Fatigue crack propagation characteristics of spheroidal graphite cast irons with various dual phase matrix microstructures.

Abstract

The fatigue crack propagation characteristics at stage 2 in spheroidal graphite cast iron with various dual phase matrix microstructures have been investigated. Fatigue tests were carried out at stress ratio R = 0.1 and 0.8, using the CT specimen. The main results obtained were as follows; (1) In the low-ΔK region at R = 0.1, the fatigue crack propagation resistance in as-cast material with dual phase matrix microstructure consisting of ferrite and pearlite was superior to those of heattreated materials whose matrix microstructures were changed into single phases of ferrite or pearlite. (2) In the whole ΔK region at R = 0.1 and the high-ΔK region at R = 0.8, it was possible to improve the fatigue crack propagation resistance by changing only the pearlitic phase in the matrix microstructure of as-cast materials into sorbitic or bainitic phases, utilizing the intercritical treatment.