Abstract: A process for heat treating a metallic workpiece comprises the steps of first heating the metallic workpiece in a gas stream fluidized bed made from a plurality of refractory particles for 2 min to 10 min under an inert-gas atmosphere to a treatment temperature of from about 500.degree. to 650.degree. C. Then the heated workpiece is preoxidized with an oxidizing gas stream in the fluidized bed. Finally the heated workpiece is nitrocarburized by contacting it for between 0.5 h and 10 h in the fluidized bed with a gas mixture composed of nitrogen, ammonia, and a carbon-rich gas.