Article – Effects of Metallurgical Factors on Microporosity in Ductile Iron

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Effects of Metallurgical Factors on Microporosity in Ductile Iron

Simon N. Lekakh and Michael Khayat

Missouri University of Science and Technology, Rolla, Missouri, USA

Copyright 2019 American Foundry Society

 

Abstract

The prevention of microporosity in SGI castings improves fatigue life; however, there is no standard foundry practice which will promote or eliminate sporadic appearance of microporosity. This study was a comprehensive evaluation of how metallurgical factors affected microporosity formation in SGI castings. The design of experiment (DOE) test matrix included five variables at two levels: melt quality (with and without SiC in the charge), nodulizer composition (low vs. high rare earth materials [REM]), inoculant composition (foundry grade FeSi vs. Ce-bearing inoculant), inoculant additions (0.3% and 0.6%), and low-pouring temperature (1280−1300°C/2336−2372F) vs. high-pouring temperature (1380−1400°C/2516−2552F). Four experimental heats, with four variations in metallurgical parameters per heat were performed according to the DOE matrix. Each mold was equipped with a cone (to study the total volume of shrinkage) and a horizontal plate with attached vertical cylinders (to study microporosity using Archimedes density method, metallography, scanning electron microscopy [SEM], optical profiler, and high-resolution 3D computed tomography [CT]. Minitab® software was used for statistical analyses of individual and joint effects of studied metallurgical parameters on microporosity and microstructure. Optimal metallurgical parameters for the prevention of microporosity were discussed.

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