The aim of this work is to perform a detailed dilatometric analysis of the decomposition of austenite during the cooling process using experimentally derived continuous cooling transformation (CCT) diagrams for two specific tool steels, X153CrMoV12 Bohdan Bolzano, Bratislava, Slovakia and 100MnCrW4. The dilatometric curves were compared with metallographic evaluations using scanning electron microscopy (SEM). In addition, hardness measurements were performed to obtain additional information about the mechanical properties of the materials. All experimental work was performed using a DIL 805A. The accuracy of the resulting CCT diagrams was verified by comparing them with those calculated with the JMatPro software v12.4. The cooling rates ranged from 20 °C/s to 0.01 °C/s, depending on the specific type of steel tested. The novelty of this research is the combination of experimental and simulation methods to analyze the influence of alloying elements on the kinetics of phase transformations in tool steels. It was found that one of the most significant factors affecting the CCT diagrams is the weight percentage of alloying elements in the steels. These results clearly show that increasing the weight percentage of the content of alloying elements has a significant impact on the accuracy of the simulation results derived from the JMatPro software.

The paper deals with the dilatometric study of high-alloy martensitic tool steel with the designation M398 (BÖHLER), which is produced by the powder metallurgy process. These materials are used to produce screws for injection molding machines in the plastic industry. Increasing the life cycle of these screws leads to significant economic savings. This contribution focuses on creating the CCT diagram of the investigated powder steel in the range of cooling rates from 100 to 0.01 °C/s. JMatPro^® API v7.0 simulation software was used to compare the experimentally measured CCT diagram. The measured dilatation curves were confronted with a microstructural analysis, which was evaluated using a scanning electron microscope (SEM). The M398 material contains a large number of carbide particles that occur in the form of M₇C₃ and MC and are based on Cr and V. EDS analysis was used to evaluate the distribution of selected chemical elements. A comparison of the surface hardness of all samples in relation to the given cooling rates was also carried out. Subsequently, the nanoindentation properties of the formed individual phases as well as the carbides, where the nanohardness and reduced modulus of elasticity (carbides and matrix) were evaluated.

The presented work deals with the investigation of mechanical tribological properties on Inconel 625 superalloy, which is welded on a 16Mo3 steel pipe. The wall thickness of the basic steel pipe was 7 mm, while the average thickness of the welded layer was 3.5 mm. The coating was made by the cold metal transfer (CMT) method. A supercritical bending of 180° was performed on the material welded in this way while cold. The mechanical properties evaluated were hardness, wear resistance, coefficient of friction (COF) and change in surface roughness for both materials. The UMT Tribolab laboratory equipment was used to measure COF and wear resistance by the Ball-on-flat method, which used a G40 steel pressure ball. The entire process took place at an elevated temperature of 500 °C. The measured results show that the materials after bending are reinforced by plastic deformation, which leads to an increase in hardness and also resistance to wear. Superalloy Inconel 625 shows approximately seven times higher rate of wear compared to steel 16Mo3 due to the creation of local oxidation areas that support the formation of abrasive wear and do not create a solid lubricant, as in the case of steel 16Mo3. Strain hardening leads to a reduction of possible wear on Inconel 625 superalloy as well as on 16Mo3 steel. In the case of the friction process, the places of supercritical bending of the structure showed the greatest resistance to wear compared to the non-deformed structure.

Microstructure and mechanical properties of polymer matrix composites (PMCs) using as-received biochar derived from kitchen bio-waste and Hexion LR160 epoxy as the matrix material were investigated. The PMCs were produced via glass moulding with higher biochar contents of 10 wt.%, 20 wt.%, and 30 wt.%. Scanning electron microscopy (SEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) were used to analyze the microstructure, chemical composition, and interfacial bonding. SEM analysis revealed biochar agglomeration at lower concentrations and increased homogeneity at higher biochar contents. Raman spectroscopy confirmed biochar’s disordered carbon structure (ID/IG = 1.10), while FTIR analysis identified characteristic functional groups suggesting mechanical adhesion between biochar and the epoxy matrix. Mechanical testing showed a modulus increase from 3.61 GPa (pure epoxy) to 4.98 GPa (PMC-C30). Tensile strength, initially lower than pure epoxy (62.00 MPa), increased from 21.00 MPa (PMC-C10) to 32.2 MPa (PMC-C30) with higher biochar content, indicating its reinforcing potential. Hardness increased from 175 HB (pure epoxy) to 237 HB (PMC-C30), further confirming biochar’s strengthening effect. The results of this study contribute to demonstrating biochar’s potential as a sustainable filler, supporting eco-friendly composite development while reducing the environmental footprint of polymer-based materials.

Copper–graphite composites are promising functional materials exhibiting application potential in electrical equipment and heat exchangers, due to their lower expansion coefficient and high electrical and thermal conductivities. Here, copper–graphite composites with 10–90 vol. % graphite were prepared by hot isostatic pressing, and their microstructure and coefficient of thermal expansion (CTE) were experimentally examined. The CTE decreased with increasing graphite volume fraction, from 17.8 × 10⁻⁶ K⁻¹ for HIPed pure copper to 4.9 × 10⁻⁶ K⁻¹ for 90 vol. % graphite. In the HIPed pure copper, the presence of cuprous oxide was detected by SEM-EDS. In contrast, Cu–graphite composites contained only a very small amount of oxygen (OHN analysis). There was only one exception, the composite with 90 vol. % graphite contained around 1.8 wt. % water absorbed inside the structure. The internal stresses in the composites were released during the first heating cycle of the CTE measurement. The permanent prolongation and shape of CTE curves were strongly affected by composition. After the release of internal stresses, the CTE curves of composites did not change any further. Finally, the modified Schapery model, including anisotropy and the clustering of graphite, was used to model the dependence of CTE on graphite volume fraction. Modeling suggested that the clustering of graphite via van der Waals bonds (out of hexagonal plane) is the most critical parameter and significantly affects the microstructure and CTE of the Cu–graphite composites when more than 30 vol. % graphite is present.

This study evaluates the tribological properties of lean medium manganese advanced high-strength steel (AHSS) subjected to five different heat treatment processes. The tests were conducted under dry reciprocating conditions using the ball-on-flat method, with a G40 steel ball, a 10 N load, and 1000 cycles at room temperature. Friction behavior, wear resistance, nanoindentation hardness, surface roughness, and microstructural changes were examined. The results showed that heat treatment significantly influenced the microstructure and hardness of the samples. The Mn-Q sample, with fresh martensite, achieved the highest hardness (483 HV5), while the Mn-Q&P 500 °C sample had the lowest (336 HV5), with a 30% reduction due to tempering. The Mn-HR 500 °C sample showed the highest surface roughness (Sa = 1.876 μm) due to microstructural heterogeneity. Despite similar coefficients of friction across all samples (0.55–0.57), the Mn-Q&P 500 °C sample exhibited the best wear resistance, 18% higher than the Mn-HR 500 °C variant. Wear mechanisms were identified as a combination of abrasion and oxidation, where the latter slightly reduced the coefficient of friction (COF) but increased surface degradation. These findings highlight the potential of lean medium Mn AHSS for tribological applications, offering a favorable balance of wear resistance and frictional stability.