What can excessive heat input cause during the welding process?

Excessive heat input during the welding process can lead to significant distortion and alterations in the properties of the metal being welded. High heat can cause the base metal and the weld metal to expand and contract unevenly, which often results in warping or bending of the welded parts. Additionally, the heat can also affect the microstructure of the metal, leading to a reduction in hardness or strength, and potentially making the weld more susceptible to defects like cracking or porosity.

The other options do not accurately reflect the effects of excessive heat input. While increased strength, reduced spatter, or improved penetration may be associated with optimal heat levels, they do not hold true when excessive heat is applied. In fact, a careful balance is necessary to achieve a quality weld without compromising the integrity of the materials involved.