P 1105 - Determination of the influence of processing and environmental hydrogen sources on the tendency of high-strength steels to hydrogen-induced cold cracking

P 1108 - Microstructure and property prediction for the welding of high-manganese steels in dissimilar joints The primary aim of the research project was to improve the welding processing of high-manganese steels in dissimilar joints by predicting the microstructure and properties of the dissimilar weld metal using a newly developed constitution diagram. Three economically relevant Fe-Mn steels with different alloying concepts were used as test materials. The steels HC340LA (1.0548) and 22MnB5 (1.5528), which are widely used in car body construction, were used as joining partners. Various high-manganese metal powder flux-cored wire electrodes were also available. Using a TIG arc melting furnace, a remelting method was developed for experimental weld metal simulation, which makes it possible to produce mixed weld metals of any material combination in defined mixing ratios under MSG-adequate cooling conditions. Using this method, a large number of remelting samples (dissimilar weld metal) were produced in a wide range of different chemical compositions, which were characterised in terms of microstructure type, microstructure proportions, hardness and ferrite number. A total of eight microstructure groups were determined, which can occur in the mixed weld metal depending on the material combination and mixing. The different martensite types ε and α' are of particular importance, as these cannot always be clearly distinguished metallographically, but differ significantly in their properties. The results show that the paramagnetic ε-martensite mainly occurs in dissimilar weld metal with a relatively high Mn content. The α'-martensite, on the other hand, is found in dissimilar weld metals with lower Mn contents, i.e. with higher admixtures of low-alloy ferritic or martensitic joining partners or when using low-alloy filler metals. A high hardness in the dissimilar weld metal investigated here is directly associated with the formation of α'-martensite, which is why it is essential to differentiate between the two types of martensite. Investigations into the influence of the cooling rate showed that a significant increase in the cooling rate only has a significant influence on the microstructure and hardness in a few mixing ratios. This applies in particular to dissimilar weld metals with a very high admixture of low-alloy ferritic or martensitic joining partners or low-alloy filler material. It can therefore be assumed that very similar microstructural states and hardness values can be expected in the dissimilar weld metal in welding processes with higher cooling rates than in MIG welding (assuming homogeneous mixing). On the basis of the experimentally simulated dissimilar weld metals and the weld metal properties determined from them, a comprehensive data set was recorded, with the help of which equivalents were derived using statistical evaluation methods, which span the axes of the newly developed constitution diagram, the so-called COHMS diagram. In addition to the microstructure prediction in MSG weld metals, the COHMS diagram enables a rough estimation of the resulting weld metal hardness on the basis of HV-ISO lines. validation of the COHMS diagram using real MSG welds resulted in a very good prediction accuracy. 89 % of the MSG weld metals were predicted correctly. The remaining 11 % were close to the limit lines. The investigations into the influence of the microstructure type - in particular the martensite content - in the mixed weld metal on the mechanical-technological properties of the welded joints showed that a weld metal microstructure of austenite + α'-martensite in particular is to be regarded as extremely critical. The tested joints with this weld metal microstructure exhibited significantly poorer strength values under both static and dynamic impact loads compared to the other welds and predominantly failed in the weld metal Publication: September 2019 Institute of Materials and Joining Technology at Otto von Guericke University Magdeburg Prof. Dr.-Ing. Sven Jüttner M. Sc. Benjamin Wittig Dr Manuela Zink Participating companies: ArcelorMittal Global R&D, Zelzate Benteler Steel/Tube GmbH, Paderborn CIF GmbH, Grünstadt Corodur Verschleiss-Schutz GmbH, Thale Dr Rosert RCT GmbH, Dresden Kirchhoff Automotive Deutschland GmbH, Attendorn MSS Magdeburger Schweißtechnik GmbH, Barleben MSZ GmbH, Blankenburg Outokumpu Nirosta GmbH, Krefeld Salzgitter Mannesmann Forschung GmbH, Salzgitter thyssenkrupp Hohenlimburg GmbH, Hagen Volkswagen AG, Wolfsburg Vorrichtungsbau Giggel GmbH, Bösdorf Research institution(s): Institute for Materials and Joining Technology at Otto von Guericke University Magdeburg Responsible for FOSTA - Forschungsvereinigung Stahlanwendung e. V. Dipl.-Ing. Rainer Salomon

P 1101 - Innovative overhead line pylons for the energy transition, taking into account design, technical and economic aspects The politically driven energy transition requires numerous expansion and grid reinforcement measures. For overhead line masts made of steel, lattice masts are still used almost exclusively, which were already manageable 100 years ago in terms of planning, production and calculation. Today, these are often seen as a visual disturbance or detriment to the aesthetics of the landscape and the townscape. This research project aims to improve the image of overhead power lines and make them a necessary and accepted part of our industrial society. The aim is to develop a new type of steel overhead line mast that not only fulfils the highest technical and economic requirements but also meets the design requirements of the energy transition. The work was therefore carried out by an interdisciplinary team of engineers and architects. This research report first presents the basic principles of overhead line construction as well as the electrical and mechanical requirements for the development of the pylon design. Based on this, various optimisation approaches developed for the lattice tower construction are presented. For the development of the innovative shape for the overhead line mast, four variants of the overhead line mast designs are explained and the detailed investigations in the form of FE analyses of the favoured variant are presented. The experimental approach is then used to analyse the load-bearing behaviour of the innovative pipe-in-pipe press connection. All of the developments are incorporated into the profitability analysis of the innovative design, taking series production into account. As part of the investigations, an attractive and economical alternative to the previous lattice mast constructions was created. The objective of the research project was thus achieved. Publication: March 2020 Participating companies: IHT Ingenieur-, Hoch- und Tiefbau GmbH J.J.Brühl Stahlbau GmbH & Co KG KINA Ingenieurgesellschaft GmbH OCAS N.V. Poetsch GmbH CNC turning and milling PSP - Prof. Sedlacek & Partner R. Lange GmbH Salzgitter Mannesmann Forschung GmbH SSF Ingenieure AG Stahlbau Raulf GmbH thyssenkrupp Steel Europe AG Vallourec Germany GmbH

