Abstract
The heat treatment after cold forming is used to decrease the residual stresses of springs, but the mechanical characteristics of the spring steel wires alters, too. This presentation describes the influence of the heat treatment technology (oven equipment, temperature, duration,…) to the properties and quality of helical compression springs made from oil hardened and tempered spring steel wire.
Highlights
Spring steel wires are made from very special manufactured high-tech steels with extremely high tensile strengths Rm. These spring steel wires are characterized by an extremely high yield point, because they have to withstand high loads without plastic deformation. This specific spring wire property is useful for the spring function, but it leads to significant residual stresses after spring cold forming due to high leveled spring-back
The residual stresses on the inner spring side were determined by X-ray diffractometer, paticularly after cold forming without heat treatment and after different heat treatments of the springs
Typical heat treatment temperatures of springs made from oil hardened and tempered wires are in a range of 350°C to 420°C
Summary
These spring steel wires are characterized by an extremely high yield point, because they have to withstand high loads without plastic deformation This specific spring wire property is useful for the spring function, but it leads to significant residual stresses after spring cold forming due to high leveled spring-back. The residual stresses on the inner spring side were determined by X-ray diffractometer, paticularly after cold forming without heat treatment and after different heat treatments of the springs. Typical heat treatment temperatures of springs made from oil hardened and tempered wires are in a range of 350°C to 420°C. The bending residual stresses after cold forming determined at springs made from oil hardened and tempered wire with d = 6 mm and a spring index w = 5, (w = Dm / d) were about 1100 MPa (Fig. 1). The effect of heat treatment with these temperatures depends on the heat treatment duration, too
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