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How to weld > How to weld Hardox® wear plate > Heat input

Calculations of heat input

Heat input, crucial for determining the quality and mechanical properties of a weld, represents the amount of heat energy applied to the base metal during welding. In most welding procedures, either DC or AC welding currents are employed, with the heat input calculated using specific formulas.

Heat input formula

Pulsed arc welding heat input

The heat input for pulsed arc welding can be determined by either of the two following formulas:

or

Definitions

Q = Heat input kJ/mm (kJ/inch)
k = Arc efficiency (dimensionless)
U = Voltage V
I = Current A
v = Travel speed mm/min (inch/min)
L = Length of a weld run mmorinch
IE = Instantaneous energy J
IP = Instantaneous power W

Different welding processes have varying thermal efficiencies, approximate values in the table below.

Weld Method
Weld Method
 MAG / GMAW
Thermal Efficiency (k)
 0.8
Weld Method
Weld Method
 MMA / SMAW
Thermal Efficiency (k)
 0.8
Weld Method
Weld Method
 SAW
Thermal Efficiency (k)
 1.0
Weld Method
Weld Method
 TIG / GTAW
Thermal Efficiency (k)
 0.6

Thermal efficiency factors of different welding methods.

Excessive heat input widens the heat-affected zone (HAZ), thereby impairing its mechanical properties and wear resistance. Welding with low heat input offers benefits such as:

  • Increased wear resistance of the HAZ
  • reduced distortion (single-pass welded joints)
  • Enhanced joint toughness and strength

However, very low heat input negatively affects the impact toughness, indicated by cooling time (t₈/₅) values below 3 seconds. 

The recommended maximum heat input (Q) for Hardox® steel is outlined in the graph below.

Recommended maximum heat input for all Hardox® steels

Plate thickness (mm)
Plate thickness (mm)
 2
Max heat input (kJ/mm)
 0.25
Plate thickness (inch)
 0
Max heat input (kJ/inch)
 5
Plate thickness (mm)
Plate thickness (mm)
 20
Max heat input (kJ/mm)
 2
Plate thickness (inch)
 0.79
Max heat input (kJ/inch)
 50
Plate thickness (mm)
Plate thickness (mm)
 30
Max heat input (kJ/mm)
 2.5
Plate thickness (inch)
 1.18
Max heat input (kJ/inch)
 62.5
Plate thickness (mm)
Plate thickness (mm)
 40
Max heat input (kJ/mm)
 2.5
Plate thickness (inch)
 1.57
Max heat input (kJ/inch)
 62.5

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How to weldHow to weld Hardox® wear plate

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