High-strength lightweight constructions are a crucial part of transportation systems and steel constructions optimised for low energy consumption. In this investigation, the aim is to understand the influence of different alloying elements on the mechanical properties of all-weld metal samples of high-strength filler metals. Metal-cored wires with adjusted chemistry were produced and the measured yield strength is compared with calculated values which were obtained by thermodynamic and kinetic simulations. By increasing the content of the matrix alloying elements, no increase in strength could be achieved, but compared to that, higher strength was obtained by the addition of Ti, Nb and Al in combination. Furthermore, the influence of different Ti, Al and N contents is presented and discussed.

Welded high-strength steel components have great potential for use in lightweight constructions or highly loaded structures. Welding of steels with a yield strength of more than 1100 MPa is particularly challenging because of the toughness requirements for the weld metal. Currently, a new generation of welding consumables with a minimum yield strength of 1100 MPa has been developed. Based on electron backscatter diffraction and atom probe tomography, a concept for toughening and strengthening of all-weld metal samples was deployed. Starting from a martensitic all-weld metal sample with an approximate yield strength of 1000 MPa, a reduction in manganese and silicon content resulted in a refined microstructure with a lower prior austenite grain size and effective grain size. Furthermore, a higher average grain boundary misorientation was measured, which influences the toughness positively. An addition of vanadium caused the formation of vanadium-rich clusters, which increased the strength of the all-weld metal significantly. With a combination of these two mechanisms, it was possible to produce an all-weld metal sample with the required yield strength of more than 1100 MPa and an acceptable toughness.

Recently, a new, vanadium alloyed welding consumable with a minimum yield strength of 1100 MPa was developed. The mechanical properties of welding consumables for gas metal arc welding are usually classified by producing and testing allweld metal samples, which are typically a multipass weld. Chemical and microstructural fluctuations of a vanadium alloyed allweld metal sample on a macro-and microscale and their influence on the local mechanical properties were investigated. On a macroscale, hardness mappings show a pattern of hard and soft zones which can differ up to 60 HV. Despite the existence of these fluctuations, undersized Charpy V-notch tests revealed no significant difference between the last weld bead and the underlying ones. It is explained how vanadium and its tendency to form precipitates affect both the hardness inhomogeneity and the toughness homogeneity. On a microscale, segregations of several alloying elements and significant grain size fluctuations were found. Their influence on fluctuations of the mechanical properties is discussed as well.

Martensitic steel welds show promising results regarding their strength while they may tend to be brittle. As martensite is a quite complex microstructure, high resolution techniques like electron backscatter diffraction (EBSD) and atom probe tomography (APT) are valuable tools for an in-depth characterisation. In this study, the average block size and misorientation distribution of martensitic all-weld samples were evaluated with EBSD. A lower carbon content led to a smaller block size and consequently a higher toughness of the all-weld sample. Furthermore, APT revealed a concentration fluctuation of the main alloying elements and particles with a high carbon content. It is discussed how these methods can be used in the future to design the microstructure to achieve optimum properties.

Gas metal arc welding with metal-cored filler wires is frequently used to weld high strength steel constructions for lightweight and transportation applications. In the current study, microalloying is considered as strengthening concept for reaching the required mechanical properties by precipitation hardening. For this purpose, the typical microalloying elements Ti, Nb, V, and Al were added to the filler metal in a comparatively high amount (up to 0.5 m.%). All-weld metal samples with a yield strength of 1000 MPa and more were produced by gas metal arc welding. Laser-pulsed atom probe tomography was used to evaluate the potential of these elements to form clusters or precipitates and strengthen the weld metal. While Al and Nb did not form clusters, a strong tendency for clustering was found for V-and Ti-alloyed samples. The cluster size evolution and changes in chemical composition depending on the microalloying contents are discussed. Furthermore, the challenges arising from local alloying element enrichments and local differences in thermal history in the all-weld metal are addressed regarding sample preparation and data evaluation.

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Microstructural Characterization of Ultra-high Strength All-weld MetalAbstract: Welded steel structures are a crucial part of lightweight constructions in several industrial segments. The filler metal plays a vital role in optimizing the properties of welded joints. In this study different methods were used to characterize the microstructure of ultra-high strength allweld metal samples with different chemical compositions. It was evaluated which method can be used to link the grain size of a sample to its toughness.