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

Abstract

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.

Investigation of Mechanical Tests for Hydrogen Embrittlement in Automotive PHS Steels

“…The extrapolation of a regression curve ( Figures 6 and 7) can describe the behavior of steel [21,22], and the corresponding equation was derived here as…”

Assessment of Critical Hydrogen Concentration in As‐Cast and Hot‐Rolled Billets in Medium Carbon Steels

“…Nonetheless, this test is widely adopted to evaluate the effects of hydrogen embrittlement in steel. [25][26][27] In standard SSRT procedure, hydrogen is introduced from external sources. However, the hydrogen distribution in microstructural features can be different in case hydrogen comes from an external source (exogenous hydrogen) with respect to the case in which hydrogen is already present in steel (endogenous hydrogen).…”