Microstructure and stress corrosion cracking of a SA508-309L/308L-316L dissimilar metal weld joint in primary pressurized water reactor environment

doi:10.1016/j.jmst.2019.08.035

Abstract

Abstract:

Stress corrosion cracking (SCC) of an SA508-309 L/308 L-316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at γ/δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal. The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.

Key words: Dissimilar metal weld joint, Stress corrosion cracking, Microstructure, Primary pressurized water reactor, environment

Lijin Dong, Cheng Ma, Qunjia Peng, En-Hou Han, Wei Ke. Microstructure and stress corrosion cracking of a SA508-309L/308L-316L dissimilar metal weld joint in primary pressurized water reactor environment[J]. J. Mater. Sci. Technol., 2020, 40: 1-14.

Figures/Tables 15

Fig. 1. Schematic illustration of the SA508-309 L/308 L-316 L weld joint and specimens:. (a) the location of SSRT and microstructure-analysis specimens, (b) the geometry and dimension of the SSRT specimen. All units are in mm.

Table 1 Chemical composition (wt%) of the base and weld metals used for manufacturing the SA508-309 L/308 L-316 L weld joint.

Material	Fe	Cr	Ni	Mn	Si	C	Mo	P	S
SA508	Bal.	0.12	0.75	1.35	0.18	0.187	0.47	0.009	0.004
316 L	Bal.	17.98	11.72	1.73	0.49	0.023	2.37	0.020	0.031
308 L	Bal.	19.88	10.03	1.33	0.32	0.016	-	0.015	0.011
309 L	Bal.	23.26	13.43	1.76	0.38	0.017	-	0.011	0.002

Fig. 2. OM observation of the SA508-309 L/308 L-316 L weld joint: (a) the FB region of the 308 L-316 L similar metal weld, (b) the LAS part of the SA508-309 L dissimilar metal weld, (c, d) the 309 L part of the SA508-309 L dissimilar metal weld, (e, f) the FB region of the 309 L-308 L similar metal weld.

Fig. 3. Microhardness distribution and composition profiles of the SA508-309 L/308 L-316 L weld joint: (a-c) microhardness distribution in the FB region of the SA508-309 L, 309 L-308 L and 308 L-316 L metal welds, respectively, (d-f) composition profiles of the FB region of the SA508-309 L, 309 L-308 L and 308 L-316 L metal welds, respectively.

Fig. 4. EBSD analyses of FB region of the SA508-309 L/308 L dissimilar metal weld: (a, d), inverse pole figures, (b, e), KAM maps, (c, f), grain boundary character distribution maps. In (b) and (e), the black lines represent high angle grain boundaries (∑ values bigger than 29), the white lines represent low angle grain boundaries (∑1), the red lines represent ∑3 grain boundaries, and the blue lines represent the coincidence site lattice grain boundary with ∑ values ranging from 5 to 29.

Fig. 5. KAM and GBCD distribution in the 308 L and 309 L weld metals: (a) the KAM versus distance to the FB, (b) GBCD distribution.

Fig. 6. SEM observation and TEM analyses of 308 L weld metal: (a) SEM back-scattered electron image of γ/γ boundary, (b) SEM back-scattered electron image of γ/δ boundary, (c) TEM image of the γ/δ boundary in DZ, (d) diffraction pattern of the carbide, (e) EDX mappings of the carbides, (f) composition profile across the carbide.

Fig. 7. SEM observation and TEM analyses of 309 L weld metal in different distances to the FB of SA508-309 L dissimilar metal weld: (a, b), about 50 μm to the FB, (c, d) about 200 μm to the FB, (e, f) about 500 μm to the FB, (g) observation of γ/γ boundary, (h) composition profile across the γ/γ grain boundary. (a), (c) and (e) are SEM back-scattered images, (b), (d) and (f) are TEM images.

Fig. 8. TEM-EDX analysis of the chemical composition of the ferrite and austenite phase in different regions of the 308 L and 309 L weld metals: (a) ferrite phase, (b) austenite phase.

Fig. 9. SEM observations of cracking in the 308 L weld metal on specimen S1: (a) surface morphology following 15% strain by SSRT, (b) surface morphology following 20% strain by SSRT, (c) an overall observation of fracture surface after SSRT test, (d) observation at higher magnification showing the cracking morphology, (e) schematic drawing showing the location of facture surface on specimen S1.

