Verification on Possibility of Nitrogen Diffusion into Steel by High Temperature N-Quench

Abstract

N-Quench, which is a new surface heat treatment to infiltrate nitrogen into steel parts followed by quenching to achieve hardening, is gathering attention in the nitriding field as it affords low distortion while maintaining a higher effective case depth (ECD) compared with conventional nitriding. N-Quench is conducted mainly between 680°C and 800°C, where the two-phase region of ferrite and austenite exists in the Fe-N phase diagram. However, a few studies have reported on nitriding at temperatures higher than 800°C due to decomposition of NH3, which is a key source of nitrogen infiltration. Our results revealed that in a conventional furnace such as resistance heating furnace, no nitrogen infiltrated the specimen at 930°C, which is the general carburizing temperature. On the other hand, in the infrared heating furnace, nitrogen infiltrated the specimen at 930°C successfully with lesser NH3introduction than that required by the conventional furnace. Therefore, in this study, the limit of NH3decomposition is assessed and possibility of extending the applicability of N-Quench, especially increasing the ECD while maintaining a low distortion, is examined.