JP2007063668A

JP2007063668A - High-tension steel sheet and process for producing the same

Info

Publication number: JP2007063668A
Application number: JP2006213321A
Authority: JP
Inventors: Tamako Ariga; 珠子有賀; Takeshi Yokota; 毅横田; Satoo Kobayashi; 聡雄小林; Kazuhiro Seto; 一洋瀬戸
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2005-08-05
Filing date: 2006-08-04
Publication date: 2007-03-15
Anticipated expiration: 2026-08-04
Also published as: JP5076394B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-tension steel sheet having a tensile strength as high as 980 MPa or above, whose elongation and stretch flangeability as the indexes of workability are both excellent and whose production is easy compared with the conventional one, and which is suitable for use in applications where the sheet is pressed so as to have a complicated sectional shape, as in the formation of automotive members, and to provide a process for producing the high-tension steel sheet, which has a reduced equipment load. <P>SOLUTION: The high-tension steel sheet has a structure consisting substantially of a ferrite phase only and has dispersed/precipitated carbide particles containing Ti, Mo, and V and having an average particle diameter smaller than 10 nm, the carbides containing Ti, Mo and V having an average composition satisfying the relationship V/(Ti+Mo+V)≥0.3 (atomic ratio). The steel sheet has a tensile strength as high as 980 MPa or above. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、自動車用部材の素材に適した、高張力鋼板ならびにその製造方法に関する。 The present invention relates to a high-tensile steel plate suitable for a material for automobile members and a method for producing the same.

環境保全につながる燃費向上の観点から、自動車用鋼板の高強度薄肉化が強く求められている。自動車用部材はプレス成形により得られる複雑な形状のものが多く、高強度でありながら加工性の指標である伸びと伸びフランジ性がともに優れた材料が必要である。近年、鋼板強度はますます高強度化し、９８０ＭＰａを超えるものが要望されている。また、鋼板をより軽量化する観点からさらなる薄肉化が指向されており、板厚２．５ｍｍ以下の薄物に対する要望も強くなってきている。 From the viewpoint of improving fuel efficiency leading to environmental conservation, there is a strong demand for reducing the strength and thickness of automotive steel sheets. Many automotive members have complicated shapes obtained by press molding, and materials that have both high strength and excellent elongation and stretch flangeability, which are indexes of workability, are required. In recent years, the strength of steel sheets has been increasing further, and those exceeding 980 MPa have been desired. Further, from the viewpoint of reducing the weight of the steel sheet, further thinning is directed, and a demand for a thin object having a thickness of 2.5 mm or less is also increasing.

従来、この種の鋼板は種々提案されており、例えば特許文献１には、転位密度の高いベイニティック・フェライト組織が生成した、伸びフランジ性に優れた鋼板が提案されている。しかし、この鋼板は、転位密度の高いベイニティック・フェライト組織を含むために伸びが乏しいという欠点がある。また、ベイニティック・フェライト生成のために、ランナウトテーブル上での強冷却が不可避であり、薄物製造時にはランナウトテーブルでのストリップの走行性に問題が生じるため、板厚２．５ｍｍ以下の薄物を生産するには不向きである。 Conventionally, various steel sheets of this type have been proposed. For example, Patent Document 1 proposes a steel sheet excellent in stretch flangeability, in which a bainitic ferrite structure having a high dislocation density is generated. However, this steel sheet has a drawback that it has poor elongation because it contains a bainitic ferrite structure with a high dislocation density. In addition, strong cooling on the run-out table is inevitable for the production of bainitic ferrite, and a problem arises in strip runnability on the run-out table when manufacturing a thin product. Not suitable for production.

特許文献２には、組織の大部分をポリゴナルフェライトとし、ＴｉＣを中心として析出強化および固溶強化した伸びフランジ性に優れる鋼板が提案されている。しかし、この鋼板に用いられている一般的によく知られた析出物で９８０ＭＰａ以上に高張力化することは困難である。すなわち、９８０ＭＰａ以上の高強度化を図って多量のＴｉを添加すると、サイズの大きい析出物が生成しやすくなり、狙いどおりの強度を得ることが難しく、特性が不安定になりやすいという欠点がある。また、Ｔｉ添加量の増大と共に、ＴｉＣを固溶させるために必要なスラブ加熱温度が増大し、通常の設備では製造が困難となりやすい。 Patent Document 2 proposes a steel sheet excellent in stretch flangeability in which most of the structure is polygonal ferrite and precipitation strengthening and solid solution strengthening are centered on TiC. However, it is difficult to increase the tension to 980 MPa or more with generally well-known precipitates used in this steel sheet. That is, when a large amount of Ti is added to increase the strength of 980 MPa or more, precipitates having a large size are likely to be generated, and it is difficult to obtain the intended strength and the characteristics are likely to become unstable. . Moreover, the slab heating temperature necessary for dissolving TiC increases with an increase in the amount of Ti added, and manufacturing is likely to be difficult with normal equipment.

特許文献３には、微細なＴｉＣおよび／またはＮｂＣが析出したアシキュラー・フェライト組織を有した、伸びフランジ性に優れた鋼板が提案されている。しかし、この鋼板も先に述べた特許文献１で提案された鋼板同様に、アシキュラー・フェライトという転位密度の高い組織であるため十分な伸びが得られていない。 Patent Document 3 proposes a steel sheet having an acicular ferrite structure in which fine TiC and / or NbC is precipitated and having excellent stretch flangeability. However, since this steel sheet is a structure having a high dislocation density called acicular ferrite as well as the steel sheet proposed in Patent Document 1 described above, sufficient elongation cannot be obtained.

特許文献４には、平均粒径１〜５μｍのフェライトを主相とし、平均粒径５０ｎｍ以下のＶの炭窒化物で析出強化した熱延鋼板が提案されている。ここでＶ析出物を微細に析出させるには低温での巻取りが必要であるが、その結果、析出物の量を増大させることが困難であり、強化に限界がある。このため、特許文献４の技術では、前述したフェライトの細粒化と組み合わせることが高強度化のため必要である。ここで、特許文献４の技術では、フェライトを微細化するため、仕上げ圧延の際、タンデム圧延機列の最終から１段前の圧延スタンドにおいてＡｒ_３点以上で圧延し、その後５０℃／秒以上の平均冷却速度で「Ａｒ_３点−５０℃」以下の温度まで冷却した後、最終スタンドにおいて２０％以下の圧下を施すことが必要であり、通常の製造ラインでは製造に困難性を伴う。また、この鋼板では、パーライト等の生成が許容されるため、伸びや伸びフランジ性が低下する懸念がある。 Patent Document 4 proposes a hot-rolled steel sheet having a ferrite having an average particle diameter of 1 to 5 μm as a main phase and precipitation strengthened with V carbonitride having an average particle diameter of 50 nm or less. Here, in order to finely precipitate the V precipitate, winding at a low temperature is necessary. As a result, it is difficult to increase the amount of the precipitate, and there is a limit to strengthening. For this reason, in the technique of Patent Document 4, it is necessary to combine with the above-described finer ferrite to increase the strength. Here, in the technique of Patent Document 4, in order to refine the ferrite, at the time of finish rolling, rolling is performed at Ar ₃ points or more in the rolling stand one stage before the final stage of the tandem rolling mill row, and then 50 ° C./second or more. After cooling to a temperature of “Ar ₃ points−50 ° C.” or less at an average cooling rate of 20% or less, it is necessary to apply a reduction of 20% or less in the final stand, which is difficult to manufacture in a normal production line. Moreover, in this steel plate, since generation | occurrence | production of pearlite etc. is accept | permitted, there exists a possibility that elongation and stretch flangeability may fall.

また、超高張力鋼板を得る技術として、特許文献５や特許文献６に開示された技術が開発されている。この技術は、フェライト単相中にＣ、Ｔｉ、Ｍｏよりなる微細炭化物を分散させ、伸びと伸びフランジ性がともに優れた超高張力鋼板を得ることができる技術である。しかしながら、上記特許文献２の技術と同様に、この技術では、９８０ＭＰａ以上の引張強度を得るために多量のＣやＴｉを添加すると、通常のスラブ加熱温度（１１５０℃〜１２５０℃程度）ではスラブ中に析出しているＴｉＣなどを完全には溶解させることができない場合がある。すなわち、高強度を得るべくＴｉＣなどを完全に溶解させるにはより高温が必要となって製造が困難となる場合があり、また可能であっても設備に大きな負担がかかる。
特開平６−１７２９２４号公報特開平６−２００３５１号公報特開平７−１１３８２号公報特開２００４−１４３５１８号公報特開２００３−８９８４８号公報特開２００２−３２２５３９号公報 Moreover, the technique disclosed by patent document 5 and patent document 6 is developed as a technique of obtaining an ultra high strength steel plate. This technique is a technique in which fine carbides composed of C, Ti, and Mo are dispersed in a ferrite single phase to obtain an ultra-high-strength steel sheet having excellent elongation and stretch flangeability. However, similar to the technique of Patent Document 2, in this technique, when a large amount of C or Ti is added to obtain a tensile strength of 980 MPa or more, the slab is in the slab at a normal slab heating temperature (about 1150 ° C. to 1250 ° C.). In some cases, TiC and the like deposited on the film cannot be completely dissolved. That is, in order to completely dissolve TiC or the like in order to obtain high strength, a higher temperature may be required, which may make manufacture difficult, and even if possible, a large burden is placed on the equipment.
JP-A-6-172924 Japanese Patent Laid-Open No. 6-200351 JP-A-7-11382 JP 2004-143518 A JP 2003-89848 A JP 2002-322539 A

本発明は自動車用部材のようにプレス成形における断面形状が複雑な用途に適した、加工性の指標である伸びと伸びフランジ性がともに優れ、製造も従来に比べ容易な、９８０ＭＰａ以上の強度を有する高張力鋼板およびそのような高張力鋼板の製造方法を提供することを目的とする。本発明はまた、そのような高張力鋼板のより設備負担の少ない製造方法を提供することを目的とする。 The present invention is suitable for applications where the cross-sectional shape in press molding is complicated, such as automotive parts, and has excellent elongation and stretch flangeability, which are indexes of workability, and has a strength of 980 MPa or more, which is easy to manufacture. It aims at providing the manufacturing method of the high-tensile steel plate which has, and such a high-tensile steel plate. Another object of the present invention is to provide a method for manufacturing such a high-tensile steel sheet with less equipment burden.

本発明者らは、上記目的を達成すべく鋭意検討を行った結果、以下の知見を得た。
（１）転位密度が低い組織とし、微細析出物で強化すると、強度−伸びバランスが向上する。
（２）実質的にフェライト単相組織とし、微細析出物で強化すると、強度−伸びバランスが向上する。
（３）Ｃ、Ｔｉ、Ｍｏ、Ｖを添加し、さらにその添加バランスを適宜制御すると、これらが複合した炭化物が微細に析出する。
（４）複合析出物中のＶの割合が低くなると、析出物が粗大化するため、伸びと伸びフランジ性がともに低下する。
（５）Ｖを添加した鋼は、Ｔｉ、Ｍｏのみを添加した鋼に比べて低温で炭化物が溶解し、強化に効く微細析出物が効率よく得られる。 As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.
(1) When the structure has a low dislocation density and is strengthened with fine precipitates, the strength-elongation balance is improved.
(2) The strength-elongation balance is improved when a ferrite single phase structure is substantially formed and strengthened with fine precipitates.
(3) When C, Ti, Mo, and V are added and the addition balance is appropriately controlled, carbides in which these are combined are finely precipitated.
(4) When the proportion of V in the composite precipitate is lowered, the precipitate is coarsened, so that both elongation and stretch flangeability are lowered.
(5) Steel added with V dissolves carbides at a lower temperature than steel added only with Ti and Mo, and fine precipitates effective for strengthening can be obtained efficiently.

