Seznam abstraktů 2024: POSTEROVÁ SEKCE C

This paper focuses on the effect of contact force on dynamic electrical resistance in resistance spot welding. The dynamic resistance effects amount of heat generated in time. Methods for welding parameters monitoring and signal processing are presented. Changes in the positions of significant peaks (corresponding to certain events during the welding cycle) with increasing forces (1.3 - 3.8 kN) are used to describe resistance curves. The diameters of the weld nuggets were measured and the correlation with the peaks was evaluated. The results show that the welding force has a significant effect on the dynamic resistance curve shape and also affects final weld size. Approach to monitoring with given method for signal processing used in this study has proven to be useful for measuring dynamic resistance signals during different welding forces and it can find its use in real-time quality monitoring.

Super Duplex Stainless Steels (SDSS) represent a special class of stainless steels from the iron-chromium-nickel (Fe-Cr-Ni) system, showing high chromium (Cr) (24−27 wt%) and nickel (Ni) (6−8 wt%) contents while the carbon content (<0.03 wt%) is relatively low. Besides the primary alloying elements, the SDSS can, also, contain other secondary alloying elements, such as: molybdenum (Mo) (3−4 wt%), nitrogen (N) (0.2−0.3 wt%) and, possible copper (Cu) (0−2 wt%) or tungsten (W) (0−2 wt%). The SDSS steels show a bi-phasic microstructure, composed of proportionally equal phases of δ-ferrite and γ-austenite,where ferrite (δ-phase) represens the matrix.
The influence of solution treatment duration on the microstructure and mechanical properties of a hot-rolled UNS S32750 / F53 / 1.4410 SDSS alloy was investigated in this study. The UNS S32750 / F53 / 1.4410 SDSS alloy was thermomechanical (TM) processed by hot-rolling deformation at a temperature of 1100 °C with a total deformation degree (total applied thickness reduction) of 70%, followed by a solution treatment. The solution treatment was performed at temperatures between 1080 °C to 1180 °C, in 20 °C increments, with a treatment duration of 10min. The microstructure evolution during TM processing was investigated by XRD and SEM-EBSD techniques, while the mechanical properties by tensile and impact testing techniques. The following microstructural characteristics were analysed: constituent phases, weight fraction, grain-size and phase morphology. The mechanical behaviour was assessed through the following properties: absorbed energy, ultimate tensile strength, yield strength and, elongation to fracture. The performed solution treatments induced significant changes in relation to alloy's microstructure and showed a direct influence on the exhibited mechanical behaviour.

In this approach, we have tried to describe the flattening of welded tubes, and its test experimental application. Usually the final products (tubes) undergo a series of offline welding, and obviously destructive mechanical testing (bending, flattening, flaring, etc.). For this and for the purpose of implementing the flattening test, which applies to the processing of round tubes in other forms, it took some sections of welded tubes, it was also noted the report 'health' flattened tubes must not show or crack or tear. The test is considered poor if it reveals a lack of ductility of the metal. We finishing this study by simulation by finite elements (FE) by Castem2012.

The article concerns the determination of the operating temperature of forging tools intended for the hot precision forging process of a selected series of die forgings, due to the operational durability of the forging equipment. The durability of forging tools is one of the important aspects affecting the price of the final product in the form of a forging, especially in the case of fine forging, up to 45% of the price of the forging. The optimal operating temperature of forging tools is usually selected for a given technology, but also based on the heat balance resulting from the heat generated as a result of plastic deformation and friction of the forging and the heat released by the tools during their cooling and lubrication. Only proper selection and maintenance of temperature ensures high durability. Therefore, as part of the research work, a permanent system for measuring and recording the temperature of forging tools in the die forging process on a hammer with ongoing temperature registration for the full set of tools was presented. Various methods of heating and heating forging tools dedicated to die forging processes were presented and analyzed, including heating using natural gas as a medium and induction heating using a developed system based on two 2x10kW inductors. The obtained results indicate that appropriate control of the temperature of the tools and their induction heating/reheating gives the best results in terms of minimizing the energy consumption necessary to ensure the stability of the tool operating temperature conditions.

