Characterization of hydrogen embrittlement in automotive advanced high strength steels

Hydrogen embrittlement is the limiting factor when it comes to the utilization of advanced highest strength steels in a car body frame. Steels with a tensile strength of greater than 1000 MPa are deemed to be susceptible to hydrogen induced delayed fracture and therefore are not yet widely used. To characterize the deleterious effects of hydrogen embrittlement in advanced highest strength steels the slow strain rate testing in gaseous hydrogen atmosphere is a suitable method for investigating the effect of hydrogen on the materials ductility. Additionally the hydrogen content after slow strain rate testing was measured by means of thermal desorption spectroscopy. By using this technique it is possible to differentiate between diffusible and trapped hydrogen. Diffusible hydrogen may interact with dislocations and therefore changes the fracture behaviour of metals. This was also documented by analysing the fracture surface of the tensile specimen by optical and scanning electron microscopy. The investigations yield a comprehensive view on the susceptibility towards hydrogen induced cracking and allow a comparative view among different steel grades.