Investigation on the behaviour of medium carbon and vanadium microalloyed steels by hot forging test

Highlights: • Higher strength can be achieved in steels by forging followed by air cooling. • Oil quenching leads to a formation of fine ferrite, pearlite or martensite in steels. • Sand cooling from forging temperature results in a decrement of strength in steels. • Fine ferrite, pearlite and martensite increase strength but decrease ductility. • The cooling rate has an effect on the microstructure and mechanical properties. - Abstract: Two medium carbon steel grades were used in the present investigation. One of them was microalloyed with vanadium. Both steel grades were subjected to a controlled closed die forging followed by cooling in sand, air or oil mediums. Final microstructures and mechanical properties were evaluated by optical microscopy, scanning electron microscopy, hardness and tensile tests. The results indicated that the microstructures of all close die forging and cooling conditions are dominated by ferrite and pearlite phases with different morphologies and grain sizes according to both chemical composition and cooling rate. Oil quenching leads to a formation of relatively fine ferrite and pearlite in medium carbon steel (MC) or martensite in medium carbon microalloyed steel (MC–MA). Relatively fine ferrite, pearlite and martensite increase strength but decrease ductility. The cooling rate has a remarkable effect on the microstructure and mechanical properties at room temperature