New low-activation austenitic steel for nuclear power engineering

Abstract

Vacuum induction melting is used to fabricate a new low-activation chromium-manganese austenitic steel with an increased, compared to well-known analogues, manganese content and additional alloying with strong carbide-forming elements (with a high tendency to carbide formation). Using the methods of transmission and scanning electron microscopy, the features of its microstructure, elemental and phase compositions in the solution treated state are studied. It is shown that the steel has an austenitic structure with a grain size of tens of micrometers. Its dislocation substructure is represented by flat dislocation pileups, which is typical for materials with low stacking fault energy. Coarse (submicron) particles of MC carbides (M = Ti, Ta, Zr, W) are found along the boundaries and inside the grains. Nanosized particles of the MC type fix the grain and subgrain boundaries and the dislocation substructure of the steel. Mechanical tensile tests are carried out at room and elevated temperatures. It is shown that the new steel has higher yield and tensile strength values, as well as elongation to failure compared to the austenitic chromiumnickel steels currently used in nuclear power engineering and well-known chromium-manganese low-activation steels.

Microstructure Features and Mechanical Properties of Modified Low-Activation Austenitic Steel in the Temperature Range of 20 to 750 °C

“…Compositions based on Fe-12Cr-(20-25)Mn-0.25C [7][8][9][10], with minor alloying additions of V, W, Ti, B, P, as well as various variants of steels with similar compositions [6,[11][12][13][14], were developed. However, the austenite stability of these steels, determined by the nickel equivalent, is (17)(18)(19)(20), which is lower than that of the latest generation of chromium-nickel steels (19)(20)(21)(22)(23)(24)(25)(26). The formation of chromium-manganese steels with an addition of Ni and N for austenite stabilization, and with Mn and C, was also reported [15][16][17][18].…”

“…%, and a carbon content of 0.25 wt. %, additionally alloyed with strong carbide-forming elements [19,20]. It has a nickel equivalent of 22.5, calculated from the actual composition.…”