Fatigue life of cold-forging dies with various values of hardness

Four selected die materials commonly used in the cold-forging process were examined in the present study to obtain the relationship between the hardness and the die fatigue life. The die materials were first heat-treated by a developed process to obtain different values of hardness, while the ductility was retained at a favorable level. The material properties of these die materials were then obtained from tension and impact tests. By investigating the experimental data, the relationship between the mechanical properties and the hardness was established. A theoretical model was also proposed in the present study to predict the die fatigue life, considering the mechanical properties of the die material obtained in the experiments and the fatigue total strain as parameters. Since the material properties can be expressed in terms of hardness, it is convenient for a die design engineer to establish a simple guideline for the prediction of the fatigue life of cold-forging dies using the proposed theoretical model.