Effect of warm working on the precipitation of vanadium carbide in a medium carbon austenitic steel

Abstract

Electrical resistance measurements and electron microscope observations have been used to interpret the ageing characteristics of a 0.4% carbon-24% manganese-0.7% vanadium steel in the temperature range 550 to 700° C. It has been shown that vanadium carbides form in a diffusion controlled process, activation energy 295 kJ mol⁻¹, producing precipitate densities in the matrix of ∼10¹⁶ cm⁻³. The kinetics suggest that nucleation depends on the existence of critical sized substitutional solute atom-vacancy clusters and that once the incubation period has elapsed the nucleation rate falls rapidly and beyond 0.1 fraction transformed further reaction takes place by growth only. Increasing amounts of deformation at the ageing temperature reduces the incubation period and total reaction time, progressively. The relevance of these results to help explain the ausforming behaviour of low alloy steel is stressed.