Abstract A method for clarifying the effect of nitrided case on the fracture of anodular cast iron has been proposed. Assuming that the effect of the nitrided caseis a linear superimposure of the strengthening of matrix in the case and theresidual stress, quantitative expressions of the fracture toughness as well as thethreshold of fracture toughness are achieved. Results obtained from the nodularcast iron appear to be in reasonable agreement with the experimental data.
