここで、静動比と
は、静的引張試験(歪み速度が10-4/秒前後)での強
度に対する、自動車が衝突する際に構造部材に作用する
歪み速度(103 /秒前後)における強度の比を意味
し、静動比が小さい鋼では静的強度が高くても高速変形
時の強度が小さい。この課題に対しては、動的引張試験
における強度もしくは静動比を高める方法が開示されて
いる。Further, there is a problem that the static-dynamic ratio becomes smaller as the strength of the steel sheet is increased, and the collision resistance is not improved for the use of the high-strength steel sheet. Here, the static-dynamic ratio is defined as the strain rate (approximately 10 3 / sec) acting on a structural member when a vehicle collides with the strength in a static tensile test (strain rate of about 10 −4 / sec). It means the ratio of strength. In steels with a small static-dynamic ratio, the strength during high-speed deformation is small even if the static strength is high. To solve this problem, a method for increasing the strength or static-dynamic ratio in a dynamic tensile test is disclosed.
【0006】例えば、特開平11−80879号公報に
は、C:0.04〜0.30%、SiとAlの一方また
は双方を合計で0.3〜3.0%含有し、フェライトと
3体積%以上のオーステナイトを含む第2相からなり、
予変形を加える前後におけるオーステナイト相の体積率
変化と、予変形した鋼板の準静的変形強度と動的変形強
度の差を特定した、動的変形特性に優れた加工誘起変態
型高強度鋼板が開示されている。For example, Japanese Patent Application Laid-Open No. H11-80879 discloses that C: 0.04 to 0.30%, one or both of Si and Al are contained in a total of 0.3 to 3.0%, and ferrite and A second phase containing at least a volume% of austenite,
A high-strength work-induced transformation type steel sheet with excellent dynamic deformation characteristics that identifies the change in the volume fraction of the austenite phase before and after the pre-deformation and the difference between the quasi-static deformation strength and the dynamic deformation strength of the pre-deformed steel sheet. It has been disclosed.
【0007】また、特開平7−34186号公報には、
C:0.01%以下、Si:0.01〜1.5%、M
n:0.01〜3.0%、Al:0.02〜0.06
%、P:0.15%以下を含有し、鋼板表面から50μ
mまでの領域がフェライト組織中にベイナイトまたはマ
ルテンサイトを含む複合組織、それを除く領域がフェラ
イト単相組織であり、成形、塗装焼付け後における鋼板
の表面から1/4t(t:板厚)までの平均硬度が、板
厚中央部(1/4t〜3/4t)の平均硬度の1.5倍
以上の硬度になる組織を有する、耐衝撃性に優れる成形
加工用薄鋼板が開示されている。Further, Japanese Patent Application Laid-Open No. 7-34186 discloses that
C: 0.01% or less, Si: 0.01 to 1.5%, M
n: 0.01 to 3.0%, Al: 0.02 to 0.06
%, P: 0.15% or less, 50μ from the steel sheet surface
The region up to m is a composite structure containing bainite or martensite in the ferrite structure, and the region other than that is a ferrite single phase structure, from the surface of the steel sheet after forming and baking to 1 / 4t (t: sheet thickness). Which has a structure in which the average hardness is 1.5 times or more the average hardness of the central part (1/4 t to 3/4 t) of the sheet thickness and has excellent impact resistance is disclosed. .
【0008】[0008]
【発明が解決しようとする課題】以上述べたように、強
度−延性バランスに優れた鋼板や静動比が高い鋼板が種
々開発されてはいるものの、従来の方法では必ずしも満
足な解決を得るに至っていないのが現状である。すなわ
ち、特開平5−117761号公報に開示された技術で
は、残留オーステナイト鋼板を得る製造方法において熱
延条件には言及されておらず、焼鈍前組織が好ましくな
い場合などでは必ずしも良好な特性向上効果が得られな
いという問題がある。特に残留オーステナイト鋼板は、
局部延性が乏しく、孔拡げ加工や微小曲げ加工など局部
延性が左右する加工に供するにはその性能が十分ではな
いという問題もある。As described above, although various steel sheets having an excellent balance between strength and ductility and steel sheets having a high static-dynamic ratio have been developed, it is not always possible to obtain a satisfactory solution by the conventional method. It has not been reached yet. That is, in the technique disclosed in Japanese Patent Application Laid-Open No. HEI 5-117762, the hot rolling conditions are not mentioned in the production method for obtaining a retained austenitic steel sheet, and a good property improving effect is not necessarily obtained when the structure before annealing is not preferable. There is a problem that can not be obtained. In particular, retained austenitic steel sheets
There is also a problem that the local ductility is poor, and the performance thereof is not sufficient for use in a process in which the local ductility is affected, such as a hole expanding process and a minute bending process.
【0009】また、特開平11−80879号公報にお
いては成形の影響は相当歪みで評価され、動的強度は引
張試験で評価されている。しかしながら実際のプレス製
品は成形時にダイ肩部で曲げ曲げ戻し変形を受けるため
に機械的性質が板厚方向で異なったものになること、お
よび、衝突時に鋼板に作用する変形様式は、上記のよう
な単純な引張変形ではないこと、などから、上記方法で
は十分な効果が得られない場合があるという問題があ
る。例えば衝突時に鋼板が曲げ変形される時には表面ひ
ずみが特に大きくなるので、鋼板表面の強度は高いこと
が望ましいが、引張試験方法では、板厚方向の平均値の
強度しか評価できないので、正確な評価が困難であっ
た。In Japanese Patent Application Laid-Open No. H11-80879, the influence of molding is evaluated by a considerable strain, and the dynamic strength is evaluated by a tensile test. However, the actual pressed product undergoes bending and bending back deformation at the die shoulder at the time of forming, so that the mechanical properties differ in the thickness direction, and the deformation mode acting on the steel plate at the time of impact is as described above. There is a problem that the above method may not provide a sufficient effect because the method is not a simple tensile deformation. For example, since the surface strain is particularly large when the steel sheet is bent and deformed in the event of a collision, the strength of the steel sheet surface is desirably high, but the tensile test method can only evaluate the average strength in the thickness direction. Was difficult.
【0010】特開平7−34186号公報では、歪み速
度感受性(静動比)を向上させるには、歪み速度感受性
に関して異なる特性を有する組織を同一鋼板の組織内に
分布させることが有効と記載されており、鋼板表面のみ
に硬質な複合組織を得る方法として、焼鈍中の表面浸炭
や、表層部のみを二相域温度に加熱急冷することが述べ
られている。しかしながらこれらの方法は、鋼板の一般
的な製造プロセスにて実現することは必ずしも容易では
ない。Japanese Patent Application Laid-Open No. 7-34186 describes that in order to improve strain rate sensitivity (static-dynamic ratio), it is effective to distribute structures having different characteristics with respect to strain rate sensitivity in the structure of the same steel sheet. As a method of obtaining a hard composite structure only on the surface of a steel sheet, it is described that surface carburization during annealing and heating and quenching of only the surface layer portion to a two-phase region temperature. However, these methods are not always easy to realize in a general steel plate manufacturing process.
【0011】本発明の目的はこれらの問題点を解決し、
より成形性が良好で、耐衝突特性に優れ、かつ、低コス
トで製造できる高強度鋼板およびその製造方法を提供す
ることにある。The object of the present invention is to solve these problems,
It is an object of the present invention to provide a high-strength steel sheet which has better formability, has excellent impact resistance, and can be manufactured at low cost, and a method for manufacturing the same.
【0012】[0012]
【課題を解決するための手段】衝突安全にかかわる構造
部材においては、成形した部材を高速圧壊変形した際に
吸収されるエネルギが大きいことが重要となる。構造部
材としては薄鋼板で製造された閉断面構造のものが多い
が、これらが高速圧壊変形されると蛇腹状に圧壊した
り、折れ曲がり変形などが生じて運動エネルギを吸収す
る。In structural members related to collision safety, it is important that a large amount of energy is absorbed when a molded member is subjected to high-speed crush deformation. Many of the structural members have a closed cross-sectional structure made of a thin steel plate. However, when these members are subjected to high-speed crushing deformation, they are crushed in a bellows shape or bent to generate kinetic energy.
【0013】高速圧壊変形時に薄鋼板製の部材に生じる
このような変形様式は単純な引張変形ではなく、曲げ曲
げ戻し変形(曲げ変形に続いて曲げ戻しが生じる変形)
が主体になっている。曲げ曲げ戻し変形に伴って、曲げ
の外側面では、引張変形の後に圧縮変形が生じ、曲げの
内側面では圧縮変形の後に引張変形が生じる。いずれに
しても鋼板の板厚中心部よりも表面部のほうが生じる歪
みが大きい。[0013] Such a deformation mode generated in a thin steel plate member at the time of high-speed crushing deformation is not a simple tensile deformation but a bending-bending-back deformation (a deformation in which bending-back occurs after bending-bending).
Is the main subject. Along with the bending-back deformation, the outer surface of the bending undergoes a compression deformation after the tensile deformation, and the inner surface of the bending undergoes a tensile deformation after the compression deformation. In any case, the distortion generated at the surface portion is larger than that at the center portion of the thickness of the steel plate.
【0014】本発明者の研究結果によれば、鋼板表面部
の硬度と板厚中心部の硬度が特定の関係を満足する場合
に、衝撃変形を加えた際に部材で吸収することができる
衝突吸収エネルギ吸収能を飛躍的に改善できることを知
った。According to the research results of the present inventor, when the hardness of the surface portion of the steel sheet and the hardness of the central portion of the thickness satisfy a specific relationship, the impact can be absorbed by the member when impact deformation is applied. I learned that the energy absorption capacity can be dramatically improved.
【0015】図1は、構造部材で多用されている閉断面
構造をした部材を模した試験体の斜視図であり、符号1
はハット断面部品、符号12は平板部品で、両者はスポ
ット溶接で接合されている。符号2はハット断面部品1
の縦壁部、符号11はその底部である。FIG. 1 is a perspective view of a test body simulating a member having a closed cross-section structure frequently used as a structural member.
Is a hat cross-section part, and reference numeral 12 is a flat plate part, both of which are joined by spot welding. Reference numeral 2 denotes a hat cross-section part 1.
