Inorganic Materials (v.52, #15)

Phase analysis of new composition of high-strength structural steel by V. I. Titov; L. V. Tarasenko; A. N. Utkina; A. B. Shal’kevich (1461-1466).
The basic type of carbide for making high-carbon wear-resistant structural steel without using a thermochemical treatment was defined. With consideration of the phase composition of the matrix after tempering, the preliminary intervals of alloying of high-carbon structural steel for gearwheels were recommended.
Keywords: phase physicochemical analysis; carbide phases; steels; gearwheels; thermochemical treatment

The effect of Sc and Sc + Zr on the structure and properties of Al–Mg–Si alloys is studied using the methods of hardness measurement, resistivity, mechanical properties, and light and electron microscopy. A considerable strengthening of Al–Mg2Si alloys doped with transition metals (Sc or Sc + Zr) during natural aging and its almost complete absence during artificial aging are established. The observed effects are explained using electron microscopy and local X-ray analysis.
Keywords: aluminum alloys; doping; hardness; strength; resistivity; supersaturated solid solution; strengthening phases

The problem of the recovery of the orientation distribution function (ODF) of a magnesium sample according to the approximation by circular normal distributions is considered. Initial data represent incomplete unnormalized X-ray pole figures (PFs). The choice of the procedure is related to its possible application for materials with the low symmetry of the sample, unique solution in the chosen class of functions, and measurement error stability of pole figures.
Keywords: recovery of orientation distribution function by pole figures; equal-channel angular pressing; existence and uniqueness of solution

A study of the heat capacity of coated metal materials by the laser flash method by Yu. V. Loshchinin; Yu. I. Folomeikin; S. I. Pakhomkin (1478-1482).
Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.
Keywords: specific heat capacity; thermal diffusivity; thermal conductivity; laser flash method; heat-resistant silicate enamel coatings; adiabatic calorimeter; emissivity of total radiation

Quality control of heat treatment of oil and gas pipes using magnetic structuroscopy by E. S. Gorkunov; S. M. Zadvorkin; E. A. Putilova; A. A. Bakunova (1483-1488).
The problem of the development of in-line nondestructive testing of mechanical properties of heat-strengthened oil and gas steel pipes remains topical. In this work, the effect of heat treatment conditions represented by the quenching temperature (in the range of 765–980°C) and cooling rate from the quenching temperature (in the range of 500–720°C, after quenching in water) on the structure, hardness, and magnetic properties (coercive force, residual induction, maximum magnetic permittivity, and saturation magnetization) is studied for the widely used pipe steels of 22KhG2A, 30KhMA, and 32G2 brands. The magnetic parameters are measured both in a closed magnetic circuit and using the attached magnetic devices on model and full-scale samples. A possible application of the coercimetric method as an alternative for the durametric one is shown for continuous underheating testing for quenching and the tempering quality of the pipes made from the steels under study during fabrication.
Keywords: pipe steels; quenching; tempering; nondestructive testing; coercive force

Mechanical and tribological properties of “substrate–material” multifunctional composite with shape memory effect by Zh. M. Blednova; N. A. Makhutov; P. O. Rusinov; M. A. Stepanenko (1489-1497).
The properties of steel–TiNi, TiNiCu, NiAl alloy multifunctional composite with shape memory effect are studied. The system is obtained under high-energy exposure (argon arc and laser surfacing, plasma and high-rate gas flame sputtering) with the formation of a structure with fine-grained to nanoscale dispersity. The experimental studies reveal the efficiency of the elaborated technique of the synthesis of composites to increase the wear resistance, fatigue strength, and endurance at frictionally cyclic low-cycle loading of material. The increase in fatigue and wear characteristics are explained by the processes caused by the combined cyclic loading and reverse friction. As is shown, the friction and mechanical fatigue in a surface-modified layer of the material undergoing the shape memory effect in the friction domain causes an increase in temperature that favors the martensite–austenite transformation, whereas the pressure arising in friction induces the transformation plasticity effect owing to the formation of stress martensite.
Keywords: steel–alloy with shape memory effect; high-energy exposure; tribological properties; friction and mechanical fatigue; martensite–austenite transformations

Possible scenarios of accidents in reservoirs and pipelines at low operating temperature by N. A. Makhutov; A. M. Bolshakov; M. I. Zakharova (1498-1502).
Oil and gas facilities—reservoirs, gas pipelines, oil pipelines—belong to industrial facilities of high risk. Uncontrolled development of accident scenarios at oil and gas facilities associated with explosions and fire may lead to significant damages and human casualties. This article presents possible scenarios of occurrence, development, and probability of realization of accidents at oil and gas facilities operated in extreme natural and climatic conditions of the North. Measures aimed at reducing the hazards are suggested.
Keywords: risk assessment; hazard; scenarios; probability

Testing mechanical properties of materials by indentation curves at different scale levels by V. M. Matyunin; A. Yu. Marchenkov; P. V. Volkov; A. N. Demidov (1503-1508).
Techniques and instruments for the determination of mechanical properties of materials by scratch and indentation curves are discussed. The capabilities and advantages of the indentation techniques at different scale levels of the deformed volume are shown. A new technique for the hardness determination by the indentation curve of a pyramid is proposed. The scope of application of the indentation techniques for testing mechanical properties of materials is determined.
Keywords: indentation; indentation curves; mechanical properties; scale effect; materials testing

