No 4 (2023)

The processes occurring during autoclave oxidative leaching of refractory sulfide gold ores concentrates are discussed, as a result of which difficult-to-remove deposits (sediments) are formed on all internal surfaces of autoclaves, reducing equipment performance. It is shown that the phase composition of the sediments varies across autoclave sections and that the main component of the sediments is potassium jarosite KFe3(SO4)2(OH)6. The mechanism of sediments formation is analyzed and possible ways to prevent appearance them are discussed.

The results of studying the effects of pulsed flows of helium ions (HI) and helium plasmas (HP) on the Inconel 718 alloy prepared by additive technology by selective laser melting followed by heat treatment are presented. The main structural changes in the irradiated surface layer (SL) are determined for two modes of irradiation - soft (with radiation power density q = 2 ∙108 W/cm2 at pulse duration τ = 50 ns) and hard (at q = 1.5 ∙109 W/cm2, τ = 25 ns). The number of pulsed actions in each mode was N = 10 and 20. It has been found that in the initial state and after irradiation, the alloy under study is a single-phase nickel-based solid solution with an fcc lattice. The impact on the alloy of pulsed HI and HP flows leads to a change in the initial texture in the <220> direction to texture <111>. This change in the texture favored the occurrence of the plastic deformation (PD) process observed in the irradiated SL, during which in metals with an fcc lattice, under the action of applied thermal stresses, slip occurs predominantly along the {111} planes. The influence of the irradiation mode of the investigated alloy on the parameter of its crystal lattice is noted. In the soft mode of exposure to HI and HP flows, the lattice parameter a decreases compared to the initial value, which may be due to the action of residual macrostresses, as well as to the evaporation of atoms of impurity elements located in lattice interstices from the SL. In the hard irradiation regime, the parameter a increases, which is due to the dominant influence of the mechanism of implantation of helium ions into the alloy, which contributes to the increase in the value of a. It have been shown that the observed structural changes in the SL of the alloy lead to a decrease in microhardness and softening of the remelted layer. The role of thermal and shock-wave effects in the processes of PD and structural changes in SL under the implemented irradiation conditions was estimated by numerical simulation.

X-ray diffraction methods were used to study the influence of the degree of deformation during tensile testing on the phase composition, texture and stress state of the α- and ɣ-phases of the VNS9-SH alloy. It is shown that during testing to failure, the amount of the α-phase increases on the surface from 75 to 91% and from 45-50 to ~70% in the subsurface layers. To assess the susceptibility of two-phase steels to the trip effect, a parameter of austenite metastability is proposed in the form of the relative fraction of decomposed austenite at individual stages of tensile deformation. It has been established that in the initial steel strip 0.3 mm thick, as a result of the positive volumetric effect of the transformation ɣ => α, compressive stresses are formed in austenite, reaching a value of –1000 MPa on the surface, in contrast to tensile stresses in martensite. Their presence is associated with heating of the metal, the cooling of which leads to tensile stresses in martensite due to its significantly lower temperature coefficient of linear expansion value compared to austenite.

Tribotechnical characteristics of high nitrogen austenitic steel VNS-53 under conditions of dry sliding friction in contact with steel ShH15-ShD have been studied. It was found that in a thin surface layer the work hardening occurs without martensitic transformation, as a result the hardness increases by more than 90 %. It is established that this steel has a lower coefficient of friction and a greater increase in hardness in the contact zone of the surfaces compared to the steel 08H18N10T

The process of metal cooling by heat emission and convection is considered. Refrigerators used in modern varietal mills are calculated by the amount of heat transfer. A formula is proposed for calculating the cooling duration of the metal from 850 to 50 ° C, which gives a result 1.78 times less than the formula that does not take into account the effect of convective heat transfer. For workpieces of large thicknesses, the surface temperature differs from the average, so averaging the temperature by volume leads to errors. Refinement of the calculation of radiation surfaces increases the accuracy of calculations of cooling process.