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Fractographic Analysis of Fatigue Specimens of Annealed Type 304 Stainless Steel

出版	[Department of Defense], Navy Department, [Office of Naval Research], Naval Research Laboratory, 1978
URL	http://books.google.com.hk/books?id=BaEhzQEACAAJ&hl=&source=gbs_api

註釋The fracture surfaces of fatigue specimens of Type 304 stainless steel previously tested at elevated temperatures in air were examined by scanning electron microscopy (SEM) to characterize the failure processes and establish correlations with previous studies performed at NRL of fatigue crack propagation in Type 316 stainless steel. The SEM observations showed significantly different types of fatigue behavior which could be explained in terms of differences in material processing history and test conditions. Solution-annealed (SA) material tested at 427 C (800 F) exhibited a transgranular failure mode with fatigue striations indicative of a ductile failure process. Solution-annealed material tested at 593 C (1100 F) showed a change in failure mode to partially intergranular failure and an increase in the crack growth rate relative to tests at 427 C. Imposition of a hold time up to 1 min further increased the proportion of the fracture surface characterized by intergranular failure, and the crack growth rate also increased. The material that had been aged at 593 C and tested at 427 C and at 593 C showed a return to transgranular failure. The crack growth rate in the aged material tested at 427 C was comparable to that of the SA material tested at the same temperature, while the growth rate of the aged material at 593 C was somewhat higher than at 427 C. Observations were consistent with a model in which the grain boundaries were embrittled by diffusion of oxygen ahead of the crack tip, resulting in intergranular failure and an increased crack growth rate.