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Brazing is a joining process whereby a non-ferrous filler metal and an alloy are heated to melting temperature (above 450C) and distributed between two or more close-fitting parts by capillary attraction. At its liquidus temperature, the molten filler metal interacts with a thin layer of the base metal, cooling to form an exceptionally strong, sealed joint due to grain structure interaction. The brazed joint becomes a sandwich of different layers, each metallurgically linked to each other.

In the more common, more specific usage, brazing is the use of a bronze filler rod coated with flux, together with an oxyacetalyene torch, to join pieces of steel. Soldering is the process of using a filler wire made of an alloy traditionally containing tin and lead to join pieces of copper, bronze, tin, or galvanized steel; for this process, with its lower temperature requirements, any of a wide variety of heat sources are used. Silver soldering is a like process where silver is included in the alloy for the filler wire.

Brazing is similar to welding except that lower temperatures are used, and the filler metal has a significantly different composition and lower melting point than the materials being joined.

The "welding" of cast iron is usually a brazing operation, with a filler rod made chiefly of nickel being used allthough true welding with cast iron rods is also available.