PSI - Issue 54

Daria Pałgan et al. / Procedia Structural Integrity 54 (2024) 322 –331

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Daria Pałgan et al./ Structural Integrity Procedia 00 (2023) 000 – 000

Figure 2. Typical TDMS curves recorded after cathodic hydrogen charging of (a) A516, (b) 304L and (c) 316L. Black TDMS curves are recorded for non-charged samples in as-received state of the steels. Note that the scale of the y-axis is different between the diagrams.

Figure 3. Typical TDMS curves recorded after gaseous hydrogen charging of (a) A516, (b) 304L and (c) 316L. Black TDMS curves are recorded for non-charged samples in as-received state of the steels. Note that the scale of the y-axis is different between the diagrams.

3.2 Cathodic charging Figures 4-6 illustrate the effect of changing the cathodic charging parameters on the hydrogen uptake of diffusible, trapped, and total hydrogen. Parameters varied are current density (Figs. 4a-6a), charging time (Figs. 4b-6b) and temperature of electrolyte (Figs. 4c-6c). Note that in non-charged condition only trapped hydrogen content was measured for all steels, which represents the hydrogen content at position 0 at the x-axis for the parameters investigated. Close analysis of the trends seen in Figs. 4-6 provides insight into how changing of the cathodic charging parameters influence the hydrogen uptake for the diffusible and trapped hydrogen in the investigated steels. Increase of the current density from 1 mA/cm 2 to 10 mA/cm 2 for A516 steel did not result in any changed uptake of diffusible or trapped hydrogen content. In addition, the trapped hydrogen contents were in similar range as for the non-charged A516 samples. For the 304L and 316L steels it was observed that an increase of current density from 20 mA/cm 2 to 100 mA/cm 2 have a small influence on the trapped hydrogen content, which increased compared to the non-charged samples. Also, the diffusible hydrogen content was not affected in these steels. Thus, it may be corroborated that an increased current density during cathodic charging for the investigated charging conditions affect the trapped hydrogen uptake in the austenitic stainless steels. Analyzing the trends of hydrogen uptake as a function of increased charging time revealed that both the diffusible and trapped hydrogen content can be influenced for all samples. The obtained trends for diffusible hydrogen uptake in 304L and 316L steels indicates that a prolonged charging time i.e., more than 48 hours, saturation with hydrogen is achieved, which was not the case for the A516 steel. Finally, the electrolyte temperature during cathodic charging showed to have the highest influence on hydrogen uptake. An increase of the electrolyte temperature increased both diffusible and trapped hydrogen uptake, where more pronounced hydrogen increase was seen for the diffusible hydrogen than for the trapped hydrogen in all steels. Moreover, it should be noted that comparing the hydrogen uptake trends for the austenitic stainless steels as function of electrolyte temperature revealed notable difference in the trapped hydrogen uptake between the steels. Much higher trapped hydrogen contents were measured in the 304L as compared to the 316L. It is suspected that one of the main reasons for this is different amounts of delta ferrite between the alloys, see Fig. 1, where 304L has higher amount. It is well known that hydrogen