Seznam abstraktů 2025: POSTEROVÁ SEKCE C
Datum: 22.5.2025
High-strength steels, such as S460 and S690, are frequently utilized in structural applications due to their exceptional mechanical properties. Nevertheless, protracted exposure to corrosive environments can substantially impact their fatigue performance. Corrosion results in localized surface damage, which functions as a stress concentrator, expediting fatigue crack initiation and propagation. It is imperative to comprehend how corrosion affects the fatigue life of HSSs to ensure the durability of steel structures in severe environmental conditions.
This study investigates the impact of corrosion on the fatigue resistance of S460 and S690 steel specimens. Specimens were exposed to controlled corrosive conditions before undergoing cyclic loading to evaluate their fatigue behavior. Stress distribution around corroded regions was analyzed to determine how surface degradation influences fatigue crack initiation. The results provide insight into differences in corrosion susceptibility between S460 and S690 steels, highlighting the role of stress concentration in fatigue performance reduction.
Acknowledgment
This research work was supported by the Faculty of Civil Engineering, Brno University of Technology under the project FAST-S-25-8839.
The article discusses the analysis of the durability of suspension springs in a passenger car after long-term operation. The spring failed after 14 years of use, the car covered 225,000 km during that time. The aim of the study was to evaluate the durability of suspension springs in the context of their long-term operation, taking into account material fatigue and factors affecting failure. The article considers the causes of failure and the impact of operating conditions on the durability of suspension components.
The experiment was focussed to the material choice process by several parameters. First, the ability to achieve excellent mechanical properties in high-strength quenching and partitioning (QP) structure and in medium-strength structure like bainitic or complex-phase structures as well. Secondly, the price of the steel. The alloying concept had to be simple and suitable for large scale production in highly competitive automotive industry.
The QP process is able to achieve excellent combination of strength and ductility in a low alloyed steels. However, the process itself is rather difficult to implement into a serial production of high strength parts as it is demanding precisely controlled temperature cycle for each part. Hot metal gas forming (HMGF) is a technology with potential to provide QP thermal treatment within tight constraints. Moreover, the tool for HMGF can be segmented from materials with different thermal conductivity. This results in a different cooling rates, different microstructures and ultimately in a different mechanical properties in different areas of the part which can be favourable for the for lightweight design.
Phase transitions knowledge is essential for assessing the steel potential. First selection was done by computing austenite decomposition diagrams in JmatPro software for various chemical compositions. Three selected steels have been casted as 500 kg test batches and dilatometer analysis was performed to map the austenite decomposition. Steels 42SiCr, 38SiCr and 32MnB5 were able to achieve favourable microstructures at different strength levels.
The growing concern for environmental sustainability in industrial processes has led to the development of an environmentally friendly electrolyte for hydrogen embrittlement testing of steels. In this study, a new electrolyte composed of sodium dihydrogen phosphate (NaH₂PO₄), disodium hydrogen phosphate (Na₂HPO₄), L-cysteine (C₃H₇NO₂S), and citric acid (C₆H₈O₇) was tested as an alternative to the conventional 0.5 N sulfuric acid (H₂SO₄) electrolyte combined with thiourea (CH₄N₂S). The samples, made from ČSN 13 030 steel, were subjected to electrolytic hydrogen charging for two different durations: 6 hours and 24 hours. After 6 hours, Charpy impact tests were conducted, followed by fractographic analysis to assess the fracture morphology. After 24 hours, the hydrogen content in the samples was measured. The results showed that after 24 hours, the hydrogen content in the samples treated with the new electrolyte was comparable to, or even higher than, that obtained with the traditional sulfuric acid-based electrolyte. This indicates that the new electrolyte not only offers effective hydrogen charging but also presents a more sustainable and environmentally friendly alternative. These findings suggest the potential of the new electrolyte for future applications in hydrogen embrittlement testing without the environmental drawbacks associated with conventional electrolytes.
Digital image analysis in the study of geometric structures of machine parts and engineering materials is a complex issue that the author tries to systematize and generalize, treating it as a process.
The article proposes a comprehensive approach independent of the observation scale, material type, and purpose of analysis. Key stages of analysis have been identified, from determining technological needs and the research goal to selecting the scale, devices, and methods of assessing the structures of the tested object based on digital images, which leads to obtaining results.
The process approach proposed in the article, identification of key objects, their features, and mutual relations, will allow for creating an expert system that, regardless of the researcher's experience, will enable consulting in selecting the optimal research plan.
Materials for Ag-rare earth (RE) binary alloys are used in electronic applications. They attract theoretical and industrial research interests.In the production of these materials, knowledge of the phase diagram and thermodynamic properties is essential. There are many literature data on binary RE-Ag systems, especially those from phase diagrams. But large discrepancies exist between the data from different sources.
The alloys to be studied are binary alloys based on rare earth silver (R-Ag) with R= Ce, Gd, La and Yb). These alloys have a large number of defined compounds at different concentrations. The common compositions between these binary alloys are: 〖R_2 〖Ag〗_9,R_2 〖Ag〗_7,R_3 〖Ag〗_2,R〗_5 〖Ag〗_2,R_2 〖Ag〗_4,RAg,R_5 〖Ag〗_3. In this work we present results of prediction of enthalpies of formation fpr AgRE binary compounds using Miedema’s model.
