Structure characteristics of iron powder treated slightly hypereutectic grey irons

Abstract

The purpose of the present paper is to investigate the structure characteristics of slightly hypereutectic grey irons (carbon equivalent = 4·3–4·5%) in resin sand and metal moulds after either a separate addition of iron powder or inoculation (Ca,Ba,Al–FeSi) or in a double treatment both in different variants. Iron powder favours austenite dendrite formation (up to 40% increase in area in metal moulds) as reinforcement for eutectic cells, but it led to unsuitable morphologies for graphite nuclei [large irregular polygonal (Mn,X)S compounds] and lower eutectic cell count. Inoculation by itself showed the strongest graphitising effect and increase in eutectic cell count. The ‘double treatment’ (Fe powder+inoculant) can be recommended as there is a residual benefit of an Fe powder addition on austenite dendrite formation and inoculation restores the effectiveness of the MnS morphology and size for control of chill and eutectic cells, especially if inoculation is carried out after the iron powder treatment.