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BIZOMAT 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

InputUnitTypical 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 thicknessmmThickness of the plate being welded.
Arc voltageVArc voltage.
Welding currentAWelding current.
Travel speedmm/minTravel speed of the arc.
Process thermal efficiency%Thermal efficiency of the process (about 60% GTAW, 80% SMAW and GMAW, 100% SAW).
Preheat (interpass) temperature°CPreheat and interpass temperature used.
Joint shape factor, thick plateJoint 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 plateJoint shape factor for two-dimensional heat flow (from your welding standard).
Your procedure limits
CE above which preheat is requiredCarbon equivalent above which your code requires preheat (your value).
Shortest t8/5 wantedsShortest cooling time your procedure allows (hardness and cracking).
Longest t8/5 wantedsLongest cooling time your procedure allows (toughness).

What each input means

Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.

Composition (%)

What this means: Carbon
Illustration: CarbonA bar of 100 parts with the share marked; Carbon is that share out of 100. The bar follows the value you type.0 %100 %CExample: 0.18%Carbon
What it is
The carbon content of the steel by mass, from the mill certificate. It is the element with the strongest effect on hardenability and cold cracking.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 2%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.18% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE, Pcm and the Séférian preheat estimate.
Get it right
Type the percentage itself (0.18 for 0.18 %), not a fraction of one.
What this means: Manganese
Illustration: ManganeseA bar of 100 parts with the share marked; Manganese is that share out of 100. The bar follows the value you type.0 %100 %MnExample: 1.3%Manganese
What it is
The manganese content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 20%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 1.3% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE, Pcm and the Séférian preheat estimate.
Get it right
Use the certificate value for the actual heat of steel, not the specification maximum, unless that is all you have.
What this means: Silicon
Illustration: SiliconA bar of 100 parts with the share marked; Silicon is that share out of 100. The bar follows the value you type.0 %100 %SiExample: 0.3%Silicon
What it is
The silicon content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 5%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.3% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises Pcm only, which is reported but not used in the checks.
Get it right
Silicon appears only in Pcm here; it does not change CE or the preheat estimate.
What this means: Chromium
Illustration: ChromiumA bar of 100 parts with the share marked; Chromium is that share out of 100. The bar follows the value you type.0 %100 %CrExample: 0.1%Chromium
What it is
The chromium content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 30%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.1% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE, Pcm and the Séférian preheat estimate.
Get it right
Use 0 if the certificate does not report it, and note that the estimate then assumes none.
What this means: Molybdenum
Illustration: MolybdenumA bar of 100 parts with the share marked; Molybdenum is that share out of 100. The bar follows the value you type.0 %100 %MoExample: 0.02%Molybdenum
What it is
The molybdenum content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 10%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.02% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE, Pcm and the Séférian preheat estimate.
Get it right
Use 0 if it is not reported.
What this means: Vanadium
Illustration: VanadiumA bar of 100 parts with the share marked; Vanadium is that share out of 100. The bar follows the value you type.0 %100 %VExample: 0.01%Vanadium
What it is
The vanadium content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 5%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.01% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE and Pcm; it is not in the Séférian preheat estimate.
Get it right
Use 0 if it is not reported.
What this means: Nickel
Illustration: NickelA bar of 100 parts with the share marked; Nickel is that share out of 100. The bar follows the value you type.0 %100 %NiExample: 0.1%Nickel
What it is
The nickel content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 30%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.1% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE, Pcm and the Séférian preheat estimate.
Get it right
Use 0 if it is not reported.
What this means: Copper
Illustration: CopperA bar of 100 parts with the share marked; Copper is that share out of 100. The bar follows the value you type.0 %100 %CuExample: 0.15%Copper
What it is
The copper content of the steel by mass, from the mill certificate.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 5%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.15% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises CE and Pcm; it is not in the Séférian preheat estimate.
Get it right
Use 0 if it is not reported.
What this means: Boron
Illustration: BoronA bar of 100 parts with the share marked; Boron is that share out of 100. The bar follows the value you type.0 %100 %BExample: 0%Boron
What it is
The boron content of the steel by mass, from the mill certificate. Small amounts strongly raise hardenability.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 0.1%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises Pcm only, which is reported but not used in the checks.
Get it right
Boron is reported in very small amounts; check the decimal place, since it is multiplied by 5 in Pcm.

