PRODUCTION OF Zn-Al-Si ALLOY PLATED STEEL SHEET EXCELLENT IN DESIGNING PROPERTY

• Main Authors: TSUJIMOTO YASUO, MASUMOTO HIROTO, HIKINO SHINYA, MATSUNAGA TAKAHIRO
• Format: Patent
• Language: English
• Published: 08.08.2000
• Edition: 7
• Subjects: CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; METALLURGY; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION

PROBLEM TO BE SOLVED: To reduce the variation of spangle patterns by executing annealing under the conditions that the reducing gas atmosphere and dew point in an annealing furnace satisfy specified relations. SOLUTION: A base metal steel sheet is subjected to Zn-Al-Si alloy plating by using continuous hot dip plating equipment provided with an inline annealing device. The compsn. of the plating bath is composed of, by weight, 30 to 70% Al, 0.05 to 2.0% Si, and the balance Zn with inevitable impurities. This steel sheet is first heated in an oxidizing furnace to remove oil contents adhered to the surface, which is cleaned, and, after that, annealing is executed in a reducing atmosphere in an annealing furnace. By this annealing, together with the removal of strains, iron oxide in the surface of the steel sheet is reduced to activate the surface, so that the plating adhesion therein can be secured. For this purpose, the gas atmosphere in the annealing furnace is controlled so as to satisfy the following three relations: +10 deg.C >= dew point >= -40 deg.C; 2% hydrogen concn. <=30%, and the balance nitrogen; dew point >= (hydrogen concn. × 2-annealing temp./10+10) deg.C.