Role of Dislocations and Interfaces on the Nanoscale Random Precipitation Kinetics in Vanadium-Alloyed Steels Studied by SANS
Zamran Zahoor Khan (TU Delft - Applied Sciences)
Amir Sabet Ghorabaei (Rijksuniversiteit Groningen)
Sonia Guehairia (KTH Royal Institute of Technology)
Steven R. Parnell (ISIS Neutron and Muon Source)
Dirk Honecker (ISIS Neutron and Muon Source)
Peter Hedström (KTH Royal Institute of Technology)
Bart J. Kooi (Rijksuniversiteit Groningen)
S. Erik Offerman (TU Delft - Mechanical Engineering)
Niels H. Van Dijk (TU Delft - Applied Sciences)
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Abstract
This study uses small-angle neutron scattering (SANS) to investigate vanadium carbide (VC) random precipitation (RP) kinetics in two nanosteels with varying vanadium and carbon contents during aging for up to 10 hours at 600 and 650 °C. Starting from a martensitic microstructure, the evolution of the VC precipitate size distributions is tracked over time. Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) provide complementary characterization of precipitate shape, morphology, and composition. The precipitation process follows a sequence of burst nucleation, rapid growth, and coarsening, driven by enhanced diffusion along dislocations and interfaces. VC precipitates form primarily at martensitic interfaces, adopting predominantly oblate ellipsoidal particles. Analysis of the time-dependent precipitate size indicates that pipe diffusion along dislocations is the dominant diffusion mechanism during coarsening. Using the Ashby-Orowan model, we estimate the strength enhancement from VC precipitation. Maximum VC strengthening occurs at different aging times depending on steel composition. For steels with a high carbon and vanadium content, peak strengthening occurs after 120 minutes of aging at 650 °C. Reducing the carbon and vanadium content prolongs the time required to reach peak strengthening, extending it to 300 minutes at 650 °C. The nuclear-to-magnetic scattering ratio shows a time-dependent evolution indicating a temporal compositional change in the VC precipitates during aging.
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