| 摘要 |
PURPOSE:To form a uniform bluing film at a low cost by loosely coiling a steel strip with spacers so as to leave a gap and by heating the steel strip at a specified temp. in an oxidizing atmosphere having a specified compsn. to carry out box annealing. CONSTITUTION:A steel strip is loosely coiled with spacers so as to leave >=1.0mm gap. The steel strip is then heated at 300-500 deg.C for >=1hr in an oxidizing atmosphere consisting of 5-75vol% H2 and the balance inert gas and having 30-60 deg.C dew point to carry out box annealing. By this box annealing, a steel sheet having a fine uniform bluing film is obtd. at a low cost.
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