本発明はこれらの知見に基づいて完成されたものであり、以下の（１）〜（６）を提供する。
（１）実質的にフェライト単相組織であり、平均粒径１０ｎｍ未満のＴｉ、ＭｏおよびＶを含む炭化物が分散析出するとともに、該Ｔｉ、ＭｏおよびＶを含む炭化物は、原子％で表されるＴｉ、Ｍｏ、Ｖが、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たす平均組成を有することを特徴とする、引張強度が９８０ＭＰａ以上の高張力鋼板。
（２）上記（１）の高張力鋼板において、質量％で、Ｃ：０．０６超〜０．２４％、Ｓｉ≦０．３％、Ｍｎ：０．５〜２．０％、Ｐ≦０．０６％、Ｓ≦０．００５％、Ａｌ≦０．０６％、Ｎ≦０．００６％、Ｍｏ：０．０５〜０．５％、Ｔｉ：０．０３〜０．２％、Ｖ：０．１５超〜１．２％を含み、残部がＦｅおよび不可避的不純物であるとともに、Ｃ、Ｔｉ、Ｍｏ、Ｖ含有量が以下の（Ｉ）式を満足する成分組成を有することを特徴とする高張力鋼板。
0.8≦(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}≦1.5 …（Ｉ）
（ただし、C、Ti、Mo、Vは各成分の質量％を表す）
（３）上記（１）または（２）の高張力鋼板において、該高張力鋼板が板厚２．５ｍｍ以下の薄物熱延鋼板であることを特徴とする高張力鋼板。
（４）上記（１）から（３）のいずれかの高張力鋼板において、表面に溶融亜鉛系めっき皮膜を有することを特徴とする高張力鋼板。
（５）質量％で、Ｃ：０．０６超〜０．２４％、Ｓｉ≦０．３％、Ｍｎ：０．５〜２．０％、Ｐ≦０．０６％、Ｓ≦０．００５％、Ａｌ≦０．０６％、Ｎ≦０．００６％、Ｍｏ：０．０５〜０．５％、Ｔｉ：０．０３〜０．２％、Ｖ：０．１５超〜１．２％を含み、残部がＦｅおよび不可避的不純物からなるとともに、Ｃ、Ｔｉ、Ｍｏ、Ｖ含有量が以下の（Ｉ）式を満足する成分組成を有する鋼片に、仕上圧延終了温度８８０℃以上、巻取温度５７０℃以上の条件で熱間圧延を施すことを特徴とする、引張強度が９８０ＭＰａ以上の高張力鋼板の製造方法。
0.8≦(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}≦1.5 …（Ｉ）
（ただし、C、Ti、Mo、Vは各成分の質量％を表す）
（６）上記（５）の製造方法において、前記熱間圧延後の鋼板の表面に溶融亜鉛系めっきを施すことを特徴とする、高張力鋼板の製造方法。 The present invention has been completed based on these findings and provides the following (1) to (6).
(1) A carbide containing Ti, Mo and V having a ferrite single-phase structure and an average particle size of less than 10 nm is dispersed and precipitated, and the carbide containing Ti, Mo and V is expressed in atomic%. A high-tensile steel sheet having a tensile strength of 980 MPa or more, wherein Ti, Mo, and V have an average composition satisfying V / (Ti + Mo + V) ≧ 0.3.
(2) In the high-strength steel sheet of (1) above, in mass%, C: more than 0.06 to 0.24%, Si ≦ 0.3%, Mn: 0.5 to 2.0%, P ≦ 0 0.06%, S ≦ 0.005%, Al ≦ 0.06%, N ≦ 0.006%, Mo: 0.05 to 0.5%, Ti: 0.03 to 0.2%, V: 0 More than .15 to 1.2%, the balance being Fe and inevitable impurities, and the content of C, Ti, Mo, V has a composition that satisfies the following formula (I) High tensile steel plate.
0.8 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} ≦ 1.5 (I)
(However, C, Ti, Mo and V represent mass% of each component)
(3) The high-tensile steel sheet according to (1) or (2), wherein the high-tensile steel sheet is a thin hot-rolled steel sheet having a thickness of 2.5 mm or less.
(4) The high-tensile steel sheet according to any one of (1) to (3) above, which has a hot dip galvanized coating on the surface.
(5) By mass%, C: more than 0.06 to 0.24%, Si ≦ 0.3%, Mn: 0.5 to 2.0%, P ≦ 0.06%, S ≦ 0.005% , Al ≦ 0.06%, N ≦ 0.006%, Mo: 0.05-0.5%, Ti: 0.03-0.2%, V: Over 0.15-1.2% A steel slab having a component composition in which the balance is composed of Fe and unavoidable impurities and the contents of C, Ti, Mo and V satisfy the following formula (I): Finishing rolling finish temperature 880 ° C. or higher, coiling temperature A method for producing a high-tensile steel sheet having a tensile strength of 980 MPa or more, wherein hot rolling is performed under conditions of 570 ° C. or more.
0.8 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} ≦ 1.5 (I)
(However, C, Ti, Mo and V represent mass% of each component)
(6) In the manufacturing method of said (5), hot galvanizing is given to the surface of the steel plate after the said hot rolling, The manufacturing method of the high strength steel plate characterized by the above-mentioned.

なお、本発明において実質的にフェライト単相組織とは、本発明の析出物以外に、微量の他の相ないしは析出物を許容することをいい、好ましくはフェライトの面積比率が９５％以上である。 In the present invention, the substantially single-phase ferrite structure means that a small amount of other phases or precipitates are allowed in addition to the precipitates of the present invention, and preferably the ferrite area ratio is 95% or more. .

また、引張強度が９８０ＭＰａ以上である本発明鋼板において、上記の平均粒径１０ｎｍ未満のＴｉ、ＭｏおよびＶを含む炭化物は、１μｍ^３当たり約５×１０^５個以上、さらに高強度である場合には１μｍ^３当たり約５×１０^６個以上が分散析出していると考えられる。 Further, in the steel sheet of the present invention having a tensile strength of 980 MPa or more, the carbide containing Ti, Mo, and V having an average particle size of less than 10 nm is about 5 × 10 ⁵ or more per 1 μm ³ , and has a higher strength. It is considered that about 5 × 10 ⁶ or more per 1 μm ³ are dispersed and precipitated.

本発明によれば、Ｔｉ、Ｍｏに加えてＶを適正なバランスで添加して、Ｔｉ、ＭｏおよびＶを含む微細な炭化物を分散析出させることにより、加工性に優れた高張力鋼板が得られる。 According to the present invention, in addition to Ti and Mo, V is added in an appropriate balance, and fine carbides containing Ti, Mo and V are dispersed and precipitated, thereby obtaining a high-tensile steel plate having excellent workability. .

以下、本発明について、金属組織、化学成分、製造方法等に分けて具体的に説明する。 Hereinafter, the present invention will be specifically described by dividing it into a metal structure, a chemical component, a production method, and the like.

［金属組織］
本発明に係る高張力鋼板は、実質的にフェライト単相組織であり、Ｔｉ、Ｍｏ、Ｖを含む炭化物が析出している。 [Metal structure]
The high-tensile steel sheet according to the present invention has a substantially ferrite single-phase structure, and carbides including Ti, Mo, and V are precipitated.

・実質的にフェライト単相組織：
マトリックスを実質的にフェライト単相組織としたのは、伸びの向上には転位密度の低いフェライトが有効であるとともに、伸びフランジ性の向上には単相組織とすることが有効であり、特に延性に富むフェライト単相組織でその効果が顕著であるためである。ただし、マトリックスは必ずしも完全にフェライト単相組織でなくともよく、実質的にフェライト単相組織であればよい。すなわち微量の他の相ないしは析出物は許容される。好ましくは面積比率で９５％以上フェライトであればよく、本発明において、実質的にフェライト単相組織とは、面積比率で９５％以上フェライトであることを意味する。なお、ベイニティックフェライトやアシキュラーフェライト等の転位密度の高いフェライトは本発明におけるフェライト相には含まれず、他の相として扱う。・ Substantially ferrite single phase structure:
The reason why the matrix has a substantially single-phase ferrite structure is that ferrite with a low dislocation density is effective for improving elongation, and a single-phase structure is effective for improving stretch flangeability, especially ductility. This is because the effect is remarkable in a ferrite single phase structure rich in. However, the matrix does not necessarily have a complete ferrite single phase structure, and may be substantially a ferrite single phase structure. That is, trace amounts of other phases or precipitates are acceptable. Preferably, the ferrite may have an area ratio of 95% or more, and in the present invention, the ferrite single phase structure substantially means 95% or more of ferrite in the area ratio. Note that ferrite having a high dislocation density such as bainitic ferrite and acicular ferrite is not included in the ferrite phase in the present invention, and is handled as another phase.

・Ｔｉ、Ｍｏ、Ｖを含む炭化物：
Ｔｉ、Ｍｏ、Ｖを含む炭化物は、微細となり、析出量も確保しやすいため鋼を強化するのに有効である。従来は、析出物としてＭｏ、Ｖを含まないＴｉＣを用いることが主流であった。しかしながら、Ｔｉは析出物形成傾向が強いため粗大化しやすく、強化に対する効果が低くなることから、必要な強化量を得るには加工性を劣化させるまでの析出物が必要となる。 -Carbides containing Ti, Mo, V:
Carbides containing Ti, Mo, and V are fine and effective in strengthening steel because the amount of precipitation is easily secured. Conventionally, it has been mainstream to use TiC containing no Mo or V as a precipitate. However, since Ti has a strong tendency to form precipitates, it is likely to be coarsened and the effect on strengthening is reduced. Therefore, precipitates are required until the workability is deteriorated in order to obtain a necessary strengthening amount.

一方、上記特許文献５に開示されているように、ＴｉにＭｏを加えるだけでも析出物が微細化し、ある程度の高強度化は達成できる。しかし、単にＴｉ、Ｍｏを含む炭化物のみで９８０ＭＰａ以上の引張強度を得るべく、これに見合ったレベルのＴｉを添加すると、前述のように一般的な熱延前の加熱温度を上回る高温が要求される場合があり、高温化を図るためには例えば特殊な設備を要するためコストアップとなる。他方、ＴｉにＶだけを加えた場合は、充分な析出物微細化が得られない。 On the other hand, as disclosed in the above-mentioned Patent Document 5, the precipitates are refined by adding Mo to Ti, and a certain degree of strength can be achieved. However, in order to obtain a tensile strength of 980 MPa or more with only carbides including Ti and Mo, if a Ti corresponding to this is added, a high temperature exceeding the heating temperature before general hot rolling is required as described above. In order to increase the temperature, for example, special equipment is required, which increases the cost. On the other hand, when only V is added to Ti, sufficient precipitate refinement cannot be obtained.

これに対し、ＴｉとＭｏ、Ｖを含む複合炭化物は、微細に析出する上、析出物の量（数）の確保も容易であるため、加工性を劣化させずに鋼を強化することができることを、発明者らは発見した。 On the other hand, composite carbide containing Ti, Mo, and V precipitates finely, and since it is easy to ensure the amount (number) of precipitates, the steel can be strengthened without degrading workability. The inventors have discovered.

