| 摘要 |
PURPOSE:To obtain a steel plate having a good cold toughness and weldability and less expensive than Nb steel, a molten metal having a special composition is cooled at a particular rate, heated and rolled under a special condition. The steel includes C, Si, Mn, S, Al, Ti and the balance Fe. CONSTITUTION:A molten steel is treated which includes C:0.02 to 0.13%, Si: equals or less than 0.8%, Mn:1.0to 1.8%, S:equals or less than 0.010%, total Al: 0.005 to 0.08%, Ti:0.04 to 0.15% N:0.001 to 0.008%, the balance Fe and unavoideble impurities. The composition further satisfies relations such that o.01 <= Ti%- 3.4%<= 0.12 and Ti%/C% <= 4. The molten steel is cooled from a temperature just bolow liquid phase at a rate of 60 deg.C/min to 1000 deg.C at which temperature TiC (or TiCN) completely precipitates, and then cooled at any rate below 1000 deg.C until Ar1 point or below. The steel is then heated up to 1050 to 1250 deg.C and applied such condition that accumulated reduction below 850 deg.C reaches more than 50% and finishing temperature is 700 to 800 deg.C. The process provides a steel plate having characteristic with 85% ductile fracture in DWTT having a transition temperature below-10 deg.C and Charpy absorption energy in welding heat affected zone being more than 5kg-m at-10 deg.C. |
