Volume 47, Nº 3 (2017)

The degassing of 09Г2C steel produced in an arc furnace and treated in a ladle–furnace unit at AO Uralskaya Stal is analyzed. The vacuum-treatment parameters that determine the effectiveness of hydrogen removal from the steel are identified: the depth and duration of vacuum treatment; the argon flow rate; the steel temperature; the thickness of the slag layer; and the free board in the vacuum chamber. The hydrogen content changes most significantly when the degassing time is increased to 20 min. Longer treatment is not recommended. The greatest effect of the residual pressure in degassing is observed with simultaneous decrease in the minimum pressure to 2 mbar. Vacuum treatment of the steel is considerably impaired with increase in the residual pressure. Hydrogen removal is improved with increase in the steel temperature to 1600–1620°C, but slows considerably at higher temperatures. The influence of the vacuum-treatment parameters is established quantitatively, and a regression equation is derived for predicting the results of hydrogen removal and selecting the parameter values corresponding to specified hydrogen content in the steel. Vacuum-treatment parameters that permit the economical production of steel with 2.1 ppm are determined: steel heating before vacuum treatment by 100–110°C; vacuum treatment for 20 min at a pressure no higher than 1.5 mbar in the vacuum chamber; argon flow rate 0.05 m³/t. The temperature losses of the metal are determined by the total treatment time, consisting of the active degassing time and the auxiliary time (the preliminary evacuation time), which depends on the capabilities of the equipment and the organization of the process. The minimum residual hydrogen content in the steel for the given equipment (1.6 ppm) is ensured by vacuum treatment for 40 min at a pressure no higher than 1 mbar in the vacuum chamber, with preliminary heating of the steel by 120–125 °C and with an argon flow rate up to 0.072 m³/t.

The stages of structure formation during cold rolling are investigated in bcc (110)[001] single crystals of Fe–3% Si alloy, within the deformation zone. To obtain a visible deformation zone, the laboratory mill is abruptly stopped at the instant of sample rolling. To reduce the frictional coefficient, lubricant is used for some of the samples. The deformational structure is studied by metallography and orientational electron microscopy (EBSD). Deform-3D software is used to analyze the relation between the experimental data and the calculated stress state in rolling, for various values of the frictional coefficient. Depending on the frictional coefficient, the stress state may significantly affect the mesostructure formation and the texture development. In a single crystal rolled with elevated friction, when the deformation is relatively small, deformation bands are formed. Orientational analysis of the contact point of deformation bands reveals alternating microbands, each with slight different orientation, which are separated by small-angle boundaries. In the rolling of a (110)[001] single crystal with lubrication (reduced friction), twinning is observed even with slight deformation. The twinning is evidently due to the reduced contribution of surface energy to the total energy of twin nucleation. Throughout the whole deformation process, either the twins of both systems retain the strict Σ3 crystallographic relation with the matrix or else, on account of the local lattice reorientation, Σ3 disorientations are converted to similar special Σ17b and Σ43c disorientations. On the basis of experimental data, a dislocation model is proposed for the formation of deformational mesostructures in the cold rolling of a (110)[001] single crystal. This model includes the formation of microbands in the initial stage of deformationband generation; the formation of transition bands parallel to the rolling plane with the dynamic retention of the initial orientation; and the formation of transition bands inclined to the rolling plane with a habitus parallel to the {112} matrix plane. These inclined planes are equivalent to shear bands whose habitus is inclined at ~17° to the rolling plane.

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO₂) =–7.194; logK(TiO₂) =–6.125; logK(Ti₃O₅) =–16.793; logK(Ti₂O₃) =–10.224) to cobalt (logK(CoO · TiO₂) =–8.580; logK(TiO₅) =–7.625; logK(Ti₃O₅) =–20.073; logK(Ti₂O₃) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO₂, TiO₂, Ti₃O₅, and Ti₂O₃ are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO₂ ↔ TiO₂ decreases from 1.0 × 10^–4% Ti in iron to 1.9 × 10^–6% Ti in cobalt. The titanium content at the equilibrium point TiO₂↔Ti₃O₅ increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti₃O₅ ↔ Ti₂O₃ decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.

Recommendations are made for calculation of the total energy of the hearth-gas flux in pulverized-coal injection. That permits monitoring of the mean total energy and the energy at each tuyere in the blast furnace. On that basis, the penetration depth of the hearth-gas flux toward the center of the furnace may be regulated for each tuyere, and hence the gas-dynamic and reducing conditions in the blast furnace may be improved.

Crack formation at the lock of the dummy bar in continuous slab-casting machines is analyzed. The cracks are due to the thermocycling stress. Cooling periods in thermocycling are particularly hazardous. This problem may be addressed by redesigning the head.

The expansion of large-diameter welded pipe is modeled by the finite-element method. The dependence of the oval distortion of the pipe on that of the pipe blank is studied. The equivalent stress is changed by the first expansion step.

A method is proposed for predicting the critical stress-intensity coefficient K_1c of structural steels (their crack resistance) on the basis of uniaxial tensile tests of standard samples. The derivation of this method relies on the concepts of mechanical stability and embrittlement when nonuniform force fields act on a metal. The strain-hardening index n of the metal at the critical transition temperatures from the plastic state to the quasi-brittle state (T_c or T₀) and from the quasi-brittle state to the brittle state (T_k2) plays a key role here. The proposed method may prove effective in monitoring the crack resistance of steels certified in scientific and plant laboratories.