PSI - Issue 79

Giuseppe Macoretta et al. / Procedia Structural Integrity 79 (2026) 508–516

515

Fig. 8. Details of the fracture surfaces of an H-free sample a), with evidence of diffused microvoid coalescence, and a sample featuring an H concentration of 2.1 ppmw b), showing brittle intergranular fracture.

4. Conclusions

The effects of H intake on the static mechanical properties of the QP1180 were preliminarily investigated by means of tensile SSRT, H permeation and desorption tests, and fractographic examinations. The H was introduced in the sample via electrochemical charging before the test. The H concentration present in the specimen was measured after the tensile test via the hot extraction method, allowing us to correlate the specimen's mechanical properties and the H content. The material turned out to be susceptible to HE and presented a significant decrease in the elongation at fracture and ultimate tensile strength for elevated H contents. A reduction in the elongation at fracture was found for H content greater than 1.2 ppmw, where the H affected the post-necking region of the tensile curve. H contents greater than 2 ppmw also impacted the ultimate tensile strength. Coherently, H affected the fracture mechanisms. While the as received material featured a ductile fracture, H concentrations greater than 2 ppmw led to an extended intergranular brittle failure However, these hydrogen levels exceed those typically observed in automotive components manufactured from cold-stamped steels such as QP1180 under standard service conditions. Hydrogen contents below 1 ppmw did not negatively impact the material's strength or ductility; in fact, elongation at fracture was found to be greater than or comparable to the lowest values recorded for hydrogen-free material. Further investigation will deal with the effect of H on specimens extracted along different orientations with respect to the rolling direction, as well as with increasing the repeatability of data preliminarily obtained in the present campaign.

Acknowledgements

Financed by the European Union - NextGenerationEU (National Sustainable Mobility Center CN00000023, Italian Ministry of University and Research Decree n. 1033 - 17/06/2022, Spoke 11 - Innovative Materials & Lightweighting). The opinions expressed are those of the authors only and should not be considered as representative of the European Union or the European Commission’s official position. Neither the European Union nor the European Commission can be held responsible for them. The activity was carried out within the framework of the Call for Scalability project “Multiphase high strength steel forming and testing for robust Automotive lightweight Design” (MADE).

The authors gratefully acknowledge Eng. Randa Anis Ishak Nakhla for the SEM investigations.