Grain boundary segregation
Grain boundary segregation is the enrichment of foreign atoms or alloying elements at the boundaries between crystallites. This leads to uneven distribution and can increase hardness and cause cracking.
Physical-Chemical Mechanism of Action
During melting and cooling of metals, certain atoms or elements can concentrate at the boundaries between crystallites (grain boundaries). This process, called grain boundary segregation, occurs due to thermodynamic reasons and leads to an uneven distribution of these atoms or elements.
Metallurgical Relevance & Welding Risks
Grain boundary segregation can increase hardness in weld areas, especially when there are high concentrations of foreign atoms or alloying elements. This increases susceptibility to cracks and hot cracking, as the material at these grain boundaries is softer and more deformable than in other areas. Additionally, it can lead to uneven stress distribution, causing further damage to the workpiece.
Shop Practice & Action Instructions
To minimize grain boundary segregation and control weld hardness, carefully select weld material and processes. This includes using stable alloys with low susceptibility to segregation and maintaining optimal melting and cooling conditions. For certain metals or alloys, special treatments like austenitizing or martensitic hardening may be needed to optimize hardness and mechanical properties.