PURPOSE: To prevent the breakage of a tapered rod and improve the productivity in forming a tapered rod by stretching a specified material giving temperature gradient in an axial direction by operating so that the strain rate of the smallest diameter part becomes within a specified range.
CONSTITUTION: A wire rod containing 0.35W1.10wt% C, and if required, ≤ 2.5wt% Si, ≤1.5wt% Mn, ≤3.0wt% Cu, ≤3.0wt% Ni, ≤5.0wt% Cr, ≤1.0wt% Mo, ≤1.0wt% V, ≤0.05wt% B, ≤0.1wt% Al, ≤0.5wt% Ti, Nb, Zr, Ta, W, Hf, respectively, and the rest is composed of Fe is heated at heating temperature of 600W1,000°C making the temperature gradient lower with increase of diameter from the smallest diameter part of the wire rod. Next, a tapered rod is formed by stretching the wire rod so that the strain rete, i.e. the change of sectional area of the smallest diameter part per unit time is set to the range of 0.5W 1,000%/sec. The composition, temperature, strain rate are limited to prevent breakage of a wire rod and improve fatigue life.
ABEYAMA SHIYOUZOU
SAITOU MAKOTO
