Abstract
The relationship of the aging treatment conditions, hardness, and torsional fatigue strength of the β type titanium alloy for the springs was examined, in addition observation of micro-structure change due to aging was conducted. As a result, the maximum hardness occurs at the aging treatment temperature of 450°C, while beyond this temperature it decreases. On the other hand, the torsional fatigue strength rises above 450°C, and reaches maximum at 540°C aging treatment temperature. The notch sensitivity factor, β of the specimen for 600μm diameter-drilled hole is 1.29 at 480°C and 1.24 at 540°C aging treatment temperature, and the notch sensitivity factor, β of the specimen treated at 540°C shows a lower value. Furthermore,the increases in the amount of α-phase precipitation due to aging increase the torsional fatigue, which becomes maximum when α-phase precipitation amount reaches 35%.
