PSI - Issue 42

Simon Vander Vennet et al. / Procedia Structural Integrity 42 (2022) 813–820 / Structural Integrity Procedia 00 (2019) 000–000 S. Vander Vennet

817

5

0.15

1

0.8

0.1

TRIP Q&P

TRIP Q&P

0.6

0.4

0.05

0.2

Intensity (normalised)

Intensity (normalised)

0

31.8 32 32.2 32.4 32.6 32.8 33 2 (°) 0

25

30

35

40

2 (°)

(a)

(b)

Fig. 3: (a) Full view of the measured XRD spectrum with the respective BCC ( α ) and FCC ( γ ) peaks indicated. (b) Close-up of the γ { 220 } peak highlighted in (a)

10

DP TRIP Q&P

8

6

D app (10 -11 m²/s)

4

2

0 20 40 60 80 100 120 Constant applied load (%YS) 0

Fig. 4: Apparent di ff usion coe ffi cients ( D app ) obtained from electrochemical hydrogen permeation at a constant applied load relative to the yield strength (YS) of the material

similar in TRIP and Q&P, with Q&P showing the lowest hydrogen apparent di ff usivity of the tested materials. The trend displayed by the di ff usivities in DP and TRIP at increasing constant applied loads is significantly di ff erent compared to Q&P. The D app in both DP and TRIP increases with increasing applied load in the elastic region, reaching a maximum when plastic deformation becomes significant and decreasing further in the plastic region. The apparent di ff usivity of hydrogen in Q&P, however, already decreases significantly at a small applied constant load and slightly decreases further with increasing applied constant load.

4. Discussion

Despite the presence of RA in both steels, TRIP and Q&P show a di ff erent trend in di ff usion coe ffi cient with increased constant applied load during the permeation test. In the unloaded state, the di ff usivity of Q&P is lower than in TRIP, which is to be expected due to the significantly higher hardness of the BCC matrix in Q&P (Van den Eeckhout et al. (2017)) as evidenced by the higher yield strength in Figure 2. The response of TRIP when testing at a constant applied load is more similar to DP, where a maximum in apparent di ff usivity with respect to applied constant load is observed. Although, this maximum is reached at a higher stress relative to the YS for TRIP. In their study