Original paper(Vol.46 No.12 pp.1396)
Fatigue fracture of low alloy steel at ultra-high-cycle region under elevated temperature condition
Kanazawa Kenji; Nishijima Satoshi
Abstract:Elevated temperature, high-cycle fatigue behavior of low alloy steel SCMV 2 was discussed from viewpoints of the effect of oxidation on fracture mechanism by using the data published previously and some additional data. The results obtained are as follows:
(1)Stepwise S-N curves were obtained for the fatigue data tested at 300 and 400 degree. Surface fracture was dominant at the low cycle region. On the other hand, fish-eye fracture was observed at the high cycle region.
(2)Fatigue limit was not observed at 400 degree by the tests up to 109 cycles.
(3)At the high cycle region tested at 300 and 400 degree, surface fracture did not occur because of oxidation effect; nevertheless, fish-eye fracture occurred by the initiation and propagation processes of internal crack.
(4)The temperature dependence of fatigue strength due to dynamic strain aging was not estimated by tensile strength but cyclic proof stress.
(5)sa/syc-Nf curves, where sa/syc and Nff are the stress amplitude, cyclic proof stress and number of cycles to failure, respectively, were classified into two cases independent of test temperature; surface fracture and internal fracture such as fish-eye pattern.
(6)Fatigue behavior under internal fracture should be called ultra-high-cycle fatigue and be discussed in distinction from fatigue behavior under surface fracture which is called high-cycle fatigue.
Key Words:ultra-high-cycle fatigue, low alloy steel, fish-eye fracture, cyclic proof stress, oxidation effect