Reference numeral 11 denotes a bottom wall of the vertical wall.
【0016】図2はハット断面部品1のプレス成形状態
を説明するための断面図であり、符号3はポンチ、符号
4はポンチ肩、符号5はダイ、符号6はダイ肩、符号7
はダイ溝、符号8はしわ押さえである。FIG. 2 is a cross-sectional view for explaining a press-formed state of the hat cross-sectional part 1. Reference numeral 3 denotes a punch, reference numeral 4 denotes a punch shoulder, reference numeral 5 denotes a die, reference numeral 6 denotes a die shoulder, and reference numeral 7
Denotes a die groove, and reference numeral 8 denotes a wrinkle holder.
【0017】ダイ5としわ押さえ8間で挟持された鋼板
は、ポンチ3の下降に伴ってポンチ肩6の曲面に沿って
曲げ変形され、ダイ溝7に引き込まれる。ポンチ肩6を
通過するした曲げ部はダイ側壁により曲げ戻しされる。The steel sheet sandwiched between the die 5 and the wrinkle holder 8 is bent and deformed along the curved surface of the punch shoulder 6 as the punch 3 descends, and is drawn into the die groove 7. The bent portion passing through the punch shoulder 6 is bent back by the die side wall.
【0018】縦壁部2はダイ肩6で曲げ曲げ戻し変形が
加えられることにより、厚さ方向でひずみ量が異なり、
硬度差が生じる。すなわち鋼板表面部の硬度が板厚中心
部に比較して高くなる。また縦壁部2には、曲げ曲げ戻
し変形に加えて、ポンチとしわ押さえ間で生じる引張り
力が作用するので板厚ひずみが発生し、その厚さが薄く
なる。The vertical wall portion 2 is subjected to bending and bending-back deformation at the die shoulder 6, so that the amount of strain differs in the thickness direction.
A hardness difference occurs. That is, the hardness of the surface of the steel sheet is higher than that of the center of the thickness. Further, in addition to the bending and bending-back deformation, a tensile force generated between the punch and the wrinkle retainer acts on the vertical wall portion 2, so that a thickness distortion occurs, and the thickness becomes thin.
【0019】プレス加工された部品は、溶接などにより
構造部材として組み立てられ、塗装された後、170℃
で20分間程度保持される塗装焼付け処理(以下、単に
「焼付け処理」とも記す)が施される。この段階で鋼中
の固溶原子(C、N原子など)が析出して歪み時効が発
生し、鋼の硬度が高くなる。The pressed parts are assembled as structural members by welding or the like, painted, and then heated to 170 ° C.
For about 20 minutes (hereinafter, also simply referred to as "baking treatment"). At this stage, solid solution atoms (C, N atoms, etc.) in the steel precipitate and strain aging occurs, thereby increasing the hardness of the steel.
【0020】本発明者の研究結果によれば、特定の条件
で製造された残留オーステナイト鋼は、上記のような引
張り曲げ変形を伴う予成形と焼付け処理を施すと、表面
部の硬化性が従来の鋼に比較して遙かに高くなり、これ
を構造部材に使用すれば、高速の軸方向圧壊変形する際
のエネルギ吸収能が大幅に向上し、極めて優れた耐衝撃
特性を発揮することが判明した。According to the research results of the present inventor, the residual austenitic steel manufactured under specific conditions, when subjected to the preforming and baking treatment with the above-described tensile bending deformation, hardens the surface portion in a conventional manner. If it is used as a structural member, the energy absorption capacity during high-speed axial crush deformation is greatly improved, and it is possible to exhibit extremely excellent impact resistance. found.
【0021】そのメカニズムは必ずしも明らかでない
が、以下のように推定される。一般的な、曲げ曲げ戻し
では、表面部に大きい歪みが生じて加工硬化(転位密度
が上昇することよる硬化)が生じるが、バウシンガ効果
により、曲げによる加工硬化と曲げ戻しによる加工硬化
は加算的にはならないと考えられる。The mechanism is not necessarily clear, but is presumed as follows. In general bending and bending back, large strain is generated on the surface and work hardening (hardening due to increase in dislocation density) occurs, but due to the Bauschinger effect, work hardening by bending and work hardening by bending back are additive. It is not considered to be.
【0022】残留オーステナイトを含有する鋼において
は、歪みの増加に伴って転位が増殖して生じる加工硬化
に加え、残留オーステナイトが硬質なマルテンサイトへ
変態することによる硬化も生じる。このマルテンサイト
による硬化は、バウシンガ効果とは無関係であり、曲げ
と曲げ戻しの両方において、硬度が加算的に増加する結
果、表面部の硬度が著しく高くなるものと考えられる。In the steel containing retained austenite, in addition to work hardening generated by dislocations multiplying with an increase in strain, hardening due to transformation of the retained austenite into hard martensite also occurs. This hardening by martensite is irrelevant to the Bauschinger effect, and it is considered that the hardness of the surface part is significantly increased as a result of the additional increase in hardness in both bending and unbending.
【0023】また、所望の表面硬化特性を得るために、
残留オーステナイトを5体積%以上含有し、残部は実質
的にフェライトからなる結晶組織を有する鋼が好ましい
ことを知った。実質的にとの意味は、冷間圧延後の焼鈍
において残留オーステナイトを得る際に、不可避的に生
成するベイナイト組織などが混在しても構わないことを
意味する。In order to obtain desired surface hardening characteristics,
It has been found that a steel containing 5% by volume or more of retained austenite and the remainder having a crystal structure substantially consisting of ferrite is preferable. The meaning of "substantially" means that when obtaining retained austenite in annealing after cold rolling, bainite structure or the like which is inevitably generated may be mixed.
【0024】本発明者はさらに、残留オーステナイト鋼
板の成形性、特に従来の残留オーステナイト鋼板におい
て問題とされている局部延性不足を改善する方法につい
て種々研究を重ねた結果、残留オーステナイト鋼板の局
部延性は、特定の化学組成を有する鋼を特定の条件で製
造することにより、大幅に改善できることを知った。The present inventor further conducted various studies on methods for improving the formability of the retained austenitic steel sheet, in particular, the insufficient local ductility which is a problem in the conventional retained austenitic steel sheet. It has been found that by producing a steel having a specific chemical composition under specific conditions, it can be greatly improved.
【0025】すなわち、残留オーステナイトを有する冷
間圧延鋼板の局部延性向上には、冷間圧延鋼板の母材と
なる熱延板の製造に際して熱延条件を最適化し、熱延板
の結晶組織における硬質第2相の体積率を低減させるこ
と、および、硬質第2相は、ベイナイトやマルテンサイ
トではなくて、より軟質なパーライトにするのが重要で
ある。さらに、熱延板において、MnやPの凝固偏析に
起因する第2相のバンド状組織(点列状組織)を低減さ
せることが冷間圧延鋼板の延性向上に有効である。That is, in order to improve the local ductility of a cold-rolled steel sheet having retained austenite, the hot-rolling conditions are optimized in the production of a hot-rolled sheet as a base material of the cold-rolled steel sheet, and the crystal structure of the hot-rolled sheet is hardened. It is important to reduce the volume fraction of the second phase and to make the hard second phase a softer pearlite instead of bainite or martensite. Further, in the hot-rolled sheet, it is effective to reduce the band-like structure (dot-like structure) of the second phase caused by solidification segregation of Mn and P to improve the ductility of the cold-rolled steel sheet.
【0026】そのメカニズムは必ずしも明らかでない
が、以下のように推定される。フェライト相と第2相の
間に大きな硬度差があると、冷間圧延時に一様に塑性変
形が起きず、第2相との界面でミクロボイドが発生す
る。第2相の硬度が著しく高かったり、第2相が点列状
に存在するバンド状組織であると、多数のミクロボイド
が点列状に発生し、焼鈍後も残留してしまう。製品の成
形時に、大きな歪みを受けた領域では、これらのミクロ
ボイドが連結して破断に至りやすい。すなわち、このよ
うなミクロボイドが多い場合には局部延性が著しく損な
われ、引張試験における局部伸びが小さくなってしま
う。したがい、第2相の体積率と硬度を低下させ、バン
ド状組織を解消することが、局部延性の改善に有効であ
ると考えられる。The mechanism is not necessarily clear, but is presumed as follows. If there is a large difference in hardness between the ferrite phase and the second phase, plastic deformation does not occur uniformly during cold rolling, and microvoids occur at the interface with the second phase. If the hardness of the second phase is extremely high, or if the second phase has a band-like structure in which dots exist in a row, a large number of microvoids will be generated in a row of dots and will remain after annealing. At the time of molding of the product, these microvoids are liable to be connected to each other in a region where a large strain has been applied. That is, when there are many such microvoids, the local ductility is significantly impaired, and the local elongation in a tensile test is reduced. Accordingly, it is considered that reducing the volume ratio and hardness of the second phase and eliminating the band-like structure is effective for improving the local ductility.
【0027】本発明はこれらの知見を基にして完成され
たものであり、その要旨は下記(1)〜(3)に記載の
延性および耐衝撃特性に優れた高張力鋼板および
(4)、(5)に記載のその製造方法にある。The present invention has been completed based on these findings, and the gist of the present invention is to provide a high-tensile steel sheet excellent in ductility and impact resistance described in the following (1) to (3) and (4): (5) The manufacturing method described in (5).
【0028】(1)質量%で、C:0.05〜0.25
%、Si:2.0%以下、Al:0.005〜2.0
%、Mn:0.8〜2.5%、P:0.05%以下を含
有し、かつ、(Si+Al):1.0〜2.5%を満足
し、残部がFeおよび不可避的不純物からなる化学組成
を備え、板厚ひずみにして10%の引張り曲げ変形を伴
う予成形を施し、次いで170℃で20分間保持する焼
付け処理を施した後の鋼板表面部と板厚中心部の硬度が
下記式を満足することを特徴とする延性と耐衝撃特性に
優れた高張力鋼板; (HVs−HVc)/HV0 ≧0.12、 ただし、HV0 :上記予成形前の板厚中心部のビッカー
ス硬度、 HVc:上記予成形と焼付け処理後の板厚中心部のビッ
カース硬度、 HVs:上記予成形と焼付け処理後の表面部のビッカー
ス硬度。(1) In mass%, C: 0.05 to 0.25
%, Si: 2.0% or less, Al: 0.005 to 2.0
%, Mn: 0.8-2.5%, P: 0.05% or less, and (Si + Al): 1.0-2.5%, the balance being Fe and unavoidable impurities. The hardness of the steel sheet surface and the center of the sheet thickness after a preforming with a chemical composition of 10% and a bending deformation of 10% to a sheet thickness strain and then a baking treatment at 170 ° C. for 20 minutes is performed. (HVs-HVc) / HV 0 ≧ 0.12, where HV 0 is the center of the sheet thickness before the preforming, characterized by satisfying the following formula: Vickers hardness, HVc: Vickers hardness at the center of the plate thickness after the above preforming and baking treatment, HVs: Vickers hardness of the surface part after the above preforming and baking treatment.
