JP2005187863A - High strength cold rolled steel sheet having excellent coating film adhesion - Google Patents

High strength cold rolled steel sheet having excellent coating film adhesion Download PDF

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JP2005187863A
JP2005187863A JP2003429151A JP2003429151A JP2005187863A JP 2005187863 A JP2005187863 A JP 2005187863A JP 2003429151 A JP2003429151 A JP 2003429151A JP 2003429151 A JP2003429151 A JP 2003429151A JP 2005187863 A JP2005187863 A JP 2005187863A
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steel sheet
less
coating film
oxide
film adhesion
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JP3934604B2 (en
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Masahiro Nomura
正裕 野村
Ikuo Hashimoto
郁郎 橋本
Yoshinobu Omiya
良信 大宮
Shinji Kamitsuma
伸二 上妻
Manabu Kamura
学 嘉村
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Kobe Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength cold rolled steel sheet having excellent coating film adhesion and tensile strength of ≥550 MPa. <P>SOLUTION: The cold rolled steel sheet is a DP (Dual Phase) steel sheet satisfying regulated components, wherein (I) Si-Mn double oxides of ≤5 μm in the diameter of equivalent circle exist at ≥10 pieces/100 μm<SP>2</SP>on the surface of the steel sheet and the surface coverage of the oxides mainly composed of Si is ≥10% and/or (II) the cracks of a width ≤3 μm and a depth ≥5 μm do not exist within arbitrary 10 visual fields when the section near the surface of the steel sheet is observed at 2,000 times by using an SEM (scanning electron microscope). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、塗膜密着性に優れた高強度冷延鋼板に関するものであり、殊に、引張強度が５５０ＭＰａ以上で、且つ優れた塗膜密着性を有し自動車部品用鋼板等として最適な冷延鋼板に関するものである。   The present invention relates to a high-strength cold-rolled steel sheet excellent in coating film adhesion, and in particular, has a tensile strength of 550 MPa or more and has excellent coating film adhesion and is an optimal cold-rolled steel sheet for automobile parts. It relates to rolled steel sheets.

自動車の燃費向上や軽量化を背景に鋼材の高強度化が求められており、冷延鋼板の分野でもハイテン化（高硬度化）が進んでいる。一方、冷延鋼板は部品製造時にプレス成形が施されるため、伸び等の延性を十分確保することが前提となる。高強度化を図るには合金元素の添加が有効であるが、該合金元素量の増加に伴い、延性は低下する傾向にある。   Higher strength of steel materials is demanded against the background of improving fuel economy and weight reduction of automobiles, and high tempering (hardening) is also progressing in the field of cold-rolled steel sheets. On the other hand, since cold-rolled steel sheets are press-formed at the time of component production, it is assumed that sufficient ductility such as elongation is secured. Addition of an alloy element is effective for increasing the strength, but the ductility tends to decrease as the amount of the alloy element increases.

しかし上記合金元素の中でも、Ｓｉは延性低下の比較的小さい元素であり、延性を確保しつつ高強度化を図るのに有効な元素である。ところがＳｉ含有量が増加すると、化成処理性が劣化して塗装後の塗膜密着性が低下する。そのため化成処理性が重視される場合にはＳｉ含有量の低減を余儀なくされていた。またＳｉ含有量が増加すると、鋼板表面に生成するＳｉ含有粒界酸化物を原因とするクラックが発生し易くなり、これが塗膜密着性を劣化させる要因となっていた。   However, among the above alloy elements, Si is an element having a relatively small ductility reduction, and is an element effective for achieving high strength while ensuring ductility. However, when the Si content is increased, the chemical conversion processability is deteriorated and the coating film adhesion after coating is lowered. For this reason, when the chemical conversion treatment is important, the Si content has to be reduced. Moreover, when Si content increased, it became easy to generate | occur | produce the crack resulting from the Si containing grain-boundary oxide produced | generated on the steel plate surface, and this became a factor which deteriorates coating-film adhesiveness.

これまで機械的特性と化成処理性を両立させる技術としては、クラッド材を鋼板表面に被覆し、鋼板表面に低Ｓｉ濃度層を設けることで化成処理性を高め、内部の高Ｓｉ濃度層で機械的特性を確保する技術がある（例えば特許文献１）。しかしクラッド構造としなければならないため、製造工程が複雑になりコストアップにつながるという問題点がある。   Until now, as a technology to achieve both mechanical properties and chemical conversion treatment, the steel sheet surface is coated with a clad material, and a low Si concentration layer is provided on the steel sheet surface to improve chemical conversion treatment. There is a technique for ensuring the target characteristics (for example, Patent Document 1). However, since the clad structure is required, there is a problem that the manufacturing process is complicated and the cost is increased.

また、化成処理性を阻害するＳｉが表面に濃化しないよう特殊な合金元素を添加する従来技術もある（例えば特許文献２や特許文献３）。この方法では、ＮｉやＣｕを添加することで鋼板表層へのＳｉ濃化を抑制し、化成処理性を確保している。しかし該方法では、高価なＮｉやＣｕを使用するためコストアップを招くという問題がある。   In addition, there is a conventional technique in which a special alloy element is added so that Si that inhibits chemical conversion treatment does not concentrate on the surface (for example, Patent Document 2 and Patent Document 3). In this method, by adding Ni or Cu, concentration of Si on the steel sheet surface layer is suppressed, and chemical conversion processability is ensured. However, this method has a problem that the cost is increased because expensive Ni or Cu is used.

またこれらの技術は、Ｃ含有量が０．００５％以下と低濃度であり、再結晶温度を規定し集合組織制御によって、深絞り性の向上を図ったいわゆるＩＦ鋼板に関するものであるが、この様にＣ量の非常に少ないＩＦ鋼板で、本発明が意図する様な高強度を達成することは難しい。   These techniques relate to a so-called IF steel sheet that has a low C content of 0.005% or less, and has improved redrawing temperature by controlling the recrystallization temperature and controlling the texture. Thus, it is difficult to achieve a high strength as intended by the present invention with an IF steel sheet having a very small amount of C.

特許文献４では、ＮｂＣを析出させ、これをりん酸亜鉛結晶の核生成サイトとして活用することで化成処理性を確保している。しかしこの技術も、０．０２％以下の低Ｃ濃度域で集合組織を制御することで深絞り性を確保した技術であり、上記ＩＦ鋼に比べると若干Ｃ濃度は高いものの、強度不足は否めない。該技術によると、第１発明では５５ｋｇｆ／ｍｍ２（５３９ＭＰａ）、第２発明では６０ｋｇｆ／ｍｍ２（５８８ＭＰａ）が強度の上限値であり、第２発明では５５０ＭＰａを超えている。しかしこの強度はＰやＭｏ含有量を高めることによって実現したものであり、これらの元素が含まれると十分な溶接性を確保できなくなる。 In Patent Document 4, NbC is precipitated, and this is used as a nucleation site for zinc phosphate crystals to ensure chemical conversion treatment. However, this technique is also a technique that secures deep drawability by controlling the texture in a low C concentration range of 0.02% or less. Although the C concentration is slightly higher than the IF steel, the strength is insufficient. Absent. According to the technique, in the first invention 55kgf / mm 2 (539MPa), in the second invention is the upper limit of 60kgf / mm 2 (588MPa) strength, in the second invention is greater than 550 MPa. However, this strength is realized by increasing the P and Mo contents, and if these elements are contained, sufficient weldability cannot be secured.

特許文献５では、表層のＳｉＯ２／Ｍｎ２ＳｉＯ４比率を規定することで化成処理性を確保した残留オーステナイト含有鋼板が提案されている。この技術では、表層酸化物を制御したりＳｉ／Ｆｅの元素比率を制御するため、連続焼鈍後の表面を酸洗またはブラシ処理してＳｉ酸化物を除去するか、またはＡｃ１変態点以下の温度で露点を−３０℃以上に調整し、Ｓｉ酸化物の生成量を抑える必要がある。 Patent Document 5 proposes a retained austenite-containing steel sheet that ensures chemical conversion processability by defining the SiO 2 / Mn 2 SiO 4 ratio of the surface layer. In this technique, in order to control the surface layer oxide or to control the element ratio of Si / Fe, the surface after continuous annealing is pickled or brushed to remove the Si oxide, or below the Ac 1 transformation point. It is necessary to adjust the dew point to −30 ° C. or higher with temperature to suppress the amount of Si oxide produced.

