PSI - Issue 54

Magdalena Eškinja et al. / Procedia Structural Integrity 54 (2024) 123–134 M. Eškinja et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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hydrogen trapped in reversible sites mobilizes and diffuses within microstructure [7,8]. Firstly, the specimens were subjected to slow strain rate test (SSRT) in air and afterwards to induce uptake of hydrogen, specimens were fixed in electrochemical cell and solution of 3.5% NaCl and 1 g/L CH 4 N 2 S was added to avoid the recombination of hydrogen atoms to molecular hydrogen. Prior to the start of test, specimens were pre-charged ex situ with 1 mA/cm 2 applied current for 24 h, then the cell was fixed in tensile test machine and charging was continued in situ throughout whole duration of test. To assess valid results, each test was repeated three times and relevant results are shown. Mechanical properties of examined steels can be seen in Table 2.

Table 2. Mechanical properties of HMoS and LMoS.

Yield strength (MPa)

Ultimate Tensile Strength (MPa)

Fracture elongation (%)

Reduction in area (%)

Sample Environment

HMoS LMoS

Air Air

969± 2 807± 9

1038±24 900±21

19.1±0.15 18.1±0.15

42.6±3.5 37.6±1.6

2.3. Hydrogen related experiments

2.3.1. Electrochemical hydrogen charging and thermal desorption spectroscopy (TDS) For studying the hydrogen absorption, specimens with dimensions of 30 × 6 x 1 mm were manufactured and electrochemically charged using the two-electrode cell consisting from the studied material as cathode and cylindrical platinum mesh as anode. Charging was conducted for 72 h in solution of 3.5% NaCl and 1 g/L CH 4 N 2 S at 1 mA/cm 2 to promote hydrogen generation and saturate material with hydrogen. After charging period, specimens were removed from the cell, rinsed in acetone and instantly placed in liquid nitrogen to limit hydrogen losses. Thermal desorption spectroscopy (TDS) analysis were used to measure total content of hydrogen as well as to identify trapping sites within the material. For this purpose, measurements were conducted at four different heating rates (200, 400, 800 and 1200 K/h) for each material in temperature range from 30 °C to 950 °C to validate the results with the reasonable peak shift due to change in heating rate [9]. 2.3.2. Pressurized gaseous hydrogen experiments Gaseous hydrogen charging was carried out in pressurized hydrogen facility. The chamber is comprised of tube with threaded lid on end and corresponding regulatory system. A cuboidal sample with geometry of 30 × 6 x 6 mm was used as a test sample for hydrogen content measurement after test beside the tensile specimen (Figure 2) preloaded with a 80% (elastic region) and 1.05% (plastic region) of the yield strength value. Elastic and plastic loading regimes are important regimes that should be considered for performance of the martensitic steels in gaseous hydrogen content [10].