GRAIN-BOUNDARY SEGREGATION UNDER ELECTRON-IRRADIATION IN AUSTENITIC STAINLESS-STEELS MODIFIED WITH OVERSIZED ELEMENTS

Effects of modification with oversized elements (Ti. Zr, Hf, V, Nb or Ta) on radiation-induced grain boundary segregation (RIS) in austenitic stainless steels were studied by means of electron irradiation in an HVEM and analytical electron microscopy. Solution-annealed 316L steels modified with the oversized elements were electron irradiated up to a dose of 10 dpa at temperatures of 673 to 773 K. Segregation behaviors of Cr and Ni near the grain boundary were strongly affected by the additional elements. Addition of Hf or Zr was particularly effective in preventing RIS. It was deduced from damaged microstructures that when the amount of irradiation-produced point defects decreased as a result of recombination and/or development of secondary defects in the matrix, segregation at the grain boundary was retarded. The change in net concentration of point defects in the matrix was associated with the trapping effect of point defects by the added elements, which depended on their size factor.