これは、ＭｏおよびＶ、特にＭｏは析出物形成傾向（炭化物形成傾向）がＴｉよりも弱いことから、ＴｉとＭｏ、Ｖを含む複合炭化物は強化に寄与しない粗大な析出物となることなく安定して微細に存在することができ、加工性を低下させない比較的少量の添加量で有効に鋼を強化することができるためと推定される。 This is because Mo and V, especially Mo, has a tendency to form precipitates (carbide formation tendency) weaker than Ti, so composite carbide containing Ti, Mo and V is stable without becoming coarse precipitates that do not contribute to strengthening. It is presumed that the steel can be effectively strengthened with a relatively small addition amount that does not deteriorate the workability.

一方、ＶとＣの組み合わせは溶解温度が非常に低く、９８０ＭＰａ以上という高強度を得るために比較的多量に添加しても通常の加熱温度で容易に溶解することができる。ただしＶ単独添加では、Ｖの析出率が低くなる。このため、引張強度９８０ＭＰａ以上の高張力を得るだけの寸法と量の析出物を析出させるには、Ｔｉの他にＭｏとＶとの両方を添加することが有効であるものと考えられる。 On the other hand, the combination of V and C has a very low melting temperature, and can be easily dissolved at a normal heating temperature even when added in a relatively large amount in order to obtain a high strength of 980 MPa or more. However, when V is added alone, the deposition rate of V becomes low. For this reason, it is considered effective to add both Mo and V in addition to Ti in order to deposit a precipitate having a size and amount sufficient to obtain a high tensile strength of 980 MPa or more.

また、従来、Ｔｉ、Ｍｏ等を含有する鋼に、多量のＶを添加すると、伸びが低下する傾向にあるとされており、Ｖの添加は比較的低い範囲に抑えられていた。しかしながら、本発明者らが詳細に検討した結果、Ｖの添加量を増大させるに従いＶの析出率が高くなり、すなわち添加したＶが炭化物として十分に析出するようになり、炭化物を安定して微細に析出させることができるため、十分な伸びを確保した上で、高強度化を達成できることを見出した。 Conventionally, when a large amount of V is added to steel containing Ti, Mo or the like, the elongation tends to decrease, and the addition of V has been suppressed to a relatively low range. However, as a result of detailed studies by the present inventors, as the amount of V added is increased, the precipitation rate of V is increased, that is, the added V is sufficiently precipitated as carbides, and the carbides are stably fined. It was found that high strength can be achieved while ensuring sufficient elongation.

炭化物が安定して微細に存在できるためには炭化物の組成が影響する。具体的には、炭化物の平均組成が原子％で表されるＴｉ、Ｍｏ、Ｖが、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たすようになると析出物の粗大化を抑制する効果が高くなり、所望の微細析出物を得ることができる。したがって、本発明では、原子％で表されるＴｉ、Ｍｏ、Ｖが、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たす範囲でＴｉ、Ｍｏ、Ｖを含む炭化物が分散析出していることを要件とする。なお、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）の上限は０．７程度に限定することが望ましい。 In order for the carbide to exist stably and finely, the composition of the carbide influences. Specifically, when Ti, Mo, and V, in which the average composition of carbides is expressed in atomic%, satisfy V / (Ti + Mo + V) ≧ 0.3, the effect of suppressing the coarsening of precipitates increases, Desired fine precipitates can be obtained. Therefore, in the present invention, it is a requirement that carbides containing Ti, Mo, and V are dispersed and precipitated in a range where Ti, Mo, and V expressed in atomic% satisfy V / (Ti + Mo + V) ≧ 0.3. To do. The upper limit of V / (Ti + Mo + V) is preferably limited to about 0.7.

本発明者らが見出したところでは、微細化に最適な炭化物組成はＴｉ：Ｍｏ：Ｖの原子比で概ね１：１：２である。このため、炭化物の平均組成においてＴｉ：Ｍｏ：Ｖの原子比が、Ｔｉ＝０．６〜１．４、Ｍｏ＝０．６〜１．４、Ｖ＝１．４〜２．８、ただし、Ｔｉ＋Ｍｏ＋Ｖ＝４を満足することがさらに好ましい。 As the inventors have found, the optimum carbide composition for miniaturization is approximately 1: 1: 2 in terms of atomic ratio of Ti: Mo: V. Therefore, in the average composition of carbides, the atomic ratio of Ti: Mo: V is Ti = 0.6 to 1.4, Mo = 0.6 to 1.4, V = 1.4 to 2.8, It is more preferable to satisfy Ti + Mo + V = 4.

また、この複合炭化物の平均粒径を１０ｎｍ未満とすることで、析出物周囲の歪みが転位の移動の抵抗としてより効果的となり、効率よく鋼を強化できる。このため、本発明では、平均粒径１０ｎｍ未満のＴｉ、Ｍｏ、Ｖを含む炭化物が析出していることを要件とする。さらに好ましくは、平均粒径が５ｎｍ以下である。 Further, by setting the average particle size of the composite carbide to less than 10 nm, the distortion around the precipitate becomes more effective as the resistance of dislocation movement, and the steel can be strengthened efficiently. For this reason, in this invention, it is required that the carbide | carbonized_material containing Ti, Mo, and V with an average particle diameter of less than 10 nm has precipitated. More preferably, the average particle size is 5 nm or less.

なお、強度にほとんど影響しない粗大析出物にＴｉ、Ｍｏ、Ｖを含む炭化物が析出するような場合も有り得る。このような析出物を粒径の評価対象とすることは不適切であるので、粒径１００ｎｍを超える析出物は除外して、平均粒径を測定するものとする。 In some cases, carbides containing Ti, Mo, and V are precipitated on coarse precipitates that hardly affect the strength. Since it is inappropriate to use such a precipitate as an object of particle size evaluation, the average particle size is measured by excluding precipitates having a particle size exceeding 100 nm.

引張強度（ＴＳ）が９８０ＭＰａ以上である本発明鋼板において、前記の平均粒径１０ｎｍ未満の複合炭化物は、従来のＴＳ７８０ＭＰａクラスの鋼板より多数観察される。本発明鋼におけるこの複合炭化物は、上記特許文献６のデータを基にした概算により、１μｍ^３当たり約５×１０^５個以上が分散析出していると考えられる。なお、ＴＳ８００ＭＰａを超える領域でのデータは上記特許文献６には開示されていないので、単純にＴＳの対数と微細炭化物密度の対数の間に直線関係が成り立つとしてＴＳ９８０ＭＰａの対数に外挿した。 In the steel sheet of the present invention having a tensile strength (TS) of 980 MPa or more, a larger number of the composite carbides having an average particle size of less than 10 nm are observed than a conventional TS780 MPa class steel sheet. It is considered that about 5 × 10 ⁵ or more per 1 μm ³ of this composite carbide in the steel of the present invention is dispersed and precipitated based on an estimation based on the data of Patent Document 6 above. Since data in a region exceeding TS800 MPa is not disclosed in Patent Document 6, the logarithm of TS980 MPa was extrapolated simply assuming that a linear relationship is established between the logarithm of TS and the logarithm of fine carbide density.

［化学成分］
本発明では、上記金属組織さえ満たしていれば所望の伸びおよび伸びフランジ性および９８０ＭＰａ以上の強度が得られ、化学成分は特に限定されないが、質量％で、Ｃ：０．０６超〜０．２４％、Ｓｉ≦０．３％、Ｍｎ：０．５〜２．０％、Ｐ≦０．０６％、Ｓ≦０．００５％、Ａｌ≦０．０６％、Ｎ≦０．００６％、Ｍｏ：０．０５〜０．５％、Ｔｉ：０．０３〜０．２％、Ｖ：０．１５超〜１．２％を含み、残部がＦｅおよび不可避的不純物からなり、Ｃ、Ｔｉ、Ｍｏ、Ｖ含有量が以下の（Ｉ）式を満足する成分組成を有することが好ましい。
0.8≦(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}≦1.5 …（Ｉ）
ただし、上記（Ｉ）式中、C、Ti、Mo、Vは各成分の質量％を表す。
以下、これら各成分について説明する。なお、以下、特に説明のない限り、成分についての記載において“％”は“質量％”を表す。 [Chemical composition]
In the present invention, as long as the above metal structure is satisfied, desired elongation and stretch flangeability and strength of 980 MPa or more can be obtained, and chemical components are not particularly limited, but by mass%, C: more than 0.06 to 0.24 %, Si ≦ 0.3%, Mn: 0.5 to 2.0%, P ≦ 0.06%, S ≦ 0.005%, Al ≦ 0.06%, N ≦ 0.006%, Mo: 0.05 to 0.5%, Ti: 0.03 to 0.2%, V: more than 0.15 to 1.2%, with the balance being Fe and inevitable impurities, C, Ti, Mo, It is preferable that the V content has a component composition satisfying the following formula (I).
0.8 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} ≦ 1.5 (I)
However, in said Formula (I), C, Ti, Mo, and V represent the mass% of each component.
Hereinafter, each of these components will be described. Hereinafter, unless otherwise specified, “%” represents “mass%” in the description of the components.

Ｃ：０．０６超〜０．２４％
Ｃは炭化物を形成し、鋼を強化するのに有効である。しかし、０．０６％以下では、鋼の強化が不十分であり、０．２４％を超えて添加するとスポット溶接が困難となるため、Ｃ含有量は０．０６超〜０．２４％が好ましい。より好ましくは、０．０７％以上であり、特に１１００ＭＰａ以上の引張強度を得るためには０．１％以上であることが望ましい。より望ましいＣ含有量範囲は、０．１１〜０．２％である。 C: Over 0.06 to 0.24%
C forms carbides and is effective for strengthening steel. However, if it is 0.06% or less, the steel is not sufficiently strengthened, and if it exceeds 0.24%, spot welding becomes difficult, so the C content is preferably more than 0.06 to 0.24%. . More preferably, it is 0.07% or more. In particular, in order to obtain a tensile strength of 1100 MPa or more, 0.1% or more is desirable. A more desirable C content range is 0.11 to 0.2%.

Ｓｉ：０．３％以下
Ｓｉは固溶強化に有効な元素として、従来は積極的に用いられており、高張力鋼に約０．４％以上添加されることも多いが、本発明ではＳｉの含有量を０．３％以下とする。これは、０．３％を超えて添加すると、フェライトからのＣ析出が促進されて粒界に粗大な鉄炭化物が析出しやすくなり、伸びフランジ性が低下するためである。また、本発明においては、Ｓｉを低減することによりオースナイト域での圧延荷重を低減し、薄物の製造が容易となる。すなわち０．３％を超えて添加すると、２．５ｍｍ以下の材料の圧延が不安定となり、板形状も悪くなる。これらの理由により、Ｓｉ含有量は０．３％以下が好ましい。さらに好ましくは０．１５％以下であり、望ましくは０．０５％以下である。なお、Ｓｉを極端に低減することは、製造コストを悪化させる。そのため、製造コストを大きく上昇させない実用的な下限値は０．００１％程度となる。 Si: 0.3% or less Si has been actively used as an element effective for solid solution strengthening in the past, and is often added to high-tensile steel by about 0.4% or more. The content of is 0.3% or less. This is because if added over 0.3%, C precipitation from the ferrite is promoted, and coarse iron carbide tends to precipitate at the grain boundaries, and the stretch flangeability is lowered. Moreover, in this invention, the rolling load in an austenite area | region is reduced by reducing Si, and manufacture of a thin material becomes easy. That is, if added over 0.3%, rolling of a material of 2.5 mm or less becomes unstable, and the plate shape also deteriorates. For these reasons, the Si content is preferably 0.3% or less. More preferably, it is 0.15% or less, and desirably 0.05% or less. In addition, extremely reducing Si worsens manufacturing cost. Therefore, a practical lower limit value that does not significantly increase the manufacturing cost is about 0.001%.