【0029】(2)質量%で、C:0.05〜0.25
%、Si:2.0%以下、Al:0.005〜2.0
%、Mn:0.8〜2.5%、P:0.05%以下を含
み、かつ、(Si+Al):1.0〜2.5%を満足
し、さらに、Tiおよび/またはNbを、Ti:0.0
03〜0.05%、Nb:0.003〜0.05%、か
つ、(Ti+Nb)≦0.05%を満足する範囲で含有
し、残部がFeおよび不可避的不純物からなる化学組成
を備え、板厚ひずみにして10%の引張り曲げ変形を伴
う予成形を施し、次いで170℃で20分間保持する焼
付け処理を施した後の鋼板表面部と板厚中心部の硬度が
下記式を満足することを特徴とする延性と耐衝撃特性に
優れた高張力鋼板; (HVs−HVc)/HV0 ≧0.12、 ただし、HV0 :上記予成形前の板厚中心部のビッカー
ス硬度、 HVc:上記予成形と焼付け処理後の板厚中心部のビッ
カース硬度、 HVs:上記予成形と焼付け処理後の表面部のビッカー
ス硬度。(2) In mass%, C: 0.05 to 0.25
%, Si: 2.0% or less, Al: 0.005 to 2.0
%, Mn: 0.8-2.5%, P: 0.05% or less, and (Si + Al): 1.0-2.5%, and further, Ti and / or Nb Ti: 0.0
A chemical composition containing 0.3 to 0.05%, Nb: 0.003 to 0.05%, and (Ti + Nb) ≦ 0.05%, with the balance being Fe and unavoidable impurities, The hardness of the steel sheet surface and the center of the sheet thickness after preforming with tensile bending deformation of 10% in sheet thickness strain and then baking treatment at 170 ° C for 20 minutes should satisfy the following formula. (HVs-HVc) / HV 0 ≧ 0.12, where HV 0 is the Vickers hardness at the center of the sheet thickness before the preforming, and HVc is the above. Vickers hardness at the center of the sheet thickness after the preforming and baking treatment, HVs: Vickers hardness of the surface after the above preforming and baking treatment.
【0030】(3)化学組成がさらに、質量%で、C
u、Ni、Coからなる群の内の1種、または、2種以
上を、Cu:0.2〜1.0%、Ni:0.1〜0.5
%、Co:0.0005〜1.0%、かつ(Cu+Ni
+Co)≦1.5%を満足する範囲で含有する、上記
(1)または(2)に記載の延性と耐衝撃特性に優れた
高張力鋼板。(3) The chemical composition further comprises C
one or more of the group consisting of u, Ni, and Co, Cu: 0.2 to 1.0%, Ni: 0.1 to 0.5
%, Co: 0.0005 to 1.0%, and (Cu + Ni
(+ Co) ≦ 1.5%, a high-tensile steel sheet excellent in ductility and impact resistance as described in (1) or (2) above.
【0031】(4)上記化学組成を備えた鋼片に、熱間
仕上圧延開始温度が1050℃以下、終了温度が800
℃以上である熱間仕上圧延を施した後、20℃/秒以上
の冷却速度で750℃まで冷却し、700℃以下、下記
式で計算されるTc(℃)以上で巻取る工程を有する熱
間圧延を施し、得られた鋼板を酸洗し、その後、合計圧
下率が40%以上、80%以下となる範囲で冷間圧延を
施し、次いで、フェライト+オーステナイトの2相温度
域で30秒以上、90秒以下保持し、その後700℃以
下、450℃以上の温度範囲を30℃/秒以上で冷却
し、450℃以下、370℃以上の温度範囲で200秒
以上、400秒以下保持した後、室温まで冷却する焼鈍
を施すことを特徴とする、上記(1)〜(3)のいずれ
かに記載の延性と耐衝撃特性に優れた高張力鋼板の製造
方法; Tc( ℃) =430+70×Mn( %) +1000×P
( %) 。(4) A steel slab having the above chemical composition has a hot finish rolling start temperature of 1050 ° C. or less and an end temperature of 800
After performing hot finish rolling at a temperature of at least 20 ° C., the heat is cooled to 750 ° C. at a cooling rate of at least 20 ° C./sec, and is wound at a temperature of 700 ° C. or less and Tc (° C.) or more calculated by the following formula. The resulting steel sheet is pickled, cold-rolled in a range where the total draft is 40% or more and 80% or less, and then in a two-phase temperature range of ferrite + austenite for 30 seconds. After holding for 90 seconds or less, and then cooling at a temperature of 700 ° C. or less and 450 ° C. or more at 30 ° C./sec or more, and holding at a temperature of 450 ° C. or less and 370 ° C. or more for 200 seconds or more and 400 seconds or less, A method for producing a high-strength steel sheet excellent in ductility and impact resistance according to any one of the above (1) to (3), characterized by performing annealing to cool to room temperature; Tc (° C.) = 430 + 70 × Mn (%) + 1000 × P
(%).
【0032】(5)熱間仕上圧延を施す前の鋼片に補助
加熱を施すことを特徴とする上記(4)に記載の延性と
耐衝撃特性に優れた高張力鋼板の製造方法。(5) The method for producing a high-tensile steel sheet excellent in ductility and impact resistance according to (4), wherein the steel slab is subjected to auxiliary heating before hot finish rolling.
【0033】[0033]
【発明の実施の形態】本発明の実施の形態を詳細に述べ
る。 鋼板の化学組成; C:最も強力なオーステナイト安定化元素であり、本発
明の必須構成要素の一つである。焼鈍後室温において安
定なオーステナイトを得るには、焼鈍温度におけるオー
ステナイトのC濃度を1%程度以上に高めておく必要が
ある。そのため鋼のC含有量を0.05%以上とする。DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail. Chemical composition of steel sheet: C: The most powerful austenite stabilizing element and one of the essential components of the present invention. In order to obtain stable austenite at room temperature after annealing, it is necessary to increase the C concentration of austenite at the annealing temperature to about 1% or more. Therefore, the C content of the steel is set to 0.05% or more.
【0034】C含有量を増すことにより、鋼の強度を高
めることができるが、0.25%を超えて含有させると
強度が高くなりすぎて塑性加工用途に適さず、溶接性も
劣化する。従ってC含有量の上限は0.25%とする。
好ましくは0.20%以下である。By increasing the C content, the strength of the steel can be increased. However, when the content exceeds 0.25%, the strength becomes too high, which is not suitable for plastic working and the weldability is deteriorated. Therefore, the upper limit of the C content is set to 0.25%.
Preferably it is 0.20% or less.
【0035】SiおよびAl:これらの元素はフェライ
ト安定化元素である。これらを適量含有させることによ
り、焼鈍時のフェライト+オーステナイト2相域温度に
おいてフェライトの体積率が増加し、平衡するオーステ
ナイトのC濃度が高められて、オーステナイトが安定に
なるという効果が得られる。Si and Al: These elements are ferrite stabilizing elements. By containing these in an appropriate amount, the volume ratio of ferrite increases at the temperature of the ferrite + austenite two-phase region during annealing, and the C concentration of austenite to be equilibrated is increased, whereby the effect of stabilizing austenite is obtained.
【0036】Siは必須元素ではないが、Siには炭化
物の析出を抑制する作用があり、2相域焼鈍からの冷却
時のベイナイト変態時にもオーステナイト中にCを濃縮
させる効果も得られる。Although Si is not an essential element, Si has the effect of suppressing the precipitation of carbides, and also has the effect of enriching C in austenite during bainite transformation during cooling from two-phase annealing.
【0037】これらの効果を十分に得るために、Siお
よび/またはAlを、Alはsol.Alとして、合計
で1.0%以上含有させる。なお、本発明におけるAl
含有量は、すべてsol.Alを意味する。これらの元
素によるフェライト安定化作用は、その含有量が合計で
2.5%を超えると飽和し、それを超えて含有させるの
は経済性を損なうのみであるので、両元素の含有量合計
で2.5%以下とする。In order to obtain these effects sufficiently, Si and / or Al, Al is sol. As Al, 1.0% or more is contained in total. Note that, in the present invention, Al
The contents are all sol. It means Al. The ferrite stabilizing action of these elements saturates when the content exceeds 2.5% in total, and when the content exceeds that, only impairs the economic efficiency. 2.5% or less.
【0038】Siはフェライトを強化する作用があるの
で鋼の強度を高めるのにも有用であるが、Si含有量が
2.0%を超えると、Si添加鋼板特有の高Siスケー
ルによる表面品質の劣化が顕著になる。これを避けるた
めにSi含有量は2.0%以下とする。Siには溶融亜
鉛の濡れ性を阻害する作用があるので、溶融亜鉛めっき
や合金化溶融亜鉛めっきを施す場合には、Si含有量を
0.8%以下とすることが好ましい。より好ましくは
0.6%以下である。Since Si has the effect of strengthening ferrite, it is also useful for increasing the strength of steel. However, when the Si content exceeds 2.0%, the surface quality due to the high Si scale peculiar to the Si-added steel sheet is reduced. Deterioration becomes remarkable. To avoid this, the Si content is set to 2.0% or less. Since Si has an effect of inhibiting the wettability of hot-dip zinc, when performing hot-dip galvanizing or alloyed hot-dip galvanizing, the Si content is preferably set to 0.8% or less. More preferably, it is 0.6% or less.
