A mixture of nitric acid and fluoric acid is used in pickling. However, because descaling is somewhat difficult in comparison with Type 304, alkali immersion before acid pickling, and if possible, shot blasting are extremely effective.
Sodium hydride baths are necessary to descale this alloy. After the sodium hydride treatment, the material should be immersed in a sulfuric acid bath 165 Degrees F (74 Degrees C) for approximately 3 minutes. A 25-minute immersion in a nitric-hydrofluoric bath 145 Degrees F (63 Degrees C) is then necessary. Rinse. Sulfuric solution: 16% by weight, H2SO4. Nitric solution: 8% HNO3 by weight and 3% HF by weight. Acid etching for macro-inspection-expose material electrolytically to a 3-to-1 HCl to HNO3 solution, saturated with CuCl2 at a current density of 0.645 amp/in (25.4 A/m).
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