Localized segregation zone
Local segregation zone: A limited area in the metal where alloying elements are concentrated or depleted. This leads to property variations and can cause cracks or deformation.
Physical-Chemical Mechanism of Action
The local segregation zone forms due to uneven solidification, where certain areas cool faster than others. In these faster-cooling areas, alloying elements concentrate, while in other areas they deplete.
Metallurgical Relevance & Welding Risks
This segregation zone can lead to local hardness variations. Stronger areas are prone to cracking and deformation, especially under mechanical load. The toughness of the material is impaired, reducing the weld's service life.
Workshop Practice & Action Instructions
To minimize local segregation zones, ensure even cooling. Use appropriate shielding gases and pressures to control the diffusion of alloying elements. Keep the weld as short as possible and avoid high stresses during cooling. For heavily loaded applications, post-weld heat treatment (PWHT) may be required to homogenize hardness.