Soon-Gi Lee

Fatigue crack propagation behavior of Fe24Mn steel weld at 298 and 110 K

The fatigue crack propagation (FCP) tests were conducted on Fe24Mn steel in the region of base metal (BM), weld metal (WM) and fusion line (FL) at 298 and 110 K. The FCP rates of Fe24Mn specimens in the region of BM, WM and FL were greatly decreased, while no notable difference in the fracture mode was observed, with decreasing temperature from 298 to 110 K. The FCP rates of Fe24Mn WM and FL specimens were slightly lower than those of BM specimen at both room and cryogenic temperatures. The SEM fractographic analyses suggested that each specimen showed the transgranular facets at both temperatures in low and intermediate ΔK regimes. However, the morphological details varied depending on the region of weld and testing temperature. Relatively large sized facets were observed for the WM specimen with the columnar grain boundary playing the same role as the grain boundary in the BM and the FL specimens in the near-threshold ΔK regime. The FCP behavior of Fe24Mn steel in the region of BM, WM and FL is discussed at 298 and 110 K based on the fractographic and micrographic observation.

Factors influencing fatigue crack propagation behavior of austenitic steels

In the present study, the fatigue crack propagation (FCP) behaviors of austenitic single phase steels, including STS304, Fe18Mn and Fe22Mn with different grain sizes ranging from 12 μm to 98 μm were investigated. The FCP tests were conducted in air at an R ratio of 0.1 using compact tension specimens and the crack paths and fracture surfaces were documented by using an SEM. The highest ΔKth value of 9.9MPa·m1/2 was observed for the Fe18Mn specimen, followed by 5.2MPa·m1/2 for the Fe22Mn specimen and 4.6MPa·m1/2 for the STS304 specimen, showing a substantial difference in the near-threshold FCP resistance for each microstructure. The crack path and fractographic analyses suggested that the near-threshold FCP behavior of these austenitic steels was largely influenced by the degree of slip planarity, as determined by stacking fault energy and grain size, rather than the tensile properties. In the Paris’ regime, the slip planarity still played an important role while the tensile properties began to affect the FCP. The FCP behavior of austenitic steels with different microstructural features are discussed based on detailed fractographic and micrographic observations.

Effect of applied potential on fatigue crack propagation behavior of Fe24Mn steel in seawater

In the present study, the fatigue crack propagation (FCP) tests were conducted on X80 steel in air and artificial seawater (ASW) under various applied potentials to establish optimum and safe working limits of cathodic protection (CP). The slow strain rate test (SSRT) was also conducted on the X80 BM specimens in ASW under CP potential to identify the susceptibility of hydrogen affecting the FCP behavior. The CP potential of −850 and −1,050 mVSCE suppressed the environmental effect of seawater on the FCP behavior of X80 BM and WM specimens, showing almost identical da/dN-ΔK curves for both air and ASW environments. The SSRT in ASW under CP potential of −1,050 mVSCE suggested that the X80 BM specimen steel is susceptible to hydrogen embrittlement, but the effect of hydrogen was believed to be marginal in affecting the FCP behavior of the X80 specimens at a loading frequency of 10 Hz. The FCP behavior of high strength X80 steel is discussed based on the fractographic observation to understand the FCP mechanism in seawater under various CP potentials.

Erratum to: Microstructural Evolution in Fe-22Mn-0.4C Twinning-Induced Plasticity Steel During High Strain Rate Deformation

YUMI HA, Graduate Student, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea. HYUNMIN KIM, Post Doctoral, formerly with the Center for Advanced Aerospace Materials (CAAM), Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea, is now with the Brown University, Providence, RI 02912. KI HYUK KWON, Senior Researcher, is with the Research Institute of Industrial Science and Technology, Pohang 790-330, South Korea. SOON-GI LEE, Senior Researcher, is with the Plate Research Group, Technical Research Laboratories, POSCO, Gwangyang 790-300, South Korea. SUNGHAK LEE, Professor, is with the Center for Advanced Aerospace Materials (CAAM), Pohang University of Science and Technology (POSTECH), and also with the Department of Material Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, South Korea. NACK J. KIM, Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology (POSTECH), and also with the Center for Advanced Aerospace Materials (CAAM), Pohang University of Science and Technology (POSTECH). Contact e-mail: njkim@postech.ac.kr The online version of the original article can be found under doi: 10.1007/s11661-014-2705-3. Article published online 23 January 2015