Cryogenic S–N Fatigue and Fatigue Crack Propagation Behaviors of High Manganese Austenitic Steels

In the current study, the S–N fatigue and the fatigue crack propagation (FCP) behaviors of high manganese austenitic steels, including Fe24Mn and Fe22Mn, were studied, and the results were compared with STS304 (Fe-1Si-2Mn-20Cr-10Ni). The S–N fatigue tests were conducted at 298 K and 110 K (25 °C and −163 °C), respectively, and at an R ratio of 0.1 under a uniaxial loading condition. The FCP tests were conducted at 298 K and 110 K (25 °C and −163°C), respectively, and at R ratios of 0.1 and 0.5, respectively, using compact tension specimens. The resistance to S–N fatigue of each specimen increased greatly with decreasing temperature from 298 K to 110 K (25 °C to −163 °C) and showed a strong dependency on the flow stress. The FCP behaviors of the austenitic steels currently studied substantially varied depending on testing temperature, applied ΔK (stress intensity factor range), and R ratio. The enhanced FCP resistance was observed for the Fe24Mn and the Fe22Mn specimens particularly in the near-threshold ΔK regime, while the enhancement was significant over the entire ΔK regimes for the STS304 specimen, with decreasing temperature from 298 K to 110 K (25 °C to −163 °C). The S–N fatigue and the FCP behaviors of high manganese austenitic steels are compared with STS304 and discussed based on the fractographic and the micrographic observations.