Carbon Equivalent Calculator

The carbon equivalent (CE) is a single numerical value that represents the combined effect of all alloying elements in steel on its hardenability and weldability, expressed as if the entire effect were due to carbon alone. It helps welding engineers predict how a steel will behave during and after welding, including the risk of cold cracking.

This calculator uses two widely accepted formulas. The IIW (International Institute of Welding) formula is: CE = C + (Mn + Si)/6 + (Cr + Mo + V)/5 + (Cu + Ni)/15. The AWS (American Welding Society) formula uses: CE = C + Mn/6 + (Cr + Mo + V)/5 + (Cu + Ni)/15, omitting Silicon from the numerator of the first term.

AISI 1018 steel has a typical composition of approximately C=0.18%, Mn=0.80%, and trace amounts of other elements. Using the IIW formula, this gives a CE of roughly 0.31–0.33%, which places it in the 'Excellent' to 'Very Good' weldability category with no preheat required under normal conditions.

Steel with a CE of 0.40% is considered to have 'Good' weldability. Preheating may not always be mandatory but is recommended for thicker sections, higher restraint, or cold ambient conditions. The risk of hydrogen-induced cracking increases as CE approaches and exceeds 0.40%.

As a general guideline, preheating is strongly recommended when CE exceeds 0.40–0.45%. For CE values above 0.45%, preheating to 100–200°C is typically required, and above 0.60% welding becomes very difficult, requiring significant preheat and post-weld heat treatment to prevent cracking.

Hardenability and weldability are inversely related. A higher CE indicates greater hardenability — meaning the steel forms hard martensite more readily when cooled quickly, such as in the heat-affected zone (HAZ) during welding. High hardenability increases the risk of cold cracking, which is why high-CE steels require careful preheat and heat input control.

These elements increase the hardenability of steel by delaying the transformation from austenite to softer phases like ferrite and pearlite during cooling. This promotes martensite formation in the heat-affected zone, which is hard and brittle and more susceptible to hydrogen-induced cold cracking. The CE formula quantifies each element's relative contribution to this effect.

Yes, CE is one of the primary inputs for calculating preheat temperature, often used alongside plate thickness and hydrogen content. Standards such as AWS D1.1 and EN 1011 provide preheat calculation methods based on CE values. As a rule of thumb: CE below 0.35% typically requires no preheat, 0.35–0.45% may need low preheat, and above 0.45% requires progressively higher preheat temperatures.