Indentation Size Effect on the Microhardness of Ductile Iron

The indentation size effect on the microhardness of as-rolled ductile iron has been investigated. Vickers microhardness measurements were made at different loads ranging from 10 g to 1000 g. The measured values were analyzed with the popular Nix-Gao’s plasticity model and a microstructural material-length scale parameter was determined. The hardness value was found to decrease with increasing indentation load with the indentation size effect shown to be very pronounced below about 100g and almost negligible above about 300 g. The measured hardness values were shown to be in good agreement with the well-described Nix-Gao strain gradient plasticity model with a material length scale parameter of 5.80 micrometers.