On Improving Mesostructure of FDI by Super Rapid Heating Induction Treatment and Appearance of High Level Fatigue Reliability.

Abstract

Fatigue reliability of ferritic ductile iron FDI hardened by Micropulse system was evaluated with an attention to meso-scopic fatigue mechanism. Especially, the influence of the martensite phase around graphite nodules on the fatigue crack initiation and propagation was examined. The main results were as follows ; (1) By Micropulse system, the fatugue strength of FDI was improved, and the fatigue limit of the hardened material could be increased by 30%. (2) The fatigue crack initiation in hardened FDI was induced by slip in the ferritic matrix, because debonding between graphite and matrix was prevented from the martensite phase around graphite nodules. Thus, it could be interpreted that the crack initiation stress would be increased by improved mesostructure in the surface. (3) The fatigue crack propagation in the hardened layer was restricted by the presence of the martensite phase and compressive residual stress, and the crack propagation behavior was zigzag path in the ferritic matrix.