When using filler metal, what is the critical consideration regarding its compatibility with the base metal?

The key consideration when using filler metal in welding is understanding that filler metal is not always necessary for every welding application. Some welding processes, particularly those dealing with thin materials or specific techniques such as autogenous welding, may not require filler metal at all. In these cases, the focus is on joining the base metals without introducing additional material, which can sometimes lead to better control over the weld pool and minimize contamination or porosity.

While it is important to choose filler metal that is compatible with the base metal in certain applications for effective bonding and to achieve desired mechanical properties, there are instances where including filler metal is not required. Thus, this understanding of when filler metal is needed versus when it is not is crucial for effective welding practices.