Vol 48, No 5 (2018)

The development of specialized self-propagating high-temperature synthesis (SHS) for complex ferroalloys used in steel smelting and in blast-furnace technology is discussed. To that end, a new approach to the SHS process has been conceived: the metallurgical SHS process, in which the basic raw material consists of various metallurgical alloys including dusty waste from ferroalloy production. In that case, synthesis involves exchange exothermal reactions. The product is a composite based on the initial inorganic compounds; the binder is iron or an iron alloy. Depending on the state of the initial reagents, the metallurgical SHS processes may be gas-free, gas-absorbing, or gas-liberating. For each case, the combustion conditions will be very different. Thermal matching may be used in organizing the metallurgical SHS process in systems that are not strongly exothermal. The self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome is investigated. It is shown that the phase composition of the initial alloy strongly affects the combustion of ferrovanadium in nitrogen. In the nitriding of σ ferrovanadium, transformation of the intermetallide to an α solid solution is activated on reaching the phase-transition temperature (~1200°C). The composite structure of the nitriding products of ferrovanadium is formed under the influence of solid–liquid droplets consisting of molten iron and solid vanadium nitride. Solid-phase reaction of ferrochrome with nitrogen facilitates high degrees of nitriding. The combustion rate of ferrochrome on nitriding during coflow filtration, as in chromium, increases with increase in the nitrogen flow rate. The degree of nitriding of the ferrochrome in forced filtration (4.7–7.5% N) is much less than that in natural filtration (8.8–14.2% N).

Recently, amorphous and nanocrystalline magnetically soft iron alloys have been used to create protective materials that are effective in a broad range of magnetic and electromagnetic fields. These alloys are obtained in strip form by superfast quenching of a plane melt jet on a rapidly spinning cooled disk. In the production of amorphous strip, metal melted in a high-frequency inductor is supplied through a cut on the surface of the cooling disk. The surface layers of the congealing strip in contact with the cooled disk are cooled more rapidly than higher layers in no contact with the disk. As a result, residual compressive stress may be formed on the contact side of the strip, while tensile stress may be formed on the free side. This may lead to anisotropic structure and properties over the strip thickness. In the present work, the structure is investigated by transmission microscopy (planar geometry and cross-sectional geometry) over the thickness of AMAG-200 Fe–Nb–Cu–Si–B alloy strip obtained by spinning. A relation is established between AMAG-200 Fe–Nb–Cu–Si–B alloy strip produced in controlled crystallization and the structure of the amorphous strip obtained by superfast quenching of melt at rates up to 10⁶ K/s. That explains the structural anisotropy over the strip thickness. Heat treatment at 530°C forms excellent magnetic characteristics and decreases the work of destruction on account of the formation of optimal amorphous–nanocrystalline structure in terms of the bulk content and size of the crystallites. A scanning electron microscope is used to study the destruction of strip associated with the structure formed in the strip on superfast quenching from melt and after heat treatment at 530°C. In the state supplied, the surface fracture of the strip on sudden decrease in grain size is ductile; after heat treatment, it is consistently brittle.

The interaction of tungsten carbide and low-carbon steel in contact and contact-free is investigated in systems with contact and contact-free heating. Substrates of pressed tungsten-carbide powder sintered in a vacuum furnace are impregnated with low-carbon steel of specific chemical composition. A high-speed video recording of the process permits measurement of the contact wetting angle at any time during the experiment. The experiment is conducted at the Center for High-Temperature Studies, Foundry Research Institute, Krakow, Poland. The microstructure of the substrates obtained is investigated. The chemical composition of the reaction products is studied by means of a Jeol JSM-6460 LV scanning electron microscope. All the samples are successfully impregnated. The same structure is observed throughout the substrate cross section. It consists of three phases: tungsten-carbide grains; and iron–tungsten–carbon compounds with different iron content (86.72 and 22.86–23.68%). At the edges adjacent to the upper face, large quantities of the iron–tungsten–carbon compound with 22.86–23.68% Fe may be observed. This is explained in that such regions are impregnated last, and the iron dissolves the carbide more than in other regions. At points of direct substrate–iron interaction, grains of tungsten carbide are clearly identified; they are bound together by iron-based melt (with different iron content in different phases). Partial coverage of the sample surface by an iron film is seen on both samples at the horizontal face of the substrate adjacent to the impregnation region. The edges of the substrate’s horizontal face are completely covered with iron film, under which lie tungsten-carbide grains. Despite the use of different methods to study the interaction of tungsten carbide with low-carbon steel (contact and contact-free heating), no great difference in sample structure is observed.

The continuous casting of steel is simulated by means of Sn–Pb alloy on two models of the mold. One of the models, which has been patented, has a closed loop for two-phase coolant circulation. The following characteristics are compared: the cooling of the two castings; the temperature of the models’ cylindrical walls; the thickness of the crust formed; the structure of the castings; and their surface quality. The results are used in simulation of the thermal processes in a model with the continuous supply of an increasing heat flux and the correction of the processes for steel casting.

Continuous roll forming of thin- and superthin-walled pipe is considered. In shaping the pipe blank, stability loss at the edges (corrugation) is analyzed. Possible means of eliminating such corrugation are proposed.

The mechanical properties (strength σ_u, yield point σ_0.2, relative elongation ψ; and hardness HB and HRC) of 40X steel depend monotonically on the tempering temperature T_te after quenching and are closely correlated. Their relationships are described by linear regression equations. The corresponding correlation coefficients and computational errors are determined. The coercive force H_c of 40X steel is not clearly related to its physicomechanical properties over the whole range of T_te. However, magnetic analysis of the structure of 40X steel may be based on an algorithm that employs Hc and the ratio of the residual magnetization to the saturation magnetization. The results given by this algorithm depend uniquely on T_te over its practical range and are highly sensitive to change in the physicomechanical properties of 40X steel.