Boronizing is one of the chemical methods for case hardening of steels. The hardness of the boronized layer is above 1400 Vickers hardness and it has a high resistance, especially against wear.
In the present study, plane and rotating bending fatigue tests of boronized steels with various thickness of boronized layers were conducted. The effects of thickness and compressive residual stress of boronized layer on fatigue strength were investigated. Furthermore, the X-ray method was successfully applied to measure the changes in residual stress and half-value breadth during plane bending fatigue.
The results obtained are summarized as follows;
(1) Fatigue crack initiation occured both in the boronized surface layer and at the boundary between the boronized layer and the matrix.
(2) The surface compressive residual stress hardly changed during fatigue, but half-value breadth increased.
(3) The compressive residual stress is effective to increase fatigue strength when crack initiation occured at the surface. The maximum fatigue strength was obtained when the boronized area was controlled to be about 1.5% of the total area.
