Modelling of layer development and nitrogen distribution on different microstructures during plasma nitriding

Abstract

Nitriding is a common thermochemical treatment to improve surface properties of steels with focus on corrosion and wear resistance as well as hardness. To meet the requirements of specific application fields, surface properties can be adjusted in a wide range by varying the process parameters such as nitriding temperature, processing time and atmosphere. Aim of this work is the numerical description of a plasma-nitriding process for a high-alloy tool steel X153CrMoV12 and a nitriding steel 15CrMoV5-9 to investigate the infuence of the microstructure on the nitriding layer development. In addition, the developed model is intended to serve as a prediction tool for the resulting layer thicknesses and nitrogen distributions depending on process temperature and time. The intended nitriding model was developed using the commercial FE-program DEFORM® and validated based on the results of plasma-nitrided samples at three different nitriding temperatures (480, 520, 560 °C) and processing times (2, 4, 16 h). DEFORM® enables the implementation of a real microstructure using a script-based approach. Up to now, only a few simulation concepts exist for nitriding processes on materials with a defined microstructure. With the developed model, a prediction of the resulting nitriding zone and nitrogen distribution within the validated range is possible for a carbide-free and carbide-rich microstructure. As expected the resulting nitriding zone increases with rising temperature and time. In addition, the nitriding steel (15CrMoV5-9) reaches significantly higher layer thicknesses than the high-alloy steel (X153CrMoV12). Furthermore, it is observed that areas with many carbides show lower layer thicknesses compared to carbide-free areas.