HIGH-STRENGTH STEEL SHEET, HIGH-STRENGTH GALVANIZED STEEL SHEET, AND METHOD FOR MANUFACTURING SAME

• Main Authors: HASEGAWA Kohei, KAWAMURA Kenji, FURUYA Shinichi, ONO Yoshihiko, KARIYA Nobusuke
• Format: Patent
• Language: English; French; German
• Published: 04.11.2020
• Subjects: ALLOYS; CASTING; CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES; CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; PERFORMING OPERATIONS; POWDER METALLURGY; PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OFWROUGHT-IRON OR STEEL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TRANSPORTING; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

Provided are a high-strength steel sheet and a high-strength galvanized steel sheet having a tensile strength of 980 MPa or more and excellent bending workability and methods for manufacturing these steel sheets. A high-strength steel sheet has a specified chemical composition, in which a Mn-segregation degree in a region within 100 µm from a surface of the steel sheet in a thickness direction is 1.5 or less, in a plane parallel to the surface of the steel sheet in a region within 100 µm from the surface of the steel sheet in the thickness direction, the number of oxide-based inclusion grains having a grain long diameter of 5 µm or more is 1000 or less per 100 mm 2 , a proportion of the number of oxide-based inclusion grains having a chemical composition containing alumina in an amount of 50 mass% or more, silica in an amount of 20 mass% or less, and calcia in an amount of 40 mass% or less to the total number of oxide-based inclusion grains having a grain long diameter of 5 µm or more is 80% or more, a specified metallographic structure, and a tensile strength of 980 MPa or more.