Ph.D. thesis for the degree of candidate of technical sciences (PhD) in specialty 05.02.01. – material science– Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, Lviv, 2018.
The thesis is devoted to the determination of the peculiarities of the influence of liquid lead on the mechanical properties of ferrous, ferrite-martensitic and austenitic steels of the static and cyclic loads and elevated temperatures.
The adsorption effect of the melts on the mechanical properties of the solid metal manifests itself primarily in the liquid metal embrittlement (LME), that is, in the significant reduction of plasticity, and transition from the plastic nature of the destruction to the fragile. The factors influencing the LME depend on both the properties of the liquid metal and the nature of the material (in particular, its structural-phase state) and on the conditions of its deformation.
Often, the non-availability of information on the interaction of liquid leads with solid metal to catastrophic effects caused by accelerated destruction of metal structures. In particular, very limited information on the interaction of liquid lead with chromium steels, which, in their technological and techno-economic properties, have been widely used in the power industry.
Therefore, studies and the determination of the patterns of adsorption influence of liquid metal on the solid metal under the action of static and cyclic loads and elevated temperatures are relevant.
The influence of the liquid lead enviroment and eutectic lead-bismuth on the mechanical properties of chromium steels of ferrite, ferrite-martensitic and austenitic classes under conditions of static and cyclic loads in the temperature range of 200...600 °С was investigated.
It has been established that the liquid lead negatively influence on the strength and plasticity of ferrite and ferrite-martensitic steels.
For A-Fe, the maximum embrittlement in lead in comparison with the vacuum was observed at a temperature of 300 °C with a plasticity decrease of up to 35%. For steel ferrite class Fe-11Cr (SUH 409L), the maximum reduction on the plasticity in lead was observed at 450 °C. Plasticity loss was maximum and is 14%. That is, in comparison with A-Fe (300 °С), the steel embrittlement at the higher temperatures, and the effect of the environment decreases (more than twice). Using fractographic studies, the ocular effect of liquid lead has been confirmed. In the near-surface layer, an increase in the fraction of the fragile component of the fracture of steel Fe-11Cr ferrite grade and A-Fe under the action of lead was detected in comparison with the vacuum. The destruction was a mixed – visco-fragile mechanism.
For steel ferrite-martensitic class 20Cr13 was established that liquid lead and lead-bismuth eutectics contribute to the reduction of the temporary resistance to the destruction of samples in comparison with the vacuum medium, and with increasing temperature this effect is enhanced. It has been established that the maximum negative influence of lead was at 350 °С and is 11% in comparison with the vacuum medium. In the eutectic lead-bismuth embrittlement was occur at a temperature of 400 °C with a decrease in plasticity by 20%. Fractographic studies confirmed the ocular effect of liquid lead.
For steel of the austenitic class Cr18Ni10Ti it has been established that over the temperature interval of tests, the value of the coefficient of influence of the medium exceeds one, that is, the plasticity in liquid lead and the eutectic lead-bismuth is higher than the corresponding values in the vacuum environment, and thus the appearance of steel under a static load by uniaxial stretching under the action of the liquid liquid is not observe.
The dependence of the effect of liquid metal embrittlement to the grain size of steel was studied. The research was conducted on the ferrite Fe-11Cr
(SUH 409L) and austenitic (Cr18Ni10Тi) steel. Ferrite (Fe-11Cr) and austenitic (Cr18Ni10Тi) steels were subjected to different heat treatments, resulting in three grain sizes: 35, 50 and 70 μm, and 90,110 and 160 μm respectively.
It has been established that for a Fe-11Cr ferrite class steel with an increase in the grain size, the temperature of the maximum manifestation of the liquid metal embrittlement shifts to the lower temperature zone and the influence of the environment increases (the plasticity reduction increases from 11 to 18%). With an increase in grain from 90 to 160 μm for the steel of the austenitic class Cr18Ni10Ti at temperatures above 400 °С, was observe the effect of plasticization and decreases from 8 to 6%.
The influence of the liquid liquid on the fatigue properties of steels of ferrite, ferrite-martensitic and austenitic classes on the embrittlement in conditions on the cycle load was investigated. In the liquid lead, the experiment was conducted at a temperature of 350 °C and 500 °C, the amplitude of the deformation was 0.5; 0.8 and 1.
