| 摘要 |
PROBLEM TO BE SOLVED: To improve durability of springs that hardly improve in durability by nitriding. SOLUTION: Springs which are applied low temperature annealing for removing macroscopic residual stress after cold forming, springs tempered after cold forming, or springs refined after hot forming, which are in the scope of Hv 400-750 in surface layer hardness, are taken up for the surface processing. On the surface of the spring of which surface layer hardness is Hv 400-750, the hard metallic particles, Hv 350-1100 in hardness, 7.0-9.0 in specific gravity, and 20-100μm in average article diameter are projected at colliding speed 50 m/sec-160 m/sec. The limit of the temperature rise on the spring surface layer by the collision is controlled to be lower in temperature that causes hardening of spring surface layer by restored recrystallization. And the projection is performed so that minute cracks to obstruct fatigue strength can not be generated on the surface layer to improve hardness and compressed residual stress of the surface layer under 30μm from the surface.
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