Question

Temperature attained in soldering of metals is about

• A. 750 -- 1000\(^\circ\)C
• B. 500 -- 750\(^\circ\)C
• C. 150 -- 300\(^\circ\)C
• D. 1000 -- 1250\(^\circ\)C

Hint:

Remember the magic number: 450\(^\circ\)C.

• Filler metal melts BELOW 450\(^\circ\)C \(\rightarrow\) Soldering.

• Filler metal melts ABOVE 450\(^\circ\)C \(\rightarrow\) Brazing.
(In both cases, the base metal does not melt).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Joining processes are often categorized by the temperature used and whether the base metal is melted. The question asks for the typical temperature range for soldering.

Step 2: Detailed Explanation:
Let's define the three main thermal joining processes by their filler metal melting points:

• Soldering: A process where a filler metal (solder) is melted and flows into a joint, but the base metals are not melted. By definition, the solder used has a melting point

below 450\(^\circ\)C. Common solders like tin-lead alloys melt around 183\(^\circ\)C, and lead-free solders (e.g., SAC alloys) melt in the 217-227\(^\circ\)C range. Therefore, the typical working temperature is in the 150 -- 300\(^\circ\)C range.

• Brazing: Similar to soldering in that the base metals are not melted, but it uses a filler metal with a melting point

above 450\(^\circ\)C. The ranges in options (A) and (B) fall into the brazing category.

• Welding: This process involves melting the base metals (and often a filler metal) to fuse them together. Temperatures are much higher, typically well above 800\(^\circ\)C, and reaching the melting point of the base metal (e.g., \(\sim\)1500\(^\circ\)C for steel). The range in option (D) is approaching welding temperatures.
Based on the definition, soldering is the lowest temperature process of the three.

Step 3: Final Answer:
The temperature range for soldering is defined as being below 450\(^\circ\)C, with common processes operating in the 150 -- 300\(^\circ\)C range.