Hardface Weld Overlay
Weld overlays are metallic coatings welded directly onto the substrate. The high-heat welding process forms a molecular-level bond with the base metal, essentially alloying the coating to the substrate at the interface. The result is a durable, almost completely nonporous and impenetrable coating with excellent resistance to high-stress gouging wear.
Weld overlays are typically applied in greater thicknesses than thermal sprayed coatings. As such, substantial amounts of material may be applied in a comparatively short time.
The long history of hardfaced weld overlays has given rise to an impressive array of engineered materials available for application. The weld alloying process makes the applied material an integral part of a component’s physical structure. By nature of the process, highly customized surfaces may be developed by layering and alloying several different materials.
High Resistance to Chipping and Peeling
Once a coating has been welded onto a substrate, it is virtually impervious to the problems of coating separation, lifting, and peeling that can sometimes occur in thermal sprayed coatings under high stress. The alloyed material also combines the high resistance to sliding abrasion offered by thermal sprayed coatings with an equally exemplary resistance to gouging and plowing wear.
Parts are exposed to high surface temperatures (in excess of 2,300°F) and must be resistant to thermal deformation. Consideration needs to be given to any prior heat treatment of the substrate material and the thermal effects of the welding process on substrate metallurgy. Careful control of preheat, interpass and post-weld heat treat temperatures may be required for certain substrate alloys in order for the weld overlay process to be successful.
Hardfaced weld overlays are applied in substantial thicknesses (typically > .100”), and significant machining may be necessary to bring finished thickness below that value.
Coefficients of expansion for the base metal and applied coating should be similar. Dissimilar coefficients can lead to cracking in the coating and possible damage to the component as the material and substrate cool.
Weld overlays may not be applied to nonmetallic base materials.