PURPOSE: To prevent injuring of a tool during the working and to obtain a high tensile bolt with improved tensile strength by drawing a steel wire having comparatively low tensile strength at a specified reduction ratio, forming a bolt, and limiting temp. in the succeeding process.
CONSTITUTION: The steel wire with <55kg/mm2 tensile strength is drawn by ≥25% reduction and work hardened thoroughly. Next the shearing, head forming and screw rolling are performed to form the bolt. In the process performed subsequently such as quenching, annealing, galvanizing, baking and bluing, ≤350°C heating is treated at least once to improve the strength. In this way, the load imposed on the tool such as dies during the forming is reduced and the high tensile bolt of ≥70kg/mm2 tensile strength can be manufactured in good productivity together with extending the tool life.
| JPS58163812 | STRETCHING BOLT |
MIKI TAKESHI
TATEYAMA MICHIAKI
OCHIAI YUKIO
SERIKAWA OSAMICHI
| JPS57134515A | 1982-08-19 |