Vol 49, No 5 (2019)

Existing methods of determining the onset of slag flow in the discharge of liquid steel from the casting ladle to the tundish are analyzed. Two aspects are considered: (1) selection of the best method of generating a diagnostic signal in terms of cost and quality; (2) development of a method of signal processing so as to derive useful information. The proposed method is to obtain a vibrational-acceleration signal from a sensor on the protective-tube manipulator in the casting ladle. A prototype is developed for installing the sensor on the manipulator. This prototype protects the sensor from industrial disturbances. In signal analysis, the onset of slag flow is determined by calculating the entropy energy. The corresponding system is tested in an industrial casting system. To ensure effectiveness of the approach, a manual subsystem maintaining the steel level in the tundish in the last stage of casting must be introduced, so as to rule out perturbations associated with motion of the gate valve controlling the flow of steel melt. Industrial experiments indicate that the automatic system must be switched off when the ladle contains only around 18–19 t of steel. In tests, the operator has always been able to select the casting rate such that the steel level in the tundish is consistent with the regulations. As a result, the algorithm triggers slag segregation for each casting run before the operator does so. When using this method, the steel residue with the slag in the casting ladle differs by no more than 3.8 t from the value for slag segregation by the operator.

A simple theory is proposed for the thermodynamic properties of nitrogen solutions in Fe–Cr melts. The theory is based on a lattice model of the solution. An fcc model lattice is adopted. Iron and chromium atoms are distributed at the lattice sites. Nitrogen atoms are located in octahedral interstices. The nitrogen atoms only interact with metal atoms at neighboring lattice sites. The energy of this interaction is assumed to depend neither on the composition nor on the temperature. The liquid Fe–Cr solutions are assumed perfect. Within this framework, the constant in the Sieverts law governing the solubility of nitrogen in liquid chromium may be expressed in terms of its value for the solubility of nitrogen in liquid iron and the value of the Wagner parameter for N–Cr interaction in liquid iron alloys. In addition, the partial enthalpy of solution of nitrogen in liquid chromium at infinite dilution is expressed in terms of the corresponding enthalpy for the solution of nitrogen in liquid iron and the Wagner parameter for N–Cr interaction in liquid iron alloys. A relation is also established between the Wagner parameter for N–Fe interaction in liquid chromium alloys and the Wagner parameter for N–Cr interaction in liquid iron alloys. On that basis, the constant in the Sieverts law governing the solubility of nitrogen in liquid chromium is calculated, along with enthalpy of solution of nitrogen in liquid chromium at infinite dilution and the Wagner parameter for N‒Fe interaction in liquid chromium alloys at 1873 K. The calculation results are compared with experimental data regarding the solubility of nitrogen in liquid chromium and Cr–Fe alloys obtained by various methods. The theoretical data are in best agreement with experimental data obtained by quenching. The values of the Wagner parameter for N–N interaction in liquid chromium alloys and iron alloys are discussed.

None of the existing approaches to the extraction of metals from ore can completely explain the practical findings. This suggests that reduction occurs by more than one pathway. The solid-phase reduction of metals by carbon in complex and lean iron ores from different sources and also in individual oxides of silicon, chromium, and aluminum is investigated. The electrical characteristics of ores and individual oxides are studied in order to refine theoretical concepts regarding reduction. In all cases, the reduction of metals is found to involve the conversion of the oxide’s crystal lattice into the crystal lattice of the metal. On the basis of quantum mechanics and solid-state physics and chemistry, new fundamental principles are identified in the electronic theory of the reduction of metals. Reduction consists in electron exchange between the reducing agent and the metal cations in the oxide. As a result, anionic vacancies with free electrons are formed at the oxide surface. Depending on the concentration of the cations to be reduced, the conversion of the ionic bond of the oxide’s cations to the metallic bond of the metal’s cations involves the coalescence of charged anionic vacancies at the surface of the oxide or at greater depth. This process does not require motion of the cations over considerable distances or the formation of metal atoms; the thermodynamic constraints associated with the formation of new-phase nuclei do not apply. This theory is able to explain all the known experimental results regarding the solid-phase reduction of metals in oxides: the formation of continuous metallic shells at the surface of pieces of rich iron ore; the deposition of metal particles within lean and complex ores; and the formation and sublimation of suboxides. In the deposition of metallic phase within the complex oxide, there is no direct contact between the metal and reducing agent; therefore, in the reduction of iron in complex or lean ores by carbon, no sulfur or carbon is transferred to the metallic phase from the reducing agent. In the reduction of such ore, fuel coal may be used as the reducing agent. The product is a metal–oxide composite containing pure iron and valuable oxides of magnesium, titanium, and vanadium.

The influence of the one-time reduction in the first pair of matched grooves in a three-high stand on the cracking at the end of the billet is simulated. The traditional six-pass procedure in the three-high stand is compared with the new six-pass procedure and the eight-pass procedure proposed in the present work. The comparison shows that, by milder reduction in the first pair of matched grooves, the effective stress may be decreased, along with the likelihood of cracking at the end of the billet. The damage at the ends of the multiple billets in the three-high roughing stand may be minimized by means of further decrease in deformation in the first passes on rolling multiple continuous-cast billets made of high-quality structural steel, along with decrease in the initial rolling temperature and division of the billet into measured lengths on a band saw.

A universal formula is proposed for calculating the optimal strip width and tube-billet perimeter at each stage of bending in the production of electrowelded low- and medium-diameter straight-seam tube and pipe of round and complex cross section. This formula determines the conditions of tube deformation in machines of different type and allows the increase in tube-billet perimeter in a group of stands with an open gauge profile to be taken into account for different forming behavior. For the tube and pipe range produced, the reduction at the tube-billet perimeter in a group of stands with a closed gauge profile should be no more than 0.6%. That decreases the steel consumption by decreasing the width of the initial billet, without loss of pipe quality, and increases the product yield by eliminating edge buckling in the course of forming.

Stainless steel with appropriate phase composition and improved physicomechanical properties for use in the production of titanium sponge is developed. A production system is proposed for 03Kh17N3G9MBDYuch steel, taking account of the martensitic transformation in cold deformation.