The Influence of Inclusions on the Toughness and Fatigue Properties of A516-70 Steel

The influence of inclusions on the tensile ductility, upper shelf Charpy-V-notch, dynamic tear and J-integral fracture toughness and the fatigue crack propagation behavior and the fatigue endurance limit of A516-70 normalized, carbon plate steel is reported. Three plates made by conventional steelmaking techniques and 4 plates produced using calcium treatment are examined in thickness from 51 mm (2 in.) to 254 mm (10 in.) in up to 6 different testing orientations per plate. Quantitative image analysis is used to establish correlations between the measured mechanical properties and certain inclusion parameters. Inclusions were found to be detrimental to tensile ductility, upper shelf impact and fracture toughness, and the fatigue endurance limit with predominant effect found to be on the fracture toughness properties. Although inclusions were found to influence adversely the fatigue crack propagation behavior, the effect was not substantial in the steels studied. Quantitative image analysis was used to establish that the fatigue crack propagation behavior and tensile ductility are controlled by the average area of an inclusion on the metallographic cross-section corresponding to the plane of fracture, while the upper shelf toughness properties are controlled by the average length of an inclusion. In general A516-70 was found to be less sensitive to inclusions in both toughness and fatigue crack propagation behavior than A533B Class 1.