The article presents the results of research on the development and mastery of the technological process of rolling reinforcement in coils with a nominal diameter of 6 mm of strength class A500C of a double‑sided periodic profile of the 2f form, ensuring the required mechanical properties, improving complex quality indicators based on improving the chemical composition and technological modes of two‑stage cooling on the Stelmor line taking into account its cooling and transporting abilities. A method of hot rolling of reinforcement with a double‑sided crescent (2f) profile is proposed; technological factors influencing the strength, plastic and operational properties of reinforcing bars through the formation of its effective microstructure are considered. The chemical composition of steel was proposed and modes of thermomechanical hardening of reinforcement with rolling heating were developed, providing high consumer properties. The results of mechanical tests of rolled reinforcing bars in coils and comparative data on the mechanical properties and geometric parameters of the reinforcement are also presented.

The article presents the results of the study of the effect of the initial metal microstructure in the surface layer of bunched rolling at the existing technology of rolling in the low-temperature range from bearing steel grades ШХ15 on the formation of decarburized layer after spheroidizing annealing. To meet the customer’s requirements for the metal quality, some studies of the microstructure of the subsurface zone of coiled steel have been carried out. There is a description of the developed process for cooling coiled steel made of bearing steel on an air-cooled roller table for wire rod. The effect of temperature-speed modes of coiled steel cooling on the size of the decarburized layer after spheroidizing annealing has been determined. The microstructure of coiled steel samples with a diameter of 16.5 mm, rolled according to the standard and experimental modes, as well as after spheroidizing annealing, has been studied. The causes of incomplete spheroidization of coiled steel in the subsurface layer have been revealed. The microstructure of hot-rolled samples rolled according to standard conditions has been evaluated and the effect of pearlite dispersion in the subsurface layer, which leads to overestimated values of the depth of the decarburized layer after spheroidizing annealing, has been established. An effective mode of cooling of coiled steel made of a bearing steel grade for subsequent spheroidizing annealing has been determined, which ensures the minimization of the decarburized layer and the uniformity of the microstructure along the entire coil length. The experimental mode, which consists in shifting the initial cooling temperature (in the laying coiler zone) by 30 °C, to the temperature range of 840‒860 °C, with 4 fans involved and the switching-on power of 30%, allowed to obtain a uniform structure in the surface zone (subsurface), both in the hot-rolled state (sorbite-like, fine-lamellar perlite) and in the annealed state (spheroidized), as well as to determine directions of further improvement of the technology

Welded joints are subject to increased requirements for structural condition, as well as a complex of mechanical and special properties. A promising way to regulate the structure of the deposited metal directly in the welding process is its inoculation with ultrafine refractory components. This article presents the results of a study of the structure and mechanical properties of metal deposited with electrodes with basic and rutile coatings containing 5% ultrafine titanium monocarbide powder. It is shown that the addition of ultrafine TIC powder to the electrode coating of the basic type leads to a decrease in the average cross-sectional area of crystallites in the deposited metal by 5 times, from 73000 - 74000 μm2 to 14,000 - 15,000 μm2 and an increase in the shape factor by 1,5 times, from 0,27 to 0,46. The addition of TiC to the rutile-type electrode coating leads to a decrease in the average cross-sectional area of crystallites in the deposited metal by 12-13 times, from 163000 - 164000 μm2 to 11000 to 12000 μm2 and an increase in the shape factor by 2 times, from 0,28 to 0,57. It is established that the effect of inoculation is manifested when using both basic-type coatings and rutile-type coatings. This is due to the fact that the viscosity of liquid welding slags in the crystallization temperature range of a steel welding bath is at the same level of 0,15 – 0,2 Pa·s, and remains so in the flesh up to temperatures of 1325 - 1350 °С, both for basic and rutile slag systems, and equally affects the process of assimilation of ultrafine refractory particles by the metal of the welding bath. It is shown that, despite the inoculation of the metal of the welding bath with refractory particles and the realization of the effect of volumetric crystallization, the final shape of the crystallites depends on the temperature gradient when the heat of the bath is removed into the base metal.The work was carried out within the framework of state support for young Russian scientists — grant of the President of the Russian Federation (No. MK-3849.2021.4).

