Seznam abstraktů 2025: SEKCE C - OCELI, VLASTNOSTI, VÝROBKY Z OCELÍ, TESTOVÁNÍ

Modern scanning electron microscopes are equipped with sophisticated detection systems and enable to visualization of a pecimen surface at various landing energies of the primary beam. Signal electrons emitted from the specimen surface are effectively filtered based on their initial energy and emission angle. Filtering of the signal electrons enables us to optimize the desired contrast in the micrographs and suppress artifacts. Recent SEMs can be operated at energies from 30 keV up to tens of eV. This combination of detection flexibility together with the variability of landing energies of the primary electrons opens a new world of contrast mechanisms and enables more precise and accurate insight into the microstructure of advanced steels.

We present a software to automate the circular line method to determine interlamellar distance in pearlite, two-phase steel. Such a distance is a material parameter that closely relates to material properties including strength, toughness and ductility.
Use-workflow is the following. User performs initial configuration, and they select positions of circles in the microscopic images to analyse. This user input is followed by internal segmentation of the images into the individual lamellae and counting intersections of the relevant lamellae with the circles. This means that the manual processing of individual files and circles is automated using this software once the circle positions are selected.
Data output is a collection of CSV files of three types - circle center positions, intersection count per both file and circle and finally a statistical overview.

The presented Python-based software is distributed in form of compiled binary files provides a simple GUI to improve the user experience, both Windows and several Linux distributions (successfully built on Windows 11 and a Debian-based distribution) are supported. The only external dependency is Tesseract OCR tool if one wishes to uses automated pixel size determination from data-bar.

Induction thermography is a well-established method for detecting and analyzing cracks in metal products, such as rails. However, quantifying defects, particularly those with complex geometries, remains a challenging and intricate task. This paper addresses one critical aspect of defect quantification: the determination of crack inclination angles, which is essential for accurate depth estimation and hazard level assessment. We propose a novel approach that combines induction thermography data analysis with machine learning regression models to estimate crack angles. The regression model is trained on a dataset generated through numerical simulations, ensuring robust and reliable performance. The effectiveness of the proposed method is demonstrated through both numerical and experimental results, showcasing its potential for improving crack characterization in industrial applications. This work advances the field of non-destructive testing by providing a more precise and automated solution for crack inclination angle determination, contributing to enhanced structural integrity assessments.

This research investigates the influence of semi-elliptical cracks, postulated near the plastic deformation region during pipe whip failure conditions. Pipe whip is a high-energy phenomenon resulting from sudden rupture in pressurized piping systems and pose a significant threat to the structural integrity and safety. This research focuses on how the presence of semi-elliptical cracks alter the stress distribution, deformation behaviour and failure characteristics during such dynamic failure events. With the applications of numerical simulations and the principles of fracture mechanics, the manuscript presents the interaction between crack geometry, pipe curvature due to plastic deformation, and dynamic loading conditions. Key findings include the amplification of stress intensity factors in the postulated cracked regions which exacerbates local plastic deformation due to their curvature under whipping forces. Additionally, this study highlights the critical role of crack dimensions and orientation in determining failure thresholds and provides insights into the energy dissipation caused by defects. The results aim to enhance predictive models for pipe failure assessment and adopt design strategies for mitigating risks associated with pipe whip. This research contributes to safer pipeline operations by integrating crack behaviour into dynamic response analyses, offering a foundation for improved structural resilience in high-energy piping environments.

High-strength, low-alloy (HSLA) steels, although known for years, are not very popular in the industry. Controlled thermo-mechanical rolling poses significant challenges for process engineers and is only feasible in a few rolling mills worldwide. An example is the Krakow Hot Rolling Mill of ArcelorMittal Poland S.A., where such steels can be produced. When designing a process for the production of HSLA steels, it is extremely important to know the temperature at which the recrystallization stops (so called recrystallization stop temperature, RST) - the process should be carried out in such a way that the last passes are already below this temperature, and at the same time care should be taken to ensure that the transformation from austenite to ferrite is close to this temperature - the rolling should take place entirely in the single-phase range. In this study, the authors analyzed the current production process in Krakow, Poland, with a view to the occurrence of a recrystallization stop temperature. The equations available in the literature to calculate the RST were also analyzed. Laboratory tests were carried out on representative HSLA steels to determine the actual level of RST. What’s more, the authors proposed their own approach to determine the level of RST based on the process parameters. The work is an important contribution to improving the design process of HSLA steel production at the Krakow rolling mill.

