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This paper proposes a comparative study on the microstructure and photocatalytic performances of titanium dioxide coatings elaborated by various thermal spraying methods (plasma spraying in atmospheric conditions, suspension plasma spraying, and high-velocity oxyfuel spraying). Agglomerated spray dried anatase TiO 2 powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were studied mainly by scanning electron microscopy and x-ray diffraction. The photocatalytic behavior of the TiO 2 -base surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure depended strongly on the technique of thermal spraying deposition. Moreover, a high amount of anatase was suitable for the photocatalytic degradation of the pollutants. Suspension plasma spraying has allowed retention of the original anatase phase and for very reactive TiO 2 surfaces to be obtained for the removal of nitrogen oxides.

Results of modification of the HSMM model (Hot Strip Mill Model) for enhancing precision of the mechanical properties prediction for hot rolled steels after rolling on the mill 2000 of OAO Severstal are pre sented.

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An integral mathematical physically based model is developed for prediction of the microstructure and mechanical properties of steels processed in accordance with a given hot deformation and accelerated cooling regimes. The model predicts austenite microstructure evolution under hot deformation, as well as its transformation during subsequent cooling with account of formation of ferrite, pearlite, bainite and martensite. Structure-property relationships are developed using an extensive experimental database chemical composition - microstructure - mechanical properties obtained for 10 steel grades. Austenite transformation depending on grain size, cooling rate and preliminary plastic deformation was investigated with the help of Gleeble 3800 system to obtain a set of practically important morphologically different microstructures for each steel grade. A quantitative analysis of the microstructures was performed using optical and scanning electron microscopy (EBSD-method). Investigation of the mechanical properties of steels with wide spectrum of obtained microstructures was carried out on the double-samples processed using Gleeble 3800. The predicted microstructure parameters for investigated steels obtained using the developed model, as well as their mechanical properties, are in good agreement with the experimental data.

A quantitative model is presented to describe the kinetics of grain growth in complexly alloyed austenite. The model assumes that the activation energy of grain growth is proportional to the activation energy of bulk self-diffusion, which is calculated as a function of the chemical composition of the solid solution using the previously obtained formula. The empirical parameters of the model are determined on the basis of experimental data on the kinetics of isothermal grain growth in steels with the chemical composition varying in a wide range: C (0.05 ÷ 0.32), Mn (0.30 ÷1.88), Si (0.01÷ 0.29), Ni (0.0 ÷ 4.0), Cr (0.0 ÷ 2.0), Mo (0.0 ÷ 0.5), Nb (0.00 ÷ 0.05) available in the literature. The model allows one to obtain good agreement with the experiment for the considered steels in which the minimum (~ 79.7 kJ / mol) and maximum (~ 243.7 kJ / mol) values of the activation energy of grain growth differ by 3 times. The average absolute value of the relative error in calculating the grain size is about 11 % that is comparable to the measurement error. Taking into account the influence of the chemical composition on the activation energy of grain growth, implemented in the developed model, it is possible to obtain agreement with the experiment without accounting for the solid-solution pinning of moving boundaries (the solute drag effect) requires a large number of additional empirical parameters (two exponential parameters for each alloying element). This result deserves further consideration from the physical viewpoint and verification on both simple carbon steels and steels with various quantities of Mn, Mo and Nb, which, according to literature, exert the strongest solute drag effect.

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