Abstract
In the previous study, it was found that heat treatments of quenching and tempering after TiC coating improved the fatigue strength, and also the fatigue life of TiC coated steels depended on the hardness of substrate.
In this study, the authors investigated in detail the effect of condition of quenching and tempering after TiC coating on the fatigue strength of tool steel. Four kinds of quenching and tempering conditions after TiC coating were selected, but TiC coating condition was all the same. Fatigue tests were conducted using the smooth specimens of a flat plate. The residual stresses were measured by an X-ray diffraction method. As the results, it was found that the condition of heat treatment of quenching and tempering influenced the hardness of substrate and consequently the fatigue strength which was not necessarily dominated by the hardness of substrate, and there existed an optimal hardness of substrate in relation to the fatigue strength. And it was reconfirmed that tensile stress existing in the top part of substrate, which was balanced by the compressive stress in TiC layer, was not only the main factor controlling the fatigue strength, and the secondary tempering condition played some role.
