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摘要

In the box annealing of ferrous metal sheets, the occurrence of carbon deposits and staining is materially reduced by initially heating the sheet in a protective atmosphere which is essentially a mixture of N.sub. 2 and H. sub.2 and then modifying the atmosphere so that during the soak period it contains at least about 3% CO.sub.2, 3% CO, 4% H.sub.2 and 0.5% H.sub.2 O, balance N. sub.2. Atmosphere modification is effected only after the sheet portions, which are exposed to the protective atmosphere, reach a predetermined, minimum replacement temperature within the range 1000° - 1400°F.