Influence of different initial microstructure on the process of spheroidization in cold forging

In the study, an investigation has been carried out for spheroidization of medium carbon steel (AISI 4140) used in forging industry. Two different spheroidization processes were considered. The first one was the annealing of normalized steel under A1 temperature for a long time. The second was the annealing of hardened steel under A1 temperature for a long time. Specimens which were normalized and hardened before the experiments were exposed to spheroidization annealing at 700 °C temperature for five different time periods as 4, 8, 12, 24 and 48 h. For evaluation of cold forgeability with different spheroidization annealing periods, the hardness, percentage of reduction in area in unaxial tension and reduction of area in notched tensile test were recorded. The results of reduction of area in notched tensile test showed that the highest performance is reached with 12 h spheroidization time after being hardened.