Effect of Unstable Tapping of Smelting Products on the Performances of the Evraz Ntmk Blast Furnaces

Metallurgist - Timely and full tapping of liquid smelting products is an important condition for forcing the blast-furnace process. Unstable tapping of iron and slag leads to fluctuations of the...     

Technology of Blast-Furnace Smelting of Iron using Pulverized Coal at the NLMK

Metallurgist - The problems of using pulverized coal to save coke during iron smelting in the NLMK blast furnaces are considered. The iron smelting technology was implemented in two stages: (i)...     

Peculiarities of Mechanical Alloying of High-Concentration Fe–Cr Alloys

The kinetics of the mechanical alloying of Fe and Cr powder mixtures with Cr contents of 20–48 at % has been studied by Mössbauer spectroscopy, X-ray diffraction analysis, and temperature measurements of dynamic magnetic susceptibility. It has been found for the first time that the processes of mechanical alloying differ for initial mixtures with chromium contents of 30 at % or more and contents of less than 30 at %. For the first case, the unidirectional dissolution of Cr in Fe is observed through the whole process of mechanical alloying of the mixture in a planetary ball mill. For the second case, the dissolution of Cr in Fe is observed at the beginning stage of milling; however, after milling for 2 h (t_mil), the reverse process, namely, the dissolution of Fe in Cr is likely to dominate. The mechanically alloyed samples are characterized by inhomogeneous Cr and Fe concentration distribution in powder particles, in particular at a Cr concentration in the initial mixture of more than 30 at %.     

Smelting low-silica hot metal at OAO NTMK

In the blast-furnace shop at OAO Nizhnetagil’skii Metallurgicheskii Kombinat (NTMK), the smelting of low-silica vanadium hot metal is being introduced. Theoretical and experimental data reveal the influence of the pressure in the furnace’s working space and coke quality on the reduction of titanium and the formation of refractory titanium compounds. The residence time of the melt in the hearth depends on its dimensions.     

Magnetic Properties of Mechanically Alloyed and Annealed Powders Fe100 – X C X (X = 5 and 15 at.%)

The effect of the structural state and the phase composition on the magnetic hysteresis properties of Fe(95)C(5) and Fe(85)C(15) powders after mechanical alloying and annealing is investigated. It is shown that in the initial stage of grinding in a ball planetary mill the coercive force of the Fe–C powders is determined by the degree of defectiveness of the -Fe phase and the relative volume and dimensions of nonmagnetic graphitic inclusions in iron powder particles. As the grinding time increases, the -Fe phase goes over into a nanostructure state and carbon from graphite inclusions goes over into an amorphous Am(Fe–C) phase. After annealing on the temperature interval 300–600°C, the amorphous Am(Fe–C) phase is transformed into Fe₃C ferric carbide. The coercive force of the Fe₃C phase strongly depends on the degree of distortion of its crystal lattice and amounts to 80 A/cm for the phase with distorted lattice and 240 A/cm for the phase with equilibrium undistorted lattice. The magnetic characteristics of the powder after mechanical alloying and subsequent annealing are determined by the type, amount, and structural state of the phases containing in the samples.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: I. Magnetic properties and structural state of cementite

Magnetic properties of cementite after strong plastic deformations and subsequent annealing in a broad range of temperatures are studied. The plastically deformed cementite is shown to exist in a soft (H _c ≈ 80 A/cm) state; the annealed cementite, in a hard (H _c ≈ 240 A/cm) state. The nature of the cementite’s soft and hard states is discussed. The field dependence of the cementite’s magnetostriction is measured. The longitudinal magnetostriction of the polycrystalline cementite’s saturated state is shown to be negative and approximately four times smaller than iron’s magnetostriction in the saturated state.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: II. Magnetic properties of patented wire made of steel 70

It is shown that, during discussion of the mechanism reliable for formation of the coercive force in high-carbon steel, in addition to the interaction between the domain walls and weakly magnetic cementite inclusions, the contribution from the cementite’s magnetic hardness should be considered. With the use of the temperature dependence of the coercive force in deformed and annealed specimens, the contribution of each of the considered mechanisms to the specimens’ coercive force is estimated.     

Structure and magnetic properties of mechanically synthesized (Fe<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>75</Subscript>C<Subscript>25</Subscript> nanocomposites

X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements have been used to study the phase formation in (Fe_1–xNi_x) (with х = 0–0.20) nanocomposites upon severe plastic deformation in a planetary ball mill and subsequent annealings. It has been shown that the mechanical synthesis results in the formation of mainly a nickel-alloyed nanocrystalline (Fe, Ni)₃C cementite with a distorted crystal lattice and an amorphous Fe–Ni–C phase. During heating above 300°С, the amorphous phase crystallizes with the formation of cementite, which is characterized by a higher Ni content compared to that in mechanically synthesized cementite. The mechanically synthesized samples exhibit low coercive force (equal to several tens ampere per centimeter). In the course of annealing at temperatures of up to 500–550°С, crystal lattice distortions are removed; this results in reliving the magnetic anisotropy constant and high-coercivity state of cementite. At the same time, Ni-rich cementite areas decompose with the formation of γ-(Fe, Ni, C) phase (austenite); as a result, the average nickel content in the cementite substantially decreases. Annealings at higher temperatures cause the complete decomposition of cementite and lead to an abrupt decrease in the coercive force (Н _с) of samples. Alloying with nickel leads to an increase in the Curie temperature of cementite and a decrease in its specific saturation magnetization, coercive force, and thermal stability.     

Effect of anneal on magnetic properties and structural state of iron powders ground in carbon-rich medium

Intense milling of iron powders in a carbon-rich liquid leads to carbonization of powder particles to concentrations of up to several weight percents, alongside the notable reduction in the dimensions of mosaic blocks and formation of a nanocrystalline structure, which results in a lower coercive force of the powder. X-ray and Mössbauer data indicate that Fe?C disordered solid solutions are formed in the regions of mosaic-block boundaries in the process of the powder milling. The anneal forms the Fe₃C ordered carbide phase from the disordered solid solution, which raises the coercive force in the powders beyond 100 A/cm.     

Introduction of Energy Efficient Solutions During Cast Iron Smelting at PJSC “NLMK”

Metallurgist - The use of coke with hot strength of 60–65% in the blast furnaces of PJSC “NLMK” allowed to increase the intensity of the blast furnace smelting and utilize the...