しかし上記酸洗やブラシ処理を行うと、工程数の増大により製造コストの上昇を招く。また露点制御は、連続焼鈍炉内で行われるが、文献に示された実施例を見る限り、該露点を制御したとしても最表層におけるＳｉＯ２／Ｍｎ２ＳｉＯ４比率は１．０程度であり、化成処理皮膜結晶の生成を阻害するＳｉＯ２がＭｎ２ＳｉＯ４と同程度生じていることから、化成処理性が十分に改善されているとは言い難い。 However, when the pickling or brush treatment is performed, the manufacturing cost increases due to an increase in the number of steps. Although the dew point control is performed in a continuous annealing furnace, as long as the examples shown in the literature are seen, even if the dew point is controlled, the SiO 2 / Mn 2 SiO 4 ratio in the outermost layer is about 1.0. Further, since SiO 2 that inhibits the formation of the chemical conversion film is generated to the same extent as Mn 2 SiO 4 , it is difficult to say that the chemical conversion property is sufficiently improved.

また当該技術は、残留オーステナイトを活用した鋼板であり、残留オーステナイトを確保するためＣ，Ｓｉ，Ｍｎ，Ａｌ等の合金元素を多く含んでおり、そのため溶接性に劣るという問題がある。   In addition, this technique is a steel sheet using retained austenite, and contains a large amount of alloying elements such as C, Si, Mn, and Al in order to secure retained austenite, and therefore has a problem of poor weldability.

特許文献６では、ＸＰＳで鋼板表面を観察し、酸化物を構成するＳｉとＭｎの比（Ｓｉ／Ｍｎ）を１以下に抑えて化成処理性を高める技術が提案されている。   Patent Document 6 proposes a technique for observing the surface of a steel sheet by XPS and suppressing the ratio of Si to Mn (Si / Mn) constituting the oxide to 1 or less to improve chemical conversion property.

Ｓｉ／Ｍｎ比が１以下である鋼として、例えばＳｉ量がほぼゼロの軟鋼が化成処理性に優れていることは一般に知られている。しかし上述の通り、高強度と延性を共に高めるにはＳｉをある程度含有させる必要があり、Ｓｉ量を低減してＳｉ／Ｍｎ比を１以下にするには限界がある。また適量のＳｉ量を確保しつつＭｎ量を制御してＳｉ／Ｍｎ比を１以下にした場合でも、良好な化成処理性を発揮する鋼板を安定して得ることができないことがわかった。
特開平５−７８７５２号公報 特許２９５１４８０号公報 特許３２６６３２８号公報 特許３０４９１４７号公報 特開２００３−２０１５３８号公報 特開平４−２７６０６０号公報 As steel having a Si / Mn ratio of 1 or less, for example, it is generally known that mild steel having almost no Si content is excellent in chemical conversion treatment. However, as described above, in order to increase both the high strength and the ductility, it is necessary to contain Si to some extent, and there is a limit in reducing the Si amount and making the Si / Mn ratio 1 or less. Further, it was found that a steel sheet exhibiting good chemical conversion treatment properties could not be obtained stably even when the Si / Mn ratio was controlled to 1 or less by controlling the Mn amount while securing an appropriate amount of Si.
Japanese Patent Laid-Open No. 5-78752 Japanese Patent No. 2951480 Japanese Patent No. 3266328 Japanese Patent No. 3049147 JP 2003-201538 A JP-A-4-276060

本発明は上記事情に鑑みてなされたものであって、その目的は、引張強度が５５０ＭＰａ以上で優れた塗膜密着性を有し、更には優れた溶接性も確保できる冷延鋼板を提供することにある。   The present invention has been made in view of the above circumstances, and an object thereof is to provide a cold-rolled steel sheet having excellent coating film adhesion at a tensile strength of 550 MPa or more and further ensuring excellent weldability. There is.

本発明に係る高強度冷延鋼板とは、質量％で（化学成分について以下同じ）、Ｃ：１％以下（０％を含まない）、Ｓｉ：０．０５〜２％、Ｍｎ：１〜５％を含み、且つ下記式（１）を満たす引張強度が５５０ＭＰａ以上のフェライト−焼戻マルテンサイト系のＤＰ（Dual Phase）鋼板であって、
（I）鋼板表面において、円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物が１０個／１００μｍ２以上存在すると共に、Ｓｉを主体とする酸化物の鋼板表面被覆率が１０％以下であるところに特徴がある（以下「本発明鋼板１」ということがある）。 The high-strength cold-rolled steel sheet according to the present invention is expressed by mass% (the same applies to chemical components below), C: 1% or less (excluding 0%), Si: 0.05-2%, Mn: 1-5 And a ferrite-tempered martensite DP (Dual Phase) steel sheet having a tensile strength satisfying the following formula (1) of 550 MPa or more,
(I) On the surface of the steel sheet, there are 10/100 μm 2 or more Si-Mn composite oxides having an equivalent circle diameter of 5 μm or less, and the steel sheet surface coverage of the oxide mainly composed of Si is 10% or less. There is a characteristic (hereinafter sometimes referred to as “the steel sheet 1 of the present invention”).

［Si］／［Mn］≦ 0.4 …（１）
｛式中［Si］はSi含有量（質量％）を示し、［Mn］はMn含有量（質量％）を示す｝ [Si] / [Mn] ≦ 0.4 (1)
{In the formula, [Si] indicates the Si content (% by mass) and [Mn] indicates the Mn content (% by mass)}

尚、上記Ｓｉを主体とする酸化物とは、酸化物を構成する酸素以外の元素のうちＳｉが原子比で７０％以上占めるものをいう。また当該酸化物は、分析の結果、非晶質であると考えられる。   The oxide mainly composed of Si is an element other than oxygen constituting the oxide, in which Si occupies 70% or more by atomic ratio. Further, the oxide is considered to be amorphous as a result of analysis.

Ｓｉを主体とする酸化物の鋼板表面被覆率は、後述する実施例で示す通り、抽出レプリカ法で処理したサンプルをＴＥＭ（transmission electron microscope）で観察し、ＥＤＸ（Energy Dispersive X-ray）分析でＳｉ、Ｏ（酸素）、Ｍｎ、Ｆｅのマッピングおよび定量分析を行い、このデータを用いて画像解析法により求めた。尚、抽出レプリカのＴＥＭ観察が煩雑であれば、ＡＥＳ（auger electron spectroscopy）で倍率：２０００〜５０００倍のＳｉ、Ｏ、ＭｎおよびＦｅについて表面マッピングをを行い、そのデータを画像解析してもよい。   As shown in the examples to be described later, the surface coverage of the oxide mainly composed of Si is obtained by observing a sample processed by the extraction replica method with a transmission electron microscope (TEM) and analyzing with an EDX (Energy Dispersive X-ray) analysis. Mapping and quantitative analysis of Si, O (oxygen), Mn, and Fe were performed, and the data was obtained by an image analysis method. If TEM observation of the extracted replica is complicated, surface mapping may be performed for Si, O, Mn, and Fe with a magnification of 2000 to 5000 times by AES (auger electron spectroscopy), and the data may be subjected to image analysis. .

上記課題を解決し得た本発明の別の鋼板は、Ｃ：１％以下（０％を含まない）、Ｓｉ：２％以下（０％を含まない）、Ｍｎ：１〜５％を含み、且つ引張強度が５５０ＭＰａ以上のフェライト−焼戻マルテンサイト系のＤＰ（Dual Phase）鋼板であって、
（II）ＳＥＭ（scanning electron microscope）を用いて２０００倍で鋼板表面近傍の断面を観察したときに、任意の１０視野において幅３μｍ以下で深さ５μｍ以上のクラックが存在しないところに特徴を有している（以下「本発明鋼板２」ということがある）。 Another steel sheet of the present invention that can solve the above problems includes C: 1% or less (not including 0%), Si: 2% or less (not including 0%), Mn: 1 to 5%, And a ferrite-tempered martensitic DP (Dual Phase) steel sheet having a tensile strength of 550 MPa or more,
(II) When a cross section near the surface of the steel sheet is observed at a magnification of 2000 using a scanning electron microscope (SEM), it is characterized in that there are no cracks with a width of 3 μm or less and a depth of 5 μm or more in any 10 fields of view. (Hereinafter sometimes referred to as “the present steel plate 2”).

尚、上記クラックの幅および深さとは、ＳＥＭ（日立製作所製 Ｓ−４５００）を用いて２０００倍で鋼板断面の表面近傍を観察したときの、図１（鋼板断面概略図）に示す部分をいうものとする。   The width and depth of the cracks refer to the portion shown in FIG. 1 (schematic cross section of steel plate) when the vicinity of the surface of the steel plate cross section is observed at 2000 times using SEM (S-4500 manufactured by Hitachi, Ltd.). Shall.

