Carbide precipitation kinetics in austenite of a Nb-Ti-V microalloyed steel

Highlights: → Carbide precipitation kinetic was fastest at 950 deg. C and accelerated by strain. → Nucleation sites for (Nb,Ti)C above 950 deg. C were mainly undissolved (Ti,Nb)(C,N). → Strain enabled (Nb,Ti)C to nucleate on all sides of (Ti,Nb)(C,N) above 950 deg. C. → Strain changed nucleation sites from (Ti,Nb)(C,N) to dislocations below 900 deg. C. → Strain also accelerated the change in particle composition to equilibrium one. - Abstract: The isothermal precipitation kinetics of carbides in both strain-free and strained austenite (γ) of a microalloyed steel were quantitatively investigated through the electrical resistivity and transmission electron microscopy. The (Nb,Ti)C carbides at the interfaces of the undissolved (Ti,Nb)(C,N) carbonitrides were observed at all temperatures in strain-free γ. However, for strain-induced precipitation, above 950 deg. C, the precipitation of (Nb,Ti)C carbides near the undissolved (Ti,Nb)(C,N) carbonitrides was predominant due to the recrystallization of strained γ. Meanwhile, the fine (Nb,Ti,V)C carbides were homogeneously precipitated in non-recrystallized γ at 850 deg. C and 900 deg. C, as well as near the undissolved (Ti,Nb)(C,N) particles. The electrical resistivity method was successfully used to quantitatively measure the isothermal precipitation kinetics of carbides in both strain-free and strained γ. The precipitation-time-temperature diagrams of the carbide in strain-free and strained γ, with nose temperatures of 950 deg. C, were generated and the precipitation kinetics were greatly accelerated by the applied strain.