What does weld penetration refer to?

Weld penetration specifically measures how deeply the weld metal fuses into the base material during the welding process. This factor is crucial for ensuring the joint's strength and integrity, as adequate penetration creates a robust bond that can withstand mechanical stresses and loads. In welding, achieving optimal penetration helps in preventing issues such as incomplete fusion, which can lead to weak points in the weld.

The other options do not accurately define weld penetration. The amount of filler material used relates more to the volume of the weld rather than its depth. The width of the weld bead concerns the size of the external appearance of the weld rather than how deeply it penetrates the base material. The duration of the welding process pertains to the time taken to complete the weld but does not inform the depth of the fusion achieved between the weld and the base metal.