This paper presents an experimental electro-thermo-mechanical simulation of high-frequency induction (HFI) welding to investigate the effect of temperature and contact normal stress on the weld seam quality. Therefore welding experiments at different temperatures and contact pressures are performed using flat specimens of 34MnB5 steel sheet. In order to characterize the weld seam strength of the welded specimens, tensile and bending tests are performed. To obtain a relative weld seam strength, the bending specimens were additionally hardened prior to testing. With the hardened specimens, it can be shown that the weld seam strength increases with increasing temperature and contact normal stress until a kind of plateau is formed where the weld seam strength remains almost constant. In addition to mechanical testing, the influence of the investigated process parameters on the weld seam microstructure is studied metallographically using light optical microscopy, scanning electron microscopy, EBSD and hardness measurements. It is shown that the weld seam strength is related to the amount of oxides in the bonding line.
Steel, with its enormous variety of compositions, process routes and heat treatments as well as the resulting versatile mechanical properties, is interesting for a wide variety of applications. At the same time, steel is still in high demand as a material for research and continues to deliver new innovations. A paradigm shift has been taking place in the steel industry for some years now -from the experiencebased process-property correlation to a microstructure-based material development. For this purpose, the microstructure is understood as the central information carrier that stores information on the various process steps across all scales and thereby determines the mechanical properties. Accordingly, the microstructure plays a central role in research, development and quality assurance. The appropriate tools for preparation, contrasting, quantifying and classifying, grouped under the term metallography, are therefore essential to sustainably guarantee the progress and innovative power of steel in particular and other materials in general.The aim of the presented work is to provide new approaches and solutions in the field of microstructure analysis of low-alloyed steels (Figure 1). Metallographic preparation is of utmost importance as the basis for every structural analysis. Accordingly, the main focus of the present work is on contrasting by means of chemical etchings by LePera and Beraha in order to work out and make visible the microstructure of low carbon steels with its partly very fine differences in the best possible way. In addition to technical concepts, the focus is also on understanding the reactions that take place during contrasting in order to significantly increase reproducibility. For these purposes, a setup will be presented to keep all critical parameters during etching constant. In combination with an insitu-flowcell, it is even possible to monitor and control the process of contrasting.[1], [2] In the field of image processing, methodological work and new concepts of image registration, which is necessary when different methods for imaging are used, and segmentation, which is still done by thresholding mostly and thus causing a lot of artifacts, are presented. For these tasks, approaches to use correlative microscopy data to extract features for further analysis [3] as well as segmentation algorithms based on an "Active Contours without Edges" [4] approach will be shown.The final goal of all these approaches is the microstructural analysis which consists of a quantification and classification. By combining different sources of information -summarized under the keyword correlative microscopy -it is shown that even complex microstructures can be evaluated qualitatively and quantitatively [5]. By machine learning methods based on Deep Learning [6] and Support Vector Machine [7] using texture and morphological parameters, promising tools will be presented to reach unbiased and objective classification results.Based on these concepts, new standards in both research and quality assurance for th...
Although metallography is a very old discipline, its importance is growing steadily. High-performance materials need an accurate evaluation of the microstructure to guarantee the ever-tightening specifications in the range of properties and to control the production process. With the continuously growing demand of well-tailored microstructures, in most cases with smaller and more complex constituents of defined geometry, the requirements for reproducible metallography are also more and more challenging. In this contribution, we want to show how new trends in metallography can help scientists and engineers ensure reproducibility in their daily work with etching routines governed by controlled and monitored systems. The presented setup keeps all critical parameters during color-etching constant. Thus the reproducibility and homogeneity of LePera etching on low-alloyed steel can be guaranteed. Furthermore, a parameter study for LePera was conducted not only to show the application range of critical parameters such as temperature and time but also to find the best parameter setting for an automated phase-separation toward image analysis and microstructural classification. With the help of a focused ion beam, quantitative correlations of the etching mechanism can also be derived.
This paper presents a standardized methodology for determining the process window for ductile machining of brittle materials. Its application for CaF2 is reported, identifying an optimized process window for single-point diamond turning on UPM machines by determining optimized process parameters.
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