PROCESS FOR PRODUCING HIGH-STRENGTH COLD ROLLED STEEL SHEET EXCELLING IN CHEMICAL TREATABILITY AND RELEVANT PRODUCTION EQUIPMENT.

摘要

A process for producing a high-strength cold rolled steel sheet through continuous annealing of a cold rolled steel sheet by a continuous annealing furnace wherein the cooling system for a cooling zone involving a part or the whole of 600Ë¿ to 250Ë¿C steel sheet temperature range subsequent to heating for recrystallization consists of at least one member selected from among gas cooling, diffusion cooling and cooling tube cooling, or equipment for simultaneous use in cold rolled steel sheet/hot-dip galvanized steel sheet furnished with the continuous annealing furnace, characterized in that the surface of the steel sheet is exposed toan atmosphere capable of oxidizing iron within the above steel sheet temperature range to thereby oxidize the surface, pickled on the exit side of the annealing furnace and provided with 1 to 50 mg/m2 iron or Ni plating.