The study is devoted to changes in the structural and physical properties of AISI 304 austenitic stainless steel exposed to sever plastic deformation at room temperature. The steel was deformed using two methods, namely by pressure corresponding to compressive forces of 100 kN and 150 kN and by Dual Rolling Equal Channel Extrusion (DRECE) technique, resulting in the transformation of paramagnetic austenite into ferromagnetic martensite. The results of the X-ray diffraction (XRD) from the surface depth of about 10 m were correlated with the bulk magnetic properties measured using the vibrating sample magnetometer. The analyses of results have pointed the low stability of the austenitic structure. The partial transformation of austenite into martensite was evidenced by XRD with an amount of martensite up to 38% and 45% detected after application of DRECE and compressive force of 150 kN. The change in structure was also reflected in the bulk magnetic properties of the steel. In comparison to the as-cast state the magnetization in a magnetic field of 2 Tesla was approximately 2.3, 3 and 6 times higher after application of 100 kN force, DRECE, and 150 kN force. The partial transformation of austenite into martensite was also demonstrated by metallographic analysis and microhardness measurements. In both methods of plastic deformation, strain hardening of the steel occurs, which led to an increase in microhardness in comparison to the as-cast state. Recovery of the fully paramagnetic state was achieved after annealing the steel at 950 °C for 30 minutes. These results provide valuable information for optimizing the steel in practical applications.
A comparable study was conducted for the tribology behaviour of wrought and LPBF C300 maraging steel. Additionally, a heat-treatment was applied to both conditions at 490 ⁰C for 6 hours. At a load of 20 N for 30 minutes, the tribo-tests were conducted. Pre-tribology characterization such as microstructural analysis, phase detection, dislocation density, and length of HAGBs were analyzed using Field Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), and EBSD, respectively. The characterization of wear scars was carried out using FESEM-EDX, and X-ray Photoelectron Spectroscopy (XPS). In all the four samples Fe3O4, Ni(OH)2, CoO, and MoO3 were detected. Due to the combined effect of grain size, length of HAGBs, and dislocation density in the LPBF samples, the wear resistance of samples was higher. LPBF samples have shown higher wear resistance and less wear depth when compared with wrought samples. Moreover, after heat treatment, the wear resistance increased, and wear depth decreased.
The European Union is committed to replacing natural gas with hydrogen by 2050 as part of its search for clean and sustainable energy sources. Given these goals, it is crucial to examine the materials used in current gas infrastructure and assess their susceptibility to hydrogen embrittlement, a common form of material degradation. In this article, a comparative evaluation of fracture toughness was assessed on CT specimen from operated X-60 steel used in Czech gas distribution infrastructure. J-R curves in air and in-situ 10 MPa hydrogen gas were constructed and initiation value J0.2 was determined, followed by SEM fractographic analysis. The results showed significant decrease in initiation value in high-pressure hydrogen which was accompanied by fracture morphology change in stable growth region from ductile dimple with microvoid coalescence to quasi-cleavage/cleavage.
The goal of this review is to examine the possible use of ex-post quantitative fractography in development of aircraft design concepts. The resent investigations using quantitative fractography for the reconstitution of fatigue process history indicated limitations of fatigue crack growth and material toughness based tests in interpreting fatigue behavior. Inevitable deviations in the in-service load histories, changes in mission types, increase in weight and severity of service conditions resulted in fatigue problems that could not be foreseen by the initial Safe-life and Damage-tolerant designs. However, to ensure the validity of results, there is a need for standardization and unified methodology in fractographic analysis, particularly when it comes to failure analysis.
The article describes the corrosion attack and premature damage in stainless steel drinking water piping installed in a hospital. After only two years of service, intensive pitting and crevice corrosion was observed near welded joints, resulting in wall perforation. The analyses performed on damaged tubes revealed that corrosion attack started in the root parts of weldments due to welding defects, mainly incomplete root penetration, lack of fusion, and inadequate weld root shielding. Such defects formed narrow crevices in which a restricted exchange of ions and electric charge with the environment caused fast and extensive corrosion damage. The presence of chlorine dioxide, used for water disinfection, also played a significant role in the initiation of corrosion, as chlorine or chloride ions disrupt the protective oxidic film on the metal surface and facilitate the penetration of oxygen. However, the parts of the same piping where no welding defects were found, were completely unaffected by any corrosion.