The work is devoted to the research of cracks causes in welded joints of high­strength steel for arctic purposes based on the study of the structure and mechanical properties of the weld metal and the zone of thermal influence. Consumers of machine­building products make increasingly high demands on welded joints of metal structures. This necessitates the use of rolled steels for their production, which have increased mechanical and special properties. When welding MAGSTRONG W700 type steels, cracks are observed in local sections of welded joints. It was established that the structure of the weld metal of welded joints of MAGSTRONG W700 steel is characterized by the presence of columnar crystals with a hardness of 312 – 323 HV. The metal structure in the overheating area of thermal influence zone is characterized by the presence of enlarged primary grain, as well as batch formations of bainite and bainite-martensite with hardness of 338 – 352 HV. The level of temporary resistance to rupture of the metal in thermal influence zone is 618 – 627 MPa. Depending on the test temperature, values of the impact strength of the metal in thermal influence zone vary from 62 to 86 J/cm2. MAGSTRONG W700 steel has good resistance to the formation of hot cracks during welding (UCS = 20,3), however, it has an increased tendency to form cold cracks (CE = 0,48). Analysis of the data obtained showed that destruction of welded joints of the studied steel occurs due to its unsatisfactory weldability. Such weldability is due to a complex chemical composition, as well as a whole set of factors (such as the formation of unfavorable structures in the metal of welded joints under the influence of thermal welding cycles, a complex picture of welding stresses, the level of which exceeds the temporary resistance to metal rupture). Also, the structure of the weld metal has a large­crystalline structure, which significantly weakens the connection.

In the manufacture of welded reinforcing mesh, rolled products of various strength classes are used. High requirements for mechanical properties and structural condition are imposed on welded joints. Connections must provide a set of operational properties. This article presents the results of studies of the structure and mechanical properties of welded joints of reinforced rolled products of strength classes A500C and B500C, performed by spot welding. It is established that the weld (core) of A500C strength class steel is characterized by the presence of a layer of cast metal (hardness 180–190 HV) with slag inclusions. In the heat-affected zone, widmanstett ferrite and bainite — like structures with a hardness of 251–268 HV are observed. The temporary breaking resistance of A500C steel joints is 322–350 MPa. It is shown that the welded joint of steel of strength class B500C does not have a clear division into structural zones. Similar bainite structures in the form of batch formations are observed in the seam and the heat-affected zone. The hardness of the metal of the welded joint is in the range from 205 to 241 HV, and the level of temporary resistance is 510–525 MPa. It is established that the probable cause of premature failure of welded joints of A500C steel is the presence of large slag formations in the metal seam (core). This may be due to insufficient cleaning and preparation of the weld site. Particles of scale and other contaminants fall into the molten metal of the core and "freeze" in it, forming slag inclusions. Cavities filled with slag reduce the cross-section of the seam and as a result significantly weaken it. In addition, slag inclusions are additional stress concentrators and act as a source of destruction when an external load is applied. For the manufacturer of reinforcing nets, it is proposed, as a technological recommendation, to use additional tools for cleaning the welding site in the form of metal brushes or abrasive tools with additional surface degreasing.

Metal processing in ladle by calcium-containing cored wires is one of the most spread methods of ladle treatment and modifying. Results of analysis of efficiency induces of existing cored wires application depending on their diameter, wall thickness and filling coefficient presented. It was shown that the basic efficiency index of a cored wire application – recovery coefficient – depending on wire quality (homogeneity of filling by calcium along the wire length), wire grade, conditions of its injection into liquid steel and other parameters can vary within a range from 50 to 95%. Reasons of unsatisfactory calcium recovery at usage of calcium-containing wires of 14–15 mm diameter with steel shell 0.4 mm thick and filling of mechanical mixture of steel shots and metallic calcium in various proportions was considered. Advantages of the modern calcium-containing cored wire with thicker wall were highlighted, including their higher wire rigidity and stability of its supply by a wire feeder into liquid steel. It was established that calcium content in a cored wire at the level of 100 g/m was the most effective composition. It was noted that increase of speed of cored wire feeding into steel will result in an increase of calcium recovery and in a decrease of probability of metal splashing out the steel ladle.

