What type of grain structure do multi-pass welds produce?

What type of grain structure do multi-pass welds produce?

• A. Finer grain with each pass refines the grain of the previous pass
• B. Coarser grain with more passes
• C. No change in grain structure
• D. Random grain distribution

Answer: (A)

With multiple passes, the heat from each new weld deposit re-heats the metal from the previous pass. This partial remelting and subsequent solidification create new grain nucleation sites and can promote recrystallization of the prior grains. As a result, the grain structure becomes finer with each additional pass because the repeated thermal cycles break up the larger grains from earlier passes and form smaller, more uniform grains. This refinement improves toughness and strength in the weld area. Coarser grain, no change, or a random distribution wouldn’t reflect the way repeated heating and re-solidification influence grain growth and nucleation during multi-pass welding.

With multiple passes, the heat from each new weld deposit re-heats the metal from the previous pass. This partial remelting and subsequent solidification create new grain nucleation sites and can promote recrystallization of the prior grains. As a result, the grain structure becomes finer with each additional pass because the repeated thermal cycles break up the larger grains from earlier passes and form smaller, more uniform grains. This refinement improves toughness and strength in the weld area. Coarser grain, no change, or a random distribution wouldn’t reflect the way repeated heating and re-solidification influence grain growth and nucleation during multi-pass welding.