Optimization of protective atmospheres for annealing and hardening operations in continuous furnaces

Nitrogen (N₂) atmospheres with different, not always optimized levels of reducing and carburizing gases are often used to prevent decarburizing and oxidation of steel parts during annealing in continuous furnaces.  The type and concentration of these additives in N₂ should correlate to the extent of air leakage into furnace, entrainment of air with loaded parts, steel composition, and complex reaction kinetics in the gradients of oxygen and temperature existing between the entrance and hot zones of the furnace.   This study explores the effect of small, 0.1 vol.%--0.4 vol.% propane additions on composition of air-contaminated N₂ atmosphere in the temperature range of 500^oC--860^oC.  Microstructures and microhardness data is also presented for AISI 1045 steel exposed to the atmospheres produced.  Atmosphere compositions compared include those produced by a novel, plasma-activated, in-situ reformer of N₂-diluted propane.  The second method extends the atmosphere protection to the lower range of annealing temperatures.