Abstract
Cast duplex stainless steel (CDSS) components suffer embrittlement after long-term thermal aging. The deformation and fracture behaviors of un-aged and thermally aged (at 400 °C for 20,000 h) CDSS were investigated using in situ scanning electron microscopy (SEM). The tensile strength of CDSS had a small increase, and the tensile fracture changed from ductile to brittle after thermal aging. Observations using in situ SEM indicated that the initial cracks appeared in the ferrite perpendicular to the loading direction after the macroscopic stress exceeded a critical value. The premature fracture of ferrite grains caused stress on the phase boundaries, leading the cracks to grow into austenite. The cleavage fracture of ferrite accelerated the shearing of austenite and reduced the plasticity of the thermally aged CDSS.
Highlights
Cast duplex stainless steel (CDSS), widely used in pressure water reactors (PWRs) as the primary circuit piping and the reactor coolant pump casing, is sensitive to thermal aging embrittlement after long-term service [1,2,3,4,5,6]
Spinodal decomposition in ferrite is considered to be the primary mechanism of thermal aging embrittlement, which has been widely investigated by transition electron microscopy (TEM) [3,7,8,12,13,14,15] and atom probe tomography (APT) [2,7,14,16,17,18]
After long-term thermal aging, the ferrite in CDSS decomposed into two kinds of coherent and interconnected regions with different chemical compositions and mechanical properties
Summary
Cast duplex stainless steel (CDSS), widely used in pressure water reactors (PWRs) as the primary circuit piping and the reactor coolant pump casing, is sensitive to thermal aging embrittlement after long-term service [1,2,3,4,5,6]. Spinodal decomposition in ferrite is considered to be the primary mechanism of thermal aging embrittlement, which has been widely investigated by transition electron microscopy (TEM) [3,7,8,12,13,14,15] and atom probe tomography (APT) [2,7,14,16,17,18] While it has not resulted in any reported problems, thermal aging embrittlement of CDSS components may become an issue when the service lifetimes of PWRs extend to 60 years or even. The mechanisms of thermal aging embrittlement have been confirmed to be identical to accelerated aging and reactor operating conditions according to previous studies [2,4,11]
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