Abstract: A steel sheet; a related member; and methods for manufacturing them are disclosed. The steel sheet has a chemical composition including specific amounts of C, Si, Mn, P, S, sol. Al, and N in mass %. The steel sheet has a specific ratio of the total of polygonal ferrite, upper bainite, retained ?, fresh martensite, tempered martensite, and lower bainite, and a specific ratio of a remaining microstructure. The steel sheet has a specific ratio of the number of fresh martensite grains and retained ? grains having an equivalent circular diameter of less than 1.2 ?m, and has a specific ratio of the number of fresh martensite grains and retained ? grains having an aspect ratio of 2.5 or more and an equivalent circular diameter of 1.2 ?m or more.

Abstract: A steel sheet; a related member; and methods for manufacturing them are disclosed. The steel sheet has a chemical composition including specific amounts of C, Si, Mn, P, S, sol. Al, and N in mass %. The steel sheet has a specific ratio of the total of polygonal ferrite, upper bainite, retained ?, fresh martensite, tempered martensite, and lower bainite, and a specific ratio of a remaining microstructure. The steel sheet has a specific ratio of the number of fresh martensite grains and retained ? grains having an equivalent circular diameter of less than 0.8 ?m, and has a specific ratio of the number of fresh martensite grains and retained ? grains having an aspect ratio of 2.0 or more and an equivalent circular diameter of 0.8 ?m or more.

Abstract: Provided are a steel sheet; a related member; and methods for manufacturing the same. The steel sheet has a chemical composition including, in mass %, C: 0.06 to 0.25%, Si: 0.4 to 2.5%, Mn: 1.5 to 3.5%, P: 0.02% or less, S: 0.01% or less, sol. Al: less than 1.0%, and N: less than 0.015%, the balance being Fe and incidental impurities, the steel sheet being such that the steel sheet includes a steel microstructure including, in area fraction, polygonal ferrite: 10% or less (including 0%), tempered martensite: 30% or more, fresh martensite: 20% or less (including 0%), lower bainite: 5 to 50%, and, in volume fraction, retained austenite: 5 to 20%, and the steel sheet has SC?0.5/SC?0.3×100 of 15% or more.

Abstract: A steel sheet has a specified chemical composition and a specified steel microstructure. An average grain size of ferrite and/or bainitic ferrite is 7.0 ?m or less. On the basis of a distribution in the width direction of the steel sheet, a ratio of a deviation of the grain size of the ferrite and/or the bainitic ferrite to the average grain size of the ferrite and/or the bainitic ferrite is 10% or less. On the basis of a distribution in the width direction of the steel sheet, a ratio of a deviation of the area fraction of as-quenched martensite to the area fraction of the as-quenched martensite is 10% or less. On the basis of a distribution in the width direction of the steel sheet, a ratio of a deviation of the area fraction of retained austenite to the area fraction of the retained austenite is 10% or less.

Abstract: A thin steel sheet has a specific chemical composition. The thin steel sheet has a microstructure in which ferrite is present in an area fraction of 5% or more and 60% or less, as-quenched martensite is present in an area fraction of 10% or less (including 0%), retained austenite is present in an area fraction of 5% or more and 20% or less, and upper bainite, lower bainite, and tempered martensite are present in a total area fraction of more than 15% and less than 85%; BCC iron that has a misorientation of 1° or less and surrounds retained austenite having an aspect ratio of 2.5 or higher is present in an area fraction of 5% or more and 70% or less; and a top 10% of retained austenite in terms of an equivalent circular diameter has an average aspect ratio of 2.5 or higher.

Abstract: A thin steel sheet has a specific chemical composition. The thin steel sheet has a microstructure in which ferrite is present in an area fraction of 4% or less (including 0%), as-quenched martensite is present in an area fraction of 10% or less (including 0%), retained austenite is present in an amount of 7% or more and 20% or less, and upper bainite, lower bainite, and tempered martensite are present in a total area fraction of more than 71% and less than 93%; and BCC iron that has a misorientation of 1° or less and surrounds retained austenite having an equivalent circular diameter of 1 ?m or less is present in an area fraction of 4% or more and 50% or less, and BCC iron that has a misorientation of more than 1° is present in an area fraction of 25% or more and 85% or less.