Segregation Coefficient for Alloying Elements
The segregation coefficient indicates how the concentration ratio of an element in the weld changes relative to the remaining melt. It is crucial for predicting microsegregation and hot cracking.
Physicochemical Mechanism of Action
The segregation coefficient (Sk) describes how strongly the concentration ratio of an element between the solidifying crystal and the residual melt changes. It is a thermodynamic value and is calculated from the difference between the partial pressure of the element in the crystal and in the melt.
Metallurgical Relevance & Risks in Welding
A high segregation coefficient means the element concentrates strongly. This can lead to microsegregation and hot cracking, especially when the weld cools quickly. A low segregation coefficient prevents strong concentrations and minimizes crack risks.
Workshop Practice & Action Guidelines
To minimize microsegregation and hot cracking, it is important to know the segregation coefficient of the alloy used. For high values, the cooling step size should be reduced (e.g., by speed-limited cooling or using cooling water). For low values, the cooling rate can be increased to achieve a uniform grain structure.