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Friday, 26 February 2016

Liquid Carburizing

          Where a fairly thin case is required a more economical process is to carburize the parts in a liquid bath. A molten salt bath which will give up carbon to the steel, thus producing a carburized surface, has certain advantages, in that heating is rapid and distortion is minimized. The development of such salt baths is comparatively recent. Briefly, the salt baths usually contains sodium cyanide, barium chloride, sodium carbonate, and other salts, which is heated by electrical immersion elements or by a gas burner. For a constant time and temperature of carbonization, the depth of case depends on the cyanide content. The sodium cyanide content will not exceed 12% of the weight of the bath if a deep case is desired, and may go up to 23% for lighter cases. The temperature range is 1550°F-1750°F. With the lower temperatures more nitrogen will enter the case, which is benificial, and at higher temperatures more carbon will be taken in. This general process may be thought of as an extension of the cyanide process, wherein different compositions of the salt bath and higher operating temperatures are used. The parts leave the bath with a clean, bright finish, the scaling experienced during pack hardening being avoided.

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