| 摘要 |
PROBLEM TO BE SOLVED: To provide hollow parts having superior fatigue characteristics after having been cold-worked from an electric resistance welded steel pipe into a predetermined shape and high-frequency-hardened, because the parts for automobiles and machine structures are required to have the fatigue characteristics. SOLUTION: The hollow parts are manufactured by cold-working the electric resistance welded steel pipe including, by mass%, 0.25-0.50% C, 0.35% or less Si, 0.60-1.50% Mn, 0.0025% or less S and 0.010% or less P into the predetermined shape; and have a hardness Hv of 500 or higher over the whole area of the hollow parts after having been high-frequency-hardened, in a wall thickness direction and a circumferential direction. The hollow parts after having been high-frequency-hardened have a hardness difference of 150 or lower by Hv between an outer surface side and an inner surface side. The hollow parts after having been high-frequency-hardened have compression residual stresses of 50 MPa or higher on both of the outer surface and the inner surface. COPYRIGHT: (C)2006,JPO&NCIPI
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