STEEL SHEET

Provided are a steel sheet having a predetermined chemical composition and having the following steel structure, and a method of manufacturing the steel sheet.(1) In area ratio%, ferrite: 0 to 5%, martensite: 90 to 100%, a ratio of tempered martensite to total martensite: 80 to 100%, and retained au...

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Bibliographische Detailangaben
Hauptverfasser: OBUCHI, Tatsuya, HAYASHI, Kunio, YOKOYAMA, Takafumi, SHIOKAWA, Kazuki
Format: Patent
Sprache:eng ; fre ; ger
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Beschreibung
Zusammenfassung:Provided are a steel sheet having a predetermined chemical composition and having the following steel structure, and a method of manufacturing the steel sheet.(1) In area ratio%, ferrite: 0 to 5%, martensite: 90 to 100%, a ratio of tempered martensite to total martensite: 80 to 100%, and retained austenite: 0.5 to 6.0% are contained.(2) The number density of inclusions satisfying the maximum diameter ≥ 3 µm is 40 inclusions/mm2 or less.(3)When the number density of the inclusions satisfying the maximum diameter ≥ 3 µm in each section is calculated, the number density in the section where the number density of inclusions is in the top 10% is 80 inclusions/mm2 or less.(4) Formula (A) is satisfied. Vγ′/Vγ≥0.1 Vγ: Initial retained austenite, Vy': Retained austenite after deep cooling at -196°C(5) The tensile strength is 1470 MPa or more.