Rebars and coiled bar have a tendency to softening over time. After holding at the room temperature the ductility of the rolled products can be partially restored due to the processes of return and relaxation and also deposition of the diffusion-movable hydrogen from the steel. The reverse hydrogen brittleness and ageing are often observed, during production of the thermally strengthening rolled products. The variability of the mechanical properties of rebars and coiled bar of 25G2S, С70D and С82D steels with different diameters has been studied. It has been shown that tendency to softening is decreases during increasing of the strength class of the rebars (steel 25G2S) and it is related to deposition of the hydrogen in different quantities. Dynamics of increase of specific elongation for rebars turns out to be maximum in the first 30 days and growing rapidly (till 4,0…4,5 % abs.) over 90...120 days, then stabilizes and practically does not change over time. After use of the accelerated cooling at the final stage of the deformation heat treatment of the coiled bar of С70D high carbon steel the variability of specific elongation and reduction of area are characterized by a significant increase of ductility indexes within 3 days after primary testing. By research of variability of mechanical properties of coiled bar of С82D steel was established that during initial testing of samples (immediately after rolling) were recorded a low values of specific elongation and reduction of area (7,6…8,4 % and 15…24 % respectively) and while the progress of embrittlement have a tends to growth with increasing diameter. After holding of the coiled bar within 48...72 hours the parameters of the ductility for all diameters of rolled products are grow to 30...34% and stabilize over time. It has been shown that variability of the mechanical properties have a direct relations with the parameters of the structure, the initial hydrogen content in the steel and with degree of deformation processing of blank continuous casting.

Problem statement. The production of various metal products using hot plastic deformation or heat treatment is inevitably linked to the processes of oxidation of steel because of its interaction with the air or atmosphere of the furnace. At the same time, changes occur in the chemical composition of the surface metal layer, the formation of oxides (scale), the transformation of their phase composition during the processing, which, in turn, depends on the temperature, speed and method of cooling the metal.The most widespread type of metal products, for which the scale is standardized not only by the requirements of the relevant standards, but also has a significant impact on the process of subsequent processing, is wire rod. The carbon steel scale, formed at high temperatures, consists of three oxides (FeO, Fe3O4 and Fe2O3), the actual content of which affects the formation of various density, and, consequently, different specific mass of scale with the same thickness of its layer on the rolled surface. In view of the fact that the known methods for determining the specific mass of the scale are rather laborious and require appropriate qualifications of technical personnel, there is a need to develop a universal method for qualitative and quantitative assessment of oxides formed on the surface of carbon steel, depending on changes in the technological parameters of production. Purpose. Development of a method for determining the specific mass or thickness of the scale layer formed on the surface of a wire rod of various diameters, with its actual chemical composition. Results. Based on the known chemical and physical patterns of processes occurring during high-temperature interaction of the surface of carbon steels and atmospheric air, a universal mathematical model has been developed that allows to elaborate one of the standardized quality indicators and it can be recommended as an alternative method for determining the specific mass or thickness of the scale on the surface wire rod in the research laboratories of metallurgical enterprises.

Problem statement. Ingots and continuous cast billets are hot deformed when the steel is in the austenitic state. The temperature range of steel deformation in industrial conditions is quite diverse (1 080…1 200 °C). For each steel the heating temperature is determined taking into account its chemical composition and propensity to grow austenitic grains. Plastic deformation of metals and alloys in the austenitic state is accompanied by two competing processes: an increase of the density of dislocations, which causes the hardening, and rebuilding of the microstructure and substructure (dynamic softening). In the intervals between reductions the steel partially restores its structure, therefore the formation of the final microstructure is the result of the total number of reductions at different temperatures and pauses between them, that is, it depends on static and dynamic processes. Purpose. To establish the peculiarities of the influence of the parameters of post-deformation heat treatment and the chemical composition of carbon steel on the formation of the size of pearlite grains in the structure of rolled products. Results. The established specific features of the influence of post- deformation heat treatment parameters and chemical composition indicate that when the air cooling temperature is decreased for high carbon steel C82DV, along with dispersion hardening, grain-boundary hardening can develop, which is caused not only by the release of carbides or nitrides, but also by slowing down the recrystallization processes. At the same time, when steel C82DCr is doping with chromium in an amount up to 0.27 %, hardening occurs due to the solid-solution mechanism (carbides and chromium nitrides are not detected). It is shown that the study of the features of the formation of the grain structure and mechanical properties of high carbon steels, including those doped with carbide-forming elements (vanadium and / or chromium), should be carried out from temperatures of at least 1 040 °C, at which the barrier mechanism does not significantly affect the migration of austenite grain boundaries and the formation of austenite structure before the start of continuous air cooling of wire rod.

