The Effects of the Shapes and the Distributions of Inclusions on the Fatigue Strength of Bearing Steels in Rotary Bending

Abstract

The relations between the fatigue strength of bearing steels in rotary bending and the shape and the distribution of inclusion were investigated. The material used were normal steel (N), normal Swedish steel (S) and steel melted in vacuum (V). Plane specimens and specimens with two kinds of groove were made from each sort of steel. The results obtained were as follows : (1) When the steel had less and smaller inclusions, its fatigue strength became higher. (2) In this experiment, the inclusion whose mean diameter was smaller than 8 μ did not affect the fatigue strength. The mean diameters of detected inclusions were 10∼40 μ for S-steel, 30∼70 μ for N-steel and 35∼130 μ for V-steel. (3) It was clarified that the fatigue life of bearing steel was affected by the mean diameter, the shape of inclusions and the distance from the surface of specimens to the inclusion. (4) The inclusions found on fatigue fracture surfaces were inspected by X-ray analyzer and it was clarified that they were composite of Si and Mn.