Experimental and numerical study on multiaxial creep behavior of 16MND5 steel at 700℃.

• The multiaxial creep tests of 16MND5 steel for reactor pressure vessel are carried out at 700℃, and the macroscopic properties are obtained. • The mechanism of material failure under uniaxial stress and multiaxial stress is explained by microscopic observation (OM, SEM). • A new model based on the continuous damage theory is established by considering the activation energy parameter Q and stress combination. • The simulation results are in good agreement with the tests results. The effect of stress triaxiality on creep damage is fully understood,. • It is found that the highly-concentrated damage occur at the center as well as the notch root with increasing the notch acuity ratio. In-vessel retention (IVR) is an effective strategy of ensuring the structural integrity of RPV under severe accidents. In the IVR condition, due to the geometric discontinuity of pressure vessel, multiaxial creep is the main form of failure of RPV. Moreover, 16MND5 steel undergoes a phase transition from bainite to austenite. In order to study the multiaxial creep failure mechanism, creep tests on different notched bar are carried out at 700℃. The influence of grain boundary precipitation on creep behaviors was studied by micro-structural observation. Furthermore, based on the Kachanov-Robotnov continuous damage model (CDM), the term of activation energy Q is adopted in the newly-developed model as the correction parameter that is used to study the damage evolution and multiaxial creep behaviors of 16NND5 steel. Finally, the good agreement is achieved between theoretical prediction and experimental results. [ABSTRACT FROM AUTHOR]