Abstract: Ferrous material such as tool steel is annealed in a batch or continuous furnace into which inward leakage of an ambient oxidant occurs. The hot zone is heated to a temperature of about 1250.degree.-1650.degree. or higher and the material passed therethrough under a nitrogen based atmosphere comprised of nitrogen, methane and a minor addition of propane with nitrogen comprising approximately 90% of the hot zone atmosphere. Propane reacts with the oxidants to form a relatively active form of methane which, together with methane introduced as such into the hot zone, reacts effectively at low temperatures (1400.degree. F. or below) to avoid both decarburization and sooting. The hot zone atmosphere evinces considerably lesser tendencies to decarburize or soot than atmospheres formed only of N.sub.2 --C.sub.3 H.sub.8 mixtures and is considerably more reactive than atmospheres formed only of N.sub.2 --CH.sub.4 mixtures at these lower temperatures.