A study of precipitation following reversion and high temperature ageing in a 25% Ni, 15% Cr,4% Ti steel

Abstract

The rate of reageing at 700°C in a 25% Ni-15% Cr-4% Ti austenitic steel has been studied following reversion and interrupted quenching treatments. After complete reversion, reageing proceeds without an incubation period although at a reduced rate due to the loss of vacancies. However, in the presence of γ′ particles the reageing reaction at 700°C proceeds, after an incubation period, by the formation of zones between the γ′-particles. In the presence of large amounts of c.p.h. Ni 3Ti needles or cellular Ni 3Ti, produced by holding for 100 min at 900°C, the reageing at 700°C proceeds spontaneously with the nucleation of fine cellular Ni 3Ti on the existing precipitate. After 10–20 min this reaction ceases and the ageing continues by the formation and growth of γ′-particles in the austenite.