Inhibited Ferric Chloride Corrosion Test of Lean Duplex Stainless Steel Welds

摘要

The materials specifier is in need of test methods for acceptance and qualification testing to ensure that the supplied material exhibit desired properties. In the case of duplex stainless steels the ASTM A923 standard is used extensively as a qualification test for duplex grades UNS S32205 and S31803, and superduplex UNS S32750, to detect presence of detrimental intermetallic phases in base material or weldments. In the case of lean duplex stainless steel, ASTM A923 is unsuitable since the lean duplex grades, such as UNS S32101 and S32304, show a very different behavior if they are subjected to inappropriate heat treatment, compared to UNS S32205 and S32750.Recent developments towards creating a new version of ASTM A923 for lean duplex grades have resulted in a standard proposal where the corrosion testing is based on an inhibited ferric chloride solution, 5% FeCI_3 + 1% NaNO_3 which has been accepted as a standard, ASTM A1084. However, the new standard does not state criteria for welded conditions. The purpose of this work is to investigate the applicability of this inhibited solution on welded lean duplex stainless steel. Lean duplex grade UNSS32101 which has been flux cored arc welded with different filler metals according to recommended welding procedures, will be tested and evaluated according to the new standard.All the welded specimens tested in this study pass the corrosion test acceptance criteria for base metal given in ASTM A1084 Method C. All samples showed a corrosion rate lower than 10 mdd at 25°C, regardless of filler metal with proper post weld cleaning, while the weld metal showed lower values than the acceptance criteria given for the impact toughness for the base material at 70 J at room temperature. Impact toughness depends to a large extent on welding method, welding parameters, filler metal used and weld metallurgy.