Life Extension of Furnace and Fixture Alloys by Surface Engineering in Carburizing Atmospheres

The heat-treating industry is in need of heat-treatment furnace materials and fixtures that have a long service life and reduced heat capacity. Aluminizing is widely used to increase the high temperature oxidation and carburization resistance of nickel-based alloys. The thickness of the aluminide layer on the alloys increases with increasing aluminizing time. The intermetallic nickel aluminides that formed during aluminizing act as the reservoir of aluminum to maintain a protective alumina layer on the material surface during high temperature services.  Alpha alumina is an effective protection for high temperature and aggressive gaseous environments. Failure mechanisms during prolonged exposure to carburization heat treatment have been investigated. APMT, RA330, RA602CA, 304L, 316L and Inconel 625 alloys were selected to study the anti-corrosion properties. The alloys were exposed to 0.7%C carburizing atmosphere at 900C for 3 months, 6months, and 12months. In this paper the microstructural development of aluminized alloys during the prolonged exposure in the carburizing environment will be presented and discussed.