Based on mathematical and physicochemical modeling a studied the effect of alloying elements (chromium, molybdenum, vanadium) in the formation of the mechanical properties of steel. The intervals of the content of alloying elements that ensure the fulfillment of the required norms are determined. Dependences of the change in the mechanical properties of doped rolled steel from the index of the structural state d are constructed.

The aim of the work is to determine the content intervals of alloying elements in structural alloyed steels, which ensure the obtaining of mechanical properties and the conformity of rolled products to the requirements of European standards. The studies were conducted using a predictive model developed by the Iron and Steel Institute of the National Academy of Sciences of Ukraine, taking into account the full chemical composition of the steel. The regularities of changes in the interatomic interaction parameter on the number of alloying elements in the steel composition and its relationship with mechanical properties are revealed. The dependences of mechanical properties (tensile strength, relative elongation) on the chemical composition of steel are constructed through the physicochemical criterion – the average statistical distance between interacting atoms (structural parameter d). The interrelation between the chemical composition and mechanical properties of chrome-molybdenum structural steels has been established. It is shown that increasing the chromium content increases the tensile strength, and doping with molybdenum and vanadium increases the ductility of rolled products. It was determined that in order to guarantee compliance with the requirements of the ultimate strength (900-1100 MPa) and relative elongation (> 11%) for steel 31CrMoV9, the content of alloying elements should correspond to the following intervals: 2.42-2.62%Cr, 0.2-0, 23%Mo and 0.17-0.20%V. The results obtained make it possible to predict the mechanical properties of doped steel, depending on the actual chemical composition of the steel.

Formulation of the problem. Modern trends in the construction industry make this industry one of the main consumers of high-strength cold-deformed steel products. The high requirements imposed on the strength classes of such reinforcement (1 670, 1 770, 1 860 and 2 000 MPa) necessitate the use of rutile rolled products with a carbon content of 0,8...0,9 % in diameter 8,0...14,0 mm with the value of the temporary rupture resistance is not less than 1 150 MPa and a high level of plastic indicators (δ10 ≥ 10 %, y ≥ 30 %). In practice, when cooling is rolled with an increase in its diameter, the effect of the scale factor is manifested – the actual cooling rate is reduced, and in order to achieve the required structural state of steel, it is necessary to search for reserve possibilities for increasing the stability of the supercooled austenite and adapting the cooling rates to the operating conditions of the operating Purpose. Investigation of the influence of the heating temperature on the stability of austenite and the change the kinetics of decomposition of high-carbon vanadium-containing steel under continuous cooling with different rates. Results. The features of the kinetics of the decomposition of austenite and the regularities in the formation of the structure of vanadium-containing steel С82DV heated to a temperature of 1 040 °C and subjected to continuous cooling at various rates have been studied. Heating of С82DV steel to a temperature of 1 040 °C allows us to somewhat lower the temperature of the onset of the diffusion decomposition of austenite (Аr1), as a result of which the degree of dispersion of perlite increases, and the actual cooling rate increases with all other conditions being equal. The most rational intervals of air cooling rates for С82DV steel are established, which allow to ensure formation of at least 90 % of sorbitol-like perlite in the structure of steel, exclude the appearance of secondary cementite, and also structures formed by intermediate and shear mechanisms.

