Aging Degradation of Austenitic Stainless Steel Weld Probed by Electrochemical Method and Impact Toughness Evaluation
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INTRODUCTION
LOW-TEMPERATURE sensitization-enhanced intergranular corrosion and intergranular stress corrosion cracking are the frequent cause of failure of stainless steel components in nuclear industry. These specific forms of corrosion are more prevalent in the base and heat-affected zone than in the weld zone, as latter is much less susceptible to sensitization.[1–3] Weld zone, however, has several issues that cause the failure of components. Stainless steel weld contains delta ferrite and a variety of microstructural features including defects and flaws.[3] Thermal aging of the weld zone at temperature above 823 K (550 C) results in the transformation of d-ferrite to sigma (r) phase whereas the aging at temperature below 823 K (550 C) results in the formation of the silicide (G) phase and occurrence of spinodal decomposition. These products, as a result of phase transformation, contribute to hardening and embrittlement leading to the degradation in the mechanical properties of the component. The spinodal decomposition is related to the dissociation of d-ferrite into iron-rich (a) and chromium-rich (a¢) ferrite and evolves primarily due to the miscibility gap in the Fe-Cr phase diagram. Such transformation is further favored by the prolong heating at
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