【0039】Alは溶融亜鉛めっき時のめっき濡れ性を
阻害しないので、溶融亜鉛めっきを施す場合にはAlを
含有させるのが好ましい。また、Alは製鋼時に脱酸材
として使われるが、十分な脱酸効果を得るために、0.
005%以上含有させる。Al含有量が2.0%を超え
ると鋼板中に介在物が多くなり延性を損ねるので、Al
含有量は2.0%以下とする。Since Al does not hinder plating wettability during hot-dip galvanizing, it is preferable to include Al when hot-dip galvanizing is performed. Also, Al is used as a deoxidizing material during steelmaking.
005% or more. If the Al content exceeds 2.0%, inclusions increase in the steel sheet and impair ductility.
The content is 2.0% or less.
【0040】Mn:オーステナイト安定化作用があり、
本発明の高張力鋼板の必須元素の一つである。2相域焼
鈍後の冷却過程において、オーステナイトをマルテンサ
イトに変態させることなく室温まで残留させるためにM
n含有量は0.8%以上とする。他方、Mnは凝固時に
偏析し易い元素であり、過剰に含有させると偏析してバ
ンド状組織が生じ、延性が低下する。これを避けるため
にMn含有量は2.5%以下とする。好ましくは、2.
0%以下である。Mn: has an austenite stabilizing effect,
It is one of the essential elements of the high-tensile steel sheet of the present invention. In order to allow austenite to remain at room temperature without transforming it to martensite in the cooling process after annealing in the two-phase region, M
The n content is 0.8% or more. On the other hand, Mn is an element that is liable to segregate during solidification, and when contained in excess, segregates to form a band-like structure, which reduces ductility. To avoid this, the Mn content is set to 2.5% or less. Preferably, 2.
0% or less.
【0041】P:必須元素ではないが、フェライトに固
溶して鋼を強化する作用がある。また、Cuと共存させ
ると鋼の表層に安定な保護皮膜を形成して耐食性を改善
する作用もあるので、これらの効果を得るためにPを
0.01%以上含有させてもよい。しかしながらPは凝
固時に偏析し易く、過剰に含有させると偏析に起因する
バンド状組織が生じて延性を損なううえ、鋼の溶接性も
劣化する。したがって含有させる場合でも0.05%以
下とする。好ましくは0.02%以下である。P: Although not an essential element, it has a function of strengthening steel by forming a solid solution in ferrite. Further, when coexisting with Cu, a stable protective film is formed on the surface layer of steel to improve the corrosion resistance, so that P may be contained at 0.01% or more in order to obtain these effects. However, P is easily segregated at the time of solidification, and if P is excessively contained, a band-like structure due to segregation is generated to impair ductility and also deteriorate the weldability of steel. Therefore, even if it is contained, the content is made 0.05% or less. Preferably it is 0.02% or less.
【0042】Ti、Nb:これらの元素は必須ではない
が、いずれも炭化物生成元素であり、微細な析出物を形
成し、熱延板結晶組織を微細化して鋼板の強度を高める
作用がある。このような効果を得るためにこれらの元素
のいずれかまたは双方を、0.003%以上、0.05
%以下含有させても構わない。ただし、2種の合計含有
量が0.05%を超えると強度の上昇よりも延性の低下
が顕著になるので、2種類を同時に含有させる場合には
その合計量の上限は0.05%とする。Ti, Nb: These elements are not essential, but are all carbide-forming elements and have the effect of forming fine precipitates, refining the crystal structure of a hot-rolled sheet and increasing the strength of the steel sheet. In order to obtain such an effect, one or both of these elements are added in an amount of 0.003% or more and 0.05% or more.
% Or less. However, when the total content of the two exceeds 0.05%, the ductility decreases more remarkably than the increase in strength. Therefore, when two types are simultaneously contained, the upper limit of the total amount is 0.05%. I do.
【0043】またTiはNと結合し易く、AlNの析出
に優先してTiNが析出し、AlNによるスラブ割れを
防止する効果もある。この効果を得るためには、Tiを
0.003%以上、かつ、(Ti/48)/(N/1
4)≧2を満足する範囲で含有させるのが好ましい。Further, Ti is easily bonded to N, and TiN is precipitated in preference to the precipitation of AlN, and has an effect of preventing slab cracking due to AlN. In order to obtain this effect, the content of Ti should be not less than 0.003% and (Ti / 48) / (N / 1
4) It is preferable that the content is contained in a range satisfying ≧ 2.
【0044】Cu、Ni、Co:これらの元素は必須で
はないが、いずれも鉄炭化物中に溶け難く、ベイナイト
変態時に炭化物の析出を抑制するので、残留オーステナ
イトが得やすくなるという効果が得られる。これらの効
果を得るために、Cu、Ni、Coからなる群の内の1
種または2種以上を、Cuは0.2%以上、Niは0.
1%以上、Coは0.0005%以上含有させてもよ
い。いずれの元素も過剰に含有させるとベイナイト変態
が不十分になるので、含有させる場合の上限は、Cuは
1.0%、Niは0.5%、Coは1.0%、2種以上
を含有させる場合にはその合計量で1.5%以下とす
る。また、CuはPと共存すると耐食性を向上するので
この目的のために添加してもよい。Cu, Ni, Co: These elements are not essential, but all of them are hardly soluble in iron carbide and suppress precipitation of carbides during bainite transformation, so that an effect of easily obtaining residual austenite is obtained. To obtain these effects, one of the group consisting of Cu, Ni, and Co is used.
Species or two or more, Cu is 0.2% or more, Ni is 0.1% or more.
1% or more and Co may be contained 0.0005% or more. If any of the elements is excessively contained, the bainite transformation becomes insufficient. Therefore, the upper limit in the case of containing Cu is 1.0%, Ni is 0.5%, and Co is 1.0%. When it is contained, the total amount is 1.5% or less. Further, Cu improves the corrosion resistance when coexisting with P, and may be added for this purpose.
【0045】なお、Cuはスラブ割れの要因となるの
で、Cuを含有させる場合には、Niを、Ni≧Cu/
2を満足する範囲で複合して含有させるのが好ましい。
残部はFeおよび不可避的不純物である。不可避的不純
物の中でも、Sは、MnSとして析出し、延性を阻害す
るのみならず、オーステナイト安定化元素として添加さ
れるMnを析出物として消費するので、その含有量は
0.01%以下とするのがよい。また、N含有量が多い
とAlNにるスラブ割れの原因になるほか、製品中でも
AlNの延性を低下させるので、その含有量は0.00
5%以下とするのがよい。Since Cu causes slab cracking, when Cu is contained, Ni is replaced by Ni ≧ Cu /
It is preferable that the compound is contained in a range that satisfies 2.
The balance is Fe and inevitable impurities. Among unavoidable impurities, S precipitates as MnS and not only impairs ductility, but also consumes Mn added as an austenite stabilizing element as a precipitate, so the content is 0.01% or less. Is good. Also, if the N content is large, it causes slab cracking due to AlN, and also reduces the ductility of AlN in products, so the content is 0.00
It is good to make it 5% or less.
【0046】表面硬化特性;前述したように、予成形し
て焼付け処理を施した部材において、鋼板表面部の硬度
が中心部の硬度よりも一定の割合以上に高いという表面
硬化特性を備えていることが、本発明の高張力鋼板にと
って極めて重要である。構造部材には種々の形状があ
り、成形方法、歪み分布などが様々であるので、この表
面硬化特性は、鋼板に、板厚ひずみにして10%の引張
り曲げ曲げ戻し変形(以下、単に「引張り曲げ変形」と
も記す)を伴う予成形を施し、次いで170℃で20分
間保持する焼付け処理を施した後の鋼板表面部と板厚中
心部の硬度の差の、予成形前の鋼板の板厚中心部の硬度
に対する比(下記式で表されるX、以下、単に「硬度
比」とも記す)が、0.12以上となる関係を満足する
もの、と規定する。 X=(HVs−HVc)/HV0 ここで、HV0 は、上記予成形前の鋼板の板厚中心部
のビッカース硬度、HVcは、上記予成形と焼付け処理
を施した後の板厚中心部のビッカース硬度、HVsは上
記予成形と焼付け処理を施した後の表面部のビッカース
硬度である。ここで、表面部のビッカース硬度とは、鋼
板表面から板厚の1/8離れた部分で測定した硬度を両
表面について平均した値を意味する。また、上記予成形
における曲げ半径は板厚(t)の2.5倍(2.5t)
とする。Surface hardening characteristics: As described above, the preformed and baked member has surface hardening characteristics such that the hardness of the steel sheet surface is higher than the hardness of the central part by a certain ratio or more. This is extremely important for the high strength steel sheet of the present invention. Since structural members have various shapes and various forming methods, strain distributions, and the like, the surface hardening characteristics are determined by applying a 10% tensile bending / bending-back deformation (hereinafter simply referred to as “tensile strength”) to a steel sheet. Bending deformation), followed by baking at 170 ° C. for 20 minutes, the difference in hardness between the surface and the center of the thickness of the steel sheet, the thickness of the steel sheet before preforming. The ratio to the hardness at the center (X represented by the following formula, hereinafter simply referred to as “hardness ratio”) satisfies a relationship of 0.12 or more. X = (HVs−HVc) / HV 0 where HV 0 is the Vickers hardness at the center of the thickness of the steel sheet before the preforming, and HVc is the center of the thickness after the preforming and the baking process. Is the Vickers hardness of the surface after the above-mentioned preforming and baking treatment. Here, the Vickers hardness of the surface portion means a value obtained by averaging the hardness measured at a portion 1/8 of the plate thickness away from the surface of the steel plate for both surfaces. The bending radius in the above preforming is 2.5 times (2.5t) of the plate thickness (t).
And
【0047】本発明の硬度比が高い鋼板によれば、高速
変形した際の衝突吸収エネルギが高い構造部材を得るこ
とができる。硬度比が0.12に満たない場合には得ら
れる部材の衝突特性は不十分であり、良好な衝突特性を
備えた構造部材を得るには、硬度比が0.12以上であ
る鋼板を使用するのが有効である。従って本発明の高張
力鋼板は、硬度比、つまりXが0.12以上のものとす
る。より優れた衝突特性を選るには、硬度比が0.15
以上である鋼板が好ましい。According to the steel plate having a high hardness ratio of the present invention, a structural member having a high collision absorption energy when deformed at a high speed can be obtained. When the hardness ratio is less than 0.12, the obtained members have insufficient collision characteristics. To obtain a structural member having good collision characteristics, use a steel plate having a hardness ratio of 0.12 or more. It is effective to do. Therefore, the high strength steel sheet of the present invention has a hardness ratio, that is, X of 0.12 or more. To select better collision properties, a hardness ratio of 0.15
The above steel sheet is preferable.
