Effect of Rare-Earth Cerium on Impurity Tin-Induced Hot Ductility Deterioration of SA508-III Reactor Pressure Vessel Steel

The samples of SA508-III reactor pressure vessel steel, undoped, doped with Sn, and doped with Sn + Ce, are heated at 1300 degrees C and then cooled down to different temperatures between 650 and 1050 degrees C, followed by tensile deformation until fracture using a Gleeble machine. The steel hot ductility evaluated by the reduction of area (RA) is determined at each test temperature. The tested samples are characterized using scanning electron microscopy, optical microscopy, and field emission gun scanning transmission electron microscopy. The steel exhibits a hot ductility trough and Sn substantially deteriorates the hot ductility of the steel by deepening and widening the ductility trough. However, Ce can well suppress this Sn-induced hot ductility deterioration. Grain boundary segregation of Sn or Sn + Ce occurs in the Sn-doped or Sn + Ce-doped samples. The segregation of Sn is primarily responsible for the hot ductility deterioration as it weakens grain boundary, thereby enhancing grain boundary sliding and deteriorating hot ductility. The segregation of Ce is mainly responsible for the suppression of the deterioration as it strengthens grain boundary, thereby restraining grain boundary sliding and suppressing Sn-induced hot ductility deterioration.