Influence of Oxygen-Containing Lead Melts on the Fatigue Strength of AISI 409L Steel at Elevated Temperatures
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INFLUENCE OF OXYGEN-CONTAINING LEAD MELTS ON THE FATIGUE STRENGTH OF AISI 409L STEEL AT ELEVATED TEMPERATURES О. І. Yas’kiv,1, 2 V. М. Fedirko,1 and І. S. Kukhar1
UDC 669.295: 621.795
We study the regularities of the influence of lead and lead−bismuth eutectic melts on the fatigue strength of AISI 409L (Fe−11Cr) steel of the ferritic class within the temperature range 500–600°С. It is shown that they reduce the resistance to long-term static loading of steel as compared with its resistance in a vacuum. As temperature increases, the negative influence of the eutectic becomes more pronounced as a result of the corrosive action of lead melts, namely, as a result of the selective dissolution of chromium along grain boundaries and the formation of iron oxides, which rapidly embrittle under loading and, thus, facilitates the fracture processes in the material. Keyword: ferritic steel, lead and lead–bismuth eutectic melts, fatigue strength, liquid metal embrittlement.
The development of nuclear power plants (NPP) of a new generation with elevated safety includes, parallel with the other factors, the use of liquid-metal cooling systems. Due to their physicochemical properties, melts of heavy metals (Рb, Ві, Pb−Bi, and their eutectic mixture) serve as candidates for application as cooling media of fast reactors (of the LEADER, ALFREDO, BREST, SFBR, and MBIR types) and subcritical hybrid accelerator-driven systems (ADS) [1−3].
As the main structural materials in NPP, it is proposed to use steels of the ferritic–martensitic class (based on the Fe−Cr system). Due to their high physicomechanical characteristics, compatibility with the main cooling media, and low susceptibility to swelling, these steels prove to be promising materials for the first wall and blanket of fusion reactors, fuel elements, steam generators, and structural elements of the coolant pumps of fast reactors [4, 5].
In service, the melts of hard metals negatively affect the corrosion and mechanical properties of structural materials [6]. The problem of corrosive action of lead media upon steels is solved by using coolants with controlled oxygen content, which promotes the formation of protective oxide films on steel surfaces [7]. In the course of long-term operation, when the creep-induced damage of materials may serve as the cause of fracture of the structural elements of NPP, it is important to study the influence of these media on the mechanical behavior of materials under stresses lower than the yield strength. Under the conditions of interaction of steel with adsorption-active media (lead melts), these media become additional factors of the decrease in fracture stresses and change the picture of development of the corresponding stages of fracture of the material.
The aim of the present work is to establish the regularities of the influence of liquid-metal media (Рb and Рb−Bi) on the strength of the (Fe−11Cr) reactor steel under long-term static loads at elevated temperatures. 1 2
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sc
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