Fracture toughness and atom probe characterization of a highly embrittled RPV weld

Mikhail A. Sokolov, Randy K. Nanstad, Michael K. Miller

Research output: Contribution to journalConference articlepeer-review

11 Scopus citations

Abstract

The Heavy-Section Steel Irradiation Program at Oak Ridge National Laboratory (ORNL) includes a task to investigate the shape of the fracture toughness master curve for reactor pressure vessel steel highly embrittled as a consequence of irradiation exposure. A radiation-sensitive reactor pressure vessel (RPV) weld with intentionally enhanced copper content, designated KS-01, is characterized in terms of static initiation (KIc, KJc) and Charpy impact toughness in the unirradiated and irradiated conditions. The objective of this project is to investigate the ability of highly embrittled material to maintain the shape of the unirradiated transition fracture toughness curve, as well as to examine the ability of the Charpy 41-J shift to predict the fracture toughness shift at such a high level of embrittlement. Irradiation of this weld was performed at the University of Michigan Ford Reactor. Specimens of KS-01 weld were irradiated to about 0.74 × 10 19 neutron/cm2 at 288°C. Irradiation resulted in Charpy ductile-to-brittle transition temperature (DBTT) shift of 169°C. It was anticipated that this shift would result in a fracture toughness transition temperature (at 100 MPa√m) in the irradiated condition near or slightly above the pressurized thermal shock screening criterion for weld metals, T oPTS = 129°C. The fracture toughness characterization of KS-01 weld in the unirradiated and irradiated conditions was mainly performed by testing 1T C(T), although some 0.5T C(T) and precracked Charpy specimens were used in this study. The master curve analysis showed that this material exhibited shift of reference fracture toughness transition temperature, T o, of 165°C as result of radiation, which is in remarkable agreement with Charpy DBTT shift. The absolute value of To in the irradiated condition was determined to be equal to 139°C. This weld exhibited a low ductile initiation toughness (JQ) after irradiation. It left a relatively narrow temperature window to examine the shape of the transition region. Irradiated median fracture toughness values up to 148 MPa√m follow the master curve shape. However, low toughness brittle fractures occurred at temperatures further above To (To + 61°C) than expected with a leveling of the KJc data from the master curve shape. The microstructure of the weld was characterized with the ORNL's energy-compensated optical position-sensitive atom probe. Atom probe tomography revealed a high number density (∼3 × 1024 m -3) of Cu-, Mn-, Ni-, Si-, and P-enriched precipitates and a lower number density (∼1 × 1023 m-3) of P clusters.

Original languageEnglish
Pages (from-to)123-137
Number of pages15
JournalASTM Special Technical Publication
Issue number1447
StatePublished - 2004
EventEffects of Radiation on Materials: 21st International Symposium - Tucson, AZ, United States
Duration: Jun 18 2002Jun 20 2002

Keywords

  • Atom probe
  • Charpy
  • Fracture toughness
  • Master curve
  • Precipitates
  • Radiation embrittlement
  • Reactor pressure vessel

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