Thermal aging embrittlement of cast stainless steel for nuclear primary pipes

To study the thermal aging of the nuclear primary pipe material Z3CN20-09M, accelerated thermal aging experiments were performed at 300, 350 and 400℃ for 30000 h. Charpy impact energy and nanohardness of ferrite phase were tested for samples with different thermally aged time. Taking Charpy impact energy as the standard of thermal aging embrittlement, the thermal aging activation energy of the material was obtained to be 51.962 kJ·mol^-1 by the fitting method. Meanwhile, the thermal aging parameter P was used to describe the kinetics of thermal aging embrittlement with Charpy impact energy. Finally, the Charpy impact energy and nanohardness of the material during 40 operation years at the actual operation temperature were estimated by the thermal aging activation energy and the thermal aging kinetics. The predicted results show that the toughness of the material decreases fast in the early 5 years, and then undergoes a slowly-decreased operation process.