MANUFACTURE OF STEEL MATERIAL HAVING LITTLE SURFACE FLAW

摘要

PURPOSE: To make the number of generated surface flaws less as much as possible by reheating a cast bloom obtd. by a continuous casting method after cooling in the specific condition and executing blooming, at the time of manufacturing a steel material by using a Cr-Mo case hardening steel which contains Al and N and easily develops the surface flaw. ;CONSTITUTION: The Cr-Mo case hardening steel containing, by weight 0.01-0.07% Al and 0.007-0.2% N is made to the case bloom by the continuous casting method. The surface of the high temp. case bloom is cooled with high pressure water and held within the temp. range of 250-550°C for ≥30 sec, and after the bainite transformation on the surface layer part starts, this bloom is reheated to execute the blooming. The time held in this temp. range should be over 30 sec and the upper limit is not particularly limited, but is desirable to be about 3 min. By this method, the austenitic grains in the steel material are made fine, and the surface flaw on the steel material after blooming can be reduced.;COPYRIGHT: (C)1994,JPO&Japio