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 A degrees C and -163 A degrees 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 A degrees C and -163A degrees 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 A degrees C to -163 A degrees 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 Delta K (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 Delta K regime, while the enhancement was significant over the entire Delta K regimes for the STS304 specimen, with decreasing temperature from 298 K to 110 K (25 A degrees C to -163 A degrees 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. (C) The Minerals, Metals & Materials Society and ASM International 2013