Microstructural Evolution of Compound Layers During Gaseous Nitriding of AISI1045 Carbon Steels

摘要

Compound layers developed at 520 degrees C during gaseous nitriding of AISI 1045 steels were investigated. The nitriding potential (Kn) of a gas atmosphere of dissociating ammonia gas was checked by observation of the partial pressure of hydrogen gas. The microstructural evolution of the compound layer was studied by using optical microscopy and scanning electron microscopy. It was observed that the surface hardness was about 600 Hv after the nitriding treatment and the case depth was about 0.5mm after a nitriding treatment of 1440 min. The compound layer was composed of gamma'(Fe4N) and epsilon(Fe2-3N). The thickness of the compound layer was simultaneously increased to 16 mu m during the nitriding treatment of 1440 min. The kinetics of the compound layer growth were discussed with a modified Lehrer diagram of AISI 1045 steels, which was obtained from the thermodynamic calculation.