Method for calculating film thickness of grain boundary oxide layer, method for determining plating properties, method for manufacturing plated steel sheet, and film thickness calculation device

A film thickness calculation device configured for measuring a film thickness of a grain boundary oxide layer remaining on a steel sheet after a pickling treatment, the film thickness calculation device comprising:

• an intensity measurer configured for measuring a fluorescent X-ray intensity of an element being comprised in the steel sheet and constituting an oxide in the grain boundary oxide layer;
• a distance measurer configured for measuring a measurement distance being a distance between the steel sheet and a measurement position of the fluorescent X-ray intensity of the intensity measurement portion;
• an intensity corrector configured for correcting, based on the measurement distance, the fluorescent X-ray intensity measured by the intensity measurement portion;
• and
• a film thickness calculator configured for calculating a film thickness of the grain boundary oxide layer based on:
• a correlation between a pre-extracted fluorescent X-ray intensity and the film thickness of the grain boundary oxide layer;
• and the fluorescent X-ray intensity corrected by the intensity correction portion.