Novel concepts for new generation of high strength hot dip galvanizing steel with extra formability (NEWGENHSS) : final report

High strength steels with improved formability offer the potential of thickness reductions in forming automotive parts and thus contribute to lightweight concepts. In this context the NEWGENHSS Research Project aimed at the definition of innovative hot dip galvanized high strength steels for the automotive market. The dual phase and the interstitial free/HSS steel concepts were studied. The main objective was to select one dual-phase (DP) and one Interstitial Free high strength steel (IF-HSS) for a real industrial and application trial, with the purpose of obtaining the validation of the selected steel grades by the customers. . In the frame of NEWGENHSS Project, WPs structure followed a full material development path, starting from definition of laboratory scale investigations to final real car parts evaluation. WP1 was addressed to the definition and preparation of laboratory casts of DP (ST1 and ST2) and IF-HSS (ST3, ST4 and ST5) steels, and their full characterization, by means of thermomechanical processing, microstructure investigation, mechanical properties and CCT curves. Results lead to the selection of several chemical compositions to be produced and tested in WP2 in a larger scale, in which such steels have been characterized to prepare the final industrial trials scheduled in WP3. On the basis of the new alloying concepts, an efficient processing route was defined for the DP steels that skip the cold-rolling step by making use of a low coiling temperature. This energyefficient processing route allows to reduce the production costs by around 10%. Aluminum addition concept in IF-HSS allowed to define a robust reduced temperature annealing cycle, meeting the high formability requirements together with targeted high strength. After all the above mentioned production and characterization steps, WP4 was devoted to the final evaluation of the selected materials. For this purpose, cooperation with car-makers was established to produce real car parts for weight saving potential evaluation, as well as overall formability. The results allowed, an improved hole expansion ratio by 5% to 23% depending on composition and processing route (absolute values) and a higher FLC of the cold-rolled and annealed materials (10% higher for DP-Si and 14% higher for DP-B). In addition, complex forming operations could be realized without failure and welding was performed without problems due to the low carbon equivalent. The project outcome is potential weight reductions up to 20% in comparison to conventional microalloyed grades, allowing CO2 reductions in the transportation sector and the newly developed DP steels are ready for the market.