An Alternate Approach to Accelerated Spheroidization in Steel by Cyclic Annealing

In this work an annealed 0.6 wt.% carbon steel was subjected to cyclic heat treatment process that consisted of repeated short-duration (6 min) holding at 810 °C (above Ac3 temperature) followed by cooling in a flowing air medium (flow rate: 6 m3/h). After 8 cycles (about 1 h and 20 min), the microstructure mostly contains spheroidized cementite and ferrite along with trace amount (3%) of pearlite. In addition to the diffusion within lamella, the disintegration of lamellae through dissolution of cementite at preferred sites of lamellar faults during short-duration holding above Ac3 temperature, and the generation of defects (lamellar faults) during non-equilibrium cooling in a flowing air medium are the main reasons of accelerated spheroidization.