Volume 62, Issue 9-10

As climate change and resource scarcity become more critical, demand for energy efficiency, emission reduction, and resource conservation increases. Forming technology offers high potential for lightweight design, cost effectiveness, and resource efficiency. However, forming-induced ductile damage, such as void formation, is often overlooked in component design, which focuses on mechanical properties and safety factors. A deeper understanding of forming-induced ductile damage can lead to more efficient, lightweight structures. Therefore, the void distribution was analyzed using focused ion beam and scanning electron microscopy, enabling the development of a 3D model via AI-based image segmentation. To assess void inclusion interactions, an intersection analysis was performed in Fiji ImageJ by merging in-lens images of sulfides with secondary electron images of voids, allowing a volumetric representation of their intersections.

The findings from the Hallstatt period cementery at Getzersdorf an der Traisen, Lower Austria, are currently being re-examined (HaC, approx. 800–450 BC). Among the iron findings, a roll-headed pin was made available for metallographic examinations. The metallographic preparation clearly showed the curled roll-head, corrosion products, and slag inclusions. Somewhat larger inclusions were noticeable and could not be identified as common iron slag. A SEM-EDS analysis revealed that these particles contain a lot of chromium so that it could be the mineral chromite (FeCr 2 O 4 ). This chromite was probably introduced during the forging process. As would be expected from the Damascus technique, the iron matrix revealed a layered structure. The clearly demarcated iron layers are remarkable and can only be explained by a forging process at low temperatures. Given that it is a Hallstatt roll-headed pin, this microstructure is very surprising.

This paper presents a characterization of the microstructural evolution and its correlation with the magnetic structure due to flow forming of semi-finished tubes of austenitic stainless steel AISI 304L. The plastic deformation triggers a phase transformation of the metastable austenite into α’-martensite. Depending on the combination of production parameters, different fractions of strain-induced α’-martensite were measured by means non-destructive micromagnetic techniques and correlated with the evolution of hardness and the microstructure using electron backscatter diffraction analyses. The magneto-optical Kerr effect analysis was used as a tool to perform a qualitative analysis of the evolution of the magnetic domain structure correlated with the formation of α’-martensite. An analysis of these data allowed to derive surface magnetization hysteresis loops that were compared with integral hysteresis loops of the specimens. It was proven by both methods that the formation of martensite increases the magnetic energy and the spontaneous magnetization of the specimens. The results of this investigation contribute to a better understanding of micromagnetic sensors to monitor and control the formation of α’-martensite in a flow forming. Furthermore, various techniques have demonstrated the evolution of the magnetic properties of the material, which can be applied in applications for invisible coding of workpieces.

Compared to other steel groups, high-alloy tool steels are particularly associated with a high energy and resource intensity. Cold-work and high-speed steels, in particular, can reach macro-hardnesses of up to 70 HRC. The steels, in their hardened and tempered condition providing them with relevant performance characteristics, are therefore processed in grinding processes accompanied by considerable metal removal rates to manufacture products for numerous applications. In line with a circular economy and aiming at minimizing the loss of high-quality and partially critical raw materials, it therefore makes sense to directly utilize the waste materials generated during grinding using powder metallurgical (PM) methods. This work highlights existing material scientific challenges and their impact on directly recycled tools on the example of the manufacture of cutting tools made from PM high-speed steel HS 12-0-5-5. The focus is on the accompanying metallographic investigations based on which correlations can be established between the grinding process, the introduction of impurities, powder metallurgical recycling, and the performance properties. It is shown that the processing of waste materials is of central importance and that circular economy must start at an earlier stage in the production process chain.

A piece of a Kort nozzle, a ring-shaped component enclosing a ship’s propeller severely damaged by cavitation was examined. The nozzle was made of stainless steel grade AISI 316L. The piece of steel examined exhibits a damage gradient which can be explained by cavitation of regionally varying severity. Areas severely stressed by cavitation are characterized by an increased material removal and high surface roughness. Since cavitation-induced material removal can be attributed to a mechanical damage to the surface, the aim was to investigate the microstructural changes in the steel. Samples were taken along the gradient and cross-sections were prepared. The etched metallographic section revealed clear evidence of deformation. Toward the lower load, a decreasing amount of deformation twins can be observed along the cavitation gradient and also from the surface toward the base material. It can also be assumed that severe deformation leads to the formation of deformation martensite. Against the background of a significant increase in magnetizability from the unaffected material toward the damage zone identified through qualitative analysis, magnetic measurements were performed and confirmed a higher magnetizability in the damaged near-surface areas. The steel’s base metal has a uniform, austenitic microstructure.

In the sector of flexible primary packaging for food and pharmaceutical aluminum films and film laminates are currently undergoing a transformation toward the use of a steadily increasing proportion of recycled material. Further development of the metallographic sample preparation of these composite materials is required to ensure that the often subtle changes in the material involved can be analyzed in a meaningful way. The conventional preparation technique using microtome sections is compared to an analysis of metallographic sections on the example of two laminate structures. This method is intended to replace microtome sections for layer thickness analyses and present a correlative approach in the field of material and structural analysis. Mechanical preparation allowed achieving sufficient sample qualities and visualizing the basic structure of the laminates under investigation. The two methods were furthermore correlated.

