PSI - Issue 13

A. Laureys et al. / Procedia Structural Integrity 13 (2018) 1330–1335 Author name / Structural Integrity Procedia 00 (2018) 000–000

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48 h in air prior to insertion into the TDS furnace. Condition (iii) and (iv) allowed to assess the effect of irreversible traps or damage on TDS, as the waiting time allowed the reversibly trapped hydrogen to leave the sample. Additionally, tests were performed without the presence of hydrogen induced damage by applying shorter charging times, i.e. 5 and 20 mA/cm² for 5 min and 2 min, respectively. These combinations of test conditions allow to assess if hydrogen induced damage manifests itself on TDS spectra .

Figure 3: Melt extraction curves for cold deformed ULC steel charged at a) 20 mA/cm² for 20’, b) 5 mA/cm² for 50’, c) 0.8 mA/cm² for 60’, d) uncharged.

1.2E-02

1.6E-02

5 mA/cm² - 5' 5 mA/cm² - 50' 5 mA/cm² - 50' + 48 h air

20 mA/cm² - 2' 20 mA/cm² - 20' 20 mA/cm² - 20' + 48 h air

1.4E-02

1.0E-02

1.2E-02

8.0E-03

1.0E-02

6.0E-03

8.0E-03

6.0E-03

4.0E-03

4.0E-03

2.0E-03

2.0E-03

Hydrogen desorption rate (wppm/s)

Hydrogen desorption rate (wppm/s)

0.0E+00

0.0E+00

0

200

400

600

800

0

200

400

600

800

Temperature (°C)

Temperature (°C)

a)

b)

Figure 4: TDS curves for cold deformed ULC steel charged at various conditions.

The various conditions showed that four types of hydrogen sites can be identified in the alloy, with corresponding desorption peak temperatures at about 30, 100, 160, and 320 °C. The first two peaks were related to diffusible and reversibly trapped hydrogen. The last two peaks also remained present in the material after 48 h of waiting, which indicated that they were irreversibly trapped or originated from hydrogen induced damage. Since the samples charged for a very short time also showed the latter peaks, these two higher temperature peaks might be rather related to