KEVOS® MAKEOS · Fabrication
Weld Preheat and Cooling Time Check (CE, Heat Input, t8/5)
Does this steel need preheat for this thickness, and will my heat input and preheat give a cooling time in the range my procedure wants?
Screening check of a welding procedure for carbon and low-alloy steel: carbon equivalent CE (IIW) and Pcm from the composition (as the carbon equivalent tool), a preheat estimate by Séférian’s formula for the plate thickness, heat input from voltage, current, travel speed and process efficiency (as the welding heat input tool), and the cooling time from 800 to 500 °C (t8/5) for thick-plate (three-dimensional) and thin-plate (two-dimensional) heat flow, with the governing case compared to your window.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Composition (%) | ||
| Carbon | % | Carbon content from the mill certificate. |
| Manganese | % | Manganese content. |
| Silicon | % | Silicon content. |
| Chromium | % | Chromium content. |
| Molybdenum | % | Molybdenum content. |
| Vanadium | % | Vanadium content. |
| Nickel | % | Nickel content. |
| Copper | % | Copper content. |
| Boron | % | Boron content. |
| Joint and welding | ||
| Plate thickness | mm | Thickness of the plate being welded. |
| Arc voltage | V | Arc voltage. |
| Welding current | A | Welding current. |
| Travel speed | mm/min | Travel speed of the arc. |
| Process thermal efficiency | % | Thermal efficiency of the process (about 60% GTAW, 80% SMAW and GMAW, 100% SAW). |
| Preheat (interpass) temperature | °C | Preheat and interpass temperature used. |
| Joint shape factor, thick plate | Joint shape factor for three-dimensional heat flow (1 for a bead on plate; lower for fillet and T joints; from your welding standard). | |
| Joint shape factor, thin plate | Joint shape factor for two-dimensional heat flow (from your welding standard). | |
| Your procedure limits | ||
| CE above which preheat is required | Carbon equivalent above which your code requires preheat (your value). | |
| Shortest t8/5 wanted | s | Shortest cooling time your procedure allows (hardness and cracking). |
| Longest t8/5 wanted | s | Longest cooling time your procedure allows (toughness). |
Method and formulas
- CE = C + Mn ÷ 6 + (Cr + Mo + V) ÷ 5 + (Ni + Cu) ÷ 15; Pcm = C + Si ÷ 30 + (Mn + Cu + Cr) ÷ 20 + Ni ÷ 60 + Mo ÷ 15 + V ÷ 10 + 5B.
- Séférian: C_c = (360C + 40(Mn + Cr) + 20Ni + 28Mo) ÷ 360; C_t = C_c (1 + 0.005 t); preheat ≈ 350 √(C_t − 0.25) °C.
- Heat input Q = η U I × 60 ÷ (v × 1000) kJ/mm.
- t8/5 thick plate = (6700 − 5T₀) Q [1 ÷ (500 − T₀) − 1 ÷ (800 − T₀)] F₃; thin plate = (4300 − 4.3T₀) × 10⁵ Q² ÷ d² × [1 ÷ (500 − T₀)² − 1 ÷ (800 − T₀)²] F₂; the larger governs.
- Example: CE 0.43933 steel 25 mm thick suggests about 128.84 °C preheat; at 1.344 kJ/mm and 150 °C, t8/5 is 10.545 s.
Limitations
- Screening estimates only; preheat must be set by the welding code (AS/NZS 1554, AWS D1.1, EN 1011-2) and a qualified procedure.
- Hydrogen level and restraint are not in Séférian’s formula.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Screen a welding procedure before qualification
- See how preheat and heat input change the cooling time
- Check whether a thicker plate needs preheat
Who it is for
- Welding engineers
- Welding inspectors
- Fabrication supervisors
What you get
- Carbon equivalent and Pcm
- Séférian preheat estimate
- Heat input and t8/5 cooling time
Interpreting the result
- Raising preheat and heat input both lengthen t8/5: too short risks hard, crack-prone zones; too long lowers toughness.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1431–1449. Topic reference; no source tables or recommended settings are reproduced.
- EN 1011-2 Welding — Recommendations for welding of metallic materials (cooling time formulas); International Institute of Welding carbon equivalent
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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