| 摘要 |
PURPOSE:To produce efficiently a steel bar having high toughness by subjecting a steel composed specifically of C, Si, Mn, sol.Al and Fe, etc. to specific rolling in a two phase region of austenite and ferrite after a heat treatment and cooling the rolled steel. CONSTITUTION:A steel which contains 0.02-0.17wt% C, <=0.7% Si, 0.6-2.0% Mn and 0.01-0.07% sol.Al, contains, if necessary, >=1 kind among <=0.01% La, <=0.01% Ce and <=0.01% Ca, or further contg. >=1 kind among <=0.50% Cu, <=0.5% Cr, <=3.0% Ni, <=0.20% Mo, <=0.15% V, <=0.10% Nb, <=0.10% Ti, and <=0.10% Zr, and consists of the balance Fe with inevitable impurities is heated to a temp. range of Ac3 transformation point-Ac3 transformation point +300 deg.C and thereafter the heated steel is subjected to rolling at >=40% cumulative draft in the two phase region of austenite and ferrite and at the draft after the even number pass counted from the final stand of 10-20% per pass. The rolled steel is allowed to cool or is forcibly cooled and a steel bar having excellent cryogenic strength and toughness is obtd. |
