| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a hot-rolled steel plate for a steel tube for machine structural purposes which is excellent in fatigue characteristics and bending formability and a process for production of the plate. Ž<P>SOLUTION: In the hot-rolled steel plate for a steel tube for machine structural purposes, in the surface layer part of the steel, ≥80% of the microstructure is composed of bainite, Vickers hardness Hv is 210 to 300, the average value of the major axis length of the bainite is ≤5 μm, and the average boundary carbide particle diameter is ≤0.5 μm. Since the structure of the surface layer part causing fatigue and cracks upon bending forming is a uniform, fine structure essentially comprising bainite, both of its fatigue properties and bending formability are excellent. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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