Effect of Nitrocarburizing and Post-oxidation Processes on the Microstructure and Surface Properties of AISI 4140 Steel

AISI 4140 steel is in the class of medium carbon low-alloy steels and widely used industry due to its high hardenability being a relatively economical steel. also among that can be nitrided. With nitriding process, thanks hard nitride layer obtained on surface, not only wear-resistant surface provided, but an increase fatigue strength. In this study, microstructural properties steel, which has been treated with low pressure gas nitrocarburizing post-oxidation process at different times, investigated. For aim, samples were austenitized 850 °C for 60 min quenched into oil °C. After quenching, tempered 630 min. Gas steps; pre-oxidation 350 45 minutes, 550 90 minutes 480 applied, then subjected using steam 180 minutes. Microstructural characterization studies performed by optical microscope, scanning electron microscope (SEM), energy-dispersive X-ray spectrum analysis (EDX), diffraction (XRD) analysis, microhardness roughness measurements. The results revealed consisting iron-nitride phases ɛ-Fe2-3N ɣ’-Fe4N during iron oxide (Fe3O4). It was determined (Fe3O4) thickness increased time. Among nitrocarburized post-oxidized, best combination hardness depth, hardness, after 150 post oxidation.