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D2.1 Report on the selection of best performing 10.9 and 12.9 steel grades - EXECUTIVE SUMMARY

The main objective of this deliverable is the selection of the most suitable steel composition for large size fasteners applied in aggressive environments and the selection of the two best performing coatings to protect the fasteners.
In WP1, the HELIX project optimized a B mid-carbon low alloyed steel to fulfil the mechanical properties established at the Euronorm (EN ISO 898-1:2015) and, at the same time, reducing the alloying costs. Two different new steel compositions were proposed and casted in grades 10.9 and 12.9 each. The present deliverable reports the chemical, microstructural and thermo-mechanical characterization of these steel grades that allowed to the consortium carrying out an informed selection. After the completion of the tests, the consortium has selected the best performing 10.9 and 12.9 steel grade among the studied tempered steels. The selected materials will be further studied in terms of corrosion resistance in different environments, fracture mechanics and hydrogen interaction with the material in Tasks 2.3 and 2.4.
On the other hand, this deliverable also reports the selection of two coatings from an initial set of 6 different coatings documented in deliverable 3.1. The coatings have been characterized according to their higher performance in terms of corrosion resistance and higher HE resistance and the results have been used to select the two coatings. Further studies with the selected coatings and steels will be carried out in Task 3.3.