BIZOMAT MAKEOS · Fabrication
Carbon Equivalent and Weldability
What carbon equivalent does this steel have, and does it suggest preheat?
Carbon equivalent (IIW) and Pcm (Ito–Bessyo) from a steel’s chemical composition, with commonly cited weldability guidance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Carbon | % | Carbon content from the mill test certificate (weight %). |
| Manganese | % | Manganese from the certificate. |
| Silicon | % | Silicon from the certificate (used in Pcm only). |
| Chromium | % | Chromium from the certificate. |
| Molybdenum | % | Molybdenum from the certificate. |
| Vanadium | % | Vanadium from the certificate. |
| Nickel | % | Nickel from the certificate. |
| Copper | % | Copper from the certificate. |
| Boron | % | Boron from the certificate (used in Pcm only). |
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.
What this means: Carbon
- What it is
- The carbon content of the steel by weight, from the mill test certificate. Carbon has the largest effect on hardenability in both formulas.
- 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
- Each step adds its full value to both CE and Pcm.
- Get it right
- Enter weight percent as shown on the certificate, not a fraction.
What this means: Manganese
- What it is
- The manganese content of the steel by weight, from the mill test 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 by a sixth of its value and Pcm by a twentieth.
- Get it right
- Use the cast analysis on the certificate for this heat of steel.
What this means: Silicon
- What it is
- The silicon content of the steel by weight, from the mill test certificate. It appears only in the Pcm formula.
- 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 by a thirtieth of its value; CE does not change.
- Get it right
- Silicon does not change the IIW carbon equivalent.
What this means: Chromium
- What it is
- The chromium content of the steel by weight, from the mill test 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 by a fifth of its value and Pcm by a twentieth.
- Get it right
- Enter 0 if the certificate does not report it, and note that the result may then be low.
What this means: Molybdenum
- What it is
- The molybdenum content of the steel by weight, from the mill test 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 by a fifth of its value and Pcm by a fifteenth.
- Get it right
- Small amounts still count; copy the certificate figure exactly.
What this means: Vanadium
- What it is
- The vanadium content of the steel by weight, from the mill test certificate, often present in microalloyed steels.
- 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 by a fifth of its value and Pcm by a tenth.
- Get it right
- Enter weight percent; vanadium is often reported with three decimal places.
What this means: Nickel
- What it is
- The nickel content of the steel by weight, from the mill test 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 40%. 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 by a fifteenth of its value and Pcm by a sixtieth.
- Get it right
- Enter 0 if not reported, and note the result may then understate the true value.
What this means: Copper
- What it is
- The copper content of the steel by weight, from the mill test 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 0.15% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises CE by a fifteenth of its value and Pcm by a twentieth.
- Get it right
- Residual copper from scrap-based steelmaking still counts.
What this means: Boron
- What it is
- The boron content of the steel by weight, from the mill test certificate. It appears only in the Pcm formula, where even tiny amounts are weighted heavily.
- 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 by five times its value; CE does not change.
- Get it right
- Boron is reported in very small amounts; check the decimal places carefully.
Method and formulas
- CE(IIW) = 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.
- Example: the default chemistry gives CE = 0.43933 and Pcm = 0.2715.
Limitations
- Preheat also depends on thickness, heat input, hydrogen level and restraint; the bands are screening guidance, not a procedure.
- Pcm is intended for low-carbon steels (C below about 0.18%).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Screen a steel for welding preheat
- Compare mill certificate chemistry
- Choose a welding procedure category
Who it is for
- Welding engineers
- Welding supervisors
- Quality inspectors
What you get
- Carbon equivalent CE (IIW)
- Pcm
- Weldability band
Interpreting the result
- Commonly cited guidance: CE up to about 0.40 is readily weldable; 0.40–0.60 usually needs preheat and low-hydrogen practice; above about 0.60 needs careful procedures. Determine preheat with AS/NZS 1554.1 or your welding procedure.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1431–1449. Topic reference; no source tables or recommended settings are reproduced.
- AS/NZS 1554.1 Structural steel welding (preheat determination); International Institute of Welding carbon equivalent
Learn the Concepts Behind This Tool
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Method explained here · BIZOMAT original book
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