Fig. 10. SEM observations of cracking behavior of the 316 L-308 L similar metal weld on specimen S2: (a, b) surface morphology following 20% strain by SSRT, (c) an overall observation of fracture surface after SSRT test, (d) observation at higher magnification showing the cracking morphology, (e) schematic drawing showing the location of facture surface on specimen S2.

Fig. 11. SEM observations of cracking behavior of the 309 L-308 L similar metal weld on specimen S3: (a, b) SEM back-scattered electron images following 10% and 20% strains by SSRT, respectively, (c) an overall SEM observation of fracture surface after SSRT test, (d) SEM observations at higher magnification showing the cracking morphology, (e) schematic drawing showing the location of facture surface on specimen S3.

Fig. 12. SEM observations of cracking behavior of the SA508-309 L dissimilar metal weld with a tensile direction approximately parallel to the FB on specimen S4: (a, b) surface morphology following 10% and 15% strains by SSRT, respectively, (c) an overall observation of fracture surface after SSRT test, (d) observation at higher magnification showing the transgranular cracking morphology, (e) observation at higher magnification showing the intergranular cracking morphology, (f) schematic drawing showing the location of facture surface on specimen S4.

Fig. 13. SEM observations on the surface of the FB region of the SA508-309 L/308 L dissimilar metal weld with a tensile direction approximately perpendicular to the FB following 15% strain by SSRT on specimen S5: (a) the intergranular cracking morphology in the FB region, (b) the transgranular cracking morphology in the FB region, (c) necking in 308 L weld metal, (d) transgranular cracking morphology in 308 L weld metal.

Table 2 The minimum strain for crack initiation and the area percentage of different failure modes on the fracture surface of various regions of the SA508-309 L/308 L-316 L weld joint following SSRT tests.

Material	Initiation strain	SCC		Ductile fracture area percentage
Material	Initiation strain	Intergranular area percentage	Transgranular area percentage	Ductile fracture area percentage
309 L	5%-10%	18.3%	56.4%	25.3%
HAZ of 316 L	15%-20%	few	6.2%	93.0%
308 L	15%-20%	0	few	~100%
SA508	-	0	0	100%

