Heat-affected zone
= Heat-affected zone
The <heat-affected zone> is the region of a material whose <microstructure> or properties are changed by nearby <welding> or thermal cutting without itself melting. It lies outside the fusion region and can contain different subregions corresponding to different thermal histories.<What is the Heat Affected Zone? by TWI>[Definition and thermal-cycle mechanism]{ref}
In a <steel>, heating and cooling can change phases, grain size and <hardness>; in another alloy the thermal cycle may soften a previously strengthened region. Heat input, travel speed, geometry and thermal transport determine the affected region together. Measuring a weld therefore requires examining both the joint and adjacent material. Surface heat-tint colours alone do not uniquely identify the extent of the metallurgically altered region.<What is the Heat Affected Zone? by TWI>[HAZ regions, property changes and distinction from heat tint]{ref}