上記課題を解決し得た本発明の更に別の鋼板は、Ｃ：１％以下（０％を含まない）、Ｓｉ：０．０５〜２％、Ｍｎ：１〜５％、および上記式（１）を満たす引張強度が５５０ＭＰａ以上のフェライト−焼戻マルテンサイト系のＤＰ（Dual Phase）鋼板であって、
上記要件（I）および（II）を満たすところに特徴を有している（以下「本発明鋼板３」ということがある）。 Still another steel sheet of the present invention that can solve the above problems is C: 1% or less (excluding 0%), Si: 0.05-2%, Mn: 1-5%, and the above formula (1) A ferrite-tempered martensitic DP (Dual Phase) steel sheet with a tensile strength satisfying
It is characterized by satisfying the above requirements (I) and (II) (hereinafter sometimes referred to as “the steel sheet 3 of the present invention”).

これらの鋼板において、更なる付加的要件として、下記式（２）および（３）を満たすように成分調整すれば、優れた溶接性も確保できるので好ましい。   In these steel plates, as a further additional requirement, it is preferable to adjust the components so as to satisfy the following formulas (2) and (3), since excellent weldability can be secured.

[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.25 …（２）
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.34 …（３）
｛式中[Ｃ]，[Si]，[Mn]，[Ｐ]，[Ｓ]は各元素の含有量（質量％）を示す｝ [P] +3 [S] +1.54 [C] <0.25 (2)
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.34 (3)
{Wherein [C], [Si], [Mn], [P], [S] represents the content (% by mass) of each element}

本発明の鋼板は、５５０ＭＰａ以上の強度を確保しつつ、優れた化成処理性を発揮するか、および／または規定の微細クラックが抑制されて優れた塗膜密着性を発揮し、更には溶接性を確保できる自動車用に最適な鋼板を、クラッドを構成したり高価格元素を使用することなく効率良く実現することができる。   The steel sheet of the present invention exhibits excellent chemical conversion properties while ensuring a strength of 550 MPa or more and / or exhibits excellent coating film adhesion by suppressing specified fine cracks, and further has weldability. It is possible to efficiently realize a steel plate that is optimal for automobiles that can secure the above-mentioned without using a clad or using a high-priced element.

塗膜密着性に優れた鋼板を得るべく検討したところ、特に、下記要件（I）および／または（II）を満足させればよいことを見出し本発明に想到した。更にこれらの要件を満足させると共に、５５０ＭＰａ以上の引張強度と延性を確保するため成分組成や製造条件についても検討を行った。   As a result of studying to obtain a steel sheet having excellent coating film adhesion, it has been found that the following requirements (I) and / or (II) may be satisfied. Furthermore, while satisfying these requirements, the component composition and production conditions were also examined in order to ensure a tensile strength and ductility of 550 MPa or more.

（I）鋼板表面において、
(i）円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物を１０個／１００μｍ２以上存在させ、かつ
(ii）Ｓｉを主体とする酸化物（酸化物を構成する酸素以外の元素のうちＳｉが原子比で７０％以上占める酸化物）の鋼板表面被覆率を１０％以下とする。 (I) On the steel sheet surface,
(i) 10/100 μm 2 or more Si—Mn composite oxide having an equivalent circle diameter of 5 μm or less is present, and
(ii) The steel sheet surface coverage of an oxide mainly composed of Si (an oxide in which Si is 70% or more by atomic ratio among elements other than oxygen constituting the oxide) is 10% or less.

（II）ＳＥＭを用いて２０００倍で鋼板表面近傍の断面を観察したときに、任意の１０視野において、幅３μｍ以下で深さ５μｍ以上のクラックが存在しないようにする。   (II) When observing a cross section in the vicinity of the steel sheet surface at a magnification of 2000 using an SEM, no cracks having a width of 3 μm or less and a depth of 5 μm or more are present in any 10 visual fields.

以下、まず上記要件（I)，(II）を規定した理由について詳述する。   The reason why the requirements (I) and (II) are specified will be described in detail below.

＜鋼板表面における円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物：１０個／１００μｍ２以上＞
本発明者らは、塗膜密着性に優れた高強度鋼板を得るべく以前から研究を進めており、Ｓｉを比較的多く含む鋼板の化成処理性向上技術について、既に提案している（特願２００３−１０６１５２号）。この技術は、焼鈍雰囲気を制御することで、化成処理性に悪影響を及ぼす非晶質のＳｉ酸化物を細かく分散させることにより化成処理性の向上を図ったものである。しかしＳｉ濃度の比較的低い領域では、主な酸化物として、非晶質のＳｉ酸化物ではなくＳｉ−Ｍｎ複合酸化物が生成する。この複合酸化物も、非晶質のＳｉ酸化物と同様に塗膜密着性を低下させると考えられる。そこで、該Ｓｉ−Ｍｎ複合酸化物を化成処理性の向上に積極的に活用することはできないかと考え、その線に沿って研究を進めてきた。 <Si-Mn composite oxide having an equivalent circle diameter of 5 μm or less on the steel sheet surface: 10/100 μm 2 or more>
The present inventors have been researching for a long time to obtain a high-strength steel sheet excellent in coating film adhesion, and have already proposed a chemical conversion treatment improving technique for a steel sheet containing a relatively large amount of Si (Japanese Patent Application). 2003-106152). This technique aims to improve chemical conversion treatment by finely dispersing amorphous Si oxide that adversely affects chemical conversion treatment by controlling the annealing atmosphere. However, in a region where the Si concentration is relatively low, an Si—Mn composite oxide is generated as a main oxide, not an amorphous Si oxide. This composite oxide is also considered to reduce the adhesion of the coating film in the same manner as the amorphous Si oxide. Then, the Si-Mn composite oxide was thought to be actively utilized for improving chemical conversion treatment, and research has been conducted along that line.

その結果、鋼板表層部に形成される鉄系酸化物基地中に、該Ｓｉ−Ｍｎ複合酸化物を微細分散させて、後述する通り、りん酸亜鉛結晶の核生成サイトとして作用する「酸化物界面の不均一場」を形成することで、化成処理性を高めることができた。本発明で規定するＳｉ−Ｍｎ複合酸化物が、りん酸亜鉛結晶の生成核に有効である理由は明確ではないが、次の様に考えられる。   As a result, the Si-Mn composite oxide is finely dispersed in the iron-based oxide matrix formed on the surface layer portion of the steel sheet, and as described later, the “oxide interface that acts as a nucleation site for zinc phosphate crystals. The chemical conversion processability could be improved by forming a “non-uniform field”. The reason why the Si—Mn composite oxide defined in the present invention is effective for the nuclei of zinc phosphate crystals is not clear, but is considered as follows.

化成処理工程において、りん酸亜鉛結晶は、例えば結晶粒界や予め表面調整処理時に鋼板表面に付着させたＴｉコロイド周辺などに形成される「電気化学的不均一場」に生成し易いことが知られている。そして本発明においても、Ｓｉ−Ｍｎ複合酸化物の周辺に電気化学的な不均一場が形成されることで、化成処理時にりん酸亜鉛結晶が付着しやすくなり良好な化成処理性が発揮されるものと考えられる。   In the chemical conversion treatment process, it is known that zinc phosphate crystals are likely to be generated in the “electrochemical inhomogeneous field” formed around the grain boundaries and around the Ti colloid previously deposited on the steel plate surface during the surface conditioning treatment. It has been. Also in the present invention, an electrochemical heterogeneous field is formed around the Si-Mn composite oxide, so that zinc phosphate crystals are easily attached during the chemical conversion treatment, and good chemical conversion treatment performance is exhibited. It is considered a thing.

化成処理後のりん酸亜鉛結晶は、塗膜密着性の観点から数μｍ以下であることが好ましいとされている。よって上述の電気化学的不均一場も、数μｍオーダーで形成されることが望ましいと考えられる。そこで円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物を１００μｍ２に１０個以上存在させて（平均して１０μｍ２に１個以上存在させて）、該複合酸化物粒子の平均粒子間隔が数μｍとなるようにし、上記サイズの電気化学的不均一場が形成されやすい状態とした。 It is said that the zinc phosphate crystal after the chemical conversion treatment is preferably several μm or less from the viewpoint of coating film adhesion. Therefore, it is considered that the above-mentioned electrochemical non-uniform field is desirably formed on the order of several μm. Therefore, 10 or more Si-Mn composite oxides having an equivalent circle diameter of 5 μm or less are present in 100 μm 2 (on average, one or more in 10 μm 2 ), and the average particle spacing of the composite oxide particles is several μm. Thus, an electrochemical heterogeneous field having the above size is easily formed.

