Coated steel sheet, member, and methods for producing the same

A coated steel sheet comprising:

• a steel sheet having a chemical composition containing, in mass %,
• C:
• 0.10% or more and 0.30% or less,
• Si:
• more than 1.20% and 2.00% or less,
• Mn:
• 2.5% or more and 4.0% or less,
• P:
• 0.050% or less,
• S:
• 0.020% or less,
• Al:
• 0.10% or less,
• N:
• 0.01% or less,
• Ti:
• 0.100% or less,
• Nb:
• 0.002% or more and 0.050% or less,
• B:
• 0.0008% or more and less than 0.0015%, and
• the balance being Fe and incidental impurities,
• wherein the chemical composition satisfies formula (1) below,
• a total area fraction of martensite and bainite is 95.0% or more,
• a retained austenite area fraction is 4.8% or less,
• a ferrite area fraction is 0.2% or more and 3.0% or less,
• a prior-austenite grain size is 10 μm or less,
• a B concentration in a prior-austenite grain boundary present between adjacent grains of martensite is 0.05% or more in mass %,
• a variation in B concentration within the same prior-austenite grain boundary present between adjacent grains of martensite is less than 0.010% in mass %, and
• a variation in B concentration within the same prior-austenite grain boundary present between martensite and ferrite is 0.010% or more in mass %;
• and
• a coating layer formed on at least one surface of the steel sheet,
• (
• [
• %
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• N
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• 14
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• (
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• %
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• Ti
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• 47.9
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• 1.
• formula
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• in formula (1), [% N] and [% Ti] respectively represent a N content and a Ti content (mass %) in steel.