SYMPOSIA PAPER Published: 01 January 1950

Sigma Phase in Chromium-Molybdenum Alloys with Iron or Nickel


Because the brittleness of chromium-base alloys for high-temperature duty was believed to be due in part to sigma formation, research was undertaken to study the formation of sigma in simple alloys of chromium, molybdenum, and iron. The extent of the sigma phase in the chromium-molybdenum-iron ternary diagram has been determined, and some of the properties of the sigma occurring in this system have been described. The experiments indicate that molybdenum increases the high-temperature stability of sigma in iron-chromium alloys, and that the sigma phase in the 60Cr-25Mo-15Fe alloy is stable at 1100 C. With regard to this alloy, the temperature effect is such that at lower temperatures the tendency for the formation of sigma is increased provided that sufficient time be allowed for the transformation. The sigma phase has been found to occur in the chromium-molybdenum-nickel ternary alloys, although its occurrence has not been reported in any of the three constituent binaries. X-ray diffraction data on chromium-molybdenum-nickel sigma are included.

Author Information

Putman, John, W.
Massachusetts Institute of Technology, Cambridge, Mass.
Grant, N., J.
Massachusetts Institute of Technology, Cambridge, Mass.
Bloom, D., S.
Massachusetts Institute of Technology, Cambridge, Mass.
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Developed by Committee: E04
Pages: 61–70
DOI: 10.1520/STP46104S
ISBN-EB: 978-0-8031-6741-4
ISBN-13: 978-0-8031-6506-9