PURPOSE: To obtain fine crystal structure and toughness without anisotropy by specifying the composition of low carbon steel, imparting plastic strain by executing repeated bending succeeding to control rolling and recrystallizing austenite.

CONSTITUTION: The composition of steel consists of, by weight, 0.02-0.30% C, 0.1-2.0% Si, 0.30-3.5% Mn, 0.003-0.10% Al and the balance Fe with inevitable impurities. It is preferable to add 0.001-0.10% Nb, further 0.001-0.10% Ti to the composition and, as necessary, certain quantities of Ni, Cr, Mo, REM, etc., may be added. Just after casting an ingot or slab of this composition, or at the time of repeating heating rolling, repeated bending is executed succeeding to rolling in the austenitic non-recrystallization temp. region and strain hot less than a value shown by the inequality I is imparted. In this way, material isotropy becomes ≤1kgf/mm2 in tensile strength and within 2°C in fracture appearance transition temp. of Charpy impact test.