Viscoplasticity characteristics of heat-resisting steels in a multiaxial stress state

Results are presented of the experimental examination of the viscoplastic properties of 15Kh2MFA, 15Kh2NMFA, and VK2 (KP-100) heat-resisting steels simulating radiation-embrittled 15Kh2NMFA steel, at different ratios of the main stresses in the temperature range 20–350°C, carried out using a specially prepared method. The experimental results are used to draw conclusions according to which the generalized quasistatic (equilibrium) deformation diagram, obtained at a strain rate tending to zero, is invariant to the type of stress state, and also that the toughness factors of the examined steels are invariant to the type of stress, state and cumulated plastic strain in the entire temperature range examined.Translated from Problemy Prochnosti, No. 11, pp. 52–57, November, 1991.     

Effect of aqueous media on the cyclic cracking resistance of steels at 300°C

We investigate the influence of reactor water (of the boron control system) on the fatigue crack growth rates in 15Kh2NMFA and 08Kh18N10T steels at 300°C. Corrosion-fatigue cracking is found to be typical of 15Kh2NMFA steel. The kinetics of the potentials of newly formed steel surfaces in high-temperature reactor water is studied. A phenomenological model that describes the influence of high-temperature aqueous media on the fatigue crack growth rates in steels is developed on the basis of data of corrosion-mechanical and electrochemical investigations. The results obtained by this model are in good agreement with experimental data.Karpenko Physicomechanical Institute, Ukrainian Academy of Science, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 34–42, January–February, 1994.     

Investigation of the regularities of deformation of heat-resistant steels under conditions of creep in the complex stressed state

We study the regularities of deformation of 1Kh18N9T steel under long-term static loading along different paths of radial loading with regard for the influence of the type of stressed state. The viscoplastic properties of 08Kh18N10T-VD steel subjected to stepwise static loading under conditions of complex stressed state are analyzed.     

Viscoplastic properties of steel 10GN2MFA with a complex stressed state

Results are given for experimental studies of the viscoplastic properties of steel 10GN2MFA with different ratios of principal stresses in the temperature range 20–320°C performed under conditions of stepwise loading. The invariance of the generalized equilibrium deformation curve towards the forms of stressed state and also the material quasiviscosity characteristics towards the form of stressed state and the amount of accumulated irreversible strain for the test material is established by experiment.Translated from Problemy Prochnosti, No. 4, pp. 30–35, April, 1994.     

Kinetics of plastic strain zone formation near crack tip in fracture of construction materials under plane stress and plane strain

X-ray-diffraction analysis is used to determine the depth of the plastic deformation zones in steel. 15Kh2MFA and alloy D16 beneath the surface of fractures that are obtained under plane stress (PS) and plane deformation (PD) conditions. We propose a scheme illustrating the kinetics of the formation of two plastic deformation zones near the crack tip under one-time loading in conditions of the plane stress state: a strongly deformed microzone and a weakly deformed macrozone.Translated from Problemy Prochnosti, No. 4, pp. 57–63, April, 1993.     

Analysis of deformation of steel 15Kh5MF under rigid low cycle loading

The article examines the regularities of cyclic elastoplastic deformation of steel 15Kh5MF under asymmetric reversed loading. On the basis of the obtained experimental data a method was worked out for determining the parameters of the equations of state of the endochronic theory of plasticity as applied to weakly singular kernels. The article describes the kinetics of the state of stress and strain of specimens with different paths of uniaxial cyclic deformation of metals. The theoretical data are compared with the experimental data.Translated from Problemy Prochnosti, No. 4, pp. 37–43, April, 1990.     

Use of linear and nonlinear fracture mechanics for assessing resistance to crack propagation in 15Kh2NMFA structural steel

This note considers a possibility of application of linear and nonlinear fracture mechanics for the assessment of resistance to crack propagation in the 15Kh2NMFA steel of a special melt using the results obtained in testing specimens of different sizes.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 1, pp. 40–44, January, 1978.     

Mathematical simulation of the thermomechanical condition of a punch in hot forming processes

The results are presented of a calculation-experimental investigation of the thermal, stressed and strained, and limiting conditions of 5KhNM and 5Kh2MNAF steel punches used in hot forming processes. Data of variations of calculation for pure force and thermal action and also for the case of combined and thermomechanical loading is analyzed. The increase in the operating parameters for punches of nitrided 5Kh2MNFA steel is substantiated.Translated from Problemy Prochnosti, No. 6, pp. 60–64, June, 1990.     

