Influence of Bauschinger effect and aging on heading stress and shank-strength of high-tensile bolts without heat treatment
Miki Takeshi; Toda Masahiro; Kada Osamu; Kanisawa Hideo
Abstract:At the heading of high-tensile bolt with work-hardened 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 Bauschinger 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 573 K 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 generated under compression is nearly equal to that which distinguishes by the Bauschinger effect. Key Words:Baushinger effect, Iron and steel, High tensile bolt, Plastic working, Flow stress, Work hardening