Meaning
Solute redistribution during solidification can cause high concentrations of alloying elements to collect at grain boundaries. This localized solute accumulation leads to chemical inhomogeneities that can promote microsegregation and degrade the mechanical properties of the cast material. The phenomenon is governed by the partition coefficient of the solute and the local solidification rate.
Phase Precipitation
When the concentration of solute exceeds the solubility limit in the liquid phase, secondary phases begin to precipitate in the intergranular regions. These secondary phases are often brittle and act as initiation sites for cracks. This structural vulnerability decreases the ductility of the metal.
Weld Cracking
In heavy industrial manufacturing, this segregation is a major cause of hot cracking in welded joints. During the final stages of weld solidification, the solute-rich liquid forms thin films between the solidifying grains, which cannot support the thermal stresses generated by cooling. This stress results in the formation of microcracks along the weld centerline.
Welders avoid this problem by controlling the heat input and using filler metals that minimize solute segregation.
Mitigation Strategy
Post-weld heat treatment is often utilized to homogenize the solute distribution through solid-state diffusion. This thermal process dissolves the brittle precipitates and restores the mechanical properties of the joint. This treatment is standard practice in the construction of high-pressure vessels.
