Influence of tempering on the dislocation substructure and scalar density for cast construction intermediate-alloyed steel

The method of diffraction electron microscopy is used to study the influence of the tempering period on the defect structure of the Fe-0.38C-3.5Ni-1.3Cr-0.24Si-0.35Mn-0.4Mo-0.15V-0.3Cu cast construction steel. It is demonstrated that tempering causes the substructural nonfragmented → fragmented substructure transformation, which is the main substructural transformation. Three types of fragments are formed, including initial and anisotropic secondary fragments with network and cellular dislocation substructures and tertiary isotropic dislocation-free fragments. The fragmentation process at tempering is accompanied by a continuous decrease in the scalar dislocation density. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 44–50, January, 2006.     

Study of creep and features of the dislocation structure in single crystals of Ni3Ge alloy

Data from investigating the dislocation structure of Ni₃Ge alloy single crystals formed during creep are presented. The creep of the Ni₃Ge single crystals with the [001] orientation of the deformation axis was studied. It was found that a fragmented substructure with varying degrees of disorientation occurs in the areas of macrolocalized deformation. A polycrystalline substructure consisting of fragments with a low dislocation density is formed in the local areas.     

Dynamics of fractoluminescence and electromagnetic and acoustic emission upon an impact against the marble surface

The blow of a steel striker against the marble surface induces strain waves and electromagnetic emission. Simultaneously, microcracks appear in the marble single crystal with excited free CO ₂ ^? radicals at the microcrack banks. Relaxation of electronic excitation leads to the emergence of fractoluminescence bursts. The burst intensity is proportional to the area of the microcrack surfaces. Measurements show that the linear size of the microcracks varies from ～2 to ～47 μm.     

Emission kinetics of light,sound, and radio waves from single-crystalline quartz after impact on its surface

A steel striker impacting the surface of single-crystalline quartz generates strain waves and their related acoustic and electromagnetic emissions. Simultaneously, microcracks with free excited SiO• radicals at their edges appear in the single crystal. The relaxation of the electronic excitation causes bursts of fractoluminescence. The intensity of the bursts is proportional to the microcrack surface area. It is found that the linear sizes of microcracks vary from 15 to 70 μm. Cracking changes the slope of the time dependences of the acoustic and electromagnetic emission intensities. The microcrack size distribution obeys a power law with an exponent of about two.     

Influence of structural interfaces on the statistics of corrosion microcracks

The amplitude distributions of acoustic emission signals generated during the formation of corrosion microcracks in loaded welded joints connecting two corrosion-resistant steel tubes are studied. For acoustic emission signal amplitudes of less than 0.6 mV and a microcrack concentration of ～10 mm^?3, the distribution density of the signal amplitudes is described by a gamma function. For acoustic emission signal amplitudes exceeding 1.0 mV and a microcrack concentration of greater than or equal to 10² mm^?3, the distribution density of the amplitudes exhibits two maxima, whose shape is described by a Gaussian function. The mean amplitudes of acoustic emission signals differ by a factor of 3. The change in the amplitude distribution of acoustic emission signals is explained by the effect exerted by the weld-metal interface on the microcrack formation.     

Fatigue life of metal treated by magnetic field

This paper investigates theoretically the influence of magnetization on fatigue life by using non-equilibrium statistical theory of fatigue fracture for metals. The fatigue microcrack growth rate is obtained from the dynamic equation of microcrack growth, where the influence of magnetization is described by an additional term in the potential energy of microcrack. The statistical value of fatigue life of metal under magnetic field is derived, which is expressed in terms of magnetic field and macrophysical as well as microphysical quantities. The fatigue life of AISI 4140 steel in static magnetic field from this theory is basically consistent with the experimental data.     

Evolution of a Martensite Packet under Multicycle Fatigue Loading

The methods of diffraction electron microscopy of thin metal foils are used to study the defect substructure and the phase content of preliminary quenched Fe–0.60C–1Mn–2Si steel subjected to multicycle fatigue tests. It is demonstrated that steel loading is accompanied by the initial stage of dynamic recrystallization. One of the mechanisms of forming dynamic recrystallization centers is the pair coalescence of packet martensite crystals.     

Structural and phase states in austenitic steel subjected to high-cycle fatigue

The destruction surface and defect substructure of the Fe-0.1C-1.71Mn-0.92Ti-18.2Cr-10.4Ni-0.71Si steel subjected to high-cycle fatigue tests is investigated by the methods of scanning and transmission electron microscopy. It is demonstrated that the fatigue tests, irrespective of the loading scheme (continuous or under conditions of intermediate stimulation by pulse current), result in the formation of a structural gradient in the material manifested through regular changes of the relief parameters of the destruction surface and defect substructure with increasing distance from the loading surface (face or back specimen side). It is revealed that scalar and excess dislocation density, volume fraction of grains that comprise deformation microtwins, and degree of dislocation substructure organization maximize near the free specimen surface. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 88–95, January, 2006.     

