Effect of Low-Temperature Sensitization on the Corrosion Behavior of AISI Type 304L SS Weld Metal in Simulated Groundwat
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JMEPEG https://doi.org/10.1007/s11665-018-3357-z
Effect of Low-Temperature Sensitization on the Corrosion Behavior of AISI Type 304L SS Weld Metal in Simulated Groundwater Girija Suresh, T. Nandakumar, and A. Viswanath (Submitted December 22, 2017) The manuscript presents the investigations carried out on the effect of low-temperature sensitization (LTS) of 304L SS weld metal on its corrosion behavior in simulated groundwater, for its application as a canister material for long-term storage of nuclear vitrified high-level waste in geological repositories. AISI type 304L SS weld pad was fabricated by multipass gas tungsten arc welding process using 308L SS filler wire. The as-welded specimens were subsequently subjected to carbide nucleation and further to LTS at 500 °C for 11 days to simulate a temperature of 300 °C for 100-year life of the canister in geological repositories. Delta ferrite (d-ferrite) content of the 304L SS weld metal substantially decreased on carbide nucleation treatment and further only a marginal decrease occurred on LTS treatment. The microstructure of the aswelded consisted of d-ferrite as a minor phase distributed in austenite matrix. The d-ferrite appeared fragmented in the carbide-nucleated and LTS-treated weld metal. The degree of sensitization measured by double-loop electrochemical potentokinetic reactivation method indicated an increase in carbide nucleation treatment when compared to the as-welded specimens, and further increase occurred on LTS treatment. Potentiodynamic anodic polarization investigations in simulated groundwater indicated a substantial decrease in the localized corrosion resistance of the carbide-nucleated and LTS 304L SS weld metals, when compared to the as-welded specimens. Post-experimental micrographs indicated pitting as the primary mode of attack in the as-welded, while pitting and intergranular corrosion (IGC) occurred in the carbidenucleated weld metal. LTS-treated weld metal predominantly underwent IGC attack. The decrease in the localized corrosion resistance of the weld metal after LTS treatment was found to have a direct correlation with the degree of sensitization and the weld microstructure. The results are detailed in the manuscript. Keywords
304L SS weld, corrosion, low-temperature sensitization, simulated groundwater
1. Introduction India has adopted a closed nuclear fuel cycle for energy sustenance; wherein, the spent nuclear fuel is reprocessed to recover the valuables before disposal into geological repositories (Ref 1-3). In tandem, is produced a large volume of highlevel liquid waste (HLW) that contains 99% of the radioactivity witnessed in the entire nuclear fuel cycle. The chemistry of HLW is dependent on multiple factors such as the nature of radionuclides, type of reactors, burn up, spent fuel reprocessing chemistry, corrosion products from storage tanks (Ref 4, 5). The major inventory of radionuclides present in HLW is the fission products with half lives ranging from seconds to millions of years, and the minor actinides formed by transmut
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