非熱処理型高張力ボルトの頭部成形応力と軸部強度に及ぼすバウシンガー効果と時効の影響

Abstract

At the heading of high-tensile bolt with work-hardend drawing wire, Bauschinger effect appears and raises the tool life. On the other hand, this effect reduces the shank strength of bolt. This paper proposes the steel which has large Bauchinger effect at the heading of drawing wire and the aging process which reduces the Bauschinger effect in the bolt shank. Mn or Si do not raise the Bauschinger effect. Carbon raises this effect and the high cooling rate after rolling of wire is useful too. Reduction of yield strength and tensile strength of bolt shank after compression are 15-17% and 6-7%, respectively. These reductions in strength are recovered by aging. It is concluded that aging at 573K recovers the reduction of yield strength and tensile strength of bolt-shank by the compression under strain no more than 0.03. During the compression of drawing wire, X-ray diffraction half value breadth which corresponds to the dislocation density indicates constant value. This fact suggests that the number of dislocations which are newly genereted under compression is nearly equal to that which distinguishes by the Bauschinger effect.