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Sulfur and Oxygen Effects on High-Si Ductile Iron Casting Skin Formation

Materials Science and Engineering Faculty, Politehnica University of Bucharest, 313 Spl. Independentei, 060042 Bucharest, Romania
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Coatings 2020, 10(7), 618; https://doi.org/10.3390/coatings10070618
Received: 27 May 2020 / Revised: 23 June 2020 / Accepted: 27 June 2020 / Published: 29 June 2020
(This article belongs to the Section Surface Characterization, Deposition and Modification)
The main objective of the present paper is to evaluate by thermal (cooling curve) analysis the solidification pattern and the occurrence of the layer of degenerate graphite at the surface of ductile iron castings (3.15% Si, typically as 450-18 grade, ISO 1563/2011), with or without a mold coating, including S or O, and different agents (carbonic material, iron powder), supposed to act to block their diffusion into the iron melt. It is found that the mold coating materials temperately influence the parameters of the solidification cooling curves and, more visibly, the occurrence and the thickness of the undesired skin layer. Different graphite morphologies comparable to the casting body are present, at a large range of thicknesses, from 50 up to 200 µm. The sulfur presence in the mold coating will promote a higher skin thickness compared to oxygen (up to 50% by oxygen and 2.5–3.3 times for sulfur action), despite the fact that in the casting body, the graphite nodularity undergoes a limited decrease (from 85% up to 82%–83% level). Carbonic material or iron powder supplementary addition decreases these undesired effects, but the solidification undercooling compared to the equilibrium system is increased. It is found that carbonic material is more efficient at limiting oxygen than iron powder is at limiting the negative effects of sulfur on the casting skin thickness. More experiments are necessary to quantify their capacity to block the oxygen or sulfur transfer into the iron melt. View Full-Text
Keywords: thermal analysis; solidification cooling curves; eutectic undercooling; ductile cast iron; mold coating; sulfur; oxygen; degenerated graphite surface layer; structure thermal analysis; solidification cooling curves; eutectic undercooling; ductile cast iron; mold coating; sulfur; oxygen; degenerated graphite surface layer; structure
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MDPI and ACS Style

Anca, D.; Chisamera, M.; Stan, S.; Stan, I.; Riposan, I. Sulfur and Oxygen Effects on High-Si Ductile Iron Casting Skin Formation. Coatings 2020, 10, 618.

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