No 4 (2025)

High-boron 9–10 % chromium martensitic steels are an advanced material for manufacturing various components of thermal power units in coal-fired power plants operating under ultra-supercritical steam conditions (up to 650 °C and 35 MPa), enabling an increase in efficiency to 44 % and reduction of harmful environmental emissions. The work studies the influence of various testing conditions on the behaviour of a 10 % Cr martensitic steel with high boron and low nitrogen content, additionally alloyed with cobalt, tungsten, molybdenum, copper, and rhenium, under lowcycle fatigue (LCF). After heat treatment, the steel microstructure consisted of tempered lath troostite with a high dislocation density. The main strengthening phases were identified: grain-boundary M23C6 carbide particles with an average size of 70 nm and uniformly distributed NbX carbonitrides with an average size of 30 nm. Increasing the strain amplitude during low-cycle fatigue significantly reduces the number of cycles to failure regardless of test temperature, due to intensive development of plastic deformation. Microstructural analysis revealed no significant changes in the lath structure after low-cycle fatigue testing at room temperature, while at elevated temperatures, structural recrystallisation initiates and a well-developed subgrain structure with an average subgrain size of about 600±50 nm forms.

Modern industrial technologies place high demands on materials used in aggressive environments, high mechanical loads, and long-term service. One of the effective solutions to this problem is the creation of bimetallic joints that combine the advantages of dissimilar materials. In particular, the combination of carbon steels possessing high strength and availability with austenitic stainless steels characterized by high corrosion resistance and ductility allows producing composite materials with optimal performance characteristics. This paper examines a bimetallic material produced by arc surfacing of Er308LSi austenitic stainless steel wire on St3 carbon steel. The main objective was to determine the feasibility of using magnetic nondestructive testing methods to assess the phase composition of the bimetallic joint, including taking into account its possible changes after deformation. Metallographic and X-ray diffraction studies of the resulting material were conducted. Step-by-step plastic deformation tests were performed on samples cut from different parts of the resulting material. After each step of plastic deformation (in the unloaded state), magnetic hysteresis loops of the tested samples were measured. It was found that the use of existing approaches for estimating the martensite phase content based on magnetic properties is difficult. This is due to the complex structural and phase composition of the studied material manifested by the presence of a second peak of differential magnetic permeability for ferrite in St3 steel, the presence of ferrite in the upper deposited austenitic layers, and martensite in the first layer. The authors proposed a parameter based on the asymmetry of the difference in the field dependences of differential magnetic permeability. This parameter has a clear correlation with the magnitude of plastic deformation and, consequently, with the content of deformation martensite.

Russian 12-% chromium ferritic-martensitic EK-181 steel (RUSFER-EK-181 Fe–12Cr–2W–V–Ta–B) is a promising structural material for power plants. This paper investigates the effect of thermomechanical processing with plastic deformation in the austenitic region at 1000 °C and 1100 °C on the structural and phase state of EK-181 ferritic-martensitic steel and its microhardness value. The results of the study demonstrated that under these thermomechanical processing conditions, a microstructure forms characterized by martensitic laths, fine plates of cementite and retained austenite, as well as MX-type carbonitride particles (M – V, Ta, Ti; X – C, N). Under high-temperature tempering (720 °C, 1 h), the thermomechanically processed steel exhibits coarsening of structural elements, a reduction in dislocation density, and precipitation of M₂₃C₆ carbides (M – Cr, Fe, Mn, W). Meanwhile, MX carbonitrides exhibit high thermal stability and retain their sizes. After tempering, cementite and retained austenite were not detected. A decrease in the deformation temperature leads to an increase in crystal lattice microdistortions and a reduction in coherent scattering regions. The obtained results were compared with the microstructural characteristics of the studied steel after conventional heat treatment (CHT). It was demonstrated that plastic deformation in the austenitic region ensures a reduction in the average size of prior austenite grains by 2 times, martensitic laths by 1.5 times, and M₂₃C₆ particles by 2 times compared to the CHT condition. Furthermore, higher dislocation densities and crystal lattice microdistortion values are observed. After thermomechanical processing with deformation at 1000 °C and 1100 °C, microhardness values reach 4.6 GPa and 3.9 GPa, respectively. Subsequent high-temperature tempering reduces microhardness to 2.8 GPa and 2.9 GPa, respectively. These microhardness values after thermomechanical processing and tempering are 10 % higher than values achieved after conventional heat treatment.

The paper deals with the development of a system for integrated assessment of machinability based on monitoring tool displacements and cutting temperatures. This system is characterised by its simplicity and low cost. The proposed approach to evaluating material machinability combines static and dynamic components of cutter displacements, as well as cutting temperature, each assigned specific weighting coefficients. The material machinability evaluation is differentiated for roughing and finishing operations through weighting coefficients that take into account the specific influence of each parameter on the machining results. This differentiated approach enables assessment of material machinability both from the perspective of resistance to deformation and fracture and considering specific cutting process characteristics. The dynamic displacement component serves as a diagnostic characteristic for the chip formation process (elemental, segmented, or continuous), surface roughness quality, and, when combined with temperature, for cutting tool life. Experimental results from end milling of 45 and 09G2S steels, along with VT6 and VT8M-1 titanium alloys with varying grain sizes, demonstrate the practical application of this methodology. Standardised experiments provided displacement and temperature data used to evaluate the machinability of tested materials. The results confirm the feasibility of using the proposed comprehensive indicator for assessing material machinability in cutting processes. This approach forms the basis for the development of a new comprehensive machinability assessment method that considers individual parameters and their combinations to determine technological constraints, thereby enabling process optimisation and production cost reduction.

Simultaneous doping of TiNi alloy with copper and zirconium by substituting zirconium for titanium and copper for nickel while maintaining the quasi-binary (Ti₃₅Zr₁₅)(Ni₃₅Cu₁₅) composition enables the formation of two fundamentally different phase states – amorphous and crystalline – as a result of exposure of the material to low- and medium-energy ion beams. An amorphous layer synthesised from the same alloy on the surface of a medical implant made of a Ti–Ni–Cu–Zr alloy, not functional (stents, occluders), but structural (intervertebral discs, orthopedic braces), will allow protecting effectively the implant from the permanent effects of aggressive biological environments of any type (biological fluids, soft tissue, and bone). However, ion-beam modification of the Ti–Ni–Cu–Zr alloy surface can induce residual stresses that can change the properties of the original material. According to X-ray diffraction analysis, niobium ion treatment results in the formation of a layered structure with an amorphous-crystalline surface layer, a B2 matrix phase, and secondary (Ti,Zr)₂(Ni,Cu) and TiZr phases. It was found that the B2 phase is a superposition of two phases, one of which, B2^core, predominates in the deeper layers of the sample, while B2^surf, conversely, is formed primarily in the surface layers. Analysis of the elastic stress state revealed that beneath the ion-modified surface layer, the B2^surf phase is in a tensile state, while the B2^core phase is in a compressed state, which indicates a complex interaction between the phases and the fact that the stresses in them can mutually compensate for each other. The obtained results are important for understanding the influence of ion implantation on the structure and properties of Ti₃₅Ni₃₅Cu₁₅Zr₁₅ alloys and optimising processing modes for medical applications.