Degradation of mechanical properties of CrMoV and CrMoVW steam turbine rotors after long-term operation at elevated temperatures. Part I: tensile properties, intergranular fracture strength and impact tests

Autor: I. Dlouhý, M. Holzmann, J. Krumpos, B. Vlach
Rok vydání: 1996
Předmět:
Zdroj: International Journal of Pressure Vessels and Piping. 68:99-111
ISSN: 0308-0161
DOI: 10.1016/0308-0161(94)00044-1
Popis: The influence of long-term operation at elevated temperature on tensile properties, brittle fracture initiation stress and on the Charpy V-notch transition behaviour of CrMoV and CrMoVW rotor steels has been investigated. A decrease in the 0·2% proof strength and tensile strength was observed in the CrMoVW steel after operation of 1·1 x 10 5 h at a temperature about 510°C. For the CrMoV steel only a small reduction of these characteristics was noted after operation at temperatures about 475°C. The initiation of brittle fracture of both steels after long-term operation was due to intergranular cracking, the intergranular fracture strength, established by testing smooth and notched-bars at low temperatures, was lower than the cleavage fracture stress of undegraded states (cold location). The fracture appearance transition temperature (FATT) determined by the Charpy impact test was increased by about 55°C and 37°C for CrMoV and CrMoVW steel, respectively. De-embrittling heat treatment (640°C/2 h/air-cooled) both of the service exposed and the undegraded state of CrMoV steel caused the shift in Charpy transition curve of exposed state by about 35°C to the lower temperature and the fracture was of a cleavage mode. On the contrary, no change in location of transition curve was noted for the undegraded state. The difference of a 20°C between these curves is likely to be a result of carbide induced embrittlement.
Databáze: OpenAIRE
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