The carbonitriding process enhances parts with a hard, wear resistant surface. Desired part case depths are designed by product engineers and controlled by several heat treat process variables.

A part’s carbonitrided surface is produced by diffusing carbon and nitrogen into the surface of the heated part via carbon and nitrogen rich carrier gasses. Carbon is derived from endothermic gas and natural gas, nitrogen is derived from ammonia gas additions to the furnace atmosphere. The five main carbonitride process variables are temperature, time at temperature, carbon potential of the atmosphere gasses, ammonia volume, and part loading density.

Temperature control instrumentation reviews furnace temperatures and adjusts burner output appropriately. Time at temperature is controlled on continuous belt furnaces by establishing belt speeds, usually in inches per minute. In row-furnaces, time at temperature is described as “minutes per cycle”, in batch furnaces as “hours per event.” Carbon potential, usually described as percentage of carbon, is a measure of the furnace atmosphere’s capability to provide nascent carbon to the heated surface of the work piece. It is controlled via oxygen sensing probes placed at designated locations within the furnace; the sensors provide feedback to a system which varies the input of natural gas and air to the furnace in order to balance the process gas appropriately. Established nitrogen flows are controlled through flow meters.