Effects of dynamic recrystallization on γ grain refinement and improvement of micro segregation of as cast austenite in 9% Ni steel

S. Hotta, T. Murakami, T. Narushima, Y. Iguchi, C. Ouchi

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)

Abstract

Effects of dynamic recrystallization on γ grain refinement and improvement in micro segregation of elements such as Ni and Mn of as cast austenite in 9% Ni steel were investigated by two kinds of experimental methods. The first one was a hot compression test using the specimens prepared from the strand cast slab and the hot rolled plate of 9% Ni steel, and the other was a hot tensile straining test in the austenitic region after levitation melting and solidification. In the hot compression test, variations in onset strain and flow stress of steady state flow of dynamic recrystallization with hot deformation conditions were investigated. The onset strain was found to decrease below 0.25 at the temperatures above 1 523 K and the strain rate below 1 × 10-2s-1. The activation energy value obtained from steady state flow stress was 421 kJ/mol. Dynamically recrystallized γ grain size in as cast austenite of this steel was controlled simply by Z value with no dependence on the initial γ grain size. This beneficial feature of dynamic recrystallization was confirmed by the experiment of tensile straining in austenite formed after levitation melting and solidification, where extremely coarse initial γ grain size of around 1.9mm was markedly refined down to 140 μm by straining such a small strain as 0.40. Micro segregation ratio of Ni and Mn in the strand cast 9% Ni steel examined by EPMA analysis was 1.20 and 1.36, respectively. These values were found to decrease continuously with reduction in strain rate in hot deformation of austenite. That is, dynamic recrystallization in austenite taken place at lower strain rate deformation is much more effective for homogenization of segregated elements compared with high strain rate deformation.

Original languageEnglish
Pages (from-to)338-346
Number of pages9
JournalIsij International
Volume45
Issue number3
DOIs
Publication statusPublished - 2005

Keywords

  • 9% Ni steel
  • Dynamic recrystallization
  • Levitation melting
  • Micro segregation
  • S-S curve
  • Strand cast slab
  • γ grain refinement

ASJC Scopus subject areas

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

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