Low-Temperature Gaseous Nitriding of 2205 Duplex Stainless Steel: Effect of Temperature and Nitriding Potential

The present work addresses the response of 2205 duplex stainless steel to low-temperature gaseous nitriding. The dependence of the formation of cracks and nitrides on nitriding parameters, i.e. temperature and nitriding potential, was revealed. Gaseous nitriding was performed in pure ammonia or ammonia/hydrogen mixtures in the temperature range of 380‒430 °C. The case developing during nitriding was examined using reflected light microscopy, X-ray diffraction analysis, electron microscopy and hardness indentation. Depending on the temperature and the gas composition, nitriding resulted in the development of expanded austenite or mixtures of expanded austenite and expanded ferrite in the surface adjacent zone. A combination of relatively low temperature and gentle nitriding potential led to the formation of a sound nitrided case, where neither chromium nitrides nor cracks developed.