DIRECT SPHEROIDIZING TREATMENT OF STEEL MATERIAL

摘要

PURPOSE:To obtain a hot-rolled wire rod and steel bar having the characteristic equivalent to those by ordinary spheroidizing annealing by combining a specific hot rolling condition and cooling condition. CONSTITUTION:A steel material is subjected to finish rolling continuously under the condition of >=80% total draft in a temp. region from the Ar1 transformation point temp. to the temp. which is not as low as 50 deg.C or below in the hot rolling stage of the steel material. Spheroidization is thus advanced fairly in the finish rolling stage. The steel material is treated at the finishing temp. in the range of the Ac1 transformation point temp. or above and the Ac3 transformation point temp. or below by the working heat thereof and thereafter the steel material is slowly cooled. A cementite nucleus glows quickly and the spheroidization advances quickly in the process when the steel material is slowly cooled.