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The aim of the work is to study the non-uniformity of mechanical properties in the cross section of continuously cast billets of various manufacturers in Ukraine. Mechanical properties were determined by the method of measuring Brinell hardness. Mathematical relationships were developed to describe them and determine the need to take this factor into account when calculating the stress-strain state of blanks. It is established that the hardness of the surface layer of blanks, as a rule, is higher than the central zone by 0.5-7.6%. This is due to the smaller and dense dendritic structure of the surface layers. The biggest difference is observed in workpieces with a thickness of 410 mm made of steel grade 20. In workpieces made of steel grade 45, the difference in hardness of the surface layer and the central zone is 0.5-4.7% and practically does not depend on the thickness of the workpiece in the investigated interval (135-350 mm). It is shown that in the study of the stress-strain state of the metal when rolling continuously cast billets of low-carbon steels, it is advisable to take into account the uneven distribution of mechanical properties over the cross section. For medium carbon steel blanks, this factor is optional. On the basis of literature data and the results of experimental studies performed, dependencies describing the change in strength and plastic properties in the cross section of continuously cast billets of low carbon steels are proposed. These dependencies should be used in the calculation of the stress-strain state of the metal. For medium-carbon steel blanks, this factor is optional.

The aim of this work is to study modern methods of production of corrosion-resistant and fire-resistant stress-free reinforcing bars in the world. Non-stressed reinforcing bars are used as working, structural and assembly reinforcement in conventional building structures, as well as in various types of prestressed structures: from openwork prefabricated to huge monolithic hydraulic structures, therefore, its assortment produced by the domestic metallurgical industry in the range from 5,5 to 40 mm in the nominal diameter of a smooth profile and from 6,0 to 40 mm for a periodic profile. Recently, in the world, much attention is paid to the design and construction of buildings and structures with an improved complex of consumer properties, intended, in particular, for work in corrosive and fire hazardous environments. Such developments are not currently being conducted in Ukraine. In the world and in Europe, to increase corrosion resistance and fire resistance, as well as for the manufacture of seismically resistant reinforcing bars (δmax≥7,5 %), hot-rolled low-alloyed (additionally alloyed with V and Mo) and microalloyed steel grades without the use of heat treatment or cold-deformed (cоld stretched) from hot rolled strip of periodic profile. In GOST 34028-2016 for the countries of the Customs Union, it is clearly stated that for the reinforcement of prefabricated reinforced concrete structures and monolithic reinforced concrete, unstressed reinforcing bars in bars or coils with a nominal diameter of 4,0 to 40 mm are also used for the production of such rolled products, low-carbon and low-alloy steel grades are used, which microalloy V, Nb, Mo or add nitride-forming elements Al, Ti, V, Nb. In this case, either hot rolling or cold deformation or heat treatment in the flow of the rolling mill is used. An alternative way of producing corrosion-resistant and fire-resistant stress-free reinforcing bars in the world is the use of stainless steel as a material. Such profiled reinforcing bars are produced in the range of 3,0 to 50 mm by hot rolling or cold deformation. The use of modern technologies for the production of stainless steel reinforcing bars, starting with the addition of effective and high-quality alloying elements and additives in the production of liquid steel and effective methods of metal pressure treatment, which allows us to guarantee the material saving from corrosion and high temperatures in case of fire. A significant disadvantage of this rolled product is its rather high cost.

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