The Microstructure of Discontinuously Precipitated Lamellae in Austenitic Fe-42.4wt%Ni-4.15wt%Al-0.45wt.%C Alloy

Abstract

Phase decomposition of austenitic Fe-42.4 wt pct Ni-4.15 wt pct Al-0.45 wt pct C on aging at 823 K was investigated by means of electron microscopy, selected area diffraction and microdiffraction, and microprobe chemical analysis. During annealing, kappa phase of L'1(2) structure fully coherent with the matrix formed via the nucleation and growth mechanism. The matrix phase and cubic kappa carbide were later gradually encroached upon by discontinuously precipitated lamellar phases. The duplex fine lamellae are composed of alternately arranged carbon-depleted L1(2) phase and cementite. Between the two constituents in the lamellae, the Pitsch orientation relationship is fulfilled, and at the same time, the matrix phase of the grain which the discontinuously precipitated lamellar colony has left behind maintains the crystallographic cube-to-cube correspondence with the product L1(2) phase.