A Model Experiment on Relationship between Fatigue Properties of Steel and Size, Shape, and Distribution of Inclusions

Abstract

The effect of inclusions on fatigue properties was mainly discussed from the viewpoint of size, shape and distribution (amount) of inclusions. Specimens were prepared by using powder-metallurgical method in order to control conditions of inclusions in steel. Angular and spherical Al₂O
3 powders of 10μ, 30μ, 45μand 100μ in size were used as inclusions. Some specimens were carburized and heat-treated to intensify the effect of Al₂O
3 on fatigue. Main results obtained are as follows:
1) In the case of non-carburized specimens.
(a) Endurance limit increases with an increase of Al₂O
3 content. The trend is remarkable, when the size of Al₂O
3 is large for a constant mean particle spacing.
(b) UTS and lower yield stress increase also with an increase of Al₂O
3 content. But the rates of increase with Al₂O
3 are small compared with those of endurance limit.
(c) Elongation and reduction of area decrease with an increase of Al₂O
3 content independently of the size.
2) In the case of carburized and heat-treated specimens.
(a) Endurance limit decreases with an increase of Al₂O
3 content. The trend is remarkable when the work hardening coefficient of specimen is small.
(b) Th effect of angular Al₂O
3 on endurance limit is larger than that of spherical Al₂O
3 when their size is constant.
(c) The effect of large Al₂O
3 on endurance limit is larger than that of small Al₂O
3 when their shapes and distribution are constant.
(d) The rate of decrease of endurance limit by Al₂O
3 decreases with an increase of Al₂O
3 content.
(e) Elongation and reduction of area decreases with an increase of Al₂O
3 content.