Microstructure and mechanical properties of spheroidized D6AC steel

The influence of spheroidization on the microstructure and mechanical properties of D6AC steel was investigated by means of dilatometry, micrograph analysis, and tensile testing. The continuous cooling transformation diagram was presented, and the critical cooling rate to obtain a fully martensitic microstructure was determined. Undissolved Mo carbide particles in the martensite matrix were observed after the solid solution treatment at 860 °C. The kinetics of the spheroidized cementite particles accelerated due to the carbide particles that were undissolved during the solid solution treatment. As the holding time for the spheroidization was increased, the total elongation increased, while the tensile strength and hardness were reduced according to a proportional relationship.