Cold-rolled steel sheet



PROBLEM TO BE SOLVED: To attain a high tensile cold-rolled steel plate excellent in ductility, work-hardenability, and stretch flange formability.SOLUTION: The cold-rolled steel sheet contains, by mass%, >0.020 and <0.30% C, >0.10% and ≤3.00% Si, and >1.00 and ≤3.50% Mn, and optionally further contains an appropriate amount of one or more elements of Ti, Nb, V, Cr, Mo, B, Ca, Mg, REM and Bi, and has a metallic structure in which a main phase is a low-temperature transformation-produced phase and a second phase includes retained austenite and polygonal ferrite, wherein the retained austenite counts for >4.0% and <25.0% by a volume fraction, and has an average diameter of <0.80 μm, and a number density of the retained austenite particles having a particle size of ≥1.2 μm among the retained austenite is ≤3.0×10pieces/μm, and the polygonal ferrite counts for >2.0% and <27.0% by a volume fraction, and has an average particle size of <5.0 μm.
【課題】延性、加工硬化性、伸びフランジ性に優れた高張力冷延鋼板の実現。 【解決手段】質量%で、C:0.020%超0.30%未満、Si:0.10%超3.00%以下、Mn:1.00%超3.50%以下、場合によりさらに適量のTi、Nb、V、Cr、Mo、B、Ca、Mg、REMおよびBiの1種又は2種以上を含有し、主相が低温変態生成相で第二相に残留オーステナイトおよびポリゴナルフェライトを含む金属組織を備え、前記残留オーステナイトは体積率が4.0%超25.0%未満、平均粒径0.80μm未満であり、前記残留オーステナイトの内、粒径1.2μm以上の残留オーステナイト粒の数密度が3.0×10 −2 個/μm 2 以下、前記ポリゴナルフェライトは体積率が2.0%超27.0%未満、平均粒径5.0μm未満である。 【選択図】図3




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