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A pinboard by
Abdullah Alomari

PhD Candidate , North Carolina State University

PINBOARD SUMMARY

Creep Properties and Dynamic Strain Aging in Austenitic Stainless Steels

Stainless steels may be classified by their crystalline structure into three main types: austenitic, ferritic and martensitic. Austenitic stainless steels are frequently used for high temperature applications including conventional and nuclear power plants due to its higher creep properties coupled with more corrosion/oxidation resistance at high temperature than ferritic steels. Moreover, newly developed austenitic stainless steels with high Chromium and Nickle contents have superior mechanical properties at high temperature relative to the widely used stainless steel such as 304 and 316 type stainless steels make it primary options for Gen-IV nuclear reactors structural application. In general, the materials are deformed faster at high temperature. The time-dependent plastic (i.e. permanent) deformation of materials at a constant temperature and constant stress or load is known as creep and it is playing the major rules for design criteria at high temperature applications. The plastic elongation during creep test is a result of several mechanisms operating in the microstructure levels and understanding the creep mechanisms in austenitic stainless steels is essential not only to predict the performance of the steel under the operating conditions but also to help improve the microstructural design of such advanced creep resistant metals. In addition to the importance of creep properties at high temperature applications, austenitic stainless steels exhibit serrations in stress-strain curves commonly known as Portevin-Le Chatelier effect. The serrated yielding in austenitic stainless steel is commonly attributed to dynamic strain aging (DSA) resulting from the interaction between diffusing solute atoms and mobile dislocations during plastic deformation at intermediate temperatures. The DSA has been shown to degrade mechanical properties such as ductility and fracture toughness so investigation into this phenomenon should be carried out for a comprehensive understanding of the underlying mechanisms as well as for design and safety considerations. To investigate the creep mechanisms and dynamic strain aging in austenitic stainless steels used in nuclear power plant, extensive experimental and theoretical works have been done through the last decades. In this pinboard, recent works in these properties are to be mentioned and discussed.

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