Influence of wall thickness

How mechanical properties depend on the wall thickness of the casting.

The slower the cooling speed, i.e. the thicker the casting wall, the larger the grain and the lower tensile strength.Especially in flake graphite cast iron (GJL), there is a significant influence of wall thickness. (Figure 1). The structure and thus the mechanical properties of the casting are not only determined by the chemical composition of the alloy but very much of the wall thickness. The influence of the wall thickness is defined in DIN EN 1561. Within the casting as well, thinner cross-sections have a higher tensile strength and hardness than massive cross-sections. In this case, however, the influence of adjacent casting parts on each other reduces the influence of the wall thickness on the material properties.

All castings produced from the same iron belong to the same material type, irrespective of the properties prevailing in the casting. Thin-walled parts have higher strength and thick-walled part have lower strength compared to the nominal strength of the according type.The different properties based on geometry influencing the E-module and the machining properties must be taken into account for construction (see Design of castings, Favorable casting design, Favorable casting engineering).

If the wall thickness is too thin for the given chemical composition, or if the cooling speed is increased too much by the quickly cooling mold material or by using chills, carbon cannot completely or not at all crystallize to form graphite but only iron carbide (Fe3C, cementite) is formed.

  • Fig. 1: Expected minimum values for tensile strength (left) and average values for Brinell hardness (right) depending on the wall thickness in the casting (according to H. Werning, “konstruieren +  giessen” 2000, No. 2)