No 4 (2021)

Ion-plasma saturation with interstitial atoms (nitrogen or carbon) is a promising method for enhancing the surface strength and wear resistance of austenitic stainless steel parts and products. The paper considers the influence of method and temperature of ion-plasma treatment (IPT) on phase composition, thickness, and strength properties (microhardness) of the surface layers in 01H17N13M3 austenitic stainless steel specimens. Steel specimens with a coarse-grained structure were nitrided in the arc and glow discharge plasma at different temperatures (400 °C, 550 °C, and 700 °C). Regardless of temperature and IPT-method, ion-plasma nitriding leads to the formation of hardened surface layers in steel specimens. In this case, the thickness and phase composition of IPT-hardened layers depend on both the method and temperature of nitriding. Nitrogen saturation of specimen surfaces in the glow discharge at a temperature of 400 °C promotes the formation of a thin S-phase layer (nitrogen-expanded austenite, 4 μm in thickness). At the same IPT temperature in the arc discharge plasma, the authors observed the formation of a heterophase (Fe-γN, Fe4N, CrN, and Fe-α) surface layer with a significantly greater thickness (40–45 μm). Regardless of the IPT-method, a saturation of specimens at temperatures of 550 °C and 700 °C is accompanied by the formation of thick heterophase hardened layers (40–60 μm). In this case, the IPT method has a negligible effect on the phase composition of layers but significantly affects the ratio of the volume content of the hardened phases. After being IPT-processed in different modes, the microhardness distribution profile for all specimens has three typical zones: a composite layer (or S-phase at the IPT in a glow discharge at T_a=400 °C), a diffusion zone, and a matrix. With an increase in the saturation temperature, the thickness of the transition diffusion zone increases regardless of the IPT method.

The increased anticorrosive, strength, tribological, and physical characteristics are the specific features of steels with high nitrogen content. Searching for the ways to strengthen high-nitrogen steels is a promising area of contemporary metal science. Heat treatment is one of the methods of hardening nitrogen steels as a result of precipitation hardening with nitride particles. The authors studied the influence of short-term high-temperature aging and large plastic deformations implemented by shear under the pressure of 8 GPa (SP method) on Bridgman anvils (three revolutions of anvils with the rotation velocity of 0.3 rev/min) at room temperature on the structural-phase transformations and micromechanical properties of the 08H22GA1.24 high-nitrogen steel with the mixed γ (austenite) + a (ferrite) metal matrix structure. The study identified that aging (0.5 h) at the temperature of 650 °С of steel quenched at the temperature from 1180 °С causes the formation of the mixed austenitic-ferritic structure of metal matrix in the ratio of 50 vol. % of g and 50 vol. % of α and the release of extended secondary Cr₂N chromium nitrides, together with ferrite interlayers forming the areas with the pearlite-like structure. These areas cause the increased microhardness of steel with the austenitic-ferritic matrix structure (385±8 HV 0.025) compared to one of steel aged at the temperature of 550 °С (0.5 h) and having an austenitic matrix structure strengthened with secondary CrN nitrides (364±8 HV 0.025). The SP deformation of steel aged at the temperature of 650 °С (0.5 h) with the initial g+a+Cr₂N structure leads to g→aʹ transformation and the formation of submicro- and nanocrystalline structures. It causes the effective strength improvement of steel (up to 900±29 HV 0.025) and the growth of resistance to elastoplastic deformation compared to aged at the temperature of 550 °C (0.5 h) condition.