Endurance of structural materials in complex low-cycle loading

The results of examination of the relationships governing damage cumulation on complex low-cycle loading are presented. A phenomenological criterion of evaluating the kinetics of damages cumulation in the structure of the material is proposed for this purpose. The components of the deviator of additional stresses is determined on the basis of the mutlisurface theory of plastic yielding with Pisarenko-Lebedev loading surfaces. A method of determining the mean parameters of the model is described. The calculated endurance data are compared with the experimental values for VT14 alloy and 14Kh17N2 steel at T=293°K. Experiments were carried out on tubular specimens in the conditions of piecewise-polygonal trajectories of low-cycle deformation.Translated from Problemy Prochnosti, No. 3, pp 3–9, March, 1991.     

Crack resistance of chromium-nickel steels with impact loading under cryogenic temperature conditions

Results are presented for an experimental study of the effect of cooling to 77 K on resistance to crack development of chromium-nickel steels 12Kh18N10T and 03Kh20N16AG6 with impact loading. The crack resistance characteristics with a rate of crack growth of 1.5 m/sec were determined from the deformation diagram recorded during testing. Features are noted for crack advance with cooling under conditions of a dynamically applied load.Translated from Problemy Prochnosti, No. 7, pp. 26–29, July, 1992.     

Corrosion-Mechanical Properties of Materials for Reactor Vessels

We established that, in the course of electrolytic hydrogenation, an aqueous medium of boron regulation with pH 8 significantly accelerates the growth of fatigue cracks in 15Kh2MFA and 15Kh2NMFA hull steels, especially in the metal of welded joints, as a result of hydrogen embrittlement at the tip of a crack. An increase in the strength of steels by means of heat treatment, a decrease in the frequency of alternating loading, and an increase in the stress ratio significantly accelerate the growth of fatigue cracks. We discovered the strongest influence of hydrogenation in the near-threshold region for low values of the stress intensity factor. The tendency toward passivation and the anticorrosive properties of 15Kh2MFA steel (i _cor = 5 mA/m²) are higher than those of 15Kh2NMFA steel (i _cor = 20 mA/m²), which can be explained by the higher inhomogeneity of the structure of the latter. The metal of welded joints has the lowest cyclic corrosion crack resistance and the highest tendency toward hydrogen embrittlement under conditions of stable or transient modes.     

Version of the endochronic theory of plasticity for describing complicated cyclic loading histories

Equations of state for the endochronic theory of plasticity are suggested for describing processes of nonproportional cyclic deformation of materials. New rules are introduced for characteristics of isotropic and kinematic strengthening with regard to the nonproportionality parameter of the plastic deformation cycle path. Basic experiments are considered with the aim of specifying characteristic relationships. As applied to different complex plastic deformation paths, stress distribution is determined in single-crystal tubular specimens with the combined action of an axial force and torsional moment in relation to the number of loading cycles. Calculated and experimental data are compared.Translated from Probiemy Prochnosti, No. 5, pp. 3–12, May, 1993.     

Energy method of calculating longevity under an irregular loading. Report 1. Consideration of loading sequence

A method of predicting longevity under a programmed loading to the formation of a fatigue crack, which is based on an energy criterion of fatigue failure, is proposed. Kinetic diagrams and a model of the cyclic deformation of the material were used to calculate energy dissipation during the loading cycles. A differential equation of the accumulation of relative energy, which enables us to derive the equation of the fatigue curve from single positions, and relationships for calculating longevity under irregular symmetric and axisymmetric loadings are formulated. The computed results are compared with experimental data for 40Kh steel with stepwise variation in loading.Translated from Problemy Prochnosti, No. 7, pp. 3–12, July, 1995.     

