Abstract
Torsional fatigue tests were conducted for spring steel SUP7 with smooth surface and artificial pits whose Vickers hardness were 430,480,550 and 620. The effect of notch, hardness and corrosive environment on the fatigue strength was studied. Following conclusions were obtained. (1) The relationship between torsional fatigue strength and hardness in the specimen with smooth surface in air environment was not linear and approximated by third function of hardness revealing the maximum value around 550Hv. (2) The notch factor of torsional fatigue strength in the specimen with artificial pits was the constant value of 1.7 with no relation to hardness and fatigue life in air environment. (3) The notch factor of torsional fatigue strength in the specimen with artificial pits was decreased with the increment of hardness approaching to the value of 1 for long-term fatigue life in corrosive environment. (4) The empirical formulas were derived indicating the fatigue strength in the specimen with artificial pits, the corrosive fatigue strength in the specimen with smooth surface, and the corrosive fatigue strength in the specimen with artificial pits by the third function of hardness.
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