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1 Zeszyty Naukowe. Mechanika / Politechnika Opolska

1 2008

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Influence of arsenic as a hydrogenation promoter during cathodic hydrogen charging of very high strength steels

Sojka J., Ly C., Jérome M., Ruscassier N., Guillot J.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2008

z. 92

59-60

Hydrogen embrittlement mechanisms of two very high strength steels (VHSS) with ultimate tensile strength reaching 1000 MPa were studied in severe hydrogen charging conditions. These VHSS were a TRIP steel (A) and a Cr-V alloyed high strength steel (B). They were submitted to cathodic charging in a sulfuric acid solution (0.1 N) with an addition of 5 nig L-1 of As2O3 as a promoter of hydrogen absorption. Electrochemical permeation technique and subsequent hydrogen dosage by thermal desorption tests provided values for hydrogen diffusion characteristics. A and B present diffusivity of respectively 2.6 10-11 nr s-1 and 2.2 10-10 m2 s-1. Blistering occurred at high charging currents, but residual hydrogen content appeared to be very low for both steels. The results can be attributed to the fine homogeneous microstructures with very few lattice defects like inclusions, impurities or microcracks that are the most potential sites for hydrogen trapping. Otherwise, tensile tests performed on hydrogenated steels showed higher loss of ductility in the presence of arsenic. Fracture surface observations suggest brittle fractures: transgranular brittle fracture for the steel A and intergranular brittle fracture for the steel B. Diffusible hydrogen is to be incriminated in the loss of plasticity since diffusion to crack tips is rather easy in these steels. All the results highlight the role of As2O3 in enhancing the steels susceptibility to hydrogen embrittlement.