| 摘要 |
<P>PROBLEM TO BE SOLVED: To improve impact absorption performance of a steel pipe constituting a front side frame or a rear side frame of an automobile. <P>SOLUTION: A steel pipe W of a closed cross-sectional surface linearly fed from a steel pipe feeding device is inductively heated by a high-frequency heating coil, subjected to bending work by adding bending moment thereto by a bending device, and subjected to a hardening treatment by being rapidly cooled by a cooling device, and thereafter a first brittle part 32a is formed in a curved part 32 of the steel pipe W by an annealing treatment, whereby the first brittle part 32a is easily bent when a collision load in the front-back direction is inputted, and thereby impact absorption performance can be improved by securing impact absorption stroke. Since the brittle part 32a is formed at the curved part 32 of the steel pipe W, the first brittle part 32 can not be formed by partially suspending the heating of the steel pipe W by the high-frequency heating coil, but the first brittle part 32a can be formed without any trouble by subjecting the first brittle part 32 to post-processing by an annealing treatment in a subsequent process. <P>COPYRIGHT: (C)2012,JPO&INPIT |