Ｍｎ：０．５〜２．０％
Ｍｎは固溶強化により鋼を強化する観点からは０．５％以上が好ましいが、２．０％を超えて添加すると偏析し、かつ硬質相が形成され、伸びフランジ性が低下する。このため、Ｍｎ含有量は０．５〜２．０％が好ましい。より好ましくは１．０〜２．０％である。 Mn: 0.5 to 2.0%
Mn is preferably 0.5% or more from the viewpoint of strengthening the steel by solid solution strengthening, but if added over 2.0%, segregation occurs, a hard phase is formed, and stretch flangeability deteriorates. For this reason, the Mn content is preferably 0.5 to 2.0%. More preferably, it is 1.0 to 2.0%.

Ｐ：０．０６％以下
Ｐは固溶強化に有効であるが、０．０６％を超えて含有すると偏析して伸びフランジ性を低下させるため、０．０６％以下とすることが好ましい。なお、Ｐを極端に低減することは、製造コストを悪化させる。そのため、製造コストを大きく上昇させない実用的な下限値は０．００１％程度となる。 P: 0.06% or less P is effective for solid solution strengthening, but if it exceeds 0.06%, it segregates and lowers the stretch flangeability. Therefore, it is preferably made 0.06% or less. Note that extremely reducing P worsens the manufacturing cost. Therefore, a practical lower limit value that does not significantly increase the manufacturing cost is about 0.001%.

Ｓ：０．００５％以下
Ｓは少ないほど好ましく、０．００５％を超えると伸びフランジ性が低下するため、０．００５％以下が好ましい。なお、Ｓを極端に低減することは、製造コストを悪化させる。そのため、製造コストを大きく上昇させない実用的な下限値は０．０００５％程度となる。 S: 0.005% or less S is preferably as small as possible, and if it exceeds 0.005%, the stretch flangeability deteriorates, so 0.005% or less is preferable. In addition, extremely reducing S worsens manufacturing cost. Therefore, a practical lower limit that does not significantly increase the manufacturing cost is about 0.0005%.

Ａｌ：０．０６％以下
Ａｌは脱酸剤として添加してよい。しかし、鋼中のＡｌ量が０．０６％を超えると伸びおよび伸びフランジ性が低下するため、０．０６％以下が好ましい。下限は特にないが、脱酸剤としての効果を十分に得るためにはＡｌ量を０．０１％以上とすることが好ましい。 Al: 0.06% or less Al may be added as a deoxidizer. However, if the amount of Al in the steel exceeds 0.06%, elongation and stretch flangeability deteriorate, so 0.06% or less is preferable. There is no particular lower limit, but in order to sufficiently obtain the effect as a deoxidizer, the Al content is preferably 0.01% or more.

Ｎ：０．００６％以下
Ｎは少ないほど好ましく、０．００６％を超えると粗大な窒化物が増え、伸びフランジ性が低下するため、０．００６％以下が好ましい。なお、Ｎを極端に低減することは、製造コストを悪化させる。そのため、製造コストを大きく上昇させない実用的な下限は０．０００５％程度となる。 N: 0.006% or less N is preferably as small as possible. If it exceeds 0.006%, coarse nitrides increase and stretch flangeability deteriorates, so 0.006% or less is preferable. In addition, extremely reducing N worsens manufacturing cost. Therefore, a practical lower limit that does not greatly increase the manufacturing cost is about 0.0005%.

Ｍｏ：０．０５〜０．５％
Ｍｏは本発明において重要な元素であり、０．０５％以上添加することでパーライト変態を抑制する効果がある。さらにＴｉ、Ｖと微細な析出物（複合炭化物）を形成し、優れた伸びおよび伸びフランジ性を確保しつつ鋼を強化することができる。しかし、０．５％を超えて添加すると硬質相が形成され伸びフランジ性が低下するため、Ｍｏ含有量は０．０５〜０．５％が好ましい。なお、より好ましい下限値は０．１５％、より好ましい上限値は０．４％である。 Mo: 0.05-0.5%
Mo is an important element in the present invention, and has an effect of suppressing pearlite transformation by adding 0.05% or more. Furthermore, Ti, V and fine precipitates (composite carbides) can be formed, and the steel can be strengthened while ensuring excellent elongation and stretch flangeability. However, if added over 0.5%, a hard phase is formed and stretch flangeability is lowered, so the Mo content is preferably 0.05 to 0.5%. A more preferred lower limit is 0.15%, and a more preferred upper limit is 0.4%.

Ｔｉ：０．０３〜０．２％
Ｔｉは本発明において重要な元素である。Ｍｏ、Ｖと複合炭化物を形成することで、優れた伸びおよび伸びフランジ性を確保しつつ、鋼を強化することができる。しかし、０．０３％未満では、鋼を強化する効果が不十分であり、０．２％を超えると伸びフランジ性が低下するとともに、熱延前のスラブ加熱温度を１３００℃以上という高温にしなければ炭化物が溶解しないため、これ以上添加しても微細析出物として有効に析出させることができない。したがって、Ｔｉ含有量は０．０３〜０．２％が好ましい。より好ましくは０．０８〜０．２％である。 Ti: 0.03-0.2%
Ti is an important element in the present invention. By forming composite carbide with Mo and V, steel can be strengthened while ensuring excellent elongation and stretch flangeability. However, if it is less than 0.03%, the effect of strengthening the steel is insufficient. If it exceeds 0.2%, the stretch flangeability deteriorates, and the slab heating temperature before hot rolling must be 1300 ° C or higher. Since the carbide does not dissolve, it cannot be effectively precipitated as a fine precipitate even if it is added more than this. Therefore, the Ti content is preferably 0.03 to 0.2%. More preferably, it is 0.08 to 0.2%.

Ｖ：０．１５超〜１．２％
Ｖは本発明において重要な元素である。前述のように、炭化物が安定して微細に存在できるためには炭化物の組成が影響する。具体的には、炭化物の平均組成が原子％で表されるＴｉ、Ｍｏ、Ｖで、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たすようになると、析出物の粗大化を抑制する効果が高くなり、所望の微細析出物を得ることができる。この点、本発明者らが詳細に検討した結果、Ｃを０．０６％を超えて多量に添加するとともに、Ｖを多量に添加することでＶの析出効率が上昇し、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たす析出物を得られるようになることが判った。また、所望の析出物を得るためには、上述のように、炭化物の平均組成が原子％で表されるＴｉ、Ｍｏ、Ｖで、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たすことに加えて、炭化物の平均組成においてＴｉ：Ｍｏ：Ｖの原子比が、Ｔｉ＝０．６〜１．４、Ｍｏ＝０．６〜１．４、Ｖ＝１．４〜２．８、ただしＴｉ＋Ｍｏ＋Ｖ＝４を満たすことが好ましい。この場合にも、上述したようにＣを０．０６％超えて多量に添加するとともに、Ｖを多量に添加することで、炭化物の平均組成においてＴｉ：Ｍｏ：Ｖの原子比が、Ｔｉ＝０．６〜１．４、Ｍｏ＝０．６〜１．４、Ｖ＝１．４〜２．８、ただしＴｉ＋Ｍｏ＋Ｖ＝４を満たす析出物を得られるようになることが判った。 V: Over 0.15 to 1.2%
V is an important element in the present invention. As described above, the composition of the carbide has an influence on the fact that the carbide can exist stably and finely. Specifically, when Ti, Mo, and V, in which the average composition of carbides is expressed in atomic%, satisfy V / (Ti + Mo + V) ≧ 0.3, the effect of suppressing the coarsening of precipitates is enhanced. A desired fine precipitate can be obtained. In this regard, as a result of detailed studies by the present inventors, addition of C in excess of 0.06% and addition of a large amount of V increase the precipitation efficiency of V, and V / (Ti + Mo + V) It was found that a precipitate satisfying ≧ 0.3 can be obtained. In addition, in order to obtain a desired precipitate, as described above, in addition to satisfying V / (Ti + Mo + V) ≧ 0.3 with Ti, Mo and V in which the average composition of the carbide is expressed in atomic%. In the average composition of carbides, the atomic ratio of Ti: Mo: V is Ti = 0.6 to 1.4, Mo = 0.6 to 1.4, V = 1.4 to 2.8, where Ti + Mo + V = 4 It is preferable to satisfy. Also in this case, as described above, C is added in a large amount exceeding 0.06%, and by adding a large amount of V, the atomic ratio of Ti: Mo: V becomes Ti = 0 in the average composition of carbides. 6 to 1.4, Mo = 0.6 to 1.4, V = 1.4 to 2.8, but it was found that a precipitate satisfying Ti + Mo + V = 4 can be obtained.

図１に、鋼へのＶの添加量と、Ｖの析出率の関係を示す。ここで、Ｖの析出率は、添加されたＶに対して析出物を実際に形成したＶの比率を意味し、Ｖの析出効率を示す。なお、この結果は、Ｃ：０．１１〜０．１５％、Ｓｉ：０．０１％、Ｍｎ：１．３５％、Ｐ：０．０１％、Ｓ：０．００１％、Ａｌ：０．０５％、Ｎ：０．００３％、Ｍｏ：０．３２％、Ｔｉ：０．１６％とし、Ｖ：０．１〜０．３％で変化させた鋼を素材とし、仕上圧延終了温度９２０℃、巻取温度６２０℃として熱間圧延を行って得た熱延鋼板を用いて得たものである。ここで、Ｃ量とＶ量は、Ｃと（Ｔｉ＋Ｍｏ＋Ｖ）の原子数比がほぼ一定（約１．０〜１．１）となるよう、（Ｃ量，Ｖ量）＝（０．１１％，０．１％）、（０．１３％，０．２％）、（０．１５％，０．３％）として変化させた。また、熱延鋼板の析出Ｖ量は抽出残渣の定量分析により測定し、
Ｖの析出率（％）＝（析出Ｖ量（mass％）／Ｖ添加量（mass％））×１００
として求めた。 FIG. 1 shows the relationship between the amount of V added to steel and the precipitation rate of V. Here, the precipitation rate of V means the ratio of V that actually formed precipitates to the added V, and indicates the deposition efficiency of V. The results are as follows: C: 0.11 to 0.15%, Si: 0.01%, Mn: 1.35%, P: 0.01%, S: 0.001%, Al: 0.05 %, N: 0.003%, Mo: 0.32%, Ti: 0.16%, and V: 0.1% to 0.3% of steel, the finish rolling finish temperature 920 ° C, It is obtained using a hot-rolled steel sheet obtained by hot rolling at a coiling temperature of 620 ° C. Here, the amount of C and the amount of V are (C amount, V amount) = (0.11%, so that the atomic ratio of C and (Ti + Mo + V) is substantially constant (about 1.0 to 1.1). 0.1%), (0.13%, 0.2%), and (0.15%, 0.3%). Moreover, the amount of precipitation V of the hot rolled steel sheet is measured by quantitative analysis of the extraction residue,
V precipitation rate (%) = (precipitation V amount (mass%) / V addition amount (mass%)) × 100
As sought.

