The rules of the increase in gray iron part dimensions in chromizing

Conclusions

• 1. The increase in dimensions of gray iron parts in chromizing is caused by processes occurring both in the whole volume of the material and in the diffusion surface layer and may be described by the equation Δl=lx+y, where x is the relative change in specimen length as the result of occurrence of volumetric processes and y is its absolute change as the result of processes occurring only on the surface.

• 2. Preliminary graphitization promotes a decrease in Δl of the specimens in chromizing as the result of a decrease in the parameter x.

• 3. The increase in dimensions of iron parts on chromizing depends upon the cooling rate, the depth of impregnation, the surface condition of the part, and the chemical analysis of the iron. The influence of manganese is favorable in this respect. Specimens of heats containing 1.6–1.87% Mn had the minimum change in dimensions.

The increase in part dimensions in chromizing may be the minimum with preliminary graphitizing using the optimum cycle and the use of gray iron with a high mangangese content.