| 摘要 |
PROBLEM TO BE SOLVED: To obtain a steel sheet excellent in adhesion to paint and film, corrosion resistance and weldability and further in resistance to tin release by conducting tinning at specified current density and tinning weight in a tinning bath contg. phenolsulfonic acid and sulfuric acid in a specified ratio. SOLUTION: One or both sides of a steel sheet are degreased and pickled, a tinning bath contg. 20-40 g/L Sn<2+> , 10-25 g/L phenolsulfonic acid, expressed in terms of sulfuric acid, and 30-150 g/l sulfuric acid is used, and tinning is conducted at 10-40 ASD current density and 300-2000 mg/m<2> tinning weight. This tinning coat formed on the steel sheet surface consists of tin grains having 0.3-1.5μm average diameter and distributed sparsely and closely, sparse plating regions having <=10% tin grain coverage are scattered, the average area of the regions is controlled to 100-200μm<2> and the total area rate on the sheet surface to 10-50%, the tin grains are more closely distributed in the region other than the sparse region than in the sparse plating region, and the average tin coverage rate by the tin grains is >=40%.
|
