An attempt has been made to improve the toughness of low carbon steels containing total nitrogen from 58 to 150 mass ppm by hot rolling at temperatures lower than the A(1) point (control-rolling). The control-rolled steels had fine microstructures and Charpy impact values higher than 100 J at 273 K. Strain aged steels had Charpy impact values higher than those as control-rolled. The cause is discussed.