STEEL SHEET, MEMBER, METHODS FOR MANUFACTURING THE SAME, METHOD FOR MANUFACTURING HOT-ROLLED STEEL SHEET FOR COLD-ROLLED STEEL SHEET, AND METHOD FOR MANUFACTURING COLD-ROLLED STEEL SHEET

Abstract: a steel sheet, a member, and methods for manufacturing both are disclosed. the steel sheet has a chemical composition satisfying a carbon equivalent of 0.46% or more and a specific steel microstructure. in the steel sheet, an average crystal grain size of ferrite is 25 �m or less, coefficient of variation of ferrite grain size�carbon equivalent is 0.28 or less, when the steel sheet is bent by 90� in a rolling direction with a width direction as an axis at radius of curvature/sheet thickness: 4.2 and then unbent to be flattened again, the ratio of ferrite grains having a void at an interface to all ferrite grains is 15% or less in an l section in a region extending by 0 to 50 �m from a steel sheet surface on a compressive-tensile deformation side, and a tensile strength is 780 mpa or more.

Inventor(s): Shinsuke KOMINE, Tatsuya NAKAGAITO

CPC Classification: C21D9/46 (MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class and at least one process covered by this subclass ; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials ))

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