What is the fundamental metallurgical difference between brazing and soldering?

• A. Brazing uses a filler metal with a melting point above 450°C while the base metals do not melt; soldering uses filler metal melting below 450°C with no base-metal melting.
• B. Both brazing and soldering require melting the base metals to form a joint.
• C. Brazing uses capillary flow without any filler metal.
• D. Soldering produces a stronger joint than brazing due to higher temperatures.

Answer: (A)

The main idea is the temperature at which the filler metal melts relative to the base metals. In brazing, the filler metal melts at a high temperature (above about 450°C) and flows into the joint by capillary action while the base metals stay solid. The joint forms from the molten filler metal bonding to the surface, not by melting the base metals themselves. In soldering, the filler metal melts at a lower temperature (below about 450°C) and, again, the base metals do not melt; the liquid solder wets the surfaces and provides the joint as it cools. So the key metallurgical difference is the melting point of the filler metal and whether the base metals remain solid during the process. The other statements mischaracterize the role of the filler metal, capillary action, or the relative temperatures.