【0048】本発明の高張力鋼板は、ダイ、ポンチおよ
びしわ押さえを有するプレス工具で成形され、その成形
過程において少なくともダイ肩部近傍で曲げ曲げ戻し変
形があり、成形後には通常の塗装焼付け処理が施される
部品に使用すれば、優れた耐衝撃特性を有する構造部材
が得られる。プレス工具がしわ押さえビードなどを備え
ている場合には、鋼板がそのビード部を通過する際に受
ける曲げ曲げ戻しも、表面硬化に寄与する。The high-strength steel sheet of the present invention is formed by a press tool having a die, a punch and a wrinkle holder. In the forming process, there is a bending / bending-back deformation at least in the vicinity of the die shoulder. When used for a part to be subjected to the above, a structural member having excellent impact resistance can be obtained. When the press tool is provided with a wrinkle holding bead or the like, the bending / bending returned when the steel sheet passes through the bead portion also contributes to surface hardening.
【0049】上記曲げ曲げ戻し変形される部分は構造部
材を構成する部品の一部分に使用するだけでも耐衝撃特
性改善の効果が得られる。図1に示す閉断面構造部材を
例として説明すれば、曲げ曲げ戻し変形される部分はハ
ット断面部品の縦壁部2である。ハット断面部品の底部
11や、平板部品12には曲げ曲げ戻し変形はされてお
らず、従って表面硬化特性もないが、それでも構わな
い。The effect of improving the impact resistance can be obtained even by using the above-mentioned bent and unfolded portion only for a part of the component constituting the structural member. Taking the closed-section structural member shown in FIG. 1 as an example, the portion to be bent and returned is the vertical wall portion 2 of the hat-section component. The bottom portion 11 and the flat plate component 12 of the hat cross-section component are not bent and bent back and thus have no surface hardening characteristics, but may be used.
【0050】本発明の高張力鋼板は、鋼板冷間圧延鋼板
のほか、電気めっき、溶融めっき、などの処理を施した
表面処理鋼板としても、所望の効果が得られる。 製造方法;本発明の延性と耐衝撃特性に優れた高張力鋼
板は、上記化学組成を有する鋼を以下の方法で熱間圧延
し、冷間圧延し、再結晶焼鈍を施して製造するのが好適
である。The high-strength steel sheet of the present invention can provide desired effects not only as a cold-rolled steel sheet but also as a surface-treated steel sheet which has been subjected to electroplating, hot-dip coating, and the like. Production method: The high-tensile steel sheet having excellent ductility and impact resistance of the present invention is produced by hot rolling, cold rolling, and recrystallization annealing a steel having the above chemical composition by the following method. It is suitable.
【0051】上記化学組成を有する鋼は常法により鋳造
されて鋳片(スラブ)とされる。鋳塊を分解圧延して鋼
片とし、この鋼片をスラブとしても構わない。スラブは
常法により加熱して粗圧延されたのち、仕上圧延に供さ
れるが、鋳造後のスラブ温度が高く、後述する仕上温度
が確保できる場合には、スラブ加熱を省略して粗圧延し
ても構わない。また、ストリップキャストなど公知の方
法により薄い鋳片が得られる場合には、粗圧延を省略し
ても構わない。The steel having the above chemical composition is cast by a conventional method to form a slab. The ingot may be disassembled and rolled into a billet, and this billet may be used as a slab. The slab is heated and rough-rolled by a conventional method, and then subjected to finish rolling.If the slab temperature after casting is high and a finishing temperature described later can be ensured, the slab heating is omitted and rough rolling is performed. It does not matter. When a thin cast piece can be obtained by a known method such as strip casting, rough rolling may be omitted.
【0052】仕上圧延:本発明の高張力鋼板の母材とな
る熱延板は、最終製品において優れた局部延性を有する
鋼板とするために、フェライトと軟質なパーライトから
なり、かつパーライトの分散状態が均一な結晶組織を備
えたものとする。Finish rolling: The hot-rolled sheet, which is the base material of the high-tensile steel sheet of the present invention, is composed of ferrite and soft pearlite and has a dispersed state of pearlite in order to obtain a steel sheet having excellent local ductility in the final product. Have a uniform crystal structure.
【0053】熱間圧延における仕上圧延開始温度が過度
に高温であると、圧延中のオーステナイトの回復再結晶
が急速に進行して歪み蓄積が不十分となり、圧延後の冷
却過程でのフェライト変態が遅延し、軟質なフェライト
の体積率が減少する。これを避けるために、仕上圧延開
始温度は1050℃以下とする。仕上圧延開始温度の下
限は特に限定するものではなく、以下に述べる仕上圧延
出側温度を満足する限り、低いことが望ましい。If the finish rolling start temperature in the hot rolling is excessively high, the recovery and recrystallization of austenite during rolling progresses rapidly and the strain accumulation becomes insufficient, and the transformation of ferrite in the cooling process after rolling may occur. Delays and reduces the volume fraction of soft ferrite. In order to avoid this, the finish rolling start temperature is set to 1050 ° C. or less. The lower limit of the finish rolling start temperature is not particularly limited, and is preferably low as long as the finish rolling exit side temperature described below is satisfied.
【0054】仕上圧延終了温度は800℃以上とする。
仕上圧延終了温度が800℃に満たない低温になると圧
延中にフェライト変態が生じ、結晶粒が伸展した加工フ
ェライト組織を有するものとなり、第2相が均一に分散
した熱延鋼板組織が得られなくなる。The finish rolling end temperature is 800 ° C. or higher.
When the finish rolling end temperature is lower than 800 ° C., ferrite transformation occurs during rolling, resulting in a processed ferrite structure in which crystal grains are extended, and a hot-rolled steel sheet structure in which the second phase is uniformly dispersed cannot be obtained. .
【0055】補助加熱:前述の仕上圧延の入り側温度と
出側温度は、熱延コイルの全長にわたって満足する必要
がある。鋼片が長い場合には、圧延途中で鋼片温度が低
下し、熱間圧延後期などにおいて上記仕上げ温度が確保
できない場合が生じる。また、仕上圧延の入り側温度を
低く制限しているので鋼片幅方向端部などでの温度低下
が原因で上記仕上げ温度が確保できない場合も生じる。
このような場合には仕上圧延入り側で補助加熱を施すの
がよい。補助加熱方法は限定しないが、仕上圧延入り側
でのスラブの温度分布に応じて加熱入熱量の制御が容易
である電磁誘導加熱方式が好ましい。Auxiliary heating: The above-mentioned entrance and exit temperatures of finish rolling must be satisfied over the entire length of the hot-rolled coil. If the steel slab is long, the temperature of the steel slab decreases during the rolling, and the finishing temperature may not be ensured in the latter half of hot rolling. In addition, since the entry-side temperature of the finish rolling is limited to a low value, there is a case where the above-mentioned finishing temperature cannot be ensured due to a temperature drop at an end portion of the billet in the width direction.
In such a case, it is preferable to perform auxiliary heating on the side including the finish rolling. Although the auxiliary heating method is not limited, an electromagnetic induction heating method in which the heating heat input amount can be easily controlled in accordance with the temperature distribution of the slab on the entry side of the finish rolling is preferable.
【0056】仕上圧延後の冷却:仕上圧延完了後は、フ
ェライト変態を促進するため、750℃まで20℃/秒
以上の冷却速度で急速冷却する。急速冷却終了温度が7
50℃よりも高かったり、冷却速度が20℃/秒に満た
ない場合には、上記冷却途中でオーステナイトの回復が
生じて加工歪みが消失し、フェライト変態が進行しにく
くなるのでよくない。Cooling after finish rolling: After finish rolling, the steel is rapidly cooled to 750 ° C. at a cooling rate of 20 ° C./sec or more to promote ferrite transformation. Rapid cooling end temperature is 7
When the cooling rate is higher than 50 ° C. or the cooling rate is less than 20 ° C./sec, the recovery of austenite occurs during the cooling, the work distortion disappears, and the ferrite transformation hardly proceeds, which is not good.
【0057】フェライト変態を促進させるため、上記急
速冷却に引き続き、巻取り開始までの温度領域で2秒以
上滞留させるのが望ましい。この滞留処理は、上記温度
範囲の冷却を空冷もしくは緩冷却とすることによりおこ
なうのがよい。上記滞留時間が2秒間に満たない場合に
はフェライト変態が不十分となるのでよくない。より好
ましい滞留時間は5秒以上である。滞留時間が10秒間
を超えると、必要な冷却テーブルが長くなるので滞留時
間は10秒以下とするのがよい。上記滞留処理後は巻取
温度まで任意の冷却速度で急速冷却しても構わない。In order to promote the ferrite transformation, it is desirable that, after the above-mentioned rapid cooling, the ferrite be retained in a temperature region up to the start of winding for 2 seconds or more. This staying treatment is preferably performed by cooling the above temperature range by air cooling or slow cooling. If the residence time is less than 2 seconds, the ferrite transformation becomes insufficient, which is not good. A more preferred residence time is 5 seconds or more. If the residence time exceeds 10 seconds, the required cooling table becomes long, so the residence time is preferably set to 10 seconds or less. After the above-mentioned staying treatment, rapid cooling at an optional cooling rate to the winding temperature may be performed.
【0058】巻取温度:巻取温度が高温になるとスケー
ルロスが増加するうえ、鋼が軟らかくなり巻き取ったコ
イルの巻姿が崩れる。これを避けるために巻取温度は7
00℃以下とする。好ましくは680℃以下、さらに好
ましくは650℃以下である。Winding temperature: When the winding temperature is high, the scale loss increases, and the steel becomes soft and the wound shape of the wound coil collapses. To avoid this, take-up temperature is 7
It should be below 00 ° C. It is preferably at most 680 ° C, more preferably at most 650 ° C.
