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Microstructural degradation in power plant steels and life assessment of power plant components
Published in Elsevier Ltd
2013
Volume: 55
   
Pages: 394 - 401
Abstract
Extensive creep testing was carried out on 1Cr1Mo1/4V low alloy forging and casing steels in as received (normalized and tempered) and aged condition. Both the steels exhibited considerable secondary and tertiary stages in the creep tests conducted in the temperature range between 813 and 873 K (540°C and 600°C). The primary stage, though present, was rather negligible in higher temperature ranges. Casting steel showed wedge type cavities which grew as cracks along the grain boundaries. In the case of forged steel, the voids were elliptical and flat which developed during the tertiary stage of creep deformation. Tertiary creep deformation and creep ductility of the two steels investigated have been analyzed based on the type of voids developed during the tertiary stage. Based on detailed microstructural investigations using scanning and transmission electron microscope, prevailing damage mechanisms such as structural transformation, particle coarsening, grain boundary thickening have been identified and applied for remaining life assessment of the two steels. Hardness and other mechanical properties were observed to decrease slightly on aging; both for rotor forging and casing casting steel. The softening occurred due to dissolution of M3C and Mo2C carbides and coagulation of others resulting in reduced creep strength. Gradual fall of creep strength at intermediate aging times was due to recovery in ferrite, gradual depletion of solid solution carbides from the ferrite matrix, metastability and transitional character of precipitated carbides. Creep crack growth studies have also been carried out on both the steels. Life assessment calculations have also been carried out using creep crack growth methodology. © 2013 The Authors.
About the journal
JournalData powered by TypesetProcedia Engineering
PublisherData powered by TypesetElsevier Ltd
ISSN18777058
Open AccessYes