Effect of cyclic heat treatments on spheroidizing behavior of cementite in high carbon steel

The spheroidizing behavior of cementite in Fe–0.8C mass% steel during cyclic heat treatment was investigated. The effect of cyclic numbers on the microstructure and mechanical properties of the experimental steel was discussed. In the present work, each cyclic heat treatment consisted of a short-duration (5 min) held at 1043 K (above A1 temperature 1003 K) and a short-duration (3 min) held at 953 K. The spheroidizing ratio of cementite and the average size of particles grow with the increase of cyclic numbers. After five cyclic heat treatments, the cementite spheroidizes completely, the average size of cementite particles is about 0.49 μm and the larger particles ratio is below 4%. After cyclic heat treatment, the plasticity of the experimental steel clearly increases. The elongation of the as-transformed specimen is about 8%, the elongation of the 1-cycle specimen is 25.4%, and the elongation of the 5-cycle specimen reaches a peak value of 33.9%. The ultimate tensile strength (UTS) of as-transformed specimens is about 680 MPa, and the UTS of the 1-cycle specimen decreases to about 620 MPa; however, the UTS of the 3-cycle specimen increases to about 650 MPa. The ratio of yield strength to tensile strength is about 0.70 after cyclic heat treatments.