Microstructure-property relationships in thermomechanically processed microalloyed medium carbon steels

Hot forged plates of two microalloyed grades of 1541 steel have been produced by thermomechanical (TMP) forging schedules. The yield strength and Charpy impact toughness are both increased by TMP treatment, compared to a conventional forging schedule. The strength increase is due to reductions in the ferrite grain size and pearlite colony size. There is also significant precipitation strengthening in the Ti,V microalloyed steel (1541 + Ti,V). The lowering of the impact transition temperature and the increase in Charpy energy produced by the TMP treatments are attributed to the decreases in ferrite grain size and pearlite colony size. In addition, for Nb microalloyed steel, the elongated microstructure and intragranular ferrite produced by TMP forging make the effective pearlite colony size very small in the direction of crack propagation.