Several samples made of the stainless steels AISI 316L and 17-4PH (equivalent to AISI 630) in different compositions were investigated as part of the Collaborative Research Center/Transregio (TRR) 375 on Multifunctional High-Performance Components made of hybrid porous materials (HyPo). The samples were manufactured under the subproject B01 at the Institute for Manufacturing Technology and Production Systems (Fertigungstechnik und Betriebsorganisation, FBK) by laser metal deposition. Individual blocks consisting of four welding layers which are, in turn, composed of eight printed tracks, respectively, were built using different powder compositions. The powder mixture was gradually varied from 100 % 316L to 100 % 17-4PH. This contribution addresses the specifics of visualizing the microstructure of samples with different material compositions. One challenge lies in selecting the appropriate etchants for the samples made of mixed powders. For the investigations, the samples were embedded as longitudinal and transverse sections. Various etching solutions were then tested to visualize the microstructure. The results of the etching experiments and the light micrographs are presented and interpreted based on the findings of energy-dispersive X-ray spectroscopy (EDS) analyses in the scanning electron microscope. They can be used to derive strategies for adjusting the microstructure of graded samples which may serve in the future to obtain specific properties.

The DGM working group “Quantitative Structural Analysis” (QGA, Quantitative Gefügeanalyse) within the Expert Committee “Materialography” is concerned with current issues and methods for analyzing micrographs. The following gives an overview of the focal areas and activities of this working group. Furthermore, the results of a round robin test on the determination of grain boundaries involving 28 participants from 12 different laboratories are presented. As part of the round robin test, grain sizes were determined in micrographs of various materials using both the line intercept method and grain boundary segmentation. In addition to reviewing the round robin test against the background of a comparison of the results of different laboratories and participants, special attention is paid to evaluating the various measurement parameters and image processing steps with regard to their precision. Best practice recommendations are drawn from this review.

Understanding precipitate evolution in microalloyed high-strength low-alloyed (HSLA) steels is essential for optimizing their processing and mechanical properties. In this work, we present an automated workflow for precipitate quantification in scanning transmission electron microscopy (STEM) images of niobium and titanium HSLA steels, combining deep learning-based semantic segmentation with conventional image processing techniques. Among the different STEM image contrasts tested, the high-angle annular dark-field-based model delivered the best segmentation performance, achieving a mean intersection over union of 0.8111 and a deviation of only 5.37 % in the measured mean particle diameter. The workflow’s robustness and generalizability were demonstrated on unseen images of different HSLA steels, with particle counts and size distributions aligning well with expectations based on the respective alloying concepts.

Carnuntum on the Danube River in Lower Austria is a significant archaeological site from the Roman Imperial period. A bronze fibula foot, one of numerous stray findings collected in the 1950's, was available for metallographic examinations. According to the scanning electron microscopy/energy dispersive X-ray spectroscopy analyses, the metallic base material is composed of 10 wt.% Pb, 5.3 wt.% Sn, and 8 wt.% Zn in the copper. It is characterized by a dendritic solidification structure with Pb and the phase Cu 41 Sn 11 enriched in the interdendritic zones. This microstructure indicates that the fibula foot was manufactured in a casting process. The sample exhibits the particularity of a blue azurite patina. The otherwise common corrosion products Cu 2 O and malachite are present only in small amounts. Holes in the azurite layers can be attributed to textile fibers which were originally present. Since azurite forms at elevated CO 2 partial pressures and lower pH values, the textile may have altered the reaction conditions towards this formation.

The preparation process of highly metastable austenitic steels can cause a mechanically induced martensitic phase transformation, significantly affecting the quality and validity of subsequent microstructural examinations. In the as-built (untreated) state, specimens additively manufactured from the corrosion-resistant, martensitic knife steel 1.4116 (X50CrMoV15-1, DIN EN 10088) by powder bed fusion-laser beam/metal exhibit the peculiarity of an almost fully austenitic microstructure. This microstructure is, however, thermodynamically metastable, thus forming undesirable deformation martensite during the metallographic preparation for electron backscatter diffraction (EBSD) investigations. This article therefore discusses the application and optimization of metallographic preparation methods with a focus on minimizing preparation-related artifacts. The core question in this work is whether varying the preparation methods and parameters leads to a reduction in the formation of deformation martensite. The α’ content was measured in between the preparation steps using a Ferritscope ® to investigate the impact of the preparation on the microstructure. The resulting microstructures were analyzed using EBSD and compared to assess the preparation method’s impact on the quality of the EBSD data. The investigations showed that the grinding/polishing pressure and relatively small differences in the alloy composition considerably affect the preparation result.