Steel sheet, member, and methods for producing same

Abstract

A base steel sheet is disclosed having a specified chemical composition and a steel microstructure at a quarter thickness position containing specified ranges of ferrite, fresh martensite, retained austenite, bainite, tempered bainite, and tempered martensite, the value obtained by dividing the total area fraction of isolated island-like fresh martensite and isolated island-like retained austenite by the sum of the area fraction of fresh martensite and the volume fraction of retained austenite in a ferrite grain is 0.65 or more, the isolated island-like fresh martensite and the isolated island-like retained austenite in the ferrite grain has an average grain size of 2.0 μm or less, and the amount of diffusible hydrogen in the base steel sheet is 0.50 ppm by mass or less.

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