Welding Heat Input.
Calculate heat input (kJ/mm) for SMAW, GMAW, GTAW, SAW and FCAW from voltage, current, and travel speed. With process efficiency factor — required for WPS qualification per ASME IX, AWS D1.1.
Per AWS D1.1 / ASME IX standard efficiency values
volts — arc voltage
amperes — welding current
mm/min — welding travel speed
mm — for cooling rate estimate
HEAT INPUT
—
kJ/mm — gross heat input
Net heat input
—
Arc power
—
Travel speed (mm/s)
—
HAZ classification
—
Heat Input (gross) = (V × I × 60) / (S × 1000)
Net Heat Input = η × Gross HI
Units: V (volts), I (amps), S (mm/min) → kJ/mm
Net Heat Input = η × Gross HI
Units: V (volts), I (amps), S (mm/min) → kJ/mm
Typical heat input ranges
| Material | Recommended HI (kJ/mm) | Risk if too high | Risk if too low |
|---|---|---|---|
| Carbon steel (mild) | 0.8 – 2.5 | HAZ softening, distortion | Lack of fusion, hard HAZ |
| Low-alloy steel (Cr-Mo) | 1.0 – 2.0 | Toughness loss | Hydrogen cracking |
| Stainless 304/316 | 0.5 – 1.5 | Sensitisation, distortion | Lack of penetration |
| Duplex stainless | 0.5 – 2.5 | Sigma phase, intermetallics | Wrong ferrite/austenite ratio |
| Aluminium alloys | 0.4 – 1.2 | Burn-through, strength loss | Cold lap, porosity |
| HSLA / Q&T steels | 1.0 – 2.5 | HAZ softening (softens martensite) | Cracking, brittle HAZ |