LOCALIZED CORROSION RESISTANCE OF WELDED AUSTENITIC AND LEAN DUPLEX STAINLESS STEELS

Weld oxides are known to decrease the pitting resistance of welded stainless steel, so post- weld cleaning is needed for optimum corrosion performance. The drop in corrosion resistance is larger for low-alloyed stainless steels than the higher alloyed grades, but corrosion testing of the former is more difficult due to their low corrosion resistance. Residual weld oxides can cause an initial current peak during electrochemical corrosion testing according to ASTM G150, with the result that the test is terminated prematurely and interpreted as poor corrosion performance. The objective of this work was to investigate the effect of weld oxide on the austenitic stainless steels 304 (EN 1.4301), 304L (EN 1.4307), 316L (EN 1.4404) and the lean duplex LDX 2101 (R) (EN 1.4162). Pitting potentials have been measured based on the ASTM G61 standard and compared with critical pitting temperatures using ASTM G150. The aim was to rank the grades based on the pitting resistance of base metal, polished and pickled welds, but it was found that the pitting potential ranking did not match that typically seen with critical pitting temperatures. The larger sensitivity to surface roughness of the ASTM G61 method was identified as a contributing factor. In addition, it is demonstrated that oxide dissolution, but no visible pitting attack could be identified after the first current peak for both ASTM G61 and ASTM G150 testing. This indicates that the corrosion resistance of as-welded samples is actually higher than the standard measuring techniques indicate.