13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Influence of high temperature ageing on the toughness of advanced heat resistant materials Mattias Calmunger1,*, Guocai Chai1, 2, Sten Johansson1, Johan Moverare1 1 Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping, Sweden 2 AB Sandvik Material Technology R&D center, SE-81181 Sandviken, Sweden * Corresponding author: mattias.calmunger@liu.se Abstract Advanced biomass, biomass co-firing in coal-fired and future advanced USC coal-fired power plants with high efficiency require the materials to be used at even higher temperature under higher pressure. The reliability and integrity of the material used are therefore of concern. In this study, the influence of ageing at temperatures up to 700°C for up to 3 000 hours on the toughness of two advanced heat resistant austenitic steels and one nickel alloy are investigated. The influence on toughness due to differences in the chemical composition as well as the combined effect of precipitation and growth of the precipitates has been analysed by using SEM techniques. The fracture mechanisms that are active for the different ageing treatments are identified as a function of temperature and time. Local approach methods are used to discuss the influence of the precipitation and growth of precipitates on the toughness or fracture in the different aged materials. Keywords High-temperature, ageing, toughness, austenitic stainless steel, nickel base alloy 1. Introduction Renewable and more efficient energy resources such as biomass, biomass co-firing in coal-fired power plants and future advanced ultra-super critical (AUSC) coal-fired power plants for sustainable energy production are greatly desired. To increase efficiency higher temperature and pressure are used. Today austenitic stainless steels are commonly used as structural material in these power plants and they need to have good reliability and structure integrity with respect to the higher temperature and pressure [1, 2]. High-temperature long term ageing provides a range of precipitates that differ with ageing conditions and alloy composition. Precipitates from ageing of austenitic stainless steel and nickel base alloys have been studied by others [3-7]. Austenitic stainless steels are expected to provide reliable service for 30 years or more [3]. Their detailed mechanical properties are dependent on the stability of the microstructure particularly the formation, dissolution and coarsening of participates. In this study the influence of precipitation and growth of precipitates on toughness due to different compositions and high-temperature treatment are investigated. 2. Materials and experimental details 2.1. Materials The experiments were conducted on two austenitic stainless steels (AISI 304 and Sanicro 28) and one nickel base alloy (Alloy 617), supplied by Sandvik Material Technology, see table 1 for nominal compositions in wt%. The materials are heat treated for normalizing.
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