Abstract: Steel casings are heated to above the transformation temperature and then quench hardened to achieve a fully martensitic structure. Thick-walled casings are quenched with an internal-external quench system, the casing passing within an external spray of quenching liquid and about a mandrel and a nozzle that apply a conical spray within the casing. After quenching, the mandrel and nozzle are rapidly and automatically withdrawn from the moving casing in the direction of casing travel. The casing is then moved out of its initial path and the nozzle is returned to within the external quench. Thin-walled casings are quenched with only an external spray directed both toward the casing and in the direction of casing travel when the casing enters the external quench and, prior to entry of the trailing end of the casing into the quench, the spray is directed both toward the casing and in a direction counter to that of casing travel, so quenching liquid is not directed into the ends of the casing.