GALVANNEALED STEEL SHEET EXCELLENT IN SPOT WELDABILITY AND PHOSPHATE TREATMENT PROPERTY AND ITS PRODUCTION

摘要

PURPOSE: To improve spot weldability and phosphate treatment property by heating a hot dip galvanized steel sheet to make an alloy, subjecting the steel plate to oxidation treatment, and further tempering and rolling the steel plate to control the flat area rate. ;CONSTITUTION: A hot dip galvanized steel sheet is heated to make an alloy to form a galvannealed layer having 8-12wt.% iron content. Then the steel sheet is oxidated to be coated with an inert oxide film. Then the steel sheet is tempered and rolled in a manner that the area rate of a flat area formed by contact of tempering rolls with the steel sheet is 20-70%. It is preferable that oxidation is performed by bringing the steel sheet into contact with a treating liquid controlled to pH1 to 3 containing 0.01-0.5wt.% hydrogen peroxide. Thereby, frequencies for dressing and exchanging of electrodes for spot welding are decreased.;COPYRIGHT: (C)1993,JPO&Japio