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Creep and fatigue interaction behavior in Sanicro 25 heat resistant austenitic stainless steel
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Sandviken, Sweden.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Sanicro 25 is a newly developed advanced high strength heat resistant austenitic stainless steel. The material shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than other austenitic stainless steels available today. It is an excellent candidate for superheaters and reheaters for advanced ultra-super critical power plants with efficiency higher than 50 %. This paper provides a study on the creep-fatigue interaction behavior of Sanicro 25 at 700 °C. Two strain ranges, 1 % and 2 %, and three dwell times, 0, 10 and 30 minutes, were used. The influences of dwell time on the cyclic deformation behavior and life time has been evaluated. Due to stress relaxation the dwell time causes a larger plastic strain range compared to the tests without dwell time. The results also show that the dwell time leads to a shorter fatigue life for the lower strain range, but has no or small effect on the life for the higher strain range. Fracture investigations show that dwell times result in more intergranular cracking. With use of the electron channeling contrast image (ECCI) technique, the influences of dwell time on the cyclic plastic deformation, precipitation behavior, recovery phenomena and local plasticity exhaustion have also been studied.

Place, publisher, year, edition, pages
2015.
Keyword [en]
Sanicro 25, Advanced ultra-super critical power plant, Creep, Low cycle fatigue, Cyclic plastic deformation.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-122944OAI: oai:DiVA.org:liu-122944DiVA: diva2:875061
Available from: 2015-11-30 Created: 2015-11-30 Last updated: 2015-11-30Bibliographically approved
In thesis
1. On High-Temperature Behaviours of Heat Resistant Austenitic Alloys
Open this publication in new window or tab >>On High-Temperature Behaviours of Heat Resistant Austenitic Alloys
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Advanced heat resistant materials are important to achieve the transition to long term sustainable power generation. The global increase in energy consumption and the global warming from greenhouse gas emissions create the need for more sustainable power generation processes. Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO2. Biomass offers no net contribution of CO2 to the atmosphere. To obtain greater efficiency of power plants, one option is to increase the temperature and the pressure in the boiler section of the power plant. This requires improved material properties, such as higher yield strength, creep strength and high-temperature corrosion resistance, as well as structural integrity and safety.

Today, some austenitic stainless steels are design to withstand temperatures up to 650 °C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of future operation conditions in biomass-red power plants is not yet fully understood.

This thesis presents research on the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture, and the influence of high-temperature environment and cyclic operation conditions on the material behaviour. Mechanical and thermal testing have been performed followed by subsequent studies of the microstructure, using scanning electron microscopy, to investigate the material behaviours.

Results shows that long term ageing at high temperatures leads to the precipitation of intermetallic phases. These intermetallic phases are brittle at room temperature and become detrimental for the impact toughness of some of the austenitic stainless steels. During slow strain rate tensile deformation at elevated temperature time dependent deformation and recovery mechanisms are pronounced. The creep-fatigue interaction behaviour of an austenitic stainless steel show that dwell time gives shorter life at a lower strain range, but has none or small effect on the life at a higher strain range.

Finally, this research results in an increased knowledge of the structural, mechanical and chemical behaviour as well as a deeper understanding of the deformation, damage and fracture mechanisms that occur in heat resistant austenitic alloys at high-temperature environments. It is believed that in the long term, this can contribute to material development achieving the transition to more sustainable power generation in biomass-red power plants.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 56 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1725
National Category
Metallurgy and Metallic Materials Materials Engineering
Identifiers
urn:nbn:se:liu:diva-122945 (URN)10.3384/diss.diva-122945 (DOI)978-91-7685-896-7 (print) (ISBN)
Public defence
2015-12-21, ACAS, Hus A, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-11-30 Created: 2015-11-30 Last updated: 2015-12-02Bibliographically approved

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