Seznam abstraktů 2022: POSTEROVÁ SEKCE C

Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual sample handling. An etchant or electrolyte results in inhomogeneous surface quality because the solution runs off the specimen surface during its removal from the beaker. High-quality specimen cleaning is absolutely crucial for the acquisition of the specimen suitable for characterization by a scanning electron microscope operated at very low landing energies of the primary electrons (SLEEM). The SLEEM technique is a powerful tool for the characterization of advanced steels, as described by many scientific papers. The SLEEM requires the specimen absolutely free of water and any organic residues on the surface. This work presents a novel unique apparatus enabling automatic specimen cleaning and drying after the etching or electropolishing processes. Automation reduces the influence of dependent variables that would be introduced into the process by the metallographer. These variables include cleaning time, kinematics, and motion dynamics, but the process can also be affected by variables that are not obvious. Performed experiments clearly demonstrate our in-house designed apparatus as a useful tool improving efficiency and consistency of the sample cleaning process. The high quality of the specimen surface is verified using a light optical microscope, an electron scanning microscope, and above mentioned SLEEM technique.

This paper describes the use of reverse engineering to creating a digital model of face gear from 3D point cloud. The construction of a computational model of a physical ob-ject was carried out using an optical three-dimensional scanner. Based on the cloud of points obtained in the process of scanning, a spatial digital model reflecting the geometry of an ex-isting element was developed. Polygonization and mesh reconstruction allowed to create a discretized model that enabled the precise reproduction of the scanned object. The created model could be subsequently used to conduct appropriate analysis and simulation to verify the correctness and possible modification of the construction of scanned elements. Coordi-nate measurement technology to digitize surfaces in order to compare and evaluate real component parts with their theoretical data using a PC is needed in many different industrial sectors like design, construction, manufacturing, quality assurance etc.

Medium manganese steels belong to the group of third generation high-strength steels. These steels show an excellent combination of strength and ductility. Their manganese content ranges from 3 to 12 %. After hot forming, the structure is usually martensitic. During intercritical annealing, martensite partly transforms to austenite. The choice of the correct alloying and intercritical annealing parameters, especially the heating temperature, leads to sufficiently stable retained austenite, which significantly affects the mechanical properties. The retained austenite exhibits TRIP effect during cold deformation and contributes to a significant deformation strengthening of the material.
Medium manganese steel with 0.2 % C, 5 % Mn and 3 % Al was subjected to various intercritical annealing regimes after hot forming. To increase the stability of the retained austenite, isothermal hold at different temperatures was performed in the bainitic transformation region. To verify the effect of deformation, incremental deformation was applied during cooling. After processing, martensitic structures were obtained with varying fractions of bainite, ferrite and retained austenite. The ultimate tensile strength up to 1940 MPa was reached and the elongation was about 10 %.

The main objectives of the project are to define the design requirements for the future SCW-SMR technology, to develop the pre-licensing study and guidelines for the demonstration of the safety in the further development stages of the SCW-SMR concept including the methodologies and tools to be used and to identify the key obstacles for the future SMR licencing and propose strategy for this process. The project consortium consists of laboratories from Europe, Canada and China.
Beside the thermo-hydraulics, safety, neutronics, and reactor physics, assessment of the corrosion behaviour of cladding candidate materials (alloy 800H, stainless steel 310S, alumina forming austenitic alloy - AFA) in supercritical water (SCW) at 380/500 °C and 25 MPa is one of the key activities. For this purpose, experiments such as long-term (1000-8000 hours) exposure tests in autoclaves, neutron irradiation, electrochemistry, and radiolysis are involved. The paper describes the progress made on the ECC-SMART project with focus on microstructural characterization and evaluation of selected mechanical properties of candidate cladding materials. In addition, the description of the setup of corresponding experiments is included.

Titanium stabilized stainless steel 08Ch18N10T is widely used in VVER nuclear power plants. The alloy 800H is a very promising structural material for application in future nuclear power plants working under more severe working conditions. Thus, both materials were exposed above the critical point of water at 395 °C, 25 MPa for 500 and 2700 h. The effect of such exposures was evaluated based on analyses of microstructure via scanning electron microstructure involving chemical and crystallographic analyses. The thin oxide layers were further described by X-ray diffraction. The stainless steel 08Ch18N10T proved very good and comparable corrosion resistance as highly alloyed 800H at the given environment. In both cases, the oxide layer was very thin even after long exposure.

With the growing popularity of additive manufacturing (AM) in recent years, the metallic materials processed by powder bed fusion (PBF) have gained a lot of attention from researchers, especially for their use in the aeronautics and space industries. However, the use of AM cannot be overlooked in other applications, like tooling for forges, extrusion, or moulds for die casting. Dies and injection moulds with conforming cooling channels and complex tooling would greatly extend the life of hot-work tools, due to the lower amplitude of the thermal cycles. However, there are numerous problems of AM of hot-work tool steels, not only limited to: cracking and part deformation due to high residual stress, under melting and key-hole porosity, as well as relatively low mechanical properties in the as-processed state (compared to steel made via conventional methods). The problem of porosity can be in large part eliminated by using proper PBF parameters (laser power, scanning speed, layer thickness and laser spot size). Residual stress, caused by the transition from liquid to solid, and the transformation from austenite to martensite, can cause cracks. Another issue of residual stress is PBF sample deformation, which can tear the supports from the base plate, twisting the part upward at the corners. Retained stress can be measured with multiple methods, one of those being the focus ion beam (FIB) core milling technique, which will be also presented. The retained stress can be avoided using base plate preheating during the printing of the part, also part of our research.

Material parts can be separated either mechanically or thermally. During the thermal cutting of the material, the base material is locally melted, burned, or vaporized. The different methods are distinguished by the heat sources that supply them with the necessary energy. The application of the different thermal cutting methods varies depending on the type of material to be cut, its thickness, the resulting desired cut quality, and the overall economic efficiency. This paper deals with the study of temperature cycles during thermal cutting of carbon steel type S355 by oxy-acetylene flame thermal cutting and air plasma cutting. The obtained experimental data are used in the numerical simulation of the thermal cutting process by the given technologies.