The paper presents the results of research concerning the influence of hot deformation parameters on the structure and substructure as well as the plastic properties of a Fe–Ni austenitic alloy. The research was performed on a torsion plastometer in the range of temperatures of 900÷1150°C, at a strain rate 0.1 and 1.0 s-1. Plastic flow curves have been drawn up and the interrelations have been determined between the process parameters and the recrystallized grain
size, inhomogeneity and shape. Functional relations between the Zener-Hollomon parameter and the mean grain size after dynamic recrystallization have been developed and the hot deformation activation energy has been estimated. The examination of substructure on TEM allowed the calculation of structural parameters: the average subgrain area and the mean dislocation density. A
detailed investigation has shown that the substructure is inhomogeneous, consists of dense dislocation walls, subgrains and recrystallized regions.
The influence of prolonged ageing on the precipitation process of the secondary phases in an Fe-Ni superalloy of A-286 type has been studied. The samples were subjected to a solution heat treatment at 980°C for 2 h and water quenched, and then aged at temperatures of 715, 750 and 780°C at holding times from 0.5 to 500 h. Structural investigations were conducted using TEM and X-ray diffraction methods. The X-ray phase analyses performed on the isolates were obtained by anodic dissolution of the solid samples. After solution heat treatment the alloy has the structure of twinned austenite with a small amount of undissolved precipitates, such as carbide TiC, carbonitride TiC0.3N0.7, nitride TiN0.3, carbosulfide Ti4C2S2, Laves phase Ni2Si, and boride MoB. The application of ageing causes precipitation processes of γ-Ni3(Al,Ti), G (Ni16Ti6Si7), η (Ni3Ti), β (NiTi) and σ (Cr0.46Mo0.40Si0.14) intermetallic phases, as well as the carbide M23C6. It was found that the main phase precipitating during alloy ageing was the γ intermetallic phase.
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