Weld overlay, sometimes referred to as cladding or hard facing, is a welding process where a corrosive or wear resistant coating is applied onto a base material to improve parent material properties or restore the original dimension of a worn part.
Types of Weld Overlay
Plasma Transferred Arc (PTA)
PTA is a high energy, low heat inert gas weld overlay process that provides minimal interaction with the substrate material while allowing application of very thick coatings, often up to 3/16”. Commonly applied coatings include tungsten carbide, chrome carbide, Stellite and stainless steels.
Spray and Fuse Tungsten Carbide
Spray and fuse is a two step continuous brazing process that first applies the coating and then fuses it to the base material. This process does not melt the base material and consequently there is no dilution of the overlay alloy. The bond is created by the diffusion of atoms between the overlay alloy and base material resulting in a very dense, hard coating with high bond strength.
Flux-cored Arc Welding (FCAW)
FCAW is a flexible, conventional weld overlay process where a cored wire is fed through an electric arc to create a weld deposit on the base material. The cored wire consists of a metal sheath, usually nickel, that is wrapped around a powder center containing tungsten carbide particles, alloying elements and flux. Arc temperature is 6,000 – 8,000°C which creates significant melting and dilution of the base material.
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