Some material toughness properties of a series of turbine casing bolts removed from service after over 100 000 hours

The present study was aimed at examining the effects of temperature on both the Charpy and slow strain rate fracture toughness properties of a series of large steam turbine casing bolts which had been subjected to temperature s of around 500 degrees C for some 122 000 h. Also, the various toughness p roperties were assessed in terms of the existing fracture toughness-Charpy correlations. The present CrMoV steel bolts had suffered varying degrees of Reverse Tempe r Embrittlement (RTE) during service and exhibited strong fracture toughnes s-temperature trends. Although no single fracture toughness-Charpy correlat ion effectively described the full toughness-temperature transition curves, it was evident that, for embrittled and partially embrittled bolts, the Wa llin correlation best decribed the lower temperature portion of the curves. At the upper temperature region all embrittlement conditions exhibited rea sonable agreement with the upper bound correlation of Barsom and Wolfe. Finally, it was shown that the fracture toughness transition temperatures, T-K, and the Charpy Fracture Appearance Transition Temperatures (FATT) exhi bited good agreement with the fracture toughness transition temperature bei ng equal to the temperature at which the fracture toughness value was 3000 N/MM3/2. (C) 1998 Elsevier Science Ltd. All rights reserved.