Development of high strength ductile eutectoid steel through cyclic heat treatment involving incomplete austenitization followed by forced air cooling

Annealed AISI 1080 steel bars were subjected to cyclic heat treatment up to 3 cycles. Each cycle consisted of short duration holding (incomplete austenization) for 6 min at 775 °C (in fully austenitic region) followed by forced air cooling (air flow rate: 38.4 m3 h− 1) to the room temperature. Such a typical thermal cycling resulted in a significant increase in hardness and strength on execution of 2 cycles. This was attributed to a novel microstructure consisting of matted fine pearlite containing submicroscopic cementite spheroids. The hardness (368 HV) and strength (UTS = 1095 MPa) achieved after 2 cycles of heat treatment was much higher and ductility (%Elongation = 16) was quite reasonable when compared with that in annealed condition (Hardness = 222 HV, UTS = 740 MPa, %Elongation = 21). Execution of third cycle resulted in decrease in hardness and strength due to disappearance of matted fine pearlite region. Furthermore, with regard to previously carried out research by the authors, the process efficiency has been greatly enhanced (heat treatment duration is reduced) on adoption of more intense forced air cooling without compromising strength and ductility.