The article provides an analysis of methods for strengthening structural shapes in a stream of section mills, a series of active experiments was carried out, and a calculation of predictive regression equations for the dependence of mechanical properties and microstructure indicators on the geometry of profile dimensions and technological parameters of cooling. An algorithm has been developed for iterative refinement of the forecast accuracy using such equations, which provides the minimum error in determining the specified characteristics. Metal microstructure at various modes of accelerated cooling in calm water of shaped rolled in the flow of a section mill confirms the patterns of structure formation and corresponds to the theory and practice of science of metals and heat treatment of metals. The developed techno logy of accelerated water cooling provides for shaped rolling increase in strength to a class of 600 MPa and higher for a wide assortment of structural shapes and for critical purposes for pipe and ship-car building. The use of accelerated cooling in calm water of shaped rolled gives a significant economic effect (80-100 USD per 1 ton of rolled steel) instead of using microalloying steel with elements such as vanadium and niobium, which reduce the size of the austenitic and then the real grain of the metal and thereby increase the yild point and its relation to the ultimate tensile strength, providing substantial strengthening of rolled products. As a result, an efficient technology have been developed for thermal hardening of structural shapes in the flow of a section mill.

Surface defects of sheet rolled products have a significant impact on its quality, performance and further processing of products, for example, on application of a protective anticorrosive coating. Therefore, the elimination of such defects and their accurate identification is an important aspect of sheet rolling production. Reducing the rejection of metal for surface defects enables to get a significant technical and economic effect. Investigation of the causes of defectiveness of the surface of sheet rolled products will make it possible to determine the source of the appearance of the defects and methods to prevent them. Determination of the nature and morphology of surface defects, the sources of which being metallic and non-metallic inclusions, as well as remnants of slag surface layer, scales from metallurgical and rolling stages, rolled into the surface of a hot-rolled sheet, is often difficult, since the appearance of the defects is very similar. It was shown that application of a scanning electron microscope (SEM) with micro-X-ray spectral analysis (MXSA), thermodynamic analysis makes it possible to determine the chemical composition of micro-areas and associate it with the end-to-end technology of sheet production. The article presents the results of identifying surface defects of cold-rolled sheet steel.

The results of self-protective powder wire with diameter of 1.6 mm are presented. The working purpose is to create small-section powder wire and its manufacturing technology, designed for automatic welding of the root layer of the seam of non-rotating joints of main pipe-lines transporting oil and gas with admixture of hydrogen sulfi de, and providing increase of at least 1.5 times the productivity of pipe welding. The forming rollers for the initial billet with diameter of 2.4 mm of two-bend powder wire are developed. The composition of the charge fl uxcored wire, providing the requirements of product development: reliable penetration of the root layer of the seam fi xed joints of pipe-lines with tensile strength of the weld metal at 490 MPa. Recommendations on the production technology of self-protective powder wire of two-bend design are developed.

The results of petrographic studies of the welding slags of electrodes UONI-13/55, Philips 27P, OZS-4, and VSTs-4 are presented. These electrodes are found to form welding slags having various phase compositions and morphologies. The phase compositions of the slags are shown to affect the physical properties of their melts, in particular, viscosity. The data obtained in the work are necessary for the development of new advanced grades of electrodes for welding and surfacing.

The article presents the reasons of strength reduction of welded joints of reinforcing bars of A500C strength class. The joints were made of reinforcing steel with a diameter of 12 mm, with one of the joints made of thermomechanical hardened steel (sample 1 ), and the other – of hot-rolled steel without further processing (sample 2 ). It was established that the structure of welded joint 1 is characterized by the presence of products of tempering of martensite – martensite-bainite structure with hardness of 327 – 339 HV. Characteristic needle and packet formations are observed. The weld metal (core) has a structure identical to the structure of heat-affected zone on the overheating area. The structure of welded joint 2 is represented by more expressed zoning. The boundary is traced between the weld metal (core) and the heat-affected zone. In plane of the section, the cast core is observed as a thin light layer of 30 – 40 microns thickness and with hardness of 180 – 190 HV; it consists of ferrite, not fully subjected to post-welding heat treatment. Also slag inclusions present in all volume of the welded joint metal. In the heat affected zone, in the area of overheating the widmanstatten bainitic structure is also observed. Metal hardness of the heat-affected zone is at the level of 250 – 265 HV. The most likely reasons for the reduced strength of welded joints are increased fragility of the weld metal and the zone of thermal influence, due to the high hardness, more than 300 HV, as well as the presence of slag inclusions in the weld metal of the joint (core), which act as stress concentrators and under external loads are a source of destruction.