Technical diagnostics in accident risk assessment by V. I. Ivanov; A. V. Kornilova; V. V. Musatov (1509-1514).
For a comprehensive assessment of safety of hazardous facilities, an accident risk ratio is used. Existing methodologies of risk assessment do not account for technical conditions of the facility and the degree of its defectiveness. This work demonstrates the possibility and necessity of a broader use of nondestructive testing (NDT) and technical diagnostics (TD) to estimate the probability of an accident, formulates the requirements for analyzing the risk, and establishes the line of development for these approaches. We consider the issues related to introducing new requirements for NDT and TD, which deal with representing the quantitative values of NDT, i.e., reliable data on the size of defects and measurement errors. We prove the necessity of using the methods of probabilistic fracture mechanics for assessing the real values of accident probability.
Keywords: fracture risk; probability; technical diagnostics; NDT; reliability

Effects of elastoplastic deformation and creep in threaded connections by N. A. Makhutov; V. V. Zatsarinnyi (1515-1519).
The specificity of loading conditions for critical threaded connections of power equipment is shown. Approaches to determination of their stress-strain states, which are dictated by redistribution of stresses and strains in turns of the thread under the static and low-cycle loading, are considered. The technique for experimental investigations of plastic deformations and creep deformations of bolts at the normal temperature is represented. This makes it possible to determine the tightening reduction in bolts.
Keywords: threaded connection; static and cyclic loading; elastoplastic deformation; creep; tightening loss

Static, dynamic, and cyclic strength of stud metal in large hydraulic units by V. M. Matyunin; B. M. Orakhelashvili; A. Yu. Marchenkov; A. G. Kazantsev; M. Zh. Kakhadze; K. A. Soin (1520-1527).
The microstructure and the mechanical properties of stud metal (steel 40Kh) M90×4 for fixing covers of large hydraulic units were studied. The mechanical properties were determined by static, dynamic, and cyclic tests of samples cut out of a stud in the longitudinal and transverse directions and at different distances from the surface. The character of the change in the microstructure and the mechanical properties over the cross section of a stud was determined. Static and cyclic tests of model and actual studs together with nuts were performed. The load and stress values under which the chain cutting of turns of a threaded joint occurs were determined. A strong influence of the scale factor on the durability of studs was established by cyclic tests.
Keywords: mechanical properties; microstructure; strength; dynamic fracture toughness; durability; scale effect

A technique allowing the rapid evaluation of the impact strength KCV of steels within the ductile–brittle transition temperature range is proposed in this work. A unified diagram of impact strength for different steels within the ductile-brittle transition range is built. A linear dependence $$frac{{KC{V_T}}}{{KC{V_P}}} = fleft( {frac{{KC{V_T}H{B_p}}}{{KC{V_T}H{B_T}}}} ight)$$ K C V T K C V P = f ( K C V T H B p K C V T H B T ) is established within the temperature range of 77–473 K, where the subscripts T and p refer to the temperature of the impact strength to be estimated and the end temperature of the Peierls–Nabarro plastic deformation mechanism accordingly. The method for prediction of the impact strength is developed on the basis of the above diagram. It enabled us to reduce the number of needed tests and to gather information unavailable before because of the limited volume of material.
Keywords: Impact strength; Brinnel hardness; ductile–brittle transition

This article presents a review of safety validation, calculations of initial and residual life, reliability, and survivability of equipment critical structures based on analyzing stress-strain states following the results of diagnostics and monitoring of parameters of their current and limit states with consideration of accumulation of operational damageability. On the basis of the assessment of the stress-strain states and changes in properties of structural materials and their defectiveness, we studied the possibility of determining the consumed part of the lifespan, residual life, survivability, and reliability of critical elements in machines and structures. We proved that integrated implementation of control, nondestructive testing, defectometry, technical diagnostics, fracture diagnostics, and monitoring of critical equipment elements offers new opportunities of controlling the lifespan and safety of highly hazardous facilities.
Keywords: diagnostics; monitoring; condition monitoring; strength; lifespan; survivability; damage accumulation; limit states; safety; risk; equipment; structural materials

The influence of the structural and phase state in nanocrystalline and amorphous alloys, as well as the pulsed current modes, on the electroplastic effect is studied under their tension. The decreasing grain size to nanoscale, the emergence of secondary phases, and amorphization in alloys cause the attenuation or disappearance of the electroplastic effect. The application of current pulses upon tension of alloys with a reversible thermoelastic martensitic transformation suppresses the step down of stress on the tensile diagrams caused by the electroplastic effects, but activates the jump up of stress attributed to the shape memory effect.
Keywords: electroplastic effect; shape memory effect; pulsed current; nanostructure; amorphous alloys

Kinetics of crack development in power engineering steels under high-temperature creep by N. A. Makhutov; E. A. Grin’; V. A. Sarkisyan (1545-1553).
Features of crack development kinetics in steels under creep are investigated from positions of fracture mechanics. It is shown that the creep crack growth rate can be approximated by a power dependence on parameter C* or on the stress intensity factor. At the same time, exponents of these dependences are a function of characteristics of long-term strength or material creep. For description of the creep crack rate, it is proposed to use the reduced stress intensity factor, which takes into account the character of the stress distribution in the design section and the crack development time. The experiment verifies the advantages of using the reduced stress intensity factor as a correlation parameter describing the creep crack growth rate.
Keywords: steels; creep; temperature; crack development rate; parameter C*; stress intensity factor (SIF); long-term strength; stress state; crack growth time; kinetic diagram of crack growth resistance