METHOD OF MANUFACTURING FOR HIGH TENSILE STRENGTH HOT- DIP ZN-Al ALLOY COATED STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide a manufacturing method capable of solving, without requiring more restrictions in manufacturing than is needed, the problem of deterioration in platability such as bare spot at hot-dip Zn-Al alloy coating in the conventional technique. ;SOLUTION: In manufacturing a hot-dip Zn-Al alloy coated steel sheet using a high tensile strength steel sheet containing 0.3-2 mass% Si as a basis material, Sn plating of (0.1 to 10) g/m2 coating weight is performed. The resultant Sn plated steel sheet is subjected to temperature raise up to 400-900°C in a reducing atmosphere or further to holding for the prescribed time after the temperature raise to undergo the diffusion treatment of Sn into ferrite. Then the steel sheet is subjected to hot-dip Zn-Al alloy coating having a composition consisting of 0.05-70 mass% Al and the balance Zn with inevitable impurities. In this way, the high tensile strength hot-dip Zn-Al alloy coated steel sheet can be manufactured. Al content in the hot dipping can be made to 0.05-0.5 mass%, and further, alloying treatment can be performed at 450-550°C after the hot dipping.;COPYRIGHT: (C)2001,JPO