尚、存在する全てのＳｉ−Ｍｎ複合酸化物において、電気化学的不均一場が有効に形成されるとは限らないので、好ましくは１００μｍ２あたり５０個以上、より好ましくは１００個以上、さらに好ましくは１５０個以上の上記Ｓｉ−Ｍｎ複合酸化物を存在させるのがよい。該Ｓｉ−Ｍｎ複合酸化物としては、例えばＭｎ２ＳｉＯ４が挙げられる。また観察できるＳｉ−Ｍｎ複合酸化物のサイズは、５０ｎｍ程度が限界であると思われる。 In all Si-Mn composite oxides present, the electrochemical heterogeneous field is not necessarily formed effectively, and is preferably 50 or more, more preferably 100 or more, even more preferably 100 μm 2. It is preferable that 150 or more Si-Mn composite oxides exist. An example of the Si—Mn composite oxide is Mn 2 SiO 4 . Also, the size of the observable Si-Mn composite oxide seems to be about 50 nm.

＜Ｓｉを主体とする酸化物の鋼板表面被覆率：１０％以下＞
りん酸亜鉛結晶の生成核として有効なＳｉ−Ｍｎ複合酸化物を適量存在させても、化成処理を阻害するその他の物質が存在すれば、優れた化成処理性は発揮されず、結果として塗膜密着性に劣るものとなる。 <Stainless steel sheet surface coverage of oxide mainly composed of Si: 10% or less>
Even if an appropriate amount of Si-Mn composite oxide that is effective as a nucleus for formation of zinc phosphate crystals is present, if there is another substance that inhibits chemical conversion treatment, excellent chemical conversion treatment performance will not be exhibited. It becomes inferior to adhesiveness.

上述した様に、Ｓｉを主体とする酸化物が鋼板表面に存在すると、当該部位には、りん酸亜鉛結晶が生成せず化成処理性が著しく低下する。そこで、Ｓｉを主体とする酸化物の鋼板表面被覆率を１０％以下とした。   As described above, when an oxide mainly composed of Si is present on the surface of the steel sheet, zinc phosphate crystals are not generated at the site, and the chemical conversion treatment performance is significantly reduced. Therefore, the steel sheet surface coverage of the oxide mainly composed of Si is set to 10% or less.

尚、本発明者らは、上述の通りＳｉを主体とする酸化物を細かく分散させて化成処理性を高める技術を提案しているが、Ｓｉ−Ｍｎ複合酸化物の前記作用を活用する本発明においては、酸化物を極力存在させない方が好ましいことがわかった。よってＳｉを主体とする酸化物の鋼板表面被覆率は、５％以下に抑えることがより好ましく、最も好ましくは０％である。   The inventors of the present invention have proposed a technique for improving the chemical conversion property by finely dispersing an oxide mainly composed of Si as described above. However, the present invention utilizes the above-described action of the Si—Mn composite oxide. It has been found that it is preferable that no oxide exist as much as possible. Therefore, the steel sheet surface coverage of the oxide mainly composed of Si is more preferably suppressed to 5% or less, and most preferably 0%.

＜ＳＥＭを用いて2000倍で鋼板表面近傍の断面を観察したときに、任意の10視野において、幅３μｍ以下で深さ５μｍ以上のクラックが存在しないこと＞
鋼板表面に鋭利なクラックが存在すると、化成処理時に当該部位にりん酸亜鉛結晶が付着せず、その結果、当該部位の腐食が進行しやすくなり、塗膜密着性が低下すると考えられる。つまり塗膜密着性を高めるには、りん酸亜鉛結晶の付着しない鋭利なクラックを極力抑制することが重要となる。 <When observing a cross section near the steel sheet surface at 2000 times using SEM, there should be no cracks with a width of 3 μm or less and a depth of 5 μm or more in any 10 fields of view>
If sharp cracks are present on the surface of the steel plate, it is considered that zinc phosphate crystals do not adhere to the site during the chemical conversion treatment, and as a result, corrosion of the site is likely to proceed, resulting in a decrease in coating film adhesion. That is, in order to improve the adhesion of the coating film, it is important to suppress as much as possible sharp cracks to which zinc phosphate crystals do not adhere.

本発明者らは、既に、Ｓｉと酸素を含む線状化合物（幅３００ｎｍ以下）の存在深さを１０μｍ以下にすることで塗膜密着性を高める技術を提案している。該技術では、連続焼鈍後に酸洗を施さないことを前提としているが、鋼板にはむしろ連続焼鈍後に酸洗を施す場合の方が多く、その場合には、線状酸化物が除去されてクラックが生じる。   The present inventors have already proposed a technique for improving the adhesion of a coating film by setting the existing depth of a linear compound (width: 300 nm or less) containing Si and oxygen to 10 μm or less. In this technique, it is assumed that pickling is not performed after continuous annealing, but the steel sheet is more often subjected to pickling after continuous annealing, in which case, the linear oxide is removed and cracks occur. Occurs.

クラック深さと線状酸化物の定量的な関係は明確ではないが、線状酸化物が、上記の通り酸溶解されるか、又は機械的に脱落してクラックが生じると考えられ、上記線状酸化物が除去されたあとも、酸等によりクラック部分の溶解が進むので、線状酸化物のサイズよりもクラックの方が深いと考えられる。   Although the quantitative relationship between the crack depth and the linear oxide is not clear, it is considered that the linear oxide is dissolved in the acid as described above or mechanically dropped to cause cracks. Even after the oxide is removed, the crack portion is dissolved by an acid or the like, so the crack is considered deeper than the size of the linear oxide.

そこで本発明では、上記提案済の技術のように線状酸化物の存在深さを規定するよりも、クラックを制御する方が塗膜密着性をより確実に高めることができると考え、制御すべきクラックの形態について調べたところ、クラックの幅が、りん酸亜鉛結晶粒径と同程度かそれ以下であると、該クラックにりん酸亜鉛結晶が付着し難く、また、特に深さが５μｍ以上のクラックにりん酸亜鉛結晶が付着し難いことから、幅３μｍ以下でかつ深さが５μｍ以上のクラックを抑制の対象とした。   Therefore, in the present invention, it is considered that controlling the cracks can more reliably improve the adhesion of the coating film than controlling the depth of existence of the linear oxide as in the proposed technique. When the shape of the power crack was examined, if the crack width was the same as or smaller than the zinc phosphate crystal grain size, it was difficult for the zinc phosphate crystal to adhere to the crack, and the depth was particularly 5 μm or more. Since zinc phosphate crystals hardly adhere to the cracks, cracks having a width of 3 μm or less and a depth of 5 μm or more were targeted for suppression.

そして上記クラックが、ＳＥＭを用いて２０００倍で鋼板表面近傍の断面を観察したときに、任意の１０視野において存在しないことを要件とした。   And when the said crack observed the cross section near the steel plate surface by 2000 times using SEM, it made it a requirement that it did not exist in arbitrary 10 visual fields.

本発明では、上記酸化物を効率良く析出させると共に規定するクラックを抑制し、また高強度鋼板としての特性を備えるため化学成分を下記の通り規定した。   In the present invention, the chemical components are specified as follows in order to efficiently precipitate the oxides and suppress the specified cracks and to provide the characteristics as a high-strength steel plate.

［Si］／［Mn］≦ 0.4 …（１）
｛式中［Si］はSi含有量（質量％）を示し、［Mn］はMn含有量（質量％）を示す｝
上述の通り、Ｓｉを主体とする酸化物は、化成処理性に悪影響を及ぼすため、該酸化物を細かく分散させるよりも極力抑制する方が好ましい。そこで本発明者らは［Si］／［Mn］の比率を０．４以下とすることで、Ｓｉを主体とする酸化物を抑制する。［Si］／［Mn］は好ましくは０．３％以下である。 [Si] / [Mn] ≦ 0.4 (1)
{In the formula, [Si] indicates the Si content (% by mass) and [Mn] indicates the Mn content (% by mass)}
As described above, since an oxide mainly composed of Si adversely affects chemical conversion properties, it is preferable to suppress it as much as possible rather than finely dispersing the oxide. Therefore, the inventors suppress the oxide mainly composed of Si by setting the ratio of [Si] / [Mn] to 0.4 or less. [Si] / [Mn] is preferably 0.3% or less.

