Weldability of steels: The importance of carbon equivalents

The role of carbon equivalents in welding technology

The weldability of steels is determined by the carbon equivalent (CE), which takes into account the chemical elements in the molten steel – such as manganese, nickel or chromium. The carbon equivalent is calculated as the sum of the properties of these elements and provides a reference value in product lists. Practitioners in production can use this value to assess whether and how the sheet steel can be welded or thermally cut. At the same time, this value is used by purchasers to specify the requirements for the weldability of the steel when ordering.

Various methods for calculating carbon equivalents

In practice, various calculation methods have been established depending on the application and steel grade. These methods are based on the respective welding requirements, product standards and processing conditions.

CEV (or CE)

Formula: C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5

• Objective: To avoid cracks due to excessive hardening of the steel as a result of rapid cooling near the weld seam.
• Standards: Maximum CEV values are specified for European structural steels in accordance with EN 10025.
• Application: The EN 1011-2 standard defines method A, with which the preheating temperature can be calculated as a function of the CEV.

CET

Formula: C + (Mn + Mo)/10 + (Cr + Cu)/20 + Ni/40

• Objective: To prevent cracks caused by hydrogen embrittlement, which can occur due to insufficient hydrogen diffusion in the temperature range from 100 °C to 300 °C.
• Standards: Here too, EN 1011-2 with method B provides guidance for calculating the safe preheating temperature.

PCM

Formula: C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B

• Aim: Special application for very rapid cooling, such as occurs with root seams.
• Standards: PCM is widely used in offshore standards such as EN 10225 as well as in AWS D1, the US manufacturing standard.

Significance of carbon equivalents

All carbon equivalents have one thing in common: the lower the value, the easier and more cost-efficient it is to process the steel. This realization has led to significant progress in steel production.

Application in practice

Choosing the right method for calculating the carbon equivalent is crucial for welding technology. Practitioners can use these values to determine the appropriate preheating temperatures and processing techniques. This precision ensures not only safety but also cost-effectiveness when processing steels in various applications – from offshore platforms to demanding construction projects.