Effect of Cyclic Annealing on Microstructure and Mechanical Properties of Medium Carbon Steel

摘要

The microstructure and mechanical properties of medium carbon steel after cyclic heat treatment were in-vestigated.The effects of cyclic numbers and long time annealing on the microstructure and mechanical properties of the experimental steel were compared.A short-duration (5 min)holding at 1 023 K (above A1 temperature)and a short-duration (3 min)holding at 893 K are adopted in each cyclic heat treatment.The spheroidization is accelerated during cyclic heat treatment,and the spheroidizing ratio grows with cyclic numbers.After 1 2-cycle heat treatments, there are few incompletely spheroidized regions in the specimens,and cementite lamellae mostly change into cement-ite 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 (10 h).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.