The microstructure and mechanical properties of medium carbon steel after cyclic heat treatment were investigated.The effects of cyclic numbers and long time annealing on the microstructure and mechanical properties of the experimental steel were compared.A short-duration(5min)holding at 1 023K(above A_1 temperature)and a short-duration(3min)holding at 893 Kare adopted in each cyclic heat treatment.The spheroidization is accelerated during cyclic heat treatment,and the spheroidizing ratio grows with cyclic numbers.After 12-cycle heat treatments,there are few incompletely spheroidized regions in the specimens,and cementite lamellae mostly change into cementite particles.The morphological character of cementite for 12 cycles is similar to that undergoing annealing for 10 h at 973 K.The strength of the experimental steel after 5-cycle heat treatment is the lowest in the following cyclic heat treatment,but it is still higher than that of specimens with subcritical annealing over a long period(10h).After 12-cycle heat treatment,the strength of the experimental steel is close to that of the normalized steel,and the plasticity is the best in all heat-treated specimens. The microstructure and mechanical properties of medium carbon steel after cyclic heat treatment were investigated. The effects of cyclic numbers and long time annealing on the microstructure and mechanical properties of the experimental steel were compared. A short-duration (5min) holding at 1023K above A_1 temperature) and a short-duration (3min) holding at 893 Kare adopted in cyclic heat treatment. and the spheroidizing ratio grows with cyclic numbers. After 12-cycle heat treatments, there are few incompletely spheroidized regions in the specimens, and cementite lamellae mostly change into cementite particles. The morphological character of cementite for 12 cycles is similar to that undergoing annealing for 10 h at 973 K. The strength of the experimental steel after 5-cycle heat treatment is the lowest in the following cyclic heat treatment, but it is still higher than that of specimens with subcritical annealing over a long per iodine (10h). After 12-cycle heat treatment, the strength of the experimental steel is close to that of the normalized steel, and the plasticity is the best in all heat-treated specimens.