Micro-structure refinement in low carbon high manganese steels through ti-deoxidation: Austenite grain growth and decomposition

Naoki Kikuchi, Seiji Nabeshima, Yasuo Kishimoto, Yasuhide Ishiguro, Seetharaman Sridhar

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

This paper investigates the effect of de-oxidation inclusions on micro-structure evolution in low-carbon steels. Low carbon (0.07 wt%), high Mn (0.9 wt%) steel in a Al203 or MgO crucible was deoxidized by adding either aluminum (0.05 wt%) or titanium (0.05, 0.03 or 0.015 wt%) in a 400g-scale vacuum furnace, and cast in a Cu mold at cooling rates between 2.0-6.0 K/s. These cast samples were re-melted and cooled at various cooling rate, 1 through 100 K/s in the hot-stage of a conforcal laser scanning microscope (CSLM) in order to investigate the effect of cooling rate. Oxide inclusion sizes in all the Ti-killed steels were smaller and inclusion densities higher than those in the Al-killed steel. In Ti-killed steel, inclusion size and densities increased with increasing the oxygen content, inclusion size decreased and their densities increased with increasing the cooling rate. A Confocal Scanning Laser Microscope (CSLM) was used to study the differences in solid state microstructural evolution between the Ti-killed and theAI-killed samples. The growth of austenite grains were studied under isothermal conditions and it was found that both grain-boundary mobility and final grain size were lower in the Ti-killed sample than for the others. With regards to austenite decomposition, during continuous cooling from a comparable austenite grain structure, the resulting austenite decomposition structure was finer for the Ti-killed sample due to a higher Widmanstätten lath density due to precipitation at. The inclusion size was found to have a significant effect on both austenite grain size and austenite decomposition structure. Different orientations of ferrite precipitates originating at inclusions were observed in the Ti-killed samples. The highest lath concentration was obtained for the sample that had the smallest average inclusion size rather than the sample with highest density of sub micro-meter inclusions.

Original languageEnglish (US)
Pages (from-to)1036-1045
Number of pages10
JournalISIJ International
Volume49
Issue number7
DOIs
StatePublished - 2009
Externally publishedYes

Keywords

  • Aluminum
  • Confocal-laser-scanning-microscopy
  • De-oxidation
  • Grain growth
  • Inclusion
  • Low-carbon steel
  • Phase transformation
  • Solidification microstructure
  • Titanium

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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