Dynamic Strain Aging in New Generation Cr-Mo-V Steel for Reactor Pressure Vessel Applications
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FERRITIC steels are well-known materials of construction of various structural components in nuclear reactors.[1] Reactor pressure vessels and reactor support structures in the pressurized water reactor (PWR) and boiling water reactor, heat transport piping, and end fitting in the pressurized heavy water reactor are some of the important examples of applications where ferritic steels were employed as component materials. In the application of materials for structural applications as critical components of nuclear reactor systems, there exists a great concern for the influence of embrittlement phenomena on properties such as strength, toughness, and ductility that are essential for sustenance of designed functions of component throughout its lifetime. Thus, the research to prevent premature failures of components due to enervated technological properties under the influence of thermal, irradiation, and C. GUPTA, Scientific Officer, and J.K. CHAKRAVARTTY, Head, are with the Mechanical Metallurgy Section, Materials Group, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India. Contact e-mail: [email protected] S. BANERJEE, Chairman Atomic Energy Commission and Secretary to Government of India, is with the Department of Atomic Energy, Government of India, CSM Marg, Mumbai 40001, India. Manuscript submitted August 9, 2009. Article published online October 19, 2010 3326—VOLUME 41A, DECEMBER 2010
environmental embrittlement have resulted in the development of a number of alloys with better resistance to operating embrittlement phenomena.[2,3] The performance of structural materials was known to be adversely affected by the presence of plastic instabilities. In ferritic steels, many alloy grades are known to display plastic instabilities. A commonly found example of this is the yield point phenomenon occurring during elastic to plastic transition in mild steels.[4] A related but distinctly different phenomenon is the Portevin Le Chatelier (PLC) effect, which also occurs in structural steels. It was first reported by Le Chatelier in 1909 during elevated temperature deformation of mild steels and subsequently by Portevin and Le Chatelier in 1924 during room temperature deformation of ‘‘Duralumin’’ (Al-3.5Cu-0.5Mg-0.5Mn).[4] The flow curves characterized by appearance of discontinuities were the first anomalies to be associated with the phenomenon, subsequently coined as the PLC effect. Intensive research was devoted to characterize the experimental conditions favoring the display of the phenomenon in various ferrous and nonferrous alloys,[4–8] as well as understand the mechanisms[9–11] and physics[12–15] of the processes (such as the formation and propagation of various deformation bands) during serrated flow. It is now widely accepted that the observed characteristics of the PLC effect arise from an interaction between solutes and mobile dislocations, METALLURGICAL AND MATERIALS TRANSACTIONS A
also known as dynamic strain aging (DSA).[4,11,16] As the experimental evidence became stronger that the PLC phenomenon adversely in
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