1999 年 1999 巻 44 号 p. 1-6
High carbon steel wire containing approximately 1 mass% Si was developed for spring wire. Mechanical properties of this wire were evaluated and high tensile strength after annealing, high sag resistance at 150°C to 250°C and a high limit of fatigue strength were confirmed.
Mechanisms of these high performances were investigated by morphologies using TEM.
The observations of the developed steel after annealing at 400°C revealed the presence of a high amount of Si in lamella ferrite, significantly fine lamella cementite with suppression of spheroidizing and lowered lattice distortion in lamella pearlite.
These results lead to the conclusion as follows,
1) Tensile strength and sag resistance are enhanced by solid solution hardening of Si in lamella ferrite.
2) A high limit of fatigue strength is caused by reduction of lattice distortion, which is considered as the origin of fatigue fracture, in lamella pearlite due to high temperature annealing such as 400°C.