As a candidate package material for high level radiation waste disposal, the crevice corrosion behavior of Q235 low carbon steel weld joint was investigated in a solution simulated to the groundwater in the northwest part of China. The influences of temperature and oxygen content were evaluated. The microstructure of the weld joint was observed by OM, and SEM and surface profile were employed to analyze the crevice corrosion behavior of the weld joint. Open circuit potential of different regions of the weld joint was measured by electrochemical method. Experimental results indicated that the increases of temperature and oxygen content could promote the occurrence of crevice corrosion, and facilitate the corrosion processes both inside and outside the crevice. Fusion zone with a microstructure of clustered ferrite was the most severe corroded area in the weld joint, followed by weld metal, which was characterized by a coarse widmanstaetten structure. The microstructures of base metal and heat affected zone were fine and homogeneous, so these two regions underwent slighter corrosion.
Fig.1 Metallographic structures of different regions of Q235 weld joint
Fig.2 Macro morphologies of Q235 weld joint with corrosion product removal after immersing for 30 d (a, b), 90 d (c, d) and 180 d (e, f) in the aerated (a, c, e) and deaerated (b, d, f) simulated groundwater at 90 ℃ (BM—base metal, WM—weld metal, IC—inside crevice, OC—outside crevice, CE—around crevice edge)
Condition
Immersing time / d
DMAX, IC / μm
DMAX, CE / μm
DUNI, OC / μm
Aerated
30
31
-
25
90
109
-
50
180
209
-
WM 90, BM 20
Deaerated
30
2
42
≈0
90
10
WM 57; BM 22
≈0
180
155
60
WM<8, BM<4
Table 1 Corrosion depths of Q235 weld joint after immersing for different times in the aerated and deaerated simulated groundwater at 90 ℃
Fig.3 Macro morphologies of Q235 weld joint with product removal after immersing for 180 d in the aerated (a) and deaerated (b) simulated groundwater at 25 ℃
Fig.4 Crevice corrosion depths of Q235 weld joints after immersing for 180 d in the aerated (a) and deaerated (b) simulated groundwater at 25 ℃ (The curves 1~4 are measured across the direction of lines 1~4 in Fig.3 respectively)
Immersing temperature / ℃
Condition
DMAX, IC / μm
DMAX, CE / μm
DUNI, OC / μm
90
Aerated
209
-
WM 90, BM 20
Deaerated
155
60
<8
25
Aerated
<5
-
WM 66, BM 30
Deaerated
<4
-
<8
Table 2 Corrosion depths of Q235 weld joint after immersing for 180 d in the aerated and deaerated simulated groundwater at 25 and 90 ℃
Fig.5 SEM images of Q235 weld joint inside the crevice after immersing for 30 d (a) and 90 d (b, c, d) in the aerated simulated groundwater at 90 ℃
Fig.6 SEM images of weld metal (a, c) and base metal (b, d) of Q235 weld joint inside the crevice after immersing for 90 d (a, b) and 180 d (c, d) in the deaerated simulated groundwater at 90 ℃
[1]
Yin K J, Li C, Qiu S Y, Luo Q. Nucl Power Eng, 2007; 28(2 suppl): 76