【0059】MnはAr3点を低くし、Pは高くする作
用がある。従って鋼が凝固する際にこれらの元素の偏析
が生じると、Mnの場合は正偏析、Pの場合は負偏析の
部分でフェライト変態が遅延してパーライトがバンド状
に析出してバンド状組織が生じる。このような鋼は冷間
圧延後にミクロボイドが生じやすく、製品鋼板の局部延
性を損なうことがある。MnとPの含有量が高い鋼で
は、巻取温度を高くしてフェライト変態を促進させるこ
とにより、パーライトのバンド状組織を軽減することが
できる。このため、本発明においては、巻取温度の下限
(Tc)をMnおよびP含有量と関連づけて規定する。Mn has the effect of lowering the Ar3 point and increasing P. Therefore, when segregation of these elements occurs when the steel is solidified, in the case of Mn, the segregation of ferrite is delayed in the part of positive segregation and in the case of P, the segregation of ferrite is delayed, and pearlite precipitates in a band-like manner, and a band-like structure is formed. Occurs. Such steel is liable to cause microvoids after cold rolling, and may impair the local ductility of the product steel sheet. In steels with high contents of Mn and P, the banding structure of pearlite can be reduced by increasing the winding temperature to promote ferrite transformation. For this reason, in the present invention, the lower limit (Tc) of the winding temperature is defined in relation to the Mn and P contents.
【0060】すなわち巻取温度の下限Tc( ℃) は、4
30+70×Mn( %) +1000×P( %) で計算さ
れる値以上とする。巻取温度を低くしすぎると、第2相
としてベイナイトおよびマルテンサイトが生成するの
で、この観点でも、前述のTc以上の温度で巻取る必要
がある。That is, the lower limit of the winding temperature Tc (° C.) is 4
30 + 70 × Mn (%) + 1000 × P (%). If the winding temperature is too low, bainite and martensite are generated as the second phase. Therefore, from this viewpoint, it is necessary to wind at a temperature equal to or higher than the above Tc.
【0061】冷間圧延:上記方法で熱間圧延して得られ
た熱延鋼板は常法により酸洗などでスケールを除去した
後、冷間圧延される。冷間圧延は常法に従っておこなえ
ばよいが、冷間圧下率は合計で40%以上、80%以下
とする。冷間圧下率が40%に満たない場合には圧延効
率が低下し、80%を超えるとフェライトと第2相間の
ミクロボイドが増加して再結晶焼鈍後の延性に悪影響を
及ぼすのでよくない。好ましい冷間圧下率は合計で70
%以下である。Cold rolling: The hot-rolled steel sheet obtained by hot rolling according to the above method is subjected to cold rolling after removing scale by pickling or the like by a conventional method. The cold rolling may be performed according to a conventional method, and the cold rolling reduction is 40% or more and 80% or less in total. If the cold rolling reduction is less than 40%, the rolling efficiency decreases, and if it exceeds 80%, microvoids between the ferrite and the second phase increase, which adversely affects ductility after recrystallization annealing, which is not good. A preferred cold reduction is 70 in total.
% Or less.
【0062】焼鈍:焼鈍温度は、フェライト+オーステ
ナイトの2相にしてCをオーステナイトに濃縮するため
Ac1変態点以上、Ac3変態点以下の温度域とする。
焼鈍温度が低すぎるとセメンタイトが再固溶するのに時
間がかかりすぎ、高すぎるとオーステナイトの体積率が
大きくなりすぎてオーステナイト中のC濃度が以下す
る。好ましくは800℃以上、850℃以下の範囲であ
る。Annealing: The annealing temperature is in a temperature range from the Ac1 transformation point to the Ac3 transformation point in order to concentrate C into austenite by forming two phases of ferrite and austenite.
If the annealing temperature is too low, it takes too much time for the cementite to re-dissolve in solid form. If the annealing temperature is too high, the volume fraction of austenite becomes too large and the C concentration in the austenite decreases. Preferably, it is in the range of 800 ° C. or more and 850 ° C. or less.
【0063】均熱時間は、セメンタイトの再溶解を十分
におこなわせるために30秒以上とする。均熱時間が9
0秒を超えるとオーステナイト粒が粗大化して好ましく
ないので均熱時間は90秒以下とする。The soaking time is at least 30 seconds in order to sufficiently re-dissolve cementite. Soaking time 9
If the time exceeds 0 second, the austenite grains become coarse, which is not preferable. Therefore, the soaking time is set to 90 seconds or less.
【0064】均熱終了後は、パーライト変態を抑制する
ために、700〜450℃の温度範囲を30℃/秒以上
で急速冷却する。均熱温度から700℃までの間の冷却
速度は限定しないが、フェライトの体積率を増やして、
オーステナイト中にCを濃縮するために、700℃まで
を10℃/秒以下で冷却することが好ましい。After completion of the soaking, in order to suppress the pearlite transformation, the temperature range of 700 to 450 ° C. is rapidly cooled at a rate of 30 ° C./sec or more. The cooling rate between the soaking temperature and 700 ° C is not limited, but the volume ratio of ferrite is increased,
In order to concentrate C in austenite, it is preferable to cool down to 700 ° C. at a rate of 10 ° C./sec or less.
【0065】上記急速冷却に引き続く450℃以下、3
70℃以上の温度範囲で200秒間以上、400秒間以
下滞留させる。この滞留方法は、一定温度に保持する方
法でもよいし、450℃以下、370℃までの間を、2
00秒間以上、400秒間以下の範囲で徐々に温度を低
下させる方法でもよい。上記滞留温度が450℃を超え
るとベイナイト変態が生じず、370℃に満たない場合
には、下部ベイナイトになり、オーステナイトへのCの
濃縮があまり起こらなくなり、所望の残留オーステナイ
ト鋼板が得られない。Below 450 ° C. following the rapid cooling,
It is kept in a temperature range of 70 ° C. or more for 200 seconds or more and 400 seconds or less. This retention method may be a method of maintaining a constant temperature, or a method of maintaining the temperature at 450 ° C. or less and 370 ° C.
A method of gradually lowering the temperature in a range from 00 seconds to 400 seconds may be used. If the residence temperature exceeds 450 ° C., bainite transformation does not occur, and if it is less than 370 ° C., it becomes lower bainite, and the concentration of C in austenite hardly occurs, and a desired retained austenite steel sheet cannot be obtained.
【0066】上記滞留後の冷却については限定しない
が、設備を簡素にするために、冷却速度を速めても構わ
ない。また、溶融めっき鋼板を製造するために、連続溶
融めっきラインを用いて上記焼鈍処理を行ってもよい。
合金化溶融亜鉛めっきとするために、合金化熱処理を行
っても良い。The cooling after the stay is not limited, but the cooling rate may be increased to simplify the equipment. Further, in order to manufacture a hot-dip coated steel sheet, the above-described annealing treatment may be performed using a continuous hot-dip coating line.
An alloying heat treatment may be performed in order to obtain galvannealing.
【0067】調質圧延:焼鈍後は、表面粗度調整、平坦
強制、降伏点伸びの低減を目的にして、公知の方法によ
り、調質圧延を施しても構わない。その場合には、延性
を低下させないために、調質圧延伸び率は2.0%以下
にすることが好ましい。Temper rolling: After annealing, temper rolling may be performed by a known method for the purpose of adjusting the surface roughness, forcing flatness, and reducing the yield point elongation. In that case, the temper rolling elongation is preferably 2.0% or less so as not to lower the ductility.
【0068】上記以外は公知の方法によって製造すれば
よい。Other than the above, it may be manufactured by a known method.
【0069】[0069]
【実施例】(実施例1)表1に記載の化学組成を有する
鋼を実験室において溶解し、厚さ:60mm、幅:15
0mm、質量:17kgの鋼塊とし、これを熱間鍛造し
て厚さ25mm、幅:150mmの鋼片を得た。EXAMPLES (Example 1) A steel having the chemical composition shown in Table 1 was melted in a laboratory and had a thickness of 60 mm and a width of 15 mm.
A steel ingot having a thickness of 0 mm and a mass of 17 kg was hot forged to obtain a steel slab having a thickness of 25 mm and a width of 150 mm.
【0070】[0070]
【表1】 これらの鋼片を加熱炉に装入し、1200℃で30分間
保持した後、炉から取り出して1000℃まで自然冷却
し、圧延開始温度を1000℃とする熱間仕上圧延を施
した。仕上圧延のパス回数は合計3パスで、仕上圧延後
の厚さは3.5mmであり、仕上圧延終了温度は850
℃であった。熱間仕上圧延終了後、ただちに4秒間水ス
プレー冷却して720℃とし(平均冷却速度33℃/
秒)、次いで8秒間自然放冷して680℃とし、さらに
2秒間の水スプレー冷却を施して620℃とし(平均冷
却速度30℃/秒)、これを620℃に加熱した炉に装
入して30分間保持した後、20℃/時で室温まで冷却
した。[Table 1] These steel slabs were placed in a heating furnace and maintained at 1200 ° C. for 30 minutes, then taken out of the furnace and naturally cooled to 1000 ° C., and subjected to hot finish rolling at a rolling start temperature of 1000 ° C. The number of passes of the finish rolling is a total of 3 passes, the thickness after the finish rolling is 3.5 mm, and the finish rolling end temperature is 850.
° C. Immediately after the hot finish rolling, water spray cooling was performed for 4 seconds to reach 720 ° C (average cooling rate: 33 ° C /
Second), and then naturally cooled to 680 ° C. for 8 seconds, and further subjected to water spray cooling for 2 seconds to 620 ° C. (average cooling rate: 30 ° C./second), and charged into a furnace heated to 620 ° C. , And cooled to room temperature at 20 ° C / hour.
【0071】得られた熱延板は、塩酸溶液を用いて酸洗
してスケールを除去した後、合計圧下率66%で1.2
mmまで冷間圧延した。得られた冷延板を、820℃に
加熱して40秒間均熱した後、5℃/秒で700℃まで
徐冷した後、50℃/秒で400℃まで冷却し、400
℃で300秒間保持した後、30℃/秒で室温まで冷却
した。得られた焼鈍板に伸び率1.0%の調質圧延を施
した。The obtained hot-rolled sheet was pickled with a hydrochloric acid solution to remove scale, and then subjected to a total reduction of 66% at 1.2%.
mm. The obtained cold rolled sheet was heated to 820 ° C., soaked for 40 seconds, gradually cooled at 5 ° C./second to 700 ° C., cooled to 50 ° C./second to 400 ° C.
