溶融塩浸漬法によるVC被覆鋼の曲げ耐久限度と残留応力の関係

抄録

Bending fatigue tests were carried out on the specimens coated with VC by immersing in a molten borax bath and on the base specimens hardened by quenching and tempering. The residual stresses in the carbide layer and substrate, the hardness and grain size of the substrate were also examined.
In the VC layer, the compressive residual stress of 1000-2000MPa appeared, while in the substrate of the VC coated specimen and the surface of the hardened base specimen, the tensile residual stress of 0-400MPa appeared. This tensile residual stress was generally higher in the VC coated specimen than in the hardened base specimen.
The bending fatigue limit of the VC coated specimen was influenced not only by the hardness but also by the residual stress in the substrate. In the case that the hardness is constant, the bending fatigue limit is linearly correlated to the residual stress in the substrate, and also this correlation holds good between the bending fatigue limit and the residual stress on the surface of the hardened base specimens.
The bending fatigue limit was not increased by tempering at high temperature which lowers both the tensile residual stress and the substrate hardness. On the other hand, diffusion soaking was effective in increasing the bending fatigue limit, because the tensile residual stress becomes lower and the substrate hardness becomes higher.