| 摘要 |
<p>Provided is a cold-finished seamless steel pipe for an integrally molded drive shaft, which is obtained by cold-extracting a material pipe hot-rolled by the Mannesmann piercing method. In order to retain the maximum inner face wrinkle depth of 0.1 mm or less of the seamless steel pipe for the drive shaft and the maximum wrinkle depth of 0.20 mm or less of the inner face at the internal diameter reduction ratio of 30 % or more in the radially reduced portion, the material used is the steel of the kind having specific chemical compositions. This steel material is subjected to a piercing-rolling treatment by the Mannesmann method, and is adjusted in the hole molding shape in the routine rolling after drawing-rolled, and then adjusted in the thickness treatment in the later cold-extraction. As a result, the seamless steel pipe can retain excellent torsional fatigue characteristics as the integrally molded automotive drive shaft having radially reduced portions at its two end portions, so that it can be used as a hollow member optimum for weight reduction and quietness. As a result, the automotive drive shaft can be efficiently manufactured.</p> |
