HIGH-STRENGTH GALVANNEALED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME (AS AMENDED)

A high-strength galvannealed steel sheet has a chemical composition containing, by mass %, C: 0.14% or more and 0.24% or less, Si: 0.8% or more and 1.8% or less, Mn: 1.0% or more and 3.0% or less, P: 0.020% or less, S: 0.0040% or less, Al: 0.01% or more and 0.1% or less, N: 0.01% or less, Ca: 0.0001...

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Hauptverfasser: KAWABE HIDETAKA, YOKOTA TAKESHI
Format: Patent
Sprache:eng
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Zusammenfassung:A high-strength galvannealed steel sheet has a chemical composition containing, by mass %, C: 0.14% or more and 0.24% or less, Si: 0.8% or more and 1.8% or less, Mn: 1.0% or more and 3.0% or less, P: 0.020% or less, S: 0.0040% or less, Al: 0.01% or more and 0.1% or less, N: 0.01% or less, Ca: 0.0001% or more and 0.0020% or less, and the balance including Fe and incidental impurities, and a microstructure, in which the total area ratio of a ferrite phase and a bainite phase with respect to the whole microstructure is 30% or more and 70% or less, in which the area ratio of a tempered martensite phase with respect to the whole microstructure is 20% or more and 40% or less, in which the area ratio of a retained austenite phase with respect to the whole microstructure is 1% or more and 5% or less, in which the area ratio of a martensite phase with respect to the whole microstructure is 2% or more and 20% or less, and in which the total area ratio of cementite and a pearlite phase with respect to the whole microstructure is 10% or less.