Mechanical and microstructural characterization of heat-affected zone materials of reactor pressure vessel

Katsuyama, Jinya  ; Tobita, Toru; Nishiyama, Yutaka ; Onizawa, Kunio 

In order to provide the technical basis for the needs of surveillance specimens from heat-affected zone (HAZ) in reactor pressure vessel (RPV) steels, we performed a research on the characterization of metallurgical and mechanical properties of HAZ in RPV steels. The distributions of grain size and phases were drawn as a map based on temperature histories obtained from welding simulation. Referring to the HAZ map, typical HAZ materials were made by simulating temperature histories including PWHT. Metallurgical and mechanical characteristics for the HAZ materials were compared with those of base metal. From the results, it was clarified that mechanical properties of HAZ materials depended not on the grain size, but mostly on the phases. HAZ materials close to weld metal indicated higher toughness due to mixed structure of martensite and lower bainite, while HAZ materials close to base metal were equivalent or slightly lower toughness due to the same phase as base metal of upper bainite.