True or False: For thick plates, the cooling rate is inversely proportional to the heat input.

In welding terminology, the relationship between the cooling rate and heat input is significant, especially when dealing with thick plates. When heat is applied during the welding process, the heat input dictates how much energy is delivered to the area being welded. A higher heat input generally leads to a slower cooling rate because the additional energy allows the metal to remain molten or in a high-temperature state for a longer period of time.

This means that as the heat input increases, the time it takes for the welded metal to cool down decreases, resulting in a slower cooling rate. Conversely, if the heat input is reduced, the cooling rate increases because the metal cools down more rapidly as less energy is imparted into the weld area.

Therefore, the correct statement is that for thick plates, the cooling rate is indeed inversely proportional to the heat input. This principle is crucial in welding practices as it affects the properties of the weld, such as its microstructure and overall strength. A correct understanding of this relationship helps welders optimize their techniques for different material thicknesses and types.