The creep properties of 15Kh2NMFAA nuclear WWER (water–water energetic reactor) vessel steel in the range of 500–1200 °C temperatures, which may appear during severe nuclear reactor accidents, were investigated. The present paper attempts to analyze the creep curves obtained from tensile testing at high temperatures using the Larson–Miller parametric technique. The power law rate and material coefficient of Norton’s equation with the Monkman–Grant relationship coefficient were found for each test temperature. It is shown that in accordance with the Monkman–Grant relationship coefficient values, changing the creep type from dislocation glide to high temperature dislocation climb occurs in the temperature range of 600–700 °C, which leads to a slope change in the Larson–Miller parameter plot and the conversion of steel creep behavior. It is also shown that in the range of $A_1$–$A_3$ temperatures, a stepwise change in creep characteristics occurs, which is associated with phase transformations. In addition, the constancy of the product of the time to rupture ${\tau }_r$ and the minimum creep rate ${\dot{ϵ}}_{min}$ in the ranges of 600–700 °C and $A_3$—1200 °C was noted. The proposed approach improves the accuracy of time to rupture estimation of 15Kh2NMFAA steel by at least one order of magnitude. Based on the research results, the calculated dependence of the steel’s long-term strength limit on temperature was obtained for several time bases, allowing us to increase the accuracy of material survivability prediction in the case of a severe accident at a nuclear reactor.

The paper studies the possibility of carbide and decarburized ferrite interlayers detection formed during the production and operation of dissimilar welded joints of austenitic to pearlitic steels. Diffusion interlayers may be interpreted as welded joint microstructure defects, since their formation can cause premature failure of the product under high-temperature operation conditions. In addition, with a certain chemical and structural-phase composition of the welded metals, brittle interlayers formation and development of cracks in the weld zone may be occurred. To identify diffusion interlayers, the acoustic emission (AE) method is used in this research. Specimens cut from welded joints were tested by tension until rupture with simultaneous recording of AE signals. Based on the research results, particular AE data signatures corresponding to the specimens with diffusion interlayers were identified. The main feature indicating the presence of diffusion interlayers is an increase in the amplitudes of AE impulses and AE activity at a stress value of 300 MPa, corresponding to the ultimate strength of the ferrite phase.

The method is outlined to determine the creep parameters of structural steels at high temperatures using the instrumented indentation testing. The existing methods of high-temperature long-term indentation testing are reviewed from the standpoint of the accuracy of assessing the mechanical properties. The main challenges and bottlenecks in implementing this approach are explained. The results are given on the long-term high-temperature indentation testing steel grades, on plotting the creep diagram in the strain—time coordinates during loading at temperatures up to 700°C. For structural steel 15Kh2NMFAA, widely used in the power engineering to manufacture equipment operating at high temperatures, the relationships are obtained linking the creep rate with the temperature at a constant initial stress. Also, the functions of the creep rate against the initial stress are derived for a constant test temperature.

The instrument indentation method is considered, and its capacities in performing operative diagnostics of the physical and mechanical properties of the surface layers of structural materials and hardening coatings are demonstrated. New methods for determining the normal elasticity modulus from the initial elastic section of indentation diagram and the hardness characteristics in the areas of low and developed elastic-plastic deformation obtained by applying instrumental indentation with a ball indenter have been developed. The necessity of considering the deformation hardening parameter in establishing the link between the deformations in tensioning a specimen and in pressing-in the indenter is substantiated. A method for promptly estimating the material yield strength to ultimate strength ratio as an important diagnostic parameter of the material structural-mechanical state is proposed. It has been demonstrated that the use of the instrumental indentation method in combination with the acoustic emission method widens the capabilities of diagnosing the crack resistance characteristics of hardening coatings. Рассмотрен метод инструментального индентирования и продемонстрированы его возможности в оперативной диагностике физико-механических свойств поверхностных слоев конструкционных материалов и упрочняющих покрытий. Разработаны новые способы определения модуля нормальной упругости по начальному упругому участку диаграммы вдавливания и характеристик твердости в областях малой и развитой упругопластической деформации при инструментальном индентировании сферическим индентором. Обоснована необходимость учета параметра деформационного упрочнения при установлении связи деформаций при растяжении образца и вдавливании индентора. Предложена методика оперативной оценки отношения предела текучести к временному сопротивлению материала как важного диагностического параметра структурно-механического состояния материала. Установлено, что метод инструментального индентирования, совмещенный с методом акустической эмиссии, расширяет возможности диагностики характеристик трещиностойкости упрочняющих покрытий.