Pickling of ferrous materials Part-I-with hydrochloric acid

A comparative study has been made on the pickling of ferrous materials by hydrochloric acid and sulphuric acid. It has been seen that pickling of ferrous metal with hydrochloric acid shortens time, reduces attack on base metal and furnishes a pit-free pickled surface with less absorbed hydrogen even without inhibitor. It is possible to recover the total amount of hydrochloric acid from spent pickling bath. Tendency of hydrochloric acid pickled surface to rapid oxidation can be prevented by treatment with dilute caustic soda solution. Acid vapour in pickling shop can be held under control by suitable exhaust and by operation of the bath at comparatively lower temperature below 70°C. (Mr. J. Konar, Senior Scientific Assistant, Messrs N.G. Banerjee and H.K. Chakravarti, Scientists and Dr. T. Banerjee, Scientist-in-charge, National Metallurgical Laboratory)