Piotr Matusiewicz

The paper presents the results of experimental studies on the effect of thermal exposure (500°C and 700°C) on the microstructure, mechanical properties and acoustic emission (AE) signatures of cold‐drawn prestressing bars. Specimens in the as‐received state (RT) and after annealing at 500°C and 700°C were subjected to uniaxial tensile tests to failure, with simultaneous AE signal acquisition. The analysis was based on a three‐parameter diagnostic approach employing the Ib‐value index, the number of counts and the amplitude–duration relationship, enabling quantitative detection of the moment of load‐bearing capacity loss. It was shown that for RT specimens, the failure process is ductile with late crack localisation; for S_500 specimens, it is abrupt, while for S_700 specimens, it is dispersed and microplastic. Changes in AE parameters exhibit a clear correlation with microstructural evolution: from lamellar pearlite in the RT state, through partial spheroidisation and lamella fragmentation at 500°C, to complete spheroidisation and cementite coarsening at 700°C. A decision criterion was developed, based on a permanent exceedance of the stability threshold in at least two out of the three analysed AE parameters, which enabled consistent identification of the failure moment within the investigated specimens and constitutes a potential diagnostic tool for assessing the integrity of steel components under and after fire exposure.

DP600 steel is widely used in the automotive industry due to its exceptionally favourable combination of high tensile strength and good ductility. In the hot-rolling process, DP600 steel is produced by use of controlled cooling of the rolled strip from temperature above Ar3 to temperature below Ms. In this process, it is quite difficult to control key process parameters such as the time or temperature, and the final microstructure of the material is also affected by the degree of deformation of the material at various stages of the process. This paper presents a statistical analysis of the effect of chemical composition and selected hot rolling process parameters on the microstructure of DP600 sheet with respect to its mechanical properties. Based on industrial data from hot rolling mill combined with extended microstructure analysis, it was possible to find correlations between some of the analysed parameters and material properties. Among many correlations discussed in this work, most notable are those between martensite morphology and mechanical properties, between Mn and Si concentration and martensite morphology and between rolling speed, strain, cooling rate and mechanical properties.

This paper presents a study on optimising self-brazing powder mixtures for powder metallurgy diamond tools, specifically focusing on wire saws used in cutting natural stone. The research aimed to understand the relationship between the chemical composition of powder mixtures and the hardness of the sintered matrix. The experimental process involved the use of various commercially available powders, including carbonyl iron, carbonyl nickel, atomised bronze, atomised copper, and ferrophosphorus. The samples made of different powder mixtures were compacted and sintered and then characterised by dimensional change, density, porosity, and hardness. The obtained results were statistically analysed using an analysis of variance (ANOVA) tool to create linear regression models that relate the material properties to their chemical composition. The investigated materials exhibited excellent sintering behaviour and very low porosity, which are beneficial for diamond retention. Very good sinterability of powder mixtures can be achieved by tin bronze addition, which provides a sufficient content of the liquid phase and promotes the shrinkage during sintering. Statistical analysis revealed that hardness was primarily affected by phosphorous content, with nickel having a lesser but still significant impact. The statistical model can predict the hardness of the matrix based on its chemical composition. This model, with a determination coefficient of approximately 80%, can be valuable for developing new metal matrices for diamond-impregnated tools, particularly for wire saw beads production.

The aim of the present study was to develop a concept for the inverse analysis of wear mechanisms in cast steel wheels of a pig iron wagon after long-term operation. Samples were taken from the flange and the tread edge area of fourteen wheels. The impact of wheel parameters and repair methods on their wear was assessed. An analysis was carried out to determine whether welds were made as part of casting correction or as repair welds. Changes in the microstructure of the weld area, the heat-affected zone, and the parent material resulting from operation were determined. The main wear mechanism in the area of the welds and the parent material is the plastic flow of the material resulting from high unit pressures. The hardness of the material is found to be contingent upon its chemical composition, the microstructural components, and the degree of plastic deformation resulting from wear (it has been established that increasing alloying results in increased hardness; a comparable effect is observed in the formation of non-equilibrium structures (bainite)). The increase in hardness is attributed to strain hardening, a consequence of exploitation. Research and analytical methods have been developed to differentiate the results of repair processes for wear effects in a highly loaded friction node with non-stationary lubrication conditions from repair processes applied to castings of large structural components.

