Ammonia dilution during nitriding and carbonitridingin a fluidized bed of 41CrAlMo7 constructional steel

Abstract

Nitriding of 41CrAlMo7 steel was carried out in a fluidized bed of aluminum oxide at a constant temperature of 570oC/4h in ammonia with technical nitrogen or with nitrogen-hydrogen mixture. Carbonitriding was carried out in ammonia with technical nitrogen for two different carbon carriers. In addition, one process was carried out in ammonia with the addition of 5% propane. The influence of diluting ammonia with pure and technical nitrogen upon the hardness and thickness of the nitrided layer was investigated. The hardness and thickness of the carbonitrided layer in ammonia with technical nitrogen and natural gas or carbon dioxide were compared with the parameters of the layer carbonitrided in ammonia and propan. High surface hardness and thickness of the nitrided layer were obtained with the participation of 70% of pure nitrogen or 30% of technical nitrogen in a mixture with ammonia after preliminary oxidation at 350oC/ 30min in air. In case of carbonitriding, the highest hardness and thickness of the nitrided layer were obtained in a mixture of ammonia with and the addition of 5% propane, and the highest thickness of the nitride compound zone in a mixture of ammonia and technical nitrogen with the addition of natural gas or carbon dioxide.