Masato Yamashita1, Hirokazu Tohjo1,, Hitoshi Uchida1 and Kazushige Arimochi2
1Faculty of Engineering, Himeji Institute of Technology, Himeji 671--2201
We have examined fatigue crack propagation behavior in carbon steels employing a steel containing mixed ferrite and pearlite phases and a Hybrid steel prepared by diffusion bonding between ferrite and bainite materials. No special steel--microstractural effect was observed in the ferrite--pearlite mixed steel. In the Hybrid steel, crack propagation in the ferrite phase decelerated with reaching the [ferrite/bainite]--interface, probably due to the supression of plastic deformation at the crack tip. Low crack propagation rate was also observed in the bainite phase. This can be interpreted in terms of cyclic softening at the crack tip. It is concluded that the fatigue crack propagation rate is strongly affected by phase and interphase interface in steels.
(Received September 3, 1999; In Final Form January 11, 2000)
fatigue, crack propagation, steel, microstructure, bainite, ferrite, grain boundary, Interphase boundary
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