| 摘要 |
PROBLEM TO BE SOLVED: To produce a dual-phase steel in which the strength and ductility are improved by refining its steel structure by heating a steel stock containing C of a specified ratio and consisting of a specified structure to a specified temperature, and applying the magnetic field of a specified intensity and work ing treatment to the steel stock. SOLUTION: A steel stock containing 0.05-0.80 mass % C and having a >=20% ferromagnetic phase in volume at room temperature, is heated to the temperature range between the lower limit temperature: Ac1 point, and the upper limit temperature: Ac3 point or (Ac2 point +100 deg.C), whichever is lower, and the magnetic field of 0.1-20 T is applied in this temperature range to the steel stock to work the steel stock. The magnetic field is preferably applied thereto a plurality of times, the applying direction of the magnetic field is changed step by step, and the magnetic field is applied in an arbitrary direction perpendicular to the working direction of the steel stock in the case of applying the magnetic field to obtain a dual-phase steel of fine structure. The structure is controlled by achieving the inverse transformation while heating a material having a ferromagnetic phase into two phase areas, and textures or flat grains caused by the rolling are eliminated to achieve further refining of the structure.
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