In welding, what effect can rapid cooling have on the weld?

Rapid cooling during the welding process can lead to high residual stress in the weld area and surrounding base material, which increases the likelihood of hot cracking. This phenomenon occurs because different parts of the weld cool at different rates, especially in thicker sections or when there are variations in material properties due to a non-uniform heat distribution during the weld. When the temperature drops too quickly, the material can become brittle and unable to accommodate the stresses caused by contraction. This makes it more prone to cracking, particularly in the heat-affected zone, where the material has been altered due to the welding heat.

In contrast, rapid cooling does not effectively strengthen the weld or promote uniform cooling, as uneven cooling often leads to hard zones which can also be brittle. While rapid cooling may seem to minimize distortion by constraining movement, it is overshadowed by the risk of introducing cracks and defects. Therefore, the most significant effect of rapid cooling is indeed an increased risk of hot cracking in the weld.