TEM study of NbC heterogeneous precipitation in ferrite

Abstract

International audienceThe heterogeneous precipitation of NbC in ferrite has been quantitatively characterised by Transmission Electron Microscopy in a Fe-C-Nb model alloy for different isothermal heat treatments. Elongation and size distribution of precipitates have been derived from Dark Field imaging. For each precipitation states, the precipitation of NbC is occurring on dislocations due to the as-quenched state. This precipitation mechanism leads to characteristic arrays of precipitates in which precipitates grow in a self-similar manner. A detailed study of these arrays has shown that most dislocations decorated by these arrays are edge dislocations with <112> type line vectors. There is only one variant on a given dislocation. This selection can be interpreted by the interaction between dislocation and precipitate strain fields

As-cast mechanical properties of vanadium/niobium microalloyed steels

“…4a illustrates another precipitation state in which carbonitride particles are located on dislocations. Recent studies on microalloy precipitates formed in ferrite grains, have shown that they prefer to nucleate heterogeneously on dislocations in order to reduce the strain field which stems from lattice parameter difference between the precipitates and ferrite [25][26][27][28][29].…”

The Effect of Cooling Rate, and Cool Deformation Through Strain-Induced Transformation, on Microstructural Evolution and Mechanical Properties of Microalloyed Steels

“…[33] Perrard et al detected heterogeneous precipitation in ferrite in the temperature range of 1073 K to 873 K (800°C to 600°C) with relatively long isothermal holding. [34] The location of these small precipitates is another important aspect that could be interesting to evaluate. It is reasonable to believe that such precipitates would form on the dislocations or grain boundary junctions.…”

Solute Behavior in the Initial Nucleation of V- and Nb-Containing Carbide

“…[6,7] During the nucleation stage of the alloy carbides, the dislocation and distinct interface are considered active initiators of the precipitation sequence, because it represents an initial energetically favorable stage to be nucleation sites. [8][9][10] The sophisticated understanding of the nucleation and associated diffusion behaviors of carbon and carbon-forming elements helps to obtain a reasonable explanation of the formation mechanisms of the alloy carbides, and further optimizes service performance at ambient or elevated temperatures by controlling the sizes, morphology, and density of the precipitates in the multicomponent steel.…”