Creep properties of heat affected zone in heterogeneous welded rotor

Abstract

Increasing demand on efficiency and power output of steam generators leads to new designs of welded rotors. The reason for rotor welding is the large size of rotors, which are difficult to produce in a single piece. Secondly, as there are varying operation conditions along the rotor length. In a heterogeneous rotor, several materials appropriate for local service conditions can be used. At the rotor service temperatures, creep properties are crucial for successful design. The weakest point of every welded component is the heat affected zone. Therefore, the creep properties of a heterogeneous weld are subject of the investigation here. In the current study, a heterogeneous weld of COST F and COST FB2 materials is investigated. The welding was performed by multi pass technique with overlaying welding beads that applied several heating cycles to heat affected zone. Metallographic investigation of the weld was performed and the weakest microstructure spots were detected. With the use of FEM simulation, appropriate heating/cooling cycles were obtained for the detected weak points. The temperature cycles obtained were subsequently applied to both base materials under laboratory conditions by induction heating. Creep properties of these materials were investigated. The influence of the initial base material's grain size was also considered in the investigation. Two heating/cooling schedules were applied to both base materials with two grain sizes. Altogether, 8 different microstructures were examined in short term creep tests and the results were summarized. Copyright © 2014 Electric Power Research Institute, Inc. Distributed by ASM International®. All rights reserved.