Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts

Branko Bauer,Mitja Petrič,Ivana Mihalic Pokopec,Primož Mrvar

doi:10.4028/www.scientific.net/msf.925.70

Branko Bauer, Mitja Petrič + Show 2 more

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https://doi.org/10.4028/www.scientific.net/msf.925.70

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Abstract

Metallographic analysis is applied to the study of the chunky graphite morphology in heavy-section castings of spheroidal graphite cast irons. Three castings with different Si and Ni content were prepared. Three positions in casting from the edge to the centre, with different cooling rates, were chosen for microstructure observation. The effect of the Si and Ni content on the graphite morphology and mechanical properties of heavy-section spheroidal graphite cast iron parts were investigated. Cerium containing commercial inoculant was used for in-stream inoculation. Chunky graphite area was estimated in micro-and macrostructure. Mechanical properties were determined on tensile test bars taken from the centre of the casting. Macro-and microstructure examination showed that the castings with high Si-content and Ni addition had chunky graphite present, while the castings produced by use of low Si and Ni containing charge had no chunky graphite. High Si-content is strong chunky graphite promoter, especially in castings with slow cooling rate. Ni addition also promotes chunky graphite formation, but only in thermal centre of the casting (where the cooling rate is the lowest). The elongation is severely lowered when chunky graphite appears in the microstructure.

Highlights

Spheroidal graphite cast iron is important construction material within cast iron family
Metallographic analysis is applied to the study of the chunky graphite morphology in heavy-section castings of spheroidal graphite cast irons
Macro- and microstructure examination showed that the castings with high Si-content and Ni addition had chunky graphite present, while the castings produced by use of low Si and Ni containing charge had no chunky graphite

Summary

Introduction

Spheroidal graphite cast iron is important construction material within cast iron family. Production of heavy-section spheroidal graphite cast iron castings is increasing in windmill industry, heavy automotive industry and spent-nuclear-fuel containers industry. Future applications will require even larger wall-thicknesses. The demand for good mechanical properties will be even more pronounced in these castings. Spherical morphology of the precipitated graphite is the most important factor to achieve required mechanical properties. [1,2,3,4,5,6] Heavy-sectioned parts are characterised by low cooling rate and long solidification time. As a consequence decrease in nodule count, increase in nodule size and occurrence of graphite degeneration occur, what leads to decrease of mechanical properties. As a consequence decrease in nodule count, increase in nodule size and occurrence of graphite degeneration occur, what leads to decrease of mechanical properties. [3,4,5,6,7]

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