Strain hardening features of metastable austenite-martensite steels

A physical approach is developed for describing deformation diagrams of the metastable states of austenite-martensite steels over a wide range of change in the original quantitative ratio of the phases and type of stressed state with biaxial tension. The approach is based on structural effects revealed by experiment of the reciprocal influence of the phases connected with a intentional change in their fine structure, and with development of residual tensile stresses in phase-hardened austenite and its strengthening effect on strain-induced martensite. From the standpoint of the different relationships obtained as applied to steel 07Kh16N6 the different sensitivity of yield and ultimate strengths to the quantitative phase ratio and invariance of generalized deformation curves to the principal stress ratio is substantiated.From papers at the III All-Union symposium Strength of materials and structural elements with a complex stressed state, Zhitomir (1989).Translated from Problemy Prochnosti, No. 6, pp. 23–27, June, 1991.     

Effect of loading prehistory on phase transformations in chromium-nickel steel with plastic deformation

Results are given for a study of the kinetics of phase transformations in chromium-nickel austenitic steel with repeated plastic deformation including under conditions when prior and repeated loading differ in temperature and form of stressed state. It is established that prior low-temperature deformation intensifies the process of martensite formation at room temperature whereas deformation under room temperature conditions has almost no effect on martensitic transformation kinetics at low temperature.Translated from Problemy Prochnosti, No. 10, pp. 46–50, October, 1991.     

Effect of microalloying with rare-earth metals on the resistance of steels to deformation and failure under an alternating elastoplastic load

Results of experimental investigation of the resistance of steels OKh16N15M3B and Kh13N13T3 to cyclic alternating deformation and failure at T=923K after microalloying with Sc are presented. It is established that microalloying enhanced the characteristics investigated. Radiation-induced damage(=4.5·10¹⁷ neutrons/(m²·sec), E0.1 MeV) during the loading of microalloyed steel 00Kh16N15M3B lowered resistance to cyclic deformation while increasing the strain-hardening factor and cyclic longevity as compared with similar characteristics under normal conditions.Translated from Problemy Prochnosti, No. 1, pp. 12–17, January, 1994.     

Nature of scatter of fracture toughness in static loading

The previously proposed model of unstable fatigue crack growth is used to explain a large (in comparison with other mechanical characteristics) scatter of static fracture toughness for 15Kh2MFA and 15Kh2NMFA steels at temperatures below the tactile-brittle transition temperature. The results show that for the materials for which K_fc ¹ < K_Ic the critical stress intensity factor K_Ic depends on the specific energy of inelastic strain W at the tip of the initial fatigue crack in its formation stage. The value of W is a function of the number of load cycles (in the conditions with a constant range of the stress intensity factor K) as a result of irregular fatigue crack growth. Here K_fc ¹ is the minimum cyclic fracture toughness. A method is proposed of evaluating the minimum fracture toughness of the material in static loading based on inspection of the process of irregular fatigue crack growth in the stage of crack initiation.Translated from Problemy Prochnosti, No. 2, pp. 10–16, February, 1990.     

Effect of the range of particle sizes on the heat resistance of chrome-nickel alloys

We study the effect of the range of particle sizes in KhN45Yu alloy and 12Kh18N10T and 15Kh25T steels on their heat resistance at temperatures of 800, 1000, and 1200°C in air on a base of up to 1000 h. It is shown that materials with a coarse-grained structure exhibit a much higher oxidation susceptibility than those with a fine-grained structure. For the materials under investigation, the oxidation rates are greater in the stressed state and increase as a result of thermal cycling.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 5, pp. 45–49, September–October, 1994.     

Deformation and fracture of high-temperature steels at different temperatures and loading rates

Charpy impact tests were conducted at different temperatures and loading rates. Temperature dependences of the crack initiation and propagation energies were determined for carbon steel 45, steels St. 3 and 15Kh2NMFA from the load-time curves obtained with due account of the impact test results. The effect of the loading rate on the temperature dependence of the impact toughness was analyzed within the range from 1 to 4.4 m/s. __________ Translated from Problemy Prochnosti, No. 1, pp. 29–34, January–February, 2009.     

The stressed state of a broad strip in uniaxial tension

The character of the stressed state of a broad strip in uniaxial tension in relation to the load level is investigated. Using 60 and 65G carbon steels as an example it is shown that in the material of the strip in the area of elastoplastic strains together with the longitudinal stress there is a purely transverse one which occurs with a plastic tensile deformation of about 2–3%. The transverse stress depends upon the level of plastic deformation and with an increase in the latter it increases. In this case the loading is complex and its trajectory has the form of a curve.Translated from Problemy Prochnosti, No. 8, pp. 48–51, August, 1995.