Role of pre-deformation in age hardening of a niobium-microalloyed steel

The effect of pre-deformation on the age hardening of a niobium-microalloyed steel is investigated by virtue of mechanical testing in conjunction with microstructural observations. The steel is aged at three temperatures 600 degrees C, 640 degrees C and 680 degrees C, respectively, after solution-treated at 1 200 degrees C. The precipitation of Nb(C, N) is markedly accelerated by a pre-deformation of 15 % prior to ageing, resulting in very fine particles being formed and a considerable increase in the strength of the steel with no large decrease in the ductility. Compared with the hot-rolled state, the yield strength of the deformed steel increases by about 280 MPa while that of the undeformed steel only by about 60MPa after peak-aged at 640 degrees C. Overall, the yield strength of the deformed steel may reach about 710 MPa with an elongation of about 19 %.