The paper shows the demand of the chemical industry for corrosion-resistant materials, as well as the prospects of the creation of laminated metal materials with internal protectors (LMM with IP). The authors offer the architecture and composition of layers of LMM with IP ensuring stable operation within the highly aggressive environment. The study identified the possibility of improving corrosion resistance ten and more times compared to high-alloy austenitic stainless steels. The authors show the efficiency of the application of explosion welding to produce LMM with IP. The paper considers the example of the production of a four-layer material with one internal protector made of low-alloyed, low-carbon steel of the following architecture: 2-mm layers of 12H18N10T + 09G2S + 12H18N10T plates of steel and the base 10-mm layer of 09G2S. The authors developed the process diagrams for performing butt-welded joints of such material, identified special aspects of the formation of its microstructure and properties. To obtain the maps of specific chemical elements distribution in the layers and interlayer boundaries, the authors used the energy-dispersive microanalysis method. Peculiarities of corrosion damage of a welded seam and weld-adjacent area are studied. The study showed the necessity of using a facing layer in a welded seam. Microstructural, X-ray tomographic, and gravity-measuring studies proved the obtained results. To evaluate the quality of welded joint, the authors performed the corrosion tests of a welded seam and weld-adjacent area, carried out visual inspection control and X-ray tomography. The corrosion tests were carried out using 10-% III ferrous chloride water solution. The paper presents the results of the static bending tests of a welded joint. The absence of fracture, lamination, and cracks served as an estimation criterion. The study identified the possibility of obtaining a defect-free welded joint of LMM with IP with high corrosion resistance and advanced mechanical properties.

Friction treatment is an effective method to increase the strength and wear resistance of austenitic chromium-nickel steels. Previously, the authors identified that the high level of mechanical properties of metastable austenitic steels is achieved at the intensive development of deformation γ→α'-transformation. However, the presence of deformation martensite in the austenitic steel structure can negatively affect its anti-corrosion properties. The search for ways to improve the strength characteristics of stable austenitic chromium-nickel steel while maintaining high resistance to corrosion destruction is the up-to-date line of research. In this paper, to evaluate the mechanical properties of 03Cr16Ni14Mo3Ti steel in the hardened condition and after friction treatment, the authors applied the technique of measuring the hardness using the restored print and the method of instrumental micro-indentation, which allows recording the indenter loading and unloading diagrams. The corrosion failure resistance of steel was studied in general corrosion tests. The authors compared the corrosion rate of austenitic steel after grinding, electropolishing, and friction treatment; using scanning electron microscopy and optical profilometry, studied steel surfaces subjected to these treatments and determined their roughness. Nanostructuring friction treatment provides surface hardening of stable austenitic steel up to 570 HV 0.025. The study showed the high efficiency of friction treatment application to increase the strength characteristics and resistance of steel surface layer to elastic and plastic deformation. The authors identified that austenitic steel is characterized by similar corrosion rates km=(3.26-3.27)∙105 (g/cm2∙h) after electrolytic polishing (the structure of large-crystal austenite) and after frictional treatment (sub-micro/nanocrystalline austenite structure), while mechanical grinding leads to a twofold increase in the corrosion rate of 03Cr16Ni14Mo3Ti steel due to the occurrence of microcracks and metal breakouts on the polished surface. The research justified the determining role of the quality of the surface formed by various treatments (roughness, the presence of continuity defects) in ensuring the corrosion resistance of stainless steel.

Laser heat treatment is one of the effective methods to improve the operational characteristics of metal-cutting tools. In the practice of laser hardening, there are several methods to select treatment mode: experimental, calculated, and according to reference data. The finite element method is promising for estimating the treatment zone parameters, and its application is the most in-demand for calculating the temperature field of a geometrically complex tool. When organizing the hardening process, the selection and setting of processing modes for the cutting wedge tip are the most difficult. In this regard, the solution for the multifactorial problem of optimizing the hardening scheme of an area near the tool tip is relevant when designing and automating the process of blade tool laser hardening. Using the finite element method in the ANSYS Workbench software, the authors carried out the numerical experiments to optimize the laser hardening scheme of the tool cutting wedge tip on the example of an instrument with a wedge angle equal to 60°. The paper considers three variants of the hardening scheme. The first variant is the implementation of multiple processing of an area adjacent to the tool tip. The second one consists of alternate movement of laser treatment spots along the cutting edges within the tool tip area. According to the third variant, the treatment spots were sequentially located along the bisector of an angle at the tool tip. The study showed that, according to the maximum depth criterion, an optimal hardening scheme is a scheme, which consists of alternate movement of laser treatment spots along the cutting edges in the tool tip area. In this case, the hardening zone characteristics are ensured that exceed similar values describing the hardening zone for other laser treatment options for the tool cutting wedge tip.