Stacking-Fault Precipitation of Niobium Nitride in Cr–Ni–Nb Austenitic Steels

Abstract

Precipitation of niobium nitride, particularly in association with stacking faults, has been studied by electron microscopy of carbon extraction replicas prepared from iron-base austenitic alloys containing 18% chromium, 12% nickel, and various levels of niobium and nitrogen. This precipitation occurs during ageing in the range 700–800° C (975–1075 K) after solution-treatment at 1300° C (1575 K). Nucleation takes place primarily at dislocations that are present in the matrix after the solution-treatment. The growth rate of the precipitate and its morphology and distribution are dependent on the rate of quenching. The quenched-in vacancy concentration of the matrix is shown to be an important variable, but the supersaturation of solute atoms and the distribution of dislocations formed during quenching are also significant.