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 Ar.sub.1 and Ar.sub.3 or Arcm with a reduction ratio of at least 20%.PPThe cooling rate of the steel before the finish rolling should be controlled in the following manner:P PWhen 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° C./sec.PP 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° C./sec.PPWhen 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° C. /sec. PPThe 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.