Elevated temperature elastic constants of Fe-30 wt pct Ni in austenitic and martensitic conditions

A pulsed laser technique was used to measure the polycrystalline elastic moduli of the martensite and austenite phases of an Fe-30.1 wt pct Ni alloy between 298 and 900 K. The moduli of an Fe-29.5 wt pct Ni-0.1 wt pct C alloy were similarly determined at 298 K. These data showed that the shear modulus and Young’s modulus of martensite were slightly decreased by carbon. The moduli of austenite behaved in the expected manner, changing monotonically with temperature above the Curie temperature. The moduli of the martensite changed monotonically with temperature from 298 K until the martensite-to-austenite transformation temperature was reached at 650 K. At this temperature abrupt changes in moduli were observed. The same austenite start temperatures were determined both from moduli measurements and from dilatometric measurements. No unusual decrease of the martensite elastic constants was observed as a precursor to the reverse martensite-to-austenite transformation. Formerly with Sandia Laboratories, Albuquerque, New Mexico