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.

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.

Comparative analysis of qualitative characteristics for high-carbon steel 70 (1.1231according to DIN) rolled wire produced by OJSC “Moldova Steel Works” under Specifications of Ukraine 27.14-519-2002 and by company Lucchini Piombino (Italy) under Specification 6034-2 corresponding to EN 10016 was performed. We have developed the production technique of rope wire with diameter 2.20 mm by drawing with no heat treatment (patenting). Effect of qualitative characteristics of high-carbon steel 70 rolled wire on final properties of rope wire and its compliance with European requirements was determined.

The characteristic features of structure formation and changes of hardness on the section of hot-rolled large-sized quality rolled metal are explored, from the continuous cast carbon chromium-molybdenum electro-steel by the diameter of 140 mm. It is set, that at disintegration of overcooled austenite the temperature of formation of bainite is higher, than pearlite, that is confirmed by the values of micro-hardness. In a hot-rolled metal the flakes is not found out, and values of hardness meet of to the required level, therefore heat treatment is needed. Thermo-mechanical treatment effect on hardness of rolled chromium-molybdenum steel is shown.