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SEM Observations of Fracture Surfaces of Fatigue Specimens of Annealed Type 316 Stainless Steel

F. A Smidt (Jr)

出版	[Department of Defense] Naval Research Laboratory, 1977
URL	http://books.google.com.hk/books?id=6WSPMQEACAAJ&hl=&source=gbs_api

註釋

The fracture surfaces of fatigue specimens of Type 316 stainless steel previously tested at elevated temperatures in air have been examined by scanning electron microscopy (SEM) to characterize the failure processes and to establish correlations with the previous studies of fatigue crack propagation. The SEM observations show three significantly different types of behavior which can be explained in terms of the differences in materials processing history and test conditions. Solution-annealed material tested at 800 F (427 C) exhibits a transgranular failure mode with fatigue striations indicative of a ductile failure process. Solution-annealed material tested at 1100 F (593 C) shows a change in failure mode to partially intergranular failure and an increase in crack propagation rate relative to the tests at 800 F (427 C). Imposition of a hold time further increases the proportion of the surface characterized by intertranular failure, and the crack growth rate also increases. Material aged at 1100 F (593 C) and tested at 1100 F (593 C) shows a return to the transgranular failure mode and a lower crack growth rate than solution annealed material tested at 1100 F (593 C). The imposition of a hold time period had no significant effect on the failure mode. The observations are consistent with a model in which grain boundary embrittlement caused by diffusion of oxygen ahead of the crack tip produces intergranular failure and an acceleration of crack growth rate.