 The effects of welding on the material surrounding the weld can be detrimental — depending on the materials used and the heat input of the welding process used , the HAZ can be of varying size and strength . The thermal diffusivity of the base material plays a large role — if the diffusivity is high , the material cooling rate is high and the HAZ is relatively small . Conversely , a low diffusivity leads to slower cooling and a larger HAZ . The amount of heat injected by the welding process plays an important role as well , as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ . Processes like laser beam welding give a highly concentrated , limited amount of heat , resulting in a small HAZ . Arc welding falls between these two extremes , with the individual processes varying somewhat in heat input . To calculate the heat input for arc welding procedures , the following formula can be used : 
