HOT-DIP Al-BASE-PLATED SHEET STEEL SUPERIOR IN CORROSION RESISTANCE AFTER HAVING BEEN WORKED, AND MANUFACTURING METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot-dip Al-plated steel sheet superior in corrosion resistance after having been worked, by using a technology of decreasing the thickness of an alloy layer when manufacturing the Al-plated sheet steel. SOLUTION: The hot-dip Al-plated steel sheet superior in corrosion resistance after having been worked has an Al-Fe-Si alloy layer on the surface of the steel sheet. When the surface of the alloy layer is measured by an X-ray diffraction technique, and when integrated intensities of a (112) peak of Al8Fe2Si and a (-327) peak ofβ-AlSiFe are defined as (A) and (B) respectively, A/(A+B) is 0.65 or more. The alloy layer has the thickness of 2.5μm or less. An Al part in an Al-Si layer which covers the surface of the alloy layer has a hardness of 50 to 80 by Knoop hardness. A method for manufacturing the Al-plated steel sheet comprises the steps of: heating a cold-rolled steel sheet or a hot- rolled steel plate to 750 to 900°C at an arrival sheet temperature, in an atmosphere containing 1 to 8 vol.% hydrogen; dipping the heated steel sheet or plate into a molten metal of 640 to 660°C comprising 5 to 8.5% Si, 0.5 to 3% Fe and the balance Al with unavoidable impurities; and then cooling the steel sheet or plate to 610 to 500°C at a mean cooling rate of 5 to 25°C. COPYRIGHT: (C)2009,JPO&INPIT