Ｃ：１％以下（０％を含まない）
Ｃは強度確保に必要な元素であり、０．０５％以上含有させるのがよいが、過剰に存在すると溶接性が低下する。よってＣ含有量は１％以下に抑える。好ましくは０．２３％以下、更に好ましくは０．１５％以下である。 C: 1% or less (excluding 0%)
C is an element necessary for ensuring the strength and should be contained in an amount of 0.05% or more. However, if it is present in excess, weldability is lowered. Therefore, C content is suppressed to 1% or less. Preferably it is 0.23% or less, More preferably, it is 0.15% or less.

Ｓｉ：０．０５〜２％ （本発明鋼板１及び本発明鋼板３の場合）
Ｓｉ：２％以下（０％を含まない） （本発明鋼板２の場合）
Ｓｉは、延性を低下させずに強度を高めることのできる元素であるため含んでいてもよいが、上記（I）で規定する量の円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物を確保するには、少なくとも０．０５％のＳｉが必要であり、好ましくは０．１５％以上、より好ましくは０．３％以上、更に好ましくは０．５％以上である。一方、Ｓｉ含有量が過剰になると、固溶強化作用が過大となって圧延負荷が増大するため２％以下に抑える。好ましく１．５％以下である。 Si: 0.05-2% (in the case of the steel plate 1 of the present invention and the steel plate 3 of the present invention)
Si: 2% or less (not including 0%) (In the case of the steel sheet 2 of the present invention)
Si may be included because it is an element that can increase the strength without reducing ductility. However, an Si-Mn composite oxide having an equivalent circle diameter of 5 μm or less as defined in (I) above is secured. Requires at least 0.05% Si, preferably 0.15% or more, more preferably 0.3% or more, and still more preferably 0.5% or more. On the other hand, if the Si content is excessive, the solid solution strengthening action becomes excessive and the rolling load increases, so the content is suppressed to 2% or less. Preferably it is 1.5% or less.

Ｍｎ：１〜５％
Ｍｎも強度確保に必要な元素であり、１％以上、好ましくは２％以上含有させる。しかし過剰になると延性が劣化するため、５％以下、好ましくは３．５％以下に抑える。 Mn: 1 to 5%
Mn is also an element necessary for ensuring the strength, and is contained at 1% or more, preferably 2% or more. However, if it becomes excessive, ductility deteriorates, so it is suppressed to 5% or less, preferably 3.5% or less.

本発明で規定する含有元素は上記の通りであり、残部成分は実質的にＦｅであるが、鋼中に、原料、資材、製造設備等の状況によって持ち込まれる元素としてとして１％以下のＡｌ、０．０１％以下のＮ（窒素）、０．０１％以下のＯ（酸素）等の不可避不純物が含まれることが許容されるのは勿論のこと、前記本発明の作用に悪影響を与えない範囲で、更に他の元素としてＣｒ、Ｍｏ、Ｎｉ、Ｔｉ、Ｎｂ、Ｖ、ＰまたはＢを積極的に含有させることも可能である。   The contained elements specified in the present invention are as described above, and the remaining component is substantially Fe. However, 1% or less of Al as an element brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, Of course, inevitable impurities such as N (nitrogen) of 0.01% or less and O (oxygen) of 0.01% or less are allowed to be included, and a range that does not adversely affect the operation of the present invention. In addition, Cr, Mo, Ni, Ti, Nb, V, P, or B can be actively added as other elements.

即ちＣｒ、Ｍｏ、Ｎｉ、Ｔｉ、Ｎｂ、Ｖ、Ｐ、Ｂは、鋼板の強度を高める観点から添加してもよく、それぞれＣｒ：０．１％以上、Ｍｏ：０．１％以上、Ｎｉ：０．１％以上、Ｔｉ：０．００５％以上、Ｎｂ：０．００５％以上、Ｖ：０．０００５％以上、Ｐ：０．００５％以上、Ｂ：０．０００３％以上含有させてもよいが、過剰に添加すると延性低下や溶接性の低下を招くため、Ｃｒ、Ｍｏ、Ｎｉはそれぞれ１％以下、Ｔｉ、Ｎｂ、Ｐはそれぞれ０．１％以下、Ｖ、Ｂはそれぞれ０．０１％以下に抑えることが好ましい。   That is, Cr, Mo, Ni, Ti, Nb, V, P, and B may be added from the viewpoint of increasing the strength of the steel sheet. Cr: 0.1% or more, Mo: 0.1% or more, Ni: 0.1% or more, Ti: 0.005% or more, Nb: 0.005% or more, V: 0.0005% or more, P: 0.005% or more, B: 0.0003% or more However, if added excessively, ductility and weldability are deteriorated. Therefore, Cr, Mo and Ni are each 1% or less, Ti, Nb and P are each 0.1% or less, and V and B are each 0.01%. It is preferable to keep it below.

[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.25 …（２）
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.34 …（３）
｛式中[Ｃ]，[Si]，[Mn]，[Ｐ]，[Ｓ]は各元素の含有量（質量％）を示す｝
上記式（２）および（３）の左辺はスポット溶接性を評価するパラメータとして知られており｛田中ら：日本鋼管技報，No.105（1984）、Heuschkel,J.：Weld J26（10)，P560Ｓ(1947）｝、該パラメータ値が高くなるほど溶接性が低下する傾向にある。本発明では、上記式（２）において（[Ｐ]＋３[Ｓ]＋1.54[Ｃ]）が０．２５以上、または（[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ]）が０．３４以上の場合に、スポット溶接性が低下することを確認している。 [P] +3 [S] +1.54 [C] <0.25 (2)
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.34 (3)
{Wherein [C], [Si], [Mn], [P], [S] represents the content (% by mass) of each element}
The left side of the above formulas (2) and (3) is known as a parameter for evaluating spot weldability {Tanaka et al .: Nippon Steel Pipe Technical Report, No. 105 (1984), Heuschkel, J .: Weld J26 (10) , P560S (1947)}, the higher the parameter value, the lower the weldability. In the present invention, in the above formula (2), ([P] +3 [S] +1.54 [C]) is 0.25 or more, or ([C] + [Si] / 30 + [Mn] / 20 + 2 [P]) It has been confirmed that spot weldability decreases when +4 [S]) is 0.34 or more.

本発明では、引張強度が５５０ＭＰａ以上（好ましくは７５０ＭＰａ以上、より好ましくは９００ＭＰａ以上）の鋼板を対象とするが、この様な強度を確保すべくＣ、Ｓｉ、Ｍｎの各含有量を調整したりＰを含有させる場合に、併せて溶接性を確保するには、強度レベルに応じて下記範囲を満足させることが望ましい。   In the present invention, a steel sheet with a tensile strength of 550 MPa or more (preferably 750 MPa or more, more preferably 900 MPa or more) is targeted. However, in order to ensure such strength, the contents of C, Si, and Mn are adjusted. In order to ensure weldability when P is contained, it is desirable to satisfy the following range according to the strength level.

ＴＳ：５５０〜６５０ＭＰａの場合
[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.14
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.21
ＴＳ：６５０超〜７５０ＭＰａの場合
[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.18
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.27
ＴＳ：７５０超〜１０５０ＭＰａの場合
[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.22
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.30
ＴＳ：１０５０ＭＰａ超の場合
[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.25
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.34 TS: 550 to 650 MPa
[P] +3 [S] +1.54 [C] <0.14
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.21
TS: More than 650 to 750 MPa
[P] +3 [S] +1.54 [C] <0.18
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.27
TS: More than 750 to 1050 MPa
[P] +3 [S] +1.54 [C] <0.22
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.30
TS: More than 1050 MPa
[P] +3 [S] +1.54 [C] <0.25
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.34

本発明は、フェライト−焼戻マルテンサイト系のＤＰ（Dual Phase：デュアルフェーズ）鋼板を対象とする。上記組織のみ（即ち、フェライトと焼戻マルテンサイト）からなるものの他、本発明の製造過程で必然的に残存し得るパーライト、ベイナイト、残留オーステナイトが、本発明の作用を損なわない範囲で含まれる場合もある。しかし、これらは少なければ少ないほど好ましい。   The present invention is directed to a ferrite-tempered martensitic DP (Dual Phase) steel sheet. In addition to the above structure (ie, ferrite and tempered martensite), pearlite, bainite, and retained austenite that may inevitably remain in the production process of the present invention are included within a range that does not impair the function of the present invention. There is also. However, the smaller these, the better.

