Effects of Sigma Phase on the Embrittlement Behavior of Super Duplex Stainless Steel F55 under SSRT with a Cathodic Charge

In order to clarify the influence of sigma phase and hydrogen embrittlement on the mechanical properties of newly developed super duplex stainless steel F55, SSRT was conducted while performing cathodic charge. The installation potential of the constant potential SSRT was determined by polarization curve measurement. Based on the results obtained from polarization curve measurements, SSRT's were conducted in the air, in corrosive solution, at +0.5V constant potential, and at -0.5V (vs. Ag/AgCl) constant potential. In order to observe the relationship between the test environment and the fracture mode, the fracture surface was observed with a scanning electron microscope and the influence of the sigma phase on hydrogen embrittlement was examined. Hydrogen embrittlement was observed regardless of the amount of sigma phase. As specimen having a sigma phase area ratio of 30% showed larger embrittlement caused by the sigma phase in air, it was suggested that sigma phase embrittlement controls an embrittlement behavior. Enhancement of hydrogen embrittlement by sigma phase precipitations was not observed in a cathodic charge condition used in this experiment.