(1) Background: Operational properties and durability of dies in different metal-forming processes significantly depend on their surface quality. Major die failures are related to surface damage due to heat checking cracks, wear, etc. Thereby, strengthening of the working surfaces of dies for hot bending, stamping, forging, and die casting processes is an urgent engineering challenge. Surface alloying with high-energy beams improves the properties of steel products. In these processes, the alloying powders and the treated surfaces can be remelted by electron beam within a short time while the bulk structure of the component remains unchanged, resulting in minimal distortion. The paper presents the results of the electron beam surface alloying (EBSA) of H21 and L6 tool steels with the treatment pastes containing boron carbide and aluminum powders. (2) Methods: Two types of pastes were used for surface alloying: a single-component (B₄C) paste and a two-component (B₄C+Al) one. The microstructure, microhardness, wear resistance, and elemental and phase composition of the layers obtained on steels were investigated. (3) Results: Four layers up to 0.4 mm thick were distinguished on the surface of the steels after the EBSA. Metallographic analysis showed coarse dendrite formation in the layers embedded in matrices of a eutectic or a solid solution. Microhardness of the steels after the two-component EBSA was higher than after B₄C EBSA, which was related to a higher concentration of hard phases, such as iron borides and carbides. In addition, aluminum boride was revealed by the XRD analysis on L6 steel after B₄C+Al EBSA. (4) Conclusions: Wear test indicated that the most resistant samples were H21 steel after single B₄C EBSA and L6 steel after B₄C+Al EBSA. Both samples contained carbon particles in the layer contributing to the high wear resistance as a lubricant. The conducted research is beneficial for mechanical engineering, automotive engineering, medical technology, aerospace engineering, and related industries, where coatings with high microhardness, wear resistance, and surface quality are demanded.

Introduction. Boriding and aluminizing are among the effective methods for improving the performance properties (corrosion resistance, heat resistance and wear resistance) of machine parts and tools. Solid-phase methods of carrying out techniques of thermochemical treatment (TCT) require long-term exposure at elevated temperatures, which negatively affects the structure and properties of the base material. From these positions, the selection of reasonable temperature-time parameters of solid-phase boriding and aluminizing processes is an urgent task. The purpose of this work is to assess the effect of low-temperature boriding and aluminizing processes on the structure and microhardness of diffusion layers on the surface of low-carbon steels. The paper considers two grades of steels with a carbon content of up to 0.4%: low-carbon steel St3 and alloy steel 3Cr2W8V. The use of the second steel is due to the need to identify the effect of alloying elements in steel on the thickness of diffusion layers and its composition. Powder mixtures based on boron carbide and aluminum carbide are selected as sources of boron and aluminum. Results and discussions. It is found at a process temperature of 900 °C and holding for 2 hours after boriding, iron borides are formed on the surface of both steels. At the same time, two borides FeB and Fe2B are detected on St3 steel by X-ray phase analysis (XRD), and only the Fe2B phase is detected on 3Cr2W8V steel. After aluminizing, aluminum-containing phases such as Al5Fe2, Na3AlF6 and Al2O3 are formed in both steels. The thickness of the resulting diffusion layer on St3 after boriding is 35 μm, after aluminizing – 65 μm. The thickness of the diffusion layer on 3Cr2W8V steel is equal to 15 μm after boriding and 50 μm after aluminizing, which is significantly less than on carbon steel and is obviously due to the effect of alloying elements. It is established that TCT leads to a significant increase in the microhardness of the samples surface. Thus, the maximum microhardness of St3 steel increased to 2,000 HV, and the maximum microhardness of 3Cr2W8V steel increased to 1,700 HV after boriding. The microhardness after aluminizing is comparable for both steels and is equal to 1,000-1,100 HV. Elemental analysis of the upper sections of the diffusion layers shows that the content of boron (7-9%) and aluminum (50-53%) corresponds to the detected XRD iron borides and aluminides. In all cases, there is a gradual decrease in the diffusing elements in the direction from the surface to the base.

The world reserves of oxidized lead–zinc ores are large, but their processing faces significant difficulties due to their refractory nature. This paper presents a novel approach to the preparation of refractory oxidized lead ores for flotation. The proposed method is based on the co-roasting of oxidized lead-bearing ores from the Ozernoye polymetallic deposit (Western Transbaikalia, Russia) with fine-grained sulfide lead–zinc ore sourced from the same deposit and the addition of calcium oxide. This method allows for the activation of mineral complexes, the sulfidation of oxidized lead–zinc minerals, and the minimization of the amount of sulfur dioxide gas emitted. Co-roasting oxidized lead–zinc ore with sulfide ore (10–30 wt. pct) at 650–700 °C has been shown to result in the selective oxidation of pyrite and sulfidation of oxidized lead and zinc minerals. The proposed method of processing polymetallic ores is capable of simultaneously involving not only oxidized lead–zinc ores but also refractory sulfide ores, thereby extending the operational lifespan of the mining enterprise and reducing the environmental impact.

In modern conditions, due to the depletion of high-grade ore and placer gold deposits, both domestic and global gold mining industries have to deal with rebellious ores, the extraction of valuable components from which by direct cyanidation is difficult or extremely unprofitable. The most common types of rebellious ores include sulphide ores and sulphide concentrates. A variety of techniques have been developed and widely used to process such materials, including autoclave oxidation, bacterial leaching, etc. However, there is another type of rebellious ores – oxidized ores. Arsenopyrite and scorodite concentrates characterized with a high arsenic concentration, can be classified as a special type of rebellious gold ores. This research was aimed at collecting new data about the behaviour of gold concentrates with high arsenic concentrations under thermal decomposition conditions. Netzsch STA 449 F1 Jupiter was used for differential thermal analysis, which was conducted in an alumina crucible in the argon atmosphere under linear heat of up to 850 оС. The paper describes the results of the thermal analysis carried out for specimens of the monomineral scorodite FeAsO4 and arsenopyrite FeAsS, as well as for their 1:1 combination. The authors found that the thermal breakdown of scorodite includes three stages. They also determined the temperature ranges and heat effects of these reactions. A study of the thermal decomposition of arsenopyrite showed that pyrite would break down into pyrrhotines in one stage. Experiments confirmed that the mixture of scorodite and arsenopyrite concentrates would break down in three stages. The X-ray phase analysis data show that the final roasted products include hematite Fe2O3, quartz SiO2, and potassium aluminium silicate KAl3Si3O11. It was also confirmed that up to 99.9% of arsenic goes into the gas phase.