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The fatigue behavior of a high strength steel 300 M in the gigacycle regime was investigated. Fully reversed tension - compression fatigue tests at ambient temperature were performed using an ultrasonic fatigue system operating at 20 kHz.The staircase test method was employed to obtain accurate values of the mean fatigue strength corresponding to fixed numbers of cycles up to 10~9.These results were compared to the curve which is estimated by the data tested in the mid-long life regime on conventional servo hydraulic test machine at 20 Hz.Results indicate that the fatigue strength determined from ultrasonic fatigue testing is lightly higher than conventional testing in the range of 10~6-10~7 cycles.It is obvious that nucleations of fractures tend to occur below the surface, if fractures happen after more than 10~7 cycles.All the fractured specimens fails from internal SiO_2 inclusions or smaller carbides and carbide clusters.
The fatigue behavior of a high strength steel 300 M in the gigacycle regime was investigated. Twentieth. The staircase test method was employed to obtain accurate values of the mean fatigue strength corresponding to fixed numbers of cycles up to 10 ~ 9.These results were compared to the curve which is estimated by the data tested in the mid-long life regime on conventional servo hydraulic test machine at 20 Hz. Results called that that the fatigue strength determined from ultrasonic fatigue testing is lightly higher than conventional testing in the range of 10 ~ 6-10 ~ 7 cycles. It is obvious that nucleations of fractures tend to occur below the surface, if fractures happen after more than 10 ~ 7 cycles.All the fractured specimens fails from internal SiO_2 inclusions or smaller carbides and carbide clusters.