Fatigue crack initiation, propagation, and critical fracture of cast steel components subjected to variable amplitude loading are investigated in this study. Predictive techniques that have been used and appear to be applicable to wrought steels are analyzed to evaluate their accuracy with a cast steel. Predictions of crack initiation life, crack propagation life, fracture toughness, and critical crack size were compared to laboratory test results for SAE 0030 mild cast steel. The values of fracture toughness will vary as temperature changes. A fracture toughness value measured at one temperature was related to Charpy energies over a large temperature range to quantify the variation in fracture toughness. This method would ease the design and evaluation of fracture resistant parts.