Factors Affecting the Precipitation of NbC on Frank Partial Dislocations in Fe–Ni–16% Cr Austenitic Steels

Abstract

The effect of variations in alloy composition, quench rate, and deformation on the formation of FPP (Frank partial precipitation) has been studied by means of hardness measurements and electron microscopy. Solute concentration is the most important factor controlling the maximum area of FPP. The numbers of precipitate particles increase with dislocation density but the number per unit length of dislocation is generally lower the higher is the dislocation density. The efficiency of nucleation by a dislocation is therefore not increased by the prior cold work and this is consistent with nucleation by climbed loops. The free-vacancy profile near grain boundaries is used to explain the FPP-free zone (PFZ) width, and this is controlled by the rate of precipitation. Silicon additions accelerate the nucleation of NbC and promote FPP formation.