P 1108 - Microstructure and property prediction for welding of high manganese steels in dissimilar joints

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 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

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 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