HOT-ROLLED STEEL SHEET

Abstract: a hot-rolled steel sheet has a predetermined chemical composition, a microstructure of an inner region includes 40% to 80% of one or two of martensite and bainite in total and 20% to 60% of ferrite by area ratio, an area ratio of a remainder in microstructure is less than 5%, �s/�c, which is a ratio of a ferrite area ratio �s of a surface layer region to a ferrite area ratio �c of the inner region, is in a range of 1.15 to 2.50, (1−hvs/hvc), which is a hardness difference ratio between a vickers hardness hvs of the surface layer region and a vickers hardness hvc of the inner region, is 0.20 or less, and a tensile strength is 980 mpa or more.

Inventor(s): Takeshi TOYODA, Hiroshi SHUTO, Daisuke NIKKUNI

CPC Classification: C21D8/0226 (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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