Weld Behavior of Martensitic Steels and Ni-based Alloys for High Temperature Components

High efficient steam power plants are being designed to operate at temperatures higher than 700 °C and pressure up to 350 bar. Due to this increase of the steam parameters Ni-based alloys are required for the realization of the plants. However, modern martensitic steels and their welded joints can also be considedered in these new high efficient power plants at locations where the temperature is below 700 °C. This paper describes the investigations on the behaviour of components made of Ni-based Alloy 617 mod. and ferritic/martensitic steels T24, T/P92 and VM12; the materials currently being considered for these plants. Results of basic qualification programs with standard specimens including welded joints show the suitability of these materials for the intended applications. Beside results of creep rupture tests of base materials and welded joints, Weld Strength Factors (WSF) are also discussed in this paper. Microstructural investigations to obtain information on precipitation and dislocation state in the virgin and aged conditions are also presented.