MEASURING METHOD OF IRON CONTENT IN PLATED LAYER ON HIGH-SI-CONTAINED HIGH-STRENGTH GALVANNEALED STEEL PLATE

PURPOSE:To measure an iron content in a plated layer on a high-Si-contained high galvannealed steel plate by a method wherein only a part of the plated layer is stripped and dissolved by using a hydrochloric acid aqueous solution within a specific concentration range, which contains a ground-iron dissolution inhibitor within a specific range. CONSTITUTION:On a high-Si-contained high-strength galvannealed steel plate, an Si-Mn composite oxide B is formed into an island shape at an interface between a plated layer A and a ground-iron steel plate C. Then, when an iron content in a plated layer on the alloyed molten zinc-plated steel plate which uses Si a content of 0.2 to 2.0% as a ground is measured, only the part of the plated layer on the galvannealed steel plate is stripped and dissolved by using a hydrochloric acid aqueous solution which contains a ground-iron dissolution inhibitor within a range of 0.15 to 0.25% and whose concentration range is at 2 to 8%, and the iron content in the plated layer is drawn from the measured result of the iron content in the stripping liquid. When the ground- iron dissolution inhibitor is at 0.15% or lower, it is not effective, and it dissolves the ground iron. When it is at 0.25% or higher, its suppression effect is too high, and the dissolution of the plated layer is suppressed.