構造用低マンガン鋼の疲勞の強さに關する研究

Abstract

The present study was made for the purpose of obtaining a high fatigue strength constructional steel by adding different low percentages of manganese. Fatigue tests were carried out on 19 rolled specimens of the open hearth steel containing 0·10-0·36% carbon and less than 1·56% manganese, and also tests on 33 rolled specimens of the crucible steel containing 0·10-0·37% carbon and less than 234% manganese.The resulte of the tests were represented in space diagrams taking the fatigue limit, the carbon and the manganese content as coordinates in three perpendicular directions. From the results of a number of mechanical tests, space diagrams which show the relation between the mechanical properties, the carbon and the manganese contents were also obtained.Specifying a certain fatigue limit from the viewpoint of strength and the lowest elongation from the techno ogical standpoint, a range for the carbon and the manganese content was determined from the spece diagram.When the carbon content was low, a constant fatigue limit was obtained by increasing the manganese to a proper amount.Comparing two steels of a definite carbon content, the open hearth steel required a higher percentage of the manganese than the crucible steel to develop the same fatigue strength.Microscopic study showed that specimens with unifom grains were superior in fatigue strength to those with banded structure, s.ag lines or segregation, although the static tensile strength was the same.