<i>δ</i>–pearlite Reaction by Carburization in Fe–Cr Binary Alloy

Abstract

The eutectoid transformation of δ -ferrite → γ -austenite + carbide by carburization was studied comprehensively with Fe-Cr binary alloy. It was observed that δ -pearlite consisted of γ -austenite and M 23 C 6 carbide formed with unidirectional lamellar structure parallel to the carburization direction, and consequently the γ -austenite transformed to α'-martensite on quenching. The reconstruction of the parent γ -austenite orientation revealed that the both of austenite and M 23 C 6 phases have a preference growth along [011] direction while keeping a cube-on-cube orientation relationship within δ -pearlite. The growth rate of δ -pearlite followed parabolic kinetics, and thus, the interlamellar spacing of δ -pearlite was gradually increased according to the Zener-Hillert model. Furthermore, the δ -pearlite formation mechanism was discussed under PE (para-equilibrium), NPLE (non-partitioning local equilibrium), and PLE (partitioning local equilibrium) conditions. As a result, it was concluded that the PLE model with long-range Cr diffusion through the interface diffusion is dominant, which leads to the redistribution of Cr between austenite and M 23 C 6 at the eutectoid reaction front.

Alloying Effects on the Microstructure of Fe-1mass%M Binary Alloys Treated by Austenitic Nitriding and Quenching Treatment

“…On the other hand, formation of ( + Si 3 N 4 ) lamellar in the Fe-1Si alloy is, at least to the authors' knowledge, the first to be observed in the austenitic nitriding treatment. A similar reaction occurs during carburizing of alloy steels and is known as -pearlite transformation forming by eutectoid transformation [30][31][32][33][34] . Fig.…”