Effect of Applied Potential on Fatigue Crack Propagation Behavior of Fe24Mn Steel in Seawater

The fatigue crack propagation (FCP) tests were conducted on Fe24Mn steel in the region of base metal (BM) and weld metal (WM), in air and artificial seawater (ASW) under various applied potentials to establish optimum and safe working limits of cathodic protection (CP). The CP potential of -850 and -1,050 mV(SCE) suppressed the environmental effect of seawater on the FCP behavior of Fe24Mn BM and WM specimens, showing almost identical da/dN-Delta K curves for both air and ASW environments. The slow strain rate tests were also conducted on the Fe24Mn BM specimen in ASW under the CP potential of -1,050 mV(SCE) to identify the susceptibility of hydrogen affecting the FCP behavior. It was suggested that the Fe24Mn BM specimen steel is susceptible to hydrogen embrittlement, but the effect of hydrogen was marginal in affecting the FCP behavior of the Fe24Mn specimens at a loading frequency of 10 Hz. The FCP behavior of Fe24Mn steel is discussed based on the fractographic observation to understand the FCP mechanism in seawater under various CP potentials.