BEHAVIOR OF MECHANICAL PROPERTIES IN NEUTRON IRRADIATED 12Ni-5Cr-3Mo MARAGING STEEL PLATE AND COMPANION WELD METALS.

摘要

Changes of Charpy-V-notch ductility and tensile strength in neutron-irradiated 12Ni-5Cr-3Mo maraging steel have been evaluated following low (less than 250F) and elevated (550to 740F) temperature exposure. The study was performed with six heats of 1-in.-thick plate material aged at 900F for 2and 20hr to nominal yield strengths of 160and 180ksi,respectively. The long-term thermal stability of both heat-treatment conditions was investigated for the conditions of irradiation. The less than 250F and 550F irradiation performance of matching (15-5-3) and mismatching (17Ni-2Co-3Mo) TIG weld deposits maraged to 180ksi yield strength was also assessed in this study. Changes in the general properties of the 12-5-3maraging steel plate and companion weld metals were found to be rather small with less than 250F exposures,indicating good resistance to neutron-induced embrittlement. However, a marked deterioration of notch-ductility properties with long-term exposure at elevated temperature was revealed and traced to a nonnuclear thermal instability. The observed 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 550F may produce sufficient changes in properties for failure by low-energy tear. Aging treatments of 1900to 3300hours'duration increased the yield and tensile strengths of the 12-5-3alloy by as much as 52.0and 53.3ksi,respectively,while not altering appreciably the percentage of elongation and the reduction in area. (Author)