Vol 46, No 2 (2016)

Existing systems for diffusional saturation with molybdenum have numerous problems. The use of microarc treatment for this purpose is investigated. A steel sample is immersed in coal powder and heated by current transmission. Ammonium molybdate is the source of the molybdenum. The pyrolysis of coal is accompanied by the emission of hydrogen, methane, carbon dioxide, and carbon monoxide, which form a protective atmosphere and may reduce molybdenum to the atomic state. To identify the most likely chemical reactions, we calculate the standard change in Gibbs energy. The temperature ranges in which molybdenum trioxide is reduced to obtain molybdenum dioxide and atomic molybdenum are determined. The calculation results are verified experimentally. Simultaneous diffusion of carbon and molybdenum leads to the formation of a carbide coating (thickness 80–150 μm), with microhardness 13.5–15.0 GPa.

The steady heat transfer in the irrigated zone of the blast furnace is considered, taking account of the filtration of hot metal and slag through the coke bed. In this zone, the fluxes of coke, hot metal, and slag are heated simultaneously and exchange heat with one another, by both convection and radiation. Convection ensures heat treatment between the gas and all the batch materials and also between the slag and coke, since the slag running through the coke partially covers its surface. Radiant heat transfer develops among the coke, hot metal, and slag. It is more intense at higher temperatures. The heat transfer among the coke, hot metal, and slag in the irrigated zone of the blast furnace has a considerable influence on the temperature field in this zone. To calculate the heat transfer at the shoulder and hearth, information is required regarding the distribution of the thermal effects of direct reduction of iron, silicon, and manganese over the height of the irrigated zone and the proportion of the coke surface covered by slag.

In ultrasonic structure analysis, a new approach is proposed to the assessment of metal structure in terms of the amplitude ratio of the mean structural noise and the secondary Rayleigh wave. The change in structural noise in the uniaxial extension of C01Mn2Si1 steel is investigated. The influence of mechanical stress and the structural state of the metal on the structural noise is demonstrated. The parameters of the structural noise are related to the structural state of C01Mn2Si1 steel. Experiments confirm that the sharp drop in structural noise at the yield point offers a sensitive method of detecting structural changes in the metal. Hence, measurement of the structural noise may be recommended for the detection of an early stage of damage accumulation in the metal—the stage of microdefect accumulation.

Attention focuses on the macroscopic localization of the plastic deformation and structure in polycrystals of low-carbon 08ps steel sheet after hot rolling as a result of electrolytic saturation by hydrogen in a thermostatic three-electrode cell at constant potential. The basic types of macroscopic localization of the plastic deformation and its parameters (the velocity and wavelength) at different stages of strain hardening are determined by two-position speckle photography. By optical and electronic microscopy, the influence of interstitial hydrogen atoms on the defect substructure and morphology of cementite is investigated. The formation of dislocational substructure is considered. Torsional flexure of the α-phase lattice is discovered, corresponding to flexural extinction contours. The basic sources of the stress fields are the boundaries of the grains and fragments.

An algorithm is proposed for dual control, in which identification of the model of change in oxygen flow rate during injection—in particular, change in CO content in the converter’s exhaust gases—is accompanied by correction of the oxygen flow rate in the final stages of the melt. In this algorithm, a stepped control signal is applied at a specified time and monitored during the following interval. The control signal and output signal are recorded during the transient process and those data provide the basis for refinement of the coefficients employed in the model and refinement of the control signal. The calculated control signal is employed in the next control interval. The effectiveness of the proposed control algorithm is estimated in terms of the smoothness of the time series for the carbon content in the metal at the singular point and the consistency of the steel’s carbon content at converter discharge.

Statistical analysis of blast-furnace performance at NLMK between 2009 and 2014 reveals the thermodynamic and kinetic behavior of the reduction process. A method is developed for calculating the reducing potential of the hearth gas and for quantitative estimation of its utilization and the reaction rate. With the attainable productivity of 2.4–2.9 t/m day and fuel consumption 400–420 kg/t (in terms of total carbon), the properties of the hearth gases are sufficient to ensure near-optimal (around 70%) indirect reduction of Fe, but insufficient for batch heating in the shaft to the temperatures required for intense reduction.

Data on the metallurgical defects in pipe show that they may be due to nonmetallic oxide inclusions. Analysis of the formation of oxide inclusions from smelting to the continuous casting of steel shows that, in order to reduce the incidence of such defects, additional measures must be taken in the smelting and ladle treatment of the steel. Such measures reduce the content of oxide inclusions in the steel by half. The benefits of this approach are confirmed by the reduced rejection rate of the pipe on account of defects associated with the presence of nonmetallic inclusions.

New production technology for low-alloy 09ГСФ steel for rolled sheet resistant to hydrogen-sulfide corrosion is described. The quantity of modifier introduced determines the impurity content of the metal after deep refining to remove sulfur and nonmetallic inclusions, the types of inclusions formed, and hence the resistance of the metal to corrosion cracking. Row inclusions formed in the sheet after nonoptimal ladle treatment of the steel are mainly responsible for the impairment of corrosion resistance.