What factor is critical when selecting a filler metal for welding?

When selecting a filler metal for welding, the type of base metal being welded is critical. This is because the filler metal needs to be compatible with the base metal in terms of chemical composition, mechanical properties, and the intended application of the weld. Using a filler metal that is not suitable for the base metal can lead to issues such as poor weld strength, reduced ductility, or increased susceptibility to cracking.

The compatibility affects how the two materials will interact during the welding process, including their melting points, joining characteristics, and the resulting microstructure of the weld joint. Therefore, understanding the properties of both the base metal and the filler metal is key to ensuring a successful and reliable weld. Other factors, while they may have their importance, do not affect the intrinsic relationship between filler metal and base metal like this.