Nanobainite steel's high strength-to-weight ratio allows for the production of lighter components and structures without compromising on strength or durability. This lightweighting capability can lead to reductions in fuel consumption for vehicles and transportation systems, as well as lower material usage in construction projects.. Indeed, the production of nanobainite steel involves several strategies aimed at achieving the desired dual-phase microstructure consisting of alternating layers of bainitic ferrite and austenite. Here are some key strategies commonly employed. Controlling the composition of the steel is crucial to promoting the formation of the desired phases during heat treatment. Alloying elements such as carbon, manganese, silicon, and others are carefully selected to influence the kinetics of phase transformation and primary austenite grain refinement. Thermomechanical processing steps to control and refine the primary austenite grains structure and promote the formation of bainitic ferrite and carbon enriched retained austenite. After initial processing, the steel is rapidly quenched to transform the austenite into a metastable phase, typically martensite. Subsequent tempering at specific temperatures and durations induces the transformation of martensite into bainitic ferrite and retained austenite. The cooling rate during quenching and carefully strategies of tempering is controlled to facilitate the formation of nanobainite microstructure. Above mentioned parameters are precisely controlled to ensure the formation of nanobainite with the desired properties. Fine-tuning these parameters is essential for achieving the optimal balance between strength, toughness, and ductility. The combination of these strategies allows for the precise control and manipulation of the microstructure and mechanical properties of nanobainite steel, making it highly versatile for a wide range of high-performance applications. In the paper the selected strategies of promoting a nanostructured bainite was described and analysed in case of sustainability in manufacturing and construction.

The present study uncovers the softening kinetics of two cerium (Ce) modified steels after
60 % cold rolling and subcritical annealing at 600 ℃ for 2-16 h. During rolling it was found
that the strain accumulation in the ferrite matrix was severe for LCe steel (0.03 wt.% Ce)
compared to HCe steel (0.6 wt.% Ce). The role of Ce-rich precipitates and second phases
present in these steels have been assessed regarding the strain partitioning during 60 % cold
rolling. Both the steels achieved partial recovery and recrystallization even after 16 h of
annealing at 600 °0◦C. The LCe steel exhibited a recrystallized fraction of 28% after 16 hours
of annealing, inferior to the HCe sample (34%). Finally, the overall softening mechanisms for
both the investigated steels have been explained from the viewpoint of the crystallographic4
texture and competition between the recrystallization driving force and pinning force imposed
by various precipitates.

The paper deals with the manufacturing of thin walls by various additive technologies. CMT- and microMAG-based WAAM (Wire Arc Additive Manufacturing) and LMD (Laser Metal Deposition) were selected as representatives for the production of thin walls. Walls of AISI 316L (austenitic stainless steel) with a height of 100 mm were made by each of the above mentioned technologies. The geometry and materials properties of the walls were analysed. Tensile strength of specimens cut-off in the direction of the deposition and perpendicular to deposition direction as well were investigated. Higher tensile strength was observed in samples manufactured in deposition direction. Wall thickness and microhardness on the cross-section were meas-ured. The microstructure was analysed with a light microscope in the unetched and etched stage. The narrowest wall was ob-served in the case of LMD due to lower heat input. Application of LMD resulted in formation of fine dendritic microstructure. Furthermore, the amount of delta-ferrite was lower in comparison to WAAM deposited walls.

The presence and importance of cavitation damage and fracture during creep of Cr-Mo-V creep resistant steels (including martensitic grades) increases with increasing temperature and time to fracture, and at the same time, a decrease in fracture elongation can also be observed. In the case of uniaxial creep tests, the area and distance from the fracture line where the cavitation can be detected while its intensity gradually decreases also increases.
The creep cavitation behaviour of P91 and P92 steels was monitored in a series of creep tests performed in the temperature range of 575 to 625 °C and with a time to fracture of up to 35,000 hours. The extent of cavitation damage was assessed, depending on the distance from the fracture line, according to the procedure according to NORDTEST NT TR 302, in which classification into individual damage classes is based on a quantitative assessment of the number of cavities, or length of chains of cavities and/or microcracks.

The article presents the results referring to a complex wear analysis of forming tools in the process of band extrusion for ceramic roofing tiles. The materials used for such tools have to be especially resistant to abrasive wear, which occurs as a result of contact with the extruded ceramic mass band, which consists mostly of: clay (70%), quartz sand (10%) and flour from ceramics recycling (20%). The studies were conducted for samples made of tool steel NC11LV characterizing in different levels of hardness, collected directly from the forming tools. The performed tests included: an analysis of the abrasion resistence conducted with the use of a dry abradant, tests of the microstructure and topography of the worn surface, as well as nanohardness and Young modulus measurements with the use of a nanoindenter. The whole can be conftonted with the results of performance tests carried out so far, during which the tools working on the production lines were subjected to 3D scanning.
The obtained results confirm that better abrasive wear resistance parameters, with respect to its use for forming tools, is demonstrated by steel NC11LV with a higher hardness, which is illustrated by the relative wear resistance index Kb obtained during the dry abradant tests, which, for steel NC11LV with a lower hardness, equals 1,548, and for the hardened steel with a higher hardness, it is 1,810. Steel NC11LV owes its good properties mostly to the hard carbide precipitates. Steel with a higher hardness characterized in a higher niobium content, which resulted also in the formation of niobium carbides in the microstructure. This translates to a higher hardness of this material. Additionally, the performed investigations make it possible to assess other possibilities of prolonging the life of forming tools, e.g. through nitriding.

