The definition of brazed joints is: a gas tight joint obtained by the joining of metal parts with metallic fixtures or alloys which melt at a temperature of above _________ degrees F, but lower than that of the metal being joined.

• A. 600
• B. 842
• C. 1000
• D. 1200

Answer: (B)

Brazing relies on a filler metal that melts at a temperature high enough to avoid melting the parts being joined, yet low enough to flow into the joint and wet the surfaces. The filler metal used in brazing typically has a melting point around 450°C (about 842°F), which provides that necessary window: above 842°F so the filler melts, but below the melting point of the metals being joined so they stay solid during the joint formation. This is what allows the filler to flow into the joint by capillary action and form a gas-tight seal as it cools and solidifies. Choosing 842°F as the threshold reflects the common brazing filler-metal temperature range, giving the appropriate balance between melting the filler and not tempering the base metals. If the melting point were much lower, you’d risk melting the base parts; if it were much higher, the filler might not flow properly into the joint before the base metals reach problematic temperatures.