An investigation of the effect of inoculants on the metal expansion penetration in grey iron

Abstract

The effect of graphite precipitation and metal penetration have been discussed by many authors and much work has been made in the foundries to understand how to avoid metal penetration. Most of the grey-iron foundries around the world have problems with metal penetration on applicable components.

The metal penetration in this work has been studied by thermoanalysis of casting experiments and metallographic observation of the microstructure coupled to the degree of penetration. The influence of the solidification path and time when it occurs, have been measured by using a standard thermoanalysis cup, modified with a sand core to facilitate a place for metal penetration. An open thermocouple was placed in the shell-core to detect the time of penetration.

Ten different inoculants, representing five different groups of inoculants were investigated. The experiments show two main classes of eutectic cell sizes. One class nucleated at the beginning of the eutectic solidification and one at the end of the solidification.

The worst cases of metal penetration were obtained when the melt was not inoculated. A large number of small eutectic cells, and a high volume of the small cells were observed, which leads to large penetrations.

The ferro-silicon-strontium inoculant was observed to give a high tendency to metal penetration. The ferro-silicon-zirconium-manganese inoculants showed a high nucleation rate at the end of the solidification and the average volume fraction of small eutectic cells was high. The degree of penetration was in the medium range. The inoculant ferro-silicon-barium gave the best results with no or only small penetration. The ferro-silicon-titanium inoculant also showed a high nucleation rate at the end of the solidification, and the average volume fraction of small eutectic cells was high. The degree of penetration was in the medium range. The ferro-silicon-manganese inoculant showed little penetration.

A high cooling rate gave severe penetration and the eutectic cell size was as expected small.

At somewhat lower cooling rates in the thermal analysis cup, no penetration was observed in either the uninoculated or inoculated experiments.

Keywords:

• grey cast iron
• inoculation
• inoculants
• eutectic cell size
• metal expansion penetration
• thermal analysis
• thermoanalysis cup
• cooling curves