Thermochemical Corrosion of Furnace Materials in Atmospheres Containing Ammonia

Abstract

Furnace components are made from heat-resistant materials that must withstand the long-term effects of the atmospheres used during heat treatment. In a nitriding furnace, the atmosphere usually consists of various gaseous media that react not only with the treated parts but also with the furnace equipment. This leads to thermochemical corrosion, even with carefully selected heat-resistant and stainless steels or nickel-based alloys. The present research focuses on determining the long-term effects of ammonia-containing atmospheres on the metallic furnace materials AISI 309, AISI 314, Alloy 600, and Alloy 601. The materials studied were exposed to numerous nitriding or nitrocarburizing treatments for more than 10 years to investigate the long-term effects of repeated contact with ammonia-containing atmospheres. The surface layers of the samples were characterized by several methods to determine the microstructural changes due to nitrogen absorption. A different nitrogen absorption of the metallic furnace materials from the heat treatment atmosphere, depending on the material properties, could be proven by the investigations.