Industry-Norm Schweißeignung Formula

Carbon Equivalent Calculation — Schweißen CE(IIW) & Pcm

Q: Which alloying elements increase carbon equivalent the most?

Carbon has the largest effect on CE because it appears directly in the formula without a divisor. Manganese and silicon are divided by 6, making them the next most influential. Chromium, molybdenum, and vanadium are divided by 5, while nickel and copper are divided by 15 and have the smallest individual effect. A steel with 0.25% C and 1.5% Mn will have higher CE than one with 0.20% C and 2.0% Mn.

Q: Does D1.1 Annex B use a specific CE threshold for preheat?

D1.1 Annex B does not use a single CE cutoff value. Instead, it provides two calculation methods (hardness control and hydrogen control) that compute minimum preheat temperature from composition, thickness, hydrogen level, and restraint. Higher CE leads to higher calculated preheat, but the relationship is continuous, not threshold-based. The Table 5.11 method uses steel group categories instead of CE directly.

Q: Where do I find the steel chemistry for CE calculation?

Steel chemistry is listed on the mill test report (MTR) or certified material test report (CMTR) under the chemical analysis section. Key elements for CE are carbon (C), manganese (Mn), silicon (Si), chromium (Cr), molybdenum (Mo), vanadium (V), nickel (Ni), and copper (Cu). For Pcm, boron (B) is also needed. Heat analysis values from the MTR are used for CE calculation.

Free online tool for welders and fabricators — calculate CE(IIW) and Pcm from steel chemistry to assess weldability and Härtbarkeit risk.

For the prescriptive Tabelle 5.11 Vorwärmung method (no chemistry needed), use our preheat calculator.

Built on IIW and Pcm formulas per AWS D1.1:2025 Annex B.

Steel Preset (optional) Carbon (C) % Manganese (Mn) % Silicon (Si) %

Nickel (Ni) % Chromium (Cr) % Molybdenum (Mo) % Vanadium (V) % Copper (Cu) % Boron (B) %

Understanding Your Result

What Your Kohlenstoffäquivalent Means

Carbon equivalent (CE) condenses your steel's full chemistry into a single weldability index. Per D1.1:2025 Annex B6.1.1, CE = C + (Mn+Si)/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. The chemical analysis can come from mill test certificates, typical production chemistry from the mill, Spezifikation Maximum values, or user tests.

Per AWS D1.1:2025 Annex B6.1.1: “CE = C + (Mn + Si)/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. This carbon equivalent formula is used to assess the susceptibility of the Wärmeeinflusszone to Wasserstoffriss.”

D1.1 Annex B uses CE to place your steel in one of three weldability zones. Zone I (low CE) means cracking is unlikely and preheat can be determined by the hydrogen control method. Zone II (moderate CE) requires the hardness control method to determine Minimum Streckenenergie for fillet welds without preheat. Zone III (high CE) means heat input must be restricted to preserve HAZ properties, and the hydrogen control method governs preheat.

Your CE value also feeds directly into the preheat calculator. Higher CE means higher susceptibility index grouping (A through G per Table B.1), which maps to higher minimum preheat temperatures in Table B.2 depending on restraint level and Dicke. If your CE exceeds 0.38 and you are welding thick, highly restrained joints, preheat temperatures above 300 °F are common.

Why CE Matters

Why Carbon Equivalent Matters

Cracking Risk

Carbon equivalent predicts hydrogen-induced cracking susceptibility in the heat-affected zone. Higher CE means the HAZ hardens faster during cooling, trapping hydrogen that can initiate cold Risse hours after welding is complete.

Preheat Planning

D1.1 provides two methods for minimum preheat: Table 5.11 (prescriptive, by steel grade) and Annex B (analytical, by chemistry). CE and Pcm drive the Annex B method. Both methods exist to slow the Abkühlgeschwindigkeit and reduce hydrogen cracking risk in the HAZ.

Standards Compliance

D1.1 Abschnitt 5.7 requires minimum preheat for all Vorqualifizierte WPS. When Table 5.11 is too conservative or your steel grade is not listed in Table 5.6, Annex B is the alternative. Use our preheat calculator for the Table 5.11 prescriptive lookup.

A high carbon equivalent increases the risk of hydrogen-induced cracking and typically results in higher preheat and Zwischenlagentemperatur Anforderungen per D1.1 Table 5.11. In some applications, elevated CE may also indicate the need for post-Schweiß heat treatment — consult the applicable Regelwerk and the Engineer for PWHT requirements specific to your Grundwerkstoff and service conditions.

Common Questions

FAQ

What is carbon equivalent (CE)?

Carbon equivalent (CE) is a single number that expresses the combined effect of carbon and alloying elements on steel hardenability and weldability. Per D1.1 Annex B6.1.1, CE = C + (Mn+Si)/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Higher CE means higher risk of hydrogen cracking and greater need for preheat.

What is the difference between CE(IIW) and Pcm?

CE per D1.1 uses a modified IIW formula with (Mn+Si)/6, best suited for steels with carbon above 0.18%. Pcm (critical metal parameter) is better for low-carbon steels (C < 0.18%). Both include silicon, but Pcm also includes boron (5B). The pure international IIW formula omits silicon.

Which alloying elements increase carbon equivalent the most?

Carbon has the largest effect on CE because it appears directly in the formula without a divisor. Manganese and silicon are divided by 6, making them the next most influential. Chromium, molybdenum, and vanadium are divided by 5, while nickel and copper are divided by 15 and have the smallest individual effect. A steel with 0.25% C and 1.5% Mn will have higher CE than one with 0.20% C and 2.0% Mn.

Does D1.1 Annex B use a specific CE threshold for preheat?

D1.1 Annex B does not use a single CE cutoff value. Instead, it provides two calculation methods (hardness control and hydrogen control) that compute minimum preheat temperature from composition, thickness, hydrogen level, and restraint. Higher CE leads to higher calculated preheat, but the relationship is continuous, not threshold-based. The Table 5.11 method uses steel group categories instead of CE directly.

Where do I find the steel chemistry for CE calculation?

Steel chemistry is listed on the mill test report (MTR) or certified material test report (CMTR) under the chemical analysis section. Key elements for CE are carbon (C), manganese (Mn), silicon (Si), chromium (Cr), molybdenum (Mo), vanadium (V), nickel (Ni), and copper (Cu). For Pcm, boron (B) is also needed. Heat analysis values from the MTR are used for CE calculation.

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