図１に示すように、Ｖ添加量が増加するに従い、Ｖの析出率、すなわち添加されたＶの中で析出物を実際に形成するＶの比率が大きくなり、Ｖ＞０．１５％でＶの析出率＞５０％と、非常に良好な析出効率となる。なお、これら鋼板の鋼組織は、フェライト単相組織であることを確認した。また、このように良好な析出効率を得たときの析出物の一例を図２に示す。図２の左側は、析出物を示す透過型電子顕微鏡（ＴＥＭ）写真である。また、図２の右側は、析出物中のＴｉ、Ｍｏ、Ｖのエネルギー分散型Ｘ線分光装置（ＥＤＸ）による計測結果を示す図である。なおこれらの析出物が炭化物を主体とすることはＸ線回折ピークの位置等から確認した。この結果は、Ｃ：０．１５％、Ｓｉ：０．０１％、Ｍｎ：１．３５％、Ｐ：０．０１％、Ｓ：０．００１％、Ａｌ：０．０５％、Ｎ：０．００３％、Ｍｏ：０．３２％、Ｔｉ：０．１６％、Ｖ：０．３％とした鋼を素材とし、仕上圧延終了温度９２０℃、巻取温度６２０℃として熱間圧延を行って製造された熱延鋼板を用いて得たものである。また、析出物の観察は、得られた熱延鋼板を酸洗後、鋼板から薄膜を作製し、ＴＥＭによって観察したものであり、析出物中のＴｉ、Ｍｏ、Ｖの組成はＴＥＭに装備されたＥＤＸによる分析から決定した。図２の分析結果では、Ｔｉ：Ｍｏ：Ｖは原子比で１．２：０．９：１．９であり、したがって、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）は０．４８であった。 As shown in FIG. 1, as the V addition amount increases, the precipitation rate of V, that is, the ratio of V that actually forms precipitates in the added V increases, and V> 0.15% The deposition rate is> 50%, resulting in very good deposition efficiency. In addition, it confirmed that the steel structure of these steel plates was a ferrite single phase structure. Moreover, an example of a precipitate when such a good precipitation efficiency is obtained is shown in FIG. The left side of FIG. 2 is a transmission electron microscope (TEM) photograph showing the precipitate. Moreover, the right side of FIG. 2 is a figure which shows the measurement result by the energy dispersive X-ray-spectrometer (EDX) of Ti, Mo, and V in a precipitate. It was confirmed from the position of the X-ray diffraction peak that these precipitates were mainly composed of carbides. The results are as follows: C: 0.15%, Si: 0.01%, Mn: 1.35%, P: 0.01%, S: 0.001%, Al: 0.05%, N: 0.00. Manufactured by hot rolling at a finish rolling finish temperature of 920 ° C and a coiling temperature of 620 ° C using steel made of 003%, Mo: 0.32%, Ti: 0.16%, V: 0.3% It was obtained using the hot-rolled steel sheet. In addition, the precipitates are observed by pickling the obtained hot-rolled steel sheet, producing a thin film from the steel sheet, and observing by TEM. The composition of Ti, Mo, and V in the precipitate is equipped in the TEM. Determined from analysis by EDX. In the analysis result of FIG. 2, Ti: Mo: V was 1.2: 0.9: 1.9 by atomic ratio, and therefore V / (Ti + Mo + V) was 0.48.

このような実験結果を基に、発明者らがさらに検討した結果、鋼中にＶを０．１５％を超えて含有させて非常に良好な析出効率とすることにより、前述のように、炭化物の平均組成が原子％で表されるＴｉ、Ｍｏ、ＶがＶ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たすようになり、Ｔｉ、Ｍｏと微細な複合炭化物を形成し、優れた伸びや伸びフランジ性を確保しつつ鋼を強化することができることが判明した。また、鋼中にＶを０．２％以上含有させることにより、炭化物の平均組成においてＴｉ：Ｍｏ：Ｖの原子比がＴｉ＝０．６〜１．４、Ｍｏ＝０．６〜１．４、Ｖ＝１．４〜２．８、ただしＴｉ＋Ｍｏ＋Ｖ＝４となる条件を安定して満たすようになり、より効率よく高張力化することができることも判明した。したがって、Ｖの含有量は０．１５％超が好ましく、０．２０％以上がより好ましい。しかし、Ｖの含有量が１．２％を超えると中心偏析が強く現れるようになり、伸びや靭性の低下を招くため、１．２％以下が好ましい。より好ましくは０．８％以下である。したがってＶ含有量は０．１５超〜１．２％が好ましく、０．２〜０．８％がより好ましい。一層好ましい下限値は０．３％である。なお、Ｖを１．２％含有させた場合でもスラブ加熱温度は１２００℃程度の通常温度とすれば炭化物が完全に溶解する。 As a result of further investigation by the inventors based on such experimental results, it was found that carbide was included in the steel in an amount exceeding 0.15% to obtain a very good precipitation efficiency. Ti, Mo, V, whose average composition is expressed in atomic%, satisfies V / (Ti + Mo + V) ≧ 0.3, forms fine composite carbide with Ti, Mo, and has excellent elongation and stretch flangeability It was found that the steel can be strengthened while securing the above. Further, by containing 0.2% or more of V in the steel, the atomic ratio of Ti: Mo: V is Ti = 0.6 to 1.4 and Mo = 0.6 to 1.4 in the average composition of carbides. V = 1.4 to 2.8, where Ti + Mo + V = 4 is stably satisfied, and it has also been found that the tension can be increased more efficiently. Therefore, the V content is preferably more than 0.15%, more preferably 0.20% or more. However, if the content of V exceeds 1.2%, center segregation appears strongly, leading to a decrease in elongation and toughness, so 1.2% or less is preferable. More preferably, it is 0.8% or less. Therefore, the V content is preferably more than 0.15 to 1.2%, more preferably 0.2 to 0.8%. A more preferred lower limit is 0.3%. Even when 1.2% of V is contained, if the slab heating temperature is a normal temperature of about 1200 ° C., the carbide is completely dissolved.

なお、Ｔｉ、Ｍｏ、Ｖの好適な添加量の範囲は上記の通りであるが、目標とする炭化物の平均組成における好ましいＴｉ：Ｍｏ：Ｖの原子比であるＴｉ＝０．６〜１．４、Ｍｏ＝０．６〜１．４、Ｖ＝１．４〜２．８、ただしＴｉ＋Ｍｏ＋Ｖ＝４に対応する添加量比で添加することがより好ましい。 In addition, although the range of the suitable addition amount of Ti, Mo, V is as above-mentioned, Ti = 0.6-1.4 which is the atomic ratio of preferable Ti: Mo: V in the average composition of the target carbide | carbonized_material. , Mo = 0.6 to 1.4, V = 1.4 to 2.8, but it is more preferable to add at an addition amount ratio corresponding to Ti + Mo + V = 4.

また、重量％を原子比に換算するには、Ｔｉ，Ｍｏ、Ｖをそれぞれ原子量（４８，９６，５１）で除算して比率をとればよい。ただし鋼組成で上記比を満足しなくても、直ちに微細炭化物中の原子比が好適範囲を外れるわけではない。 In order to convert the weight% into the atomic ratio, Ti, Mo, and V may be divided by the atomic weight (48, 96, 51), respectively, to obtain the ratio. However, even if the steel composition does not satisfy the above ratio, the atomic ratio in the fine carbide does not immediately deviate from the preferred range.

0.8≦(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}≦1.5
（ただし、式中のC、Ti、Mo、Vは各成分の質量％を表す）
本発明においてＣ、Ｔｉ、Ｍｏ、Ｖの添加バランスは非常に重要である。理論的には、鋼中のＣと（Ｔｉ、Ｍｏ、Ｖ）との原子数比が１、すなわち(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}＝１の場合、炭素が過不足なく複合炭化物として析出することが期待されるが、本発明者らの調査によれば、上記した所定範囲のＣ、Ｔｉ、Ｍｏ、Ｖ含有量とした上で、(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}を０．８〜１．５とすることにより、Ｔｉ、Ｍｏ、ＶがＶ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３を満たす組成を有する多量の炭化物を、フェライト中に微細に、すなわち、平均粒径１０ｎｍ未満として微細に分散析出しやすくすることができることが判明した。(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}が０．８未満では、析出物が粗大となって９８０ＭＰａ以上の強度が安定して得られなくなり、(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}が１．５超えでは、Ｃが過剰となってパーライトを生じるため成形性が低下する。より好ましい範囲は０．８〜１．３である。なお、Ｃ含有量が過剰な場合も炭化物は粗大化する傾向にある。 0.8 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} ≦ 1.5
(However, C, Ti, Mo, and V in the formula represent mass% of each component)
In the present invention, the balance of addition of C, Ti, Mo and V is very important. Theoretically, the atomic ratio between C and (Ti, Mo, V) in the steel is 1, ie, (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51) } = 1, it is expected that carbon is precipitated as a composite carbide without excess or deficiency, but according to the investigation by the present inventors, the content of C, Ti, Mo, V in the predetermined range described above Then, by setting (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} to 0.8 to 1.5, Ti, Mo and V are V / (Ti + Mo + V ) It was found that a large amount of carbide having a composition satisfying ≧ 0.3 can be finely dispersed and precipitated in ferrite finely, that is, with an average particle size of less than 10 nm. When (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} is less than 0.8, the precipitate becomes coarse and a strength of 980 MPa or more cannot be obtained stably. , (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} is more than 1.5, C is excessive and pearlite is generated, so that the formability is lowered. A more preferable range is 0.8 to 1.3. Even when the C content is excessive, the carbide tends to become coarse.

その他の成分
高張力鋼板においては、他の炭化物形成元素、例えばＮｂ、Ｗ等を添加することがある。しかし本発明の場合は炭化物中の最適なＴｉ、Ｍｏ、Ｖバランスを崩す可能性があるので、これらの添加は避け、その含有量は不純物として許容される範囲とすることが好ましい。特にＮｂは熱間圧延荷重を増大させて薄物の製造を困難にするほか、本発明の鋼組成においてはＣの粗大化を促進して強度を低下させる可能性がある。したがって、Ｎｂは０．０２％以下とすることが好ましく、０．００３％以下とすることがさらに好ましい。Ｗも０．０２％以下とすることが好ましく、０．００５％以下とすることがさらに好ましい。 Other components Other carbide forming elements such as Nb and W may be added to the high-tensile steel sheet. However, in the case of the present invention, there is a possibility that the optimum balance of Ti, Mo, and V in the carbide may be lost. Therefore, addition of these is avoided, and the content thereof is preferably within a range acceptable as an impurity. In particular, Nb increases the hot rolling load and makes it difficult to produce thin materials, and in the steel composition of the present invention, it may promote the coarsening of C and reduce the strength. Therefore, Nb is preferably 0.02% or less, and more preferably 0.003% or less. W is also preferably 0.02% or less, and more preferably 0.005% or less.

本発明の鋼板の化学組成における残部は鉄及び不可避的不純物である。不可避的不純物としては、上記の他、Ｃｒ、Ｃｕ、Ｓｎ、Ｎｉ、Ｃａ、Ｚｎ、Ｃｏ、Ｂ、Ａｓ、Ｓｂ、Ｐｂ、Ｓｅ等が挙げられる。Ｃｒは１％以下の含有が許容されるが、好ましくは０．６％以下、より好ましくは０．１％以下である。他の各元素は０．１％以下の含有が許容されるが、好ましくは０．０３％以下である。 The balance in the chemical composition of the steel sheet of the present invention is iron and inevitable impurities. In addition to the above, unavoidable impurities include Cr, Cu, Sn, Ni, Ca, Zn, Co, B, As, Sb, Pb, Se, and the like. Cr is allowed to be contained in an amount of 1% or less, preferably 0.6% or less, more preferably 0.1% or less. The other elements are allowed to contain 0.1% or less, but preferably 0.03% or less.

