| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a hollow member for vehicle reinforcement capable of being advantageously produced in each respect of reliability in junction, energy cost, surface properties and a product shape. <P>SOLUTION: In the hollow member for vehicle reinforcement, an electric resistance welded tube is used for a raw pipe, the electric resistance welded tube including 0.05-0.20 mass% of C, 0.5-2.0 mass% of Si, 1.0-3.0 mass% of Mn, 0.1 mass% or less of P and 0.01 mass% or less of S, with a balance being Fe and inevitable impurities, having a two-phase structure of a ferrite phase and a martensite phase or a three-phase structure of the two-phase and a retained austenite phase, and having a tensile strength of 980 MPa or more. Heat treatment for cooling down to room temperature after heating up to 500-750°C is subjected to an entire area or a part in the pipe circumferential direction at a portion of the raw pipe in the pipe length direction. A tensile strength of a part 3 (or 3A) subjected to the heat treatment is lower by 200 MPa or more than that of a portion 4 not subjected to the heat treatment yet, and a product of the tensile strength and an elongation of the part subjected to the heat treatment is 14,000 MPa% or more. <P>COPYRIGHT: (C)2013,JPO&INPIT |
