Temper Embrittlement of CrMoV Turbine-Rotor Steels

摘要

Samples from the hot and cold ends of two retired CrMoV steam turbine rotors (Joppa No. 3 and Buck No. 6) and of the failed Gallatin rotor were studied with respect to the degree of temper embrittlement, fracture mode, impurity segregation, and microstructure in the as-received condition and after various heat treatments. The Joppa material showed no temper embrittlement, presumably due to its relatively higher purity and due to the presence of ferrite. The Buck material exhibited an extraordinarily large amount of temper embrittlement, due to its unusually large contents of P and Sn, both of which were found to be segregated to the prior austenite grain boundaries, particularly at the hot end of the rotor. The Gallatin material from the hot end exhibited some temper embrittlement due to P segregation, but because of its extraordinarily fine grain size, the FATT in the embrittled condition remained relatively low.