Formation Mechanism of Secondary Inclusions in Fe-36mass%Ni Alloy Using a Novel Combination Analysis Technique

Hiroshi Fukaya, Jonah Gamutan, Makoto Kubo, Shintaro Yano, Shigeru Suzuki, Takahiro Miki

Research output: Contribution to journalArticlepeer-review

Abstract

Controlling the size, number, and composition of secondary inclusions is vital in the production of highquality steels. In this study, experimental and computational investigation of the relationship between secondary inclusion formation in Fe-36mass%Ni alloy and cooling rate was carried out. Assuming the case of large ingots, solidification experiments using various cooling rates (0.17 to 128 K/min) were employed and the size, number, composition, and distribution of inclusions were analyzed by SEM-EDS automatic inclusion analysis. Like previous studies, inclusion number density increased with increasing cooling rate, while inclusion size decreased with increase of cooling rate. On the contrary, oxide inclusion area fraction was found to have little relationship with the cooling rate and was instead found related with oxygen content of the sample. As a new attempt to investigate the relationship between microsegregation and secondary inclusion formation, a combination of SEM-EDS analysis and EPMA mapping analysis was carried out. By superimposing information of microsegregation and inclusions, it was found that high-Al2O3 inclusions formed during the early stage of solidification, whereas low-Al2O3 inclusions formed during the later stage of solidification. These findings suggest that Al2O3 inclusions formed in the early stage of solidification reacted with the remaining Si-enriched liquid steel and changed into low-Al2O3 inclusions. Experimental results were also confirmed by thermodynamic calculations. Present work made it possible to understand deeper the relationship between microsegregation and secondary inclusion formation.

Original languageEnglish
Pages (from-to)970-980
Number of pages11
JournalISIJ International
Volume63
Issue number6
DOIs
Publication statusPublished - 2023 Jun 15

Keywords

  • cooling rate
  • Fe-Ni alloy
  • microsegregation
  • Scheil-Gulliver model
  • secondary inclusions
  • solidification

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