| 摘要 |
<p>PURPOSE:To obtain a steel for low temp. service having large Charpy impact absorbing energy and excellent brittle fracture propagation stopping characteristic by rolling a steel slab specifying C, Si, Mn, S, Al, Ti and N under the specific condition two times to make the last finished plate thickness. CONSTITUTION:The steel having composition consisting of 0.03-0.18% C, 0.1-0.5% Si, 0.7-1.8% Mn, <=0.025% S, 0.01-0.08% Al, <=0.03% Ti, and 0.0015-0.008% N, is produced. The steel slab of this steel is heated to the transformation point or higher, and after rolling to the thickness 1.3-7.5 times that of the last finishing plate, accelerated cooling is executed. Successively, this is cooled to <=500 deg.C after this primary rolling and heated to (AC3 transformation point-50 deg.C)-1100 deg.C at >=20 deg.C/min heating velocity and held for 30sec-5min. Successively, the secondary rolling is started at (Ar3 transformation point +150 deg.C) or lower, and the rolling is finished at 50% of the last finished plate thickness or lower by rolling reduction in each rolling pass and at temp. of (Ar2 transformation point +50 deg.C)-(Ar3 transformation point -50 deg.C).</p> |