［製造方法］
本発明では、上記成分組成を有する鋼を溶製して、鋼片（インゴット、スラブ、薄スラブを含む）とし、仕上圧延終了温度８８０℃以上、巻取温度５７０℃以上の条件で熱間圧延を行う。 [Production method]
In the present invention, steel having the above composition is melted to form a steel slab (including ingots, slabs, and thin slabs), which is hot-rolled under conditions of finish rolling end temperature of 880 ° C. or higher and winding temperature of 570 ° C. or higher. I do.

本発明の鋼板の板厚、すなわち熱間圧延後の板厚は、１．４〜５．０ｍｍ程度が好適であるが、特に従来困難であった板厚２．５ｍｍ以下の薄物の製造についても、本発明の鋼板は問題なく適用できる。また、９８０ＭＰａ以上の引張強度を有する２．５ｍｍ以下の薄物熱延鋼板を製造するに当たって、本願は強度を担う析出物を圧延後に析出させる。このため、圧延中は鋼が軟質であり、圧延に関する設備負担を特に増大させることなく、製造することができる。 The plate thickness of the steel plate of the present invention, that is, the plate thickness after hot rolling is preferably about 1.4 to 5.0 mm, but particularly for the production of thin materials with a plate thickness of 2.5 mm or less, which has been difficult in the past. The steel plate of the present invention can be applied without problems. Moreover, in manufacturing a thin hot-rolled steel sheet having a tensile strength of 980 MPa or more and a thickness of 2.5 mm or less, the present application deposits a precipitate bearing the strength after rolling. For this reason, steel is soft during rolling, and can be manufactured without particularly increasing the equipment burden related to rolling.

・鋼片加熱条件
鋼スラブなどの鋼片は一旦冷却後、所定の温度（いわゆるスラブ加熱温度）に再加熱してから熱間圧延を施してもよいし、また、鋼片が前記所定の温度より低温となる前に直ちに熱間圧延を行ってもよい。さらに、鋼片が冷め切る前に前記所定の温度まで短時間の加熱を行い、熱間圧延を施してもよい。スラブ加熱温度は炭化物を再固溶させるため（あるいは析出させないため）、１１５０℃〜１２８０℃程度が好適である。なお、本発明の鋼組成の場合、類似成分の従来鋼（Ｔｉ炭化物系、Ｔｉ−Ｍｏ炭化物系）よりは低いスラブ加熱温度温で再固溶を達成できる。 Steel bill heating conditions Steel bills such as steel slabs may be cooled once and then reheated to a predetermined temperature (so-called slab heating temperature) and then hot rolled. Hot rolling may be performed immediately before the temperature becomes lower. Furthermore, before the steel slab is completely cooled, it may be heated to the predetermined temperature for a short time and hot rolled. The slab heating temperature is preferably about 1150 ° C. to 1280 ° C. in order to re-dissolve the carbide (or not to precipitate it). In the case of the steel composition of the present invention, re-dissolution can be achieved at a slab heating temperature lower than that of conventional steels of similar components (Ti carbide type, Ti-Mo carbide type).

・仕上圧延終了温度：８８０℃以上
仕上圧延終了温度は伸びおよび伸びフランジ性の確保と圧延荷重の低減に重要である。８８０℃未満では表層が粗大粒となり伸びおよび伸びフランジ性が損なわれる。また、未再結晶で圧延が進行するために起こる歪みの蓄積量が増大し、圧延荷重が著しく増大することで薄物の熱間圧延が困難となる。このため仕上圧延終了温度は、８８０℃以上とする。なお、本発明の鋼組成の場合、類似成分の従来鋼（Ｔｉ炭化物系、Ｔｉ−Ｍｏ炭化物系）よりは低い仕上圧延終了温度で強度を確保することができる。また、このため、これらの従来鋼で困難な薄物の製造が容易である。仕上圧延終了温度の上限はとくに定める必要はない。ただし、高温で仕上げると結晶粒が粗大化するので、結晶組織の強度が低下し、微細炭化物等による強化が余分に必要となる。この観点から、圧延終了温度は１０００℃以下とすることが好ましい。 Finish finish rolling temperature: 880 ° C. or higher Finish finish rolling temperature is important for securing elongation and stretch flangeability and reducing rolling load. If it is less than 880 degreeC, a surface layer will become a coarse grain and elongation and stretch flangeability will be impaired. Further, the amount of strain accumulated due to the progress of rolling due to non-recrystallization increases, and the rolling load significantly increases, making it difficult to hot-roll thin materials. For this reason, finishing rolling finish temperature shall be 880 degreeC or more. In addition, in the case of the steel composition of this invention, intensity | strength can be ensured with the finish rolling completion temperature lower than the conventional steel (Ti carbide type | system | group, Ti-Mo carbide type | system | group) of a similar component. In addition, for this reason, it is easy to produce a thin object that is difficult with these conventional steels. There is no need to set the upper limit of the finish rolling finish temperature. However, since the crystal grains become coarse when finished at a high temperature, the strength of the crystal structure is lowered, and extra strengthening with fine carbides or the like is required. From this viewpoint, the rolling end temperature is preferably set to 1000 ° C. or less.

・巻取温度５７０℃以上
フェライト組織を得るため、また、十分な炭化物の析出を確保するため、さらにランナウトテーブル上での注水量を抑えて薄物を安定通板させるため、巻取温度は５７０℃以上とする。ランナウトテーブル上の鋼板の走行安定性を確保するには６００℃以上が好ましい。なお、パーライトの生成を抑制するためには、巻取温度は７００℃以下とするのが望ましい。所定の組成の鋼について、以上の熱延条件を満足することにより、析出した炭化物の平均組成において、Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）≧０．３や炭化物の平均組成においてＴｉ：Ｍｏ：Ｖの原子比がＴｉ＝０．６〜１．４、Ｍｏ＝０．６〜１．４、Ｖ＝１．４〜２．８、ただしＴｉ＋Ｍｏ＋Ｖ＝４を満足させ、また平均粒径１０ｎｍ未満が達成される。 -Winding temperature of 570 ° C or higher The winding temperature is 570 ° C in order to obtain a ferrite structure, to ensure sufficient precipitation of carbides, and to suppress the amount of water injected on the run-out table and to allow thin materials to pass through stably. That's it. In order to ensure the running stability of the steel sheet on the run-out table, 600 ° C. or higher is preferable. In addition, in order to suppress the production | generation of pearlite, it is desirable for the coiling temperature to be 700 degrees C or less. By satisfying the above hot rolling conditions for a steel having a predetermined composition, in the average composition of the precipitated carbide, the atomic ratio of Ti: Mo: V is V / (Ti + Mo + V) ≧ 0.3 or the average composition of the carbide. Ti = 0.6 to 1.4, Mo = 0.6 to 1.4, V = 1.4 to 2.8, where Ti + Mo + V = 4 is satisfied and an average particle size of less than 10 nm is achieved.

本発明の高張力鋼板には、表面に表面処理や表面被覆処理を施したものを含む。特に、本発明の鋼板は溶融亜鉛系めっき皮膜を形成し、溶融亜鉛めっき系鋼板としたものに好適に適用できる。すなわち、本発明の高張力鋼板は良好な加工性を有することから、溶融亜鉛系めっき皮膜を形成しても良好な加工性を維持できる。ここで、溶融亜鉛系めっきとは、亜鉛および亜鉛を主体とした（すなわち約８０質量％以上含有する）溶融めっきであり、亜鉛のほかにＡｌ、Ｃｒなどの合金元素を含んだものも含む。また、溶融亜鉛系めっきを施したままでも、めっき後に合金化処理を行ってもかまわない。 The high-tensile steel sheet according to the present invention includes those having a surface subjected to surface treatment or surface coating treatment. In particular, the steel sheet of the present invention can be suitably applied to a hot-dip galvanized steel sheet that forms a hot-dip galvanized film. That is, since the high-tensile steel sheet of the present invention has good workability, good workability can be maintained even when a hot dip galvanized film is formed. Here, the hot dip galvanizing is hot dip plating mainly composed of zinc and zinc (that is, containing about 80% by mass or more), and includes those containing alloy elements such as Al and Cr in addition to zinc. Moreover, even if hot dip galvanizing is performed, alloying treatment may be performed after plating.

（実施例１）
表１に示す化学成分を有する鋼片を、１２５０℃に加熱し、通常の熱間圧延工程によって仕上げ圧延終了温度８８０〜９３０℃で、板厚３．５ｍｍに仕上げた。この後、６００℃を超える巻取温度で、冷却速度と巻取温度を変化させて、種々の組織の鋼板を製造した。なお、表１中、Ａ値は、上記（Ｉ）式の(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}の値を示す。 Example 1
A steel slab having the chemical components shown in Table 1 was heated to 1250 ° C., and finished to a plate thickness of 3.5 mm at a finish rolling end temperature of 880 to 930 ° C. by a normal hot rolling process. Thereafter, steel sheets having various structures were manufactured by changing the cooling rate and the coiling temperature at a coiling temperature exceeding 600 ° C. In Table 1, the value A indicates the value of (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} in the above formula (I).

得られた鋼板を酸洗後、鋼板の板厚の１／８，１／４，３／８，１／２位置から採取して作製した薄膜を透過型電子顕微鏡（ＴＥＭ）によって組織観察を行うとともに、析出物のサイズを測定した。なお、組織観察は主に倍率５０００〜１００００倍、析出物観察は主に２６００００〜３４００００倍にて行った。析出物中のＴｉ、Ｍｏ、Ｖの組成は３４００００倍での観察においてＴＥＭに装備されたエネルギー分散型Ｘ線分光装置（ＥＤＸ）による分析から決定し、析出物のＶ比率（原子比）＝Ｖ／（Ｔｉ＋Ｍｏ＋Ｖ）（式中、Ｔｉ，Ｍｏ，Ｖは原子％）およびＴｉ：Ｍｏ：Ｖの原子比を求めた。また、得られた鋼板の板厚方向断面について走査型電子顕微鏡（ＳＥＭ）でもＴＥＭ観察を行った板厚位置について組織観察を１０００倍〜５０００倍で行い、ＴＥＭでの組織観察結果を確認した。 The obtained steel sheet is pickled, and the thin film prepared by sampling from 1/8, 1/4, 3/8, and 1/2 positions of the thickness of the steel sheet is observed with a transmission electron microscope (TEM). At the same time, the size of the precipitate was measured. Note that the structure observation was mainly performed at a magnification of 5000 to 10,000 times, and the precipitate observation was mainly performed at 260000 to 340000 times. The composition of Ti, Mo, and V in the precipitate was determined from the analysis by an energy dispersive X-ray spectrometer (EDX) equipped in the TEM in the observation at 340000 times, and the V ratio (atomic ratio) of the precipitate = V / (Ti + Mo + V) (wherein Ti, Mo, V are atomic%) and the atomic ratio of Ti: Mo: V were determined. Moreover, about the plate | board thickness direction cross section of the obtained steel plate, structure | tissue observation was performed 1000 times-5000 times about the plate | board thickness position which performed TEM observation also with the scanning electron microscope (SEM), and the structure | tissue observation result in TEM was confirmed.

