PSI - Issue 42

Guocai Chai et al. / Procedia Structural Integrity 42 (2022) 155–162 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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presence of nano FCC precipitates in the tempered material. They reduce stress localization and consequently susceptibility to hydrogen embrittlement as mentioned previously.

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Fig. 4. Fracture study, (a) overview of the fracture of the tempered reference material, (b) overview of the fracture of the as-delivered material with hydrogen charging, HE-brittle fracture surface, ductile-remaining fracture surface, (c) overview of the fracture of the tempered material with hydrogen charging, (d) fracture with dimples in the middle of the reference material in (a), (e) details in one HE area of the as-delivered material with hydrogen charging (b); IG-intergranular cracking, TG/CL-transgranular cleavage cracking, QC-Quasi-cleavage cracking, MVC-micro/nano void coalescence, (f) details in one HE area of the tempered material with hydrogen charging (c). In this study, different types of voids were observed. Fig. 5a shows the voids formed in a crack front where a severe plastic deformation zone has formed. It looks like a hydrogen induced cracking by AIDE since crack propagation is enhanced by dislocation emission at the crack surface/front. However, there is another type of void that has appeared at a little far behind the crack tip. They are dense with irregular shape (void-like void called in this paper), just like a synergetic effect of HELP and HESIV. More work needs to be done to understand the phenomenon. Another type of void is present at martensitic lath boundaries as shown in Fig. 5b. These areas usually have severe plastic strain. Elongated voids or void-like voids have appeared. These elongated voids can enhance the decohesion process that causes formation of intergranular cracking when they become coalesced as shown in Fig. 5c, a hydrogen embrittlement by a competition between fracture due to micro-void growth and coalescence and fracture in the cohesive zone, Zhang et al. (2022).