A locomotive suspension spring with a bar diameter of 36 mm failed. Outdoor exposure of a hot-rolled hardened-and tempered 5160 bars for suspension springs resulted in rusting in the seam and on the fracture surface. A step due to a seam was visible on the surface. The thumb nail looked off-center from the step, but a smaller thumb-nail shape that is concentric with the step and a second stage of growth were found to be spread principally to the right of the step. The rapid stage of failure, which began at the edge of the thumb nail, was much...