Electron Microscope Studies of the 01Cr17Ni13Mo3 Austenitic Steel Structure after Cold Rolling Combined with Hydrogen Alloying with Varying Degrees of Deformation

In this paper, we consider the effect of cold rolling and hydrogen alloying on the formation of twin boundaries of the corrosion resistance of austenitic steel 01Cr17Ni13Mo3. Using the method of transmission electronic microscopy, microdiffraction patterns were obtained. The analysis of microdiffraction patterns indicates the formation of a developed grain-subgrain structure with small-angle and large-angle misorientation. The structure has a high dislocation density, deformation twins and localized shift bands. It was established that plastic deformation by flat rolling to ε = 90 % at room temperature does not contribute to the appearance of a noticeable amount of α' and ε-martensite. At the temperature of liquid nitrogen, the samples were found to form a small fraction of the α'-martensite phase. Such a small amount of martensite can contribute to steel strengthening, and a decrease in the rolling temperature will lead to an increase in the strength properties of steel. It was detected that the density of twin boundaries under the decrease in the rolling temperature but with the same intensity of hydrogen saturation is significantly higher. A noticeable reduction in the width of the twin lamellas was revealed.

Structure heterogeneity and mechanical properties studied in thickness up to 100 mm of low-alloyed shipbuilding steel sheets with a yield strength not less than 420 MPa

This paper presents a study of changes in the structure and properties in thickness of rolled sheets up to 100 mm of low-alloyed shipbuilding steel with a yield point not less than 420 MPa. The fracture surface of samples after impact bending tests at low temperatures was investigated. It was found that the combination of the parameters of lath morphology bainite (fraction, areas average size and length) and the size of structural elements at given tolerance angles of 5 and 15° (indicating the presence or absence of a developed subgrain structure of deformation origin) determine the level of impact work at low temperatures testing.

Effect of ion irradiation on structural state and mechanical properties of naturally-aged hot-pressed D16 (Al-Cu-Mg) alloy profiles

The effect of irradiation with 20 keV argon ions on the mechanical properties, structure, and phase composition of quenched and then naturally aged, hot-pressed profiles (6 mm thick) from the D16 alloy of the Al-Cu-Mg system has been studied. It was found that short-term irradiation with Ar+ ions (E = 20 keV, j = 200 μA/cm2, F = 1×1016 cm-2, irradiation time 8 s) leads to transformation of the microstructure and phase composition of the alloy. The coarsening of the initial subgrain structure occurs near the sample surface. Both in the surface layer and at a distance of ∼ 150 μm from it, partial dissolution and fragmentation of complex intermetallic compounds of crystallization origin located along grain boundaries are observed, as well as a decrease in the size and change in the morphology of Al6(Fe, Mn) intermetallic compounds of crystallization origin are observed too: the distribution density of lamellar precipitations decreases, and equiaxial precipitations disappear. Under the influence of irradiation, the decomposition of the supersaturated solid solution is activated with the formation of a more stable phase S’. As a result of ion-beam treatment in this mode, the plasticity of the alloy increases while maintaining the strength properties.

Effect of External Impacts on the Structure and Martensitic Transformation of Rapidly Quenched TiNiCu Alloys

TiNi-TiCu quasibinary system alloys with a high Cu content produced by rapid quenching from liquid state in the form of thin amorphous ribbons exhibit pronounced shape memory effect after crystallization and are promising materials for miniaturized and fast operating devices. There is currently no complete clarity of the mechanisms of structure formation during crystallization from the amorphous state that determine the structure-sensitive properties of these alloys. This work deals with the effect of the initial amorphous state structure and crystallization method of the alloys on their structure and phase transformations. To this end the alloy containing 30 at.% Cu was subjected to thermal and mechanical impact in the amorphous state and crystallized using isothermal or electropulse treatment. We show that after all types of treatment in the amorphous state the structure of the alloy remains almost completely amorphous but the characteristic temperatures and enthalpy of crystallization become slightly lower. Isothermal crystallization of alloy specimens produces a submicrocrystalline structure with an average grain size in the 0.4–1.0 μm range whereas electropulse crystallization generates a bimorphic structure consisting of large 4–6 μm grains and 2–3 μm high columnar crystals in the vicinity of the surface. The grains have nanosized plate-like and subgrain structures. The largest grains are observed in thermally activated samples, meanwhile, mechanical impact in the amorphous state leads to the formation of equiaxed finer grains with a less defective subgrain structure and to the shift of the temperature range of the martensitic transformation toward lower temperatures.