Influence of the structure of the Ti-49.8 at % Ni alloy on its thermal expansion during the martensitic phase transformation

The temperature dependence of thermal expansion of the Ti-49.8 at % Ni alloy has been measured after rolling at temperatures of 470, 570, 670, 770, and 870 K. The maximum dilatation jump during the martensitic phase transition has been observed for the samples rolled at 570 and 670 K. A fragmented structure, in which the phase transformations are hampered, is formed during the low-temperature rolling. An increase in the rolling temperature to 770–870 K leads to the return processes and dynamic recrystallization of the material; as a result, the slope of dilatation curves changes and the range of phase transitions narrows.     

Increase in the fatigue durability of stainless steel by electron-beam surface treatment

The structure, phase composition and dislocation substructure of 20Cr23Ni18 steel subjected to electron-beam treatment and subsequent multicycle fatigue loading until destruction were studied by scanning and transmission electron microscopy. It was shown that electron-beam treatment with an energy density of 20 J/cm² increases the fatigue durability by a factor of 2.1. The cause of steel fatigue destruction is analyzed and a way of further increasing the fatigue durability is proposed.     

Influence of the grain-size and chemical composition of a MgO coating on the structure-phase state and elemental composition of the ground layer formed on an electric steel surface

The surface morphology, phase state and elemental composition, and substructure of the ground layer of anisotropic electric steel (AES) samples have been studied via scanning electron microscopy, atomic force microscopy, transmission electron microscopy, electron probe microanalysis, and x-ray diffractometry. High-temperature annealing of MgO coatings with different grain-size distributions and chemical compositions was found to lead to formation of a single-phase layer of forsterite (Mg₂SiO₄) on the AES surface. It has been revealed that the morphology and substructure of a forsterite layer depend on the grain-size distribution and chemical composition of magnesium oxide and the conditions used in preparation of MgO suspensions. When added to MgO suspensions, TiO₂ and Na₂B₄O₇ impurities promote formation of a denser coating substructure. The increased mixing speed used in suspension preparation improves the surface homogeneity of a ground layer only if a suspension contains MgO grains of different size.     

Multicyclic fatigue of stainless steel treated by a high-intensity electron beam: surface layer structure

It is shown that an electron-beam treatment of the 08X18H10T steel specimens under the condition of melting of the ~5 μm surface layer (electron beam energy density 25 J/cm²) increases their fatigue life by a factor of 3.5. The structural-phase states and defect substructure of this steel are studied by the methods of optical, scanning and transmission electron microscopy, and the factors responsible for its increased fatigue life are revealed.     

Features and mechanisms of the evolution of the structure-phase state of a quenched carbon steel under electrostimulated fatigue

Electron-microscopic examinations of the evolution of the defect substructure and phase composition have been carried out for quenched 60GS2 carbon steel subjected to multiple cycles of fatigue loading. The mechanisms by which the fatigue durability of the steel processed at an intermediate stage of loading by alternating electric current is increased have been investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 53–60, September, 2004.     

Phase transformations and mechanical properties of stainless steel in the nanostructural state

The peculiar features of structurization and changes in mechanical properties are studied during equichannel-angular (ECA) pressing treatment and cold deformation (strain) through rolling of metastable austenitic steel up to a rolling rate of e = 2.1. It is shown that the ECA pressing treatment of austenitic steel resulted in enhancement of its strength characteristics and conserved its high plasticity values, exceeding by an order of magnitude, these characteristics after cold plastic strain, which is associated with the optimization of the kinetics of γ → α transformation.     

Nanoscale experimental study of the morphology of a microcrack in silicon by transmission electron microscopy

A microcrack in a silicon single crystal was experimentally investigated using high-resolution transmission electron microscopy (HRTEM). In particular, the numerical Moiré (NM) method was used to visualize the deformations and defects. The lattice structure of the microcrack was carefully observed at the nanoscale. HRTEM images of the microcrack demonstrated that the lattice structure of most of the microcrack regions is regular with good periodicity. In addition, the microcrack cleavage expands alternately along different crystal planes, where the principal cleavage plane is the (1 1 1) crystal plane. The NM maps showed no sharp plastic deformation around the microcrack, but discrete edge dislocations can be found only near the crack tip.     

Softening and recrystallization of austenite in the conditions of controlled rolling of Ti microalloyed steel

Various variants of controlled rolling of Ti microalloyed steel were simulated on torsion plastometer. Softening, size and size distribution of recrystallized austenite grain between individual deformations were measured. Experiments allowed a more precise definition of physicometallurgically justified schedule of controlled rolling of the investigated steel.The authors are grateful to Dipl.-Ing. G. Backmann and Dr. A. Köthe of the Zentralinstitut für Festkörperphysik AdW Dresden for their valuable help in realizing the experimental programme.     

Fine Structure and Fracture Surface of Low-Carbon Steel Welds

Russian Physics Journal - Using the methods of modern physical materials science, the structural phase state, the defect substructure and the fracture surface of low-carbon alloy steel welds formed...     

Modification of the defect substructure in a quenched steel by a low-energy high-current pulsed electron beam

The regularities of evolution of the defect substructure of a previously quenched carbon steel, irradiated with a low-energy high-current microsecond electron beam, have been revealed by diffraction electron microscopy.     

Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10~(-4)s~(-1)to 1 s~(-1), the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions(n_2and n_1) and the transition strain(εL) decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.