BLACKENED STEEL SHEET AND ITS PRODUCTION

摘要

PURPOSE:To produce a steel sheet having a black surface which possesses excellent adhesion by forming an Ni or alloyed Ni plating film on the surface of the steel sheet then treating the film with nitric acid or mixed acid consisting principally of nitric acid. CONSTITUTION:An Ni plating layer or alloyed Ni plating layer 2 such as Zn- Ni alloy is formed on the surface of a steel sheet 1. The steel sheet is then dipped for 1-30sec into an aq. soln. contg. nitric acid at 1-30% concn. or a treating liquid for blackening contg. mixed acid consisting principally of nitric acid or contg. an oxidizing agent such as hypochlorous acid or the like in the mixed acid or said liquid is coated on the steel sheet by spraying. The coated steel sheet is dried 5 after rinsing 4 to form a blackened film. A chromate film or phosphate film or a film consisting principally of an org. high polymer compd. is formed on the blackened steel sheet or oil is coated thereon. The chemical converted film such as chromate film, phosphate film or the like is subjected to a surface treatment with a film consisting principally of an org. high polymer compd. then the steel is used.