Delayed Fracture in Automotive Advanced High Strength Steel: A New Investigation Approach

Nowadays Al–Si coated boron steels (that are Advanced High Strength Steels, AHSS) are largely used in vehicle bodies. If on one hand they offer great mechanical performances, on the other hand they are susceptible to hydrogen delayed fracture. As this phenomenon brings to the reject of the component during production or even worse the failure during operation, diffusible hydrogen absorbed in the component needs to be monitored during plant process. A simple procedure, by means of a solid-state innovative sensor, is developed to check diffusible hydrogen concentration during laboratory experiments and manufacturing process. The behavior of an Al–Si coated boron steel after hydrogen absorption is investigated by means of slow strain rate mechanical tests (SSRT) and correlated to the diffusible hydrogen content. Finally, in manufacturing process an extensive plant test campaign is performed on semi-manufactured vehicle parts in order to verify the laboratory's results. These tests confirmed the possibility to approach the evaluation of diffusible hydrogen content in semi-products during car manufacturing by means of an easy procedure based on a robust sensor.