Process for production of steel bar or steel wire having an improved spheroidal structure of cementite

摘要

Herein disclosed is a process for producing a steel bar or steel wire having an improved structure of spheroidal cementite. The process is characterized in that a finish rolling is conducted within a temperature range between Ar1 and Ar3 or Arcm with a reduction ratio of at least 20%. The cooling rate of the steel before the finish rolling should be controlled in the following manner: When the hardenability of the steel is not higher than that of 0.15% C plain carbon steel, it is preferable to cool the steel at a cooling rate higher than 250 DEG C./sec. When the hardenability of the steel is between those of 0.15% to 0.4% C plain carbon steel, it is preferable to cool the steel at a cooling rate higher than 10 DEG C./sec. When the hardenability of the steel is not lower than that of 0.4% C plain carbon steel, it is preferable to cool the steel at a cooling rate higher than 2 DEG C./sec. The annealing may be conducted on the same production line as the hot working of the steel for a shorter time duration by an isothermal treatment, slow cooling treatment or repeating treatment. The annealing may be conducted also by a usual annealing method.