Abstract
Continuous and extensive works have been going to develop 700°C A-USC (Advanced Ultra Super Critical) power plants worldwide. Since Japanese national project launched in 2008, Ni based alloy HR6W (45Ni-24Fe-23Cr-7W-Ti, ASME Code Case 2684) was selected as one of the promising candidate materials of A-USC boiler tube and pipe for long-term creep strength evaluation and field exposure test. In the present study, to establish the creep damage and life assessment method for Ni based alloy component, long-term creep rupture properties, microstructural stability, and creep damage morphology of HR6W weldment were experimentally investigated. Creep tests of HR6W weldment were conducted at temperature range of 700 to 800°C for durations up to 70,000 hours. Failure behavior of creep void formation and creep crack growth was identified, and damage mechanism of weldment during creep were discussed and characterized. Furthermore, uniaxial interrupted creep tests were carried out, the creep damage evaluation was conducted and life assessment approach was proposed based on the metallographic quantification evaluation of creep void and microstructure evolution. It demonstrated the possibility and validity to evaluate creep damage of Ni based alloy component with creep void and microstructure parameters.
