Characterization of Microstructure and Stress Corrosion Cracking Susceptibility in a Multi-pass Austenitic Stainless Ste
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I.
INTRODUCTION
AUSTENITIC stainless steels are generally utilized as the structural materials in vacuum vessels of international thermonuclear experimental reactors (ITERs), ocean pipes and many other industrial fields.[1–4] Meanwhile, fusion welding techniques are extensively applied to the assembly process of weldments because of their convenient operations and low costs.[5–7] Among them, NG-TIG is one of the most powerful methods for the fabrication of multi-pass weld joints due to its narrower groove and lower heat input, which reduce the shrinkage, distortion and residual stress generated during the welding process.[8] In addition, it has been widely reported that the microstructure of HAZ is greatly changed during the welding process, different from that of WM.[8,9] The content of ferrite in an
JINGWEN ZHANG, LIMING YU, ZONGQING MA, YONGCHANG LIU, CHENXI LIU, and HUIJUN LI are with the State Key Lab of Hydraulic Engineering Simulation and Safety, Tianjin Key Lab of Composite and Functional Materials, Tianjin University, Tianjin 300072, China. e-mails: [email protected] and [email protected] HUI WANG is with the Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu, Sichuan 610041, China. Manuscript submitted December 26, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
AISI316-AISI410 dissimilar weld joint was proved to vary because of the different solidification modes.[10] The grain size and orientation varied a lot with increasing distance from the fusion boundary in thick aluminum alloy plate joints,[11] and the types of boundary structure were also proved to be different with changing heat inputs in a 70/30 brass joint.[12] As a result, the mechanical properties and service performance of those weld joints were related to their specific microstructure,[13,14] especially in the multi-pass weld joints with a more complicated microstructure. Therefore, it is important to clarify the specific microstructure of multi-pass weld joints. In recent years, many serious incidents caused by SCC behaviors have been identified to occur in weld joints, and the SCC performance has a close relationship with the microstructure.[15–18] In joints with the same weld metal and base metal, it was found the closer to the fusion boundary, the higher the SCC susceptibility is, and HAZ had a higher SCC susceptibility than the base metal.[17] Meanwhile, SCC preferentially occurred at the grain boundaries with higher strain.[19] As to the dissimilar metal weld joints, the SCC behaviors were more complex. In the multi-pass 316L-52M weld joint, the gain boundary structure and residual strain varied significantly with increasing distance from the fusion boundary, and intergranular crack propagated along the random grain boundaries.[20] The SCC susceptibility of
Table I.
316LN 316L
Chemical Composition of Austenitic Stainless Steel 316LN and 316L (Wt Pct)
C
Si
Mn
P
S
Cr
Mo
Ni
Nb
N
Cu
0.021 0.02
0.77 0.58
1.109 2.08
0.039 0.012
0.001 0.003
16.92 19.06
2.03 2.54
12.16 12.
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