Strengthening and fracture mechanisms in warm forged microalloyed medium carbon steel

Microstructural evolution during warm forging in the temperature range 800-650°C and the resulting mechanical properties are described for a Nb microalloyed grade 1541 steel. Compared with thermomechanical processing (TMP) forging at higher temperatures in the austenite range, the warm forging process lowers the T NR temperature and raises the Ar 3 temperature. Warm forging produces significantly increased strength and impact toughness in the as forged + air cooled condition. The primary strengthening mechanisms in the warm forged plate are ferrite grain boundary strengthening, ferrite subgrain strengthening and pearlite lamellar strengthening. The increased Charpy impact energy is due to refined ferrite grain size. Delamination fracture ('splits') occurs in Charpy samples, which is thought to be associated with a {100} texture.