Influence of manganese on mechanical properties, irradiation susceptibility and microstructure of ferritic steels, alloys and welds

Abstract

The ferritic steels used world wide for nuclear pressure vessels and irradiated structures contain manganese but knowledge of the role of manganese is mainly confined to the unirradiated condition. Information from the mid 1950s to 2009 on the influence of manganese on unirradiated and irradiated properties is analysed. In unirradiated material manganese raises ambient strength, improves notched impact toughness, benefits high temperature strength, promotes dynamic strain aging and enhances creep resistance. However, by combining with carbon and by increasing phosphorus diffusion, manganese increases intergranular embrittlement after thermal aging. Neutron irradiated steels are deleteriously affected by manganese. First, the dose coefficients of irradiation hardening and embrittlement increase linearly with manganese, particularly in steels with uncombined nitrogen, and the morphology of irradiation induced interstitial loops is altered. Second, manganese occurs in irradiation induced Cu rich precipitates, altering their morphology and the associated hardening. Third, manganese becomes incorporated into irradiation enhanced Cu-Ni-Mn precipitates and Mn-Ni-Si nanoclusters that increase hardening and embrittlement at high doses. Finally, manganese segregates at grain boundaries under irradiation. Overall, the unirradiated benefits are outweighed by deleterious irradiation effects. These factors are important in supporting continued reactor operations, extending lifetimes of existing nuclear vessels and structures, improving steel specifications for advanced reactors and developing steels for nuclear fusion applications.

Transmission electron microscopy investigation of the microstructure of Fe–Cr alloys induced by neutron and ion irradiation at 300 °C

“…The fluence to dpa conversion was done using a dose conversion factor of 1.5 Â 10 À25 dpa/n m À2 (>1 MeV) [23]. The irradiation conditions are described with ample detail in Ref.…”

Multiscale modelling in nuclear ferritic steels: From nano-sized defects to embrittlement

“…Both databases are provided as supplementary materials. In both cases, original neutron fluence and neutron flux data provided in n cm -2 or in n cm -2 s -1 , respectively, are converted into displacement-per-atom, dpa, or dpa s -1 using a constant conversion factor: 1 dpa = 6.67 10 20 n cm -2 [53]. In addition, this work aims at predicting the embrittlement ∆𝑇 induced by radiation, but experimental data found in the literature often concern the increase in the yield strength (hardening) y instead.…”

Critical Assessment 12: Prospects for reduced activation steel for fusion plant

“…42,43 In addition, reduced activation austenitic steels need alternative austenitic stabilising elements to replace Ni (which, along with Cu and Co, is not a low activation element); 5 Mn and N offer the most attractive reduced activation alternatives. Reduced activation austenitic steels utilising Mn have received some interest from the fusion community; 44,45 however, concerns over the high decay heat and potential volatilisation of Mn in loss of coolant accident conditions caused these steels to be abandoned for use in fusion reactors. 7 High N containing austenitic steels suffer from a lack of stability at the temperatures required for operation due to the formation of Fe and Cr nitrides.…”

“…Reduced activation austenitic steels utilising Mn have received some interest from the fusion community; 44,45 however, concerns over the high decay heat and potential volatilisation of Mn in loss of coolant accident conditions caused these steels to be abandoned for use in fusion reactors. 7 High N containing austenitic steels suffer from a lack of stability at the temperatures required for operation due to the formation of Fe and Cr nitrides.…”