P 1110 - Localised laser heat treatment of work-hardened steels to improve forming and functional properties for lightweight construction in the automotive industry The overarching research objective of the project was to use a combination of cold rolling and local laser heat treatment to achieve customised properties in steel blanks with regard to formability and crash behaviour for the subsequent forming process and later use in the automobile. To investigate this approach, a cost-efficiently producible ferritic steel, the micro-alloyed S550MC, and an established steel with high application relevance, the dual-phase steel HCT780X, were selected. Firstly, the temperature ranges in which relevant softening mechanisms occur depending on the degree of rolling were determined. For this purpose, short-term heat treatments similar to laser softening were carried out in a forming dilatometer and the resulting mechanical properties were then tested in a tensile test at room temperature. The results serve on the one hand as a target value for the process development of localised laser heat treatment and on the other hand as a basis for the material data required in the simulation. In deep-drawing simulations of a work-hardened cross-section, softening strategies for maximising the drawing depth were developed, while in crash simulations of a hexagonal hollow profile, softening strategies for increasing the energy absorption were determined. The most promising strategies were verified in real tests and the methodology developed was validated using a sample component, a B-pillar. The results of this interdisciplinary collaboration prove that the design and optimisation of local heat treatment areas is possible in principle using simulation. To increase the formability, it is most effective if potential failure areas are work-hardened and surrounding areas are softened to enable flow. The improvement in crash behaviour can be demonstrated in drop tower tests: Crash boxes produced using the process combination exhibit an up to 28% shorter compression path compared to a conventional crash box with the same energy absorption. The production of the sample component shows that process limits can also be predicted with the aid of simulation. When integrating local laser heat treatment into the sheet metal forming production chain, straightening to minimise the resulting distortion and the removal of the laser-induced oxide layer before galvanising to ensure corrosion resistance must also be taken into account. A scanner and special optics with a customised beam profile were tested to increase the feed rate of the laser irradiation. The combination of cold rolling to increase strength and laser heat treatment for localised softening revealed new potential for lightweight construction and crash safety. According to the results, the potential of the investigated process combination can be rated as high. Publication: 2018 Authors: Prof. Dipl.-Ing. G. Hhirt, Prof. Dr rer. Nat. R. Poprawe

P 1112 - Statistical validation of small batches in steel processing The research project "Statistically safeguarding small series in steel processing" focussed on the development of a concept for the introduction of statistical process control (SPC) in small series production. The focus was on the steel processing value chain. The particular potential of the concept includes a sustainable increase in product quality and a reduction in scrap and quality costs. The basic approach for the concept development was the development of a similarity model for the expert-based grouping of small series on the basis of similar quality characteristics and processes with the help of a suitable classification and coding system. By analysing entire small series groups within the framework of statistical process control, it is possible to increase the number of available samples and thus also the statistical reliability. The latter can be quantified using a developed risk model. The quantified certainties provide a basis for describing similarities between small batch groups and their small batches. In addition, a similarity measure can be derived that can be used to evaluate the small series groups formed. The implemented KleiSta software demonstrator makes it possible to visualise the group samples in the context of adapted interactive quality control charts and calculates the statistical certainties for various quality statements as well as the similarity measures. The Fraunhofer Institute for Production Technology IPT developed the concept and the KleiSta software demonstrator as the executing research centre and project coordinator during the project period from 1 September 2015 to 31 August 2017 in close cooperation with a project support committee consisting of the following 14 manufacturing companies (small, medium-sized and large companies) and with the Forschungsvereinigung Stahlanwendung e.V. (FOSTA): - 3win Maschinenbau GmbH - ArcelorMittal Ruhrort GmbH - ASK GmbH - Bittner Werkzeugbau GmbH - EZM Edelstahlzieherei Mark GmbH - Innolite GmbH - Krott & Heuter GmbH - Leistritz Turbomaschinen Technik GmbH - Lemken GmbH & Co KG - Ortlinghaus-Werke GmbH - Phiesel GmbH - Rolls-Royce Germany Ltd & Co KG - Saarstahl AG - Ziehwerk Plettenberg GmbH & Co KG I n the course of the research project, regular committee meetings and topic-specific workshops provided a platform for the participating companies to define individual requirements for the concept and the KleiSta software demonstrator as well as suitable small series products and processes for the application of statistical process control. Individual meetings were also held to identify and compile available data that could be used for initial sample analyses and subsequent validation. Further information on the project can be found on the website www.kleista.de. Publication: 2018 Authors: K. Kostyszyn