International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

In this paper, bars from carbon steel grade 45 deformed by a new technology are studied. This technology consists in drawing bars from medium carbon steel on a radial-shift rolling mill and subsequent drawing. As a result of deformation, bars with gradient microstructure were obtained. The surface zone of the bar is significantly crushed, the average ferrite size is 0.5 μm. In the neutral zone the deformation is not large enough, so the structure is not so strongly crushed, the ferrite grains are reduced to 2 microns. In the central zone, the microstructure consists of large grains with an average size of 7 μm. The quantitative ratio of large-angle boundaries in the surface zone is much higher than the central zone. To understand the relationship between strength and microstructure, the microhardness of the bar was determined. Thus for three deformation cycles the average value of microhardness in the central zone was 2085 MPa, in the neutral zone – 2505 MPa, and in the surface zone – 2915 MPa. As it can be seen, the hardness decreases as we move away from the surface zone to the central zone, this can be explained in terms of dislocation and boundary hardening.

The paper studies the evolution of microstructure and mechanical properties of copper wire during a new combined deformation process. The essence of the technological process is deformation of wire in a rotating equal-channel step matrix and subsequent drawing. The matrix rotates around the wire axis and thereby creates stress due to equal-channel angular drawing and twisting in the matrix. The deformed copper wire was investigated by transmission electron microscopy and EBSD analysis, as well as tensile tests and microhardness determination. The deformation resulted in an ultrafine-grained gradient microstructure having a high component of high-angle grain
boundaries. The tensile strength of the deformed copper wire compared to the undeformed one increases more than twice from 302 to 635 MPa, and the yield strength increases from 196 to 306 MPa, an increase of 56%. The use of such hardened copper wire in construction will reduce the weight of the structure by reducing the diameter.

The results of finite element modeling of a new method with an increased metal processing level were considered. The improvement of the drawing process was achieved by changing the usual scheme of metal movement during deformation, which made it possible to achieve large strains compared to the standard drawing scheme. It is established that step drawing has the advantage of an increased processing level, but it leads to the formation of an inhomogeneous gradient strain.

The analysis of stress-strain state non axis symmetric drawing process, which was developed based on an analytical model of the process. Obtained the dependencies for the components of the stress in the plastic region. The relationship between changes in the district velocity compressive stress on the peripheral area of the amount of shear stress. On this basis, it is given a numerical grade to increase the limit drawing ratio slightly different from equivalent value determined by the equality of the greatest meridional stress to the yield strength of the material at dangerous section of the blank.

The analysis of stress-strain state of the bisector of the corner of the blank at a drawing of box-shaped parts. Analytical dependences for the meridional and circumferential stress on the bisector of the angle. It is shown that an increase in the limit drawing ratio compared with an extract of the cylindrical part is a consequence of the growth in absolute value of district compressive stresses. It was found that the maximum value of the coefficient of drawing of box-shaped parts cannot exceed the value of – K=exp(1+1/√3)≈ 4,84.

The paper presents the results of numerical modeling of the conventional drawing and free torsion processes of rods made of low-carbon steel using the "DEFORM-3D" software package. The heterogeneity of the strain intensity distribution in the investigated processes revealed in the model basically corresponds to real physical experiments with similar parameters of the structural heterogeneity. A mutual correspondence of the ductility diagram to the character of the structural changes in the samples deformed by free torsion is established, and the limiting values of the ductility margin, the excess of which leads to the development of fracture processes.

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