| 摘要 |
PURPOSE:To produce a steel bar of a large diameter having excellent strength and toughness without requiring a heat treatment after rolling by subjecting a steel ingot contg. a small amt. of elements for improving material quality to heating and blooming under a specific temp. condition. CONSTITUTION:A steel ingot or continuous casting billet contg. 0.30-0.60% C, <1.8% Si, 0.60-2.0% Mn, <0.50% Cr, 0.03-0.20% V, 0.020-0.060% solAl, and 0.008-0.020% N is put in a heating furnace or soaking pit and is heated to 1,100-1,200 deg.C. The ingot or billet is cooled in the furnace after the heating and is then discharged from the furnace at 1,000-1,050 deg.C and is hot rolled at a reduction ratio of >=30% in a temp. region of 750-1,000 deg.C so as to attain 750- 900 deg.C final finishing temp., by which a steel bar having a large diameter of 100-200mm.phi is produced. The large diameter un-tempered steel bar having >=45kg/mm.<2> yield point, >=70kg/mm.<2> tensile strength, >=15% elongation, >=40% reduction of area and >=4kg/cm<2> impact value is obtd. as rolled without requiring subsequent heat treatment. |