After holding at 300C for 300 seconds, it was cooled to room temperature at 30C / sec. The resulting annealed sheet was subjected to temper rolling at an elongation of 1.0%.
【0072】これらの鋼板の圧延方向について、JIS
−Z2201に規定された5号試験片を用い、JIS−
Z2241の規定に準拠して引張試験をおこなった。引
張試験時の応力−歪み曲線における最大荷重時の歪みを
一様伸びとし、全伸びと一様伸びの差を求めて局部伸び
値とした。Regarding the rolling direction of these steel sheets, JIS
-Using the No. 5 test piece specified in Z2201, JIS-
A tensile test was performed according to the rules of Z2241. The strain at the maximum load in the stress-strain curve during the tensile test was defined as uniform elongation, and the difference between the total elongation and the uniform elongation was determined as the local elongation value.
【0073】上記調質圧延済みの鋼板から得た圧延方向
を長手方向とするブランクを、図2に示すプレス工具を
用いてプレス成形し、幅40mm、高さ30mm、フラ
ンジ幅10mm、全長200mmのハット断面部品1を
得た。ポンチとダイの肩半径は、共に3.0mmとし
た。しわ抑え力は、縦壁部2の板厚歪みが10%となる
ように調整した。得られたハット断面部品には170℃
で20分間保持する焼付け処理を施した後、縦壁部から
小片を切り出し、圧延方向に垂直な断面のビッカース硬
さを測定した。A blank having a longitudinal direction in the rolling direction obtained from the temper-rolled steel sheet was press-formed using a press tool shown in FIG. 2 and had a width of 40 mm, a height of 30 mm, a flange width of 10 mm and a total length of 200 mm. A hat cross-section part 1 was obtained. The shoulder radius of the punch and the die were both 3.0 mm. The wrinkle suppressing force was adjusted so that the thickness distortion of the vertical wall portion 2 was 10%. 170 ° C for the obtained hat cross-section parts
After baking for 20 minutes, small pieces were cut out from the vertical wall, and Vickers hardness of a cross section perpendicular to the rolling direction was measured.
【0074】図3は、ビッカース硬さの測定位置を示す
配置図である。ビッカース硬さ試験はJIS−Z224
4の規定に準拠しておこない、試験荷重は4.9Nとし
た。断面内での測定位置は、板厚中心と両表面(板厚の
1/8だけ内側の位置)について、それぞれ、0.5m
m間隔で5点測定し、板厚中心の平均をHVc、両表面
の測定値の平均をHVsとした。なお、予成形前の鋼板
についても、圧延方向に垂直な断面の板厚中心におい
て、0.5mm間隔で5点のビッカース硬さを測定し、
その平均をHV0 とした。これらの値から硬度比Xを
計算した。FIG. 3 is a layout diagram showing the measurement positions of the Vickers hardness. Vickers hardness test is JIS-Z224
The test load was set to 4.9 N in accordance with the regulations of No. 4. The measurement position in the cross section is 0.5 m for each of the center of the thickness and both surfaces (the position inside by 8 of the thickness).
Five points were measured at m intervals, and the average at the center of the plate thickness was HVc, and the average of the measured values at both surfaces was HVs. In addition, also about the steel sheet before preforming, in the center of the thickness of the cross section perpendicular to the rolling direction, five points of Vickers hardness were measured at 0.5 mm intervals,
The average was HV 0. The hardness ratio X was calculated from these values.
【0075】上記プレス成形で得たハット断面部品と、
同じ冷間圧延し、焼鈍と調質圧延を施した鋼板から得た
幅60mm、長さ200mmの平板部品12を20mm
間隔でスポット溶接し、閉断面構造部材を作製し、これ
に170℃で20分間加熱する焼付け処理を施して試験
体を作製した。A hat cross-section part obtained by the above press molding,
The same cold-rolled, flat plate part 12 having a width of 60 mm and a length of 200 mm obtained from a steel sheet subjected to annealing and temper rolling was subjected to 20 mm.
Spot-welding was performed at intervals to produce a closed-section structural member, which was subjected to a baking treatment of heating at 170 ° C. for 20 minutes to produce a test body.
【0076】この試験体を、その長手方向を鉛直にして
試験台に装着し、上方から質量が60kgの錘体を落下
させ、10m/秒の速度で試験体上端に衝突させる落重
式軸圧壊試験をおこなった。試験体下部にはロードセル
を設置して試験体に作用する荷重を測定し、別途錘体の
位置変化を測定して、これらの荷重−変位関係から、錘
体が停止するまでに試験体に作用した荷重の平均値P
(kN)を求め、この軸圧壊平均荷重により耐衝撃特性
を判定した。The test specimen was mounted on a test table with its longitudinal direction being vertical, and a weight body having a mass of 60 kg was dropped from above, and was hit against the upper end of the test specimen at a speed of 10 m / sec. The test was performed. A load cell is installed at the bottom of the test piece to measure the load acting on the test piece, and the position change of the weight is separately measured. From these load-displacement relations, the load acting on the test piece until the weight stops is measured. Average value of applied load P
(KN) was determined, and the impact resistance was determined based on the average axial crushing load.
【0077】表2に、加工前の鋼板の引張特性、予成形
し焼付け処理したハット断面部品の縦壁部で測定した硬
度比および試験体の軸圧壊平均荷重測定結果を示す。Table 2 shows the tensile properties of the steel sheet before working, the hardness ratio measured on the vertical wall portion of the preformed and baked hat cross-section part, and the results of measuring the average axial crushing load of the test specimen.
【0078】[0078]
【表2】 表2において試番3〜11は鋼の化学組成が本発明の規
定する条件を満足するものであり、その硬度比Xは0.
12以上で、いずれも本発明例である。試番1はC含有
量が低い鋼Aを使用し、試番2、12および13はSi
+Al含有量が低い鋼B、LおよびMを使用したもの
で、これらは硬度比が0.12に満たず、いずれも比較
例として評価したものである。試験体の軸圧壊平均荷重
は、素材とした鋼板の引張強さ(TS)レベルにより異
なるので、耐衝撃特性は鋼板の引張強さに応じてその良
否を判断するのが妥当である。表2に示されているよう
に、本発明例である鋼板を用いた試番3〜11はいずれ
も優れた軸圧壊平均荷重を示していた。また、本発明鋼
はTS×ELで代表される強度−延性バランスにも優れ
ていた。[Table 2] In Table 2, Test Nos. 3 to 11 are those in which the chemical composition of the steel satisfies the conditions specified by the present invention, and the hardness ratio X is 0.1.
12 or more are all examples of the present invention. Trial No. 1 used steel A having a low C content, and Trials 2, 12, and 13 used Si
Steels B, L and M having a low + Al content were used, and their hardness ratios were less than 0.12, all of which were evaluated as comparative examples. Since the average axial crushing load of the test piece varies depending on the tensile strength (TS) level of the steel sheet used as the material, it is appropriate to determine whether the impact resistance is good or bad according to the tensile strength of the steel sheet. As shown in Table 2, all of the samples Nos. 3 to 11 using the steel sheet according to the present invention exhibited excellent axial crushing average loads. Further, the steel of the present invention was excellent in strength-ductility balance represented by TS × EL.
【0079】図4に、表2の軸圧壊平均荷重と、それぞ
れの加工前の鋼板の引張強さととの関係を示す。図4か
らわかるように、硬度比Xが0.12以上のものは、比
較例に比べ同じ引張強さでも約10%高い軸圧壊平均荷
重を示した。硬度比Xが0.15以上のものはさらに優
れていることが判る。FIG. 4 shows the relationship between the average axial crushing load shown in Table 2 and the tensile strength of each steel sheet before working. As can be seen from FIG. 4, those having a hardness ratio X of 0.12 or more exhibited about 10% higher average axial crushing load than the comparative example even at the same tensile strength. It can be seen that those having a hardness ratio X of 0.15 or more are more excellent.
【0080】(実施例2)表1に示した化学組成を有す
る鋼D、EおよびHの鋼片に、巻取温度以外は実施例1
と同一条件とする熱間仕上圧延を施して実施例1と同一
寸法の熱延板とし、実施例1と同様の酸洗、冷間圧延、
焼鈍および調質圧延を施して、種々の冷間圧延鋼板を作
製した。これらの鋼板について実施例1に記載したのと
同様の方法で試験して、引張特性と局部伸びを調査し
た。得られた結果を、巻取温度と共に表3に示す。(Example 2) Steel pieces D, E and H having the chemical compositions shown in Table 1 were applied to steel slabs except for the winding temperature.
Hot finish rolling under the same conditions as in Example 1 to obtain a hot-rolled sheet having the same dimensions as in Example 1, and pickling, cold rolling,
Various cold rolled steel sheets were produced by annealing and temper rolling. These steel sheets were tested in the same manner as described in Example 1 to investigate tensile properties and local elongation. The results obtained are shown in Table 3 together with the winding temperature.
【0081】[0081]
【表3】 表3に示されているように、熱間圧延後の巻取温度が本
発明の製造方法で規定する条件を満たす試番16、1
7、21および26は特に優れた局部延性を有してい
た。また、通常の延性(El)や、TSとElの積(い
わゆる延性バランス)も良好なものであった。[Table 3] As shown in Table 3, the winding temperatures after hot rolling satisfy the conditions specified by the production method of the present invention.
7, 21, and 26 had particularly good local ductility. The ordinary ductility (El) and the product of TS and El (so-called ductile balance) were also good.