化成処理性を高めるべく、上記要件（I）として規定する通り鋼板表面に析出する酸化物の形態を制御するには、成分組成を満足させる他、製造工程において、熱間圧延後に、液温が７０〜９０℃で１〜１８質量％の塩酸に４０秒間以上（好ましくは６０秒間以上）浸漬し、かつ連続焼鈍時の露点を−４０℃以下（好ましくは−４５℃以下）に抑えることが有効である。尚、塩酸への浸漬時間は、塩酸浴が複数設置され、断続的に浸漬する場合には、浸漬時間の合計が４０秒間以上であればよい。   In order to enhance the chemical conversion treatment property, in order to control the form of the oxide deposited on the steel sheet surface as specified in the above requirement (I), in addition to satisfying the component composition, in the production process, after the hot rolling, the liquid temperature is It is effective to immerse in 1 to 18% by mass hydrochloric acid at 70 to 90 ° C. for 40 seconds or more (preferably 60 seconds or more) and suppress the dew point during continuous annealing to −40 ° C. or less (preferably −45 ° C. or less). It is. In addition, as for the immersion time in hydrochloric acid, when a plurality of hydrochloric acid baths are installed and intermittent immersion is performed, the total immersion time may be 40 seconds or more.

また上記要件（II）として規定する通り、クラックを発生させないようにするには、成分組成を満足させる他、製造工程において、熱間圧延の巻き取り温度を５００℃以下（好ましくは４８０℃以下）とし、かつ熱間圧延後、液温が７０〜９０℃で１〜１８質量％の塩酸に４０秒間以上（好ましくは６０秒間以上）浸漬し、連続焼鈍時の露点を−４０℃以下（好ましくは−４５℃以下）とし、更に連続焼鈍時の焼き入れ開始温度（「徐冷終点温度」ということがある。）を５５０℃以下（好ましくは４００〜４５０℃）にすることが有効である。   Further, as specified in the above requirement (II), in order not to generate cracks, in addition to satisfying the component composition, in the manufacturing process, the hot rolling coiling temperature is 500 ° C. or lower (preferably 480 ° C. or lower). And after hot rolling, the liquid temperature is 70 to 90 ° C. and immersed in 1 to 18% by mass of hydrochloric acid for 40 seconds or more (preferably 60 seconds or more), and the dew point during continuous annealing is −40 ° C. or less (preferably It is effective to set the quenching start temperature during continuous annealing (sometimes referred to as “annealing end point temperature”) to 550 ° C. or less (preferably 400 to 450 ° C.).

本発明は、その他の製造条件まで規定するものでなく、通常行われている通り、溶製後に鋳造し熱間圧延を行えばよい。また後述する実施例では連続焼鈍後に酸洗を行っているが、該酸洗の有無も問わない。   The present invention is not limited to other production conditions, and may be cast after melting and hot-rolled as usual. Moreover, in the Example mentioned later, although pickling is performed after continuous annealing, the presence or absence of this pickling is not ask | required.

以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に含まれる。   EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

表１に示す化学成分組成の鋼材を溶製し、鋳造して得られたスラブを用いて熱間圧延を行いその後酸洗を行った。巻取条件と酸洗条件を表２および表３に示す。尚、酸洗は、温度が７０〜９０℃で濃度が１〜１８質量％の塩酸水溶液を用いて行った。その後、冷間圧延を行い、１．４ｍｍ厚の鋼板を得た。そして図１または図２に示す方法で得られた鋼板に連続焼鈍を施した［連続焼鈍における均熱・徐冷後の冷却が水冷（ＷＱ）の場合には図１の方法で行い、該冷却が汽水冷却（ミスト）、ガス吹き付け（ＧＪ）、水冷ロール抜熱による冷却（ＲＱ）の場合には図２に示す方法で行った］。表２，３の加熱温度、徐冷終点温度、焼き戻し温度は図１，２に示す箇所での温度を示している。また露点は連続焼鈍炉の雰囲気露点である。上記冷却後には焼戻しを行った。図１では、焼戻前後のいずれかまたは両方で酸洗を行った。   A steel material having the chemical composition shown in Table 1 was melted and cast using a slab obtained by casting, and then pickled. Tables 2 and 3 show the winding conditions and pickling conditions. The pickling was performed using an aqueous hydrochloric acid solution having a temperature of 70 to 90 ° C. and a concentration of 1 to 18% by mass. Thereafter, cold rolling was performed to obtain a steel plate having a thickness of 1.4 mm. And the steel plate obtained by the method shown in FIG. 1 or FIG. 2 was subjected to continuous annealing [when the cooling after soaking and slow cooling in continuous annealing is water cooling (WQ), the method of FIG. In the case of cooling by brackish water cooling (mist), gas spraying (GJ), cooling by water cooling roll heat removal (RQ), it was performed by the method shown in FIG. The heating temperature, annealing end point temperature, and tempering temperature in Tables 2 and 3 indicate the temperatures at the locations shown in FIGS. The dew point is the atmospheric dew point of the continuous annealing furnace. Tempering was performed after the cooling. In FIG. 1, pickling was performed either before or after tempering.

得られた鋼板を用いて、機械的特性および塗膜密着性を評価した。尚、得られた鋼板は全てフェライトと焼戻マルテンサイトの２相を主体とする組織であった。   Mechanical properties and coating film adhesion were evaluated using the obtained steel plates. The obtained steel sheets all had a structure mainly composed of two phases of ferrite and tempered martensite.

機械的特性は、ＪＩＳ５号試験片を採取して測定し、引張強度（ＴＳ）、Ｅｌ（全伸び）および降伏比（ＹＰ）を求めた。また、伸びフランジ性は、直径１００ｍｍ、板厚１．４ｍｍの円盤状試験片を用いて評価した。具体的には、試験片にφ１０ｍｍの穴をパンチで打ち抜いた後、６０°円錐パンチでバリを上にして穴広げ加工することにより、亀裂貫通時点での穴広げ率（λ）を測定した（鉄鋼連盟規格ＪＦＳＴ １００１）。   Mechanical properties were measured by collecting JIS No. 5 test pieces and determining tensile strength (TS), El (total elongation), and yield ratio (YP). The stretch flangeability was evaluated using a disk-shaped test piece having a diameter of 100 mm and a plate thickness of 1.4 mm. Specifically, after punching out a hole with a diameter of 10 mm in a test piece with a punch, the hole expansion rate (λ) at the time of crack penetration was measured by performing hole expansion processing with a burr facing up with a 60 ° conical punch ( Steel Federation Standard JFST 1001).

塗膜密着性として、化成処理性とクラックの有無を調べた。化成処理性は、鋼板表面の酸化物の状態を下記の様にして調べ、かつ下記条件で化成処理を行って化成処理後の鋼板表面を１０００倍でＳＥＭ観察し、１０視野のりん酸亜鉛結晶の付着状態を調べた。そして１０視野全てにおいてりん酸亜鉛結晶が均一に付着している場合を「○」、りん酸亜鉛結晶の付着していない部分が１視野でも存在する場合を「×」と評価した。   As the coating film adhesion, chemical conversion property and presence of cracks were examined. For the chemical conversion treatment, the state of the oxide on the surface of the steel sheet was examined as follows, and the chemical conversion treatment was performed under the following conditions, and the steel sheet surface after the chemical conversion treatment was observed by SEM at 1000 times, and 10 phosphate crystals of zinc phosphate were observed. The adhesion state of was investigated. The case where the zinc phosphate crystals were uniformly attached in all 10 fields of view was evaluated as “◯”, and the case where the portion where no zinc phosphate crystals were adhered was present as “x”.

・化成処理液：日本パーカライジング社製 パルボンド Ｌ ３０２０
・化成処理工程：脱脂 → 水洗 → 表面調整 → 化成処理
Ｓｉ−Ｍｎ酸化物の個数は、鋼材表面の抽出レプリカ膜を作製し、これを１５０００倍でＴＥＭ観察し（日立製作所製 Ｈ−８００）、任意の２０視野の平均個数（１００μｍ２あたり）を調べた。 ・ Chemical conversion treatment liquid: Palbond L 3020 manufactured by Nihon Parkerizing Co., Ltd.
・ Chemical conversion treatment process: Degreasing → Washing → Surface adjustment → Chemical conversion treatment The number of Si-Mn oxides was prepared by extracting an extracted replica film on the surface of a steel material, and TEM observation was performed at 15000 times (H-800, manufactured by Hitachi, Ltd.) The average number (per 100 μm 2 ) of any 20 visual fields was examined.

