Development of Nickel Alloys Based on Alloy 617 for Components in 700 °C Power Plants

High Temperature Nickel based alloy 617 (A 617) is considered as a candidate material for the 700 °C power plants due to its combination of creep strength and good fabricability. The alloy has been investigated in numerous publicly sponsored and privately financed programmes with regard to its use in USC boilers. Based on the gained experience, the material has been tailored to fit the specific purpose of USC boilers. The first development step resulted in a modified version of Alloy 617 labeled Alloy 617 B, with creep strength at 700 °C about 25% higher than that listed by ASME and VdTÜV. A second step focused on the definition of welding procedures and heat treatment, demonstrating that crack formation in large welded components can be avoided by suitable post-weld heat treatment. This paper will briefly describe the effect of boron and heat-treatment on the mechanical behaviour of Alloy 617 within the scope of the German USC boiler programmes.