2. Relaxation of casting stresses

Residual casting stresses (due to the complexity of the part's shape, the heterogeneity of thermal conditions during solidification and cooling in the mold, and the nature of the cast iron) are difficult to measure, but are sometimes indicated by deformation during machining, or even, exceptionally, by breakage.

In the mold, the thin parts solidify first and begin their solid state shrinkage, deforming the thicker, still incompletely solidified parts. These, in turn, contracting after solidification, develop tensile or compressive stresses throughout the part, which remain after complete cooling. It should be noted, moreover, that these stresses are distributed mainly in the surface regions, which is why deformations are particularly to be feared during the first machining passes.