NITRIDING

This method is advantageous due to the fact that a harder case is obtained than by carburizing. Many engine parts such as cylinder barrels and gears may be treated in this way. Nitriding is generally applied to certain special steel alloys, one of the essential constituents of which is aluminium. The process involves the exposing of the parts to ammonia gas or other nitrogenous materials for 20–100 h at 500–650°C. The container in which the work and ammonia gas are brought in contact must be airtight and capable of maintaining good circulation and even temperature throughout. The depth of case obtained by nitriding is about 0.2–0.4 mm if heated for 50 h. The nitriding process does not affect the physical state of the core if the preceding tempering temperature was 500°C or over.