| 摘要 |
PURPOSE:To prevent the generation of harmful gaseous NOx from a pickling bath in the stage of pickling away the scale on the surface of a worked Ti product by pickling the Ti product while a prescribed value of residual compressive stress is made to remain on the surface layer part of the product. CONSTITUTION:Scale is formed by oxidation on the Ti surface during a heat treatment in the stage of working the Ti stock to a plate, bar or pipe material by heating, hot working, cold working and annealing treatment. The Ti material is pickled with a pickling soln. of 30-60 deg.C contg. 2% HF and 15-13% HNO3 to remove said scale. The Ti material is lightly forged by a hammer or blasted with steel balls or sand prior to the pickling treatment so that 5-35kg/cm<2> residual compressive stress is formed to the part within 0.1mm thickness from the Ti surface. The material is uniformly pickled without generating the NOx which is the harmful gas during the pickling treatment and without generating brittleness by the absorption of hydrogen, by which the Ti product having high quality without oxide scale is obtd.
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