This article introduces a novel approach for assessing microstructure, particularly its degradation after extended operation. The authors focus on creep processes in power plant components, highlighting the importance of diagnostics in this field. This article emphasizes the value of combining traditional microstructure observation techniques with image analysis. A non-destructive method of evaluating microstructure parameters (matrix replicas) is presented, and its accuracy is evaluated against the conventional destructive method. The assessment utilizes quantitative data derived from classical stereological principles and image analysis. Parameters like mean chord length, relative surface area, mean cross-sectional area, and mean equivalent diameter are compared for replica and metallographic specimens. The results show that the replica method accurately reproduces the microstructure. In their conclusions, the authors highlight the importance of developing visual methods alongside the application of artificial intelligence while indicating the challenges in achieving this goal.

Alloyed high-carbon steels are materials primarily intended for components operating under conditions of intense tribological wear. The carbides present in the microstructure of these materials significantly contribute to improving the wear resistance of such alloys. However, changes in the morphology of these precipitates can considerably alter the wear rate, leading to a deterioration in the properties of the materials. Therefore, this study aims to analyze the influence of several factors on the tribological wear of alloyed high-carbon steel. The research included friction tests under various load conditions and different sliding paths. Additionally, the samples were subjected to heat treatment to change the morphology of the observed precipitates. The tribological tests were conducted in a block-on-ring configuration under dry friction conditions. The tribological tests were analyzed statistically using analysis of variance (ANOVA). The results of the statistical analysis indicated that the primary factor influencing the observed differences between the samples was the heat treatment time of the material. Additionally, there were no significant statistical differences when pressure and friction path were varied. These findings, in conjunction with the SEM studies, allowed for the evaluation of the wear mechanism. The results demonstrated that, within the adopted tribological system, no alterations in the wear mechanism were observed with changes in test parameters. The observed differences in wear properties between the samples were found to be related to their heat treatment. The heat treatment resulted in alterations to the particle size distribution, with the annealing of the material at an elevated temperature leading to the dissolution of finer particles within the material. An increase in the average diameter of the carbide present in the material was observed to improve the wear resistance of the alloy tested.

The types and volume fractions of the carbonaceous phases present in the microstructures of cast irons strongly influence their properties. In the case of materials used commercially for tools, an important parameter with regard to their use is the resistance to abrasion wear. Cementite is the main reinforcing phase in cast irons and is present in significant quantities. In addition, cast irons contain graphite precipitates, which also affect wear by interacting with the matrix of the alloys. In this study, abrasive wear tests were carried out on a group of cast irons with different chemical compositions and, consequently, different microstructural morphologies. Due to the wide scatter of the results and the commercial rather than laboratory nature of the alloys studied, it was decided to use analysis of variance (ANOVA) to determine whether there was a statistically significant difference between the volume fractions of the carbonaceous phases. The volume fractions of graphite and ledeburite were then related to the results of the tribological tests. Statistical analysis confirmed significant differences in the results obtained for the alloys tested. A continuous increase in the volume fractions of both graphite and ledeburitic cementite is unfavourable in terms of the wear resistance and friction coefficient values. Optimum results can be obtained by balancing the volume fractions of the two phases observed. In addition, the phase composition of the material matrix plays an important role in wear, as the differences in the matrix of the tested alloys modify the nature of the influence of cementite and graphite on the wear.

The paper presents the results of tests of tribological wear of two Co-Cr-Mo alloys (Wironit LA) andCo-Cr-Mo-W (Colado CC) used to make skeletal prostheses, combined works, implants and metalframeworks for ceramics. The test samples were centrifugally cast using the lost wax method and subjected tohardness measurements, microscopic observations, and a quantitative description of the microstructure. SEMexaminations and EDS analysis of micro-areas on dendritic arms and interdendritic areas were performedtogether. The abrasive wear resistance tests with the use of a T-05 tester in the friction system roller-blockwere conducted in a dry sliding contact under the conditions of a metal-metal contact with the load of 100 Nand for two friction paths, 500 and 1000 m.

The pearlite spheroidization in Fe-0.76%C high purity steel was investigated. The samples of a coarse pearlite microstructure were isothermal annealed at 700, 680, 660, 640 and 620°C for various times, up to 800 hours. For quantitative description of the spheroidization process stereological parameter, S_V (ferrite/cementite interface surface density) was used. The activation energy 104.8±11.4 kJ/mol was found for the spheroidization process. This value shows good agreement with the activation energy for iron and carbon diffusion along a ferrite/cementite interface, so the coupled interface diffusion is the rule-controlling process.