Vol 47, No 9 (2017)

Electron-microscope data show that the magnetite crystals in iron ore have different microstructure, depending on the temperature and time of ore formation. Thus, in sedimentary–metamorphic iron quartzites and magmatic skarns, the structure of the magnetite crystals is homogeneous and the composition is close to stoichiometric. In Kovdor ore, the magnetite crystals are heterogeneous. The matrix contains isomorphic Al, Mg, Ti, and other impurities as individual spinel microphases. The reduction of magnetite crystals in conditions that resemble sintering indicates that heterogeneous crystals disintegrate on sintering, with the formation of two ore phases: solid solutions of magnetite and wustite that are not involved in liquid-phase strengthening of the sinter. In the final stage of fluxed-sinter production, calcium–silicon silicate binders of melilite composition are formed in the product in place of the melt; these binders are not strong. On the basis of the research findings, it is important, in assessing iron-ore fields, to pay attention not only to the content of iron and silicon oxides in the ore but also to the structure of the magnetite crystals, since the iron in the magnetite determines the direction of melt formation in processing.

The deformability of steel grades with different strength is analyzed, from the perspective that deformation is dissipative in thermodynamic terms: some of the kinetic energy of the external mechanical perturbation is converted to internal energy of the metal being deformed, with the creation of particular dislocational structure. Accordingly, energy criteria are proposed for the deformability of steel. These criteria may be determined in standard tensile tests. They are based on the work of deformation, which is determined by the area of the extension diagram. The absorbed energy determines the work of deformation, while the rate of energy absorption determines the resistance of the steel to deformation (the pliability in plastic deformation). The energy dissipation is quantitatively estimated, with comparison of the unit work and the pliability. The research is based on standard tensile tests of samples made from steels that differ in strength as a result of alloying (changes in chemical composition) and heat treatment and are used for different purposes. The steels vary in yield point from 210 to 1660 MPa and in strength from 840 to 1940 MPa. The unit work of point deformation is found to exceed the unit work of uniform deformation by an order of magnitude. The pliability in point deformation is markedly less than the pliability in uniform deformation. A clear correlation between these quantities is noted. This may be regarded as the expression of the structural evolution of the metal at both stages of deformation. In particular, in self-organization of the dissipative system—that is, the deformable steel—the dislocation density acts as an internal parameter regulating the evolutionary transformations. A correlation is established between the pliability criteria and the limiting loads in uniform deformation and failure. Thus, steels that differ in strength may be ranked in terms of the energy absorbed in deformation. In practice, the numerical values of the unit work and the pliability may be used to predict the behavior of structural steels belonging to different steel classes under mechanical perturbations in the course of operation and machining.

HSC 6.1 Chemistry software (Outokumpu) and a simplex–lattice experiment design are employed in thermodynamic modeling of the equilibrium boron distribution between steel containing 0.2% C, 0.35% Si, and 0.028% Al (wt % are used throughout) and CaO–SiO₂–Al₂)₃–8% MgO–4% B₂O₃ slag over a broad range of chemical composition at 1550 and 1600°C. For each temperature, mathematical models (in the form of a reduced third-order polynomial) are obtained for the equilibrium boron distribution between the slag and the molten metal as a function of the slag composition. The results of simulation are presented as graphs of the composition and equilibrium distribution of boron. The slag basicity has considerable influence on the distribution coefficient of boron. For example, increase in slag basicity from 5 to 8 at 1550°C decreases the boron distribution coefficient from 160 to 120 and hence increases the boron content in the metal from 0.021% when L_B = 159 to 0.026% when L_B = 121. In other words, increase in slag basicity favorably affects the reduction of boron. Within the given range of chemical composition, the positive influence of the slag basicity on the reduction of boron may be explained in terms of the phase composition of the slag and the thermodynamics of boron reduction. Increase in metal temperature impairs the reduction of boron. With increase in temperature to 1600°C, the equilibrium distribution coefficient of boron increases by 10, on average. On the diagrams, we see regions of slag composition with 53–58% CaO, 8.5–10.5% SiO₂, and 20–27% Al₂O₃ corresponding to boron distribution coefficients of 140–170 at 1550 and 1600°C. Within those regions, when the initial slag contains 4% B₂O₃, we may expect boron concentrations in the metal of 0.020% when L_B = 168 and 0.023% when L_B = 139.

In selecting the best chemical composition of slag melts, it is expedient to take account of their viscosity and electrical conductivity, which are structure-sensitive properties. The viscosity and electrical conductivity of blast-furnace slag are studied experimentally. To permit correct selection of the slag conditions in the blast furnace, a parameter is proposed for assessing the relation between the structural particles of the melt: the heterogenization temperature, which takes account of the viscosity and electrical conductivity of the slag melts. The discharge temperature of the slag from blast furnace 8 at PJSC ArcelorMittal Kryvyi Rih is measured. Comparison of the actual discharge temperature of the slag and the calculated heterogenization temperature for blast furnace 8 permits identification of the optimal slag basicity (CaO/SiO₂).

Samples reduced by ferrosilicoalumobarium and by a traditional ferroalloy are compared. In reduction by ferrosilicoalumobarium, the quality of the steel is improved; the residual oxygen content declines; and the mechanical properties are improved.

The industrial production of low-carbon microalloyed steel plates (thickness 150–200 mm) on the NLMK Dansteel 420 reversible rolling mill is considered. Such plates are intended for operation at temperatures between–50 and +450°C in high-pressure equipment. The technologies used for steel casting and thick-sheet production ensure stable strength over the whole sheet thickness at 20–450°C, with satisfactory impact strength between +40 and–50°C. The research results are used in certification on the basis of TUV Pressure Equipment Directive (PED) DGR 2014/68/EU and the AD2000 directive regarding the production of rolled P355N, P355NH, P355NL1, and P355NL2 steel sheet of thickness up to 200 mm.