Heat Input

Heat input, expressed in kilowatt-hours per inch or joules per millimeter of weld length, directly controls the size and severity of the heat-affected zone and profoundly influences the mechanical properties of the finished joint. High heat input softens high-strength steels and widens the coarse-grained HAZ, reducing toughness and fatigue strength; conversely, excessive cold work from low heat input can promote hydrogen-assisted cracking in susceptible alloys.

Welding procedures specify current, voltage, and travel speed targets that, when combined, produce a calculated heat input within a narrow band; for critical applications, actual heat input is monitored and recorded to verify compliance. Understanding and controlling heat input is essential when executing demanding welding projects, particularly when joining materials that require post-weld thermal cycles such as post-weld heat treatment.