STEEL SHEET FOR FUEL TANKS AND PROCESS FOR MANUFATURING THE SHEET

摘要

A steel sheet for fuel tanks which has a Zn-Ni alloy coating electroplated on at least one side of the sheet and a chromate coating formed on the alloy coating. The chromate coating exhibits a change in the build-up of chromium after immersion in boiling water for 30 minutes of within 2% based on the build-up of chromium before the immersion, an L value (indicating the surface color tone of steel sheet) of 55 or above, and a difference between the maximum and minimum L values of within 3. The chromate coating can be formed by applying a chromate treatment fluid which contains chromic acid at a trivalent chromium/total chromium mass ratio exceeding 0.5, phosphoric acid at a phosphoric acid/total chromium mass ratio of 0.1 to 5.0 and an organic reducing agent onto the above alloy coating and heating the resulting sheet. The steel sheet exerts excellent corrosion resistance against fuels such as gasoline, alcohols, and alcohol blended gasolines over a long period and is excellent in surface appearance.