Q1: Brazing filler metal used for joining steel plates

ANS:A - melts below the melting points of base metals.

When referring to a brazing filler metal that "melts below the melting points of base metals," it means that the temperature at which the filler metal liquefies (melts) is lower than the melting points of the metals being joined, known as the base metals. Here's an explanation of what this means in practical terms:

1. Brazing Process: Brazing is a joining process where two or more metal components are joined together using a third material called a filler metal or brazing alloy. The brazing filler metal is heated above its melting point but below the melting points of the base metals being joined.
2. Lower Melting Point: The brazing filler metal is specifically chosen for its lower melting point compared to the base metals. This ensures that during the brazing process, the filler metal melts and flows into the joint, forming a bond between the base metals, without melting the base metals themselves.
3. Bonding Mechanism: As the filler metal melts, it wets the surface of the base metals, forming a metallurgical bond between them. The capillary action draws the molten filler metal into the joint, where it solidifies upon cooling, forming a strong and durable joint.
4. Prevents Distortion or Damage: By melting below the melting points of the base metals, the brazing process avoids subjecting the base metals to excessive heat, which could cause distortion, warping, or other damage to the components being joined.
5. Choice of Filler Metal: The selection of the brazing filler metal depends on various factors such as the types of base metals being joined, the service conditions of the final assembly, and the desired properties of the joint.

Overall, using a brazing filler metal that melts below the melting points of the base metals is essential for achieving successful brazed joints without compromising the integrity of the components being joined. It allows for effective bonding while minimizing the risk of damage to the base materials.