Precipitation and void-swelling in nickel-manganese austenitic stainless steels

Abstract

The precipitation and void-swelling characteristics of austenitic stainless steels in which nickel is partially replaced by manganese have been investigated. Alloy compositions were chosen on the basis of manganese being half as effective as nickel in stabilizing austenite, and steels with “nickel equivalent” contents of 25–37% were examined. The steels were irradiated with 46 MeV Ni 6+ ions to 60 dpa at 625°C and also aged for 1000 h at 600°C. The high-Mn alloys (20–30% Mn) were very susceptible to the formation of intermetallic phases during thermal ageing but less so in the shorter-duration irradiation experiment. Irradiation promoted the formation of Ni- and Si-rich phases—the suicide G phase (in which Mn can replace Ti) and in one instance M 6C. The Cr-rich carbide M 23C 6 formed in both the aged and irradiated steels. Among the high-Mn alloys, void-swelling decreased with increasing Ni and ( Ni+ Mn) contents, although a 25Ni-1Mn steel showed no swelling at 625°C.