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.
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