The Effect of Heat Treatment and Cold Forging on the Mechanical Properties of SCr420 Low-Alloy Steel

This study developed a new heat treatment method, normalizing and stress relief (NSR), to increase productivity compared to spheroidizing annealing (SA). The influence of different microstructures resulting from these heat treatments was investigated in cold-forged steel. Despite a shorter heat treatment time, the mechanical properties of the NSR alloy were found to be similar to those of the SA alloy. The factors influencing the mechanical properties of the experimental alloys were analyzed using the Hall–Petch equation, and the predicted values closely matched the measured strength of hyper-eutectoid steels. The primary factors affecting mechanical properties were microstructure and dislocation density. In the case of the SA alloy, the microstructure was associated with lower strength due to the spherical cementite structure. In contrast, the NSR alloy had lower strength because of a reduced dislocation density. This was achieved via stress-relief heat treatment below the A1 temperature after phase transformation. Based on the mechanical properties, cold forging simulations showed that the effective stress during cold forging of the NSR alloy was similar to that of the SA alloy.