A characteristic feature of advanced energy devices, such as Generation IV nuclear reactors, is operation combining high temperatures and pressures of working media. One of the key issues is ensuring the tightness of joints of metal components at very high temperatures (above 600 °C). At the same time, it is necessary to ensure tightness during non-nominal operating conditions associated with temporal changes in operating parameters. Commonly, seals are tested according to the ČSN EN 13 555 standard, where the combination of high operating temperature and high pressure changing over time with a chosen rate of change is not considered. For this reason, a unique device for testing seals was developed and commissioned at the Research Centre Řež. The facility allows characterization and tightness tests of different sealing products at wide temperature (up to 700 °C) and pressure (up to 40 MPa) that might also be time-dependent. The facility also allows testing of the entire gasket + flange + bolts assembly up to an outer diameter of 150 mm. In this paper, design, capabilities, and the first operational experience are mentioned. In addition, preliminary results from testing seals with a metallic core are mentioned. The device and the associated research can contribute to increasing the efficiency of sealing metal flange joints and other components and developing methodologies for evaluating sealing elements under extreme conditions, thus increasing the safety of operation of energy or other process equipment operating at high pressures and temperatures.
In hot rolling mill department of Mobarakeh Steel Company, we are producing hot steel strips in different grades and dimensions. Sometimes based on market demands, we try to produce any new steel grade which is requested by customer. So as a main strategic goal, we are going to develop our products by producing new steel grades. In this case, as we have no previous experience about the requested steel grade, we must predict related challenges and follow to that, we should find out related tests and troubleshooting. The main challenges consist of saving stable production and obtaining the best mechanical properties and having final product with no defect, regarding customer satisfaction. Recently we have produced the spring steel hot strip CK67 as a new product. It is the most hardened hot steel strip which can be used in some different purposes such as agriculture tools, springs, etc. In this paper we will describe how to define the hot rolling mill process considering predicted challenges and solutions to be able to produce this new grade.
As a rolling bearing manufacturer, the ZKL Group must maintain a comprehensive system for quality control and evaluation. A key component of this system is the testing laboratory, where bearing performance tests are conducted.
The analysis of rolling bearings for various applications helps push the limits of bearing technology and diagnostics. To verify quality, specialized metrology and metallographic laboratory equipment is used. We analysed bearing geometry with a focus on raceway condition, material microstructure and parameters, and visual inspection.
Bearings undergo rigorous quality and performance testing on specialized test rigs. These test rigs can also be used for the development of other industrial components and equipment. One example is the development of an advanced heat treatment process aimed at achieving a nanobainitic microstructure. Based on test results and expertise in bearing technology, our specialists can evaluate the quality of the heat treatment process, grinding process, and corrosion protection applied during manufacturing.
An essential part of laboratory work is determining the root cause of bearing failures in industrial applications. Real-world failure examples include wear damage (pitting), material discontinuities (cracks), electrical erosion, and lubrication-related failures (overheating).
Chromium low alloy steels exhibit a favourable balance of enhanced corrosion resistance and mechanical strength, characteristics that are critically beneficial for a wide array of structural applications. The distinct properties of these materials, in conjunction with their cost-effectiveness, render low-alloy chromium steels particularly advantageous across numerous industries without compromising safety or performance. This work deals primarily with the rheological properties of low-alloy chromium steels in the high-temperature region, investigated using an Anton Paar FRS 1800 high-temperature rheometer, capable of recording rheological data up to 1.750 °C. The temperature dependence of viscosity, viscosity at temperature dwells and flow and viscosity curves were evaluated. The acquired data were systematically fitted using two distinct models: the Vogel-Tamman-Fulcher (VTF) model and the power-law (PL) model. Additionally, the investigation encompassed the surface properties and interactions of the studied steels with corundum refractory materials at the phase interface. Wetting tests were performed using a CLASIC heating microscope, and surface tension and wetting angles were monitored as a function of temperature. Subsequent to the high-temperature wetting tests, X-ray diffraction (XRD) analysis was performed on the corundum substrate surface to confirm the formation of new phases. Furthermore, this surface, together with the contact and free surfaces of the steel droplets, underwent detailed examination through Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) microanalysis.
One of the major benefits of low-carbon steels are their cost-effectiveness which makes them a preferable choice for a wide range of applications.
In this study mechanical behavior of mild low-carbon steels are investigated, especially the change of yield strength and tensile strength after plastic deformation and heat treatment.
This article, also, includes investigations about opportunities for computer simulations and prediction of mechanical properties changes.
The obtained results are compared and analysed.
The yield strength of martensitic steel is composed of several primary contributions, including lattice friction stress, solid solution strengthening, precipitation hardening, dislocation strengthening, and grain size strengthening. In particular, the last three strengthening contributions - precipitation hardening, dislocation strengthening, and grain size strengthening - are highly dependent on the heat treatment and thermomechanical processing of the steel. The refinement of prior austenite grains (PAGs) and subunits of PAGs during the quenching and subsequent tempering, leads to multi-level refinement of hierarchical martensitic microstructure. Such processing can provide significant changes in mechanical properties, in particular, the high strengthening and fatigue properties with a satisfactory level of ductility. The proposed study has revealed the relevant processing modes for medium carbon spring steel 54SiCr6. The contribution of each microstructural feature (chemical composition, dislocation density, grains boundaries, size, number density carbides, and intertwining space) to the yield strength has been established. For the first time, it was found that the effective grain size (EGS) according to the Petch-Hall relationship for 54SiCr6 steel can be considered the intertwining space, rather than the size of the PAG, block, packet, or lath, as is commonly used as the EGS for steels with lower carbon content than steel 54SiCr6.