Under these conditions, as there is little likelihood of operating a controlled-atmosphere policy, surface damage due to oxidation or scaling and, in the case of steels, decarburization, must be removed at a later stage in the process. In addition, it is usual to expose the metal directly to a burned-fuel atmosphere containing about 1% excess oxygen necessary to ensure complete combustion and, therefore, the most economic use of the fuel. When reheating for subsequent working or shaping, the main concern is to heat the components as quickly and economically as possible to the working temperature, within the metallurgical constraint of avoiding element redistribution and thermal cracking. (2) Reheating for final heat treatment, sometimes of finished components. (1) Reheating for subsequent working or shaping. The exposure of metals to gases at high temperatures during production processes may be divided broadly under two headings.
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