PURPOSE: To obtain steel with low temp. toughness by subjecting carbon steel or low alloy steel to heating to above A3 point and working of above 50% in the temp. range of A1WA3 point.

CONSTITUTION: Carbon steel contg. C; 0.03W0.4%, Si; 0.03W1.0% and Mn≤ 3.0% or low alloy steel contg. Ni≤5%, Cr≤1.5%, Mo≤0.5%, V≤0.2%, Nb≤ 0.1% Ti≤0.2%, B≤0.005%, Al≤0.1%, etc. is heated to above A3 point to make the structure uniform, cooled, heated to the temp. range of A1WA3 point, and worked by above 50% to precipitate proeutectoid ferrite finely and uniformly, thus the low temp. toughness being enhanced. By carrying out tempering as the tertiary treatment, the mechanical properties, esp. strength and toughness are regulated and the yield ratio can be increased