Low Cycle Fatigue Behavior of HT250 Gray Cast Iron for Engine Cylinder Blocks

The strain-controlled low cycle fatigue properties were evaluated on specimens of HT250 gray cast iron (GCI) at room temperature. The material exhibited cyclic stabilization at a low strain amplitude of 0.1% and cyclic softening characteristic at higher strain amplitudes (0.15-0.30%). At a representative total strain amplitude (0.30%), the hysteresis loops of HT250 GCI were asymmetric with a large amount of plastic deformation in the compressive phases. Furthermore, the hysteresis loop became larger in both width and height with increasing total strain amplitude (from 0.10 to 0.30%), and tended to exhibit a clockwise rotation. The fatigue crack propagation mechanisms were different at various total strain amplitudes, where high stress concentration due to dislocation pile-up favored fatigue crack initiation in the examined HT250. Finally, the roughness-induced crack closure was a key to determine the crack growth rate as well as fatigue life.