Final answer:
Brazing and soldering are processes for joining metal that involve a filler metal and less heat than welding, which melts base metals. They're referred to as filler metal welding processes since they use filler metals to unite materials.
Step-by-step explanation:
Brazing and soldering are both processes used to join pieces of metal together, but they differ significantly from welding. Brazing involves the use of a filler metal with a melting point above 840°F but below the melting point of the base metals. The filler metal is heated to its melting point and then flows over the base metal and cools to form a strong joint. Soldering is similar but uses a filler metal with a melting point below 840°F. In contrast, welding typically melts the base metals themselves to form a joint.
The main difference between brazing, soldering, and welding is the amount of heat required and the state of the base metal during the process. Brazing and soldering do not melt the base metals; instead, they use a filler metal to bond the pieces together, which requires less heat. Welding, on the other hand, often involves melting the base metals themselves to create a fusion of the materials. Therefore, welding requires much more heat than brazing or soldering.
Among the given options, brazing and soldering are correctly identified as "D. Both are filler metal welding processes" because they both use a filler metal to join two pieces of metal without melting the base materials.