HIGH-STRENGTH STEEL SHEET AND METHOD FOR PRODUCING THE SAME

To provide a high-strength steel sheet that has a tensile strength of 1180 MPa or more, a uniform elongation of 6% or more, and an impact fracture resistance.SOLUTION: Provided is a high-strength steel sheet that has a component composition which contains, in mass%, C: 0.10 to 0.20%, Si: 0.7 to 1.4%, Mn: 2.3 to 4.0%, P: 0.10% or less, S: 0.03% or less, Al: 0.001 to 2.0%, N: 0.01% or less, O: 0.01% or less, and B: 0.0005 to 0.010%, has the balance of Fe and unavoidable impurities and MSC of 3.0 to 4.2 mass%, has a microstructure containing upper bainite by 70% or more in area fraction, and fresh martensite and retained austenite by 7 to 30% in total area fraction in which the area fraction of the retained austenite is 2% or more, and has a mechanical characteristic in which the uniform elongation is 6% or higher, the tensile strength is 1180 MPa or more, and the impact value at -40°C in the press notched Charpy test is 8 J/cm2 or more.SELECTED DRAWING: None 【課題】１１８０ＭＰａ以上の引張強度、６％以上の一様伸び、衝撃破壊抵抗有する高強度鋼板の提供。【解決手段】質量％で、Ｃ：０．１０〜０．２０％、Ｓｉ：０．７〜１．４％、Ｍｎ：２．３〜４．０％、Ｐ：０．１０％以下、Ｓ：０．０３％以下、Ａｌ：０．００１〜２．０％、Ｎ：０．０１％以下、Ｏ：０．０１％以下、およびＢ：０.０００５〜０．０１０％を含有し、残部Ｆｅおよび不可避的不純物からなり、ＭＳＣが３．０〜４．２質量％である成分組成を有し、面積分率で７０％以上の上部ベイナイト、合計面積分率で７〜３０％のフレッシュマルテンサイトおよび残留オーステナイトとを含み、かつ、前記残留オーステナイトの面積分率が２％以上であるミクロ組織を有し、一様伸びが６％上、引張強度が１１８０ＭＰａ以上、かつプレスノッチシャルピー試験における−４０℃での衝撃値が８Ｊ／ｃｍ2以上である機械的特性を有する、高強度鋼板。【選択図】なし