Spiral welding is a process that uses continuous full penetration MIG surfacing to rebuild damage caused by wear, erosion, corrosion, or cracking, or to increase the size of a part to match the increased size on a mating component. The use of the spiral welding process eliminates distortion of the part that may result from unbalanced stresses in the normal welding process. Spiral welding is a low-energy input process in which the layers of the weld and their associated heat-affected zones are tempered and the grain structure is refined by subsequent and overlapping tempering beads.
Spiral welding can be used to repair and improve products in the remanufacturing process. Components can be improved by this process through the use of selected advanced cover materials; this is based on two broad criteria:
Matching of the parent material to the filler wire of the same or closest available selected material.
The use of different cover materials to enhance resistance to corrosion, erosion or wear.
The post-weld grain structure in the weld and in the heat affected zone must be considered. Add to this factors such as differences in coefficients of thermal expansion, the strength and ductility of the two dissimilar materials, and the possibility of galvanic coupling between the two materials or other connected parts. Careful consideration of the relative coefficients of thermal expansion is necessary to ensure that localized strains at the interface between the cladding and the base material do not exceed acceptable levels during the welding/heat treatment cycle or in service.
Effective pre- and post-weld heat treatment is essential. The use of preheating along with carefully selected surface treatments and the use of low-hydrogen, hydrogen-resistant, self-consuming wires eliminates the risk of hydrogen cracking during the welding process. Post-weld heat treatment is used to control the more important problem of transformation of the matrix to an untempered martensitic structure during the process.