Ｓｉを主体とする酸化物の鋼板表面被覆率は、抽出レプリカ法で処理したサンプルをＴＥＭで観察し、画像解析法で被覆率を求めた。尚、抽出レプリカ法は、下記（ａ）〜（ｄ）の手順に添って行った。   As for the steel sheet surface coverage of the oxide mainly composed of Si, the sample treated by the extraction replica method was observed by TEM, and the coverage was determined by an image analysis method. The extraction replica method was performed according to the following procedures (a) to (d).

（ａ）鋼材の表面にカーボンを蒸着させる。     (A) Carbon is vapor-deposited on the surface of the steel material.

（ｂ）サンプル平面上に２〜３ｍｍ角の碁盤目状の切れ目を入れる。     (B) A grid-like cut of 2 to 3 mm square is made on the sample plane.

（ｃ）１０％アセチルアセトン−９０％メタノールエッチング液で腐食させてカーボンを浮上させる。     (C) The carbon is levitated by being corroded with 10% acetylacetone-90% methanol etching solution.

（ｄ）アルコール中に保存して観察に用いる。     (D) Store in alcohol and use for observation.

この様に処理したサンプルを用いてＴＥＭにて、倍率１５０００倍で１０視野分の写真（１３ｃｍ×１１ｃｍ）を撮影し、Ｓｉを主体とする酸化物（酸化物を構成する酸素以外の元素のうちＳｉが原子比で７０％以上占めるもの）の面積を測定し、Ｓｉを主体とする酸化物の被覆率を求めた。   Using the sample processed in this manner, a TEM image of 10 fields of view (13 cm × 11 cm) was taken at a magnification of 15000 times, and an oxide mainly composed of Si (among elements other than oxygen constituting the oxide) The area of Si (at least 70% by atomic ratio) was measured, and the coverage of the oxide mainly composed of Si was determined.

またクラックの有無は、ＳＥＭ（日立製作所製 Ｓ−４５００）を用いて２０００倍で、鋼板断面の表面近傍における任意の１０視野（１視野：１３ｃｍ×１１ｃｍ）を観察して調べた。   The presence or absence of cracks was examined using an SEM (S-4500, manufactured by Hitachi, Ltd.) at a magnification of 2000 and by observing any 10 visual fields (1 visual field: 13 cm × 11 cm) near the surface of the cross section of the steel sheet.

Figure 2005187863
Figure 2005187863

Figure 2005187863
Figure 2005187863

Figure 2005187863
Figure 2005187863

表１〜３から、以下の様に考察できる（尚、下記Ｎｏ．は実験Ｎｏ．を示す）。即ちＮｏ．３２、３８、４０は、本発明鋼板１として規定する要件を満たしているため化成処理性に優れており、塗膜密着性に優れている。該実施例において、クラックを抑制してより優れた塗膜密着性を確保するには、製造条件として特に巻取温度や徐冷終了温度を制御するのがよいことがわかる。   From Tables 1 to 3, the following can be considered (the following No. indicates the experiment No.). That is, no. Since 32, 38, and 40 satisfy the requirements defined as the steel sheet 1 of the present invention, they have excellent chemical conversion properties and excellent coating film adhesion. In this example, it can be seen that, in order to suppress cracks and ensure better coating film adhesion, it is particularly preferable to control the coiling temperature and the annealing end temperature as production conditions.

Ｎｏ．３４〜３６は、本発明鋼板２として規定する要件を満たしているため、クラックが発生しておらず、塗膜密着性に優れた鋼板が得られている。該実施例において、化成処理性を確保して塗膜密着性をより高めるには、成分組成を制御して鋼板表面に析出する酸化物の形態を規定の通りとするのがよい。   No. Since 34-36 satisfy the requirements prescribed | regulated as this invention steel plate 2, the crack has not generate | occur | produced and the steel plate excellent in coating-film adhesiveness is obtained. In this example, in order to secure chemical conversion property and further improve the adhesion of the coating film, it is preferable to control the component composition to make the form of oxide deposited on the steel sheet surface as specified.

これらに対し、Ｎｏ．２９〜３１、３３、３９、４１は、本発明鋼板１〜３の要件をいずれも満たしておらず塗膜密着性に優れていない。即ち、Ｎｏ．２９〜３１は、［Si］/［Mn］比が外れているため本発明で規定する酸化物の形態とならず、また好ましい条件で製造していないためクラックも発生しており、塗膜密着性に劣る。   In contrast, no. 29-31, 33, 39, and 41 do not satisfy any of the requirements of the steel plates 1 to 3 of the present invention and are not excellent in coating film adhesion. That is, no. Nos. 29 to 31 are not in the form of oxides defined in the present invention because the [Si] / [Mn] ratio is off, and cracks are also generated because they are not manufactured under preferable conditions. Inferior to sex.

Ｎｏ．３３、３９、４１は、好ましい条件で製造していないため、本発明で規定する酸化物形態とならず、クラックも発生しているため塗膜密着性に劣る。   No. Since 33, 39, and 41 are not manufactured under preferable conditions, they do not have the oxide form defined in the present invention, and cracks are also generated, so that the coating film adhesion is inferior.

Ｎｏ．３７は規定要件を満足するものであり塗膜密着性に優れているが、鋼板として具備すべき延性に劣るため良好に成形加工できるものでない。   No. No. 37 satisfies the specified requirements and is excellent in coating film adhesion, but is inferior in ductility to be provided as a steel sheet, and cannot be formed satisfactorily.

これらに対しＮｏ．１〜２７は、本発明鋼板３で規定する要件（即ち、本発明鋼板１および本発明鋼板２で規定する要件）と共に、上記式（２）および（３）を満足しているため、優れた化成処理性を確保でき、かつクラックの発生が抑制されて優れた塗膜密着性を発揮でき、更には優れた溶接性も発揮し得る。   No. 1 to 27 satisfy the above-described formulas (2) and (3) together with the requirements defined by the steel plate 3 of the present invention (that is, the requirements defined by the steel plate 1 of the present invention and the steel plate 2 of the present invention). The chemical conversion processability can be secured, the occurrence of cracks is suppressed, and excellent coating film adhesion can be exhibited. Furthermore, excellent weldability can also be exhibited.

Ｎｏ．２８は、本発明鋼板３で規定する要件を満足するものであるが、優れた溶接性を発揮させるには、成分組成において上記式（２）および（３）を満足させるようにするのがよいことがわかる。   No. 28 satisfies the requirements stipulated by the steel sheet 3 of the present invention, but in order to exhibit excellent weldability, it is preferable to satisfy the above formulas (2) and (3) in the component composition. I understand that.

Ｎｏ.１、Ｎｏ．２９およびＮｏ．３４の抽出レプリカをＴＥＭ観察した顕微鏡写真を図４〜６に示す。この図４〜６から、Ｎｏ．１（図４）では、微細なＳｉ−Ｍｎ複合酸化物は存在しているが、Ｓｉを主体とする酸化物は存在していないのがわかる。これに対し、Ｎｏ．２９（図５）では、鋼板表面がＳｉを主体とする酸化物で覆われているのがわかる。またＮｏ．３４（図６）では、粒状のものが観察されたが、これは錆であり、微細なＳｉ−Ｍｎ複合酸化物は析出していない。   No. 1, No. 1 29 and No. Photomicrographs obtained by TEM observation of 34 extracted replicas are shown in FIGS. From FIG. 4 to FIG. In FIG. 1 (FIG. 4), it can be seen that a fine Si—Mn composite oxide exists, but an oxide mainly composed of Si does not exist. In contrast, no. In FIG. 29 (FIG. 5), it can be seen that the steel sheet surface is covered with an oxide mainly composed of Si. No. In FIG. 34 (FIG. 6), the granular thing was observed, but this is rust and the fine Si-Mn complex oxide has not precipitated.

次に、Ｎｏ.１、Ｎｏ．２９およびＮｏ．３４の鋼板表面近傍の断面をＳＥＭで観察した顕微鏡写真を図７〜９に示す。この図７〜９から、Ｎｏ．１（図７）ではクラックが存在していないことがわかる。これに対し、Ｎｏ．２９（図８）では、深さ５μｍのクラックが存在していることがわかる。またＮｏ．３４（図９）はクラックが発生していないため、塗膜密着性に優れることがわかる。   Next, No. 1 and No. 29 and No. The micrograph which observed the cross section of 34 steel plate surface vicinity by SEM is shown to FIGS. From these FIGS. 1 (FIG. 7) shows that there are no cracks. In contrast, no. 29 (FIG. 8), it can be seen that a crack having a depth of 5 μm exists. No. Since 34 (FIG. 9) has no crack, it can be seen that the coating film adhesion is excellent.

