HIGH-STRENGTH STEEL SHEET AND METHOD FOR MANUFACTURING SAME

• Main Authors: TAKAGI, SHUSAKU, KANEKO, SHINJIRO
• Format: Patent
• Language: English; French; German
• Published: 05.11.2014
• Subjects: ALLOYS; 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; MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVINGMATERIAL; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; PERFORMING OPERATIONS; PUNCHING METAL; ROLLING OF METAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TRANSPORTING; TREATMENT OF ALLOYS OR NON-FERROUS METALS

The present invention provides a high-strength steel sheet having a tensile strength (TS) of 980 MPa or more and also excellent bending property stably over the entire steel sheet, due to a predetermined chemical composition in combination with a specific microstructure wherein an average crystallized grain diameter of ferrite phase is 10 µm or less, a volume fraction of ferrite phase is within the range from 30 % to 70%, a volume fraction of the total of martensite and retained austenite phases is 10 % or less, and a ratio of interphases each having an interphase nano-hardness difference within 4 GPa is 90 % or more.