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<p>Compacted graphite iron (CGI) has gained increasing industrial relevance due to its favorable mechanical and thermal properties. Unlike most previous studies, which evaluated fading from ductile iron or employed alternative treatments such as the sandwich process, this work investigates fading directly in compacted graphite iron (CGI) produced via a commercial proprietary cored wire treatment process. The effects of different section thicknesses and fading time after magnesium treatment were analyzed in CGI samples obtained from base metal melted in a medium-frequency induction furnace, using pig iron, steel scrap, and foundry returns. Cylindrical bars and specimens of various thicknesses were cast and tested for mechanical properties, including tensile strength, yield strength, elongation, and hardness, in addition to microstructural analysis by optical microscopy. Results revealed a clear dependency of total magnesium on fading time, decreasing from 0.0090 to 0.0061%, which led to reduced nodular graphite, increased compacted graphite, and a general deterioration of mechanical properties. This behavior occurs concurrently with a reduction in RE content, indicating a combined contribution to the fading process. Ultimate tensile strength decreased by more than 10%, while elongation exhibited a marked decreasing trend of approximately 50%. Furthermore, a quantitative relationship between section thickness and nodularity was established for thicknesses between 5 and 30 mm under a maximum fading time of 20 minutes, offering practical insights for CGI casting design and process control.</p>

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Direct Analysis of Fading in Compacted Graphite Iron: Influence of Magnesium Treatment and Thickness on Microstructure and Mechanical Properties

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Alécio Antônio Martins de Oliveira,
  • Wellington Lopes,
  • Elaine Carballo Siqueira Corrêa

摘要

Compacted graphite iron (CGI) has gained increasing industrial relevance due to its favorable mechanical and thermal properties. Unlike most previous studies, which evaluated fading from ductile iron or employed alternative treatments such as the sandwich process, this work investigates fading directly in compacted graphite iron (CGI) produced via a commercial proprietary cored wire treatment process. The effects of different section thicknesses and fading time after magnesium treatment were analyzed in CGI samples obtained from base metal melted in a medium-frequency induction furnace, using pig iron, steel scrap, and foundry returns. Cylindrical bars and specimens of various thicknesses were cast and tested for mechanical properties, including tensile strength, yield strength, elongation, and hardness, in addition to microstructural analysis by optical microscopy. Results revealed a clear dependency of total magnesium on fading time, decreasing from 0.0090 to 0.0061%, which led to reduced nodular graphite, increased compacted graphite, and a general deterioration of mechanical properties. This behavior occurs concurrently with a reduction in RE content, indicating a combined contribution to the fading process. Ultimate tensile strength decreased by more than 10%, while elongation exhibited a marked decreasing trend of approximately 50%. Furthermore, a quantitative relationship between section thickness and nodularity was established for thicknesses between 5 and 30 mm under a maximum fading time of 20 minutes, offering practical insights for CGI casting design and process control.