Effects of Ti-Mo and Ti-Nb complex additions on interphase precipitation in low-carbon steels

The purpose of this research was to study the effects of Mo and Nb additions on interphase precipitation in titanium-alloyed low-carbon steels. Sheet spacing and inter-particle spacing of interphase-precipitated carbides were quantitatively measured and evaluated by transmission electron microscopy. Besides, to elucidate these results, the transformation rate of ferrite was measured by dynamic dilatometer. Addition of 0.2 wt%Mo, which increases the super saturation for carbide nucleation, can further refine the inter-particle spacing of carbides. The Vickers microhardness has been achieved in this Ti-Mo containing steel after isothermal heat treatment at 650 °C for 20 min. Addition of 0.04 wt%Nb had no strong effect on refining the inter-particle spacing further. The precipitation of (Ti,Nb)(C,N) in the present alloy system increased the ferrite growth rate. It is suggested that the ability to refine the carbide dispersion in this Ti-Nb steel could be optimized by reducing the carbon content. These results a d discussions provide guidance for alloy design to attain strong ferrite in steels by producing dense interphase-precipitated nanometer-sized carbides. (AU) Copyright © 2014 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved.