P 1110 - Localised laser heat treatment of work-hardened steels to improve forming and functional properties for lightweight construction in the automotive industry

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

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 1114 - Feasibility and geometry prediction of sheet metal components with high and ultra-high strength steels Reducing manufacturing costs is a key factor in increasing the competitiveness of manufacturing companies. In this context, clinching offers great potential, as this process makes it possible to produce functional surfaces in just one production step and without post-processing. Push-through forming is defined in DIN 8587 as a shear forming process in which one workpiece part is displaced relative to another with a rectilinear tool movement. The plastic deformation is achieved, analogous to fine blanking or shearing shear cutting with a small cutting gap, plastic deformation is mainly caused by a state of shear stress. The tool technology and tool kinematics of the processes are also similar. This leads to the conclusion that piercing largely corresponds to a cutting process without cutting through the workpiece. In order to reduce the weight of components and to be able to dispense with a tempering process, sheet metal made of high-strength and ultra-high-strength steel is increasingly being used. However, there is hardly any experience in the design and development of these grades. In order to ensure the safety of the process in the early development phase the process is simulated using the finite element method. This poses particular challenges in terms of material modelling. It is known from shear cutting that the temperature in the shear zone can rise to over 300 °C. Furthermore, degrees of deformation and strain rates are to be expected that cannot be modelled using conventional experiments such as the tensile test. In order to reduce the experimental effort, a methodology is presented and validated in this research project in order to nevertheless enable an efficient prediction of the geometry and feasibility of a sheet metal component with through-set. For this purpose, the interleaving line is broken down into recurring mould elements. The characteristic shape of these interspersions is determined experimentally for four different sheet metal materials. materials. Subsequent material modelling based on a simple test procedure is used as the starting point for determining the correction model. This is followed by an adjustment of this model in order to minimise the deviation between simulation and experiment. By interpolating between the mould elements, it is possible to adapt the material model locally for complex interspersion geometries. This makes it possible to assess the feasibility and geometry of interspersions made of high-strength and ultra-high-strength steels at an early stage of development. Authors: Prof. Dr.-Ing. W. Volk, J.-M. Stahl M.Sc. Publication: March 2020

P 1105 - Determination of the influence of processing and environmental hydrogen sources on the tendency of high-strength steels to hydrogen-induced cold cracking A challenge in the welding processing of high-strength fine-grained structural steels is the risk of hydrogen-induced cold cracking (HIC). There is a general consensus that HIC is particularly likely to occur with a critical combination of hydrogen content, hardening structure and stress state. The influence of individual process parameters on hydrogen absorption during welding has already been investigated in the past. However, the different process boundary conditions, such as those that occur during construction site production, were often not taken into account, making the risk of cold cracks occurring in practice almost impossible to predict. As part of this project, various high-strength fine-grained structural steels (primarily structural steel S690QL and pipeline structural steel L555MB and X80) are therefore being investigated with regard to their sensitivity to hydrogen (embrittlement, cracking) in connection with welding processing in the MSG and submerged arc processes, whereby the processing conditions are specifically varied and taken into account. The combination of all the results obtained in the project should serve as a basis for estimating the material and processing-specific cold cracking tendency. The experimental test series are supplemented by numerical simulation approaches. For both welding processes, dependencies of the welding processing and environmental conditions, e.g. through variation of the welding parameters or targeted manipulation of the potential hydrogen supply, on the resulting hydrogen content in the weld metal could be worked out and quantified. The findings will be used to produce joint welds on sheets of the high-strength test materials. No cold cracks are detected under controlled conditions due to the consistently high heat content during welding in multi-layer technology and the resulting favoured hydrogen effusion in the area of the welding zone. On the basis of tensile tests with a low strain rate (slow strain rate tests, SSRT), however, clear hydrogen-related influences can be recognised. In these tests, samples are taken from the unaffected base materials and from joint welds (GMAW and SAW) at various positions and tested. In particular, additional galvanostatic hydrogen loading during the SSRT test leads to a considerable loss of elongation as a result of hydrogen embrittlement, whereby specific differences arise here depending on the materials, the welding processing conditions and the sampling position. By carrying out self-loading cold cracking tests (Tekken), the tendency to cold cracking can also be qualitatively estimated as a function of the selected preheating temperature and the energy of the line in order to narrow down the welding processing window. Publication: 2020 Authors: R. Sharma M.Sc., Dr.-Ing. Ch. Haase