| 摘要 |
PURPOSE:To simply remove oxide scale on the surface of a stainless steel material at a low cost by annealing the steel material hot worked in the form of a bar or strip and bringing it into contact with ammonium chloride vapor at a specified high temp. CONSTITUTION:A stainless steel material S hot worked in the form of a bar or strip by hot rolling or other method is annealed by heating to 800-1,200 deg.C in an annealing furnace 1. In order to remove oxide scale formed on the surface of the steel material S during the annealing, the steel material S is passed through a furnace 7 filled with an atmosphere of ammonium chloride vapor at <=400 deg.C. At this time, in case where the steel material S is ferritic, the annealed steel material S is directly passed through the furnace 7 at 600-900 deg.C. In case where the steel material S is austenitic, the annealed steel material S is cooled once in a quenching unit 2, reheated and passed through the furnace 7 at 600-900 deg.C. During passing through the furnace 7, the ammonium chloride vapor is decomposed by the high temp. of the steel material S and generated gaseous hydrogen chloride makes the oxide scale easily strippable. Most of the scale is stripped and removed in a cooling and washing unit 8 and then finish cleaning is carried out in a nitric acid-hydrofluoric acid dipping unit 5 and a washing unit 6.
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