Intermediate temperature decomposition of supercooled high nitrogen austenite

Abstract

The mechanism of decomposition transformation of Fe–N the austenite system has been investigated. An improved process of austenitic nitriding, achieved by applying controlled nitrogen potential theory, allowed high nitrogen austenite samples with a uniform nitrogen concentration to be produced. The key point of this gas nitriding process is to keep the atmosphere at very low nitrogen potential. As a result, the nitride layer on the surface of the pure iron foil was reduced and pure iron ferrite was thoroughly nitrided, forming high N austenite (γ-Fe[N]) that is thermally stable at room temperature. The nitrogen concentration of this austenite was determined as 9·32 at.-%, which is almost the maximum value achievable in Fe–N austenite.

Keywords:

• High nitrogen austenite
• Intermediate temperature transformation
• In situ high temperature X-ray diffraction