Presentation at Congrès Français de Mécanique 2025: "Influence of hydrogen on the mechanical behavior and rupture mechanisms of the 3GEN AHSS steels"

The effort of developing eco-friendlier and less expensive methods of steel parts manufacturing led to obtaining third generation Advanced High Strength Steels (3gen AHSS), which exhibit a pleasing ratio between mechanical properties and formability thanks to their microstructure composed mostly of ferrite, bainite, martensite and a controlled fraction of retained austenite [1]. During steel manufacturing 3gen AHSS may be exposed to hydrogen [2]. Hydrogen can be introduced by different chemical processes and diffuses within the material, affecting its mechanical properties especially its formability [3], [4]. This phenomenon is known as hydrogen embrittlement (HE) [5]. The present study is part of the H2FORM3G european project financed by the European Union’s Horizon 2020 research and innovation program with the aim of preventing the risk of cracking during manufacturing of automotive components and reduce the risk of delayed fracture. The main objective of the present study is to analyze the impact of hydrogen on the mechanical behavior and the fracture mechanisms of three AHSS grades: DP780GI and FORTIFORM®1180 provided by ArcelorMittal and CP1200CH provided by Voestalpine. The experimental characterization is carried out with unit-axial traction and shear tests. Standard tension samples have been extracted in different directions in order to assess the plastic anisotropy. These tests are performed on as-received materials and on hydrogen charged specimen via cathodic polarization. The results of mechanical tests are used to develop a macroscale constitutive model accounting for the effect of hydrogen on the mechanical behavior of each material grade. The fracture mechanisms have been identified using optical and SEM analyses and will be considered to set up a fracture criterion.