更に、Ｎｏ.１、Ｎｏ．２９およびＮｏ．３４の鋼板を化成処理した後の表面をＳＥＭで観察した顕微鏡写真を図１０〜１２に示す。この図１０〜１２から、Ｎｏ．１（図１０）では、りん酸亜鉛結晶が小さく隙間がないことがわかる。これに対し、Ｎｏ．２９（図１１）では、りん酸亜鉛結晶は小さいが隙間が大きく、またＮｏ．３４（図１２）では、りん酸亜鉛結晶が大きくかつ隙間が大きいことがわかる。   Furthermore, No. 1, No. 1 29 and No. The micrograph which observed the surface after performing the chemical conversion treatment of the 34 steel plate with SEM is shown to FIGS. From FIG. 1 (FIG. 10) shows that the zinc phosphate crystals are small and have no gaps. In contrast, no. 29 (FIG. 11), the zinc phosphate crystal is small but the gap is large. 34 (FIG. 12) shows that the zinc phosphate crystals are large and the gaps are large.

鋼板断面におけるクラックを模式的に示した図である。It is the figure which showed typically the crack in a steel plate cross section. 実施例における製造工程（一部）を示す図である。It is a figure which shows the manufacturing process (part) in an Example. 実施例における別の製造工程（一部）を示す図である。It is a figure which shows another manufacturing process (part) in an Example. 実施例におけるＮｏ．１のＴＥＭ観察写真（抽出レプリカ，倍率：１５０００倍）である。No. in the examples. 1 is a TEM observation photograph (extraction replica, magnification: 15000 times). 実施例におけるＮｏ．２９のＴＥＭ観察写真（抽出レプリカ，倍率：１５０００倍）である。No. in the examples. 29 TEM observation photographs (extraction replica, magnification: 15000 times). 実施例におけるＮｏ．３４のＴＥＭ観察写真（抽出レプリカ，倍率：１５０００倍）である。No. in the examples. 34 TEM observation photographs (extracted replica, magnification: 15000 times). 実施例におけるＮｏ．１の鋼板表面近傍のＳＥＭ断面観察写真である。No. in the examples. 1 is a SEM cross-sectional observation photograph of the vicinity of the steel sheet surface of No. 1; 実施例におけるＮｏ．２９の鋼板表面近傍のＳＥＭ断面観察写真である。No. in the examples. It is a SEM cross-section observation photograph of 29 steel plate surface vicinity. 実施例におけるＮｏ．３４の鋼板表面近傍のＳＥＭ断面観察写真である。No. in the examples. It is a SEM cross-section observation photograph of 34 steel plate surface vicinity. 実施例におけるＮｏ．１の鋼板表面（化成処理後）のＳＥＭ観察写真である。No. in the examples. It is a SEM observation photograph of the steel plate surface of 1 (after chemical conversion treatment). 実施例におけるＮｏ．２９の鋼板表面（化成処理後）のＳＥＭ観察写真である。No. in the examples. It is a SEM observation photograph of the 29 steel plate surface (after chemical conversion treatment). 実施例におけるＮｏ．３４の鋼板表面（化成処理後）のＳＥＭ観察写真である。No. in the examples. It is a SEM observation photograph of 34 steel plate surfaces (after chemical conversion treatment).

Claims (4)

質量％で（化学成分について以下同じ）、
Ｃ ：１％以下（０％を含まない）、
Ｓｉ：０．０５〜２％、
Ｍｎ：１〜５％を含み、且つ
下記式（１）を満たすフェライト−焼戻マルテンサイト系のＤＰ（Dual Phase）鋼板であって、
鋼板表面において、円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物が１０個／１００μｍ２以上存在すると共に、Ｓｉを主体とする酸化物の鋼板表面被覆率が１０％以下であり、引張強度が５５０ＭＰａ以上であることを特徴とする塗膜密着性に優れた高強度冷延鋼板。
［Si］／［Mn］≦ 0.4 …（１）
｛式中［Si］はSi含有量（質量％）を示し、［Mn］はMn含有量（質量％）を示す｝ % By mass (the same applies to chemical components)
C: 1% or less (excluding 0%),
Si: 0.05-2%
A ferrite-tempered martensitic DP (Dual Phase) steel sheet containing Mn: 1 to 5% and satisfying the following formula (1):
On the surface of the steel sheet, there are 10/100 μm 2 or more Si-Mn composite oxides having an equivalent circle diameter of 5 μm or less, the steel sheet surface coverage of the oxide mainly composed of Si is 10% or less, and the tensile strength is 550 MPa. A high-strength cold-rolled steel sheet excellent in coating film adhesion characterized by the above.
[Si] / [Mn] ≦ 0.4 (1)
{In the formula, [Si] indicates the Si content (% by mass) and [Mn] indicates the Mn content (% by mass)} Ｃ：１％以下（０％を含まない）、
Ｓｉ：２％以下（０％を含まない）、
Ｍｎ：１〜５％を含む
フェライト−焼戻マルテンサイト系のＤＰ（Dual Phase）鋼板であって、
ＳＥＭを用いて２０００倍で鋼板表面近傍の断面を観察したときに、任意の１０視野において幅３μｍ以下で深さ５μｍ以上のクラックが存在せず、引張強度が５５０ＭＰａ以上であることを特徴とする塗膜密着性に優れた高強度冷延鋼板。 C: 1% or less (excluding 0%),
Si: 2% or less (excluding 0%),
A ferrite-tempered martensitic DP (Dual Phase) steel sheet containing Mn: 1 to 5%,
When a cross section near the surface of the steel sheet is observed at a magnification of 2000 using an SEM, cracks having a width of 3 μm or less and a depth of 5 μm or more do not exist in any 10 visual fields, and the tensile strength is 550 MPa or more. High-strength cold-rolled steel sheet with excellent coating film adhesion. Ｃ：１％以下（０％を含まない）、
Ｓｉ：０．０５〜２％、
Ｍｎ：１〜５％含み、且つ
下記式（１）を満たすフェライト−焼戻マルテンサイト系のＤＰ（Dual Phase）鋼板であって、
（I）鋼板表面において、円相当直径５μｍ以下のＳｉ−Ｍｎ複合酸化物が１０個／１００μｍ２以上存在すると共に、Ｓｉを主体とする酸化物の鋼板表面被覆率が１０％以下であり、かつ
（II）ＳＥＭを用いて２０００倍で鋼板表面近傍の断面を観察したときに、任意の１０視野において幅３μｍ以下で深さ５μｍ以上のクラックが存在せず、
引張強度が５５０ＭＰａ以上であることを特徴とする塗膜密着性に優れた高強度冷延鋼板。
［Si］／［Mn］≦ 0.4 …（１）
｛式中［Si］はSi含有量（質量％）を示し、［Mn］はMn含有量（質量％）を示す｝ C: 1% or less (excluding 0%),
Si: 0.05-2%
A ferrite-tempered martensitic DP (Dual Phase) steel sheet containing Mn: 1 to 5% and satisfying the following formula (1):
(I) On the steel sheet surface, there are 10/100 μm 2 or more Si-Mn composite oxides having an equivalent circle diameter of 5 μm or less, and the steel sheet surface coverage of the oxide mainly composed of Si is 10% or less, and (II) When observing a cross section in the vicinity of the steel sheet surface at 2000 times using SEM, cracks having a width of 3 μm or less and a depth of 5 μm or more do not exist in any 10 fields of view,
A high-strength cold-rolled steel sheet excellent in coating film adhesion, characterized by having a tensile strength of 550 MPa or more.
[Si] / [Mn] ≦ 0.4 (1)
{In the formula, [Si] indicates the Si content (% by mass) and [Mn] indicates the Mn content (% by mass)} 下記式（２）および（３）を満たす請求項１〜３のいずれかに記載の高強度冷延鋼板。
[Ｐ]＋３[Ｓ]＋1.54[Ｃ] ＜ 0.25 …（２）
[Ｃ]＋[Si]/30＋[Mn]/20＋２[Ｐ]＋４[Ｓ] ＜ 0.34 …（３）
｛式中[Ｃ]，[Si]，[Mn]，[Ｐ]，[Ｓ]は各元素の含有量（質量％）を示す｝ The high-strength cold-rolled steel sheet according to any one of claims 1 to 3, which satisfies the following formulas (2) and (3).
[P] +3 [S] +1.54 [C] <0.25 (2)
[C] + [Si] / 30 + [Mn] / 20 + 2 [P] +4 [S] <0.34 (3)
{Wherein [C], [Si], [Mn], [P], [S] represents the content (% by mass) of each element}
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