Hydrogen Embrittlement of 2205 Duplex Stainless Steel in Synthetic Kraft White Liquor

Duplex stainless steels (DSS) may experience environmental assisted cracking (EAC) under certain conditions in the kraft white liquor solutions used by the pulp and paper industry.  Previous work showed that hydrogen absorption is possible in these solutions under applied cathodic potentials (CP) at room temperature, which is a concern because DSSs may become susceptible to hydrogen embrittlement (HE) under certain conditions; however, the effect of a CP on the EAC behavior of DSS in kraft white liquor solutions is currently unknown. Microhardness was used to evaluate the change in hardness upon exposure to white liquor (WL) composed of 150 g/L NaOH and 50 g/L Na2S at room temperature under CP. The hydrogen microprint technique (HMT) was used to observe the hydrogen distribution on the sample surface. Slow strain rate testing (SSRT) was conducted on grade 2205 DSS at a strain rate of 2 X 106 s-1 in the range of -1500 mV vs. SCE to the corrosion potential (Ecorr) at room temperature. The affect of CP on the EAC susceptibility was evaluated as a function of the reduction in area and the time to failure. The fracture morphology was examined with scanning electron microscopy (SEM). The results indicate that an increase in the CP will enhance the severity of EAC below a threshold potential, which was found to be ~ -1100 mVSCE. These findings suggest that care must be taken when DSS are used in pulping applications where there is a risk for galvanic coupling with a more active material, such as carbon or low alloy steel, or in plant equipment where cathodic protection is used.