Influence of austenitization temperature of chrome-molybdenum-vanadium steel on structure formation at the softening heat treatment is studied. It is shown that the decline of the austenitization temperature promotes to reduce the micro-hardness values due to the intensification of spheroidizing of pearlite after the overcooling and high tempering. Increasing the austenitization temperature leads to formation of an uneven structure after tempering.

Influence of austenitization temperature of chrome-molybdenum-vanadium steel on structure formation at the softening heat treatment is studied. It is shown that the decline of the austenitization temperature promotes to reduce the micro-hardness values due to the intensification of spheroidizing of pearlite after the overcooling and high tempering. Increasing the austenitization temperature leads to formation of an uneven structure after tempering.

The impact of the austenite grain growth of chromo-molybdenum steel on the kinetics of structural decomposition under continuous cooling was studied. It is shown that when the grain is enlarged with an increase in the austenitization temperature from 850 till 1050 °C, the stability of the supercooled austenite in the structure of the chromo-molybdenum steel during the decay process by the intermediate and shear mechanism increases, which contributes to a decrease in the critical quenching rate.

Influence of austenite grain size of chrome-molybdenum-vanadium steel on formation of structure at continuous cooling has been studied. It is shown, that at the coarsen of grain with increasing temperature of austenitization from 850 till 1050°С stability of the supercooled austenite in structure of chrome-molybdenum-vanadium steel is increased, that is promoted decrease in critical quenching rate.

The correlation of mechanical hardening to the degree of dispersion of the perlite (interlamellar spacings) and strength indices of rolled steel diameter of 6.5 mm made of steel grade C72D is showed. Using the method of hydrostatic weighing and X-ray analysis it was established that to increase the degree of the deformability of high-carbon rolled during hardware production is the most preferred way is high-temperature unscramble of rolled coils with following process of controlled accelerated air cooling. The results of the research could serve as a basis for the creation of an additional process of assessing the quality of cold wire by non-destructive testing.

Influence of austenite grain size of chrome-molybdenum-vanadium steel on formation of structure at continuous cooling has been studied. It is shown, that at the coarsen of grain with increasing temperature of austenitization from 850 till 1050 ° С stability of the supercooled austenite in structure of chrome-molybdenum-vanadium steel is increased, that is promoted decrease in critical quenching rate.

Austenitizing studied the effect of temperature on austenite grain size of the chrome-molybdenum-vanadium steel. It is shown that at austenitizing 850–1050ºS in the structure of chrome-molybdenum-vanadium steel nominal diameter of austenite grain varies from 0,063 to 0,084 mm.

The correlation of mechanical hardening to the degree of dispersion of the perlite (interlamellar spacings) and strength indices of rolled steel diameter of 6.5 mm made of steel grade C72D is showed. Using the method of hydrostatic weighing and X-ray analysis it was established that to increase the degree of the deformability of high-carbon rolled during hardware production is the most preferred way is high-temperature unscramble of rolled coils with following process of controlled accelerated air cooling. The results of the research could serve as a basis for the creation of an additional process of assessing the quality of cold wire by non-destructive testing.

It is shown that after thermo-mechanical processing of chrome-molybdenic rolled metal including cooling with a speed of 0,6-0,8 ° C / sec, the quantity of bainite increases to 75% and the amount of lamellar pearlite decreases to 5-10% in structure that promotes reduction of the mode of subsequent softening processing. It is established that at cooling with a specified speed the transformations in chrome-molybdenic steel come to an end at temperatures of 350-370 ° C. The offered technology of the reduced mode of thermomechanical processing provides necessary quality of rolled metal and promotes decrease of energy resources consumption.

On the basis of the drawn card of the hardness values distribution according to the temperature and time parameters of heat treatment of chrome-molybdenic steel it is revealed that required values of hardness are reached at 680–650 °C within 4 hours. It is shown that decrease of hardness occurs due to large quantity of carbides which have changed their morphology.