Steel Plate, Method For Producing Steel Plate, And Method For Producing Intermediate Steel Plate

Abstract: This steel plate contains a predetermined composition with 10-60% in total of ferrite and bainite, 40-90% in total of martensite and tempered martensite, and 0-10% in total of pearlite and retained austenite. With respect to the total number of crystal grains of ferrite and bainite, the proportion of crystal grains of ferrite and bainite having an area of 3 µm2 or less is 40% or more, and the proportion of crystal grains of ferrite and bainite having an area of 30 µm2 or greater is 5% or less. A difference ?Mn between the Mn concentration in a position at 1.0 µm from an interface between ferrite and martensite in a vertical direction with respect to the interface and toward the inside of a ferrite grain and the maximum value of the Mn concentration in a region up to 0.5 µm is 1.00 mass% or less.

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