References

[1]	P.L. Andresen, Corrosion 69 (2013) 1024-1038.
[2]	P.L. Andresen, M.M. Morra, Corrosion 64 (2008) 15-29.
[3]	W.C. Chung, J.Y. Huang, L.W. Tsay, C. Chen, Mater. Trans. 52 (2011) 12-19.
[4]	L.J. Dong, Q.J. Peng, E.-H. Han, W. Ke, L. Wang, J. Mater. Sci. Technol. 34 (2018)1281-1292.
[5]	L.J. Dong, Q.J. Peng, H. Xue, E.-H. Han, W. Ke, L. Wang, Corros. Sci. 132 (2018)(2018) 9-20.
[6]	Q.J. Peng, J. Hou, Y. Takeda, J. Kuniya, T. Shoji, Corros. Sci. 52 (2010) 3949-3954.
[7]	G.F. Li, E.A. Charles, J. Congleton, Corros. Sci. 43 (2001) 1963-1983.
[8]	G.F. Li, J. Congleton, Corros. Sci. 42 (2000) 1005-1021.
[9]	L.J. Dong, Q.J. Peng, E.-H. Han, W. Ke, L Wang, Corros. Sci. 107 (2016)172-181.
[10]	L.J. Dong, E.-H. Han, Q.J. Peng, W. Ke, L. Wang, Corros. Sci. 117 (2017) 1-10.
[11]	T. Arai, K. Kako, K. Watanabe, Y. Miyahara, Proceedings of the 14th Conferenceon Environmental Degradation of Materials in Nuclear Power Systems-WaterReactors, Virginia Beach, Virginia, August 23-27, 2009.
[12]	H. Abe, Y. Watanabe, J. Nucl. Mater. 424 (2012) 57-61.
[13]	H.P. Seifert, S. Ritter, T. Shoji, Q.J. Peng, Y. Takeda, Z.P. Lu, J. Nucl. Mater. 378 (2008) 197-210.
[14]	H.P. Seifert, S. Ritter, H.J. Leber, S. Roychowdhury, Corrosion 71 (2015)433-454.
[15]	R.L. Zhu, J.Q. Wang, L. Zhang, Z.M. Zhang, E.-H. Han, Corros.Sci. 112 (2016)373-384.
[16]	H.L. Ming, R.L. Zhu, Z.M. Zhang, J.Q. Wang, E.-H. Han, W. Ke, M.X. Su, Mater.Sci. Eng. A 669 (2016) 279-290.
[17]	R.L. Zhu, J.Q. Wang, Z.M. Zhang, E.-H. Han, Corros.Sci. 120 (2017)219-230.
[18]	Q.J. Peng, H. Xue, J. Hou, K. Sakaguchi, Y. Takeda, J. Kuniya, T. Shoji, Corros. Sci. 53 (2011) 4309-4317.
[19]	J.Y. Huang, M.F. Chiang, S.L. Jeng, J.S. Huang, R.C. Kuo, J. Nucl. Mater. 432 (2013) 189-197.
[20]	J.Y. Huang, T.Y. Yung, J.S. Huang, R.C. Kuo, Corros. Sci. 75 (2013) 386-399.
[21]	Y.L. Han, E.-H. Han, Q.J. Peng, W. Ke, Corros. Sci. 121 (2017) 1-10.
[22]	Crack in Weld Area of Reactor Coolant System Hot Leg Piping at V.C. Summer, United States Nuclear Regulatory Commission, 2019, June 8 https://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/2000/in00017.html.
[23]	J. Hou, T. Shoji, Z.P. Lu, Q.J. Peng, J.Q. Wang, E.H. Han, W. Ke, J. Nucl. Mater. 397 (2010) 109-115.
[24]	M. Kamaya, Mater. Charact. 60 (2009) 125-132.
[25]	T.W. Nelson, J.C. Lippold, M.J. Mills, Sci. Technol. Weld. Join. 3 (1998)249-255.
[26]	H.L. Ming, Z.M. Zhang, J.Q. Wang, E.-H. Han, W. Ke, Mater. Charact. 97 (2014)101-115.
[27]	C.D. Shao, F.G. Lu, X.F. Wang, Y.M. Ding, Z.G. Li, J. Mater. Sci. Technol. 33 (2017) 1610-1620.
[28]	X.D. Lin, Q.J. Peng, E.-H. Han, W. Ke, C. Sun, Z.J. Jiao, Scr. Mater. 149 (2018)11-15.
[29]	T. Takeuchi, J. Kameda, Y. Nagai, T. Toyama, Y. Nishiyama, K. Onizawa, J. Nucl. Mater. 415 (2011) 198-204.
[30]	A.L. Schaeffler, Met. Prog. 56 (1949) 680-688.
[31]	Q. Xiong, H. Li, Z. Lu, J. Chen, Q. Xiao, J. Ma, X. Ru, J. Nucl. Mater. 498 (2018)227-240.
[32]	D. Féron, E. Herms, B. Tanguy, J. Nucl. Mater. 427 (2012) 364-377.
[33]	D.H. Du, K. Chen, H. Lu, L.F. Zhang, X.Q. Shi, X.L. Xu, P.L. Andresen, Corros. Sci. 110 (2016) 134-142.
[34]	H.P. Seifert, S. Ritter, J. Nucl. Mater. 372 (2008) 114-131.
[35]	A. Turnbull, D.A. Horner, B.J. Connolly, Eng. Fract. Mech. 76 (2009)633-640.
[36]	L.T. Chang, G. Burke, F. Scenini, Scr. Mater. 164 (2019) 1-5.
[37]	K. Mukahiwa, G. Bertali, M.G. Burke, J. Duff, F. Scenini, Scr. Mater. 158 (2019)77-82.
[38]	K. Arioka, T. Yamada, T. Terachi, G. Chiba, Corrosion 62 (2006) 568-575.
[39]	K. Arioka, T. Yamada, T. Terachi, R.W. Staehle, Corrosion 62 (2006) 74-83.
[40]	Z. Shen, J.L. Liu, K. Ariok, S. Lozano-Perez, J. Nucl. Mater. 514 (2019) 50-55.
[41]	W.J. Kuang, G.S. Was, Corros. Sci. 97 (2015) 107-114.
[42]	C. Ma, Q.J. Peng, J.N. Mei, E.-H. Han, W. Ke, J. Mater. Sci. Technol. 34 (2018)1823-1834.