The heating involved in welding and cutting typically reaches temperatures at or above the melting point of the material being worked on, depending on the specific welding technique utilized. However, the heating and subsequent cooling cycle associated with these processes differ from previous treatments the base material might have undergone. This variance results in alterations to the materials microstructure during the heating and cooling phases.

 

The extent of the heat-affected zone (HAZ) is influenced by the materials thermal diffusivity, which hinges on factors such as thermal conductivity, density, specific heat, and the amount of heat applied. Materials with high thermal diffusivity can disperse heat more rapidly, leading to faster cooling and consequently a narrower HAZ. Conversely, materials with lower diffusivity retain heat longer, resulting in a wider HAZ. Generally, the size of the HAZ depends on the intensity and duration of heat exposure, as well as the materials inherent properties. Increased energy over prolonged periods results in a larger HAZ.

 

In welding, processes with lower heat input cool faster, yielding a smaller HAZ, whereas those with higher heat input exhibit slower cooling rates, resulting in a larger HAZ for the same material. Additionally, slower welding speeds tend to enlarge the HAZ. Weld geometry also affects HAZ size by influencing heat dissipation; a larger heat sink typically leads to quicker cooling.

 

Similarly, high-temperature cutting operations generate a HAZ, with processes operating at higher temperatures and slower speeds typically producing larger HAZs, while those at lower temperatures or higher speeds tend to reduce HAZ size. The width of the HAZ from the cut edge depends on the cutting process, speed, and material properties.

 

Different cutting methods have varying impacts on HAZ, regardless of the material being cut. For instance, shearing and waterjet cutting do not induce a HAZ as they do not heat the material, whereas laser cutting results in a small HAZ due to localized heating. Plasma cutting produces an intermediate HAZ, with higher currents enabling faster cutting speeds and thus a narrower HAZ. Oxyacetylene cutting generates the widest HAZ due to its high heat, slow speed, and wide flame. Arc welding falls between these extremes, with specific processes varying in heat input.