Knowledge building

Knowledge acquisition is the driving force behind research: larger projects, often supported by PhD theses, are carried out in the framework of the knowledge building programme. Furthermore, collaboration can add valuable expertise. The results obtained provide useful insights for smart product development and finally ideas arise for portfolio renewal. Knowledge building is the key activity fuelling R&D.

In 2020-2021, significant progress has been achieved in the surface, metallurgy and application related research of the knowledge building programmes. Some examples of the numerous realisations: — Mechanical properties of zinc coatings are well-known and have been studied in detail over the past decades.

Enhancement of the corrosion resistance can be achieved by adding Mg and Al to the Zn coating.

The markedly superior corrosion, friction behaviour and wear resistance of Zn-

Al-Mg coatings has been reported to be related to the element’s distribution and strong refinement of the complex microstructure. However, in-depth knowledge of the local mechanical properties of individual microstructural constituents with respect to the crystallographic orientation of the phases is lacking. Knowledge building studies during the past 2 years aimed to contribute to a better understanding of the microstructure, hardness and elastic modulus of the main eutectic microphases in the complex solidification structure of two Zn-Al-Mg systems i.e.

Zn-5Al and Zn-3.7Al-3Mg coatings. Then, the anisotropic mechanical properties of pure phases matching the composition of the different phases in these coatings were examined using nano-indentation coupled with EBSD analyses. Finally,

Voigt, Reuss and Voigt-Reuss-Hill models were used to predict the hardness and elastic modulus of the eutectic phases in the two coatings using the individual properties of the pure phases. In a next step, SEM in-situ deformation techniques were used to study the mechanical properties of these new coatings and correlate the results with the findings on the mechanical properties of the individual phases. Finally, these data were used to validate a FEM model predicting the cracking behaviour of the coating depending on the phase composition and distribution. — High Strength Steels offer a unique opportunity to reduce weight in heavy duty machinery such as trucks, trailers and agricultural machinery. However, their fatigue behaviour can be lower than expected in certain applications.

By developing a numerical FE simulation framework, the microstructural features such as phase fraction, grain size distribution, texture, inclusions, etc. on the ‘High Cycle Fatigue’ and ‘Low Cycle

Microstructure measurement • LOM • SEM Statistical analysis • Grain size • Aspect ratio • Slope • ... Grain packing & Volume fi lling • Packing-algorithm e.g. RSA • Tessellation e.g. Voronoi • ... Building the FE model • Generating geometries • Meshing geometries

Fatigue’ properties of High Strength Steel can be investigated. The numerical tool should be capable of predicting crack initiation and the fi rst phase of crack propagation (propagation through two or three grains). In order to study the underlying mechanisms in the early phase of fatigue damage, the simulation framework was established on both the macroscopic and the microscopic scale. An algorithm was developed for the generation of statistically equivalent representative volume elements. In the treatment of the statistical data, rather than working with histograms that are prone to binning and cut-off effects, a sophisticated machine learning algorithm is used, which considers grain area, aspect ratio, slope and mean misorientation angle. This development

will be a valuable tool for future product development. — In terms of metallurgical knowledge building on substrate level, 2021 has been a transition year in which several projects were fi nalised and new projects were being launched. On the ongoing projects, major progress was made on the various steel families considered: • For austenite reverted transformation (ART), the impact of upstream processing was mapped in detail • For hot rolled Quench & Partitioning (Q&P) grades, further understanding was obtained on the damage evolution in the quaternary Fe-C-Mn-Si materials • For lean maraging steels (IMCA), huge progress was made in the nanoscale intermetallic precipitation evolution via extensive atom probe tomography

(APT) experiments and the advanced in-use properties of these grades • For the medium Cr steels, the monitoring of the wear-corrosion balance came to a fi nal stage Concerning the new activities, these were aligned with the current mega-trends, i.e. nano-scale behaviour of residual elements originating from enhanced scrap usage, texture evolution in modern electrical steels for mobility and damage mechanisms in steels exposed to high pressure gaseous H2.

Joost De Strycker, Wahib Saikaly & Sofi e Vanrostenberghe