Defects of metallurgy-originated steel (sub-cored bubbles, impurities, macro- and micro-segregations of chemical elements, nonmetallic inclusions) to a large extent determines the faultiness of metal rolled products. The processes of chemical elements segregation in steel macro- and micro volumes considerably influence its quality. Reasons of microphysical dendrite segregation originating in steels of welding purpose of Св-09Г2С and Св-08ГНМ type considered. Mechanism of dendrites formation studied as well as the segregation degree of chemical elements along the continuously casted billet cross section. To estimate the segregation degree a criteria was used – the segregation coefficient, determined as relation of chemical elements mass shares in different micro-areas (dendrites, inter-dendrite gaps) of continuously casted billet cross section to those elements content by a ladle analysis of a heat or one another in different micro-areas. A heredity of segregation transfer from CC billet to finished wire rod of Св-08Г2С and Св-08ГНМ steels studied. It was determined, that decrease of the number of bainite-martensite areas as a result of decrease of dendrite segregation of chemical elements takes place by minimization within grade chemical composition of both main alloying element and impurities ones. Besides an additional alloying of steel by boron takes place based on boron to nitrogen relation at the level of B/N = 0,8±0,15. It was shown that to decrease the inter-dendrite segregation it is necessary to elaborate and implement effective steel modifying by calcium and REMs regimes as well as electro-magnetic stirring during continuous casting.

The structural transformation of thin-plate pearlite in the cold plastic deformation (drawing) of C86D steel coils with total reduction up to 83.2% is considered. In terms of the physical mesomechanics of structurally heterogeneous media, it is shown that the ferrite–cementite phase boundaries play a significant role in the localization of the deformation and the formation of fragmented mesostructure at different degrees of cold plastic deformation. The transformation of cementite in cold dynamic spheroidization is shown to be associated with the fragmentation of plates and the formation of local submicrocrystalline sections in the pearlite.

For a coil of rolled C86D steel subjected to accelerated continuous cooling from the hot-deformation temperatures, change in austenite grain size by scores no greater than 1–2 according to State Standard GOST 5639–82 has no significant influence on the impact strength. For C86D steel, the impact strength is directly related to the extent of the ferrite–cementite phase boundaries: the impact strength increases with increase in the boundary length. These results are of practical interest in developing new alloys and conditions of deformation and heat treatment for high-strength pearlitic steels.

The comparative analysis of regularities of phase-structural transformations at high-temperature thermal processing in complex doped alloy of a transitive class ofsystem Fe-Mn-Cr-Ti-V-C is given.

The development of corrosive damage in bearing steels close to nonmetallic inclusions is analyzed. The influence of the chemical and mineralogical composition of the inclusions on their activity in corrosive media is studied.

Statement of problem (relevance): the paper describes the problem of structure formation in welding low-carbon low-alloy steels. The weld metal structure forms in a complex thermal environment that predetermines the operating performance of the metal. Emergence of large columnar crystals in welds poses a potential hazard, as such structures may under certain conditions concentrate the tension and trigger destruction. The paper dwells upon the possibility of controlling the primary structure of welded metal by injecting nano- and ultrafine particles of a refractory material into the weld pool. The objective is to study how nano- and ultrafine particles of tungsten monocarbide WC) affect the structure of welded metal. Methods used: the researchers have carried out a laboratory experiment consisting in making electrodes with a coating containing a varying amount of ultrafine WC powder, then making welded-metal samples and studying the samples by optical microscopy (a Micromed-Met microscope) as well as measuring the Vickers hardness (a HV-1000 device). The novelty of this research consists in gathering new data on how the concentration of ultrafine WC powder in the electrode coating affects the structure of welded metal. The results: the structure of metal welded by electrodes with a coating containing 0, 0.02, or 0.2 % of WC powder (% of drymix weight) features columnar crystals surrounded by a grid of peripheral ferrite formed along the primary-grain boundaries. Needle-like inclusions of Widmanstätten ferrite sprouting from the crystal edges to the crystal center are observed along with bainitic structures. Electrodes with a coating containing 0.4% of WC powder produce welded metal of a finer cellular structure in the form of equiaxed crystals. The hardness of the welded-metal samples is within 184 to 189 HV. Practical significance: the research has produced data necessary for creating new coated electrodes for welding and surfacing low-carbon low-alloy steels.