Mechanical properties behavior of neutron irradiated 12Ni-5Cr-3Mo maraging steel plate and companion weld metal

Abstract

Charpy-V notch ductility and tensile properties changes in neutron irradiated 12Ni-5Cr-3Mo maraging steel have been evaluated following low (<250°F) and elevated temperature (550 to 740°F) exposure. The study was performed with 1-in, thick plate material (six heats) aged at 900°F for 2 and 20 hr to nominal yield strengths of 160 and 180 ksi respectively. Long term thermal stability of both heat treatment conditions was investigated for the conditions of irradiation. The <250°F and 550°F irradiation performance of matching (12-5-3) and mismatching (17Ni-2Co-3Mo) TIG weld deposits maraged to 180 ksi yield strength was also assessed in this study.General properties changes of the 12-5-3 maraging steel plate and companion weld metals were found to be rather small with <250°F exposures, indicating good resistance to neutron-induced embrittlement. However, a marked deterioration of notch ductility properties with long term exposure at elevated was revealed and traced to a non-nuclear thermal instability. The observed instability instability is believed to be a continuation of aging processes at temperatures well below the initial maraging temperature. Extended time-at-temperature treatments indicate that service above 550°F may produce sufficient properties changes for failure by low energy tear. Aging treatments of 1900 to 3300 hours duration increased the yield and tensile strengths of the 12-5-3 alloy by as much as 52.0 and 53.3 ksi respectively while not altering appreciably percent elongation and reduction of area values.