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On the microstructural basis of creep strength and creep-fatigue interaction in 9-12 % Cr steels for application in power plants

Abstract

As part of the efforts of preserving the environment it is necessary to reduce of the CO2 emissions from power plants. This can be done by increasing the plant efficiency. Research groups around the world are engaged in developing new steels capable of sustaining higher stresses and temperatures envisaged for high-efficiency power plants. Research carried out in Europe is organized within the COST Programme (Co-Operation in Science and Technology) aiming at replacing the conventional steels of type X20CrMoV121 by the new class of 9-12% Cr-steels with modified composition. The resistance of materials against deformation at elevated temperatures depends on their microstructure. Frequently in 9-12% Cr-steels improved short-term creep properties do not persist in the long-term service [1, 2, 3, 4, 5, 6]. This is related with insufficient microstructural stability. Hardening contributions in 9-12% Cr-steels come from solute atoms of the ferritic matrix, from dislocations, and from precipitates of foreign phases within the matrix. The term ''carbide stabilized substructure hardening'' of 9-12% Cr steels [7, 8] indicates that the hardening contributions are interdependent. The dislocations are the carriers of plastic deformation. They interact with each other, with solute atoms and with precipitates. The dislocation-dislocation interaction leads to formation of planar dislocation  More>>
Authors:
Publication Date:
Mar 06, 2007
Product Type:
Thesis/Dissertation
Report Number:
ETDE-DE-1804
Resource Relation:
Other Information: TH: Diss. (Dr.-Ing.)
Subject:
36 MATERIALS SCIENCE; CREEP; FATIGUE; CHROMIUM STEELS; POWER PLANTS; MICROSTRUCTURE; HARDENING; DEFORMATION; PRECIPITATION; HEAT TREATMENTS
OSTI ID:
21058833
Research Organizations:
Erlangen-Nuernberg Univ., Erlangen (Germany). Technische Fakultaet
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
TRN: DE08G7601
Availability:
Commercial reproduction prohibited; OSTI as DE21058833
Submitting Site:
DE
Size:
105 pages
Announcement Date:
Jul 24, 2008

Citation Formats

Chilukuru, H. On the microstructural basis of creep strength and creep-fatigue interaction in 9-12 % Cr steels for application in power plants. Germany: N. p., 2007. Web.
Chilukuru, H. On the microstructural basis of creep strength and creep-fatigue interaction in 9-12 % Cr steels for application in power plants. Germany.
Chilukuru, H. 2007. "On the microstructural basis of creep strength and creep-fatigue interaction in 9-12 % Cr steels for application in power plants." Germany.
@misc{etde_21058833,
title = {On the microstructural basis of creep strength and creep-fatigue interaction in 9-12 % Cr steels for application in power plants}
author = {Chilukuru, H}
abstractNote = {As part of the efforts of preserving the environment it is necessary to reduce of the CO2 emissions from power plants. This can be done by increasing the plant efficiency. Research groups around the world are engaged in developing new steels capable of sustaining higher stresses and temperatures envisaged for high-efficiency power plants. Research carried out in Europe is organized within the COST Programme (Co-Operation in Science and Technology) aiming at replacing the conventional steels of type X20CrMoV121 by the new class of 9-12% Cr-steels with modified composition. The resistance of materials against deformation at elevated temperatures depends on their microstructure. Frequently in 9-12% Cr-steels improved short-term creep properties do not persist in the long-term service [1, 2, 3, 4, 5, 6]. This is related with insufficient microstructural stability. Hardening contributions in 9-12% Cr-steels come from solute atoms of the ferritic matrix, from dislocations, and from precipitates of foreign phases within the matrix. The term ''carbide stabilized substructure hardening'' of 9-12% Cr steels [7, 8] indicates that the hardening contributions are interdependent. The dislocations are the carriers of plastic deformation. They interact with each other, with solute atoms and with precipitates. The dislocation-dislocation interaction leads to formation of planar dislocation networks constituting low-angle boundaries. They form a subgrain structure within the grains. At present, a full and detailed understanding of the effects exerted by the different components of microstructure on creep strength is still lacking. The present work makes a contribution to the efforts of understanding the microstructural basis of creep strength and of creep-fatigue interaction by transmission electron microscopic structure investigations coupled with creep tests. Investigations by transmission electron microscopy (TEM) were carried out with regard to hardening by subgrain boundaries and precipitates. The observation, that cyclic deformation at elevated temperature significantly modifies the subgrain structure of the steels (section 5.1), allows one to study the effect of variation of the subgrain size on subsequent creep (section 4.1). This effect is of great practical importance with regard to the so-called creep-fatigue interaction. Hardening by precipitates was studied by analyzing an in situ TEM study of dislocation-precipitate interaction and by investigating long-term crept and annealed specimens with emphasis on precipitate stability (section 5.2). It was found that the stability of precipitates is crucially dependent on details of precipitate type. This is important for alloy development and heat treatment of the steels prior to use. A microstructural model of creep was applied to provide a quantitative account of the effects of the observed changes of dislocation and precipitate structure on the creep resistance (section 6.2.5). (orig.)}
place = {Germany}
year = {2007}
month = {Mar}
}