Heat-affected zone

The cross-section of a welded butt joint, with the darkest gray representing the weld or fusion zone, the medium gray the heat-affected zone, and the lightest gray the base material.

In fusion welding, the heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which is not melted but has had its microstructure and properties altered by welding or heat intensive cutting operations. The heat from the welding process and subsequent re-cooling causes this change from the weld interface to the termination of the sensitizing temperature in the base metal. The extent and magnitude of property change depends primarily on the base material, the weld filler metal, and the amount and concentration of heat input by the welding process.

The

electron 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 is used:

Q=\left({\frac {V\times I\times 60}{S\times 1000}}\right)\times \mathrm {Efficiency}

where $Q$ = heat input (

kJ/mm),

V

= voltage (V),

I

= current (A), and

S

= welding speed (mm/min). The efficiency is dependent on the welding process used, with gas tungsten arc welding having a value of 0.6, shielded metal arc welding and gas metal arc welding having a value of 0.8, and submerged arc welding 1.0.^[1]

References

^ "What is the difference between heat input and arc energy? - TWI".

Weman, Klas (2003). Welding processes handbook. New York: CRC Press LLC.
ISBN 0-8493-1773-8
.

[1] "What is the difference between heat input and arc energy? - TWI".

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