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 Delta K 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 Delta K 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.