Environmental Effects on the Fracture Toughness of a Duplex Stainless Steel (UNS S31803)

The environmental effect on the mechanical properties of steels, specifically hydrogen embrittlement (HE), has been widely investigated and is one of the major factors responsible for in-service material failure. Testing methods like slow strain rate testing (SSRT) of tensile specimens have been used but the results are qualitative. This study aims at evaluating the effects of hydrogen on fracture toughness of a duplex stainless steel (UNS S31803). The effect of hydrogen on the J-integral and crack tip opening displacement (CTOD) was studied in this investigation. CTOD is a geometric measurement used to calculate the fracture toughness. Cathodically precharged specimens have been tested according to the ASTM E1820. It was seen that this standard fails to identify the initiation J-integral for these tough materials. Stretch zone width (SZW) was estimated from fractographs to estimate the initiation toughness. Results indicate that hydrogen pickup adversely affect the initiation toughness as well as the crack growth resistance. The stretch zone was not observed in the hydrogen precharged specimens and thus the initiation J-integral could not be evaluated. CTOD seems to be a more effective parameter to be studied for tough materials. Microhardness studies were conducted after hydrogen charging to estimate the degree of susceptibility of the phases present in the duplex steel to HE.