Thermal fatigue strength of alloy 03Kh20N45M4BCh at 200?550�C in the irradiated state

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1. There are practically no differences between the isothermal and the thermal fatigue limit of alloy 03Kh20N45M4BCh at 200–550°C in the nonirradiated state. There are no substantial differences either between the low cycle fatigue limit of the base metal and of a welding joint made by the argon arc method. 2. The changes of the mechanical properties of the alloy 03Kh20N45M4BCh at 20–400°C after being subjected to a fast neutron fluence of (0.35...1.02)·1023 neutrons/cm2 at 300–320°C are characterized by an increase of yield strength on an average by a factor of 2.8, of strength by a factor of 1.4, and by a drop of ductility to one twentieth. When the temperature of irradiation rises from 300–320 to 550°C, the differences between the respective characteristics of the alloy in the irradiated and the initial state decrease greatly, and at 550°C they amount to 1.3 times for yield strength, to 1.1 times for ultimate strength, and to 3 times for elongation. 3. The level of plastic strains upon thermal shock in alloy 03Kh20N45M4BCh, irradiated by a fast neutron fluence of (0.35...1.02)·1023 neutrons/cm2 at 300–320°C, is reduced by one half in consequence of its radiative strengthening. 4. Irradiation of the alloy by a fast neutron fluence of up to 1·1021 neutrons/cm2 at 300–320°C leads to a decrease of its thermal fatigue limit under conditions of elastoplastic strain in the range 20–300°C by a factor of five. The results of the calculation of the changes in thermal fatigue strength of the irradiated alloy on the basis of the strain criterion of low cycle fatigue according to the characteristics of the dosage dependences of strength and ductility agree quantitatively with the experimental data. 5. Irradiation of the alloy by a fast neutron fluence of up to (0.35...1.0)·1023 neutrons/cm2 at 300–320°C may lead to a drop of thermal fatigue strength at 200–550°C in the region of low cycle failure by a factor of up to four, and in the high cycle region to its increase by a factor of up to 1.25. Such changes in thermal fatigue strength are the consequence of the development of radiative embrittlement and strengthening in the alloy. 6. When the temperature of irradiation is raised from 300–320°C to 550°C, the thermal fatigue strength of the irradiated alloy approaches in magnitude the characteristic in the initial state corresponding to it because of the development of processes of high-temperature weakening.