Joint and welding

What this means: Plate thickness
Illustration: Plate thicknessThe cross-section of a plate or wall with a dimension across its thickness, marking Plate thickness.dsection through the materialExample: 25 mmPlate thickness
What it is
The thickness of the plate at the weld. Thicker plate draws heat away faster and needs more preheat.
Units and format
Enter a number in mm: millimetres. The form accepts 0.000001 mm to 300 mm. Required: the tool does not calculate until every input is valid.
Example
The form opens with 25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Raises the Séférian preheat estimate; the thin-plate cooling time falls with its square.
Get it right
For joints of unequal thickness, follow your welding code on which thickness to use.
What this means: Arc voltage
Illustration: Arc voltageA simple circuit with a supply and a load; Arc voltage is one of its electrical quantities.~loadUExample: 28 VArc voltage
What it is
The voltage across the welding arc during the run, read at the arc or from the procedure record.
Units and format
Enter a number in V: volts. The form accepts 0.000001 V to 100 V. Required: the tool does not calculate until every input is valid.
Example
The form opens with 28 V as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Heat input is directly proportional to arc voltage, so cooling time grows.
Get it right
Measure close to the arc; the voltage at the power source includes cable losses.
What this means: Welding current
Illustration: Welding currentA simple circuit with a supply and a load; Welding current is one of its electrical quantities.~loadIExample: 250 AWelding current
What it is
The welding current during the run, from the machine meter or procedure record.
Units and format
Enter a number in A: amperes. The form accepts 0.000001 A to 2000 A. Required: the tool does not calculate until every input is valid.
Example
The form opens with 250 A as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Heat input is directly proportional to current, so cooling time grows.
Get it right
Use the average current during the run, not a peak or the machine’s maximum rating.
What this means: Travel speed
Illustration: Travel speedA marker moving along a track; Travel speed is the distance it covers per unit of time.vdistance ÷ timeExample: 250 mm/minTravel speed
What it is
How fast the arc moves along the joint while depositing the run.
Units and format
Enter a number in mm/min: millimetres per minute. The form accepts 0.000001 mm/min to 5000 mm/min. Required: the tool does not calculate until every input is valid.
Example
The form opens with 250 mm/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Heat input is inversely proportional to travel speed, so cooling time shortens as it rises.
Get it right
Enter mm per minute; travel speed measured in mm per second must be multiplied by 60.
What this means: Process thermal efficiency
Illustration: Process thermal efficiencyInput on the left and useful output on the right with the loss split off; Process thermal efficiency is output divided by input.inputuseful outputlossηExample: 80%Process thermal efficiency
What it is
The share of the arc energy that actually enters the workpiece, which depends on the welding process.
Units and format
Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 10% to 100%. Required: the tool does not calculate until every input is valid.
Example
The form opens with 80% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Heat input is directly proportional to efficiency.
Get it right
Type the percentage itself. Take it for your process from the welding standard you work to.
What this means: Preheat (interpass) temperature
Illustration: Preheat (interpass) temperatureA thermometer whose level rises with Preheat (interpass) temperature; the level follows the value you type.T₀Example: 150 °CPreheat (interpass) temperature
What it is
The temperature of the plate around the joint just before each run is laid, as held by preheating and interpass control.
Units and format
Enter a number in °C: degrees Celsius. The form accepts 0 °C to 400 °C. Required: the tool does not calculate until every input is valid.
Example
The form opens with 150 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
Higher preheat lengthens the cooling time; it is also compared with the preheat estimate.
Get it right
Measure the plate near the joint, not the torch or heater setting.
What this means: Joint shape factor, thick plate
Illustration: Joint shape factor, thick plateTwo bars: a base value and the same value multiplied by Joint shape factor, thick plate, the factor.base valuewith factorF₃Example: 1Joint shape factor, thick plate
What it is
A shape factor for the joint type that corrects the thick-plate cooling time for how heat flows away from it.
Units and format
Enter a plain number with no unit. The form accepts 0.3 to 1.5. Required: the tool does not calculate until every input is valid.
Example
The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
The thick-plate cooling time is directly proportional to it.
Get it right
Take it from your welding standard for the joint type; a bead on plate is the reference case.
What this means: Joint shape factor, thin plate
Illustration: Joint shape factor, thin plateTwo bars: a base value and the same value multiplied by Joint shape factor, thin plate, the factor.base valuewith factorF₂Example: 1Joint shape factor, thin plate
What it is
A shape factor for the joint type that corrects the thin-plate cooling time for how heat flows away from it.
Units and format
Enter a plain number with no unit. The form accepts 0.3 to 1.5. Required: the tool does not calculate until every input is valid.
Example
The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
The thin-plate cooling time is directly proportional to it.
Get it right
Take it from your welding standard for the joint type.

Your procedure limits

What this means: CE above which preheat is required
Illustration: CE above which preheat is requiredA number line with a marker at the value of CE above which preheat is required, between its lowest and highest accepted values.0.21CEExample: 0.4CE above which preheat is required
What it is
The carbon equivalent above which your welding code or procedure says preheat is required.
Units and format
Enter a plain number with no unit. The form accepts 0.2 to 1. Required: the tool does not calculate until every input is valid.
Example
The form opens with 0.4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
It only raises a warning; it does not change the overall verdict.
Get it right
Take it from your code for this thickness and hydrogen level; it is a rule you set, not a calculated value.
What this means: Shortest t8/5 wanted
Illustration: Shortest t8/5 wantedA timeline from a start mark to an end mark; Shortest t8/5 wanted is the time between them.startendtExample: 10 sShortest t8/5 wanted
What it is
The shortest cooling time from 800 to 500 °C your procedure accepts, below which the weld zone may be too hard.
Units and format
Enter a number in s: seconds. The form accepts 0 s to 200 s. Required: the tool does not calculate until every input is valid.
Example
The form opens with 10 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
It does not change the cooling time, only the window check.
Get it right
Take it from the qualified procedure or steel maker’s data.
What this means: Longest t8/5 wanted
Illustration: Longest t8/5 wantedA timeline from a start mark to an end mark; Longest t8/5 wanted is the time between them.startendtExample: 25 sLongest t8/5 wanted
What it is
The longest cooling time from 800 to 500 °C your procedure accepts, above which toughness may suffer.
Units and format
Enter a number in s: seconds. The form accepts 0.000001 s to 500 s. Required: the tool does not calculate until every input is valid.
Example
The form opens with 25 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Effect on the result
It does not change the cooling time, only the window check.
Get it right
It must be longer than the shortest time; take it from the procedure or steel maker’s data.

Method and formulas

  1. 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.
  2. 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.
  3. Heat input Q = η U I × 60 ÷ (v × 1000) kJ/mm.
  4. 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.
  5. 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

Learn the Concepts Behind This Tool

These BIZOMAT Library readings explain the method this tool uses, with worked examples.

BIZOMAT 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.

Open the Weld Preheat and Cooling Time Check (CE, Heat Input, t8/5) calculator

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