Verification on possibility of nitrogen infiltration into steel by N-quench
N-Quench, which is a new surface heat treatment to infiltrate nitrogen into the steel parts in austenite phase and then they are quenched for hardening, is gathering attention today in the nitriding field in terms of low distortion while maintaining the higher effective case depth (ECD) than conventional nitriding. N-Quench is conducted mainly between 680 ℃ to 800 ℃, where the two-phase region of ferrite and austenite exist, but there are a few research reports about nitrogen behavior on the higher temperature than 800 ℃ due to ammonia decomposition. From our research results, in general furnace such as resistance heating, no nitrogen infiltrated into the specimen at 930 ℃. On the other hand, in our furnace with infrared heating, nitrogen infiltrated into the specimen at 930 ℃ successfully with less ammonia introduction than former furnace. Therefore, in this study, the limit of ammonia decomposition is assessed and possible solutions to expand N-Quench area, especially how to increase the case hardening depth, is examined.
Key words: surface heat treatment, nitrogen infiltration, quench, ammonia decomposition, nitriding