PSI - Issue 42

Lisa Claeys et al. / Procedia Structural Integrity 42 (2022) 390–397 Claeys et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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were less pronounced for 304L ASS, the stress reduction in the presence of hydrogen was not observed on the macroscopic engineering stress/strain curve presented in Fig. 2.

a

b

c

RD

2 mm

50 µm

20 µm

TD

Fig. 5: HAC initiation in 304L ASS: (a), (b) and (c) represent different magnifications

a

b

c

RD

2 mm

50 µm

TD

300 µm

Fig. 6: HAC formation in 18Mn-0.6C TWIP steel: (a), (b) and (c) represent different magnifications

4. Conclusions The present work focused on the deformation and fracture mechanisms of two austenitic steels in the presence of hydrogen. An austenitic stainless steel type 304L was compared to 18Mn-0.6C TWIP steel. Several conclusions can be drawn: • Both steels had a fully austenitic microstructure. 304L ASS was prone to α’ -martensitic transformation upon deformation at room temperature, whereas the TWIP steel showed deformation twinning as well as dynamic strain aging. The TWIP steel reached a higher strength and ductility at fracture. • Hydrogen reduced the ductility of both steels to a significant extend. For 304L ASS, hydrogen accelerated the α’ - martensitic transformation and led to the formation of a small fraction of ε -martensite . For the TWIP steel, ε martensite was formed as well, reducing the amount of deformation twinning compared to the reference condition. • Fracture appeared in a quasi-cleavage way for 304L ASS, while intergranular fracture was observed for the TWIP steel. The steels showed a different HAC sensitivity since the most vulnerable crack initiation spots varied from the austenite/α’ -martensite interface and stress concentrations at intersections of planar deformation (304L ASS) to grain boundaries with low cohesive strength due to segregation of manganese and carbon (TWIP steel).