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Show Heat Treating Processes Through Heat Treating Selective Heat Treating Through hardening-- --Carburizing --Annealing Tempering-- --Carbo-nitriding --Normalizing Austempering-- --Nitriding ---Spheroidizing Martempering-- ---Surface hardening ~Stress relieving Fig. 2 - Ferrous Metal Heat Treating Processes finished products. This category includes heat treating processes such as: • Surface hardening • Case hardening carburizing, carbo-nitriding, nitriding. These heat treatments are typically performed on steels, which are ferrous metals with up to 1.7 percent carbon, although cast irons, ranging from 1. 7 to 4.3 percent carbon, can a Iso be hea t treated. HEAT TREATING EQUIPMENT Heat treating operations can be performed in a wide variety of furnaces or other heating units, and cooling can be accomplished in various liquid quenching media or at controlled rates in air. Often, a controlled atmosphere will be used to protect or enhance the qualities of the metal workpiece. Heat treating furnaces may be of continuous or batch, direct- or indirect-fired design, with heating temperatures ranging from 250°F to 2, 500°F. In general, a heat treating furnace consists of the following: • Box-like steel shell with heating device • Access door(s) • Refractory lining • Holding and/or movement mechanisms • Quenching systems 254 • Temperature controls and indicators • Atmosphere controls. Although individual heat treating furnaces may include only some of these components, all heat treating furnaces meet the general requirement for providing accurate, uniform, and controllable temperatures during heating~ soaking, and cooling treatment periods. Batch heat treating furnaces are commonly used to process low volumes, to handle special parts that would be difficult to handle with a continuous conveyor, to process small numbers of very large parts, and to carburize parts over long periods to obtain deep cases. The major types of batch heat treating furnaces/equipment are: • Box • Car bottom • Bell • pit • Liquid batch (molten lead and salt) • Fluidized bed • Vacuum • Induction • Flame head (hardening). In general, batch furnaces provide the capabi 1 i ty of eas i ly adapt ing to accommoda te a wide variety of parts and heat treatment cycles. However, batch furnaces do require significant labor for loading and unloading workpieces. |
