ESSC & DUPLEX 2019

The new duplex steel FDX 27 should be implemented into relevant standards. As for other duplex stainless steel grades, correct solution annealing is one of the most critical aspects for achieving good material properties and a relevant standard in this respect is of great importance for delivery of material with good quality. Testing of high alloyed duplex stainless steels is covered in ASTM A923 which focuses on the detection of detrimental levels of intermetallic phases. For leaner duplex stainless steels ASTM A1084 is the standard focusing on testing appropriate material properties. This standard does not concentrate on intermetallic precipitates but rather on properties affected by nitrides that precipitate at too low solution annealing temperature or too slow cooling at solution annealing situations. For a number of thin sheet materials of FDX 27 different heat treatment conditions, as received conditions, different isothermal sensitizations as well as solution annealed under different cooling situations, has been performed. Local corrosion resistance and microstructure has then been examined according to ASTM A1084 method A and C. A modified test solution for method C has also been evaluated and is proposed as a more relevant solution for the inclusion of FDX 27 and other mid-range duplexes into ASTM A1084. As reference measurement, testing according to ASTM G150 in 0.1M NaCl has been performed and a TTT-diagram has been compiled.