Influence of thermomechanical processing route on the mechanical properties of forging quality microalloyed steels

Two low carbon (0.03-0.05Nb and 0.04C-0.15Nb) niobium microalloyed steels w ere processed through three separate forging and thermal treatment routes, and their structure-property relations were examined. The 0.05C-0.15Nb stee l exhibited the best combination of mechanical properties at room temperatu re (YS - 600 MPa, UTS - 680 MPa. % EL - 24%, impact energy > 80J) after con trolled forging and tempering. The subzero (-40 degreesC) Charpy-impact ene rgy and fracture toughness of this steel was 30 J and 86 MPa m respectively . The mechanical properties of the other steels were also reasonably good, but the inter-critically heat treated steels developed poorer mechanical pr operties.