Abstract
Various roles of oxide in high-temperature, high-cycle fatigue lives of engineering steels in air were classified and discussed to find out the dominant role for each steel and test temperature. The materials examined were 9 kinds of steels such as carbon steels, low alloy steels and austenitic and martensitic stainless steels.
As for the effect of oxidation on high-cycle fatigue, the following three roles of oxide were pointed out: (1) Oxide at the specimen surface prevents crack formation from the surface, and the fish-eye fracture occurs. (2) The propagation process at the early stage of cracks is delayed by the oxide formed on the crack surface and thus the fatigue life is prolonged. (3) Notches acting as crack initiation sites are formed by penetrating oxide from the surface.
At temperatures of 300-400°C for carbon and low alloy steels and 700-800°C for austenitic stainless steels, fish-eye fracture occurred in the high-cycle region above about 107 cycles. The oxidation effect (1) is dominant in these conditions. At 600°C for low alloy steels, the fatigue strength decreased drastically in the high-cycle region and a shell-like-pattern was formed at the crack initiation site of fracture surface. The oxidation effect (3) plays an important role in such a condition.
