A modified Ausform process has been developed which improves the fatigue properties of spring steels. In brief, the process combines metal deformation with heat treatment. The fatigue resistance of SAE 5150 and 1052 steels is greatly improved by this treatment. The amount of deformation directly influences the fatigue resistance; and with more than 50% deformation, the fatigue life is improved by 700% over that of SAE 5160 spring steel. For a 100,000 cycle minimum life, both maximum stress and stress range can be increased by 30,000 psi over that of conventionally heat treated SAE 5160 steel. Superior fatigue properties have been obtained in sections with thicknesses of 0.200-0.500 in. Surface treatments such as sandblasting, shot peening, and glass bead peening are effective in prolonging fatigue life; glass bead peening was by far the most effective. Modified Ausformed steels display an unusual fracture behavior which is beneficial in fatigue and notch toughness.
Front truck leaf springs of 2600, 3000, and 3300 lb capacities were designed and manufactured by the process. These springs are 25% lighter, have 40% fewer leaves, and have longer lives than their conventionally processed counterparts. The new springs have 20% less interleaf friction than the heavier conventionally manufactured springs. The rate of relaxation or load loss, both before and after a crack develops, is very low when compared with production springs. The fact that the load loss after crack detection is not severe is of special interest. Springs have been observed to survive more than 50,000 cycles after nucleation of a crack without exceeding a load loss of 5%.