Understanding the influence of hydrogen on the mechanical properties of metallic materials is essential for establishing the safety of hydrogen energy systems. This study focused on ferritic/pearlitic spheroidal graphite cast irons (SGCIs) as potential candidates for hydrogen energy applications and investigated the hydrogen absorption and hydrogen-induced degradation of tensile properties. SGCIs demonstrated notably higher hydrogen uptake compared to conventional steels like carbon steel, primarily attributed to the abundance of graphite nodules distributed throughout the material. Hydrogen content measurements for SGCIs with varying microstructures revealed that heat treatment significantly increases the hydrogen absorption capability of SGCIs. This series of experiments showed that hydrogen absorption capacity was greatly influenced by the state of graphite nodules. When subjected to hydrogen charging, pearlitic SGCI exhibited a reduction in ultimate tensile strength as well as ductility, while hydrogen predominantly impacted the ductility of ferritic SGCI. This study will delve into the microstructural factors influencing hydrogen absorption and the consequent deterioration in the tensile properties of SGCIs.

Cardan shafts are a system widely used for power transmission in the industrial area, especially in the automotive sector. This study carried out computer-aided design and analysis of the sliding type involute profile propeller shaft. First, gear profile dimensions of the gears of the cardan shaft and the hub were generated parametrically under the EN-5480 standard using the PTC Creo Parametric software. Then geometry was transferred to the Ansys program. Equivalent stress, total deformation, and damage-life analysis were performed by simulating working conditions. The analysis results were compared by changing the analyses' root diameter and gear length. By interpreting the results obtained, it was determined whether the system was compatible with the terms of use, and suggestions were made for improvement.

The article deals with the first results from the so-called laboratory exposure loop after 5000 h and a 10000 h operation. This loop is an experimental setup that allows the selected material to be exposed to the conditions that prevail in the boiler of a coal-fired power plant or incineration site. Among these conditions are: elevated temperature, corrosive environment, and internal pressure of water steam. In this case, the loop (consisting of two bends and six weld joints) was made from SUPER 304H (X10CrNiCuNb18-9-3) superheater tubes. Before the experiment, the welded loop was filled with water, so steam with a pressure of 20 MPa was generated when heated to 550 °C. In addition, small-scale, stripe-shaped specimens were placed inside the loop and then exposed to steam during exposure. The loop was placed partly out of the furnace, thus not fully heated, and covered up in the power plant ash. At weekly intervals, the cooler part of the loop (the one covered up in the ash) was sprayed with water to induce thermal shock. After exposure of both loops (one for 5000 h, the other for 10000 h), their bodies were cut, and mechanical tests (i.e. tensile and Charpy impact tests) were performed. The microstructure of the straight parts, bends and weld joints of the loop tubes was investigated and documented using light optical microscopy and scanning electron microscopy.

Nowadays, high-strength steels (HS) and ultra-high-strength steels (UHS) are increasingly used, especially in welded structures. These types of steels are mainly used as material for heavily loaded structures such as bridges, cranes, and excavators, as well as for pressure vessels, various types of vehicles, ships, drilling structures, etc. operating at room temperature or below. Since the requirements for the above structures are specific, the use of high-strength and ultra-high-strength steels requires research into the factors affecting their weldability. According to the usual welding rules HS steels and UHS steels can be welded by all conventional welding methods. The S960QL steel studied in this paper falls into the group of high strength quenched and tempered fine-grained grain steels. This work presents results showing the influence of the welding gap on some mechanical properties of submerged arc weldments of the high strength steel S960QL

The aim of the research was to analyze the properties and microstructure in low-alloy high-carbon 80MnSi8-6 steel intended for forgings for the automotive industry. The steel was subjected to axisymmetric hot compression test in the WUMSI simulator. The tests were carried out at temperatures from 900 °C to 1250 °C and at a strain rate of 0,1 s^-1 to 20 s^-1. The developed flow curves were used to assess the properties of the tested steel. The analysis of the microstructure in the initial state and after plastic deformation was performed using light microscopy and scanning electron microscopy techniques. After the plastometric tests, the hardness of the tested steel was measured, taking into account the strain non-uniformity. Moreover, numerical simulations were also carried out using FORGE NxT 4.0 software to determine the strain non-uniformity in the sample cross-section. The results were compared with microstructure analysis including PAGs calculations. The research will be used to select the parameters of the open-die forging of products with the partially nanobainitic microstructure, the share of which will be controlled by the appropriate selection of parameters of the hot forming process.