The Effects of Surface Treatment on Torsional Fatigue Failure in Recoil Springs

Two different steels, AISI 4150H and maraging 250, were tested in torsional fatigue to failure. Both materials were prepared with three surface conditions 1 as-machined machining grooves left on the outside surface 2 as-polished and 3 polished and shot peened. All specimens converge at low cycle life about 1,000 cycles, but at lower torsional stresses, the greatest improvement in fatigue life is shown by the shot peened specimens, followed by the as-polished specimens. This is true for both materials. The 4150H steel shows the greatest fatigue lives on the torsional S-N curves, but the maraging 250 displays the greatest degree of improvement throughout the range of surface conditions.