The Use of Carbon Equivalence Value to Assess the Weldability of Steels: Limitations and Considerations
Weldability is an important consideration when selecting steels for fabrication processes. The weldability of steels is affected by their chemical composition, particularly the proportions of carbon and other elements such as manganese, chromium, and molybdenum. The assessment of steel weldability is usually conducted by using certain criteria such as carbon equivalence value (CEV), which is determined from the combination of elements. CEV helps to predict the welding performance and provides a general guideline for the more detailed evaluation of the weldability of steel. However, it has certain limitations which should be taken into consideration when using CEV to assess a steel’s weldability.
The concept of carbon equivalence was introduced to provide a measure of the carbon content in alloy steels, known as the carbon equivalence value (CEV). This concept was developed as a convenient, approximate method of predicting the weldability of a steel, whence the CEV is considered as a general guideline for weldability of steels rather than being used as an exact measure. It is defined as CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15, where C is the carbon content, Mn is the manganese content, Cr is the chromium content, Mo is the molybdenum content, V is the vanadium content, Ni is the nickel content, and Cu is the copper content. This allows for the combination of elements to be taken into account when assessing weldability.
The lower the CEV, the more easily the steel can be welded, and vice versa for higher CEVs. In ferrous materials, weldability is usually defined relative to CEV, which is used to differentiate between steels of different chemical compositions. Generally, alloys with a CEV of less than 0.45 are considered to be easily weldable, those with a CEV of 0.45-0.85 are defined as marginally weldable, and those with a CEV in excess of 0.85 are deemed to be difficult to weld. However, these criteria should be used with caution as they may not always be applicable in practice, particularly when working with high-alloy steels.
Despite its popularity and convenience, the use of CEV in assessing the weldability of steels has its own limitations and constraints. The most important point to remember is that CEV is an approximate measure and should not be used as an exact measure. Additionally, the CEV values are informed by carbon which is not always an accurate measure of weldability. The actual weldability of a steel is determined by other elements and their proportion, particularly the levels of manganese, chromium, molybdenum, nickel, and copper. These elements are often more important than the carbon content when it comes to weldability, and thus the CEV may not accurately reflect the actual welding performance.
Moreover, it is important to note that CEV values should not be used as a substitute for a detailed analysis of the steels. A CEV value is often too broad to accurately assess a particular steel; the values may vary significantly between different types of steel. Thus the CEV should not be used as the sole criterion for assessing a steel’s weldability; other factors such as the thickness of the steel, the complexity of the weld, the type of welding process, and the environment should also be taken into consideration.
In conclusion, the use of CEV to assess the weldability of steels is a convenient approximate method which provides a general indication of weldability. However, it should not be used as an exact measure or a substitute for a detailed analysis of the welding performance. The assessment of steel weldability should also consider other factors such as the thickness of the steel, the complexity of the weld, the type of welding process, and the environment.