Although high entropy alloys (HEAs) have captured significant attention over the years, nanocrystalline microstructure of HEAs, like that of conventional alloys, are unstable against grain growth due to high volume fraction of grain boundaries that they possess. For example, our experimental results have revealed that 16 nm initial grain size of CoCrFeNi HEA experienced grain coarsening during the annealing process above 700 °C, reaching over few microns after annealing at 1100 °C. As a result, the initial hardness of nanocrystalline CoCrFeNi HEA, measured as 517.8 (±25) HV, decreased substantially to 221.5 (±11) HV after 1 h of annealing at 1100 °C, and continued to decrease with prolonged annealing, reaching 184 (±6.4) HV as the annealing time was extended. These findings suggest that nanocrystalline microstructure of CoCrFeNi HEA lacks grain size stability at elevated temperatures. Thus, the microstructural stability of nanocrystalline HEAs is of critical importance that needs to be investigated to widen their processing capabilities and potential structural applications. In this study, the effect of solute additions and second-phase incorporations was investigated with respect to grain size stability of nanocrystalline CoCrFeNi HEAs upon temperature exposures. Microstructural evolutions and grain growth behavior were characterized using focused ion beam microscopy (FIB), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The effect of final microstructure on hardness was utilized to study mechanical changes induced by temperature exposures, as well as the influence of solute additions and second-phase incorporations.

Understanding the deformation mechanisms of materials under extreme temperature conditions is crucial for their reliable application. This study presents an advanced mechanical testing methodology that integrates acoustic emission (AE) and electrical resistivity measurements during tensile loading at both elevated and cryogenic temperatures. The combination of AE and resistivity monitoring provides real-time insights into microstructural changes, and phase transformations. The results highlight the correlation between mechanical behavior, and defect evolution, offering a comprehensive approach to material characterization under non-ambient conditions.

The frames of tank semi-trailers are usually made of carbon steel. However, this steel is susceptible to corrosion. During the exploitation of the semi-trailer, the protective paint layer is damaged, and the frame is exposed to the atmospheric effects, road salts, and other reagents used in cold weather conditions. According to this metal forming company AB Astra LT aims to design and produce a lightweight tank semi-trailer for the food industry products, the production of which stainless steel would be used. For this purpose, LDX 2101 duplex steel was chosen. This steel not only looks good esthetically but also has high corrosion resistance and high mechanical strength.
This paper presents the fatigue analysis of the frame of a tank semi-trailer. To accomplish this task the experimental fatigue tests of x-type specimen were conducted, and FEM simulations were performed. Experimental tests were used for the construction of the S-N curve of welded duplex steel. Later, this curve was used in numerical simulation. The FEM simulation was performed in several steps. First of all, the dynamic analysis of the whole semi-trailer frame with a tank was analyzed, imitating the driving on the roughly paved tarmac road. This simulation allowed determining the most loaded section of the frame and stress profile vs time at this section. The second model was the x-type specimen model used for the calibration of fatigue analysis. The final model was the small portion of the most loaded part of the H beam of the semi-trailer frame. Using the H beam model, the experimentally determined S-N curve and the loading spectra were applied, and as a result, the total lifetime cycles were determined. Research has shown that the designed tank semi-trailer can travel up to 5.1 million km on roughly paved tarmac roads.

The aim of this research was to study the effect of Nickel additions to high strength steel alloys and to obtain an optimal chemical composition that does not compromise the tensile strength and wear resistance properties provided by the original equipment manufacturer (OEM) with cost saving to the manufacturing local foundry. The nickel content was added in composition from 0.5 wt.% to 3.5 wt% to the molten metal. The test bar was then cut from the keel block and sectioned for laboratory analysis for determining tensile strength properties (ultimate tensile strength. yield strength and % elongation and wear resistance.
The results obtained shows that there is significant increase in tensile strength and wear resistance and slight decrease in toughness with increase in nickel additions. The best optimal chemical composition was observed to be 2.0% nickel alloy for optimal cost to fulfil the OEM mechanical and wear properties for the high strength steel used for mining grounding application, so this meant a 22.7% cost saving when compared to the current chemical composition used in the foundry.