Microstructural Approach of Study on the Fatigue Behavior of Induction-Hardened Steel (Report 2)

抄録

It is quite well known that a remarkable rise of fatigue strength of an induction-hardened, carbon steel specimen, can be attributed to the following : 1) Quenching after rapid heating may improve the mechanical properties of material. 2) The existence of residual compressive stress in the surface layer of the specimen may prevent the fatigue crack from propagating. However, it has not been clarified which of these has a more important bearing on the fatigue behavior of induction-hardened steel. In this paper, the mechanical behavior of retained ferrite was investigated, which was considered to govern the fatigue behavior of induction-hardened steel being free from the residual stress. Results obtained are as follows : the fatigue crack originates in the part of the retained ferrite in the quenched microstructures, and the final fracture seems to be governed by the surrounding quenched microstructures.