Wrought Ni‐Base Superalloys for Steam Turbine Applications beyond 700 °C

Abstract

The development of a new steam turbine generation for use in advanced coal fired power plants with prospective operating temperatures beyond 700 °C and a projected thermodynamic efficiency of about 55 % requires, amongst other innovations, the partial substitution of ferritic steels by wrought Ni‐base superalloys. Although Ni‐base alloys are already widely used in the aerospace industry, they are faced with demands regarding component size and operation temperature, which by far exceed current aero‐engine requirements. In this article, the potential of selected alloys for 700 °C steam turbine applications is discussed with respect to their manufacturability and mechanical performance. Hereby, the focus is on the steam turbine rotor, which probably is the most critical component. It is concluded that material solutions are available for operation conditions around 600 °C but not for temperatures of 700 °C and above. Based on these results, alloy development strategies are suggested in order to close this gap and two new alloys, DT 706 and DT 750, are introduced.

Relationship Between Solidification Microstructure and Hot Cracking Susceptibility for Continuous Casting of Low-Carbon and High-Strength Low-Alloyed Steels: A Phase-Field Study

“…It is based on the phase-field concept for multiphase systems [13] which has been applied to binary alloys [14] and consequently extended to multicomponent systems [21,22] by direct coupling to thermodynamic databases via the TQ Fortran interface to Thermo-Calc. [18] Since then, the software has been developed further and applied to different alloy systems [23][24][25][26][27] and also to steels. [28][29][30][31] This study is motivated by specific problems with hot tearing in continuous casting of industrial steel grades.…”

Phase-field based simulation of microstructure evolution in technical alloy grades

“…in turbines for aero-engines, gas or steam turbines for power generation [93,94]. Many of the respective components like turbine blades and/or vanes are produced using methods of investment casting and subsequent directional solidification.…”

Analysis of localized oxides and oxide films formed on alloy 625 and 617 in supercritical water and superheated steam environments at 750°C

“…Those materials are exposed to high temperature and high pressure steam beyond 700°C. In most of the studies concerning life time and strength of the materials at high temperature, creep tests in air and oxidation tests in superheated steam had been performed (Viswanathan et al, 2010;Rosler et al 2003). However, the materials' behavior in high temperature and high pressure environments in that materials will be subjected during the plant operation are not well known due to experimental difficulties.…”