## Modelling of combined thermomechanical processing of stainless steel wire

Mathematical Modeling, Vol. 8 (2024), Issue 1, pg(s) 10-13

In this article, a number of theoretical studies have been conducted on a new combined process of multicycle thermomechanical processing, including wire drawing and subsequent cooling in liquid nitrogen. When analyzing the deformation, it was found that the presence of intermediate heating to ambient temperature allows calculating the force according to the Krasilshchikov formula and the wellknown nomogram of the tensile strength of AISI-316 steel at 20°C with minimal errors. The lack of heating leads to the fact that the second and third drawing cycles take place at partially negative temperatures in the workpiece section. This leads to an increase in the difference in the force values obtained by calculation and during modeling. To be able to use the Krasilshchikov formula and the nomogram of the tensile strength of AISI-316 steel at 20°C, it is necessary to adjust the resulting force values by increasing by about 30% for a diameter of 6 mm and 20% for a diameter of 9 mm in the absence of heating of the workpiece and by 35% for a diameter of 6 mm and 25% for a diameter of 9 mm in in case of preheating the workpiece.

## Development of a new technology for carbon steel bars processing

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.

## On the role of non-metallic inclusions in ensuring crack resistance of steel

Machines. Technologies. Materials., Vol. 17 (2023), Issue 5, pg(s) 198-201

The influence of non-metallic inclusions on the formation of defects in deformed steels and their role in providing crack resistance are considered. It is shown that non-metallic inclusions as stress and strain concentrators are one of the most dangerous sources of defect initiation in steels during pressure treatment. It has been established that the nature of cracks and the features of their growth near nonmetallic inclusions are determined by the type of inclusions, as well as by the scheme of the local stress state, which depends on the loading conditions. An analysis was made of the features of the initiation and development of the cracks near non-metallic inclusions of various types during tensile strain, compressive and bending deformation. It is shown that the most severe way of deformation for the inclusion-matrix system is tensile strain, the softest is compression.

## Structural design of the manipulator of the rotary valve for bulk materials – calculation of loads acting on individual wheels and analysis of resistances against motion

The paper is a continuation of research dealing with the structural design of the manipulator of the bulk material rotary valve based on the specifications of a food company. This issue is currently immensely topical for reasons such as increasing safety, speed, or efficiency of work. In the previous publication, the authors focused on determining the position of the center of gravity of the rotary valve due to the fact that this essential data is not provided by its manufacturer. Accordingly, the present work attends to the design of the steel structure of the trolley and the path along which the trolley in conjunction with rotary valve will move. The structural design is analyzed in the paper by means of analytical functional and dimensional calculations. On the basis of the parameters of the calculated centers of gravity of the individual components of the structure, the reactions from the track on which trolley travels to the weight transmitted by the prismatic wheels of the trolley were determined. The loads were calculated in transverse and longitudinal directions. In addition, reactions from the individual wheels were determined for the case, when the rotor valve is in a position with the rotor retracted (operating position). The achieved results demonstrate that the least favorable case for the stresses on the track travel of trolley occurs in the case with the rotor retracted. Furthermore, the calculation of the loads acting on the track beam in the most unfavorable position of the trolley was performed. Moreover, the resistive forces acting on the trolley were analyzed. The results indicate that the use of this mechanism will be feasible in operation.

• ## The features of recrystallization of steels under laser action

The features of recrystallization of steels with different chemical composition and type of crystal lattice under laser action were investigated. These processes are of great importance in high-speed laser heating and cooling, as well as in the formation of the microstructure of steels under the influence of residual heat.
It was found that recrystallization under laser action has signs of a dynamic process due to an increase in the dislocation density. In addition, the dislocation substructure of steel is inherited from the initial hot-deformed state. It is shown that the mechanism of laser recrystallization depends on the type of steel, chemical composition, and crystal lattice.
In different steels, the development of primary, collective, and secondary recrystallization was observed. In this case, the change in the grain structure of steels took place against the background of an increased density of dislocations and the formation of a cellular dislocation substructure.

## Optimization of joining parameters of thin-walled materials by flowdrill technology

Machines. Technologies. Materials., Vol. 16 (2022), Issue 5, pg(s) 176-178

This paper deals with the investigation of the effect of speed on the form fit joint of dissimilar materials. Thin -walled materials based on steel and aluminium alloy were joined by thermal drilling. The shape and size of the resulting bushing were evaluated. It turned out that the best material combination for joining by flowdrill technology are joints made of steel and aluminum alloy. Aluminum alloy must always be placed in the bottom position. The best parameters of the formed bushing were achieved with the combination of DC-Al or TL-Al materials, at tool speeds of at least 2400 rpm.

• ## Phase transformations in non-metallic inclusions under laser action

It was found that in the process of pulsed laser action, various phase and structural transformations occur in non -metallic inclusions, which take place under nonequilibrium conditions. It is shown that the melting of inclusions under laser action is corresponded with change of their structure and phase composition. Also it is shown that the nature of these transformations depends on the type of nonmetallic inclusion. It was found that nonequilibrium phase transformations contribute to a change in the structure, phase composition, properties and sizes of nonmetallic inclusions, as well as the inclusion-matrix interphase boundaries of steel. It is shown that changes in the structure and properties of non-metallic inclusions affect their behavior and the formation of defects in the laser-strengthened layer of steel
products.

