Strength and Low Temperature Toughness of High Manganese Austenitic Fe-Cr-Ni Alloys for Cryogenic Service

Abstract

Mechanical tests were carried out on high manganese austenitic iron alloys for cryogenic service to study the effect on the strength and the toughness at lower temperatures. Addition of manganese to austenitic Fe-Cr-Ni alloy can improve neither the strength nor the toughness. Impact energy decreases as manganese content increases. Although homogenization at 1000°C (1273K) for 24 hours gives rise to coarsning of the grain size, the proof stress and the toughness are remarkably improved. The improvement would be attributed to solution of carbides, which would be nucleation sites for void formation in ductile fracture. In this experiment, 30%Mn-5%Ni-15%Cr and 20%Mn-10%Ni-15%Cr iron alloys are recommended as cryogenic structural materials from the view point of the stability of austenitic phase at 4 K. However, the higher nickel alloy results in the better balance of strength and low temperature toughness than the higher manganese alloy.