The Effect of Sulphur Cracks upon the Fatigue Strength of Welded Joints

It is the purpose of this research to investigate the effect of sulphur cracks upon the fatigue strength of welded joints. With the everincreasing need for the elevation of welding operation efficiency, maintenance of uniform weld and the reduction of man-hours, there has recently been made considerable application of automatic welding in the field of ship structure. However, when automatic welding was adopted for ship structure using indigenous rimmed steel, the authors were confronted with a particular problem of sulphur crack (fig 1), originating from the point of segregation of sulphur in the direction of solidification of weld metal. So the experiments were performed in order to investigate the fatigue strength of welded joints by varying the degree of sulphur crack. The specimens used in this experiment were prepared, as shown in fig. 2 and fig. 3, with a conventional Vee edge preparation perpendicular to the rolled direction. Table 4 summarizes the chemical composition of three kinds of steel, A, B, C, utilized in this research, while Table 3 shows the welding conditions used. The specimens were repeatedly stressed under purely alternating equal load using the Schenck Fatigue Testing Machine. Fig. 5 is a summary of fatigue test results for steel C, compiled from the results for parent metal (marked), perfect welded joints (Δ marked), and the welded joints containing slight sulphur crack. Fig. 4 is a summary of data for steel A and B, when the degree of sulphur crack is varied as follows; 0%, 30%, 50%, 70% and 90%.