Abstract
When cast iron is repeatedly heated and cooled, there occurs a crack caused due to so-called thermal fatigue. Such thermal fatigue comes into problem in the case of cylinder covers for large marine diesel engines which are subjected to severe thermal stresses during service condition. As to this, ductile cast iron showed a good resistivity to the thermal fatigue. As a result of experiments, the requirements of the ductile cast iron for the thermal fatigue are given as follows: 1) To make the size of spheroidal graphites as small as possible, so as to increase the thermal fatigue strength; 2) To be free from flake graphite, since it remarkedly lowers the thermal fatigue strength. 3) The Coffin's equation N½Δεp = constant is available for ductile cast iron. The thermal fatigue strength of ductile cast iron can be estimated if the size of spheroidal graphites and their distribution are known, in consideration of the graphite area ratio and the stress concentration coefficint.
