Heat input check and t8/5 cooling time

Choose the two base metals, process and filler, then enter preheat and the welding parameters for each run. A gauge shows every run's heat input against the window that applies to these materials, together with the t8/5 cooling time and the required preheat.

What it calculates

• Heat input per run (root, fill, cap) against the material window
• t8/5 cooling time with 2D (thin plate) and 3D (thick plate) heat flow
• Joint shape factors F2/F3 for butt and fillet welds
• Required preheat and the filler metal suggestion for the pair

Formulas

Q = k × U × I × 60 / (v × 1000)
t8/5 (3D) = (6700 − 5·T0) · Q · [1/(500 − T0) − 1/(800 − T0)] · F3
t8/5 (2D) = (4300 − 4.3·T0) · 10⁵ · Q²/d² · [1/(500 − T0)² − 1/(800 − T0)²] · F2
t8/5 = the larger of the two

How to use it

1. Create a free account with Google or e-mail.
2. Open the calculator and enter your values; units can be metric or imperial.
3. Read the result with its formula and source, and export to PDF, DXF or CSV where available.

Frequently asked questions

What is t8/5?

The time the weld and heat-affected zone take to cool from 800 °C to 500 °C. It controls the microstructure, hardness and toughness of the heat-affected zone, especially in quenched and tempered steels.

When is 2D or 3D heat flow used?

Thick plates conduct heat in three dimensions (3D), thin plates in two (2D). The calculator uses the larger t8/5 of the two formulas, which picks the correct case automatically.

Which steels have a t8/5 limit?

High-strength and wear-resistant steels such as S690QL, S960QL, Strenx and Hardox; the steel maker gives the allowed range.

Guides

• How to weld Hardox wear plateHardox is a quenched and tempered wear-resistant steel.
• How to calculate welding heat inputHeat input is the energy that enters the workpiece per millimetre of weld.

Related calculators

• Welding heat input calculatorCalculate arc energy and heat input in kJ/mm from welding voltage, current and travel speed.
• Preheat temperature calculatorPick a material and plate thickness to get the minimum preheat temperature.
• Filler metal and shielding gas selectorSelect the two base metals and the welding process.
• Weld metal and consumables calculatorEnter the joint type, dimensions and weld length.

Results are engineering estimates for planning. They do not replace the applicable standard, a qualified procedure or a check by a qualified engineer.