Continuous treatment of steel sheet

Claim 1

A process for the continuous treatment of steel sheet, comprising the sequential steps of: thermally treating the steel sheet to form an oxide layer on its surface; pickling the sheet having the oxide layer by bringing the sheet into contact with a solution of formic acid, the solution having an iron content of at least 50 mg/l, while maintaining the pH of the solution between 1.5 and 4, and maintaining the temperature of the solution both above 40° C. and above a minimum value T m in C.° given by the equation T.sub.m =20+(pH of solution-1.5)32; and adding hydrogen peroxide oxidizing agent to the solution, while maintaining the concentration of the oxidizing agent in the solution between a minimum value equal to the value necessary to oxidize at least 80% of the ferrous ions in solution to ferric ions and a maximum value of up to ten times the minimum value wherein, the formic acid pickling solution is self-regenerating by the sequential steps of, reacting the formic acid with the ferrous oxide coating of the sheet to yield ferrous formiate and water, reacting the ferrous formiate, the hydrogen peroxide oxidizing agent which is added, and the formic acid together to form ferric formiate and water, and producing a hydrolysis reaction between the ferric formiate and the water to regenerate the formic acid and produce a ferric hydroxide precipitate; removing the ferric hydroxide precipitate from the pickling solution, and recycling the regenerated formic acid.