PSI - Issue 79

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

513

3.3. Tensile SSRT

Fig. 5 presents some representative tensile SSRT curves obtained using samples having the loading direction parallel to the sheet rolling direction. The H content measured at the end of the test for each specimen is reported in the legend. For each H concentration level, the average curves were reported. In the case of the H-free material, the curves presenting the upper and lower values of elongation at fracture are reported. The H-free material presented a significant scatter on the elongation at fracture value, which ranged from 21% to 25%, while the yield and ultimate strength were quite uniform. The lower curve of the H-free material presented an elongation at fracture that was slightly lower than the specimen featuring an H concentration of 0.8 ppmw. QP1180 exhibits susceptibility to HE, manifested by a reduction in elongation at fracture, and, for greater H contents, also in the ultimate strength. As shown in Fig. 6, H contents above 1.2 ppmw led to a decrease in post necking elongation, while concentrations exceeding 2 ppmw also caused a decline in ultimate tensile strength. However, such hydrogen levels are higher than those normally expected in automotive components produced from cold-stamped steels like QP1180 under typical service conditions. H contents lower than 1 ppmw did not affect the material strength and ductility, resulting in elongation at fracture even greater than the lower values observed for the H-free material.

Fig. 5. Tensile SSRT curves at different hydrogen concentrations. Specimen loading direction aligned with the sheet rolling direction.

Fig. 6. Effect of H on the static material mechanical properties. Specimen loading direction aligned with the sheet rolling direction.