| 摘要 |
PURPOSE:To produce a hub bolt having excellent surface hardness, delayed fracture characteristic, screw reusability and pull load characteristic by forming an intermetallic compd. of hard Fe and a molten Al and Al2O3 layer on the surface of the hub bolt for automobiles, then removing the Al2O3 layer and plating Zn to the surface. CONSTITUTION:An alloy steel such as Cr steel or Cr-Mo steel is worked to the hub bolt for automobiles. The hub bolt is immersed into the molten Al and after the bolt is pulled out of the molten Al, the bolt is heated for 1hr at 900 deg.C and is oil-hardened. The bolt is thereafter subjected to a tempering treatment for 0.5hr at 505 deg.C to diffuse and intrude the Al into the surface of the alloy steel, by which the high-hardness intermetallic compd. layer of the Fe and Al and further the Al2O3 layer thereon are formed. After the Al2O3 layer is removed by a shot peening treatment, the Zn is electroplated onto the surface and finally the bolt is finished by subjecting the same to a dehydrogenation treatment of the hydrogen contained therein in the stage of plating.
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