The purpose of the present paper is to investigate the solidification pattern of slightly hypereutectic grey irons (CE = 4.35 - 4.45%) after an addition of a commercial iron powder, and also in a double treatment with inoculation. Chill wedges with a 0.11 - 0.43 cm cooling modulus (CM), from using resin sand and metal moulds, were used along with different thermal analysis cups (CM = 0.75 and 0.43 cm). Relative clear/mottled/total chill measurement criteria were applied. Unfavourable Mn and S contents [(%Mn) x (%S) = 0.016] and a reduced Al residual (0.0015%) led to relatively high eutectic undercooling and chill in the base iron, especially at high cooling rates (CR). With the lower CM of cups, there was more undercooling in the entire solidification range and more difference between irons. Thermal analysis and chill parameter relationships are normal, except only for iron powder treatment and resin mould solidification, where chill is higher for a relatively lower undercooling. Conventional inoculation after addition of iron powder (double treatment) showed a strong graphitizing effect, as these irons had the lowest undercooling and chill levels, in all the irons tested. It reflects the improved properties of (Mn,X)S compounds as nucleation sites for graphite . This paper is the first of two papers reporting on this study.