Grain boundary character and superplasticity of fine-grained ultra-high carbon steel

Tadashi Furuhara, Eiichi Sato, Taichiro Mizoguchi, Shuji Furimoto, Tadashi Maki

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)

Abstract

The characteristics and superplasticity of the (α + θ) microduplex structures formed by various thermomechanical processings were studied in an ultra-high carbon steel (Fe-1.4Cr-1.0C). After heavy warm rolling of pearlite, an (α + θ) microduplex structure with equi-axed α grains of 0.4 μm in diameter and spheroidized θ particles of 0.2 μm in diameter is obtained. The α matrix exhibits a recovered structure in which most of α grain boundaries are low-angle boundaries, resulting in rather smaller elongation at 973 K. Heavy cold rolling and annealing of pearlite produces an (α + θ) microduplex structure which consists of the coarse-grain region (dα ∼ 0.4 μm) with high-angle α boundaries and the fine-grain region (dα ∼ 0.2 μm) with low-angle α boundaries. Superplasticity in this specimen is slightly better than the warm-rolled specimen. When pearlite was austenitized in the (γ + θ) region, quenched and tempered at the temperature below A1, an (α + θ) microduplex structure in which α and θ grain sizes are nearly the same as in the warm-rolled specimen and most of ce boundaries are of high-angle one is formed. Such ultra-fine α grains are formed through the recovery of the fine (α′ lath martensite + θ) mixture during tempering. This microduplex structure exhibits superior superplasticity. Heavy warm rolling prior to the quenching and tempering improves total elongation further because the distribution of prior γ grain size is more uniform. When cold-rolled pearlite was austenitized and air-cooled, an (α + θ) microduplex structure with high-angle α boundary is formed. However, since the α grain size was relatively large (ca. 2 μm), its superplastic performance is poor. Finally, more simplification of processing for superplasticity was attempted. Further improvement of superplasticity was achieved by omitting the tempering in the quenching and tempering treatment.

Original languageEnglish
Pages (from-to)2455-2462
Number of pages8
JournalMaterials Transactions
Volume43
Issue number10
DOIs
Publication statusPublished - 2002 Oct

Keywords

  • Grain boundary
  • Microstructure
  • Pearlite
  • Superplasticity
  • Tempering
  • Thermomechanical processing
  • Ultra-high carbon steel

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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