Specific Features of The Structure Formation of Aluminum Alloys During Rapid Crystallization-Deformation

The results of studies of the structure and properties of semi-finished products from aluminum and its alloys, obtained with the use of cast-free rolling-extruding are presented. It has been found that the rods obtained by the high-speed crystallization-deformation technology by the direct rolling-extrusion method have a stable ultrafine subgrain structure, which makes it possible to use them as modifiers. Experimental studies have been carried out, which confirmed the assumption that the initial structure of the modifying rod affects the melt. It was revealed that the size and density of distribution of additional crystallization centers formed in the volume of the melt based on clusters are inherited from the original subgrain structure of the modifying rod made of aluminum or its alloys. Metallographic studies have also shown that the subsequent severe plastic deformation by equal-channel angular extruding of rods obtained by direct rolling-extruding from an experimental alloy of the composition Al-0.2Zr-0.2Fe-0.4Mg makes it possible to achieve additional strengthening of the metal, since even more refines its structure, while the average grain size is 647 μm.

Dynamic recrystallization behavior of 6082 aluminum alloy during hot deformation

The dynamic recrystallization behaviors of 6082 aluminum alloy in the temperature range of 623–773 K and strain rate range of 0.01–5 s−1 were studied by electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). According to the experimental results, dynamic recrystallization occurs during hot deformation of 6082 aluminum alloy, although the true stress-strain curve has no obvious single peak characteristic, and the degree of dynamic recrystallization is closely related to the Z parameter. Hot compression with lnZ = 24.9014 (723 K, 0.1 s−1) gives rise to the highest recrystallization fraction of 38.6%. The initial critical strain of dynamic recrystallization was determined by the work hardening rate. The quantitative relationship between the critical strain and Z parameters was established: [Formula: see text]. Based on the EBSD analysis and measurement results, dynamic recrystallization kinetics models of 6082 aluminum alloy during hot deformation were deduced. Microstructure analysis showed that the subgrain structure formed in the original grain is coarsened by grain boundary migration, and the orientation difference increases continuously until a large-angle grain boundary forms, resulting in dynamic recrystallization of grains. The likely mechanism is continuous dynamic recrystallization.

Development and mastering of technologies of production at PJSC MMK a new generation steel rolled stock for m a in pipelines

In view of arising needs of Russian oil and gas sectors, elaboration and implementation into series production competi­tive pipe products became an actual task for domestic enterprises of metallurgical industry. Generalized results of elaboration of chemical compositions and automated technologies of sheet rolled stock of new generation production from low-alloyed pipe steels of various strength classes at PJSC MMK presented. It was shown that the selected chemical compositions ensure forming finedispersed ferrite-bainite structure with bainite of granular morphology in a wide range of cooling rates. The elaborated technological modes of sheet rolled stock production from pipe steels stipulate for elimination considerable growth of austenite grain at heating before the rolling, refinement of austenite grains due to recrystallization processes, forming of extensive subgrain structure of austenite at plastic deformation, forming disperse structures during phase transformation in the process of controlled accelerated cooling; forming of extensive fragmented structure in а-phase. The level of strength, tough-plastic properties and resistance against brittle destruction (based on results of tests with a falling weight with determination of tough component share in the break of full-thickness samples) of sheet rolled stock of pipe steels with various chemical composition of PJSC MMK production was demonstrated. Results of study of tests the sheet rolled stock of high-strength steels for pipes of large diameter presented. Objects of the elaborated pipe steels implementation indicated.

