Study on Aging Processes of Maraging Steels by Internal Friction Measurement

Abstract

The maraging reactions of Fe-Ni-Cr ternary and Fe-Ni-Cr-Co quaternary alloys with and without Nb addition are studied by measuring internal friction and relative shear modulus during isothermal anneal in the temperature range between 300°C and 600°C for 5 to 10000 min.
The results are summarized as follows.
1) Several stages of internal friction and relative shear modulus changes are found and related to the following processes. I₁; carbide precipitation, I₂; short range ordering, I₃, G₁, and I₄; precipitation and resolution of Nb containing metastable phase, G₂; clustering of Cr atoms, I₅ and G₃; austenite formation, I₆ and G₄; recrystallization of formed austenite. The simple TTT diagrams which give the beginning and end of the aging reactions are proposed.
2) Nb addition prevents the short range ordering in base alloys.
3) Nb containing metastable phase precipitates at temperatures lower than 450°C and this phase resolves between 400°C and 500°C.
4) The clustering of Cr atoms occurs in all samples, even in the alloy containing only 3.5%Cr.