The Results of the Compromise Task Solution Directed for Development of Polymer-Modified Binder

This work presents the results of optimization compositions of polymer-modified binder (PMB) by a compromise task. The conducted study of influence two prescription factors – containing styrene-butadiene-styrene and sulfur – on which is a set of indicators of polymer-bitumen binders were carried out. The regularities of these factors of mutual influence were established by such indicators as the Fraas brittleness temperature, penetration, softening point, ductility. The dosages of SBS and sulfur have been determined by ensuring the achievement of the required level of PBB indicators in accordance with GOST R 52056-2003 «Bitumen-polymer road binders are based on styrene-butadiene-styrene block copolymers. Specifications».

INFLUENCE OF TIME-TEMPERATURE PARAMETERS OF LONG-DURATION EXPOSURE ON TRANSFORMATIONS IN STRUCTURAL STEELS (review)

Low-temperature nitriding of steels is usually carried out in the temperature range of development of reversible temper brittleness. The holding time at these temperatures significantly exceeds the holding time during normal tempering, which can negatively affect the properties of steel. The article considers theories that explain the processes occurring in steels in the temper brittleness temperature range. It may be concluded that views linking the embrittlement of steel with alloying elements such as nickel in its content are not confirmed by the experiments; at the same time ideas based on classical views about the diffusion of chemical elements explain the processes in steel better.

Conservative estimations of irradiation embrittlement of reactor pressure vessel steels for WWER-1000 lifetime prediction

Purpose The purpose of this paper is to consider a procedure of water-water energetic reactor (WWER) reactor pressure vessel (RPV) lifetime prediction at the stages of design and lifetime extension using the standard irradiation embrittlement parameters as defined in regulatory documents. A comparison is made of the brittle fracture resistance (BFR) values evaluated using two criteria: shift in the critical brittleness temperature ΔTc or shift in the brittle-to-ductile transition temperature ΔTp and without shifts (Tc and Tp). Design/methodology/approach The radiation resistance was determined using the following three approaches: calculation based on standard values ΔTc and Tc0 or ΔTp and Tp0 (a level of excessive conservatism); calculation based on standard value ΔTc and actual value Tc0 or actual values ΔTp and Tp0 (the level of realistic conservatism); or calculation based on actual values of Tc and Tc0 or Tp and Tp0 (the level of actual conservatism). The BFR was evaluated based on the results of testing the specimens subjected to irradiation in research reactors as well as surveillance specimens subjected to irradiation immediately under operating conditions. Findings The excessive conservatism in determining the actual lifetime of nuclear reactor vessel materials can be eliminated by using the immediate values of critical brittleness temperature and ductile-to-brittle transition temperature. Originality/value Obtained results can be applied to extend WWER vessel operating time at the stages of designing and operation due to substantiated decrease in conservatism. And it will allow carrying out a statistical substantiated assessment of the resistance to brittle fracture of the RPV steels.

Brittle fracture resistance of reactor pressure vessel steels in the initial state

The authors investigate the influence of chemical and structural inhomogeneity on the brittle fracture resistance (BFR) of VVER vessel materials in the initial state (without irradiation). It is proposed to replace the brittle fracture resistance assessment using the critical brittleness temperature TC for the BFR assessment using the brittle-viscous transition temperature TT. Consideration was given to calibration charts used for studying the TT dependence on the grain size and heat treatment. A comparison of the TC and TT values in the experimental industrial 15H2NMFA-A steel billets shows that the TC values are significantly lower than the TT values: – at the lower level of conservatism, the difference between TC and TT is 22 °C; – at the upper level of conservatism, this difference is 24 °C. The array data on the critical brittleness temperature and the ductile-to-brittle transition temperature of impact test samples of 15H2NMFAA (for VVER-1000) and 15H2NMFA grade 1 (for VVER-1200) steels were statistically processed. The industrial shell samples were manufactured at the “Energomashspetsstal” plant (Kramatorsk, Ukraine). It was found that, in the metal of VVER-1000 vessel surveillance specimens with the copper content – less than 0.06%, heat treatment has a significant effect on the TT value, which changes from –99 to –28°C; – from 0.07 to 0.12%, heat treatment has a significant effect on the TT value, which changes from –60 to –40°C.

Study on High-Temperature Mechanical Properties of Low-Carbon Fe-Mn-Si-Al TWIP Steel

The high-temperature mechanical properties of twinning-induced plasticity (TWIP) steel with 0.05 % C, 25 % Mn, 3 % Al, 3 % Si have been investigated using the GLEEBLE 3500 machine. The result shows that the zero ductility temperature and the zero strength temperature of the TWIP steel are measured at 1,225 °C and 1,275 °C, respectively. The brittleness temperature interval I is from 1,200 °C to the melting point, and the brittleness temperature interval III is from 650 °C to 800 °C. The tensile fracture has been examined using the scanning electron microscope, optical microscope and electron backscatter diffraction to determine the fracture mechanisms. The result shows that the twin is not the main influencing factor of the high-temperature plasticity of TWIP steel. Instead, the degree of dynamic recrystallization determines its high-temperature plasticity. A small number of AlN particles are found near the fractures, but these particles are so coarse, therefore, have no influence on the brittle fracture, and ferrite transformation and work hardening are the main reasons that cause the brittle fracture.