• ## Transformation of heterophase inclusions “dispersed phases are in non-metallic matrix” in steels under laser action

Melting and crystallization of heterophase non-metallic inclusions “dispersed phases are in non-metallic matrix” was investigated. Mechanism of melting of the inclusions “dispersed phases are in non-metallic matrix” and inclusion-matrix boundaries under contact laser melting with steel matrix in the conditions of abnormal mass transfer connecting with formation of zones with high dislocation density and also with electron and electro-magnetic interaction between inclusion and steel matrix was proposed. That allows to create the possibilities for the influence on the inclusion-matrix boundaries and also on the chemical and phase composition of surface layer of non-metallic inclusions “dispersed phases are in non-metallic matrix”. Peculiarities of structure of non-metallic inclusions after speed crystallization were investigated. It was shown that under laser action the initial structure of inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusionmatrix to the state with minimum of the free energy. In the result of the system inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of nonmetallic inclusions “dispersed phases are in non-metallic matrix” and also of the melting of steel matrix play the great role in transformation of interphase inclusion-matrix boundaries under laser action.

## Steels with bainite structure for railway wheels

Machines. Technologies. Materials., Vol. 14 (2020), Issue 5, pg(s) 215-218

Some wheel steels inclined for the self-quenching on bainite structure were produced and investigated after hot deformation and heat strengthening. Steels contained 0,12…0,45% of carbon, and also Si, Mn, Mo, Cr, Ni, V, Ti, Al. Steels with bainite structure after hot deformation and tempering were investigated. It was shown the possibility of the railway wheels production with bainite structure and hardness of 400HB without heat strengthening treatment. The results of investigation shown the possibility of railway wheels production with bainite structure, hardness of 400 HB and high complex of the mechanical and operating properties without heat strengthening treatment. These tasks solved owning to application of new wheel steels and up-to-date technology.

• ## Transformation of non-metallic inclusions “eutectics” in steels under laser action

Melting and crystallization of heterophase non-metallic inclusions ―eutectics‖ was investigated. Mechanism of melting of the eutectic inclusions and inclusion-matrix boundaries under contact laser melting with steel matrix in the conditions of abnormal mass transfer connecting with formation of zones with high dislocation density and also with electron and electro-magnetic interaction between inclusion and steel matrix was proposed. That allows to create the possibilities for the influence on the inclusion-matrix boundaries and also on the chemical and phase composition of surface layer of non-metallic inclusions. Peculiarities of structure of non-metallic inclusions after speed crystallization were investigated. It was shown that under laser action the initial composite colonial structure of inclusions transits into abnormal eutectic structure. Also it was shown that under laser action the initial structure of inclusion-steel matrix boundaries transits into unstable equilibrium high-energy condition that cause development of the dissipation processes connecting with aspiration of system inclusion-matrix to the state with minimum of the free energy. In the result of the system eutectic inclusion-matrix transits to the state of unstable equilibrium which determines structure and properties of laser-quenched interphase boundary. Processes of melting, fusion and dissolution of non-metallic inclusions ―eutectics‖ and also of the melting of steel matrix play the great role in transformation of interphase inclusion-matrix boundaries under laser action.

• ## Computer modeling of influence of previous deformation degree and strain rate on carbonitrides precipitation kinetics in low-carbon micro-alloyed steel

Using computer modelling with originally developed semi empirical physical grounded models a study was carried out to investigate influence of previous hot deformation on carbonitrides formation from austenite in low-carbon micro-alloyed steel. Studied in the article is an influence of degree and rate of the deformation on processes of nucleation and growth of Nb and Ti carbonitride particles. The model helps to predict not only process of changing in number and average size of the particles but also to estimate their final size distribution. One of additional peculiarities of the developed model is its ability to predict composition of the cabinetries formed in certain conditions. The model takes into account process of recrystallization and returning, which affect carbonitrides precipitation and are influenced by it. Acceleration was shown of both nucleation and growth rates of the particles due to increasing of deformation degree and strain rate. Another result is that previous deformation significantly affects size distribution function of the particles precipitated with rather lesser effect on their average size. Kinetic curves and final size distribution plots are given.

• ## Modelling and finite element analysis of tensile testing for the coated specimens

In this study, the stress state of metal coating on a steel substrate under tensile straining was investigated by with finite element modelling with the aim of better understanding the mechanism of delamination for the coating. The investigations showed cracking and delamination of the coating by the application of uniaxial tensile strain to the substrate. Due to interfacial stress crack appeared in the coating-substrate interface. The stress measurements in coated substrate, using FEA, indicated interfacial shear and peeling stresses at the interface near the edges of the coating under tensile load. When tensile stress is applied externally on the coated substrate, the coating exhibits multiple cracking perpendiculars to the tensile direction, and then interfacial debonding occurs. A good agreement is found between the modelling approach and the corresponding experimental tensile tests of the coated specimens. The effect of coating thickness on the evolution of the stress distribution was also studied. The cracking and delamination of the coatings with a thickness ranging from 90 to 160 m was studied by tensile test experiments. The estimation of the stress distribution and concentration at the interface during these experiments allows the failure stress of the coating in the interface coating–substrate to be evaluated.