Metal Science and Heat Treatment最新文献

The change in the microstructure and mechanical properties of 410 stainless steel during cold drawing is studied. The Johnson–Cook equation was used to describe the behavior of the steel flow during cold drawing process. The formation of deformed and elongated ferrite grains accompanied with dispersed chromium carbides in the matrix was established using x-ray diffraction methods in combination with FESEM and EDS analyses, as well as traditional optical microscopy. After drawing, the tensile strength of steel increases by about 25% from 770 to 960 MPa. The crystalline size decreases from 85.6 to 58.9 nm, and their orientation changes from {110} to the preferred {200}. The highest texture coefficient corresponds to {200} indices. Determination of the friction coefficient value during drawing by the ring specimen method showed that the best drawing lubricant is oxalate solution with hot soap which provided lowest coefficient of friction of 0.15. Based on the simulation results, it is shown that the optimum drawing die angle is 32 degrees, which results in the lowest drawing force of 164 kN.

The effect of annealing temperature and time on the interfacial organization and properties of the liquid-solid cast-rolled 1070A/7075 aluminum alloy composite plates are investigated. Optical and electron microscopy, energy-dispersive x-ray spectroscopy, mechanical shear and tensile tests were used in the study. It is shown that annealing promotes the diffusion of elements between the 1070A/7075 aluminum alloys of the composite, and the interface region of the composite forms an obvious intermediate transition layer. It is found that in order to ensure the bonding strength of the composite plate after annealing, the width of the transition layer should be between 1.5 – 7.9 μm. After annealing at 300°C for 3 h, the element diffusion distance is 30 μm, and the width of the interface transition zone is 2.4 μm. In this case, the bond strength at the interface reaches a maximum value of 105 MPa, and the tensile strength, yield strength and relative elongation are 150 MPa; 70 MPa and 27% respectively.

The effect of point defects on the behavior of martensitic transformation in an austenitic chromium-nickel steel is investigated. The plastically deformed material is studied using the synchrotron radiation diffraction method. Results obtained by the method of molecular dynamics are presented. The data are used to consider the process of the appearance of point defects and the tendency to segregation of alloying elements under conditions of plastic deformation. It is shown that frictional loading is accompanied by an austenite-to-martensite transformation and increase in the degree of diffuse scattering. In accordance with the simulation of the deformation process, friction produces segregations of alloying elements, which lowers the stability of the austenite and is a factor participating in the development of martensitic transformation in the steel studied.

The structure and properties of chromium-nickel austenitic steel with surface layer modified with silicon during surfacing of powder silicon carbide by a beam of relativistic electrons released into air atmosphere are studied. It is shown that the process of electron beam heating yields a structure consisting a silicon-alloyed austenitic matrix, complex chromium carbides (Cr, Fe)₇C₃ with a chiefly dendritic structure, and silicon carbides Si₅C₃ in the surface layers up to 2800 μm thick. The solid solution strengthening and the presence of the carbides promote increase in the microhardness of the modified steel layer to 10 GPa, which is four times higher than the hardness of the base metal. The heat resistance of the austenitic steel with the modified layer is twice higher than that of the base metal at 850°C.

A Gleeble 3800 test facility is used to study the influence of process parameters on the characteristics of the foaming process in the production of foam aluminum. Dependences of the temperature of the start of the foaming process on the heating rate and the chemical composition of the initial charge are derived and analyzed. Mathematical simulation of the foaming process is performed. Practical recommendations for choosing the foaming process parameters for obtaining blanks of various shapes are formulated.

It is shown that a spiral wrapping a noncrystallographic spiral is a universal building unit for a wide class of structures from metals to polymers. The noncrystallographic symmetry of such a unit makes it possible to describe adequately the features of an actual configuration of such structures. Theoretical and experimental data are used to describe the structure of metallic glasses as a random packing of close-packed tetrahedral spirals instead of the traditional random packing of atoms.

The effect of heat treatment on the microstructure and mechanical properties of AA2014-T651 aluminum alloy joints produced by friction stir welding was studied. Friction stir welding is performed using a triangular probe tool at two different tool rotational speed of 1000 and 1400 rpm. During welding a constant welding speed of 63 mm/min is maintained at both tool rotational speeds. It has been established that friction stir welding leads to a significant refinement of the microstructure and partial dissolution of strengthening precipitates. The welded joints were heat treated at temperatures of 573, 673, 773 and 823 K for one hour. Re-precipitation and precipitate coarsening were observed during heat treatment. It has been shown that increasing the tool rotational speed significantly increases the thermal stability of the microstructure, practically without causing abnormal grain growth in the weld.

The structure and mechanical properties of samples of aluminum bronze of grade BrAZhNMts9-4-4-1 (BrAlFeNiMn) obtained by severe plastic deformation by the method of equal channel angular pressing (ECAP) are investigated. Mechanical tensile tests on a split Hopkinson rod at a deformation rate of about 10³ sec ^–1 are carried out for samples with the original (coarse-grained) and ultrafine-grained structures. It is shown that the refinement of the structure of the aluminum bronze leads to an increase in the dynamic yield strength and to a decrease in the plasticity and in Young’s modulus.

The effect of the cooling medium during quenching on the mechanical properties of TIG welded joints made of low-carbon, low-alloy high-strength bainitic steel 15CDV6 was studied. Air, water, sand and oil were used as the quenching medium. The tensile strength of welded joints quenched in oil was found to be the highest of the four media. However, the yield strength of welded joints is greatest after quenching in water. The highest value of the relative elongation of the joint is achieved after quenching in oil; after quenching in air and in sand, its values are lower and almost identical due to the relatively slow cooling rate; and after quenching in water —– the lowest. It has been shown that oil quenching is the most effective for ensuring a high complex of mechanical properties of welded joints made of 15CDV6 steel.

The influence the structure of medium-carbon steel on the magnitude and distribution of residual macro-stresses in different sections of a tubing coupling is investigated. Heat treatment (quenching and tempering at different temperatures) of cylindrical samples cut from the coupling is carried out. Four types of structure are obtained, i.e., quenched martensite, tempered martensite, bainite and ferrite-pearlite. It is shown that according to the degrees of reduction of the longitudinal and tangential residual macrostresses the structures formed in the steel can be arranged in the following sequence: quenched martensite → tempered martensite → bainite ferrite + pearlite. At the same time, the different types of structure do not lead to significant changes in the radial macrostresses in the coupling. It is established that the magnitude of the longitudinal and tangential residual stresses in the coupling depends on the type of the microstructure formed in the steel during the heat treatment and on its defects. It is shown that formation of a bainitic structure in a tubing coupling is the most expedient, because it ensures a relatively high strength and elevated plasticity at comparatively low longitudinal and tangential residual stresses.