【0082】[0082]
【発明の効果】本発明の高張力鋼板は、局部延性に優れ
るので自動車に代表される複雑な形状を備えた構造部材
への加工が容易であるうえ、プレス加工時の曲げ曲げ戻
しを伴うプレス成形と焼付け処理により、構造部材とし
ての耐衝撃特性を大幅に向上させることができる。従っ
て本発明の高張力鋼板は、自動車の構造部材の高強度が
容易で鋼板の薄肉化による軽量化に有効であるうえ、衝
突安全性向上にも有効であり、これらを同時に達成でき
るので利用価値が極めて大きい。The high-strength steel sheet of the present invention has excellent local ductility, so that it can be easily processed into a structural member having a complicated shape typified by an automobile, and a press accompanied by bending and bending back during press working. The impact resistance as a structural member can be significantly improved by the forming and baking treatment. Therefore, the high-strength steel sheet of the present invention is effective in reducing the weight of the steel sheet by reducing the thickness of the steel sheet, and is effective in improving collision safety. Is extremely large.
【図1】構造部材で多用される閉断面構造部材を模した
試験体の斜視図である。FIG. 1 is a perspective view of a test body simulating a closed cross-section structural member frequently used in the structural member.
【図2】ハット断面部品のプレス成形状態を説明するた
めの断面図である。FIG. 2 is a cross-sectional view for explaining a press-formed state of a hat cross-section component.
【図3】ハット断面部品の縦壁部でのビッカース硬さ測
定点を示す模式図である。FIG. 3 is a schematic diagram showing Vickers hardness measurement points on a vertical wall portion of a hat cross-section part.
【図4】鋼板の引張強さとこれを用いて作製した閉断面
構造部材の軸圧壊平均荷重との関係を示すグラフであ
る。FIG. 4 is a graph showing the relationship between the tensile strength of a steel sheet and the average axial crushing load of a closed-section structural member manufactured using the same.
1:ハット断面部品、2:縦壁部、3:ポンチ、4:ポ
ンチ肩、5:ダイ、6:ダイ肩、7:ダイ溝、8:しわ
押さえ、11:底部、12:平板部品、図2で符号であ
る。1: hat cross-section parts, 2: vertical wall part, 3: punch, 4: punch shoulder, 5: die, 6: die shoulder, 7: die groove, 8: wrinkle holder, 11: bottom, 12: flat plate, drawing 2 is a sign.
Claims (5)
Si:2.0%以下、Al:0.005〜2.0%、M
n:0.8〜2.5%、P:0.05%以下を含有し、
かつ、(Si+Al):1.0〜2.5%を満足し、残
部がFeおよび不可避的不純物からなる化学組成を備
え、板厚ひずみにして10%の引張り曲げ変形を伴う予
成形を施し、次いで170℃で20分間保持する焼付け
処理を施した後の鋼板表面部と板厚中心部の硬度が下記
式を満足することを特徴とする延性と耐衝撃特性に優れ
た高張力鋼板; (HVs−HVc)/HV0 ≧0.12、 ただし、HV0 :上記予成形前の板厚中心部のビッカー
ス硬度、 HVc:上記予成形と焼付け処理後の板厚中心部のビッ
カース硬度、 HVs:上記予成形と焼付け処理後の表面部のビッカー
ス硬度。1. A mass% of C: 0.05 to 0.25%,
Si: 2.0% or less, Al: 0.005 to 2.0%, M
n: 0.8 to 2.5%, P: 0.05% or less,
And (Si + Al): satisfying 1.0 to 2.5%, the balance being provided with a chemical composition comprising Fe and unavoidable impurities, and performing a preforming with a tensile bending deformation of 10% to a plate thickness strain, Next, a high-strength steel sheet excellent in ductility and impact resistance, characterized in that the hardness of the steel sheet surface and the center of the sheet thickness after subjected to a baking treatment of holding at 170 ° C. for 20 minutes satisfies the following formula; −HVc) / HV 0 ≧ 0.12, where HV 0 is the Vickers hardness at the center of the sheet thickness before the above preforming, HVc: Vickers hardness at the center of the sheet thickness after the above preforming and baking treatment, and HVs is the above. Vickers hardness of the surface after preforming and baking.
Si:2.0%以下、Al:0.005〜2.0%、M
n:0.8〜2.5%、P:0.05%以下を含み、か
つ、(Si+Al):1.0〜2.5%を満足し、さら
に、Tiおよび/またはNbを、Ti:0.003〜
0.05%、Nb:0.003〜0.05%、かつ、
(Ti+Nb)≦0.05%を満足する範囲で含有し、
残部がFeおよび不可避的不純物からなる化学組成を備
え、板厚ひずみにして10%の引張り曲げ変形を伴う予
成形を施し、次いで170℃で20分間保持する焼付け
処理を施した後の鋼板表面部と板厚中心部の硬度が下記
式を満足することを特徴とする延性と耐衝撃特性に優れ
た高張力鋼板; (HVs−HVc)/HV0 ≧0.12、 ただし、HV0 :上記予成形前の板厚中心部のビッカー
ス硬度、 HVc:上記予成形と焼付け処理後の板厚中心部のビッ
カース硬度、 HVs:上記予成形と焼付け処理後の表面部のビッカー
ス硬度。2. C: 0.05 to 0.25% by mass%,
Si: 2.0% or less, Al: 0.005 to 2.0%, M
n: 0.8 to 2.5%, P: 0.05% or less, and (Si + Al): 1.0 to 2.5% are satisfied, and Ti and / or Nb are further added to Ti: 0.003 ~
0.05%, Nb: 0.003 to 0.05%, and
(Ti + Nb) ≦ 0.05%
The remainder has a chemical composition consisting of Fe and unavoidable impurities, and is subjected to preforming with a tensile bending deformation of 10% at a plate thickness strain, and then subjected to a baking treatment of holding at 170 ° C. for 20 minutes, followed by a baking treatment. And a high-strength steel sheet excellent in ductility and impact resistance characterized in that the hardness at the center of the sheet thickness satisfies the following formula: (HVs−HVc) / HV 0 ≧ 0.12, where HV 0 : above Vickers hardness at the center of the sheet thickness before forming, HVc: Vickers hardness at the center of the sheet thickness after the above preforming and baking treatment, HVs: Vickers hardness of the surface part after the above preforming and baking processing.
i、Coからなる群の内の1種、または、2種以上を、
Cu:0.2〜1.0%、Ni:0.1〜0.5%、C
o:0.0005〜1.0%、かつ(Cu+Ni+C
o)≦1.5%を満足する範囲で含有する、請求項1ま
たは2に記載の延性と耐衝撃特性に優れた高張力鋼板。3. The composition according to claim 1, wherein the chemical composition further comprises Cu, N
i, one or more of the group consisting of Co,
Cu: 0.2-1.0%, Ni: 0.1-0.5%, C
o: 0.0005 to 1.0%, and (Cu + Ni + C
3. The high-strength steel sheet according to claim 1 or 2, wherein the high-strength steel sheet is contained in a range satisfying (o) ≦ 1.5%.
圧延開始温度が1050℃以下、終了温度が800℃以
上である熱間仕上圧延を施した後、20℃/秒以上の冷
却速度で750℃まで冷却し、700℃以下、下記式で
計算されるTc(℃)以上で巻取る工程を有する熱間圧
延を施し、得られた鋼板を酸洗し、その後、合計圧下率
が40%以上、80%以下となる範囲で冷間圧延を施
し、次いで、フェライト+オーステナイトの2相温度域
で30秒以上、90秒以下保持し、その後700℃以
下、450℃以上の温度範囲を30℃/秒以上で冷却
し、450℃以下、370℃以上の温度範囲で200秒
以上、400秒以下保持した後、室温まで冷却する焼鈍
を施すことを特徴とする、請求項1〜3のいずれかに記
載の延性と耐衝撃特性に優れた高張力鋼板の製造方法; Tc( ℃) =430+70×Mn( %) +1000×P
( %) 。4. A steel slab having the above chemical composition is subjected to hot finish rolling at a hot finish rolling start temperature of 1050 ° C. or less and an end temperature of 800 ° C. or more, followed by cooling at 20 ° C./sec or more. The steel sheet is cooled to 750 ° C. at a high speed, hot-rolled with a step of winding at 700 ° C. or less, at Tc (° C.) or more calculated by the following equation, and the obtained steel sheet is pickled. Cold rolling is performed within a range of 40% or more and 80% or less, and then maintained in a two-phase temperature region of ferrite + austenite for 30 seconds or more and 90 seconds or less. The method according to claim 1, wherein cooling is performed at a rate of 30 ° C./sec or more, 450 ° C. or less, 370 ° C. or more is maintained for 200 seconds or more and 400 seconds or less, and then annealing is performed to cool to room temperature. Excellent ductility and impact resistance described in either Tc (° C.) = 430 + 70 × Mn (%) + 1000 × P
(%).
を施すことを特徴とする請求項4に記載の延性と耐衝撃
特性に優れた高張力鋼板の製造方法。5. The method for producing a high-tensile steel sheet having excellent ductility and impact resistance according to claim 4, wherein the steel slab is subjected to auxiliary heating before hot finish rolling.
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2012255176A (en) * | 2011-06-07 | 2012-12-27 | Nippon Steel & Sumitomo Metal Corp | Steel material and impact-absorbing member |
KR20180119622A (en) * | 2016-03-25 | 2018-11-02 | 아르셀러미탈 | A method of manufacturing a cold rolled, welded steel sheet, |
-
2000
- 2000-05-30 JP JP2000160296A patent/JP4016573B2/en not_active Expired - Fee Related
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2012255176A (en) * | 2011-06-07 | 2012-12-27 | Nippon Steel & Sumitomo Metal Corp | Steel material and impact-absorbing member |
KR20180119622A (en) * | 2016-03-25 | 2018-11-02 | 아르셀러미탈 | A method of manufacturing a cold rolled, welded steel sheet, |
JP2019515796A (en) * | 2016-03-25 | 2019-06-13 | アルセロールミタル | Method of manufacturing cold rolled and welded steel sheet and sheet so manufactured |
KR102202758B1 (en) * | 2016-03-25 | 2021-01-14 | 아르셀러미탈 | Cold rolled, method of making welded steel sheet, and sheets thus produced |
US11220723B2 (en) | 2016-03-25 | 2022-01-11 | Arcelormittal | Method for manufacturing cold-rolled, welded steel sheets, and sheets thus produced |
US11959150B2 (en) | 2016-03-25 | 2024-04-16 | Arcelormittal | Welded steel sheets, and sheets thus produced |
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