Lattice defects of cold-drawn and aged Fe-36wt%Ni alloys and effects of additions of C and v on hardness and thermal expansion

Kazuo Nakama, Shinichi Furuya, Kazuki Sugita, Koji Inoue, Yasuharu Shirai

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Synopsis: Fe-36wt%Ni invar alloy has been widely used for precision parts where dimensional changes with temperature are unfavorable. In the viewpoint of industrial application, high-strength with low-thermal-expansion alloys are in increased demand for structural members such as power cables and electronic devices. Additions of alloying elements to and cold working on Fe-Ni alloys are effective methods that enable the alloys to strengthen, although these modifications also influence the magnitude of thermal expansion. In this study, effects of additions of 0.2wt%C and/or 0.8wt%V on hardness and thermal expansion of cold-drawn and aged Fe-36wt%Ni invar alloys are reported. Hardness in solution-treated and as-drawn conditions increased with addition of C, and, when both C and V were added, hardness of the alloy reached its maximum after aged at 650 °C. Besides an increase in hardness with addition of any of C and V, thermal expansion below Tc became smaller in as-drawn condition than in solution-treated condition. Measurements of positron lifetimes revealed that vacancies introduced by cold-drawing were annealed out through aging up to 300 °C and dislocation motion was activated at 500 °C. Both vacancies and dislocations, especially C-dislocation complexes, seemingly influence the decrease in thermal expansion. While graphite precipitation in the C-added invar alloy showed no hardening, addition of C and V to invar alloy resulted in secondary hardening by vanadium carbide precipitation when aged over 500 °C, which realized high-hardness and low-thermal-expansion.

Original languageEnglish
Pages (from-to)380-389
Number of pages10
JournalTetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan
Issue number5
Publication statusPublished - 2013


  • Aging
  • Cold-drawing
  • Hardness
  • Invar
  • Positron lifetime
  • Thermal expansion

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Metals and Alloys
  • Materials Chemistry


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