How does the grain typically change as successive passes are added in a weld?

How does the grain typically change as successive passes are added in a weld?

• A. A finer grain forms with each additional pass
• B. The grain becomes coarser with more passes
• C. The grain remains unchanged
• D. Grain orientation becomes random

Answer: (A)

Repeated welding passes create multiple heating and cooling cycles in the weld region. Each pass remelts and re-solidifies part of the weld area, and the cooling that follows typically happens relatively quickly, promoting many sites where new grains can start to form. The extra nucleation sites from successive passes encourage the formation of more, smaller grains rather than letting existing grains grow larger. The result is a finer grain structure after each additional pass, which generally improves toughness and strength.

Repeated welding passes create multiple heating and cooling cycles in the weld region. Each pass remelts and re-solidifies part of the weld area, and the cooling that follows typically happens relatively quickly, promoting many sites where new grains can start to form. The extra nucleation sites from successive passes encourage the formation of more, smaller grains rather than letting existing grains grow larger. The result is a finer grain structure after each additional pass, which generally improves toughness and strength.