Welding joins materials by heating to suitable temperature with or without filler metal; molten weld pool forms a heterogeneous structure from base metals and filler metal.

Welding joins materials by heating to suitable temperature with or without filler metal; molten weld pool forms a heterogeneous structure from base metals and filler metal.

• A. The weld pool forms a homogeneous structure identical to base metals
• B. The molten weld pool forms a homogeneous structure
• C. Welding never uses filler metal
• D. The molten weld pool forms a heterogeneous structure from base metals and filler metal

Answer: (D)

When welding, the molten pool is formed from the base metals and, if filler metal is used, the filler itself. As this pool cools and solidifies, its composition is a blend of the base metals and the filler, not simply one of the original metals. This mixture leads to a weld metal with varying chemical composition and microstructure across the weld zone, i.e., a heterogeneous structure. The presence of different elements and phases from both sources creates a region that differs from either base metal alone. That’s why the statement about the molten weld pool forming a heterogeneous structure from base metals and filler metal is the best fit. Welding with filler metal intentionally introduces a new element into the weld, so the result isn’t identical to either parent metal, and it isn’t perfectly homogeneous.

When welding, the molten pool is formed from the base metals and, if filler metal is used, the filler itself. As this pool cools and solidifies, its composition is a blend of the base metals and the filler, not simply one of the original metals. This mixture leads to a weld metal with varying chemical composition and microstructure across the weld zone, i.e., a heterogeneous structure. The presence of different elements and phases from both sources creates a region that differs from either base metal alone.

That’s why the statement about the molten weld pool forming a heterogeneous structure from base metals and filler metal is the best fit. Welding with filler metal intentionally introduces a new element into the weld, so the result isn’t identical to either parent metal, and it isn’t perfectly homogeneous.