SIZE EFFECT OF ADDITIONAL ELEMENTS ON RADIATION-INDUCED GRAIN-BOUNDARY SEGREGATION BEHAVIOR IN AUSTENITIC STAINLESS-STEEL

In the austenitic stainless steels considered to be used as the first wall or blanket of a water cooled fusion reactor, it has been suggested that radiation induced grain boundary segregation (RIS) causes not only deleterious effects on their mechanical properties but also stress corrosion cracking under irradiation. Therefore, it is of great importance to investigate RIS retardation. In this study, the additional effects of oversized elements on RIS in austenitic stainless steel was investigated using an HVEM. Solution annealed type 316L steels modified with Ti, Zr, Hf, V, Nb or Ta were electron-irradiated up to a dose of about 10 dpa at temperatures of 673 to 823 K. Radiation induced solute redistributions in the vicinity of the grain boundary were analyzed by EDX. Segregation behaviors of Cr and Ni near grain boundary were strongly affected by the additional elements. Especially, addition of Hf or Zr is a most effective way to prevent RIS. It is understood from damage microstructures that when the amount of irradiation produced point defects decreases as a result of recombination and/or cluster formation of the second defects in matrix, segregation at grain boundary is retarded. The change in net concentration of point defects in matrix is associated with trapping effect of defects with additional elements depending on size factor of additives.