| 摘要 |
PROBLEM TO BE SOLVED: To provide a bent member using a hot-dip galvannealed steel having excellent corrosion resistance after coating and high strength, and suitable for use to automobile members as the stock. SOLUTION: The invention uses a hot-dip galvannealed heat-treated steel, in which heat treatment has been performed in such a manner that at least a part of a hot-dip galvannealed steel whose at least one side has been subjected to hot-dip galvannealing is heated to a hardenable temperature region. The coating weight of the film remaining at least in the surface subjected to the heat treatment is 30 to 90g/m<SP>2</SP>per side, the concentration of Fe in the film is 8 to 50%, and further, the center line average roughness Ra in the surface of the film is≤2.0μm. A tubular metallic material whose one side is at least provided with a Zn-Fe alloy plating film in which coating weight is 30 to 90g/m<SP>2</SP>per side, the content of Fe is 8 to 35 mass%, and the center line average roughness Ra is≤2.0μm is held in an air atmosphere or in an atmosphere comprising oxygen by≤20 vol%, and the balance nitrogen, carbon dioxide and water vapor for 1 to 60 min in the temperature range of 500 to 800°C, and is thereafter bent at 3DQ. COPYRIGHT: (C)2011,JPO&INPIT |
