Modelling precipitation of niobium carbide in austenite: multicomponent diffusion, capillarity, and coarsening

Abstract

The growth of niobium carbide in austenite involves the diffusion of both niobium and carbon. These elements diffuse at very different rates. A model is presented for the overall transformation kinetics of niobium carbide precipitation in austenite that takes into account the multicomponent nature of the diffusion process while at the same time allows for the curvature of the transformation front. The inclusion of the curvature (capillarity) effect has, in a numerical scheme, permitted the precipitation and coarsening reactions to be treated in a single model. The model is compared with published experimental data.MST/4716

Precipitation sequence in niobium-alloyed ferritic stainless steel

“…There are several formulae for the rate I [19][20][21][22]. For simplicity and taking into account the consumption of nucleation-sites with the term (1 − V β /V αβ ) [10], the rate I is written as…”

“…It is important in the development process to understand the kinetics of the simultaneous precipitation and coarsening reactions. There exists a theory for NbC formation in the austenite phase of low-alloy steels [6][7][8][9][10] and for precipitation sequences in ferritic, heat-resistant steels [11][12][13][14][15]. However, there has not been much work of this kind on ferritic stainless steels [16] because of their complexity and due to a lack of appropriate thermodynamic data.…”

Nucleation Rate and Number of Precipitates in V and Nb-Microalloyed Steels

“…Neglecting the strain energy term, the Gibbs energy for the formation of a spherical nucleus of carbonitride from the elements in solution (V,Nb) is classically expressed as the sum of a volume and an interface term [6,[15][16][17]:   …”

Theoretical and Experimental Nucleation and Growth of Precipitates in a Medium Carbon–Vanadium Steel

“…The Gibbs energy for the formation of a spherical nucleus of carbonitride from the element in solution (V) is classically expressed as the sum of chemical free energy, interfacial free energy, and dislocation core energy, resulting in the following expression [14][15][16]:…”