Life cycle assessment and characterization of secondary steels used in vehicle body in white

In this work, benefits arising from the use of scrap for the creation of new steels with particular attention to the potential downcycling phenomena caused by the presence of impurities in the scrap were investigated. In particular, the advantages of scrap use in steelmaking were studied in a carbon footprint perspective. About this, a Life Cycle Assessment approach was exploited and carbon footprint comparison on different steelmaking processes was performed. Information about carbon footprint of stamped steel production is very important to understand which are the most impactful processes and create some strategies to minimize their carbon footprint. In particular, steelmaking routes is very important in the decarbonization perspective because it is the most impactful. In this way, real case studies regarding steel stamping in the Stellantis plants and brands vehicle models were realized. These studies were carried out following normative ISO 14040/44:2021. To study if scrap use in steelmaking could affect mechanical properties, different techniques as optical/electronic microscopies, tensile test, hardness test and CSM (Continued Stiffness Measurements) nanoindentation measurements were used to evaluate the properties of laminates and welded laminates by means of Resistance Spot Welding method. The aim of this activity is to verify that the steel produced with high content of recycled scrap has the same performance of the primary material and to detect any potential downcycling phenomena. Two DP600 (Dual Phase) and FB590 (Ferritic-Bainitic) laminates made with different amount of scrap and manufacturing processes were examined. In particular, standard characterization methods as those mentioned in previous paragraph, even though allows to homologate materials, they suffer some limitations to study features of multiphase steels. These as regards the low resolution of phases and microstructures using microscopy techniques and the impossibility of studying the properties of single phases and microstructures since tests such as conventional Vickers hardness create an indent size enormously larger than the average grain size. To overcome these limitations, nanoindentation (NI) and SEM-EBSD (Scanning Electron Microscopy-Electron Backscattering Diffraction) techniques were studied in depth as the most suitable techniques to investigate the complex microstructure of AHSS (Advanced High Strength Steels). Both techniques were combined in order to evaluate mechanical properties of phases and microstructures at nano-structural level. In this context, an innovative protocol developed in the NanoMECommons European project was implemented.