Influence of hydrogen saturation on the structure and mechanical properties of Fe-17Cr-13Ni-3Mo-0.01C austenitic steel during rolling at different temperatures

Introduction. The development of hydrogen energy implies a decrease in the dependence of various human activities on fossil energy sources and a significant reduction in carbon dioxide emission into the atmosphere. Therefore, the requirements for the quality of structural materials, which have the prospect of being used for storage and transportation of hydrogen, as well as for the creation of infrastructure facilities for hydrogen energy, are increasing. Therefore, the scientific researches on the hydrogen-assisted microstructure and mechanical behavior of structural materials in various loading schemes are of great importance. The aim of this work is to establish the effect of chemical-deformation treatment, including rolling combined with hydrogen saturation, on the microstructure, phase composition, and mechanical properties of 316L-type austenitic stainless steel. Methods. Transmission electron microscopy and backscattered electron diffraction, X-ray diffraction, X-ray phase and magnetic phase analysis, microindentation and uniaxial static tension are utilized. Results and Discussion. It is shown experimentally that after rolling with 25 and 50 % upset, the morphology of the defect structure and the phase composition of 316L steel substantially depends on the deformation temperature (at room temperature or with the cooling of the samples in the liquid nitrogen) and on hydrogen saturation rate (for 5 hours at a current density of 200 mA/cm2). The main deformation mechanisms of the steel in rolling are slip, twinning, and microlocalization of plastic flow, which all provide the formation of ultrafine grain-subgrain structure in the samples. In addition, deformation-induced ε and α' martensitic phases are formed in the structure of the rolled samples. Regardless of the regime of chemical-deformation processing, grain-subgrain structures with a high density of deformation defects are formed in steel, but its morphologies are dependent on the processing regime. The experimental data indicate that both preliminary hydrogen saturation and a decrease in the deformation temperature contribute to the more active development of mechanical twinning and deformation-induced phase transformations during rolling. Despite the discovered effects on the influence of hydrogen saturation on the deformation mechanisms and the morphology of a defective microstructure formed during rolling, preliminary hydrogenation has little effect on the mechanical properties of steel at a fixed degree and temperature of deformation. These data indicate that irrespective of the morphology of the defective grain-subgrain structure, grain refinement, accumulation of deformation defects and an increase in internal stresses lead to an increase in the strength characteristics of the steel.

Investigation of the Effect of Implantation of Aluminum Alloys by Gas and Metal Ions on the Structure and Phase Composition of the Implanted Layer

The article presents studies of the structure and phase composition of aluminum alloys after ion implantation. It is shown that the effect of accelerated ions (Cu + Pb) (E = 30 keV, j = 100 μA / cm2) on an alloy without a cladding layer already at a dose of 1016 cm - 2 leads to the formation of a developed subgrain structure in the initially deformed alloy. With an increase in the ion current density and radiation dose, the cellular structure of the implanted aluminum alloys becomes more regular - well-formed cells are observed practically throughout the entire volume of the sample under study. The average width of the dislocation-free regions reaches 2.5 μm with the width of the boundaries not exceeding 0.6 μm.

Increase of alloys functional properties by electronic beam processing

The article considers a review of domestic and foreign works on the use of intense pulsed electron beams for surface treatment of metals, alloys, cermet and ceramic materials. The advantages of using electron pulsed beams over laser beams, plasma flows, and ion beams are noted. The promising directions of using electron-beam processing were analyzed and are as following: 1 – smoothing the surface, getting rid of surface microcracks, while simultaneously changing the structural-phase state of the surface layer, to create high-performance technologies for the finishing processing of critical metal products of complex shape made of titanium alloy Ti-6Al-4V and titanium; steels of various classes; hard alloy WC – 10 wt. % Сo; aluminum; 2 – removal of microbursts formed during the manufacture of precision molds (SKD11 steel) and biomedical products (Ti-6Al-4V alloy); 3 – finishing the surface of molds and dies; 4 – improvement of the functional properties of metallic biomaterials: stainless steel, titanium and its alloys, alloys based on titanium nickelide with shape memory effect, and magnesium alloys; 5 – processing of medical devices and implants; 6 – formation of the surface alloys for powerful electrodynamic systems; 7 – improvement of the characteristics of aircraft engine and compressor blades; 8 – formation of thermal barrier coatings applied to the surface of the combustion chambers. It is shown that with the correct choice of process parameters, such as accelerating voltage, energy density of electron beam, number of pulses, and pulse duration, it is possible to control carefully and/or manipulate the characteristics of structural-phase state and surface properties. In order to improve the properties of the material and the durability of the products made of it, an important factor is the structure modification to form a submicro-nanosized grain (or subgrain structure).