ここで、析出物は、粒径が１００ｎｍ以下のものをランダムに３０個選択し、各々について粒径およびＴｉ、Ｍｏ、Ｖの含有量を測定した。粒径は３４００００倍の観察結果をもとに円近似を用いた画像処理で求め、上記３０個の算術平均を平均粒径とした。Ｖ比率およびＴｉ：Ｍｏ：Ｖの値については、Ｔｉ、Ｍｏ、Ｖの含有量を上記３０個の算術平均により求めて平均組成とし、これを元に算出した。このように粒径が１００ｎｍ以下の析出物について得た平均粒径、平均組成を、Ｔｉ、ＭｏおよびＶを含む炭化物の平均粒径、平均組成とした。 Here, 30 precipitates having a particle size of 100 nm or less were selected at random, and the particle size and the contents of Ti, Mo, and V were measured for each. The particle diameter was determined by image processing using circle approximation based on the observation result of 340000 times, and the arithmetic average of the 30 was used as the average particle diameter. About the value of V ratio and Ti: Mo: V, content of Ti, Mo, and V was calculated | required by said 30 arithmetic average, and it was set as the average composition, and it computed based on this. The average particle size and average composition obtained for the precipitate having a particle size of 100 nm or less were used as the average particle size and average composition of carbides containing Ti, Mo and V.

また、得られた鋼板からＪＩＳ５号引張試験片および穴広げ試験片を採取した。引張試験片は圧延垂直方向から採取した。穴広げ試験は１３０ｍｍ角の鋼板の中央に１０ｍｍφのポンチにより、クリアランス（片側）を板厚の１２．５％として打ち抜いた穴を有する試験片を準備し、６０°円錐ポンチにより打ち抜き穴のバリ側の反対方向から押し上げ、割れが鋼板を貫通した時点での穴径ｄ（ｍｍ）を測定し、穴広げ率λを次式より算出した。
λ（％）＝｛（ｄ−１０）／１０｝×１００
表２に、組織、析出物平均粒径、析出物の組成（Ｖ比率）、Ｔｉ：Ｍｏ：Ｖの原子比、引張強度（ＴＳ）、伸び（Ｅｌ）、穴広げ率（λ）を記載する。 Moreover, a JIS No. 5 tensile test piece and a hole expansion test piece were collected from the obtained steel plate. Tensile specimens were taken from the vertical direction of rolling. In the hole expansion test, a test piece having a hole punched with a clearance (one side) of 12.5% of the plate thickness is prepared in the center of a 130 mm square steel plate with a punch of 10 mmφ, and the burr side of the punched hole is formed with a 60 ° conical punch. The hole diameter d (mm) at the time when the crack penetrated the steel sheet was measured, and the hole expansion ratio λ was calculated from the following equation.
λ (%) = {(d−10) / 10} × 100
Table 2 shows the structure, the average particle size of the precipitate, the composition of the precipitate (V ratio), the atomic ratio of Ti: Mo: V, the tensile strength (TS), the elongation (El), and the hole expansion ratio (λ). .

表２に示す通り、本発明鋼のＮｏ．１〜５はいずれもフェライト組織からなり、析出物の平均粒径は１０ｎｍ未満で、析出物の組成（Ｖ比率）は０．３以上となっており、引張強度（ＴＳ）が９８０ＭＰａ以上で優れた伸びと伸びフランジ性を有していることが確認された。 As shown in Table 2, No. of the steel of the present invention. 1 to 5 are all composed of a ferrite structure, the average particle size of the precipitate is less than 10 nm, the composition of the precipitate (V ratio) is 0.3 or more, and the tensile strength (TS) is excellent at 980 MPa or more. It was confirmed that the film has stretch and stretch flangeability.

これに対して、比較例であるＮｏ．６は、Ｃ量ならびにＶ量が少ないため、鋼の強化に必要な析出物の量が少なく、引張強度（ＴＳ）が９８０ＭＰａ未満となっている。Ｎｏ．７は、Ｃ量が多すぎ、またＭｏ量が少ないため、パーライトが生成し、かつ析出物が粗大化しており、伸びおよび伸びフランジ性がともに低い。また、Ｎｏ．８は、Ｖ量が多く、析出物が粗大化しており、かつマルテンサイトが生成しているため、伸びおよび伸びフランジ性がともに低い。Ｎｏ．９は、Ｔｉ量、Ｖ量が少ないため、鋼の強化に必要な析出物が不足して引張強度（ＴＳ）が９８０ＭＰａ未満となっている。 On the other hand, No. which is a comparative example. In No. 6, since the amount of C and V is small, the amount of precipitates necessary for strengthening the steel is small, and the tensile strength (TS) is less than 980 MPa. No. In No. 7, since the amount of C is too large and the amount of Mo is small, pearlite is generated and precipitates are coarsened, and both elongation and stretch flangeability are low. No. No. 8 has a large amount of V, precipitates are coarse, and martensite is generated, so that both elongation and stretch flangeability are low. No. No. 9 has a small amount of Ti and V, so that precipitates necessary for strengthening the steel are insufficient and the tensile strength (TS) is less than 980 MPa.

（実施例２）
化学成分が質量％で、Ｃ：０．１５０％、Ｓｉ：０．０２％、Ｍｎ：１．３４％、Ｐ：０．０１０％、Ｓ：０．０００８％、Ａｌ：０．０４３％、Ｎ：０．００３２％、Ｍｏ：０．３２％、Ｔｉ：０．１５％、Ｖ：０．３０％である鋼（Ａ値：(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}＝１．０１）を溶製し鋼スラブとした。次いで、オーステナイト域（１２５０℃）に加熱後、熱間圧延を行い、表３に示す温度で圧延を完了した。圧延後は表３に示す巻取温度まで冷却し、該巻取温度で巻き取った。表３には板厚も同時に記載した。なお、表３に示す鋼Ｎｏ．１０〜１６は全て同一の化学成分とした。得られたコイルの幅方向中央部からサンプルを採取し、引張方向が圧延方向と垂直になるようにＪＩＳ５号引張試験片を採取し、引張試験を行った。また、同じ位置から採取したサンプルから、実施例１と同様の方法で析出物の調査を行い、鋼組織も観察した。さらに圧延後の板形状を目視で判定した。その結果も表３に併記する。なお、圧延後の板形状の評価基準は、目視でフラットな場合を○、波うちが顕著な場合を×とした。さらにまた析出物の組成（Ｖ比率）、Ｔｉ：Ｍｏ：Ｖの原子比を表３に併記する。 (Example 2)
Chemical component in mass%, C: 0.150%, Si: 0.02%, Mn: 1.34%, P: 0.010%, S: 0.0008%, Al: 0.043%, N : 0.0032%, Mo: 0.32%, Ti: 0.15%, V: 0.30% steel (A value: (C / 12) / {(Ti / 48) + (Mo / 96 ) + (V / 51)} = 1.01) was made into a steel slab. Next, after heating to the austenite region (1250 ° C.), hot rolling was performed, and the rolling was completed at the temperatures shown in Table 3. After rolling, it was cooled to the winding temperature shown in Table 3, and wound up at the winding temperature. Table 3 also shows the plate thickness. In addition, steel No. shown in Table 3 10 to 16 were all the same chemical components. A sample was taken from the center of the obtained coil in the width direction, a JIS No. 5 tensile test piece was taken so that the tensile direction was perpendicular to the rolling direction, and a tensile test was performed. Moreover, the deposit was investigated from the sample extract | collected from the same position by the method similar to Example 1, and the steel structure was also observed. Furthermore, the plate shape after rolling was visually determined. The results are also shown in Table 3. In addition, as for the evaluation criteria of the plate shape after rolling, the case where it was visually flat was marked with ◯, and the case where the wave was remarkable was marked with ×. Furthermore, the composition of precipitates (V ratio) and the atomic ratio of Ti: Mo: V are also shown in Table 3.

すなわち表３は、同一化学成分の１１８０ＭＰａ級鋼板において、板厚と、仕上圧延終了温度および巻取温度を変化させた例を示すものである。仕上圧延終了温度８８０℃以上、巻取り温度５７０℃以上を確保している鋼Ｎｏ．１０〜１４では、板厚に関わらず、平均粒径１０ｎｍ未満の析出物が生成しており、目標の引張強度（ＴＳ）と伸びが達成された。また板形状も良好であった。なお、これらの鋼板は、組織観察の結果、フェライト単相組織であることを確認した。一方、比較鋼のＮｏ．１５は仕上圧延終了温度が低かったため表層部で結晶粒が粗大化し、さらに析出物も粗大化したため、目標の強度を満たさず、伸びも低かった。板形状も波打ちが顕著であった。Ｎｏ．１６は巻取温度が低かったため、鋼の強化に必要な析出物が不足して引張強度(ＴＳ)が目標に達せず、また波打ちが顕著であった。なお、鋼Ｎｏ．１０〜１４では析出物の個数は１μｍ^３当たり約１×１０^６個程度であり、Ｎｏ．１５および１６では２．５〜４×１０^５個程度と概算される。 That is, Table 3 shows an example in which the thickness, finish rolling finishing temperature, and winding temperature are changed in the 1180 MPa class steel plate having the same chemical composition. Steel No. having a finish rolling finish temperature of 880 ° C or higher and a winding temperature of 570 ° C or higher is secured. In 10 to 14, precipitates having an average particle diameter of less than 10 nm were formed regardless of the plate thickness, and the target tensile strength (TS) and elongation were achieved. The plate shape was also good. These steel sheets were confirmed to have a ferrite single phase structure as a result of structural observation. On the other hand, no. In No. 15, the finish rolling finish temperature was low, so the crystal grains were coarsened in the surface layer portion, and the precipitates were also coarsened, so the target strength was not satisfied and the elongation was low. The plate shape was also wavy. No. Since No. 16 had a low coiling temperature, the precipitate required for strengthening the steel was insufficient, the tensile strength (TS) did not reach the target, and the waviness was remarkable. Steel No. 10 to 14, the number of precipitates is about 1 × 10 ⁶ per 1 μm ³ . 15 and 16 are estimated to be about 2.5 to 4 × 10 ⁵ .

（実施例３）
表４に示す化学成分を有する鋼片に対して仕上圧延終了温度９２０℃以上、巻取温度６２０℃で熱間圧延を施し、板厚１．６ｍｍの熱延鋼板を製造した。なお、鋼片の加熱温度は１２５０℃とした。これら熱延鋼板を酸洗後、亜鉛をめっき浴とする溶融亜鉛めっきを施した後、合金化処理を施し、合金化溶融亜鉛めっき鋼板とした。実施例１と同様に、得られた鋼板から作製した薄膜について、透過型電子顕微鏡（ＴＥＭ）によって組織観察を行うとともに、析出物のサイズを測定し、さらに析出物中のＴｉ、Ｍｏ、Ｖの組成をＴＥＭに装備されたエネルギー分散型Ｘ線分光装置（ＥＤＸ）による分析から決定した。なお、実施例１と同様に組織観察の結果はＳＥＭにて確認した。また、これらめっき鋼板からＪＩＳ５号引張試験片および穴広げ試験片を採取し、引張試験および穴広げ試験を行った。なお、表４中のＡ値も表１と同様、（Ｉ）式の(C／12)／{(Ti／48)＋(Mo／96)＋(V／51)}の値を示す。表５に、組織、析出物平均粒径、析出物の平均組成（Ｖ比率）、Ｔｉ：Ｍｏ：Ｖの原子比、引張強度（ＴＳ）、伸び（Ｅｌ）、穴広げ率（λ）を記載する。 (Example 3)
Steel strips having the chemical components shown in Table 4 were hot-rolled at a finish rolling end temperature of 920 ° C. or higher and a coiling temperature of 620 ° C. to produce a hot-rolled steel plate having a thickness of 1.6 mm. The heating temperature of the steel slab was 1250 ° C. These hot-rolled steel sheets were pickled, hot-dip galvanized using zinc as a plating bath, and then alloyed to obtain alloyed hot-dip galvanized steel sheets. As in Example 1, the thin film prepared from the obtained steel sheet was observed with a transmission electron microscope (TEM), the size of the precipitate was measured, and Ti, Mo, and V of the precipitate were further measured. The composition was determined from analysis by an energy dispersive X-ray spectrometer (EDX) equipped with a TEM. Note that, as in Example 1, the results of the structure observation were confirmed by SEM. Moreover, a JIS No. 5 tensile test piece and a hole expansion test piece were sampled from these plated steel sheets and subjected to a tensile test and a hole expansion test. In addition, the A value in Table 4 also shows the value of (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} in the formula (I) as in Table 1. Table 5 shows the structure, average particle size of precipitates, average composition of precipitates (V ratio), atomic ratio of Ti: Mo: V, tensile strength (TS), elongation (El), and hole expansion ratio (λ). To do.

