Galvannealed steel sheet with distinguished anti-powdering and anti-flaking properties and process for producing the same

• Main Authors: KANAMARU; TATSUYA, NAKAYAMA; MOTOHIRO, NUMAKURA; YUKIO, HAYASHI; HISAO, HONDA; TADAFUMI, SUEMITSU; YUKIMASA
• Format: Patent
• Language: English
• Published: 17.09.1991
• 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; LAYERED PRODUCTS; LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT ORNON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM; METALLURGY; PERFORMING OPERATIONS; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TRANSPORTING

A galvannealed steel sheet having distinguished anti-powdering property and anti-flaking property is disclosed. The steel sheet comprises a matrix steel sheet and a galvannealed coating layer having a coating weight of 45 to 90 g/m2, composed of 8 DIFFERENCE 12 wt. % Fe and 0.05 DIFFERENCE 0.35 wt. %, preferably 0.05 DIFFERENCE 0.30 wt. % Al, the balance being Zn, provided on at least one side of the matrix steel sheet, the galvannealed coating layer having a GAMMA phase with a thickness of not more than 1.3 mu m, preferably not more than 1.0 mu m in the region at the boundary to the matrix steel sheet, and the surface region of galvannealed coating layer has a structure either (1) eta and zeta phases do not exist in the surface region of the galvannealed coating layer, or, (2) when at least one of eta and zeta phases exist therein, the total amount of the at least one of eta and zeta phases in the galvannealed coating layer is not more than 1.5 g/m2.