表５に示すように、本発明例であるＮｏ．１７は溶融亜鉛めっきを行っても伸び、伸びフランジ性ともに良好な値を示すのに対し、比較例のＮｏ．１８は析出物が粗大化し、また析出物にＶがほとんど含まれていないため、伸び、伸びフランジ性ともに低かった。 As shown in Table 5, No. 1 as an example of the present invention. No. 17 shows a good value for both elongation and stretch flangeability even when hot dip galvanization is performed, whereas No. 17 in the comparative example. In No. 18, the precipitate was coarsened and the precipitate contained almost no V, so that both elongation and stretch flangeability were low.

（実施例４）
表６に示す化学成分を有する鋼片を、１２５０℃に加熱し、通常の熱間圧延工程によって仕上圧延終了温度８８０〜９３０℃で、板厚２．５ｍｍに仕上げ、６２０℃にてコイルに巻取った。なお、表記以外の成分については、質量％でＳｉ：０．００１〜０．１５％、Ｓ：０．０００５〜０．００５％、Ａｌ：０．０１〜０．０６％、Ｎ：０．０００５〜０．００６％の範囲内とした。得られた鋼板を酸洗後、実施例１と同様の方法で、微細炭化物および鋼板の特性（機械的特性および加工性）を調査した。調査の結果を表７に示す。 Example 4
A steel slab having the chemical composition shown in Table 6 is heated to 1250 ° C., finished at a finish rolling finish temperature of 880 to 930 ° C. by a normal hot rolling process, finished to a thickness of 2.5 mm, and wound at 620 ° C. into a coil. I took it. In addition, about components other than a description, Si: 0.001-0.15% by mass%, S: 0.0005-0.005%, Al: 0.01-0.06%, N: 0.0005 It was made into the range of -0.006%. After pickling the obtained steel plate, the characteristics (mechanical properties and workability) of the fine carbide and the steel plate were investigated in the same manner as in Example 1. The results of the survey are shown in Table 7.

炭素量を一定とし、Ａ値が好適範囲を外れない範囲で、Ｔｉ、Ｍｏ、Ｖのいずれか１種類の含有量を変化させた、Ｎｏ．２１〜２７（Ｖ変化）、Ｎｏ．２８〜３２（Ｍｏ変化）およびＮｏ．３３〜３６および３０（Ｔｉ変化）を調査した結果から、Ｔｉ、Ｍｏ、Ｖの全てを発明範囲内とすることにより、９８０ＭＰａ以上の高強度および伸び・伸びフランジ性を兼ね備えた、極めて優れた鋼板を得ることができることがわかる。また、これらの条件で製造された鋼の微細炭化物の調査結果から、Ｖ比率およびＴｉ：Ｍｏ：Ｖが好適な範囲にあり、その結果Ｔｉ、Ｍｏ、Ｖが微細に析出することで、特に加工性を劣化させずに高張力化に効果的であることが理解される。なお、Ｖ添加量については、０．２０％以上とすることで（Ｎｏ．２２）、０．２０％未満の発明例（例えばＮｏ．２３）よりさらに顕著な高強度化が得られる一方、伸びや伸びフランジ性はほとんど劣化しなかった。 No. 1 in which the content of any one of Ti, Mo, and V was changed within a range in which the carbon amount was constant and the A value did not deviate from the preferred range. 21-27 (V change), No. 28-32 (Mo change) and No. From the results of investigating 33 to 36 and 30 (Ti change), by making all of Ti, Mo and V within the scope of the invention, an extremely excellent steel sheet having high strength of 980 MPa or more and stretch / stretch flangeability It can be seen that can be obtained. Further, from the investigation results of fine carbides of steel manufactured under these conditions, the V ratio and Ti: Mo: V are in a suitable range, and as a result, Ti, Mo, and V are finely precipitated, so that it is particularly processed. It is understood that it is effective for increasing the tension without deteriorating the properties. In addition, about V addition amount, it is 0.20% or more (No. 22), while the remarkable increase in strength is obtained more than the invention example (for example, No. 23) of less than 0.20%, the elongation is obtained. And stretch flangeability hardly deteriorated.

また、鋼の化学成分におけるＴｉ、Ｍｏ、Ｖの比をほぼ一定とし、かつ、Ａ値をほぼ一定とした条件でＣ量を変化させたＮｏ．３７〜４１、および、鋼の化学成分におけるＴｉ、Ｍｏ、Ｖの比をほぼ一定とし、かつ、Ｃを一定とした条件でＡ値を変化させたＮｏ．４２〜４６の結果から、Ｃ量やＡ値も好適条件を満たすことが好ましいことがわかる。 In addition, No. 1 in which the ratio of Ti, Mo, V in the chemical composition of steel was made substantially constant and the C amount was changed under the condition that the A value was made almost constant. No. 37 to No. 41 and No. 1 in which the ratio of Ti, Mo, V in the chemical composition of steel was made substantially constant and the A value was changed under the condition that C was made constant. From the results of 42 to 46, it is understood that the C amount and the A value preferably satisfy the preferable conditions.

さらに、Ｎｏ．４７〜５０からわかるように、Ｐ量やＭｎ量により鋼板の引張強度をさらに若干調整することができる。 Furthermore, no. As can be seen from 47 to 50, the tensile strength of the steel sheet can be further slightly adjusted by the amount of P and the amount of Mn.

これに対し、Ｖ量、Ｔｉ量あるいはＣ量が不足したＮｏ．２４、３６および３７では炭化物量不足が原因と思われる鋼板強度不足を生じる。またＣ量が過剰でパーライト化が進んだＮｏ．４１においても炭化物量不足が原因と思われる鋼板強度不足を生じていた。さらに、Ｍｏ量が不足あるいはＴｉ量が過剰であるＮｏ．３２および３３は炭化物が粗大化し、やはり強度が不足した。さらにまた、Ａ値が適正値を外れた場合（Ｎｏ．４２および４６）も、炭化物不足が原因と思われる鋼板強度の不足が発生した。さらにまた、ＴｉあるいはＭｏが過剰に添加されたＮｏ．２７および２８においては伸びや伸びフランジ性が著しく低下した。 On the other hand, No. in which V amount, Ti amount or C amount was insufficient. In 24, 36 and 37, the steel sheet lacks in strength, which seems to be caused by the lack of carbide. In addition, No. with excessive amount of C and advanced perlite. In Steel No. 41, the steel sheet lacked strength, which was thought to be caused by the lack of carbide. Furthermore, No. in which Mo amount is insufficient or Ti amount is excessive. In 32 and 33, the carbides became coarse and the strength was insufficient. Furthermore, when the A value deviated from the appropriate value (Nos. 42 and 46), the steel sheet lacked strength, which was thought to be due to the lack of carbide, occurred. Furthermore, No. in which Ti or Mo was added excessively. In 27 and 28, elongation and stretch flangeability were remarkably lowered.

本発明によれば、Ｔｉ、Ｍｏに加えてＶを適正なバランスで添加して、Ｔｉ、ＭｏおよびＶを含む微細な炭化物を分散析出させることにより、加工性に優れた高張力鋼板が得られる。また、本発明によれば、加工性の指標である伸びと伸びフランジ性がともに優れ、９８０ＭＰａ以上の高強度の高張力熱延鋼板が提供される。このような鋼板は、自動車用部材のようにプレス時の断面形状が複雑な用途に適している。 According to the present invention, in addition to Ti and Mo, V is added in an appropriate balance, and fine carbides containing Ti, Mo and V are dispersed and precipitated, thereby obtaining a high-tensile steel plate having excellent workability. . In addition, according to the present invention, both high elongation and stretch flangeability, which are indexes of workability, are excellent, and a high-strength, high-tensile hot-rolled steel sheet of 980 MPa or more is provided. Such a steel plate is suitable for an application having a complicated cross-sectional shape during pressing, such as a member for an automobile.

Ｖの添加量と析出効率の関係を示すグラフ。The graph which shows the relationship between the addition amount of V, and precipitation efficiency. 本発明で得られたＴｉ、Ｍｏ、Ｖを含む微細な炭化物の一例（透過型電子顕微鏡による観察結果）。An example of the fine carbide | carbonized_material containing Ti, Mo, and V obtained by this invention (Observation result by a transmission electron microscope).

Claims

Carbides containing Ti, Mo and V having a ferrite single-phase structure and an average particle size of less than 10 nm are dispersed and precipitated, and the carbides containing Ti, Mo and V are Ti, Mo expressed in atomic%. , V has an average composition satisfying V / (Ti + Mo + V) ≧ 0.3, a high-tensile steel plate having a tensile strength of 980 MPa or more.

In mass%, C: more than 0.06 to 0.24%, Si ≦ 0.3%, Mn: 0.5 to 2.0%, P ≦ 0.06%, S ≦ 0.005%, Al ≦ 0.06%, N ≦ 0.006%, Mo: 0.05 to 0.5%, Ti: 0.03 to 0.2%, V: more than 0.15 to 1.2%, the balance being The high-tensile steel sheet according to claim 1, comprising Fe and inevitable impurities and having a component composition in which the C, Ti, Mo, and V contents satisfy the following formula (I):
0.8 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} ≦ 1.5 (I)
(However, C, Ti, Mo and V represent mass% of each component)

The high-strength steel plate according to claim 1 or 2, wherein the high-strength steel plate is a thin hot-rolled steel plate having a thickness of 2.5 mm or less.

The high-tensile steel sheet according to any one of claims 1 to 3, wherein the surface has a hot-dip galvanized coating film.

In mass%, C: more than 0.06 to 0.24%, Si ≦ 0.3%, Mn: 0.5 to 2.0%, P ≦ 0.06%, S ≦ 0.005%, Al ≦ 0.06%, N ≦ 0.006%, Mo: 0.05 to 0.5%, Ti: 0.03 to 0.2%, V: more than 0.15 to 1.2%, the balance being A steel slab consisting of Fe and unavoidable impurities and having a component composition satisfying the following formula (I) with C, Ti, Mo and V contents, finish rolling end temperature 880 ° C or higher, coiling temperature 570 ° C or higher A method for producing a high-tensile steel sheet having a tensile strength of 980 MPa or more, wherein hot rolling is performed under the following conditions.
0.8 ≦ (C / 12) / {(Ti / 48) + (Mo / 96) + (V / 51)} ≦ 1.5 (I)
(However, C, Ti, Mo and V represent mass% of each component)

The method for producing a high-strength steel sheet according to claim 5, wherein hot-dip galvanizing is performed on the surface of the steel sheet after the hot rolling.